WorldWideScience

Sample records for electronic reaction surfaces

  1. Electronic dissipation processes during chemical reactions on surfaces

    CERN Document Server

    Stella, Kevin

    2012-01-01

    Hauptbeschreibung Every day in our life is larded with a huge number of chemical reactions on surfaces. Some reactions occur immediately, for others an activation energy has to be supplied. Thus it happens that though a reaction should thermodynamically run off, it is kinetically hindered. Meaning the partners react only to the thermodynamically more stable product state within a mentionable time if the activation energy of the reaction is supplied. With the help of catalysts the activation energy of a reaction can be lowered. Such catalytic processes on surfaces are widely used in industry. A

  2. Surface chemical reactions induced by molecules electronically-excited in the gas

    DEFF Research Database (Denmark)

    Petrunin, Victor V.

    2011-01-01

    We present a model suggesting high chemical activity of electronically-excited molecules colliding with an isolator surface. Initial photochemical event is accounted for as the result of molecular evolution on the electronically-excited potential energy surface (PES), where acceleration and align...... beams inducing the reaction can be used to distinguish the new process we try to investigate from chemical reactions induced by photoexcitation within adsorbed molecules and/or gas phase photolysis....

  3. The Role of Electronic Excitations on Chemical Reaction Dynamics at Metal, Semiconductor and Nanoparticle Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Tully, John C. [Yale Univ., New Haven, CT (United States)

    2017-06-10

    Chemical reactions are often facilitated and steered when carried out on solid surfaces, essential for applications such as heterogeneous catalysis, solar energy conversion, corrosion, materials processing, and many others. A critical factor that can determine the rates and pathways of chemical reactions at surfaces is the efficiency and specificity of energy transfer; how fast does energy move around and where does it go? For reactions on insulator surfaces energy transfer generally moves in and out of vibrations of the adsorbed molecule and the underlying substrate. By contrast, on metal surfaces, metallic nanoparticles and semiconductors, another pathway for energy flow opens up, excitation and de-excitation of electrons. This so-called “nonadiabatic” mechanism often dominates the transfer of energy and can directly impact the course of a chemical reaction. Conventional computational methods such as molecular dynamics simulation do not account for this nonadiabatic behavior. The current DOE-BES funded project has focused on developing the underlying theoretical foundation and the computational methodology for the prediction of nonadiabatic chemical reaction dynamics at surfaces. The research has successfully opened up new methodology and new applications for molecular simulation. In particular, over the last three years, the “Electronic Friction” theory, pioneered by the PI, has now been developed into a stable and accurate computational method that is sufficiently practical to allow first principles “on-the-fly” simulation of chemical reaction dynamics at metal surfaces.

  4. Origin of Power Laws for Reactions at Metal Surfaces Mediated by Hot Electrons

    DEFF Research Database (Denmark)

    Olsen, Thomas; Schiøtz, Jakob

    2009-01-01

    A wide range of experiments have established that certain chemical reactions at metal surfaces can be driven by multiple hot-electron-mediated excitations of adsorbates. A high transient density of hot electrons is obtained by means of femtosecond laser pulses and a characteristic feature of such...... density functional theory and the delta self-consistent field method. With a simplifying assumption, the power law becomes exact and we obtain a simple physical interpretation of the exponent n, which represents the number of adsorbate vibrational states participating in the reaction....

  5. Electron transfer reactions

    CERN Document Server

    Cannon, R D

    2013-01-01

    Electron Transfer Reactions deals with the mechanisms of electron transfer reactions between metal ions in solution, as well as the electron exchange between atoms or molecules in either the gaseous or solid state. The book is divided into three parts. Part 1 covers the electron transfer between atoms and molecules in the gas state. Part 2 tackles the reaction paths of oxidation states and binuclear intermediates, as well as the mechanisms of electron transfer. Part 3 discusses the theories and models of the electron transfer process; theories and experiments involving bridged electron transfe

  6. Reactions at Solid Surfaces

    CERN Document Server

    Ertl, Gerhard

    2009-01-01

    Expanding on the ideas first presented in Gerhard Ertl's acclaimed Baker Lectures at Cornell University, Reactions at Solid Surfaces comprises an authoritative, self-contained, book-length introduction to surface reactions for both professional chemists and students alike. Outlining our present understanding of the fundamental processes underlying reactions at solid surfaces, the book provides the reader with a complete view of how chemistry works at surfaces, and how to understand and probe the dynamics of surface reactions. Comparing traditional surface probes with more modern ones, and brin

  7. Two-Dimensional Free Energy Surfaces for Electron Transfer Reactions in Solution

    Directory of Open Access Journals (Sweden)

    Shigeo Murata

    2008-01-01

    Full Text Available Change in intermolecular distance between electron donor (D and acceptor (A can induce intermolecular electron transfer (ET even in nonpolar solvent, where solvent orientational polarization is absent. This was shown by making simple calculations of the energies of the initial and final states of ET. In the case of polar solvent, the free energies are functions of both D-A distance and solvent orientational polarization. On the basis of 2-dimensional free energy surfaces, the relation of Marcus ET and exciplex formation is discussed. The transient effect in fluorescence quenching was measured for several D-A pairs in a nonpolar solvent. The results were analyzed by assuming a distance dependence of the ET rate that is consistent with the above model.

  8. Final Report: The Impact of Carbonate on Surface Protonation, Electron Transfer and Crystallization Reactions in Iron Oxide Nanoparticles and Colloids

    Energy Technology Data Exchange (ETDEWEB)

    Dixon, David Adams [The University of Alabama

    2013-07-02

    This project addresses key issues of importance in the geochemical behavior of iron oxides and in the geochemical cycling of carbon and iron. For Fe, we are specifically studying the influence of carbonate on electron transfer reactions, solid phase transformations, and the binding of carbonate to reactive sites on the edges of particles. The emphasis on carbonate arises because it is widely present in the natural environment, is known to bind strongly to oxide surfaces, is reactive on the time scales of interest, and has a speciation driven by acid-base reactions. The geochemical behavior of carbonate strongly influences global climate change and CO{sub 2} sequestration technologies. Our goal is to answer key questions with regards to specific site binding, electron transfer reactions, and crystallization reactions of iron oxides that impact both the geochemical cycling of iron and CO{sub 2} species. Our work is focused on the molecular level description of carbonate chemistry in solution including the prediction of isotope fractionation factors. We have also done work on critical atmospheric species.

  9. Surface patterning with natural and synthetic polymers via an inverse electron demand Diels-Alder reaction employing microcontact chemistry.

    Science.gov (United States)

    Roling, Oliver; Mardyukov, Artur; Lamping, Sebastian; Vonhören, Benjamin; Rinnen, Stefan; Arlinghaus, Heinrich F; Studer, Armido; Ravoo, Bart Jan

    2014-10-21

    Bioorthogonal ligation methods are the focus of current research due to their versatile applications in biotechnology and materials science for post-functionalization and immobilization of biomolecules. Recently, inverse electron demand Diels-Alder (iEDDA) reactions employing 1,2,4,5-tetrazines as electron deficient dienes emerged as powerful tools in this field. We adapted iEDDA in microcontact chemistry (μCC) in order to create enhanced surface functions. μCC is a straightforward soft-lithography technique which enables fast and large area patterning with high pattern resolutions. In this work, tetrazine functionalized surfaces were reacted with carbohydrates conjugated with norbornene or cyclooctyne acting as strained electron rich dienophiles employing μCC. It was possible to create monofunctional as well as bifunctional substrates which were specifically addressable by proteins. Furthermore we structured glass supported alkene terminated self-assembled monolayers with a tetrazine conjugated atom transfer radical polymerization (ATRP) initiator enabling surface grafted polymerizations of poly(methylacrylate) brushes. The success of the surface initiated iEDDA via μCC as well as the functionalization with natural and synthetic polymers was verified via fluorescence and optical microscopy, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscopy (AFM) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR).

  10. Understanding the electron-stimulated surface reactions of organometallic complexes to enable design of precursors for electron beam-induced deposition

    Energy Technology Data Exchange (ETDEWEB)

    Spencer, Julie A.; Rosenberg, Samantha G.; Barclay, Michael; Fairbrother, D. Howard [Johns Hopkins University, Department of Chemistry, Baltimore, MD (United States); Wu, Yung-Chien; McElwee-White, Lisa [University of Florida, Department of Chemistry, Gainesville, FL (United States)

    2014-12-15

    Standard practice in electron beam-induced deposition (EBID) is to use precursors designed for thermal processes, such as chemical vapor deposition (CVD). However, organometallic precursors that yield pure metal deposits in CVD often create EBID deposits with high levels of organic contamination. This contamination negatively impacts the deposit's properties (e.g., by increasing resistivity or decreasing catalytic activity) and severely limits the range of potential applications for metal-containing EBID nanostructures. To provide the information needed for the rational design of precursors specifically for EBID, we have employed an ultra-high vacuum (UHV) surface science approach to identify the elementary reactions of organometallic precursors during EBID. These UHV studies have demonstrated that the initial electron-induced deposition of the surface-bound organometallic precursors proceeds through desorption of one or more of the ligands present in the parent compound. In specific cases, this deposition step has been shown to proceed via dissociative electron attachment, involving low-energy secondary electrons generated by the interaction of the primary beam with the substrate. Electron beam processing of the surface-bound species produced in the initial deposition event usually causes decomposition of the residual ligands, creating nonvolatile fragments. This process is believed to be responsible for a significant fraction of the organic contaminants typically observed in EBID nanostructures. A few ligands (e.g., halogens) can, however, desorb during electron beam processing while other ligands (e.g., PF{sub 3}, CO) can thermally desorb if elevated substrate temperatures are used during deposition. Using these general guidelines for reactivity, we propose some design strategies for EBID precursors. The ultimate goal is to minimize organic contamination and thus overcome the key bottleneck for fabrication of relatively pure EBID nanostructures. (orig.)

  11. Mapping of upper electronic reaction surfaces by tuned laser photolysis and by absorption and emission spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    Morgan, M.A.

    1989-07-01

    Potential energy surfaces for photorotamerization of two intramolecularly hydrogen-bonded molecules, o-hydroxybenzaldehyde (OHBA) and methyl salicylate (MS), isolated in cryogenic matrices have been spectroscopically mapped. In addition, the external heavy atom effect of krypton and xenon matrices on the coupling between the S{sub 1} and T{sub 1} surfaces of 4-(dimethylamino)benzonitrile has been examined. Heavy atom matrices are known to increase rates of spin-forbidden processes. The phosphorescence intensity of DMABN increases in krypton and xenon matrices, while the fluorescence intensity, and phosphorescence and fluorescence lifetimes, decrease. These effects are interpreted in terms of a model in which the phosphorescence rate constant increases 300-fold in xenon compared to argon, while the rate constants for intersystem crossing and nonradiative relaxation from the triplet state increase by factors of less than 5. Lifetime measurements in argon matrices doped with heavy atoms indicate that even one heavy atom neighbor has a significant effect on both singlet and triplet lifetimes. 78 refs., 35 figs., 15 tabs.

  12. Cosmic-ray-driven electron-induced reactions of halogenated molecules adsorbed on ice surfaces: Implications for atmospheric ozone depletion and global climate change

    Energy Technology Data Exchange (ETDEWEB)

    Lu Qingbin [Department of Physics and Astronomy and Departments of Biology and Chemistry, University of Waterloo, Waterloo, ON, N2L 3G1 (Canada)], E-mail: qblu@uwaterloo.ca

    2010-02-15

    The cosmic-ray-driven electron-induced reaction of halogenated molecules adsorbed on ice surfaces has been proposed as a new mechanism for the formation of the polar ozone hole. Here, experimental findings of dissociative electron transfer reactions of halogenated molecules on ice surfaces in electron stimulated desorption, electron trapping and femtosecond time-resolved laser spectroscopic measurements are reviewed. This is followed by a review of the evidence from recent satellite observations of this new mechanism for the Antarctic ozone hole, and all other possible physical mechanisms are discussed. Moreover, new observations of the 11-year cyclic variations of both polar ozone loss and stratospheric cooling and the seasonal variations of CFCs and CH{sub 4} in the polar stratosphere are presented, and quantitative predictions of the Antarctic ozone hole in the future are given. Finally, a new observation of the effects of CFCs and cosmic-ray-driven ozone depletion on global climate change is also presented and discussed.

  13. Conversion electron surface imaging

    CERN Document Server

    Irwin, G M; Wehner, A

    1999-01-01

    A method of imaging the Moessbauer absorption over the surface of a sample based on counting conversion electrons emitted from the surface following resonant absorption of gamma radiation is described. This Conversion Electron Surface Imaging (CESI) method is somewhat analogous to Magnetic Resonance Imaging (MRI), particularly chemical shift imaging, and similar tomographic reconstruction techniques are involved in extracting the image. The theory behind the technique and a prototype device is described, as well as the results of proof-of-principle experiments which demonstrate the function of the device. Eventually this same prototype device will be part of a system to determine the spatial variation of the Moessbauer spectrum over the surface of a sample. Applications include imaging of variations of surface properties of steels and other iron containing alloys, as well as other surfaces over which sup 5 sup 7 Fe has been deposited.

  14. Chemical Reactions at Surfaces [Conference summary report

    Energy Technology Data Exchange (ETDEWEB)

    Henderson, Michael; Gray, Nancy Ryan

    2010-04-14

    Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

  15. Recent Developments in Electron Transfer Reactions

    OpenAIRE

    Marcus, Rudolph A.

    1987-01-01

    Earlier results and more recent developments in electron transfer reactions are reviewed. The more recent results include inverted behavior, electronic orientation effects on reaction rates, solvent dynamics, early steps in photosynthesis, and light emission from metal electrodes.

  16. Fluctuations in catalytic surface reactions

    CERN Document Server

    Imbihl, R

    2003-01-01

    The internal reaction-induced fluctuations which occur in catalytic CO oxidation on a Pt field emitter tip have been studied using field electron microscopy (FEM) as a spatially resolving method. The structurally heterogeneous Pt tip consists of facets of different orientations with nanoscale dimensions. The FEM resolution of roughly 2 nm corresponds to a few hundred reacting adsorbed particles whose variations in the density are imaged as brightness fluctuations. In the bistable range of the reaction one finds fluctuation-induced transitions between the two stable branches of the reaction kinetics. The fluctuations exhibit a behaviour similar to that of an equilibrium phase transition, i.e. the amplitude diverges upon approaching the bifurcation point terminating the bistable range of the reaction. Simulations with a hybrid Monte Carlo/mean-field model reproduce the experimental observations. Fluctuations on different facets are typically uncorrelated but within a single facet a high degree of spatial cohere...

  17. Catalysis of Nuclear Reactions by Electrons

    Directory of Open Access Journals (Sweden)

    Lipoglavšek Matej

    2017-01-01

    Full Text Available Electron screening enhances nuclear reaction cross sections at low energies. We studied the nuclear reaction 1H(19F,αγ16O in inverse kinematics in different solid hydrogen targets. Measured resonance strengths differed by up to a factor of 10 in different targets. We also studied the 2H(p,γ3He fusion reaction and observed electrons emitted as reaction products instead of γ rays. In this case electron screening greatly enhances internal conversion probability.

  18. Catalysis of Nuclear Reactions by Electrons

    Science.gov (United States)

    Lipoglavšek, Matej

    2018-01-01

    Electron screening enhances nuclear reaction cross sections at low energies. We studied the nuclear reaction 1H(19F,αγ)16O in inverse kinematics in different solid hydrogen targets. Measured resonance strengths differed by up to a factor of 10 in different targets. We also studied the 2H(p,γ)3He fusion reaction and observed electrons emitted as reaction products instead of γ rays. In this case electron screening greatly enhances internal conversion probability.

  19. Ab initio molecular dynamics study of the Eley-Rideal reaction of H + Cl-Au(111) → HCl + Au(111): Impact of energy dissipation to surface phonons and electron-hole pairs.

    Science.gov (United States)

    Zhou, Linsen; Zhou, Xueyao; Alducin, Maite; Zhang, Liang; Jiang, Bin; Guo, Hua

    2018-01-07

    The reaction between an impinging H atom and a Cl atom adsorbed on Au(111), which is a prototype for the Eley-Rideal mechanism, is investigated using ab initio molecular dynamics at different incidence angles. The reaction yielding gaseous HCl with large internal excitation proceeds via both direct and hot-atom mechanisms. Significant energy exchange with both surface phonons and electron-hole pairs has been observed. However, their impact on the reactivity and final state distributions was found to be limited, thanks to the large exothermicity and small barrier of the reaction.

  20. Theory of reversible electron transfer reactions in a condensed phase.

    Science.gov (United States)

    Dhole, Kajal; Modak, Brindaban; Samanta, Alok; Ghosh, Swapan K

    2010-07-01

    We have derived an exact analytical expression for the average forward rate of a reversible electron transfer reaction, modeled through a reaction coordinate undergoing diffusive motion in arbitrary potential wells of the reactant and the product in presence of a localized sink of arbitrary location and strength. The dynamics of diffusive motion is described by employing two coupled generalized diffusion reaction (Smoluchowski) equations with coordinate dependent diffusivity and delta sink. The average forward electron transfer rate constant obtained here for the system, with equilibrium or nonequilibrium distributions as initial condition, is determined by the forward and backward rate constants calculated based on the transition state theory and the weighted average rate for the well dynamics. We also discuss various limiting cases for the rate of electron transfer reactions corresponding to the different experimental situations. As an illustrative example, we have considered back electron transfer (ET) reaction and shown that the present theory can explain the non-Marcus free energy gap dependence of the rate of ET reactions. More importantly, the approach presented here can easily be extended to systems describing the dynamics of diffusive motion in coupled multipotential surfaces associated with electron transfer reactions.

  1. Mechanism of electron transfer reaction of ternary ...

    Indian Academy of Sciences (India)

    The rate of the reaction increases with increasing pH due to the deprotonation equilibria of the complex. The experimental rate law is consistent with a mechanism in which the deprotonated form [CrIII(DPA)(OX)(OH)]2− is more reactive than the conjugated acid. It is proposed that electron transfer proceeds through an ...

  2. Theoretical aspects of surface reactions

    Science.gov (United States)

    Nørskov, J. K.; Stoltze, P.

    1987-10-01

    A short review is given of our present understanding of the trends in the chemisorption energies and activation energies for dissociation of simple gas molecules on the transition metals. The effect of adsorbed alkali atoms on the activation energy for dissociation is also discussed. This is then used to explain the trends in activity along the transition metal rows and the promoting effect of K for the ammonia synthesis reaction. The basis for the description is the development of a kinetic model for the ammonia synthesis which can describe quantitatively the macroscopic kinetics of a commercial catalyst under industrial conditions. The model relates the reaction rate directly to the properties of the chemisorbed reactants, intermediates and product as measured for model single crystal systems under ultrahigh vacuum conditions.

  3. Computed potential energy surfaces for chemical reactions

    Science.gov (United States)

    Walch, Stephen P.; Levin, Eugene

    1993-01-01

    A new global potential energy surface (PES) is being generated for O(P-3) + H2 yields OH + H. This surface is being fit using the rotated Morse oscillator method, which was used to fit the previous POL-CI surface. The new surface is expected to be more accurate and also includes a much more complete sampling of bent geometries. A new study has been undertaken of the reaction N + O2 yields NO + O. The new studies have focused on the region of the surface near a possible minimum corresponding to the peroxy form of NOO. A large portion of the PES for this second reaction has been mapped out. Since state to state cross sections for the reaction are important in the chemistry of high temperature air, these studies will probably be extended to permit generation of a new global potential for reaction.

  4. State Space Path Integrals for Electronically Nonadiabatic Reaction Rates

    CERN Document Server

    Duke, Jessica Ryan

    2016-01-01

    We present a state-space-based path integral method to calculate the rate of electron transfer (ET) in multi-state, multi-electron condensed-phase processes. We employ an exact path integral in discrete electronic states and continuous Cartesian nuclear variables to obtain a transition state theory (TST) estimate to the rate. A dynamic recrossing correction to the TST rate is then obtained from real-time dynamics simulations using mean field ring polymer molecular dynamics. We employ two different reaction coordinates in our simulations and show that, despite the use of mean field dynamics, the use of an accurate dividing surface to compute TST rates allows us to achieve remarkable agreement with Fermi's golden rule rates for nonadiabatic ET in the normal regime of Marcus theory. Further, we show that using a reaction coordinate based on electronic state populations allows us to capture the turnover in rates for ET in the Marcus inverted regime.

  5. Contact lens surface by electron beam

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Jung Hyuck [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Suk Ju; Hwang, Kwang Ha; Jeon Jin [Dongshin Univ., Naju (Korea, Republic of)

    2011-07-01

    Contact lens materials needs good biocompatibility, high refractive index, high optical transparency, high water content etc. Surface treat method by using plasma and radiation can modify the physical and/or chemical properties of the contact lens surface. Radiation technology such as electron beam irradiation can apply to polymerization reaction and enhance the functionality of the polymer.The purpose of this study is to modify of contact lens surface by using Eb irradiation technology. Electron beam was irradiated to the contact lens surface which was synthesized thermal polymerization method and commercial contact lens to modify physical and chemical properties. Ft-IR, XP, UV-vis spectrophotometer, water content, oxygen trans-metastability were used to characterize the surface state, physicochemical, and optical property of the contact lens treated with Eb. The water content and oxygen transmissibility of the contact lens treated with Eb were increased due to increase in the hydrophilic group such as O-C=O and OH group on the contact lens surface which could be produced by possible reaction between carbon and oxygen during the Eb irradiation. All of the lenses showed the high optical transmittance above 90%. In this case of B/Es, TES, Ti contact lens, the optical transmittance decreased about 5% with increasing Eb dose in the wavelength of UV-B region. The contact lens modified by Eb irradiation could improve the physical properties of the contact lens such as water content and oxygen transmissibility.

  6. Computational Approach to Electron Charge Transfer Reactions

    DEFF Research Database (Denmark)

    Jónsson, Elvar Örn

    -molecular mechanics scheme, and tools to analyse statistical data and generate relative free energies and free energy surfaces. The methodology is applied to several charge transfer species and reactions in chemical environments - chemical in the sense that solvent, counter ions and substrate surfaces are taken...... statistics and a simple post-sampling scheme used to generate free energy surfaces - which compare to full ab initio calculations. In the last part both the molecular dynamics and hybrid classical and quantum mechanics method are used to generate a vast data set for the accurate analysis of dynamical...... in to account - which directly influence the reactants and resulting reaction through both physical and chemical interactions. All methods are though general and can be applied to different types of chemistry. First, the basis of the various theoretical tools is presented and applied to several test systems...

  7. Chemical Reactions at Surfaces. Final Progress Report

    Energy Technology Data Exchange (ETDEWEB)

    None

    2003-02-21

    The Gordon Research Conference (GRC) on Chemical Reactions at Surfaces was held at Holiday Inn, Ventura, California, 2/16-21/03. Emphasis was placed on current unpublished research and discussion of the future target areas in this field.

  8. Electron scattering and reactions from exotic nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Karataglidis, S. [University of Johannesburg, Department of Physics, Auckland Park (South Africa); University of Melbourne, School of Physics, Victoria (Australia)

    2017-04-15

    The SCRIT and FAIR/ELISe experiments are the first to attempt to measure directly electron scattering form factors from nuclei far from stability. This will give direct information for the (one-body) charge densities of those systems, about which there is little information available. The SCRIT experiment will be taking data for medium-mass exotic nuclei, while the electron-ion collider at ELISe, when constructed, will be able to measure form factors for a wide range of exotic nuclei, as available from the radioactive ion beams produced by the FAIR experiment. Other facilities are now being proposed, which will also consider electron scattering from exotic nuclei at higher energies, to study short-range correlations in exclusive reactions. This review will consider all available information concerning the current status (largely theoretical) of electron scattering from exotic nuclei and, where possible, complement such information with equivalent information concerning the neutron densities of those exotic systems, as obtained from intermediate energy proton scattering. The issue of long- and short-range correlations will be discussed, and whether extending such studies to the exotic sector will elicit new information. (orig.)

  9. Diffusion and Surface Reaction in Heterogeneous Catalysis

    Science.gov (United States)

    Baiker, A.; Richarz, W.

    1978-01-01

    Ethylene hydrogenation on a platinum catalyst, electrolytically applied to a tube wall, is a good system for the study of the interactions between diffusion and surface reaction in heterogeneous catalysis. Theoretical background, apparatus, procedure, and student performance of this experiment are discussed. (BB)

  10. Matrix photochemistry of small molecules: Influencing reaction dynamics on electronically excited hypersurfaces

    Energy Technology Data Exchange (ETDEWEB)

    Laursen, S.L.

    1990-01-01

    Investigations of chemical reactions on electronically excited reaction surfaces are presented. The role of excited-surface multiplicity is of particular interest, as are chemical reactivity and energy transfer in systems in which photochemistry is initiated through a metal atom sensitizer.'' Two approaches are employed: A heavy-atom matrix affords access to forbidden triplet reaction surfaces, eliminating the need for a potentially reactive sensitizer. Later, the role of the metal atom in the photosensitization process is examined directly.

  11. Electronic structure and catalysis on metal surfaces.

    Science.gov (United States)

    Greeley, Jeff; Nørskov, Jens K; Mavrikakis, Manos

    2002-01-01

    The powerful computational resources available to scientists today, together with recent improvements in electronic structure calculation algorithms, are providing important new tools for researchers in the fields of surface science and catalysis. In this review, we discuss first principles calculations that are now capable of providing qualitative and, in many cases, quantitative insights into surface chemistry. The calculations can aid in the establishment of chemisorption trends across the transition metals, in the characterization of reaction pathways on individual metals, and in the design of novel catalysts. First principles studies provide an excellent fundamental complement to experimental investigations of the above phenomena and can often allow the elucidation of important mechanistic details that would be difficult, if not impossible, to determine from experiments alone.

  12. Studies on electron transfer reactions of Keggin-type mixed ...

    Indian Academy of Sciences (India)

    [PVIVW11O40]5- and [PVIVVVW10O40]6-. Oxygraph measurements show that there is no uptake of molecular oxygen during the course of reaction. The reaction proceeds through multi-step electron-proton-electron transfer mechanism, with rate limiting initial one electron transfer from NADH to HPA by outer sphere ...

  13. Surface Reactions of Dicyclohexylmethane on Pt(111)

    OpenAIRE

    Gleichweit, Christoph; Amende, Max; Höfert, Oliver; Xu, Tao; Späth, Florian; Brückner, Nicole; Wasserscheid, Peter; Libuda, Jörg; Steinrück, Hans-Peter; Papp, Christian

    2015-01-01

    We investigated the surface reaction of the liquid organic hydrogen carrier dicyclohexylmethane (DCHM) on Pt(111) in ultrahigh vacuum by high-resolution X-ray photoelectron spectroscopy, temperature-programmed desorption, near-edge X-ray absorption fine structure, and infrared reflection–absorption spectroscopy. Additionally, the hydrogen-lean molecule diphenylmethane and the relevant molecular fragments of DCHM, methylcyclohexane, and toluene were studied to elucidate th...

  14. Visualization of electronic properties of molecules in chemical reactions.

    Science.gov (United States)

    Wei, S; Famini, G R

    1995-10-01

    Modern computational methods allow for the tracking of entire chemical reactions, ranging from initial reactants, through transition states, and to the final products. They also permit the computation of a variety of properties that can change as the reaction proceeds from start to finish. Visualization of these reactions is often difficult and usually limited to static displays of specific steps along the reaction paths. This article describes a program, Reaction Viewer, that we have developed to visualize a chemical reaction dynamically. The article also describes the use of this program to see the movement of electrons and other electronic effects, as well as steric ramifications during the reaction.

  15. Intrinsic Structure, Surface Properties, and Dissociation Reactions on Metal Surfaces.

    Science.gov (United States)

    Liyanage, Lalantha Saman

    The original Surface Embedded Green Function (SEGF) method has been used to perform self-consistent calculations of the surface electronic structure of (1x1)Pt(001), O/Pt(001) and (1x5)Pt(001). Calculated work functions, surface state and surface resonance bands, and densities of states are compared with experiment and with earlier slab calculations. The calculated work function for all three surfaces is in excellent agreement with experiment. In general, other results are also consistent with experiment. Total and difference charge density plots are used to illustrate details of O-Pt bonding. Analysis of the surface charge density of (1x1)Pt(001) shows an increase in sp bonding charge which leads to a compressive surface stress, and may help explain the surface reconstruction. The stress is reduced in the O/Pt(001) surface, indicating oxygen stabilization of the (1x1) phase. The calculated difference-DOS curve between (1x1)Pt(001) and (1x5)Pt(001) reveals a reduction of the DOS near the Fermi level for the (1x5) phase, which helps explain the low chemical activity of the reconstructed surface. The method of removing the two-dimensional inversion symmetry requirement from the original SEGF technique is discussed in detail. The generalized SEGF method is tested by applying it to the Al(111) surface. The results obtained by the study are in excellent agreement with experiment and with slab calculations.

  16. Reactions between monolayer Fe and Si(001) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Hasegawa, M.; Kobayashi, N.; Hayashi, N. [Electrotechnical Lab., Tsukuba, Ibaraki (Japan)

    1997-03-01

    Reactions between 1.5 monolayer(ML) Fe deposited on Si(001)-2x1 and -dihydride surfaces were studied in situ by reflection high-energy electron diffraction and time-of-flight ion scattering spectrometry with the use of 25 keV H ions. The reactions between Fe and Si which were successively deposited on Si(001)-dihydride surface were also studied. After the room temperature deposition Fe reacted with Si(001)-2x1 substrate resulting in the formation of polycrystalline Fe5Si3. By annealing to 560-650degC composite heteroepitaxial layer of both type A and type B {beta}-FeSi2 was formed. On the dihydride surface polycrystalline Fe was observed after 1.5ML Fe deposition at room temperature, and reaction between Fe and Si(001)-dihydride surface is not likely at room temperature. We observed 3D rough surface when we deposited only Fe layer on the dihydride surface and annealed above 700degC. The hydrogen termination of Si(001) surface prevents the deposited Fe from diffusing into the substrate below 500degC, however the annealing above 710degC leads to the diffusion. We obtained 2D ordered surface, which showed 3x3 RHEED pattern as referenced to the primitive unreconstructed Si(001) surface net, when we deposited 2.5ML Fe and 5.8ML Si successively onto Si(001)-dihydride surface and annealed to 470degC. (author)

  17. The mechanism of chemisorption of hydrogen atom on graphene: Insights from the reaction force and reaction electronic flux

    Energy Technology Data Exchange (ETDEWEB)

    Cortés-Arriagada, Diego, E-mail: dcortesr@uc.cl; Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Soto, Karla; Toro-Labbé, Alejandro [Nucleus Millennium Chemical Processes and Catalysis, Laboratorio de Química Teórica Computacional (QTC), Departamento de Química-Física, Facultad de Química, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Macul, Santiago (Chile)

    2014-10-07

    At the PBE-D3/cc-pVDZ level of theory, the hydrogen chemisorption on graphene was analyzed using the reaction force and reaction electronic flux (REF) theories in combination with electron population analysis. It was found that chemisorption energy barrier is mainly dominated by structural work (∼73%) associated to the substrate reconstruction whereas the electronic work is the greatest contribution of the reverse energy barrier (∼67%) in the desorption process. Moreover, REF shows that hydrogen chemisorption is driven by charge transfer processes through four electronic events taking place as H approaches the adsorbent surface: (a) intramolecular charge transfer in the adsorbent surface; (b) surface reconstruction; (c) substrate magnetization and adsorbent carbon atom develops a sp{sup 3} hybridization to form the σC-H bond; and (d) spontaneous intermolecular charge transfer to reach the final chemisorbed state.

  18. Studies on electron transfer reactions of Keggin-type mixed ...

    Indian Academy of Sciences (India)

    Administrator

    (PV2) in aqueous phosphate buffer of pH 6 at ambient temperature. Electrochemical and optical studies show that the stoichiometry of the reaction is 1: 2 (NADH : HPA). EPR and optical studies show that HPA act as one electron acceptor and the products of electron transfer reactions are one elec- tron reduced heteropoly ...

  19. Intramolecular inverse electron demand Diels-Alder reactions of pyrimidines

    NARCIS (Netherlands)

    Frissen, A.E.

    1990-01-01

    This thesis deals with the intramolecular inverse electron demand Diels-Alder reaction of pyrimidines. The main objective of the study was to investigate the synthetic applicability of this reaction and to get more insight in the electronic and steric effects which determine the reactivity

  20. Studies on electron transfer reactions: Reduction of heteropoly 10 ...

    Indian Academy of Sciences (India)

    Rates of electron transfer reaction of thioglycolic acid with vanadium(V) substituted Keggintype heteropolyanion, [PVVVVW10O40]5-, in acetate-acetic acid buffers have been measured spectrophotometrically at 25°C. The order of the reaction with respect to substrate and oxidant is unity. The reaction shows simple second ...

  1. Surfaces and interfaces of electronic materials

    CERN Document Server

    Brillson, Leonard J

    2012-01-01

    An advanced level textbook covering geometric, chemical, and electronic structure of electronic materials, and their applications to devices based on semiconductor surfaces, metal-semiconductor interfaces, and semiconductor heterojunctions. Starting with the fundamentals of electrical measurements on semiconductor interfaces, it then describes the importance of controlling macroscopic electrical properties by atomic-scale techniques. Subsequent chapters present the wide range of surface and interface techniques available to characterize electronic, optical, chemical, and structural propertie

  2. Quantifying electron transfer reactions in biological systems

    DEFF Research Database (Denmark)

    Sjulstok, Emil Sjulstok; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-01-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling...... which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between...... quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment...

  3. Reaction Kinetic Parameters and Surface Thermodynamic Properties of Cu2O Nanocubes

    Directory of Open Access Journals (Sweden)

    Xingxing Li

    2015-07-01

    Full Text Available Cuprous oxide (Cu2O nanocubes were synthesized by reducing Cu(OH2 in the presence of sodium citrate at room temperature. The samples were characterized in detail by field-emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction, and N2 absorption (BET specific surface area. The equations for acquiring reaction kinetic parameters and surface thermodynamic properties of Cu2O nanocubes were deduced by establishment of the relations between thermodynamic functions of Cu2O nanocubes and these of the bulk Cu2O. Combined with thermochemical cycle, transition state theory, basic theory of chemical thermodynamics, and in situ microcalorimetry, reaction kinetic parameters, specific surface enthalpy, specific surface Gibbs free energy, and specific surface entropy of Cu2O nanocubes were successfully determined. We also introduced a universal route for gaining reaction kinetic parameters and surface thermodynamic properties of nanomaterials.

  4. [Inelastic electron scattering from surfaces]. [Progress report

    Energy Technology Data Exchange (ETDEWEB)

    1993-10-01

    This program uses ab-initio and multiple scattering to study surface dynamical processes; high-resolution electron-energy loss spectroscopy is used in particular. Off-specular excitation cross sections are much larger if electron energies are in the LEED range (50--300 eV). The analyses have been extended to surfaces of ordered alloys. Phonon eigenvectors and eigenfrequencies were used as inputs to electron-energy-loss multiple scattering cross section calculations. Work on low-energy electron and positron holography is mentioned.

  5. Mechanisms for control of biological electron transfer reactions.

    Science.gov (United States)

    Williamson, Heather R; Dow, Brian A; Davidson, Victor L

    2014-12-01

    Electron transfer (ET) through and between proteins is a fundamental biological process. The rates and mechanisms of these ET reactions are controlled by the proteins in which the redox centers that donate and accept electrons reside. The protein influences the magnitudes of the ET parameters, the electronic coupling and reorganization energy that are associated with the ET reaction. The protein can regulate the rates of the ET reaction by requiring reaction steps to optimize the system for ET, leading to kinetic mechanisms of gated or coupled ET. Amino acid residues in the segment of the protein through which long range ET occurs can also modulate the ET rate by serving as staging points for hopping mechanisms of ET. Specific examples are presented to illustrate these mechanisms by which proteins control rates of ET reactions. Copyright © 2014 Elsevier Inc. All rights reserved.

  6. Analysis of reaction rates of single molecules on metal surfaces

    Science.gov (United States)

    Ueba, H.

    2017-10-01

    The experimental results of the action spectra i.e., reaction rate R(V) as a function of a bias voltage V are analyzed for rotation of a single CCH (D) molecule on a Cu (100) surface [5] and hopping of a single H(D)2O molecule on Pd(111) surface [6]. In the former system it is identified that rotation occurs if enough energy stored in the C-H (D) in-plane bending (IPB) mode excited by tunneling electron is transferred to the C-H (D) out of plane bending (OPB) mode (reaction coordinate mode) via the anharmonic mode coupling in a single electron process. The calculated R(V) shows an excellent agreement with the experimental results except at the low bias voltages below V ≃ 60 mV where no experimental data is available for the nonlinear current I dependence of R(I). A reproduction of the experimental R(V) at the higher voltage region allows us to determine the vibrational density of states of the C-H IPB mode and its coupling rate to the C-H (D) OPB mode as well as the inelastic tunneling current to excite IPB mode. A change of a conductance upon excitation of the C-H IPB mode enables us to evaluate the electron-vibration coupling strength inducing the rotation motion of CCH molecule. In the latter system investigated at a high temperature of about 40 K, the constant R(V) due to thermal hopping followed by the rapid increase is satisfactory explained by anharmonic inter-mode coupling between the scissor mode excited by tunneling electrons and the frustrated translation mode for H(D)2O molecule on Pd(111).

  7. Approach Matters: The Kinetics of Interfacial Inverse-Electron Demand Diels-Alder Reactions.

    Science.gov (United States)

    Sen, Rickdeb; Gahtory, Digvijay; Escorihuela, Jorge; Firet, Judith; Pujari, Sidharam P; Zuilhof, Han

    2017-09-21

    Rapid and quantitative click functionalization of surfaces remains an interesting challenge in surface chemistry. In this regard, inverse electron demand Diels-Alder (IEDDA) reactions represent a promising metal-free candidate. Herein, we reveal quantitative surface functionalization within 15 min. Furthermore, we report the comprehensive effects of substrate stereochemistry, surrounding microenvironment and substrate order on the reaction kinetics as obtained by surface-bound mass spectrometry (DART-HRMS). © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  8. Surface-electronic-state effects in electron emission from the Be(0001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Archubi, C. D. [Instituto de Astronomia y Fisica del Espacio, casilla de correo 67, sucursal 28, C1428EGA, Buenos Aires (Argentina); Gravielle, M. S. [Instituto de Astronomia y Fisica del Espacio, casilla de correo 67, sucursal 28, C1428EGA, Buenos Aires (Argentina); Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires (Argentina); Silkin, V. M. [Donostia International Physics Center, E-20018 San Sebastian (Spain); Departamento de Fisica de Materiales, Facultad de Ciencias Quimicas, Universidad del Pais Vasco, Apartado 1072, E-20080 San Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao (Spain)

    2011-07-15

    We study the electron emission produced by swift protons impinging grazingly on a Be(0001) surface. The process is described within a collisional formalism using the band-structure-based (BSB) approximation to represent the electron-surface interaction. The BSB model provides an accurate description of the electronic band structure of the solid and the surface-induced potential. Within this approach we derive both bulk and surface electronic states, with these latter characterized by a strong localization at the crystal surface. We found that such surface electronic states play an important role in double-differential energy- and angle-resolved electron emission probabilities, producing noticeable structures in the electron emission spectra.

  9. Capability of LEP-type surfaces to describe noncollinear reactions 2 - Polyatomic systems

    CERN Document Server

    Espinosa-Garcia, Joaquin

    2001-01-01

    In this second article of the series, the popular LEP-type surface for collinear reaction paths and a "bent" surface, which involves a saddle point geometry with a nonlinear central angle, were used to examine the capacity of LEP-type surfaces to describe the kinetics and dynamics of noncollinear reaction paths in polyatomic systems. Analyzing the geometries, vibrational frequencies, curvature along the reaction path (to estimate the tunneling effect and the reaction coordinate-bound modes coupling), and the variational transition- state theory thermal rate constants for the NH//3 + O(**3P) reaction, we found that the "collinear" LEP-type and the "bent" surfaces for this polyatomic system show similar behavior, thus allowing a considerable saving in time and computational effort. This agreement is especially encouraging for this polyatomic system because in the Cs symmetry the reaction proceeds via two electronic states of symmetries **3A prime and **3A double prime , which had to be independently calibrated....

  10. Oxides Surfaces and Novel Electronic Properties

    Science.gov (United States)

    Koirala, Pratik

    The scope of this thesis extends to the study of surface structures and electronic properties in a number of complex oxides. The c(6x2) surface reconstruction on SrTiO3 (001) was solved using a combination of plan view transmission electron microscopy imaging, atomic resolution secondary electron imaging, and density functional theory calculations. This work provided fundamental insights on the effects of dielectric screening in secondary electron generation. A thorough analysis on the limitation and functionality of transmission plan view imaging showed that the kinematical approximations used in the separation of top and bottom surfaces is only valid in thin samples (˜5 nm or less for SrTiO3). The presence of an inversion center in the surface structure also made separation of the top and bottom surfaces more robust. Surface studies of two other oxides, KTaO3 and NdGaO3, provided understanding on the mechanism of surface heterogeneity and segregation. In the case of KTaO3, selective ion sputtering and the loss of K resulted in large stoichiometric variations at the surface. Annealing of such samples led to the formation of a potassium deficient tetragonal phase (K 6Ta10.8O30) on the surface. A similar phenomenon was also observed in NdGaO3. Exploratory surface studies of the rare earth scandates (ReScO3 , Re = Gd, Tb, Dy) led to the observation of large flexoelectric bending inside an electron microscope. Thin rods of these scandates bent by up to 90 degree under a focused electron beam; the bending was fully reversible. Ex-situ measurements of flexoelectric coe cient performed by an- other graduate student, Christopher Mizzi, confirmed that the scandates have a large flexocoupling voltage (˜42 V). Electronic structure of the lanthanide scandates was studied using temperature depen- dent X-ray photoelectron spectroscopy and hybrid density functional theory calculations. The amount of charging under X-ray illumination was greatly reduced with increasing

  11. Spatially controlled amyloid reactions using organic electronics.

    Science.gov (United States)

    Gabrielsson, Erik O; Tybrandt, Klas; Hammarström, Per; Berggren, Magnus; Nilsson, K Peter R

    2010-10-04

    Abnormal protein aggregates, so called amyloid fibrils, are mainly known as pathological hallmarks of a wide range of diseases, but in addition these robust well-ordered self-assembled natural nanostructures can also be utilized for creating distinct nanomaterials for bioelectronic devices. However, current methods for producing amyloid fibrils in vitro offer no spatial control. Herein, we demonstrate a new way to produce and spatially control the assembly of amyloid-like structures using an organic electronic ion pump (OEIP) to pump distinct cations to a reservoir containing a negatively charged polypeptide. The morphology and kinetics of the created proteinaceous nanomaterials depends on the ion and current used, which we leveraged to create layers incorporating different conjugated thiophene derivatives, one fluorescent (p-FTAA) and one conducting (PEDOT-S). We anticipate that this new application for the OEIP will be useful for both biological studies of amyloid assembly and fibrillogenesis as well as for creating new bioelectronic nanomaterials and devices.

  12. Catalytic Reactions on Model Gold Surfaces: Effect of Surface Steps and of Surface Doping

    Directory of Open Access Journals (Sweden)

    Maria Natália D. S. Cordeiro

    2011-11-01

    Full Text Available The adsorption energies and the activation energy barriers for a series of reactions catalyzed by gold surfaces and obtained theoretically through density functional theory (DFT based calculations were considered to clarify the role of the low coordinated gold atoms and the role of doping in the catalytic activity of gold. The effect of the surface steps was introduced by comparison of the activation energy barriers and of the adsorption energies on flat gold surfaces such as the Au(111 surface with those on stepped surfaces such as the Au(321 or the Au(110 surfaces. It is concluded that the presence of low coordinated atoms on the latter surfaces increases the adsorption energies of the reactants and decreases the activation energy barriers. Furthermore, the increasing of the adsorption energy of the reaction products can lead to lower overall reaction rates in the presence of low gold coordinated atoms due to desorption limitations. On the other hand, the effect of doping gold surfaces with other transition metal atoms was analyzed using the dissociation reaction of molecular oxygen as a test case. The calculations showed that increasing the silver content in some gold surfaces was related to a considerable increment of the reactivity of bimetallic systems toward the oxygen dissociation. Importantly, that increment in the reactivity was enhanced by the presence of low coordinated atoms in the catalytic surface models considered.

  13. Electron flow generated by gas phase exothermic catalytic reactions using a platinum-gallium nitride nanodiode.

    Science.gov (United States)

    Ji, Xiaozhong; Zuppero, Anthony; Gidwani, Jawahar M; Somorjai, Gabor A

    2005-04-27

    We report steady-state conversion of chemical reaction energy into hot electrons by ballistic injection into a platinum-gallium nitride (Pt/GaN) nanodiode during the platinum-catalyzed oxidation of carbon monoxide. Surface catalytic reactions of molecules from the gas phase generated continuous steady-state hot electron currents with energies at least that of Schottky barrier energy ( approximately 1 eV). These hot electron currents were observed on two different nanodiodes (Pt/TiO2 and Pt/GaN) and represent a new method of chemical energy conversion.

  14. Electronic transmission coefficient for outer-sphere electron transfer reactions in solution: A Landau-Zener formalism

    Science.gov (United States)

    Khan, Shahed U. M.; Zhou, Zheng Yu

    1990-12-01

    The Landau-Zener formulation and literature values of electronic transition matrix were utilized to compute the theoretical values of electronic transmission coefficient of several outer-sphere electron transfer reactions in solution. The slopes of the energy surfaces that are needed for the Landau-Zener equation were obtained using both intermediate neglect of differential overlaps (INDO/2) molecular orbital and classical improved average dipole orientation (IADO) methods. Theoretical results of electronic transmission coefficient of electron transfer reaction obtained using values of slopes from INDO/2-MO (molecular orbital) as well as IADO methods are found in close agreement with the quasiexperimental values of electronic transmission coefficient obtained from experimental data of rate constant. These theoretical values of electronic transmission coefficient, as well as those from experimental values of rate constant are found to be less than unity. These results indicate that outer-sphere electron transfer reactions in solution involving aquo and amine complexes of the transition metal ions studied in this work are nonadiabatic in nature. Theoretical results of electronic transmission coefficient obtained using values of slopes from the classical improved average dipole orientation (IADO) method is found in close agreement with those obtained from the quantum chemical INDO/2-MO method and also with those from experimental values of rate constant and hence justifies the validity of the use of the former.

  15. Chemical Interface Damping Depends on Electrons Reaching the Surface.

    Science.gov (United States)

    Foerster, Benjamin; Joplin, Anneli; Kaefer, Katharina; Celiksoy, Sirin; Link, Stephan; Sönnichsen, Carsten

    2017-03-28

    Metallic nanoparticles show extraordinary strong light absorption near their plasmon resonance, orders of magnitude larger compared to nonmetallic nanoparticles. This "antenna" effect has recently been exploited to transfer electrons into empty states of an attached material, for example to create electric currents in photovoltaic devices or to induce chemical reactions. It is generally assumed that plasmons decay into hot electrons, which then transfer to the attached material. Ultrafast electron-electron scattering reduces the lifetime of hot electrons drastically in metals and therefore strongly limits the efficiency of plasmon induced hot electron transfer. However, recent work has revived the concept of plasmons decaying directly into an interfacial charge transfer state, thus avoiding the intermediate creation of hot electrons. This direct decay mechanism has mostly been neglected, and has been termed chemical interface damping (CID). CID manifests itself as an additional damping contribution to the homogeneous plasmon line width. In this study, we investigate the size dependence of CID by following the plasmon line width of gold nanorods during the adsorption process of thiols on the gold surface with single particle spectroscopy. We show that CID scales inversely with the effective path length of electrons, i.e., the average distance of electrons to the surface. Moreover, we compare the contribution of CID to other competing plasmon decay channels and predict that CID becomes the dominating plasmon energy decay mechanism for very small gold nanorods.

  16. Tracking electron-induced carbon contamination and cleaning of Ru surfaces by Auger electron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kanjilal, Aloke; Catalfano, Mark; Harilal, Sivanandan S.; Hassanein, Ahmed; Rice, Bryan [Center for Materials under Extreme Environment, School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); SEMATECH Inc., Albany, New York 12203 (United States)

    2012-07-15

    Extreme ultraviolet (EUV) radiation induced growth of carbon and oxygen desorption were investigated on a Ru surface by Auger electron spectroscopy (AES) in the presence and absence of additional photoelectrons (PEs) from a focusing Ru mirror. A decrease in EUV reflectivity with carbon growth in the presence of additional PEs has been observed. Conversely, a carbonaceous Ru surface was cleaned in sequential AES, and discussed in terms of secondary electron assisted dissociation of residual hydrocarbons and water molecules, followed by a chemical reaction between adsorbed carbon and oxygen atoms.

  17. Inverse Electron-Demand Diels-Alder Bioorthogonal Reactions.

    Science.gov (United States)

    Wu, Haoxing; Devaraj, Neal K

    2016-02-01

    Bioorthogonal reactions have been widely used over the last 10 years for imaging, detection, diagnostics, drug delivery, and biomaterials. Tetrazine reactions are a recently developed class of inverse electron-demand Diels-Alder reactions used in bioorthogonal applications. Given their rapid tunable reaction rate and highly fluorogenic properties, tetrazine bioorthogonal reactions have come to be considered highly attractive tools for elucidating biological functions and messages in vitro and in vivo. In this chapter, we present recent advances expanding the scope of precursor reactivity and we introduce new biomedical methodology based on bioorthogonal tetrazine chemistry. We specifically highlight novel applications for different kinds of biomolecules, including nucleic acid, protein, antibodies, lipids, glycans, and bioactive small molecules, in the areas of imaging, detection, and diagnostics. We also briefly present other recently developed inverse electron-demand Diels-Alder bioorthogonal reactions. Lastly, we consider future directions and potential roles that inverse electron-demand Diels-Alder reactions may play in the fields of bioorthogonal and biomedical chemistry.

  18. Magnetic resonance studies of photo-induced electron transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    van Willigen, H.

    1992-11-01

    Fourier Transform Electron Paramagnetic Resonance (FT EPR) is useful in study of photochemical reactions: a microwave pulse rotates the electron spin magnetization vector from z (magnetic field) into xy plane ([pi]/2 pulse); the time evolution of magnetization in xy plane, the free induction decay (FID), is sampled. Fourier transform of FID gives the frequency domain EPR spectrum of the free radicals, and the method is ideal for time-resolved studies of free radicals produced by pulsed-laser excitation. Investigations of electron transfer reactions focused on porphyrin (donor) - quinone (acceptor) systems. First, two hydrogen abstraction reactions were studied with FT EPR: photoreduction of acetone with 2-propanol, yielding the acetone ketyl radical, and the reaction of 2-propanol with t-butoxy radicals. Then, the FT EPR study of benzoquinone or duroquinone anion radicals generated by pulsed-laser induced electron transfer from zinc tetraphenylporphyrin (ZnTPP) or tetrasulfonated Zn(TPP), was carried out in homogeneous solution, micellar solutions, and silica gel. Finally, FT EPR was used to study electron transfer quenching of triplet C[sub 60] by electron donors.

  19. Modeling adsorption and reactions of organic molecules at metal surfaces.

    Science.gov (United States)

    Liu, Wei; Tkatchenko, Alexandre; Scheffler, Matthias

    2014-11-18

    CONSPECTUS: The understanding of adsorption and reactions of (large) organic molecules at metal surfaces plays an increasingly important role in modern surface science and technology. Such hybrid inorganic/organic systems (HIOS) are relevant for many applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. Obviously, the predictive modeling and understanding of the structure and stability of such hybrid systems is an essential prerequisite for tuning their electronic properties and functions. At present, density-functional theory (DFT) is the most promising approach to study the structure, stability, and electronic properties of complex systems, because it can be applied to both molecules and solids comprising thousands of atoms. However, state-of-the-art approximations to DFT do not provide a consistent and reliable description for HIOS, which is largely due to two issues: (i) the self-interaction of the electrons with themselves arising from the Hartree term of the total energy that is not fully compensated in approximate exchange-correlation functionals, and (ii) the lack of long-range part of the ubiquitous van der Waals (vdW) interactions. The self-interaction errors sometimes lead to incorrect description of charge transfer and electronic level alignment in HIOS, although for molecules adsorbed on metals these effects will often cancel out in total energy differences. Regarding vdW interactions, several promising vdW-inclusive DFT-based methods have been recently demonstrated to yield remarkable accuracy for intermolecular interactions in the gas phase. However, the majority of these approaches neglect the nonlocal collective electron response in the vdW energy tail, an effect that is particularly strong in condensed phases and at interfaces between different materials. Here we show that the recently developed DFT+vdW(surf) method that accurately accounts for the collective electronic

  20. The effect of intramolecular quantum modes on free energy relationships for electron transfer reactions

    DEFF Research Database (Denmark)

    Ulstrup, Jens; Jortner, Joshua

    1975-01-01

    -frequency intramolecular degrees of feedom on the free energy relationship for series of closely related reactions was investigated for various model systems involving displacement of potential energy surfaces, frequency shift, and anharmonicity effects. The free energy plots are generally found to pass through a maximum...... and to be asymmetric with a slower decrease in the transition probability with increasing energy of reaction. For high-frequency intramolecular modes this provides a rationalization of the experimental observation of ''activationless'' regions. Isotope effects are discussed as also are the oscillatory free energy......A general quantum mechanical description of exothermic electron transfer reactions is formulated by treating such reactions as the nonradiative decay of a ''supermolecule'' consisting of the electron donor, the electron acceptor, and the polar solvent. In particular, the role of the high...

  1. Preparation of carbohydrate arrays by using Diels-Alder reactions with inverse electron demand

    OpenAIRE

    Beckmann, Henning S. G.; Niederwieser, Andrea; Wiessler, Manfred; Wittmann, Valentin

    2012-01-01

    Carbohydrate microarrays are an emerging tool for the high-throughput screening of carbohydrate–protein interactions that represent the basis of many biologically and medicinally relevant processes. The crucial step in the preparation of carbohydrate arrays is the attachment of carbohydrate probes to the surface. We examined the Diels–Alder reaction with inverse-electron-demand (DARinv) as an irreversible, chemoselective ligation reaction for that purpose. After having shown the efficiency of...

  2. Reaction dynamics of electronically excited alkali atoms with simple molecules

    Energy Technology Data Exchange (ETDEWEB)

    Weiss, P.S.; Mestdagh, J.; Schmidt, H.; Vernon, M.F. Covinsky, M.H.; Balko, B.A.; Lee, Y.T.

    1985-09-01

    The reactions of electronically excited sodium atoms with simple molecules have been studied in crossed molecular beams experiments. Electronically excited Na(3/sup 2/P/sub 3/2/,4/sup 2/D/sub 5/2/, and 5/sup 2/S/sub 1/2) were produced by optical pumping using single frequency dye lasers. The effects of the symmetry, and the orientation and alignment of the excited orbital on the chemical reactivity, and detailed information on the reaction dynamics were derived from measurements of the product angular and velocity distributions.

  3. Reaction dynamics of electronically excited alkali atoms with simpler molecules

    Science.gov (United States)

    Weiss, P. S.; Mestdagh, J. M.; Schmidt, H.; Vernon, M. F.; Covinsky, M. H.; Balko, B. A.; Lee, Y. T.

    1985-05-01

    The reactions of electronically excited sodium atoms with simple molecules have been studied in crossed molecular beams experiments. Electronically excited Na(3(2)P(sub 3/2), 4(2)D(sub 5/2), and 5(2)S(sub 1/2) were produced by optical pumping using single frequency dye lasers. The effects of the symmetry, and the orientation and alignment of the excited orbital on the chemical reactivity, and detailed information on the reaction dynamics were derived from measurements of the product angular and velocity distributions.

  4. Positronium formation reaction of polarized positrons and polarized electrons

    Energy Technology Data Exchange (ETDEWEB)

    Hirade, T. [Dept. of Materials Science, Japan Atomic Energy Research Inst., Ibaraki (Japan); Kumada, T. [Advanced Science Research Centre, Japan Atomic Energy Research Inst., Ibaraki (Japan)

    2004-07-01

    Positrons injected in molecular solids or polymers will have positronium formation around the terminal spur of the positron track, the so-called positron spur, with active species in the spur, such as excess electrons. In the usual case, the electrons are not polarized. At low enough temperatures, long-lived weakly localized electrons are accumulated by irradiation in darkness, and positrons will have a chance to form positronium with these long-lived weakly localized electrons. For these electrons, it is possible to cause them to be polarized by applying a magnetic field at very low temperatures. We have successfully observed the effect on the positronium formation reaction of polarized positrons and polarized electrons. (orig.)

  5. Electronic state selectivity in dication-molecule single electron transfer reactions: NO(2+) + NO.

    Science.gov (United States)

    Parkes, Michael A; Lockyear, Jessica F; Schröder, Detlef; Roithová, Jana; Price, Stephen D

    2011-11-07

    The single-electron transfer reaction between NO(2+) and NO, which initially forms a pair of NO(+) ions, has been studied using a position-sensitive coincidence technique. The reactivity in this class of collision system, which involves the interaction of a dication with its neutral precursor, provides a sensitive test of recent ideas concerning electronic state selectivity in dicationic single-electron transfer reactions. In stark contrast to the recently observed single-electron transfer reactivity in the analogous CO(2)(2+)/CO(2) and O(2)(2+)/O(2) collision systems, electron transfer between NO(2+) and NO generates two product NO(+) ions which behave in an identical manner, whether the ions are formed from NO(2+) or NO. This observed behaviour is in excellent accord with the recently proposed rationalization of the state selectivity in dication-molecule SET reactions using simple propensity rules involving one-electron transitions. This journal is © the Owner Societies 2011

  6. Enhanced Electron-Phonon Coupling at Metal Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Plummer, Ward E.

    2010-08-04

    The Born-Oppenheimer approximation (BOA) decouples electronic from nuclear motion, providing a focal point for most quantum mechanics textbooks. However, a multitude of important chemical, physical and biological phenomena are driven by violations of this approximation. Vibronic interactions are a necessary ingredient in any process that makes or breaks a covalent bond, for example, conventional catalysis or enzymatically delivered biological reactions. Metastable phenomena associated with defects and dopants in semiconductors, oxides, and glasses entail violation of the BOA. Charge exchange in inorganic polymers, organic slats and biological systems involves charge- induced distortions of the local structure. A classic example is conventional superconductivity, which is driven by the electron-lattice interaction. High-resolution angle-resolved photoemission experiments are yielding new insight into the microscopic origin of electron-phonon coupling (EPC) in anisotropic two-dimensional systems. Our recent surface phonon measurement on the surface of a high-Tc material clearly indicates an important momentum dependent EPC in these materials. In the last few years we have shifted our research focus from solely looking at electron phonon coupling to examining the structure/functionality relationship at the surface of complex transition metal compounds. The investigation on electron phonon coupling has allowed us to move to systems where there is coupling between the lattice, the electrons and the spin.

  7. Surface resonances in electron reflection from overlayers.

    Science.gov (United States)

    Krasovskii, E E; Höcker, J; Falta, J; Flege, J I

    2015-01-28

    Electron scattering by oxygen monolayers on the Ru(0 0 0 1) surface is studied both experimentally and theoretically. Sharp transmission resonances at low energies are revealed and established to originate from critical points of a special kind in the complex band structure of the substrate. Electron reflection from the clean and oxidized Ru(0 0 0 1) is measured for kinetic energies up to 40 eV at normal incidence for oxygen coverages of 1/4, 1/2, 3/4, and one monolayer. The reflection spectra R(E) are analyzed using a Bloch-waves based ab initio scattering theory. In addition to the substrate-induced resonances the reconstructed (2 × 1) and (2 × 2) surfaces show surface resonances due to pre-emergent secondary diffraction beams. The R(E) spectra are shown to give unambiguous evidence of the hcp stacking of the oxygen layer.

  8. Exploring Reaction Mechanism on Generalized Force Modified Potential Energy Surfaces (G-FMPES) for Diels-Alder Reaction

    Science.gov (United States)

    Jha, Sanjiv; Brown, Katie; Subramanian, Gopinath

    We apply a recent formulation for searching minimum energy reaction path (MERP) and saddle point to atomic systems subjected to an external force. We demonstrate the effect of a loading modality resembling hydrostatic pressure on the trans to cis conformational change of 1,3-butadiene, and the simplest Diels-Alder reaction between ethylene and 1,3-butadiene. The calculated MERP and saddle points on the generalized force modified potential energy surface (G-FMPES) are compared with the corresponding quantities on an unmodified potential energy surface. Our study is performed using electronic structure calculations at the HF/6-31G** level as implemented in the AIMS-MOLPRO code. Our calculations suggest that the added compressive pressure lowers the energy of cis butadiene. The activation energy barrier for the concerted Diels-Alder reaction is found to decrease progressively with increasing compressive pressure.

  9. Electronic structure of bacterial surface protein layers

    Science.gov (United States)

    Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L.

    2008-01-01

    We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer ( S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

  10. Metal-Free Click Chemistry Reactions on Surfaces

    NARCIS (Netherlands)

    Escorihuela, J.; Marcelis, A.T.M.; Zuilhof, H.

    2015-01-01

    In the last decade, interest in the functionalization of surfaces and materials has increased dramatically. In this regard, click chemistry deserves a central focus because of its mild reaction conditions, high efficiency, and easy post-treatment. Among such novel click reactions, those that do not

  11. Mean field ring polymer molecular dynamics for electronically nonadiabatic reaction rates.

    Science.gov (United States)

    Duke, Jessica Ryan; Ananth, Nandini

    2016-12-22

    We present a mean field ring polymer molecular dynamics method to calculate the rate of electron transfer (ET) in multi-state, multi-electron condensed-phase processes. Our approach involves calculating a transition state theory (TST) estimate to the rate using an exact path integral in discrete electronic states and continuous Cartesian nuclear coordinates. A dynamic recrossing correction to the TST rate is then obtained from real-time dynamics simulations using mean field ring polymer molecular dynamics. We employ two different reaction coordinates in our simulations and show that, despite the use of mean field dynamics, the use of an accurate dividing surface to compute TST rates allows us to achieve remarkable agreement with Fermi's golden rule rates for nonadiabatic ET in the normal regime of Marcus theory. Further, we show that using a reaction coordinate based on electronic state populations allows us to capture the turnover in rates for ET in the Marcus inverted regime.

  12. Surface electronic structure of rare earth metals

    Energy Technology Data Exchange (ETDEWEB)

    Blyth, R.I.R.; Dhesi, S.S.; Gravil, P.A.; Newstead, K.; Cosso, R.; Cole, R.J.; Patchett, A.J.; Mitrelias, T. (Surface Science Research Centre, Univ. of Liverpool (United Kingdom)); Prince, N.P.; Barrett, S.D. (Surface Science Research Centre, Univ. of Liverpool (United Kingdom) Oliver Lodge Lab., Univ. of Liverpool (United Kingdom))

    1992-03-25

    Angle-resolved UV photoemission has been used to investigate the electronic structure of the (0001) surfaces of scandium, yttrium, praseodymium and gadolinium. Off-normal emission spectra were recorded with high angular resolution, enabling detailed mapping of the dispersion of valence band features. Yttrium and gadolinium show similar results to published data from Ho(0001), suggesting minimal 4f influence in the lanthanide bandstructures. Differences seen on praseodymium and scandium may be due to 4f-derived states and surface states respectively. (orig.).

  13. Surface studies of praseodymium by electron spectroscopies

    Science.gov (United States)

    Krawczyk, Mirosław; Pisarek, Marcin; Lisowski, Wojciech; Jablonski, Aleksander

    2016-12-01

    Electron transport properties in praseodymium (Pr) foil samples were studied by elastic-peak electron spectroscopy (EPES). Prior to EPES measurements, the Pr sample surface was pre-sputtered by Ar ions with ion energy of 2-3 keV. After such treatment, the Pr sample still contained about 10 at.% of residual oxygen in the surface region, as detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses. The inelastic mean free path (IMFP), characterizing electron transport within this region (4 nm-thick), was evaluated from EPES using both Ni and Au standards as a function of energy in the range of 0.5-2 keV. Experimental IMFPs, λ, were approximated by the simple function λ = kEp, where E is energy (in eV), and k = 0.1549 and p = 0.7047 were the fitted parameters. These values were compared with IMFPs for the praseodymium surface in which the presence of oxygen was tentatively neglected, and also with IMFPs resulting from the TPP-2M predictive equation for bulk praseodymium. We found that the measured IMFP values to be only slightly affected by neglect of oxygen in calculations. The fitted function applied here was consistent with the energy dependence of the EPES-measured IMFPs. Additionally, the measured IMFPs were found to be from 2% to 4.2% larger than the predicted IMFPs for praseodymium in the energy range of 500-1000 eV. For electron energies of 1500 eV and 2000 eV, there was an inverse correlation between these values, and then the resulting deviations of -0.4% and -2.7%, respectively, were calculated.

  14. Controlling Reaction Selectivity through the Surface Termination of Perovskite Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Polo-Garzon, Felipe [Chemical Sciences Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge TN 37831 USA; Yang, Shi-Ze [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge TN 37831 USA; Fung, Victor [Department of Chemistry, University of California, Riverside CA 92521 USA; Foo, Guo Shiou [Chemical Sciences Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge TN 37831 USA; Bickel, Elizabeth E. [Department of Chemical Engineering, Tennessee Technological University, Cookeville TN 38505 USA; Chisholm, Matthew F. [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge TN 37831 USA; Jiang, De-en [Department of Chemistry, University of California, Riverside CA 92521 USA; Wu, Zili [Chemical Sciences Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge TN 37831 USA

    2017-07-19

    Although well known in the material science field, surface reconstruction of perovskites has not been implemented in heterogeneous catalysis. In this work, we employ multiple surface sensitive techniques to characterize the surface reconstruction of SrTiO3 (STO) after thermal pretreatment (Sr-enrichment) and chemical etching (Ti-enrichment). We show, using the conversion of 2-propanol as a probe reaction, that the surface reconstruction of STO can be controlled to greatly tune catalytic acid/base properties and consequently the reaction selectivities in a wide range, which are inaccessible using single metal oxides, either SrO or TiO2. Density functional theory (DFT) calculations well explain the selectivity tuning and reaction mechanism on differently reconstructed surfaces of STO. Similar catalytic tunability is also observed on BaZrO3, highlighting the generality of the finding from this work.

  15. Surface sampling concentration and reaction probe

    Science.gov (United States)

    Van Berkel, Gary J; Elnaggar, Mariam S

    2013-07-16

    A method of analyzing a chemical composition of a specimen is described. The method can include providing a probe comprising an outer capillary tube and an inner capillary tube disposed co-axially within the outer capillary tube, where the inner and outer capillary tubes define a solvent capillary and a sampling capillary in fluid communication with one another at a distal end of the probe; contacting a target site on a surface of a specimen with a solvent in fluid communication with the probe; maintaining a plug volume proximate a solvent-specimen interface, wherein the plug volume is in fluid communication with the probe; draining plug sampling fluid from the plug volume through the sampling capillary; and analyzing a chemical composition of the plug sampling fluid with an analytical instrument. A system for performing the method is also described.

  16. Electron transfer reactions in condensed phase: effect of reversibility.

    Science.gov (United States)

    Dhole, Kajal; Jena, Naresh K; Samanta, Alok; Ghosh, Swapan K

    2012-02-01

    We propose a generalized one-dimensional kinetic equation for multidimensional reversible electron transfer (ET) reaction with a nonequilibrium situation as the initial condition. The rate constant for the forward reversible ET reaction obtained here consists of the rate for the corresponding irreversible ET reaction, and an extra term due to reversibility of the ET process which includes the rates of diffusion dynamics in the reactant and product wells. In order to understand the effect of reversibility, we consider back ET reaction in a system consisting of an electron donor-acceptor pair in a solvent modeled through low frequency solvent collective coordinates (multidimensional) characterized by the orientational polarization and slowly relaxing one-dimensional vibrational mode. We propose here a new generalized polarization energy functional corresponding to the extension of the continuum version for the same, which has opened up the possibility of inclusion of molecular nature of the solvent into the solvent reorganization energy. We then derive an exact expression for the ET rate for this model system. The numerical results calculated by using the proposed one-dimensional approach are shown to be in good agreement with the available experimental results. Non-Marcus free energy gap dependence of the rates observed here for the reversible and irreversible ET reactions are very close to each other in the barrierless region, while for other situations, the rate for the former process is found to be less than the latter. The extra term, which makes the difference between the rate constants for irreversible and reversible ET reactions, is found to be contributed by the diffusion dynamics from both reactant and product wells but the dominating contribution is provided mainly by the product well.

  17. Photogenerated carrier-induced reactions on uhv semiconductor surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Osgood, R.M. Jr.

    1992-05-28

    The objective for this experimental work was to examine the reaction mechanisms, half-collision dynamics, and other optically induced chemical effects, that are operable on a well characterized single-crystal semiconductor surface. Of particular interest were reactions induced by charge transfer from the semiconductor surface including hot carrier and thermalized carrier processes. The primary technique to measure the desorbed fragment translational energies was time-of-flight mass-spectroscopy, used in conjunction with a pulsed tunable laser source. The work was carried out in ultrahigh vacuum, thus other surface spectroscopies such as temperature-programmed desorption, (TPD), (LEED), etc. were used as needed. In the project, the photoreactions of several halogen-containing molecules on GaAs(110) surfaces have been investigated. The studies have made the first observations of several new photochemical processes on uhv prepared surfaces including intermolecular charge transfer; desorption by thermal-carrier-induced reactions (including the measurement of coverage-dependent changes in the translational energies of the desorbed products); interferometric oscillation of photoinduced reactions; and self-quenching of thermal carrier reactions on surfaces.

  18. Python framework for kinetic modeling of electronically excited reaction pathways

    Science.gov (United States)

    Verboncoeur, John; Parsey, Guy; Guclu, Yaman; Christlieb, Andrew

    2012-10-01

    The use of plasma energy to enhance and control the chemical reactions during combustion, a technology referred to as ``plasma assisted combustion'' (PAC), can result in a variety of beneficial effects: e.g. stable lean operation, pollution reduction, and wider range of p-T operating conditions. While experimental evidence abounds, theoretical understanding of PAC is at best incomplete, and numerical tools still lack in reliable predictive capabilities. In the context of a joint experimental-numerical effort at Michigan State University, we present here an open-source modular Python framework dedicated to the dynamic optimization of non-equilibrium PAC systems. Multiple sources of experimental reaction data, e.g. reaction rates, cross-sections and oscillator strengths, are used in order to quantify the effect of data uncertainty and limiting assumptions. A collisional-radiative model (CRM) is implemented to organize reactions by importance and as a potential means of measuring a non-Maxwellian electron energy distribution function (EEDF), when coupled to optical emission spectroscopy data. Finally, we explore scaling laws in PAC parameter space using a kinetic global model (KGM) accelerated with CRM optimized reaction sequences and sparse stiff integrators.

  19. Surface studies of praseodymium by electron spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    Krawczyk, Mirosław, E-mail: mkrawczyk@ichf.edu.pl; Pisarek, Marcin; Lisowski, Wojciech; Jablonski, Aleksander

    2016-12-01

    Highlights: • Pr foil. • EPES applied to measure the IMFPs in Pr samples after 3 keV Ar{sup +} ion etching. • Etched surfaces found to be formed by oxygen-containing Pr. • Measured IMFPs for E = 0.5–2 keV were approximated by Eq. (2). • The IMFPs were slightly affected by oxygen and agreed well with those from Eq. (3). - Abstract: Electron transport properties in praseodymium (Pr) foil samples were studied by elastic-peak electron spectroscopy (EPES). Prior to EPES measurements, the Pr sample surface was pre-sputtered by Ar ions with ion energy of 2–3 keV. After such treatment, the Pr sample still contained about 10 at.% of residual oxygen in the surface region, as detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses. The inelastic mean free path (IMFP), characterizing electron transport within this region (4 nm-thick), was evaluated from EPES using both Ni and Au standards as a function of energy in the range of 0.5–2 keV. Experimental IMFPs, λ, were approximated by the simple function λ = kE{sup p}, where E is energy (in eV), and k = 0.1549 and p = 0.7047 were the fitted parameters. These values were compared with IMFPs for the praseodymium surface in which the presence of oxygen was tentatively neglected, and also with IMFPs resulting from the TPP-2M predictive equation for bulk praseodymium. We found that the measured IMFP values to be only slightly affected by neglect of oxygen in calculations. The fitted function applied here was consistent with the energy dependence of the EPES-measured IMFPs. Additionally, the measured IMFPs were found to be from 2% to 4.2% larger than the predicted IMFPs for praseodymium in the energy range of 500–1000 eV. For electron energies of 1500 eV and 2000 eV, there was an inverse correlation between these values, and then the resulting deviations of −0.4% and −2.7%, respectively, were calculated.

  20. An experimental estimate of the electron-tunneling distance for some outer-sphere electrochemical reactions

    Science.gov (United States)

    Hupp, J. T.; Weaver, M. J.

    1983-11-01

    Estimates of the reaction zone thickness over which electron tunneling can effectively occur for the outer-sphere electrochemical reduction of some Cr(III) complexes are obtained by comparing the observed work-corrected rate constants with unimolecular rate constants for the electroreduction of structurally similar surface-bound Cr(III) reactants. Effective reaction zone thicknesses of ca. 0.1-0.3 A and ca. 5 A are obtained for outer-sphere electron transfer with Cr(III) reactants containing predominantly aquo or ammine ligands, respectively. This indicates that the former reactions are marginally nonadiabatic whereas the latter are decidedly adiabatic at their respective places of closest approach. These findings are compatible with the greater reactant-electrode separation distances previously noted for Cr(III) aquo relative to ammine complexes resulting from the more extensive hydration sheath surrounding the former reactants.

  1. Electronic Structure of Regular Bacterial Surface Layers

    Science.gov (United States)

    Vyalikh, Denis V.; Danzenbächer, Steffen; Mertig, Michael; Kirchner, Alexander; Pompe, Wolfgang; Dedkov, Yuriy S.; Molodtsov, Serguei L.

    2004-12-01

    We report photoemission and near-edge x-ray absorption fine structure measurements of the occupied and unoccupied valence electronic states of the regular surface layer of Bacillus sphaericus, which is widely used as the protein template for the fabrication of metallic nanostructures. The two-dimensional protein crystal shows a semiconductorlike behavior with a gap value of ˜3.0 eV and the Fermi energy close to the bottom of the lowest unoccupied molecular orbital. We anticipate that these results will open up new possibilities for the electric addressability of biotemplated low-dimensional hybrid structures.

  2. Surface Nano-Structuring by Adsorption and Chemical Reactions

    Directory of Open Access Journals (Sweden)

    Ken-ichi Tanaka

    2010-08-01

    Full Text Available Nano-structuring of the surface caused by adsorption of molecules or atoms and by the reaction of surface atoms with adsorbed species are reviewed from a chemistry viewpoint. Self-assembly of adsorbed species is markedly influenced by weak mutual interactions and the local strain of the surface induced by the adsorption. Nano-structuring taking place on the surface is well explained by the notion of a quasi-molecule provided by the reaction of surface atoms with adsorbed species. Self-assembly of quasi-molecules by weak internal bonding provides quasi-compounds on a specific surface. Various nano-structuring phenomena are discussed: (i self-assembly of adsorbed molecules and atoms; (ii self-assembly of quasi-compounds; (iii formation of nano-composite surfaces; (iv controlled growth of nano-materials on composite surfaces. Nano-structuring processes are not always controlled by energetic feasibility, that is, the formation of nano-composite surface and the growth of nano-particles on surfaces are often controlled by the kinetics. The idea of the “kinetic controlled molding” might be valuable to design nano-materials on surfaces.

  3. Surface reactions with participation of oxides of molybdenum and tungsten

    Directory of Open Access Journals (Sweden)

    A. F. Guseva

    2015-12-01

    Full Text Available The kinetics of surface reactions in one-dimensional and radial (two-dimensional distribution of diffusant MoO3 (WO3 on the surface of the substrate MeO (Me is Cd, Ni, Pb, Mn, Cu were investigated. A kinetic equation satisfactorily describes the rate of surface reactions in the case of radial distribution of diffusant on the substrate. It’s found that when the radial distribution of diffusant the growth of layer on the substrate surface eventually slows down and stops almost completely, due to the outflow of the diffusant deeps into the substrate. When the one-dimensional distribution of diffusant the surface interaction is not slowed down and does not stop at an arbitrarily large times.

  4. Diffusion-controlled sensitization of photocleavage reactions on surfaces.

    Science.gov (United States)

    Wöll, Dominik; Lukzen, Nikita; Steiner, Ulrich E

    2012-03-01

    The kinetic rate equation for the photosensitized cleavage reaction of surface-bound photolabile chromophores with free diffusion of sensitizer molecules from the bulk of a solution to the surface is derived by determining the stationary solution of a diffusion equation with suitable boundary conditions. The relation between the phenomenological rate constant for the photosensitized reaction at the surface and in the bulk is established. Applying the result to the analysis of an experimental example, the origin of the quasi zeroth-order kinetics of the sensitized reaction is revealed. A theoretical comparison of intramolecular sensitization in photocleavable protecting groups with a molecular antenna and sensitization with the freely diffusing sensitizer shows that in a typical case sensitization with free diffusion is more effective than intramolecular sensitization for sensitizer concentrations higher than 5 mM.

  5. Promotion of multi-electron transfer for enhanced photocatalysis: A review focused on oxygen reduction reaction

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Changhua [Centre for Advanced Optoelectronic Functional Materials Research, and Key Laboratory for UV-Emitting Materials and Technology of Ministry of Education, Northeast Normal University, Changchun 130024 (China); College of Chemistry and Biology, Beihua University, Jilin 132013 (China); Zhang, Xintong, E-mail: xtzhang@nenu.edu.cn [Centre for Advanced Optoelectronic Functional Materials Research, and Key Laboratory for UV-Emitting Materials and Technology of Ministry of Education, Northeast Normal University, Changchun 130024 (China); Liu, Yichun [Centre for Advanced Optoelectronic Functional Materials Research, and Key Laboratory for UV-Emitting Materials and Technology of Ministry of Education, Northeast Normal University, Changchun 130024 (China)

    2015-12-15

    Highlights: • Oxygen reduction reaction (ORR) in photocatalysis process is focused. • Multi-electron transfer ORR is reviewed. • This review provides a guide to access to enhanced photocatalysis via multi-electron transfer. - Abstract: Semiconductor photocatalysis has attracted significant interest for solar light induced environmental remediation and solar fuel generation. As is well known, photocatalytic performance is determined by three steps: photoexcitation, separation and transport of photogenerated charge carriers, and surface reactions. To achieve higher efficiency, significant efforts have been made on improvement of efficiency of above first two steps, which have been well documented in recent review articles. In contrast, this review intends to focus on strategies moving onto the third step of improvement for enhanced photocatalysis wherein active oxygen species including superoxide radical, hydrogen peroxide, hydroxyl radical are in situ detected. Particularly, surface electron-transfer reduction of oxygen over single component photocatalysts is reviewed and systems enabling multi-electron transfer induced oxygen reduction reaction (ORR) are highlighted. It is expected this review could provide a guideline for readers to better understand the critical role of ORR over photocatalyst in charge carrier separation and transfer and obtain reliable results for enhanced aerobic photocatalysis.

  6. Reaction of H2with O2in Excited Electronic States: Reaction Pathways and Rate Constants.

    Science.gov (United States)

    Pelevkin, Alexey V; Loukhovitski, Boris I; Sharipov, Alexander S

    2017-12-21

    Comprehensive quantum chemical analysis with the use of the multireference state-averaged complete active space self-consistent field approach was carried out to study the reactions of H 2 with O 2 in a 1 Δ g , b 1 Σ g + , c 1 Σ u - , and A' 3 Δ u electronically excited states. The energetically favorable reaction pathways and possible intersystem crossings have been revealed. The energy barriers were refined employing the extended multiconfiguration quasi-degenerate second-order perturbation theory. It has been shown that the interaction of O 2 (a 1 Δ g ) and O 2 (A' 3 Δ u ) with H 2 occurs through the H-abstraction process with relatively low activation barriers that resulted in the formation of the HO 2 molecule in A″ and A' electronic states, respectively. Meanwhile, molecular oxygen in singlet sigma states (b 1 Σ g + and c 1 Σ u - ) was proved to be nonreactive with respect to the molecular hydrogen. Appropriate rate constants for revealed reaction and quenching channels have been estimated using variational transition-state theory including corrections for the tunneling effect, possible nonadiabatic transitions, and anharmonicity of vibrations for transition states and reactants. It was demonstrated that the calculated reaction rate constant for the H 2 + O 2 (a 1 Δ g ) process is in reasonable agreement with known experimental data. The Arrhenius approximations for these processes have been proposed for the temperature range T = 300-3000 K.

  7. Revealing the reaction mechanisms of Li-O2 batteries using environmental transmission electron microscopy

    Science.gov (United States)

    Luo, Langli; Liu, Bin; Song, Shidong; Xu, Wu; Zhang, Ji-Guang; Wang, Chongmin

    2017-07-01

    The performances of a Li-O2 battery depend on a complex interplay between the reaction mechanism at the cathode, the chemical structure and the morphology of the reaction products, and their spatial and temporal evolution; all parameters that, in turn, are dependent on the choice of the electrolyte. In an aprotic cell, for example, the discharge product, Li2O2, forms through a combination of solution and surface chemistries that results in the formation of a baffling toroidal morphology. In a solid electrolyte, neither the reaction mechanism at the cathode nor the nature of the reaction product is known. Here we report the full-cycle reaction pathway for Li-O2 batteries and show how this correlates with the morphology of the reaction products. Using aberration-corrected environmental transmission electron microscopy (TEM) under an oxygen environment, we image the product morphology evolution on a carbon nanotube (CNT) cathode of a working solid-state Li-O2 nanobattery and correlate these features with the electrochemical reaction at the electrode. We find that the oxygen-reduction reaction (ORR) on CNTs initially produces LiO2, which subsequently disproportionates into Li2O2 and O2. The release of O2 creates a hollow nanostructure with Li2O outer-shell and Li2O2 inner-shell surfaces. Our findings show that, in general, the way the released O2 is accommodated is linked to lithium-ion diffusion and electron-transport paths across both spatial and temporal scales; in turn, this interplay governs the morphology of the discharging/charging products in Li-O2 cells.

  8. Interfacial reactions of glasses for biomedical application by scanning transmission electron microscopy and microanalysis.

    Science.gov (United States)

    Banchet, V; Michel, J; Jallot, E; Wortham, L; Bouthors, S; Laurent-Maquin, D; Balossier, G

    2006-05-01

    Short-term physico-chemical reactions at the interface between bioactive glass particles and biological fluids are studied for three glasses with different bioactive properties; these glasses are in the SiO(2)-Na(2)O-CaO-P(2)O(5)-K(2)O-Al(2)O(3)-MgO system. Our aim is to show the difference between the mechanisms of their surface reactions. The relation between the composition and the bioactive properties of these glasses is also discussed. The elemental analysis is performed at the submicrometer scale by scanning transmission electron microscopy associated with energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. After different immersion times (ranging from 0 to 96 h) of bioactive glass particles in a simulated biological solution, results show the formation of different surface layers at the glass periphery in the case of two bioactive glasses (A9 and BVA). For the third glass (BVH) we do not observe any surface layer formation or any modification of the glass composition. For the two other glasses (A9 and BVA), we observe the presence of different layers: an already observed (Si, O, Al) rich layer at the periphery, a previously demonstrated thin (Si, O) layer formed on top of the (Si, O, Al) layer and a (Ca, P) layer. We determine the different steps of the mechanisms of the surface reactions, which appear to be similar in these glasses, and compare the physico-chemical reactions and kinetics using the different immersion times. The A9 glass permits the observation of all important steps of the surface reactions which lead to bioactivity. This study shows the important relationship between composition and bioactivity which can determine the medical applicability of the glass.

  9. Photoelectron spectroscopy bulk and surface electronic structures

    CERN Document Server

    Suga, Shigemasa

    2014-01-01

    Photoelectron spectroscopy is now becoming more and more required to investigate electronic structures of various solid materials in the bulk, on surfaces as well as at buried interfaces. The energy resolution was much improved in the last decade down to 1 meV in the low photon energy region. Now this technique is available from a few eV up to 10 keV by use of lasers, electron cyclotron resonance lamps in addition to synchrotron radiation and X-ray tubes. High resolution angle resolved photoelectron spectroscopy (ARPES) is now widely applied to band mapping of materials. It attracts a wide attention from both fundamental science and material engineering. Studies of the dynamics of excited states are feasible by time of flight spectroscopy with fully utilizing the pulse structures of synchrotron radiation as well as lasers including the free electron lasers (FEL). Spin resolved studies also made dramatic progress by using higher efficiency spin detectors and two dimensional spin detectors. Polarization depend...

  10. Quantum simulation of nuclear rearrangement in electron transfer reactions

    OpenAIRE

    Zheng, Chong; McCammon, J. Andrew; Wolynes, Peter G.

    1989-01-01

    A quantum simulation scheme based on the path integral molecular dynamics technique has been used to calculate the effective activation energies associated with nuclear rearrangement in the electron transfer reactions Co(NH3)62+ + Co(NH3)63+ → Co(NH3)63+ + Co(NH3)62+ and Ru(NH3)62+ + Ru(NH3)63+ → Ru(NH3)63+ + Ru(NH3)62+. Even with a simple Hamiltonian and short time dynamic simulations, the results are in satisfactory agreement with other theoretical calculations. This simulation approach can...

  11. Comparing the temperature dependence of photosynthetic electron transfer in Chloroflexus aurantiacus and Rhodobactor sphaeroides reaction centers.

    Science.gov (United States)

    Guo, Zhi; Lin, Su; Xin, Yueyong; Wang, Haiyu; Blankenship, Robert E; Woodbury, Neal W

    2011-09-29

    The process of electron transfer from the special pair, P, to the primary electron donor, H(A), in quinone-depleted reaction centers (RCs) of Chloroflexus (Cf.) aurantiacus has been investigated over the temperature range from 10 to 295 K using time-resolved pump-probe spectroscopic techniques. The kinetics of the electron transfer reaction, P* → P(+)H(A)(-), was found to be nonexponential, and the degree of nonexponentiality increased strongly as temperature decreased. The temperature-dependent behavior of electron transfer in Cf. aurantiacus RCs was compared with that of the purple bacterium Rhodobacter (Rb.) sphaeroides . Distinct transitions were found in the temperature-dependent kinetics of both Cf. aurantiacus and Rb. sphaeroides RCs, at around 220 and 160 K, respectively. Structural differences between these two RCs, which may be associated with those differences, are discussed. It is suggested that weaker protein-cofactor hydrogen bonding, stronger electrostatic interactions at the protein surface, and larger solvent interactions likely contribute to the higher transition temperature in Cf. aurantiacus RCs temperature-dependent kinetics compared with that of Rb. sphaeroides RCs. The reaction-diffusion model provides an accurate description for the room-temperature electron transfer kinetics in Cf. aurantiacus RCs with no free parameters, using coupling and reorganization energy values previously determined for Rb. sphaeroides , along with an experimental measure of protein conformational diffusion dynamics and an experimental literature value of the free energy gap between P* and P(+)H(A)(-). © 2011 American Chemical Society

  12. Chemical Reactions of Molecules Promoted and Simultaneously Imaged by the Electron Beam in Transmission Electron Microscopy.

    Science.gov (United States)

    Skowron, Stephen T; Chamberlain, Thomas W; Biskupek, Johannes; Kaiser, Ute; Besley, Elena; Khlobystov, Andrei N

    2017-08-15

    The main objective of this Account is to assess the challenges of transmission electron microscopy (TEM) of molecules, based on over 15 years of our work in this field, and to outline the opportunities in studying chemical reactions under the electron beam (e-beam). During TEM imaging of an individual molecule adsorbed on an atomically thin substrate, such as graphene or a carbon nanotube, the e-beam transfers kinetic energy to atoms of the molecule, displacing them from equilibrium positions. Impact of the e-beam triggers bond dissociation and various chemical reactions which can be imaged concurrently with their activation by the e-beam and can be presented as stop-frame movies. This experimental approach, which we term ChemTEM, harnesses energy transferred from the e-beam to the molecule via direct interactions with the atomic nuclei, enabling accurate predictions of bond dissociation events and control of the type and rate of chemical reactions. Elemental composition and structure of the reactant molecules as well as the operating conditions of TEM (particularly the energy of the e-beam) determine the product formed in ChemTEM processes, while the e-beam dose rate controls the reaction rate. Because the e-beam of TEM acts simultaneously as a source of energy for the reaction and as an imaging tool monitoring the same reaction, ChemTEM reveals atomic-level chemical information, such as pathways of reactions imaged for individual molecules, step-by-step and in real time; structures of illusive reaction intermediates; and direct comparison of catalytic activity of different transition metals filmed with atomic resolution. Chemical transformations in ChemTEM often lead to previously unforeseen products, demonstrating the potential of this method to become not only an analytical tool for studying reactions, but also a powerful instrument for discovery of materials that can be synthesized on preparative scale.

  13. Non-adiabatic effects in elementary reaction processes at metal surfaces

    Science.gov (United States)

    Alducin, M.; Díez Muiño, R.; Juaristi, J. I.

    2017-12-01

    Great success has been achieved in the modeling of gas-surface elementary processes by the use of the Born-Oppenheimer approximation. However, in metal surfaces low energy electronic excitations are generated even by thermal and hyperthermal molecules due to the absence of band gaps in the electronic structure. This shows the importance of performing dynamical simulations that incorporate non-adiabatic effects to analyze in which way they affect most common gas-surface reactions. Here we review recent theoretical developments in this problem and their application to the study of the effect of electronic excitations in the adsorption and relaxation of atoms and molecules in metal surfaces, in scattering processes, and also in recombinative processes between impinging atoms and adsorbates at the surface. All these studies serve us to establish what properties of the gas-surface interaction favor the excitation of low-energy electron-hole pairs. A general observation is that the nature of these excitations usually requires long lasting interactions at the surface in order to observe deviations from the adiabatic behaviour. We also provide the basis of the local density friction approximation (LDFA) that have been used in all these studies, and show how it has been employed to perform ab initio molecular dynamics with electronic friction (AIMDEF). As a final remark, we will shortly review on recent applications of the LDFA to successfully simulate desorption processes induced by intense femtosecond laser pulses.

  14. Role of solvent dynamics in ultrafast photoinduced proton-coupled electron transfer reactions in solution.

    Science.gov (United States)

    Hazra, Anirban; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2010-09-30

    A theoretical formulation for modeling photoinduced nonequilibrium proton-coupled electron transfer (PCET) reactions in solution is presented. In this formulation, the PCET system is described by donor and acceptor electron-proton vibronic free energy surfaces that depend on a single collective solvent coordinate. Dielectric continuum theory is used to obtain a generalized Langevin equation of motion for this collective solvent coordinate. The terms in this equation depend on the solvent properties, such as the dielectric constants, relaxation time, and molecular moment of inertia, as well as the solute properties characterizing the vibronic surfaces. The ultrafast dynamics following photoexcitation is simulated using a surface hopping method in conjunction with the Langevin equation of motion. This methodology is used to examine a series of model photoinduced PCET systems, where the initial nonequilibrium state is prepared by vertical photoexcitation from the ground electronic state to the donor electronic state. Analysis of the dynamical trajectories provides insight into the interplay between the solvent dynamics and the electron-proton transfer for these types of processes. In addition, these model studies illustrate how the coupling between the electron-proton transfer and the solvent dynamics can be tuned by altering the solute and solvent properties.

  15. The hydrated electron and its reactions at high temperatures

    DEFF Research Database (Denmark)

    Christensen, Hilbert; Sehested, Knud

    1986-01-01

    The spectrum of the hydrated electron was determined in the temperature range 5-300 "C by using strongly alkaline solutions and high hydrogen pressure. At temperatures up to about 150 "C the temperature coefficients of E, and AE1/2 are -2.8 X and 2 X lo4 eV K-', respectively. E,, is the energy....... The rate constant of the second-order decay (2k) is (1.00 f 0.05) X 1O'O dm3 mol-] s-I at 20 "C, independent of pH. The activation energy of the reaction is 23 f 1 kJ mol-] (5.4 f 0.2 kcal mol-') at temperatures up to 150 "C. The decay at temperatures above 150 "C becomes slower with increasing...... the electron spectrum, half-width, or em& to any significant degree at ambient and higher temperatures. -Th e simplest mechanism capable of describing the kinetic data at various temperatures is the equilibrium e,; + e,; F-? (e22-)aq H2 where the dissociation reaction has a higher activation energy than...

  16. Surface photo reaction processes using synchrotron radiation; Hoshako reiki ni yoru hyomenko hanno process

    Energy Technology Data Exchange (ETDEWEB)

    Imaizumi, Y. [Tohoku University, Sendai (Japan). Institute for Materials Research; Yoshigoe, A. [Toyohashi University of Technology, Aichi (Japan); Urisu, T. [Toyohashi University of Technology, Aichi (Japan). Institute for Molecular Science

    1997-08-20

    This paper introduces the surface photo reaction processes using synchrotron radiation, and its application. A synchrotron radiation process using soft X-rays contained in electron synchrotron radiated light as an excited light source has a possibility of high-resolution processing because of its short wave length. The radiated light can excite efficiently the electronic state of a substance, and can induce a variety of photochemical reactions. In addition, it can excite inner shell electrons efficiently. In the aspect of its application, it has been found that, if radiated light is irradiated on surfaces of solids under fluorine-based reaction gas or Cl2, the surfaces can be etched. This technology is utilized practically. With regard to radiated light excited CVD process, it may be said that anything that can be deposited by the ordinary plasma CVD process can be deposited. Its application to epitaxial crystal growth may be said a nano processing application in thickness direction, such as forming an ultra-lattice structure, the application being subjected to expectation. In micromachine fabricating technologies, a possibility is searched on application of a photo reaction process of the radiated light. 5 refs., 6 figs.

  17. Self-activated, self-limiting reactions on Si surfaces

    DEFF Research Database (Denmark)

    Morgen, Per; Hvam, Jeanette; Bahari, Ali

    The direct thermally activated reactions of oxygen and ammonia with Si surfaces in furnaces have been used for a very long time in the semiconductor industry for the growth of thick oxides and nitride layers respectively. The oxidation mechanism was described in the Deal-Grove model as a diffusion...... mechanism for the direct growth of ultrathin films (0-3 nm) of oxides and nitrides under ultrahigh vacuum conditions. Neutral oxygen and a microwave excited nitrogen plasma interact directly with Si surfaces kept at different temperatures during the reaction. The gas pressures are around 10-6 Torr...... energy of an oxide system, which happened for an ordered structure, at a thickness of 0.7-0.8 nm. Thus this thin oxide structure has definite crystalline features. We have closely monitored the reaction kinetics with normal x-ray induced photoelectron spectroscopies, and also the structure, composition...

  18. Performing chemical reactions in virtual capillary of surface tension ...

    Indian Academy of Sciences (India)

    We have also successfully carried out some well-known chemical reactions in these fluidic channels to demonstrate the usefulness of these wall-less microchannels. The confined flow path of liquid was achieved on the basis of extreme differences in hydrophobic and hydrophilic characters of the surface. The flow paths ...

  19. Theory of flame spread above solids. [fuel exothermic surface reactions

    Science.gov (United States)

    Sirignano, W. A.

    1974-01-01

    A theory for flame spread above a solid fuel is presented. The special case is considered whereby the oxidation is an exothermic surface reaction. The spreading rate is predicted as a function of the thermochemical properties, fuel-bed thickness, and convective velocity. Also, the theory predicts temperature, mass fraction, and heat flux as a function of position.

  20. Evidence concerning oxidation as a surface reaction in Baltic amber

    DEFF Research Database (Denmark)

    Shashoua, Yvonne

    2012-01-01

    The aim of this study was to provide evidence about oxidation as a surface reaction during degradation of Baltic amber. A clear understanding of the amber-oxygen interaction modalities is essential to develop conservation techniques for museum collections of amber objects. Pellet-shaped samples...

  1. Competitive reactions of organophosphorus radicals on coke surfaces.

    Science.gov (United States)

    Catak, Saron; Hemelsoet, Karen; Hermosilla, Laura; Waroquier, Michel; Van Speybroeck, Veronique

    2011-10-17

    The efficacy of organophosphorus radicals as anticoking agents was subjected to a computational study in which a representative set of radicals derived from industrially relevant organophosphorus additives was used to explore competitive reaction pathways on the graphene-like coke surface formed during thermal cracking. The aim was to investigate the nature of the competing reactions of different organophosphorus radicals on coke surfaces, and elucidate their mode of attack and inhibiting effect on the forming coke layer by use of contemporary computational methods. Density functional calculations on benzene and a larger polyaromatic hydrocarbon, namely, ovalene, showed that organophosphorus radicals have a high propensity to add to the periphery of the coke surface, inhibiting methyl radical induced hydrogen abstraction, which is known to be a key step in coke growth. Low addition barriers reported for a phosphatidyl radical suggest competitive aptitude against coke formation. Moreover, organophosphorus additives bearing aromatic substituents, which were shown to interact with the coke surface through dispersive π-π stacking interactions, are suggested to play a nontrivial role in hindering further stacking among coke surfaces. This may be the underlying rationale behind experimental observation of softer coke in the presence of organophosphorus radicals. The ultimate goal is to provide information that will be useful in building single-event microkinetic models. This study presents pertinent information on potential reactions that could be taken up in these models. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Investigations of the Fundamental Surface Reactions Involved in the Sorption and Desorption of Radionuclides

    Energy Technology Data Exchange (ETDEWEB)

    Czerwinski, Ken; Heske, Clemens; Moser, Duane; Misra, Mnoranjan; McMillion, Glen

    2011-04-20

    Models for describing solution- and surface-phase reactions have been used for 30 years, but only recently applicable to complex surfaces. Duff et al., using micro-XANES, found that Pu was concentrated on Mn-oxide and smectite phases of zeolitic tuff, providing an evaluation of contaminant speciation on surfaces for modeling. Experiments at Los Alamos demonstrated that actinides display varying surface residence time distributions, probably reflective of mineral surface heterogeneity. We propose to investigate the sorption/desorption behavior of radionuclides from mineral surfaces, as effected by microorganisms, employing isolates from Nevada Test Site deep alluvium as a model system. Characterizations will include surface area, particle size distribution, x-ray diffraction (XRD), microprobe analysis, extractions, and microbiology. Surface interactions will be assessed by electron spectroscopy (XPS), x-ray absorption fine structure spectroscopy (XAFS), X-ray emission spectroscopy, transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). Desert Research Institute (DRI), University of Nevada, Reno (UNR), and University of Nevada, Las Vegas (UNLV) researchers will collaborate to enhance scientific infrastructure and the understanding of contaminant behavior on surfaces, with broader implications for the management of DOE sites.

  3. Electron uptake and delivery sites on plastocyanin in its reactions with the photosynthetic electron transport system

    DEFF Research Database (Denmark)

    Farver, O; Shahak, Y; Pecht, I

    1982-01-01

    French bean plastocyanin is stoichiometrically and specifically labeled upon reduction by Cr(II)aq ions, yielding a substitution-inert (Cr(III) adduct at the protein surface. The effect of the modification on the activity of plastocyanin in electron transfer between photosystems II and I has been...... and Cr-labeled plastocyanin were indistinguishable, the rates of photooxidation of the modified protein were markedly attenuated relative to those of the native one. This difference in reactivity clearly reflects the perturbation of the electron transfer pathway to P700. These findings, in conjunction...... with the structure of plastocyanin and the locus of CR(III) binding on its surface, lead to the following interpretation: (a) There are most probably two physiologically significant, electron transfer sites on plastocyanin. (b) The site involved in the electron transfer to P700 is most likely in the region...

  4. Dynamic flexibility in the light reactions of photosynthesis governed by both electron and proton transfer reactions.

    Science.gov (United States)

    Kramer, David M; Avenson, Thomas J; Edwards, Gerald E

    2004-07-01

    Plant photosynthesis performs the remarkable feat of converting light energy into usable chemical forms, which involves taming highly reactive intermediates without harming plant cells. This requires an apparatus that is not only efficient and robust but also flexible in its responses to changing environmental conditions. It also requires that the output of the energy-storing reactions be matched with the demands of metabolism. This article addresses the mechanisms by which this flexibility is achieved for short-term environmental changes. We argue that chloroplasts need two types of flexible mechanisms: one for modulating the output ratio of ATP:NADPH, which involves cyclic electron flux around photosystem I; and another for changing the regulatory sensitivity of the light-harvesting antenna to electron (and proton) flow.

  5. Radiation recall reaction with docetaxel administration after accelerated partial breast irradiation with electronic brachytherapy.

    Science.gov (United States)

    Chen, Sea S; Strauss, Jonathan B; Shah, Anand P; Rao, Ruta D; Bernard, Damien A; Griem, Katherine L

    2009-01-01

    Accelerated partial breast irradiation (APBI) offers several advantages over whole breast irradiation. Electronic brachytherapy may further reduce barriers to breast conserving therapy by making APBI more available. However, its toxicity profile is not well characterized. A 60-year-old woman was treated with APBI using Axxent (Xoft, Sunnyvale, CA) electronic brachytherapy. One month after APBI, a cycle of docetaxel and cyclophosphamide was given. Within 3 weeks, the patient developed an ulcerative radiation recall reaction in the skin overlying the lumpectomy cavity. To investigate this toxicity, the skin dose from electronic brachytherapy was compared with the dose that would have been delivered by an iridium-192 ((192)Ir) source. Additionally, a dose equivalent was estimated by adjusting for the increased relative biologic effectiveness (RBE) of low energy photons generated by the electronic source. Using electronic brachytherapy, the skin dose was 537cGy per fraction compared with 470cGy for an (192)Ir source. Given an RBE for a 40kV source of 1.28 compared with (192)Ir, the equivalent dose at the skin for an electronic source was 687cGy-equivalents, a 46% increase. We present a case of an ulcerative radiation recall reaction in a patient receiving APBI with electronic brachytherapy followed by chemotherapy. Our analysis shows that the use of electronic brachytherapy resulted in the deposition of significantly higher equivalent dose at the skin compared with (192)Ir. These findings suggest that standard guidelines (e.g., surface-to-skin distance) that apply to (192)Ir-based balloon brachytherapy may not be applicable to electronic brachytherapy.

  6. Theoretical studies on the reaction pathways of electronically excited DAAF

    Energy Technology Data Exchange (ETDEWEB)

    Quenneville, Jason M [Los Alamos National Laboratory; Moore, David S [Los Alamos National Laboratory

    2009-01-01

    The use of temporally and spectrally shaped ultrafast laser pulses to initiate, as well as detect, high explosives is being explored at Los Alamos. High level ab initio calculations, presented here, are employed to help guide and interpret the experiments. The ground and first excited electronic states of 3,3{prime}-diamino-4,4{prime}-azoxyfurazan (DAAF) are investigated using complete active space self-consistent field (CASSCF) and time-dependent density functional theory (TD-DFT). The geometrical and energetic character of the excited state minima, conical intersections and reaction pathways of DAAF are described. Two radiative and two non-radiative excited state population quenching mechanisms are outlined, and possible pathways for photochemical and spectroscopic control are discussed. The use of laser light to control chemical reactions has many applications. The initiation and the detection of explosives are two such applications currently under development at Los Alamos. Though inherently experimental, the project can be aided by theory through both prediction and interpretation. When the laser light is in the UV/visible region of the electromagnetic spectrum, the absorbing molecule is excited electronically and excitation decay may occur either radiatively (fluorescence or phosphorescence) or non-radiatively (through internal conversion). In many cases decay of the excitation occurs through a mixture of processes, and maximizing the desired result requires sophisticated laser pulses whose amplitude has been optimally modulated in time and/or frequency space. Control of cis-stilbene photochemistry was recently demonstrated in our group, and we aim to extend this work to high explosive compounds. Maximizing radiative decay leads to increased fluorescence quantum yields and enhances the possibility of spectral detection of the absorbing molecule. Maximizing non-radiative decay can lead to chemistry, heating of the sample and possibly detonation initiation in

  7. Theory of the reaction dynamics of small molecules on metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Jackson, Bret [Univ. of Massachusetts, Amherst, MA (United States)

    2016-09-09

    The objective of this project has been to develop realistic theoretical models for gas-surface interactions, with a focus on processes important in heterogeneous catalysis. The dissociative chemisorption of a molecule on a metal is a key step in many catalyzed reactions, and is often the rate-limiting step. We have explored the dissociative chemisorption of H2, H2O and CH4 on a variety of metal surfaces. Most recently, our extensive studies of methane dissociation on Ni and Pt surfaces have fully elucidated its dependence on translational energy, vibrational state and surface temperature, providing the first accurate comparisons with experimental data. We have explored Eley-Rideal and hot atom reactions of H atoms with H- and C-covered metal surfaces. H atom interactions with graphite have also been explored, including both sticking and Eley-Rideal recombination processes. Again, our methods made it possible to explain several experiments studying these reactions. The sticking of atoms on metal surfaces has also been studied. To help elucidate the experiments that study these processes, we examine how the reaction dynamics depend upon the nature of the molecule-metal interaction, as well as experimental variables such as substrate temperature, beam energy, angle of impact, and the internal states of the molecules. Electronic structure methods based on Density Functional Theory are used to compute each molecule-metal potential energy surface. Both time-dependent quantum scattering techniques and quasi-classical methods are used to examine the reaction or scattering dynamics. Much of our effort has been directed towards developing improved quantum methods that can accurately describe reactions, as well as include the effects of substrate temperature (lattice vibration).

  8. Polymer surface engineering via thiol-mediated reactions

    Science.gov (United States)

    Hensarling, Ryan Matthew

    Synthesis of polymer brushes to decorate a surface with desired functionality typically involves surface-initiated polymerization (SIP) of functional, but non-reactive monomers. This approach suffers major drawbacks associated with synthesizing sufficiently thick polymer brushes containing surface-attached polymer chains of high molecular weight at high grafting density (i.e. cost, synthetic effort and functional group intolerance during polymerization). The research herein seeks to circumvent these limitations by the decoration of surfaces with polymer chains bearing specific pendent functional groups amenable to post-polymerization modification (PPM). In particular, this dissertation leverages PPM via a specific class of click reactions - thiol-click - that 1) enables the rapid generation of a diverse library of functional surfaces from a single substrates precursor, 2) utilizes a structurally diverse range of commercially available or easily attainable reagents, 3) proceeds rapidly to quantitative conversions under mild conditions and 4) opens the door to orthogonal and site-selective functionalization. In the first two studies, radical-mediated thiol-yne and base-catalyzed thiol-isocyanate reactions are demonstrated as modular platforms for the rapid and practical fabrication of highly functional, multicomponent surfaces under ambient conditions. Brush surfaces expressing a three-dimensional configuration of alkyne or isocyanate functionalities were modified with high efficiency and short reaction times using a library of commercially available thiols. In the third study, two routes to multifunctional brush surfaces were demonstrated utilizing orthogonal thiol-click reactions. In the first approach, alkyne-functionalized homopolymer brushes were modified with multiple thiols via a statistical, radical-mediated thiol-yne co-click reaction; and in the second approach, statistical copolymer brushes carrying two distinctly-addressable reactive moieties were

  9. An AES Study of the Room Temperature Surface Conditioning of Technological Metal Surfaces by Electron Irradiation

    CERN Document Server

    Scheuerlein, C; Taborelli, M; Brown, A; Baker, M A

    2002-01-01

    The modifications to technological copper and niobium surfaces induced by 2.5 keV electron irradiation have been investigated in the context of the conditioning process occurring in particle accelerator ultra high vacuum systems. Changes in the elemental surface composition have been found using Scanning Auger Microscopy (SAM) by monitoring the carbon, oxygen and metal Auger peak intensities as a function of electron irradiation in the dose range 10-6 to 10-2 C mm-2. The surface analysis results are compared with electron dose dependent secondary electron and electron stimulated desorption yield measurements. Initially the electron irradiation causes a surface cleaning through electron stimulated desorption, in particular of hydrogen. During this period both the electron stimulated desorption and secondary electron yield decrease as a function of electron dose. When the electron dose exceeds 10-4 C mm-2 electron stimulated desorption yields are reduced by several orders of magnitude and the electron beam indu...

  10. Surface chemistry of rare-earth oxide surfaces at ambient conditions: reactions with water and hydrocarbons

    Science.gov (United States)

    Külah, Elçin; Marot, Laurent; Steiner, Roland; Romanyuk, Andriy; Jung, Thomas A.; Wäckerlin, Aneliia; Meyer, Ernst

    2017-03-01

    Rare-earth (RE) oxide surfaces are of significant importance for catalysis and were recently reported to possess intrinsic hydrophobicity. The surface chemistry of these oxides in the low temperature regime, however, remains to a large extent unexplored. The reactions occurring at RE surfaces at room temperature (RT) in real air environment, in particular, in presence of polycyclic aromatic hydrocarbons (PAHs), were not addressed until now. Discovering these reactions would shed light onto intermediate steps occurring in automotive exhaust catalysts before reaching the final high operational temperature and full conversion of organics. Here we first address physical properties of the RE oxide, nitride and fluoride surfaces modified by exposure to ambient air and then we report a room temperature reaction between PAH and RE oxide surfaces, exemplified by tetracene (C18H12) on a Gd2O3. Our study evidences a novel effect - oxidation of higher hydrocarbons at significantly lower temperatures (~300 K) than previously reported (>500 K). The evolution of the surface chemical composition of RE compounds in ambient air is investigated and correlated with the surface wetting. Our surprising results reveal the complex behavior of RE surfaces and motivate follow-up studies of reactions between PAH and catalytic surfaces at the single molecule level.

  11. Revealing the reaction mechanisms of Li–O2 batteries using environmental transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Langli; Liu, Bin; Song, Shidong; Xu, Wu; Zhang, Ji-Guang; Wang, Chongmin

    2017-03-27

    The capacity, Coulombic efficiency, rate, and cyclability of a Li-O2 battery critically depend on the electrode reaction mechanism and the structure/morphology of the reaction product as well as their spatial and temporal evolution1-8, which are all further complicated by the choice of different electrolyte. For the case of aprotic cell, the discharge product, Li2O2, is formed through solution and surface mechanisms9,10, but little is known on the formation mechanism of the perplexing morphology of the reaction product11-15. For the case of Li-O2 battery using solid electrolyte, neither electrode reaction mechanism nor the nature of the reaction production is known. Herein, we reveal the full cycle reaction pathway for Li-O2 batteries and its correlation with the nature of the reaction product. Using an aberration-corrected environmental TEM under oxygen environment, we captured, for the first time, the morphology and phase evolution on the carbon nanotube (CNT) cathode of a working solid-state Li-O2 nano-battery16 and directly correlated these features with electrochemical reaction. We found that the oxygen reduction reaction on CNTs initially produces LiO2, which subsequently evolves to Li2O2 and O2 through disproportionation reaction. Surprisingly it is just the releasing of O2 that inflates the particles to a hollow structure with a Li2O outer surface layer and Li2O2 inner-shell, demonstrating that, in general, accommodation of the released O2 coupled with the Li+ ion diffusion and electron transport paths across both spatial and temporal scales critically governs the morphology of the discharging/charging product in Li-O2 system. We anticipate that the direct observation of Li-O2 reaction mechanisms and their correlation with the morphology of the reaction product set foundation for quantitative understanding/modeling of the electrochemical processes in the Li-O2 system, enabling rational design of both solid-state and aprotic Li-O2 batteries.

  12. Recyclable surfaces for amine conjugation chemistry via redox reaction

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Inseong; Yeo, Woon Seok [Dept. of Bioscience and Biotechnology, Bio/Molecular Informatics Center, Konkuk University, Seoul (Korea, Republic of); Bae, Se Won [Green Materials and Process Group, Research Institute of Sustainable Manufacturing System, Korea Institute of Industrial Technology, Cheonan (Korea, Republic of)

    2017-02-15

    In this study, we extended this strategy to present a switchable surface that allows surface functionalization and removal of functional groups repeatedly. The substrate presenting a benzoquinone acid group is first used to immobilize with an amine-containing (bio)molecule using well-known conjugation chemistry. The benzoquinone group is then converted to the corresponding hydroquinone by treating with a reducing agent. We have described a strategy for the dynamic control of surface properties with recyclability via a simple reduction/ oxidation reaction. A stimuli-responsive quinone derivative was harnessed for the repeated immobilization and release of (bio)molecules, and thus, for the repeated dynamic change of the surface properties according to the characteristics of the immobilized (bio)molecules.

  13. Iso-scalar surfaces, mixing and reaction in turbulent flows

    Science.gov (United States)

    Dopazo, César; Martín, Jesús; Hierro, Juan

    2006-08-01

    Turbulent scalar mixing with chemical reaction is investigated in terms of the local geometrical features of the iso-scalar surfaces—'scalar field topologies'—, using Direct Numerical Simulation data. Two scalars with identical initial distribution, one inert and the other obeying a prescribed Arrhenius-like chemical reaction, evolve in homogeneous isotropic turbulence with a mesh size 256 3. The two local principal curvatures, k and k, of the iso-scalar surface at each point are straightforwardly obtained from the curvature tensor, n, whose elements are the spatial derivatives of the unit vector normal to the iso-surface. The scalar diffusive flux is decomposed into a 'flat-front' contribution plus a curvature induced molecular transport. Expressions for the normal propagating velocity relative to the fluid of iso-surfaces, of both the inert and the reactive scalar fields, are provided making use of the previous decomposition. The 'flat-front' and the curvature induced contributions to the diffusive fluxes, beside to the chemical reaction rate, are correlated with the principal curvatures. Results, including the joint statistics of the principal curvatures and their correlations with the scalar dissipation, are also presented. To cite this article: C. Dopazo et al., C. R. Mecanique 334 (2006).

  14. Kinetic theory of plasma sheaths surrounding electron-emitting surfaces.

    Science.gov (United States)

    Sheehan, J P; Hershkowitz, N; Kaganovich, I D; Wang, H; Raitses, Y; Barnat, E V; Weatherford, B R; Sydorenko, D

    2013-08-16

    A one-dimensional kinetic theory of sheaths surrounding planar, electron-emitting surfaces is presented which accounts for plasma electrons lost to the surface and the temperature of the emitted electrons. It is shown that ratio of plasma electron temperature to emitted electron temperature significantly affects the sheath potential when the plasma electron temperature is within an order of magnitude of the emitted electron temperature. The sheath potential goes to zero as the plasma electron temperature equals the emitted electron temperature, which can occur in the afterglow of an rf plasma and some low-temperature plasma sources. These results were validated by particle in cell simulations. The theory was tested by making measurements of the sheath surrounding a thermionically emitting cathode in the afterglow of an rf plasma. The measured sheath potential shrunk to zero as the plasma electron temperature cooled to the emitted electron temperature, as predicted by the theory.

  15. Electron Conditioning of Technical Aluminium Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Le Pimpec, F

    2004-09-02

    The effect of electron conditioning on commercially aluminium alloys 1100 and 6063 were investigated. Contrary to the assumption that electron conditioning, if performed long enough, can reduce and stabilize the SEY to low values (= 1.3, value of many pure elements [1]), the SEY of aluminium did not go lower than 1.8. In fact, it reincreases with continued electron exposure dose.

  16. Manufacture of surface reaction analysis apparatus and its application to analysis of initial oxidation processes on Si (001) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Teraoka, Yuden; Yoshigoe, Akitaka; Sano, Mutsumi [Sychrotron Radiation Research Center, Kansai Research Establishment, Japan Atomic Energy Research Institute, Mikazuki, Hyogo (Japan)

    2001-02-01

    We have joined with the construction team of JAERI soft x-ray beaming, BL23SU, in the SPring-8. An experimental apparatus for the analysis of surface reaction dynamics on semiconductor surfaces has been manufactured and installed as an end-station of the beamline. This end-station emphasizes a simultaneous use of supersonic molecular beams, an electron energy analyzer and a quadrupole mass analyzer to achieve the real 'in situ' analysis of surface reactions to obtain more deeper understanding for elementary processes of chemisorption. The effects of translational energy of incident O{sub 2} molecules for initial oxidation on Si (001) surfaces have been investigated by photoemission spectroscopy and molecular beam scattering techniques. The oxygen saturation coverage on the Si (001) surface at room temperature increased with increasing the translational energy, showing two thresholds at 1.0 eV and 2.6 eV. These values were close to the predicted values from the first-principles calculation so that the values were assigned to the backbond oxidation of top dimers and subsurface Si atoms, respectively. The oxidation number of Si atoms on the oxygen-chemisorbed Si (001) surface was found to be increased with increasing the incident energy of O{sub 2} molecules. Furthermore, the sudden increase of SiO desorption rate was found at about 700degC in the incident energy larger than 2.0 eV. (author)

  17. Atomic and electronic structures of novel silicon surface structures

    Energy Technology Data Exchange (ETDEWEB)

    Terry, J.H. Jr.

    1997-03-01

    The modification of silicon surfaces is presently of great interest to the semiconductor device community. Three distinct areas are the subject of inquiry: first, modification of the silicon electronic structure; second, passivation of the silicon surface; and third, functionalization of the silicon surface. It is believed that surface modification of these types will lead to useful electronic devices by pairing these modified surfaces with traditional silicon device technology. Therefore, silicon wafers with modified electronic structure (light-emitting porous silicon), passivated surfaces (H-Si(111), Cl-Si(111), Alkyl-Si(111)), and functionalized surfaces (Alkyl-Si(111)) have been studied in order to determine the fundamental properties of surface geometry and electronic structure using synchrotron radiation-based techniques.

  18. Surface and volume photoemission of hot electrons from plasmonic nanoantennas

    DEFF Research Database (Denmark)

    Uskov, Alexander V.; Protsenko, Igor E.; Ikhsanov, Renat S.

    2014-01-01

    We theoretically compare surface- and volume-based photoelectron emission from spherical nanoparticles, obtaining analytical expressions for the emission rate in both mechanisms. We show that the surface mechanism prevails, being unaffected by detrimental hot electron collisions.......We theoretically compare surface- and volume-based photoelectron emission from spherical nanoparticles, obtaining analytical expressions for the emission rate in both mechanisms. We show that the surface mechanism prevails, being unaffected by detrimental hot electron collisions....

  19. Laboratory measurements of heterogeneous reactions on sulfuric acid surfaces

    Science.gov (United States)

    Williams, Leah R.; Manion, Jeffrey A.; Golden, David M.; Tolbert, Margaret A.

    1994-01-01

    Increasing evidence from field, modeling, and laboratory studies suggests that heterogeneous reactions on stratospheric sulfate aerosol particles may contribute to global ozone depletion. Using a Knudsen cell reactor technique, the authors have studied the uptake, reactivity, and solubility of several trace atmospheric species on cold sulfuric acid surfaces representative of stratospheric aerosol particles. The results suggest that the heterogeneous conversion of N2O5 to HNO3 is fast enough to significantly affect the partitioning of nitrogen species in the global stratosphere and thus contribute to global ozone depletion. The hydrolysis of ClONO2 is slower and unlikely to be important under normal conditions at midlatitudes. The solubilities of HCl and HNO3 in sulfuric acid down to 200 K were found to be quite low. For HCl, this means that little HCl is available for reaction on the surfaces of stratospheric sulfate aerosol particles. The low solubility of HNO3 means that this product of heterogeneous reactions will enter the gas phase, and the denitrification observed in polar regions is unlikely to occur in the global stratosphere.

  20. Refractory phases synthesis at the surface microalloying using a wide aperture electron beam

    Science.gov (United States)

    Fedorov, S. V.; Htet Swe, Min

    2017-05-01

    The experimental results prove the ability to realize technology of chemical heat treatment of some materials by surface microalloying using a wide-aperture low-energy high-current electron beam. Such layers were produced due to initiating exothermic chemical self-propagating high-temperature reactions in the thermal explosion mode between the base and the thin film covered on the base. New phase compounds in reaction products were found.

  1. Synthesis of 3-Alkenyl-1-azaanthraquinones via Diels-Alder and Electron Transfer Reactions

    Directory of Open Access Journals (Sweden)

    Patrice Vanelle

    2002-12-01

    Full Text Available A convenient route to 3-alkenyl-1-azaanthraquinones via a hetero Diels-Alder reaction between an azadiene and naphthoquinone, a free radical chlorination and an electron transfer reaction is reported.

  2. Electronic nicotine delivery system (electronic cigarette) awareness, use, reactions and beliefs: a systematic review.

    Science.gov (United States)

    Pepper, Jessica K; Brewer, Noel T

    2014-09-01

    We sought to systematically review the literature on electronic nicotine delivery systems (ENDS, also called electronic cigarettes) awareness, use, reactions and beliefs. We searched five databases for articles published between 2006 and 1 July 2013 that contained variations of the phrases 'electronic cigarette', 'e-cigarette' and 'electronic nicotine delivery'. Of the 244 abstracts identified, we excluded articles not published in English, articles unrelated to ENDS, dissertation abstracts and articles without original data on prespecified outcomes. Two reviewers coded each article for ENDS awareness, use, reactions and beliefs. 49 studies met inclusion criteria. ENDS awareness increased from 16% to 58% from 2009 to 2011, and use increased from 1% to 6%. The majority of users were current or former smokers. Many users found ENDS satisfying, and some engaged in dual use of ENDS and other tobacco. No longitudinal studies examined whether ENDS serve as 'gateways' to future tobacco use. Common reasons for using ENDS were quitting smoking and using a product that is healthier than cigarettes. Self-reported survey data and prospective trials suggest that ENDS might help cigarette smokers quit, but no randomised controlled trials with probability samples compared ENDS with other cessation tools. Some individuals used ENDS to avoid smoking restrictions. ENDS use is expanding rapidly despite experts' concerns about safety, dual use and possible 'gateway' effects. More research is needed on effective public health messages, perceived health risks, validity of self-reports of smoking cessation and the use of different kinds of ENDS. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

  3. Evidence concerning oxidation as a surface reaction in Baltic amber.

    Science.gov (United States)

    Pastorelli, Gianluca; Richter, Jane; Shashoua, Yvonne

    2012-04-01

    The aim of this study was to provide evidence about oxidation as a surface reaction during degradation of Baltic amber. A clear understanding of the amber-oxygen interaction modalities is essential to develop conservation techniques for museum collections of amber objects. Pellet-shaped samples, obtained from pressed amber powder, were subjected to accelerated thermal ageing. Cross-sections of the pellets were analyzed by infrared micro-spectroscopy, in order to identify and quantify changes in chemical properties. The experimental results showed strong oxidation exclusively at the exterior part of cross-sections from samples subjected to long-term thermal ageing, confirming that oxidation of Baltic amber starts from the surface. Copyright © 2012 Elsevier B.V. All rights reserved.

  4. Strong electron correlation in the decomposition reaction of dioxetanone with implications for firefly bioluminescence.

    Science.gov (United States)

    Greenman, Loren; Mazziotti, David A

    2010-10-28

    Dioxetanone, a key component of the bioluminescence of firefly luciferin, is itself a chemiluminescent molecule due to two conical intersections on its decomposition reaction surface. While recent calculations of firefly luciferin have employed four electrons in four active orbitals [(4,4)] for the dioxetanone moiety, a study of dioxetanone [F. Liu et al., J. Am. Chem. Soc. 131, 6181 (2009)] indicates that a much larger active space is required. Using a variational calculation of the two-electron reduced-density-matrix (2-RDM) [D. A. Mazziotti, Acc. Chem. Res. 39, 207 (2006)], we present the ground-state potential energy surface as a function of active spaces from (4,4) to (20,17) to determine the number of molecular orbitals required for a correct treatment of the strong electron correlation near the conical intersections. Because the 2-RDM method replaces exponentially scaling diagonalizations with polynomially scaling semidefinite optimizations, we readily computed large (18,15) and (20,17) active spaces that are inaccessible to traditional wave function methods. Convergence of the electron correlation with active-space size was measured with complementary RDM-based metrics, the von Neumann entropy of the one-electron RDM as well as the Frobenius and infinity norms of the cumulant 2-RDM. Results show that the electron correlation is not correctly described until the (14,12) active space with small variations present through the (20,17) space. Specifically, for active spaces smaller than (14,12), we demonstrate that at the first conical intersection, the electron in the σ(∗) orbital of the oxygen-oxygen bond is substantially undercorrelated with the electron of the σ orbital and overcorrelated with the electron of the carbonyl oxygen's p orbital. Based on these results, we estimate that in contrast to previous treatments, an accurate calculation of the strong electron correlation in firefly luciferin requires an active space of 28 electrons in 25 orbitals

  5. Charge constrained density functional molecular dynamics for simulation of condensed phase electron transfer reactions.

    Science.gov (United States)

    Oberhofer, Harald; Blumberger, Jochen

    2009-08-14

    We present a plane-wave basis set implementation of charge constrained density functional molecular dynamics (CDFT-MD) for simulation of electron transfer reactions in condensed phase systems. Following the earlier work of Wu and Van Voorhis [Phys. Rev. A 72, 024502 (2005)], the density functional is minimized under the constraint that the charge difference between donor and acceptor is equal to a given value. The classical ion dynamics is propagated on the Born-Oppenheimer surface of the charge constrained state. We investigate the dependence of the constrained energy and of the energy gap on the definition of the charge and present expressions for the constraint forces. The method is applied to the Ru2+-Ru3+ electron self-exchange reaction in aqueous solution. Sampling the vertical energy gap along CDFT-MD trajectories and correcting for finite size effects, a reorganization free energy of 1.6 eV is obtained. This is 0.1-0.2 eV lower than a previous estimate based on a continuum model for solvation. The smaller value for the reorganization free energy can be explained by the fact that the Ru-O distances of the divalent and trivalent Ru hexahydrates are predicted to be more similar in the electron transfer complex than for the separated aqua ions.

  6. Steric Effects in the Reaction of Aryl Radicals on Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Combellas, Catherine [CNRS-ESPCI; Jiang, Deen [ORNL; Kanoufi, Frederic [CNRS-ESPCI; Pinson, Jean [Alchimer; Podvorica, Fetah [University of Prishtina, Kosovo

    2009-01-01

    Steric effects are investigated in the reaction of aryl radicals with surfaces. The electrochemical reduction of 2-, 3-, 4-methyl, 2-methoxy, 2-ethyl, 2,6-, 2,4-, and 3,5-dimethyl, 4-tert-butyl, 3,5-bis-tert-butyl benzenediazonium, 3,5-bis(trifluoromethyl), and pentafluoro benzenediazonium tetrafluoroborates is examined in acetonitrile solutions. It leads to the formation of grafted layers only if the steric hindrance at the 2- or 2,6-position(s) is small. When the 3,5-positions are crowded with tert-butyl groups, the growth of the organic layer is limited by steric effects and a monolayer is formed. The efficiency of the grafting process is assessed by cyclic voltammetry, X-ray photoelectron spectroscopy, infrared, and ellipsometry. These experiments, together with density functional computations of bonding energies of substituted phenyl groups on a copper surface, are discussed in terms of the reactivity of aryl radicals in the electrografting reaction and in the growth of the polyaryl layer.

  7. Reflow Soldering of Surface Mount Electronic Components in a Laboratory

    OpenAIRE

    Erickson, Christopher J.; Durfee, Dallin S.

    2008-01-01

    We present a basic tutorial for implementing surface mount technology in lab-built scientific instruments. We discuss the advantages and disadvantages of using surface mount chips. We also describe methods for the development and prototyping of surface mount circuitry in home-built electronics. The method of soldering surface mount components in a common toaster oven is described. We provide advice from our own experience in developing this technology, and argue that surface mount technology ...

  8. A new potential energy surface for the ground electronic state of the LiH2 system, and dynamics studies on the H((2)S) + LiH(X(1)Σ(+)) → Li((2)S) + H2(X(1)Σg(+)) reaction.

    Science.gov (United States)

    Yuan, Jiuchuang; He, Di; Chen, Maodu

    2015-05-07

    A new global potential energy surface (PES) is obtained for the ground electronic state of the LiH2 system based on high-level energies. The energy points are calculated at the multireference configuration interaction level with aug-cc-pVXZ (X = Q, 5) basis sets, and these energies are extrapolated to the complete basis set limit. The neural network method and hierarchical construction scheme are applied in the fitting process and the root mean square error of the fitting result is very small (0.004 eV). The dissociation energies and equilibrium distances for LiH(X(1)Σ(+)) and H2(X(1)Σg(+)) obtained from the new PES are in good agreement with the experimental data. On the new PES, time-dependent wave packet studies for the H((2)S) + LiH(X(1)Σ(+)) → Li((2)S) + H2(X(1)Σg(+)) reaction have been carried out. In this reaction, no threshold is found due to the absence of an energy barrier on the minimum energy path. The calculated integral cross sections are high at low collision energy and will decrease with the increase of the collision energy. The product molecule H2 tends to be forward scattering due to direct reactive collisions, which becomes more evident at higher collision energies.

  9. Tantalum surface oxidation: Bond relaxation, energy entrapment, and electron polarization

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Yongling [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Bo, Maolin [Yangtze Normal University, College of Mechanical and Electrical Engineering, Chongqing 408100 (China); Wang, Yan [School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Liu, Yonghui [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Chang Q. [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Huang, Yongli, E-mail: huangyongli@xtu.edu.cn [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China)

    2017-02-28

    Graphical abstract: The bond, electron and energy relaxation result in core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Highlights: • Increasing the oxygen coverage lowers the adsorption energy associated with lattice reconstruction. • Electrons transfer from Ta surface atoms to sp-hydrated oxygen, creating dipole moment that decreases the work function. • Oxygen chemisorption modified valence density-of-state (DOS) for Ta with four excessive DOS features: O−Ta bonding, O{sup 2−} lone pairs, Ta+ electron holes, and the lone-pair polarized Ta dipoles. • The bond, electron and energy relaxation between surface undercoordinated atoms are responsible for core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Abstract: A combination of photoelectron spectrometric analysis and density functional theory calculations has enabled reconciliation of the bond-energy-electron relaxation for the Ta(100, 110, 111) surfaces chemisorbed with oxygen at different coverages. Results show that increasing oxygen coverage lowers the adsorption energy associated with lattice reconstruction. Valence electrons transfer from Ta surface atoms to oxygen to create four excessive DOS features in terms of O−Ta bonding, lone pairs of oxygen, Ta{sup +} electron holes, and polarized Ta dipoles. Oxidation proceeds in the following dynamics: oxygen gets electrons from two neighboring Ta atoms left behind Ta{sup +}; the sp{sup 3}-orbital hybridization takes place with additional two electron lone pairs, the lone pairs polarize the other two Ta neighbors becoming dipoles. X-ray photoelectron spectral analysis results in the 4f binding energy of an isolated Ta atom and its shift upon bond formation and oxidation. Exercises provide not only a promising numerical approach for the quantitative information about the bond and electronic behavior but also consistent

  10. A full understanding of oxygen reduction reaction mechanism on Au(1 1 1) surface

    Science.gov (United States)

    Yang, Yang; Dai, Changqing; Fisher, Adrian; Shen, Yanchun; Cheng, Daojian

    2017-09-01

    Oxygen reduction and hydrogen peroxide reduction are technologically important reactions in energy-conversion devices. In this work, a full understanding of oxygen reduction reaction (ORR) mechanism on Au(1 1 1) surface is investigated by density functional theory (DFT) calculations, including the reaction mechanisms of O2 dissociation, OOH dissociation, and H2O2 dissociation. Among these ORR mechanisms on Au(1 1 1), the activation energy of \\text{O}2* hydrogenation reaction is much lower than that of \\text{O}2* dissociation, indicating that \\text{O}2* hydrogenation reaction is more appropriate at the first step than \\text{O}2* dissociation. In the following, H2O2 can be formed with the lower activation energy compared with the OOH dissociation reaction, and finally H2O2 could be generated as a detectable product due to the high activation energy of H2O2 dissociation reaction. Furthermore, the potential dependent free energy study suggests that the H2O2 formation is thermodynamically favorable up to 0.4 V on Au(1 1 1), reducing the overpotential for 2e - ORR process. And the elementary step of first H2O formation becomes non-spontaneous at 0.4 V, indicating the difficulty of 4e - reduction pathway. Our DFT calculations show that H2O2 can be generated on Au(1 1 1) and the first electron transfer is the rate determining step. Our results show that gold surface could be used as a good catalyst for small-scale manufacture and on-site production of H2O2.

  11. Surface reactivity of Ge[111] for organic functionalization by means of a radical-initiated reaction: A DFT study

    Energy Technology Data Exchange (ETDEWEB)

    Rubio-Pereda, Pamela, E-mail: rubio.pereda@gmail.com [Centro de Investigación Científica y de Educación Superior de Ensenada 3918, Código Postal 22860, Ensenada, Baja California (Mexico); Takeuchi, Noboru, E-mail: takeuchi@cnyn.unam.mx [Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Apartado Postal 14, Código Postal 22800, Ensenada, Baja California (Mexico)

    2016-08-30

    Highlights: • The surface reactivity of the Ge [111] surface is studied with DFT for the attachment of organic molecules by means of a radical-initiated reaction. • A hydrogen vacancy in the hydrogen terminated Ge [111] surface exhibits an accumulation of charge and electron pairing. • These characteristics make the hydrogen vacancy less reactive for the attachment of unsaturated organic molecules. • The adsorption of acetylene is probable to occur while the adsorption of ethylene and styrene is substantially less probable to occur. • The hydrogen terminated Ge [111] surface is found to be less reactive than its two-dimensional analogue, the hydrogen-terminated germanene. - Abstract: The study of interfacial chemistry at semiconductor surfaces has become an important area of research. Functionalities such as molecular recognition, biocompatibility of surfaces, and molecular computing, could be achieved by the combinations of organic chemistry with the semiconductor technology. One way to accomplish this goal is by means of organic functionalization of semiconductor surfaces such as the bulk-terminated germanium surfaces, more specifically the Ge[111]. In this work, we theoretically study, by applying density functional theory, the surface reactivity of the bulk-terminated Ge[111] surface for organic functionalization by means of a radical-initiated reaction of unsaturated molecules such as acetylene, ethylene and styrene with a hydrogen vacancy on a previously hydrogen-terminated Ge[111] surface. Results derived from this work are compared with those obtained in our previous calculations on the germanene surface, following the same chemical route. Our calculations show an accumulation of electronic charge at the H-vacancy having as a result electron pairing due to strong lattice-electron coupling and therefore a diminished surface reactivity. Calculation of the transition states for acetylene and ethylene indicates that the surface reactivity of the

  12. Electrodeposition of Pd based binary catalysts on Carbon paper via surface limited redox-replacement reaction for oxygen reduction reaction

    CSIR Research Space (South Africa)

    Modibedi, RM

    2014-05-01

    Full Text Available Direct alcohol fuel cells (DAFCs) continue to extensive attention as potential power sources for portable and stationary applications. The oxygen reduction reaction (ORR) involving the four electron transfer remains a challenge for DAFCs due to its...

  13. Rate constants of reactions of {kappa}-carrageenan with hydrated electron and hydroxyl radical

    Energy Technology Data Exchange (ETDEWEB)

    Abad, L.V. [Nuclear Professional School, School of Engineering Laboratory, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1188 (Japan); Philippine Nuclear Research Institute, Commonwealth Avenue, Diliman, Quezon City (Philippines)], E-mail: lvabad@pnri.dost.gov.ph; Saiki, S.; Kudo, H.; Muroya, Y.; Katsumura, Y. [Nuclear Professional School, School of Engineering Laboratory, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1188 (Japan); Rosa, A.M. de la [Philippine Nuclear Research Institute, Commonwealth Avenue, Diliman, Quezon City (Philippines)

    2007-12-15

    The rate constants for the reactions of {kappa}-carrageenan with hydrated electron and hydroxyl radical was investigated by pulse radiolysis and laser photolysis. The kinetics of the reaction of hydrated electron indicates no seeming reaction with {kappa}-carrageenan. On the other hand, hydroxyl radical reacts very rapidly with {kappa}-carrageenan at a rate constant of approximately 1.2 x 10{sup 9} M{sup -1} s{sup -1}. This rate constant varies with pH.

  14. The first organocatalytic, ortho-regioselective inverse-electron-demand hetero-Diels-Alder reaction.

    Science.gov (United States)

    Hejmanowska, Joanna; Jasiński, Marcin; Wojciechowski, Jakub; Mlostoń, Grzegorz; Albrecht, Łukasz

    2017-10-17

    The development of the unprecedented ortho-regioselective inverse-electron-demand hetero-Diels-Alder (IEDHDA) reaction is described. It has been demonstrated that by proper choice of reactants and reaction conditions the inverse-electron-demand hetero-Diels-Alder cycloaddition can be realized with unprecedented regioselectivity arising from the reaction between the terminal carbon atom of the dienophile and the heteroatom of the heterodiene.

  15. Observation of electron emission in the nuclear reaction between protons and deuterons

    Science.gov (United States)

    Lipoglavšek, M.; Markelj, S.; Mihovilovič, M.; Petrovič, T.; Štajner, S.; Vencelj, M.; Vesić, J.

    2017-10-01

    Proton-deuteron fusion reaction has been studied using a proton beam with an energy of 260 keV and a deuterium-implanted graphite target. The reaction product, 3He, usually de-excites by γ-ray emission. However, instead of a γ ray, 3He can emit an electron with a discrete energy of 5.6 MeV, due to electron screening in graphite. Such electrons were identified with the ΔE-E technique. The emission of fast electrons shows that electron screening causes the electrons to approach the nuclei during the reaction very closely. Different behavior of nuclear reactions at low and high energies was also demonstrated.

  16. The role of electron scattering in electron-induced surface chemistry

    NARCIS (Netherlands)

    van Dorp, Willem F.

    2012-01-01

    Electron-induced chemistry on surfaces plays a key role in focused electron beam induced processing (FEBIP), a single-step lithography technique that has increasingly gained interest in the past decade. It is crucial for the understanding and modelling of this process to know the role of the surface

  17. Structural and electronic properties of hydrosilylated silicon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Baumer, A.

    2005-11-15

    The structural and electronic properties of alkyl-terminated Si surfaces prepared by thermallyinduced hydrosilylation have been studied in detail in the preceding chapters. Various surfaces have been used for the functionalization ranging from crystalline Si over amorphous hydrogenated Si to nanoscaled materials such as Si nanowires and nanoparticles. In each case, the alkyl-terminated surfaces have been compared to the native oxidized and H-terminated surfaces. (orig.)

  18. Hot-electron nanoscopy using adiabatic compression of surface plasmons

    KAUST Repository

    Giugni, Andrea

    2013-10-20

    Surface plasmon polaritons are a central concept in nanoplasmonics and have been exploited to develop ultrasensitive chemical detection platforms, as well as imaging and spectroscopic techniques at the nanoscale. Surface plasmons can decay to form highly energetic (or hot) electrons in a process that is usually thought to be parasitic for applications, because it limits the lifetime and propagation length of surface plasmons and therefore has an adverse influence on the functionality of nanoplasmonic devices. Recently, however, it has been shown that hot electrons produced by surface plasmon decay can be harnessed to produce useful work in photodetection, catalysis and solar energy conversion. Nevertheless, the surface-plasmon-to-hot-electron conversion efficiency has been below 1% in all cases. Here we show that adiabatic focusing of surface plasmons on a Schottky diode-terminated tapered tip of nanoscale dimensions allows for a plasmon-to-hot-electron conversion efficiency of ∼30%. We further demonstrate that, with such high efficiency, hot electrons can be used for a new nanoscopy technique based on an atomic force microscopy set-up. We show that this hot-electron nanoscopy preserves the chemical sensitivity of the scanned surface and has a spatial resolution below 50 nm, with margins for improvement.

  19. Depth oscillations of electronuclear reaction yield initiated by relativistic planar channeled electrons: quantum versus classical calculations

    Science.gov (United States)

    Eikhorn, Yu. L.; Korotchenko, K. B.; Pivovarov, Yu. L.; Tukhfatullin, T. A.

    2017-07-01

    The first experiment on electronuclear reaction initated by axially channeled 700 MeV electrons in a Si crystal [1] revealed remarkable depth oscillations of reaction yield. The effect was satisfactory explained [2] by computer simulations using binary collisions model. In this work the oscillations effect is investigated for planar channeled electrons in a Si crystal using the new computer code BCM-1.0 which allows both classical and quantum calculations of channeled electrons flux density.

  20. Scanning electron microscopic evaluation of root canal surfaces ...

    African Journals Online (AJOL)

    2014-07-15

    50. How to cite this article: Hema BS, Chandu GS, Shiraguppi VL. Scanning electron microscopic evaluation of root canal surfaces prepared with three rotary endodontic systems: Lightspeed, ProTaper and EndoWave. Niger J.

  1. Adsorption and reaction of CO and H2O on WC(0001) surface: A first-principles investigation

    Science.gov (United States)

    Tong, Yu-Jhe; Wu, Shiuan-Yau; Chen, Hsin-Tsung

    2018-01-01

    We have performed a spin-polarized density functional theory (DFT) study for understanding the detailed reaction mechanism of CO and H2O on WC (0001) surface. The adsorption properties and vibrational frequencies of H2O, OH, O, H, CO and CO2 on the WC (0001) surface were illustrated. These results are well in consistent with the experimental observations studied by temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). Based on the adsorption results, potential energy profiles of H2O and OH dehydrogenation and HCO, COH, COOH, and CO2 formation on the WC (0001) surface were predicted. The calculation results demonstrated that the WC (0001) surface as Fe (110) surface exhibits significantly reaction activity toward the dehydrogenation of H2O and OH but less activity toward the formation of HCO, COH, COOH and CO2 compared to the Cu (111) and Pt (111) surfaces.

  2. Computational study of ethanol adsorption and reaction over rutile TiO2 (110) surfaces.

    Science.gov (United States)

    Muir, J M R; Muir, J N; Choi, Y; Idriss, H

    2012-09-14

    Studies of the modes of adsorption and the associated changes in electronic structures of renewable organic compounds are needed in order to understand the fundamentals behind surface reactions of catalysts for future energies. Using planewave density functional theory (DFT) calculations, the adsorption of ethanol on perfect and O-defected TiO(2) rutile (110) surfaces was examined. On both surfaces the dissociative adsorption mode on five-fold coordinated Ti cations (Ti(4+)(5c)) was found to be more favourable than the molecular adsorption mode. On the stoichiometric surface E(ads) was found to be equal to 0.85 eV for the ethoxide mode and equal to 0.76 eV for the molecular mode. These energies slightly increased when adsorption occurred on the Ti(4+)(5c) closest to the O-defected site. However, both considerably increased when adsorption occurred at the removed bridging surface O; interacting with Ti(3+) cations. In this case the dissociative adsorption becomes strongly favoured (E(ads) = 1.28 eV for molecular adsorption and 2.27 eV for dissociative adsorption). Geometry and electronic structures of adsorbed ethanol were analysed in detail on the stoichiometric surface. Ethanol does not undergo major changes in its structure upon adsorption with its C-O bond rotating nearly freely on the surface. Bonding to surface Ti atoms is a σ type transfer from the O2p of the ethanol-ethoxide species. Both ethanol and ethoxide present potential hole traps on O lone pairs. Charge density and work function analyses also suggest charge transfer from the adsorbate to the surface, in which the dissociative adsorptions show a larger charge transfer than the molecular adsorption mode.

  3. Computational study of ethanol adsorption and reaction over rutile TiO2 (110) surfaces

    KAUST Repository

    Muir, J. N.

    2012-01-01

    Studies of the modes of adsorption and the associated changes in electronic structures of renewable organic compounds are needed in order to understand the fundamentals behind surface reactions of catalysts for future energies. Using planewave density functional theory (DFT) calculations, the adsorption of ethanol on perfect and O-defected TiO 2 rutile (110) surfaces was examined. On both surfaces the dissociative adsorption mode on five-fold coordinated Ti cations (Ti 4+ 5c) was found to be more favourable than the molecular adsorption mode. On the stoichiometric surface E ads was found to be equal to 0.85 eV for the ethoxide mode and equal to 0.76 eV for the molecular mode. These energies slightly increased when adsorption occurred on the Ti 4+ 5c closest to the O-defected site. However, both considerably increased when adsorption occurred at the removed bridging surface O; interacting with Ti 3+ cations. In this case the dissociative adsorption becomes strongly favoured (E ads = 1.28 eV for molecular adsorption and 2.27 eV for dissociative adsorption). Geometry and electronic structures of adsorbed ethanol were analysed in detail on the stoichiometric surface. Ethanol does not undergo major changes in its structure upon adsorption with its C-O bond rotating nearly freely on the surface. Bonding to surface Ti atoms is a σ type transfer from the O2p of the ethanol-ethoxide species. Both ethanol and ethoxide present potential hole traps on O lone pairs. Charge density and work function analyses also suggest charge transfer from the adsorbate to the surface, in which the dissociative adsorptions show a larger charge transfer than the molecular adsorption mode. This journal is © 2012 the Owner Societies.

  4. Heterogeneous Reactions of Polycyclic Aromatic Hydrocarbons on Atmospheric and Terrestrial Surfaces

    Science.gov (United States)

    Simonich, S. L.

    2014-12-01

    The heterogeneous reactions of five higher molecular weight polycyclic aromatic hydrocarbons (PAHs), benzo[a]pyrene-d12 (BaP-d12), benzo(k)fluoranthene-d12 (BkF-d12), benzo[g,h,i]perylene-d12 (BghiP-d12), dibenzo(a,i)pyrene-d14 (DBaiP-d14), and dibenzo[a,l]pyrene (DalP), with NO2, NO3/N2O5, O3, and OH radicals were investigated in a 7000 L indoor Teflon chamber. Quartz fiber filters (QFF) were used as the reaction surface and substrate and the analyses of parent PAHs and Nitro-PAH (NPAH) products was conducted using electron impact gas chromatographic mass spectrometry (GC/MS) and negative chemical ionization GC/MS. In parallel to the laboratory experiments, a theoretical study was conducted to assist in determining the formation of NPAH isomers based on the OH-radical initiated reaction. The thermodynamic stability of OH-PAH intermediates was used to indicate the position of highest electron density and the most stable NPAH products were synthesized to confirm their identity. NO2 and NO3/N2O5 were the most effective oxidizing agents in transforming PAHs deposited on filters to NPAHs, under the experimental conditions. Reaction of BaP-d12, BkF-d12 and BghiP-d12 resulted in the formation of several mono-nitro PAH isomer product, while the reaction of DalP and DaiP-d14 resulted in the formation of only one mono-nitro PAH isomer product. The direct-acting mutagenicity of the products increased the most after NO3/N2O5 exposure, particularly for BkF-d12 in which the formation of dinitro- PAHs was observed. In addition, the degradation of particulate matter (PM)-bound PAHs by heterogeneous reaction with OH radicals, O3, NO3/N2O5 was also studied. Ambient PM samples collected from Beijing, China and Riverside, California were exposed in an indoor chamber under simulated trans-Pacific atmospheric transport conditions and the formation of NPAHs was studied. NPAHs were most effectively formed during the NO3/N2O5 exposure and, for all exposures, there was no significant

  5. Radiation-Reaction Trapping of Electrons in Extreme Laser Fields

    CERN Document Server

    Ji, L L; Kostyukov, I Yu; Shen, B F; Akli, K

    2014-01-01

    proposed analysis shows that the threshold of laser field amplitude for RRT is approximately the cubic root of laser wavelength over classical electron radius. Because of the pinching effect of the trapped electron bunch, the required laser intensity for RRT can be further reduced.

  6. Low-energy electron induced processes in molecular thin films condensed on silicon and titanium dioxide surfaces

    Science.gov (United States)

    Lane, Christopher D.

    The focus of the presented experimental research is to examine the fundamental physics and chemistry of electron-stimulated reactions upon adsorbate covered single crystal surfaces. Specifically, condensed SiCl4 on the Si(111) surface and condensed H2O on the TiO2 (110) surface have been studied. By varying adsorbate film thicknesses, the coupling strength of the electron target molecule to the substrate and surrounding media dictates the progression of the electron induced reactions. To investigate the electron interactions with SiCl4 on the Si(111) surface, a multilayer to monolayer approach was taken. Experiments measuring the electron stimulated desorption (ESD) of fragment cations are discussed in Chapter 3. ESD of neutrals was performed on a multilayer (100 ML) coverage of SiCl4 and is discussed in Chapter 4. These experiments remove the influence of the silicon substrate on the electron induced dissociative processes that are monitored via time of flight mass spectrometry (ToF-MS). The results in Chapter 3 and Chapter 4 have been published in Surface Science 593 (2005) 173 and in the Journal of Chemical Physics 124 (2006) 164702, respectively. Results from electron induced reactions within thin films of SiCl4 are presented in Chapter 5. In the low coverage region, the cation and neutral desorption channels are monitored simultaneously, and the adsorbate coupling strength to the silicon substrate is substantially greater. This affects the desorption yields and the autodetachment probability of the transient negative ion (SiCl4-). Chapters 6--8 discuss work that focuses on the electron-stimulated reactions within the H2O/TiO2 system. A discussion of the interactions of H2O with the TiO2(110) surface is presented in Chapter 6. The transition metal oxide surface is comprised of acidic and basic water adsorption sites along with intrinsic surface defects where surface oxygen atoms are missing. These surface defect sites significantly influence the interactions of

  7. Relaxation between electrons and surface phonons of a ...

    Indian Academy of Sciences (India)

    to the calculation of energy transfer rate from degenerate hot electrons to surface phonons. We consider the case of a homogeneously photoexcited (no spatial dif- fusion) nanoscale metal film, in which the electron mean free path is more than the film thickness (as in case of metals, in which even at high temperatures, the.

  8. Site-specific electronic structure of bacterial surface protein layers

    Science.gov (United States)

    Vyalikh, D. V.; Kummer, K.; Kade, A.; Blüher, A.; Katzschner, B.; Mertig, M.; Molodtsov, S. L.

    2009-03-01

    We applied resonant photoemission and X-ray absorption spectroscopy for a detailed characterization of the valence electronic structure of the regular two-dimensional bacterial surface protein layer of Bacillus sphaericus NCTC 9602. Using this approach, we detected valence electron emission from specific chemical sites. In particular, it was found that electrons from the π clouds of aromatic systems make large contributions to the highest occupied molecular orbitals.

  9. Treatment of surfaces with low-energy electrons

    Czech Academy of Sciences Publication Activity Database

    Frank, Luděk; Mikmeková, Eliška; Lejeune, M.

    2017-01-01

    Roč. 407, JUN 15 (2017), s. 105-108 ISSN 0169-4332 R&D Projects: GA TA ČR(CZ) TE01020118; GA MŠk(CZ) LO1212; GA MŠk ED0017/01/01 Institutional support: RVO:68081731 Keywords : Low-energy electrons * Electron beam induced release * Graphene * Ultimate cleaning of surfaces Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 3.387, year: 2016

  10. Investigation on electrochemical behavior and its catalytic effect on oxygen reduction reaction of 3-Ferrocenyl dihydropyrazole derivative as electron relay

    Science.gov (United States)

    Zeng, Han; Huo, Wen-Shan; Zhao, Shu-Xian; Zhang, Yu-He

    2017-11-01

    Amino group surface tailored multi-wall carbon nano-tubes were covalently tethered to the gold disk electrode and Laccase molecules were covalently coupled to nano-tubes to prepare Lac-based electrode. Derivative of 3-ferrocenyl dihydropyrazole (FDPFFP) was proposed to be electron mediator for mediated oxygen reduction reaction. Investigation in electro-chemical behavior and catalytic performance to enzymatic reaction of FDPFFP indicated that it displayed quasi-reversible characteristics of electro-chemical reaction with rapid dynamics of electron shuttle and had apparent catalytic effect in oxygen reduction (onset potential for catalysis at 450 mV vs NHE). This enzymatic catalysis was restrained by the step in diffusion of substrate.

  11. Spectroscopic properties of trapped electrons on the surface of MgO nanoparticles.

    Science.gov (United States)

    Sterrer, Martin; Berger, Thomas; Stankic, Slavica; Diwald, Oliver; Knözinger, Erich

    2004-11-12

    To characterise electron-trapping sites on the surface of MgO nanoparticles, surface colour centres were generated using UV light in conjunction with selected hydrogen-based electron sources. Four different colour-centre species, including the characteristic (e-)(H+) or F(S)+(H) centre, were identified due to the distinct shape of the respective electron paramagnetic resonance (EPR) signals. The analysis of the EPR saturation behaviour down to microwave powers of 5 x 10(-3) mW reveals an enhanced spin-relaxation probability of the (e-)(H+) centre compared to all other F(S)+ centres that do not exhibit significant magnetic interactions with hydroxylic protons. Beside the dipolar magnetic interaction in the (e-)(H+) centre observed by EPR, the electronic interaction between the unpaired electron and the proton of a closely spaced OH group produces a redshift of the OH stretching band by about 70 to 170 cm(-1), as observed by infrared spectroscopy. EPR and IR spectroscopic data obtained after the selective address of individual reaction channels for surface colour-centre formation point to the fact that (e-)(H+) centres are formed by trapping electrons from H atoms. Consequently, the underlying surface defect does not belong to the sites of the MgO surface, which chemisorb hydrogen via a heterolytic splitting process.

  12. Design of a multi-enzyme reaction on an electrode surface for an L-glutamate biofuel anode.

    Science.gov (United States)

    Sakamoto, Hiroaki; Komatsu, Tomohiro; Yamasaki, Koji; Satomura, Takenori; Suye, Shin-Ichiro

    2017-02-01

    To design and construct a novel bio-anode electrode based on the oxidation of glutamic acid to produce 2-oxoglutarate, generating two electrons from NADH. Efficient enzyme reaction and electron transfer were observed owing to immobilization of the two enzymes using a mixed self-assembled monolayer. The ratio of the immobilized enzymes was an important factor affecting the efficiency of the system; thus, we quantified the amounts of immobilized enzyme using a quartz crystal microbalance to further evaluate the electrochemical reaction. The electrochemical reaction proceeded efficiently when approximately equimolar amounts of the enzyme were on the electrode. The largest oxidation peak current increase (171 nA) was observed under these conditions. Efficient multi-enzyme reaction on the electrode surface has been achieved which is applicable for biofuel cell application.

  13. The Surface Reactions of Ethanol over UO2(100) Thin Film

    KAUST Repository

    Senanayake, Sanjaya D.

    2015-10-08

    The study of the reactions of oxygenates on well-defined oxide surfaces is important for the fundamental understanding of heterogeneous chemical pathways that are influenced by atomic geometry, electronic structure and chemical composition. In this work, an ordered uranium oxide thin film surface terminated in the (100) orientation is prepared on a LaAlO3 substrate and studied for its reactivity with a C-2 oxygenate, ethanol (CH3CH2OH). With the use of synchrotron X-ray photoelectron spectroscopy (XPS), we have probed the adsorption and desorption processes observed in the valence band, C1s, O1s and U4f to investigate the bonding mode, surface composition, electronic structure and probable chemical changes to the stoichiometric-UO2(100) [smooth-UO2(100)] and Ar+-sputtered UO2(100) [rough-UO2(100)] surfaces. Unlike UO2(111) single crystal and UO2 thin film, Ar-ion sputtering of this UO2(100) did not result in noticeable reduction of U cations. The ethanol molecule has C-C, C-H, C-O and O-H bonds, and readily donates the hydroxyl H while interacting strongly with the UO2 surfaces. Upon ethanol adsorption (saturation occurred at 0.5 ML), only ethoxy (CH3CH2O-) species is formed on smooth-UO2(100) whereas initially formed ethoxy species are partially oxidized to surface acetate (CH3COO-) on the Ar+-sputtered UO2(100) surface. All ethoxy and acetate species are removed from the surface between 600 and 700 K.

  14. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    2001-01-01

    Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive ...

  15. Analytical Chemistry of Surfaces: Part II. Electron Spectroscopy.

    Science.gov (United States)

    Hercules, David M.; Hercules, Shirley H.

    1984-01-01

    Discusses two surface techniques: X-ray photoelectron spectroscopy (ESCA) and Auger electron spectroscopy (AES). Focuses on fundamental aspects of each technique, important features of instrumentation, and some examples of how ESCA and AES have been applied to analytical surface problems. (JN)

  16. Vectorial electron transfer on designed surfaces

    Science.gov (United States)

    Bard, A. J.; Campion, A.; Fox, M. A.; Mallouk, T. E.; Webber, S. E.

    Bipolar CdSe/CoS semiconductor photoelectrode panels, capable of vectorial electron transfer, were used in series arrays to photodecompose water to yield hydrogen and oxygen in stoichiometric ratio with a maximum solar efficiency of about 1 precent. An analytical model was developed for these arrays which addresses the question of watersplitting and electrical power generation efficiencies as functions of the number of panels, the overpotential of the gas generating electrodes, incident light intensity, and the concentrations of the redox couples. Hydrogen production using a self-assembling zeolite system was discovered. Sensitized anatase TiO2 electrodes were used in photoelectrochemical cells employing variety of solution redox couples. The photoassisted production of hydrogen from methanol-water solutions containing mixtures of small particles of CdS/SiO2 and a wide bandgap semiconductor (TiO, ZnO, SnO2, or WO3), supported on silica and platinized was studied. The phenomenon of interparticle charge separation for Cds/SiO2 was found to be operative for CdS/SiO2 with WS sub 2/SiO2.

  17. Surface reactions with participation of oxides of molybdenum and tungsten: the influence of external factors

    Directory of Open Access Journals (Sweden)

    A. F. Guseva

    2016-03-01

    Full Text Available This work is a continuation of the article "Surface reactions with participation of oxides of molybdenum and tungsten", published in the previous issue of the journal. The influence of the electric field and the pressure of oxygen in the gas phase on the rate of surface reactions for the synthesis of molybdates of manganese and copper were investigated. It’s found that for the synthesis reaction of molybdate of copper the nature of the dependency of the rate of synthesis and rate of surface reactions from the external parameters are the same, indicating the crucial contribution of surface diffusion to the reactive mass transfer. For the synthesis reaction of molybdate of manganese the dependences of the rate of synthesis and of rate of surface reactions by external parameters differ, indicating that for this reaction, surface diffusion isn’t the main mechanism of mass transfer.

  18. A surface-electrode quadrupole guide for electrons

    Energy Technology Data Exchange (ETDEWEB)

    Hoffrogge, Johannes Philipp

    2012-12-19

    This thesis reports on the design and first experimental realization of a surface-electrode quadrupole guide for free electrons. The guide is based on a miniaturized, planar electrode layout and is driven at microwave frequencies. It confines electrons in the near-field of the microwave excitation, where strong electric field gradients can be generated without resorting to resonating structures or exceptionally high drive powers. The use of chip-based electrode geometries allows the realization of versatile, microstructured potentials with the perspective of novel quantum experiments with guided electrons. I present the design, construction and operation of an experiment that demonstrates electron confinement in a planar quadrupole guide for the first time. To this end, electrons with kinetic energies from one to ten electron-volts are guided along a curved electrode geometry. The stability of electron guiding as a function of drive parameters and electron energy has been studied. A comparison with numerical particle tracking simulations yields good qualitative agreement and provides a deeper understanding of the electron dynamics in the guiding potential. Furthermore, this thesis gives a detailed description of the design of the surface-electrode layout. This includes the development of an optimized coupling structure to inject electrons into the guide with minimum transverse excitation. I also discuss the extension of the current setup to longitudinal guide dimensions that are comparable to or larger than the wavelength of the drive signal. This is possible with a modified electrode layout featuring elevated signal conductors. Electron guiding in the field of a planar, microfabricated electrode layout allows the generation of versatile and finely structured guiding potentials. One example would be the realization of junctions that split and recombine a guided electron beam. Furthermore, it should be possible to prepare electrons in low-lying quantum mechanical

  19. Geometric phase and quantum interference in photosynthetic reaction center: Regulation of electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Yuming, E-mail: ymsun@ytu.edu.cn; Su, Yuehua; Dai, Zhenhong; Wang, WeiTian

    2016-10-20

    Photosynthesis is driven by electron transfer in reaction centers in which the functional unit is composed of several simple molecules C{sub 2}-symmetrically arranged into two branches. In view of quantum mechanism, both branches are possible pathways traversed by the transferred electron. Due to different evolution of spin state along two pathways in transmembrane electric potential (TEP), quantum state of the transferred electron at the bridged site acquires a geometric phase difference dependent on TEP, the most efficient electron transport takes place in a specific range of TEP beyond which electron transfer is dramatically suppressed. What’s more, reaction center acts like elaborately designed quantum device preparing polarized spin dependent on TEP for the transferred electron to regulate the reduction potential at bridged site. In brief, electron transfer generates the TEP, reversely, TEP modulates the efficiency of electron transfer. This may be an important approach to maintaining an appreciable pH environment in photosynthesis.

  20. Geometric phase and quantum interference in photosynthetic reaction center: Regulation of electron transfer

    Science.gov (United States)

    Sun, Yuming; Su, Yuehua; Dai, Zhenhong; Wang, WeiTian

    2016-10-01

    Photosynthesis is driven by electron transfer in reaction centers in which the functional unit is composed of several simple molecules C2-symmetrically arranged into two branches. In view of quantum mechanism, both branches are possible pathways traversed by the transferred electron. Due to different evolution of spin state along two pathways in transmembrane electric potential (TEP), quantum state of the transferred electron at the bridged site acquires a geometric phase difference dependent on TEP, the most efficient electron transport takes place in a specific range of TEP beyond which electron transfer is dramatically suppressed. What's more, reaction center acts like elaborately designed quantum device preparing polarized spin dependent on TEP for the transferred electron to regulate the reduction potential at bridged site. In brief, electron transfer generates the TEP, reversely, TEP modulates the efficiency of electron transfer. This may be an important approach to maintaining an appreciable pH environment in photosynthesis.

  1. Low energy electron bombardment induced surface contamination of Ru mirrors

    Science.gov (United States)

    Al-Ajlony, A.; Kanjilal, A.; Catalfano, M.; Harilal, S. S.; Hassanein, A.; Rice, B.

    2012-03-01

    The impact of secondary electrons induced contamination of the Ru surface was investigated. Mirror-like Ru sample was bombarded with low energy (100 eV) electrons and the change in surface chemistry was investigated using X-ray photoelectron spectroscopy (XPS).Along with XPS studies the corresponding effect on in-situ EUV reflectivity was examined by exposing the Ru surface to photons at a wavelength of 13.5 nm in an ultrahigh vacuum chamber. Detailed XPS analyses showed a sudden increase in carbon concentrations on the Ru surface in the first 60 min, followed by a slow but linear growth in carbon concentration. In parallel, a noticeable decrease in water content was observed during the time of electrons irradiation along with slight oxidation of pure Ru surface. All chemical changes were discussed in terms of the electrons bombardment mediated dissociation of water and hydrocarbon molecules. A time dependent EUV reflectivity measurements show insignificant change in reflectivity up to 510 min of electrons bombardment. The impact of water molecules on the Ru surface and the accumulation of carbon through dissociation of residual hydrocarbons is discussed in details.

  2. Stochastic surface walking reaction sampling for resolving heterogeneous catalytic reaction network: A revisit to the mechanism of water-gas shift reaction on Cu

    Science.gov (United States)

    Zhang, Xiao-Jie; Shang, Cheng; Liu, Zhi-Pan

    2017-10-01

    Heterogeneous catalytic reactions on surface and interfaces are renowned for ample intermediate adsorbates and complex reaction networks. The common practice to reveal the reaction mechanism is via theoretical computation, which locates all likely transition states based on the pre-guessed reaction mechanism. Here we develop a new theoretical method, namely, stochastic surface walking (SSW)-Cat method, to resolve the lowest energy reaction pathway of heterogeneous catalytic reactions, which combines our recently developed SSW global structure optimization and SSW reaction sampling. The SSW-Cat is automated and massively parallel, taking a rough reaction pattern as input to guide reaction search. We present the detailed algorithm, discuss the key features, and demonstrate the efficiency in a model catalytic reaction, water-gas shift reaction on Cu(111) (CO + H2O → CO2 + H2). The SSW-Cat simulation shows that water dissociation is the rate-determining step and formic acid (HCOOH) is the kinetically favorable product, instead of the observed final products, CO2 and H2. It implies that CO2 and H2 are secondary products from further decomposition of HCOOH at high temperatures. Being a general purpose tool for reaction prediction, the SSW-Cat may be utilized for rational catalyst design via large-scale computations.

  3. Preparation, characterization, surface modification and redox reactions of silver nanoparticles in the presence of tryptophan.

    Science.gov (United States)

    Jacob, Jasmine A; Naumov, Sergej; Mukherjee, Tulsi; Kapoor, Sudhir

    2011-10-15

    The synthesis and characterization of water-soluble dispersions of Ag nanoparticles by the reduction of AgNO(3) using tryptophan under alkaline synthesis conditions are reported. The Ag nanoparticle formation was very slow at low concentration and rapid at extremes. For surface modification and redox reactions, manipulating the interparticles interaction controlled the size of Ag nanoparticles aggregates. Our results suggest that the replacement of the BH(4)(-) ions adsorbed on the nanoparticle surface by tryptophan destabilizes the particles and further caused aggregation. A mechanism is proposed for the formation of silver nanoparticles by tryptophan. The experimental results are supported by theoretical calculations. The Ag nanoparticles were characterized by UV-vis absorption, dynamic light scattering and transmission electron microscopy techniques. Copyright © 2011 Elsevier B.V. All rights reserved.

  4. The Kinetics of Heterogeneous Electron Transfer Reactions in Polar Solvents

    Science.gov (United States)

    1994-04-20

    exp(-vei/ 2Vn )J (10) 2-exp(-vel/ 2Vn ) When Yel >> yn, jS is unity and the reaction is adiabatic. However, when ye, << yn, the expression for E becomes IC...approximation, IL is given by [31] TL - Em TD (13)Es where f, is the high frequency relative solvent permittivity and ID, the Debye relaxation time

  5. Nicotiana tabacum as model for ozone - plant surface reactions

    Science.gov (United States)

    Jud, Werner; Fischer, Lukas; Wohlfahrt, Georg; Tissier, Alain; Canaval, Eva; Hansel, Armin

    2015-04-01

    Elevated tropospheric ozone concentrations are considered a toxic threat to plants, responsible for global crop losses with associated economic costs of several billion dollars per year. The ensuing injuries have been related to the uptake of ozone through the stomatal pores and oxidative effects damaging the internal leaf tissue. A striking question of current research is the environment and plant specific partitioning of ozone loss between gas phase, stomatal or plant surface sink terms. Here we show results from ozone fumigation experiments using various Nicotiana Tabacum varieties, whose surfaces are covered with different amounts of unsaturated diterpenoids exuded by their glandular trichomes. Exposure to elevated ozone levels (50 to 150 ppbv) for 5 to 15 hours in an exceptionally clean cuvette system did neither result in a reduction of photosynthesis nor caused any visible leaf damage. Both these ozone induced stress effects have been observed previously in ozone fumigation experiments with the ozone sensitive tobacco line Bel-W3. In our case ozone fumigation was accompanied by a continuous release of oxygenated volatile organic compounds, which could be clearly associated to their condensed phase precursors for the first time. Gas phase reactions of ozone were avoided by choosing a high enough gas exchange rate of the plant cuvette system. In the case of the Ambalema variety, that is known to exude only the diterpenoid cis-abienol, ozone fumigation experiments yield the volatiles formaldehyde and methyl vinyl ketone (MVK). The latter could be unequivocally separated from isomeric methacrolein (MACR) by the aid of a Selective Reagent Ion Time-of-Flight Mass Spectrometer (SRI-ToF-MS), which was switched every six minutes from H3O+ to NO+ primary ion mode and vice versa. Consistent with the picture of an ozone protection mechanism caused by reactive diterpenoids at the leaf surface are the results from dark-light experiments. The ozone loss obtained from the

  6. Treatment of surfaces with low-energy electrons

    Science.gov (United States)

    Frank, L.; Mikmeková, E.; Lejeune, M.

    2017-06-01

    Electron-beam-induced deposition of various materials from suitable precursors has represented an established branch of nanotechnology for more than a decade. A specific alternative is carbon deposition on the basis of hydrocarbons as precursors that has been applied to grow various nanostructures including masks for subsequent technological steps. Our area of study was unintentional electron-beam-induced carbon deposition from spontaneously adsorbed hydrocarbon molecules. This process traditionally constitutes a challenge for scanning electron microscopy practice preventing one from performing any true surface studies outside an ultrahigh vacuum and without in-situ cleaning of samples, and also jeopardising other electron-optical devices such as electron beam lithographs. Here we show that when reducing the energy of irradiating electrons sufficiently, the e-beam-induced deposition can be converted to e-beam-induced release causing desorption of hydrocarbons and ultimate cleaning of surfaces in both an ultrahigh and a standard high vacuum. Using series of experiments with graphene samples, we demonstrate fundamental features of e-beam-induced desorption and present results of checks for possible radiation damage using Raman spectroscopy that led to optimisation of the electron energy for damage-free cleaning. The method of preventing carbon contamination described here paves the way for greatly enhanced surface sensitivity of imaging and substantially reduced demands on vacuum systems for nanotechnological applications.

  7. The Effect of Excess Electron and hole on CO2 Adsorption and Activation on Rutile (110) surface

    OpenAIRE

    Wen-Jin Yin; Bo Wen; Sateesh Bandaru; Matthias Krack; MW Lau; Li-Min Liu

    2016-01-01

    CO2 capture and conversion into useful chemical fuel attracts great attention from many different fields. In the reduction process, excess electron is of key importance as it participates in the reaction, thus it is essential to know whether the excess electrons or holes affect the CO2 conversion. Here, the first-principles calculations were carried out to explore the role of excess electron on adsorption and activation of CO2 on rutile (110) surface. The calculated results demonstrate that C...

  8. Treatment of surfaces with low-energy electrons

    Energy Technology Data Exchange (ETDEWEB)

    Frank, L., E-mail: ludek@isibrno.cz [Institute of Scientific Instruments of the CAS, v.v.i., Královopolská 147, 61264 Brno (Czech Republic); Mikmeková, E. [Institute of Scientific Instruments of the CAS, v.v.i., Královopolská 147, 61264 Brno (Czech Republic); FEI Company, Achtseweg Noord 5, 5651 GG Eindhoven (Netherlands); Lejeune, M. [LPMC – Faculte des Sciences d’Amiens, Universite de Picardie Jules Verne, 33 rue Saint Leu, 80039 Amiens Cedex 2 (France)

    2017-06-15

    Highlights: • Using proper irradiation parameters, adsorbed hydrocarbons are released from surfaces. • Slow electrons remove hydrocarbons instead of depositing carbon. • Prolonged irradiation with very slow electrons does not create defects in graphene. - Abstract: Electron-beam-induced deposition of various materials from suitable precursors has represented an established branch of nanotechnology for more than a decade. A specific alternative is carbon deposition on the basis of hydrocarbons as precursors that has been applied to grow various nanostructures including masks for subsequent technological steps. Our area of study was unintentional electron-beam-induced carbon deposition from spontaneously adsorbed hydrocarbon molecules. This process traditionally constitutes a challenge for scanning electron microscopy practice preventing one from performing any true surface studies outside an ultrahigh vacuum and without in-situ cleaning of samples, and also jeopardising other electron-optical devices such as electron beam lithographs. Here we show that when reducing the energy of irradiating electrons sufficiently, the e-beam-induced deposition can be converted to e-beam-induced release causing desorption of hydrocarbons and ultimate cleaning of surfaces in both an ultrahigh and a standard high vacuum. Using series of experiments with graphene samples, we demonstrate fundamental features of e-beam-induced desorption and present results of checks for possible radiation damage using Raman spectroscopy that led to optimisation of the electron energy for damage-free cleaning. The method of preventing carbon contamination described here paves the way for greatly enhanced surface sensitivity of imaging and substantially reduced demands on vacuum systems for nanotechnological applications.

  9. Coincident two-electron emission from surfaces by low-energy electrons

    Science.gov (United States)

    Gollisch, H.; Meinert, D.; Yi, Xiao; Feder, R.

    1997-04-01

    The simultaneous ejection of two electrons from non-magnetic surfaces due to the collision of incident low-energy electrons with valence electrons is treated in a relativistic distorted-wave Born approximation including exchange. The primary electron and the two emitted electrons are described by quasi-particle multiple scattering states. The valence electron is represented by linear combinations of Bloch waves matched at the surface. Screened Coulomb interaction matrix elements between these four states are evaluated. Numerical results for W(0 0 1) are presented and compared with one-dimensional bulk densities of states. Energy-integrated spectra and general features of the 2 e-distribution are in good agreement with recent experimental data.

  10. Surface and Core Electronic Structure of Oxidized Silicon Nanocrystals

    Directory of Open Access Journals (Sweden)

    Noor A. Nama

    2010-01-01

    Full Text Available Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to simulate silicon nanocrystals between 216 and 1000 atoms (1.6–2.65 nm in diameter that include Bravais and primitive cell multiples. The investigated properties include core and oxidized surface properties. Results revealed that electronic properties converge to some limit as the size of the nanocrystal increases. Increasing the size of the core of a nanocrystal resulted in an increase of the energy gap, valence band width, and cohesive energy. The lattice constant of the core and oxidized surface parts shows a decreasing trend as the nanocrystal increases in a size that converges to 5.28 Ǻ in a good agreement with the experiment. Surface and core convergence to the same lattice constant reflects good adherence of oxide layer at the surface. The core density of states shows highly degenerate states that split at the oxygenated (001-(1×1 surface due to symmetry breaking. The nanocrystal surface shows smaller gap and higher valence and conduction bands when compared to the core part, due to oxygen surface atoms and reduced structural symmetry. The smaller surface energy gap shows that energy gap of the nanocrystal is controlled by the surface part. Unlike the core part, the surface part shows a descending energy gap that proves its obedience to quantum confinement effects. Nanocrystal geometry proved to have some influence on all electronic properties including the energy gap.

  11. NI (II AND PB (II INHIBIT THE ENZYMATIC ACTIVITY OF DNA IN AN ELECTRON TRANSFER REACTION

    Directory of Open Access Journals (Sweden)

    B FARZAMI

    2002-03-01

    Full Text Available Introduction. Ni and Pb are metals with several suggested mechanisms for their toxicity on the biological systems. We have recently investigated involvement of DNA in an electron transfer reaction as an enzyme. In this reaction non- fluorescent dichlorofluorescin (LDCF is converted to the dichlorofluorescein (DCF in the presence of peroxides and hematin. Methods. The fluorometric technique was used in this study. The pH effect on the reaction rate was investigated. The results showed that DCF has the maximum emission on tris buffer 0.05 Mat pH 8.4. Results. DNA and carnosine catalyze the reaction, which proceeds by the electron transfer mechanism. The presence of carnosine is necessary for the catalytic action of DNA as a cofactor. Ni (II and Pb (11 are the potent inhibitors of the reaction. The kinetic parameters and determined in the presence and absence of the above ligands. Discussion. DNA, which has the electrical properties only in the double helical forms, acts as a catalyst in the conversion of LDCF to DCF. The existence of the carnosine, an endogenous dipeptide with antioxidant and free radical scavenging roles, is an important factor for the progress of the reaction. Both Ni (11 and Pb (II inhibit the reaction. These metals could act as the electron pool to cause inhibition in such electron transfer reaction. This phenomenon could be related to the carcinogenic effect of these metals.

  12. Davisson-Germer Award Talk: Surface Electron Microscopy with Slow Electrons

    Science.gov (United States)

    Bauer, Ernst

    2005-03-01

    Nearly 80 years ago Davisson and Germer demonstrated the diffraction of slow electrons from surfaces but it is only about 20 years that these electrons have been used for imaging of surfaces and thin films in the Low Energy Electron Microscope (LEEM). Since then several other surface imaging methods with slow electrons have emerged, in particular synchrotron radiation excited photo emission electron microscopy (XPEEM). In LEEM the high intensity of the diffracted slow electrons allows fast image acquisition. Therefore it is tempting to combine it with the other, slower complementary methods. This has been accomplished in the Spectroscopic Photo Emission and Low Energy Electron Microscope (SPELEEM) by adding an energy filter. Today the SPELEEM allows comprehensive structural, chemical, magnetic, electronic characterization of surfaces and thin films by imaging with 10 nm lateral resolution and atomic depth resolution, diffraction and spectroscopy. Recent developments are expected to push the resolution limit into the 1 nm range by aberration correction and the time resolution into and below the picosecond range by pulsed illumination and time-delayed triggered detection. The talk will first describe the general imaging principles and then illustrate with a number of examples the possibilities and limitations of some of the methods, LEEM, Spin-Polarized LEEM (SPLEEM) and X- ray Magnetic Dichroism PEEM (XMCDPEEM). A brief outlook will conclude the presentation.

  13. Surface and Interface Physics of Correlated Electron Materials

    Energy Technology Data Exchange (ETDEWEB)

    Millis, Andrew [Columbia Univ., New York, NY (United States)

    2004-09-01

    The {\\it Surface and Interface Physics of Correlated Electron Materials} research program provided conceptual understanding of and theoretical methodologies for understanding the properties of surfaces and interfaces involving materials exhibiting strong electronic correlations. The issues addressed in this research program are important for basic science, because the behavior of correlated electron superlattices is a crucial challenge to and crucial test of our understanding of the grand-challenge problem of correlated electron physics and are important for our nation's energy future because correlated interfaces offer opportunities for the control of phenomena needed for energy and device applications. Results include new physics insights, development of new methods, and new predictions for materials properties.

  14. Effect of electronic structures on catalytic properties of CuNi alloy and Pd in MeOH-related reactions

    Science.gov (United States)

    Tsai, An-Pang; Kimura, Tomofumi; Suzuki, Yukinori; Kameoka, Satoshi; Shimoda, Masahiko; Ishii, Yasushi

    2013-04-01

    We investigated the catalytic properties of a CuNi solid solution and Pd for methanol-related reactions and associated valence electronic structures. Calculations and X-ray photoelectron spectroscopy measurements revealed that the CuNi alloy has a similar valence electronic structure to Pd and hence they exhibited similar CO selectivities in steam reforming of methanol and decomposition of methanol. Samples prepared by various processes were found to have similar CO selectivities. We conjecture that alloying of Cu and Ni dramatically alters the valence electronic structures, making it similar to that of Pd so that the alloy exhibits similar catalytic properties to Pd. First-principles slab calculations of surface electronic structures support this conjecture.

  15. An effect of chemisorbing surface reaction poisons on the transition from internal to external oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Luckman, G.; Polizzotti, R.S.

    1985-01-01

    The authors consider the effect of a chemisorbing surface reaction poison on the transition from internal to external oxidation for a model binary alloy subject to selective oxidation. The authors solve the diffusion equations for internal oxidation, using the rate of a surface reaction as a boundary condition. Th gas-phase concentration of a strongly chemisorbing poison appears in the analysis through its retarding effect on that surface reaction. It is shown that the slow surface reaction can promote the formation of a protective oxide scale by slowing down the initial uptake of oxygen and allowing metal atoms with the highest oxygen affinity sufficient time to diffuse to the surface. As a result, a larger volum fraction of oxide forms near to the surface (with that volume fraction initially inversely proportional to the rate of the surface reaction), and the critical volume fraction required for the transition to an external scale is more easily exceeded.

  16. A value set for documenting adverse reactions in electronic health records.

    Science.gov (United States)

    Goss, Foster R; Lai, Kenneth H; Topaz, Maxim; Acker, Warren W; Kowalski, Leigh; Plasek, Joseph M; Blumenthal, Kimberly G; Seger, Diane L; Slight, Sarah P; Wah Fung, Kin; Chang, Frank Y; Bates, David W; Zhou, Li

    2017-12-14

    To develop a comprehensive value set for documenting and encoding adverse reactions in the allergy module of an electronic health record. We analyzed 2 471 004 adverse reactions stored in Partners Healthcare's Enterprise-wide Allergy Repository (PEAR) of 2.7 million patients. Using the Medical Text Extraction, Reasoning, and Mapping System, we processed both structured and free-text reaction entries and mapped them to Systematized Nomenclature of Medicine - Clinical Terms. We calculated the frequencies of reaction concepts, including rare, severe, and hypersensitivity reactions. We compared PEAR concepts to a Federal Health Information Modeling and Standards value set and University of Nebraska Medical Center data, and then created an integrated value set. We identified 787 reaction concepts in PEAR. Frequently reported reactions included: rash (14.0%), hives (8.2%), gastrointestinal irritation (5.5%), itching (3.2%), and anaphylaxis (2.5%). We identified an additional 320 concepts from Federal Health Information Modeling and Standards and the University of Nebraska Medical Center to resolve gaps due to missing and partial matches when comparing these external resources to PEAR. This yielded 1106 concepts in our final integrated value set. The presence of rare, severe, and hypersensitivity reactions was limited in both external datasets. Hypersensitivity reactions represented roughly 20% of the reactions within our data. We developed a value set for encoding adverse reactions using a large dataset from one health system, enriched by reactions from 2 large external resources. This integrated value set includes clinically important severe and hypersensitivity reactions. This work contributes a value set, harmonized with existing data, to improve the consistency and accuracy of reaction documentation in electronic health records, providing the necessary building blocks for more intelligent clinical decision support for allergies and adverse reactions.

  17. Energy relations of positron-electron pairs emitted from surfaces.

    Science.gov (United States)

    Brandt, I S; Wei, Z; Schumann, F O; Kirschner, J

    2014-09-05

    The impact of a primary positron onto a surface may lead to the emission of a correlated positron-electron pair. By means of a lab-based positron beam we studied this pair emission from various surfaces. We analyzed the energy spectra in a symmetric emission geometry. We found that the available energy is shared in an unequal manner among the partners. On average the positron carries a larger fraction of the available energy. The unequal energy sharing is a consequence of positron and electron being distinguishable particles. We provide a model which explains the experimental findings.

  18. ELECTRON AVALANCHE MODEL OF DIELECTRIC-VACUUM SURFACE BREAKDOWN

    Energy Technology Data Exchange (ETDEWEB)

    Lauer, E J

    2007-02-21

    The model assumes that an 'initiating event' results in positive ions on the surface near the anode and reverses the direction of the normal component of electric field so that electrons in vacuum are attracted to the dielectric locally. A sequence of surface electron avalanches progresses in steps from the anode to the cathode. For 200 kV across 1 cm, the spacing of avalanches is predicted to be about 13 microns. The time for avalanches to step from the anode to the cathode is predicted to be about a ns.

  19. Extremely confined gap surface-plasmon modes excited by electrons

    DEFF Research Database (Denmark)

    Raza, Søren; Stenger, Nicolas; Pors, Anders Lambertus

    2014-01-01

    High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying...... EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface-plasmon (GSP) modes excited by swift electrons in nanometre-wide gaps. We reveal the resonance behaviour associated with the excitation of the antisymmetric GSP mode for extremely small gap widths, down to ~5...

  20. Calculational aspects of electron-phonon coupling at surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Nojima, Akihiro; Yamashita, Koichi [Department of Chemical System Engineering, School of Engineering, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656 (Japan); Hellsing, Bo [Department of Physics, Goeteborg University, Fysikgraend 3, S-412 96 Goeteborg (Sweden)], E-mail: nojima@tcl.t.u-tokyo.ac.jp

    2008-06-04

    We study the validity of two frequently used approximations in calculations of electron-phonon coupling at surfaces. The rigid-ion approximation is a standard approximation used for the bulk metals. On the basis of density functional theory calculations, we find that for Be this approximation is as valid for surface atoms as for bulk atoms. In addition, the slab method for calculations of a phonon induced surface state lifetime is examined. The convergence of the electron-phonon matrix element with respect to the thickness of the slab is studied for several systems. When the number of slab layers is increased, the net effect of decreasing overlap and increasing number of final states depends strongly on the decay length of the surface state wavefunction and the band structure.

  1. Electronic structure of disordered alloys, surfaces and interfaces

    CERN Document Server

    Turek, Ilja; Kudrnovský, Josef; Šob, Mojmír; Weinberger, Peter

    1997-01-01

    At present, there is an increasing interest in the prediction of properties of classical and new materials such as substitutional alloys, their surfaces, and metallic or semiconductor multilayers. A detailed understanding based on a thus of the utmost importance for fu­ microscopic, parameter-free approach is ture developments in solid state physics and materials science. The interrela­ tion between electronic and structural properties at surfaces plays a key role for a microscopic understanding of phenomena as diverse as catalysis, corrosion, chemisorption and crystal growth. Remarkable progress has been made in the past 10-15 years in the understand­ ing of behavior of ideal crystals and their surfaces by relating their properties to the underlying electronic structure as determined from the first principles. Similar studies of complex systems like imperfect surfaces, interfaces, and mul­ tilayered structures seem to be accessible by now. Conventional band-structure methods, however, are of limited use ...

  2. Deceleration of the electron transfer reaction in the photosynthetic reaction centre as a manifestation of its structure fluctuations

    Directory of Open Access Journals (Sweden)

    Knox P. P.

    2010-07-01

    Full Text Available Aim. To extract information on the nature of protein structural relaxation from the kinetics of electron transfer reaction in the photosynthetic reaction centre (RC. Methods. The kinetic curves obtained by absorption spectroscopy are processed by a maximum entropy method to get the spectrum of relaxation times. Results. A series of distinctive peaks of this spectrum in the interval from 0.1 s to hundreds of seconds is revealed. With the time of exposure of the sample to actinic light increasing, the positions of the peak maxima grow linearly. Conclusions. Theoretical analysis of these results reveals the formation of several structural states of the RC protein. Remarkably, in each of these states the slow reaction kinetics follow the same fractional power law that reflects the glass-like properties of the protein.

  3. Density Functional Reactivity Theory Characterizes Charge Separation Propensity in Proton-Coupled Electron Transfer Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Shubin [Univ. of North Carolina, Chapel Hill, NC (United States); Ess, Daniel H. [Brigham Young Univ., Provo, UT (United States); Univ. of North Carolina, Chapel Hill, NC (United States); Schauer, Cynthia [Univ. of North Carolina, Chapel Hill, NC (United States)

    2011-04-20

    Proton-coupled electron transfer (PCET) reactions occur in many biological and artificial solar energy conversion processes. In these reactions the electron is often transferred to a site distant to the proton acceptor site. In this work, we employ the dual descriptor and the electrophilic Fukui function from density functional reactivity theory (DFRT) to characterize the propensity for an electron to be transferred to a site other than the proton acceptor site. The electrophilic regions of hydrogen bond or van der Waal reactant complexes were examined using these DFRT descriptors to determine the region of space to which the electron is most likely to be transferred. This analysis shows that in PCET reactions the electrophilic region of the reactant complex does not include the proton acceptor site.

  4. Fluorination of an Alumina Surface: Modeling Aluminum-Fluorine Reaction Mechanisms.

    Science.gov (United States)

    Padhye, Richa; Aquino, Adelia J A; Tunega, Daniel; Pantoya, Michelle L

    2017-07-19

    Density functional theory (DFT) calculations were performed to examine exothermic surface chemistry between alumina and four fluorinated, fragmented molecules representing species from decomposing fluoropolymers: F(-), HF, CH3F, and CF4. The analysis has strong implications for the reactivity of aluminum (Al) particles passivated by an alumina shell. It was hypothesized that the alumina surface structure could be transformed due to hydrogen bonding effects from the environment that promote surface reactions with fluorinated species. In this study, the alumina surface was analyzed using model clusters as isolated systems embedded in a polar environment (i.e., acetone). The conductor-like screening model (COSMO) was used to mimic environmental effects on the alumina surface. Four defect models for specific active -OH sites were investigated including two terminal hydroxyl groups and two hydroxyl bridge groups. Reactions involving terminal bonds produce more energy than bridge bonds. Also, surface exothermic reactions between terminal -OH bonds and fluorinated species produce energy in decreasing order with the following reactant species: CF4 > HF > CH3F. Additionally, experiments were performed on aluminum powders using thermal equilibrium analysis techniques that complement the calculations. Consistently, the experimental results show a linear relationship between surface exothermic reactions and the main fluorination reaction for Al powders. These results connect molecular level reaction kinetics to macroscopic measurements of surface energy and show that optimizing energy available in surface reactions linearly correlates to maximizing energy in the main reaction.

  5. Quantum state resolved gas–surface reaction dynamics experiments: a tutorial review.

    OpenAIRE

    Chadwick Helen Jane; Beck Rainer D.

    2016-01-01

    We present a tutorial review of our quantum state resolved experiments designed to study gas–surface reaction dynamics. The combination of a molecular beam state specific reactant preparation by infrared laser pumping and ultrahigh vacuum surface analysis techniques make it possible to study chemical reac tivity at the gas–surface interface in unprecedented detail. We describe the experimental techniques used for state specific reactant preparation and for detection of surface bound reaction...

  6. Real-time studies of battery electrochemical reactions inside a transmission electron microscope.

    Energy Technology Data Exchange (ETDEWEB)

    Leung, Kevin; Hudak, Nicholas S.; Liu, Yang; Liu, Xiaohua H.; Fan, Hongyou; Subramanian, Arunkumar; Shaw, Michael J.; Sullivan, John Patrick; Huang, Jian Yu

    2012-01-01

    We report the development of new experimental capabilities and ab initio modeling for real-time studies of Li-ion battery electrochemical reactions. We developed three capabilities for in-situ transmission electron microscopy (TEM) studies: a capability that uses a nanomanipulator inside the TEM to assemble electrochemical cells with ionic liquid or solid state electrolytes, a capability that uses on-chip assembly of battery components on to TEM-compatible multi-electrode arrays, and a capability that uses a TEM-compatible sealed electrochemical cell that we developed for performing in-situ TEM using volatile battery electrolytes. These capabilities were used to understand lithiation mechanisms in nanoscale battery materials, including SnO{sub 2}, Si, Ge, Al, ZnO, and MnO{sub 2}. The modeling approaches used ab initio molecular dynamics to understand early stages of ethylene carbonate reduction on lithiated-graphite and lithium surfaces and constrained density functional theory to understand ethylene carbonate reduction on passivated electrode surfaces.

  7. Reaction of Aldehydes/Ketones with Electron-Deficient 1,3,5-Triazines Leading to Functionalized Pyrimidines as Diels-Alder/Retro-Diels-Alder Reaction Products: Reaction Development and Mechanistic Studies.

    Science.gov (United States)

    Yang, Kai; Dang, Qun; Cai, Pei-Jun; Gao, Yang; Yu, Zhi-Xiang; Bai, Xu

    2017-03-03

    Catalytic inverse electron demand Diels-Alder (IEDDA) reactions of heterocyclic aza-dienes are rarely reported since highly reactive and electron-rich dienophiles are often found not compatible with strong acids such as Lewis acids. Herein, we disclose that TFA-catalyzed reactions of electron-deficient 1,3,5-triazines and electron-deficient aldehydes/ketones can take place. These reactions led to highly functionalized pyrimidines as products in fair to good yields. The reaction mechanism was carefully studied by the combination of experimental and computational studies. The reactions involve a cascade of stepwise inverse electron demand hetero-Diels-Alder (ihDA) reactions, followed by retro-Diels-Alder (rDA) reactions and elimination of water. An acid was required for both ihDA and rDA reactions. This mechanism was further verified by comparing the relative reactivity of aldehydes/ketones and their corresponding vinyl ethers in the current reaction system.

  8. The Diels-Alder-reaction with inverse-electron-demand, a very efficient versatile click-reaction concept for proper ligation of variable molecular partners.

    Science.gov (United States)

    Wiessler, Manfred; Waldeck, Waldemar; Kliem, Christian; Pipkorn, Ruediger; Braun, Klaus

    2009-12-05

    The ligation of active pharmaceutical ingredients (API) for working with image processing systems in diagnostics (MRT) attracts increasing notice and scientific interest. The Diels-Alder ligation Reaction with inverse electron demand (DAR(inv)) turns out to be an appropriate candidate. The DAR(inv) is characterized by a specific distribution of electrons of the diene and the corresponding dienophile counterpart. Whereas the reactants in the classical Diels-Alder Reaction feature electron-rich diene and electron-poor dienophile compounds, the DAR(inv) exhibits exactly the opposite distribution of electrons. Substituents with pushing electrones increase and, with pulling electrons reduce the electron density of the dienes as used in the DAR(inv).We report here that the DAR(inv) is an efficient route for coupling of multifunctional molecules like active peptides, re-formulated drugs or small molecules like the alkyalting agent temozolomide (TMZ). This is an example of our contribution to the "Click chemistry" technology. In this case TMZ is ligated by DAR(inv) as a cargo to transporter molecules facilitating the passage across the cell membranes into cells and subsequently into subcellular components like the cell nucleus by using address molecules. With such constructs we achieved high local concentrations at the desired target site of pharmacological action. The DAR(inv) ligation was carried out using the combination of several technologies, namely: the organic chemistry and the solid phase peptide synthesis which can produce 'tailored' solutions for questions not solely restricted to the medical diagnostics or therapy, but also result in functionalizations of various surfaces qualified amongst others also for array development.We like to acquaint you with the DAR(inv) and we like to exemplify that all ligation products were generated after a rapid and complete reaction in organic solutions at room temperature, in high purity, but also, hurdles and difficulties on

  9. Potential energy surface for the reaction Sm+ + CO2 → SmO+ + CO: guided ion beam and theoretical studies.

    Science.gov (United States)

    Armentrout, P B; Cox, Richard M

    2017-05-10

    The potential energy surface (PES) for the oxidation of samarium cations by carbon dioxide is explored both experimentally and theoretically. Using guided ion beam tandem mass spectrometry, several reactions are examined as a function of kinetic energy. These include the title reaction as well as its reverse along with the collision-induced dissociation of Sm+(CO2) and OSm+(CO) with Xe. Analysis of the kinetic energy dependent cross sections yields barriers for the forward and reverse oxidation reaction of 1.77 ± 0.11 and 2.04 ± 0.13 eV, respectively, and Sm+-OCO and OSm+-CO bond dissociation energies (BDEs) of 0.42 ± 0.03 and 0.97 ± 0.07 eV, respectively. BDEs for Sm+(CO2)x for x = 2 and 3 are also determined as 0.40 ± 0.13 and 0.48 ± 0.12 eV, respectively. The PESs for the title reaction along the sextet and octet spin surfaces are also examined theoretically at the MP2 and CCSD(T) levels using both effective core potential and all-electron basis sets. Reasonable agreement between theory and experiment is obtained for the experimentally characterized intermediates, although all-electron basis sets and spin-orbit effects are needed for quantitative agreement. The observed barrier for oxidation is shown to likely correspond to the energy of the crossing between surfaces corresponding to the ground state electronic configuration of Sm+ (8F,4f66s1) and an excited surface having two electrons in the valence space (excluding 4f), which are needed to form the strong SmO+ bond.

  10. Morphology, surface topography and optical studies on electron ...

    Indian Academy of Sciences (India)

    Unknown

    Abstract. Electron beam evaporated thin films of MgO powder synthesized by burning of magnesium ribbon in air and sol–gel technique are studied for their microstructure (SEM), surface topography (AFM), and optical transmission behaviour (UV-visible spectroscopy). MgO thin films are shown to be either continuous or ...

  11. Morphology, surface topography and optical studies on electron ...

    Indian Academy of Sciences (India)

    Electron beam evaporated thin films of MgO powder synthesized by burning of magnesium ribbon in air and sol–gel technique are studied for their microstructure (SEM), surface topography (AFM), and optical transmission behaviour (UV-visible spectroscopy). MgO thin films are shown to be either continuous or have mesh ...

  12. Scanning electron microscopic evaluation of root canal surfaces ...

    African Journals Online (AJOL)

    Scanning electron microscopic evaluation of root canal surfaces prepared with three rotary endodontic systems: Lightspeed, ProTaper and EndoWave. ... presence or absence of debris and smear layer and the photographs were taken at coronal, middle and apical 1/3 with a magnification of ~200 and ~1000 respectively.

  13. Comparative study of electron and laser beam surface alloying

    Science.gov (United States)

    Valkov, Stefan Ts.; Petrov, Peter, Iv.; Lazarova, Rumiana L.

    2016-01-01

    High intensity energy fluxes, such as electron beams and laser beams are widely used for surface alloying of metals and alloys. These technologies are able to cause the formation of the so called melt pool where the alloying elements interact each other. It is known that the homogenization of the surface alloy can be explained by intense Marangoni convection, caused by the high temperature gradient in the melt pool. The convection is inversely to the speed of the specimen motion during the alloying process and therefore, the choice of low alloying velocity will reflect on more homogeneous structure of the obtained alloy. In this study, a comparison of the structure and properties of electron and laser beam surface alloying of aluminium with niobium was conducted. The phase composition of the alloyed layers was determined by XRD (X-ray diffraction) with CuKα radiation. The microstructure was studied by SEM (Scanning Electron Microscopy). Chemical analysis was carried out using an EDX electron probe microanalyser. The microhardness of the obtained samples is also measured and compared with respect to the technology of the formation of each surface alloy.

  14. Assessment of root surfaces of apicected teeth: A scanning electron ...

    African Journals Online (AJOL)

    2014-05-15

    May 15, 2014 ... Objectives: The aim of this study was to determine the apical surface characteristics and presence of dental cracks in single‑rooted premolars, resected 3.0 mm from the root apex, using the Er: YAG laser, tungsten carbide bur, and diamond‑coated tip, by scanning electron microscopy (SEM). Experimental ...

  15. A micromachined surface stress sensor with electronic readout

    NARCIS (Netherlands)

    Carlen, Edwin; Weinberg, M.S.; Zapata, A.M.; Borenstein, J.T.

    2008-01-01

    A micromachined surface stress sensor has been fabricated and integrated off chip with a low-noise, differential capacitance, electronic readout circuit. The differential capacitance signal is modulated with a high frequency carrier signal, and the output signal is synchronously demodulated and

  16. Assessment of root surfaces of apicected teeth: A scanning electron ...

    African Journals Online (AJOL)

    Objectives: The aim of this study was to determine the apical surface characteristics and presence of dental cracks in single‑rooted premolars, resected 3.0 mm from the root apex, using the Er: YAG laser, tungsten carbide bur, and diamond‑coated tip, by scanning electron microscopy (SEM). Experimental design: Thirty ...

  17. Relaxation between electrons and surface phonons of a ...

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 63; Issue 5. Relaxation between ... The energy relaxation between the hot degenerate electrons of a homogeneously photoexcited metal film and the surface phonons (phonon wave vectors in two dimensions) is considered under Debye approximation. The state of ...

  18. Theory of coherent molecule to surface electron injection: An ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 121; Issue 5. Theory of coherent molecule to surface electron injection: An analytical model ... Using a quasicontinuum approach to model the substrate, analytical expressions pertaining to the time-dependent probability among the various levels of the substrate is ...

  19. Electron capture by highly charged ions from surfaces and gases

    Energy Technology Data Exchange (ETDEWEB)

    Allen, F.

    2008-01-11

    In this study highly charged ions produced in Electron Beam Ion Traps are used to investigate electron capture from surfaces and gases. The experiments with gas targets focus on spectroscopic measurements of the K-shell x-rays emitted at the end of radiative cascades following electron capture into Rydberg states of Ar{sup 17+} and Ar{sup 18+} ions as a function of collision energy. The ions are extracted from an Electron Beam Ion Trap at an energy of 2 keVu{sup -1}, charge-selected and then decelerated down to 5 eVu{sup -1} for interaction with an argon gas target. For decreasing collision energies a shift to electron capture into low orbital angular momentum capture states is observed. Comparative measurements of the K-shell x-ray emission following electron capture by Ar{sup 17+} and Ar{sup 18+} ions from background gas in the trap are made and a discrepancy in the results compared with those from the extraction experiments is found. Possible explanations are discussed. For the investigation of electron capture from surfaces, highly charged ions are extracted from an Electron Beam Ion Trap at energies of 2 to 3 keVu{sup -1}, charge-selected and directed onto targets comprising arrays of nanoscale apertures in silicon nitride membranes. The highly charged ions implemented are Ar{sup 16+} and Xe{sup 44+} and the aperture targets are formed by focused ion beam drilling in combination with ion beam assisted thin film deposition, achieving hole diameters of 50 to 300 nm and aspect ratios of 1:5 to 3:2. After transport through the nanoscale apertures the ions pass through an electrostatic charge state analyzer and are detected. The percentage of electron capture from the aperture walls is found to be much lower than model predictions and the results are discussed in terms of a capillary guiding mechanism. (orig.)

  20. Phosphate Ion Functionalization of Perovskite Surfaces for Enhanced Oxygen Evolution Reaction.

    Science.gov (United States)

    Yang, Chunzhen; Laberty-Robert, Christel; Batuk, Dmitry; Cibin, Giannantonio; Chadwick, Alan V; Pimenta, Vanessa; Yin, Wei; Zhang, Leiting; Tarascon, Jean-Marie; Grimaud, Alexis

    2017-08-03

    Recent findings revealed that surface oxygen can participate in the oxygen evolution reaction (OER) for the most active catalysts, which eventually triggers a new mechanism for which the deprotonation of surface intermediates limits the OER activity. We propose in this work a "dual strategy" in which tuning the electronic properties of the oxide, such as La1-xSrxCoO3-δ, can be dissociated from the use of surface functionalization with phosphate ion groups (Pi) that enhances the interfacial proton transfer. Results show that the Pi functionalized La0.5Sr0.5CoO3-δ gives rise to a significant enhancement of the OER activity when compared to La0.5Sr0.5CoO3-δ and LaCoO3. We further demonstrate that the Pi surface functionalization selectivity enhances the activity when the OER kinetics is limited by the proton transfer. Finally, this work suggests that tuning the catalytic activity by such a "dual approach" may be a new and largely unexplored avenue for the design of novel high-performance catalysts.

  1. Studies on electronic structure of GaN(0001) surface

    CERN Document Server

    Xie Chang Kun; Xu Fa Qiang; Deng Rui; Liu Feng; Yibulaxin, K

    2002-01-01

    An electronic structure investigation on GaN(0001) is reported. The authors employ a full-potential linearized augmented plane-wave (FPLAPW) approach to calculate the partial density of state, which is in agreement with previous experimental results. The effects of the Ga3d semi-core levels on the electronic structure of GaN are discussed. The valence-electronic structure of the wurtzite GaN(0001) surface is investigated using synchrotron radiation excited angle-resolved photoemission spectroscopy. The bulk bands dispersion along GAMMA A direction in the Brillouin zones is measured using normal-emission spectra by changing photon-energy. The band structure derived from authors' experimental data is compared well with the results of authors' FPLAPW calculation. Furthermore, off-normal emission spectra are also measured along the GAMMA K and GAMMA M directions. Two surface states are identified, and their dispersions are characterized

  2. Electron emission from MOS electron emitters with clean and cesium covered gold surface

    DEFF Research Database (Denmark)

    Nielsen, Gunver; Thomsen, Lasse Bjørchmar; Johansson, Martin

    2009-01-01

    characteristics have been investigated. It is known, that deposition of an alkali metal on the emitting surface lowers the work function and increases the emission efficiency. For increasing Cs coverages the surface has been characterized by X-ray Photoelectron Spectroscopy (XPS), Ion Scattering Spectroscopy (ISS......) and work function measurements. Energy spectra of electron emission from the devices under an applied bias voltage have been recorded for the clean Au surface and for two Cs coverages and simultaneous work function curves have been obtained. The electron emission onset is seen to appear at the surface work...... function. A method for cleaning the ex situ deposited Au top electrodes to a degree satisfactory to surface science studies has been developed, and a threshold for oxide damage by low-energy ion exposure between 0.5 and 1 keV has been determined....

  3. A reaction diffusion model of pattern formation in clustering of adatoms on silicon surfaces

    Directory of Open Access Journals (Sweden)

    Trilochan Bagarti

    2012-12-01

    Full Text Available We study a reaction diffusion model which describes the formation of patterns on surfaces having defects. Through this model, the primary goal is to study the growth process of Ge on Si surface. We consider a two species reaction diffusion process where the reacting species are assumed to diffuse on the two dimensional surface with first order interconversion reaction occuring at various defect sites which we call reaction centers. Two models of defects, namely a ring defect and a point defect are considered separately. As reaction centers are assumed to be strongly localized in space, the proposed reaction-diffusion model is found to be exactly solvable. We use Green's function method to study the dynamics of reaction diffusion processes. Further we explore this model through Monte Carlo (MC simulations to study the growth processes in the presence of a large number of defects. The first passage time statistics has been studied numerically.

  4. Lanthanum-Based Compounds: Electronic Band-Gap-Dependent Electrocatalytic Materials for Oxygen Reduction Reaction.

    Science.gov (United States)

    Gu, Weiwei; Song, Ye; Liu, Jingjun; Wang, Feng

    2017-07-26

    The electronic energy level of lanthanum compounds plays an important role in the oxygen reduction reaction (ORR) electrocatalytic process. In this work, three lanthanum compounds, LaOHCO3 , La2 O2 CO3 , and La2 O3 , have been synthesized through an in situ urea hydrolysis method, followed by annealing at different temperatures. Among these lanthanum compounds, the layer-structured La2 O2 CO3 has the smallest band gap and moderate values of the conduction band (CB) and valence band (VB). Electrochemical measurements in 0.1 m KOH solution have shown that, compared with the other catalysts, La2 O2 CO3 exhibits the best electrocatalytic activity with the lowest H2 O2 production and highest durability for ORR, which proves the close correlation between electronic energy level and electrocatalytic ORR activity. During the ORR process over La2 O2 CO3 , some covalent electrons from the VB are first excited to the CB and then transfer to the unoccupied π*2p orbitals of an active oxygen molecule, leading to strengthened oxygen adsorption and promotion of the reduction of oxygen. Moreover, La2 O2 CO3 has an ability to chemically disproportionate hydrogen peroxide (to give HO2(-) ), and the produced HO2(-) at the energy level of O2 /HO2(-) can undergo prompt chemical disproportionation into O2 and OH(-) . The O2 generated at this stage is adsorbed on the catalyst surface, which can be utilized for further oxygen reduction. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Hydrogen and surface excitation in electron spectra of polyethylene

    Science.gov (United States)

    Orosz, G. T.; Gergely, G.; Menyhard, M.; Tóth, J.; Varga, D.; Lesiak, B.; Jablonski, A.

    2004-09-01

    The inelastic mean free path (IMFP) of electrons of polyethylene was determined by elastic peak electron spectroscopy (EPES). Hydrogen cannot be detected directly by conventional electron spectroscopies, such as Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), reflection electron energy loss spectroscopy (REELS) and EPES. The evaluation of electron spectra on polyethylene (PE) and other polymers needs corrections for hydrogen and surface excitation. Electron elastic backscattering on H atoms appears in the splitting of the elastic peak, shifting and Doppler broadening of the H peak produced by recoil effect. This shift is 0.34-3.8 eV for E=0.2-2.0 keV. Experiments resulted in separating the very low H elastic signal from the background. Surface excitation is characterised by the parameter Pse( E) which was described by formulae of Tanuma, Werner and Chen, using different definitions. The Pse( E) of PE was determined by our new procedure. Si and Ag were used as reference samples for its determination by EPES experiments. Experiments were made with a HSA spectrometer of high energy resolution. Their Monte Carlo evaluation was based on the NIST 64 database and IMFP of Tanuma et al., Gries and Cumpson. Pse( E) of PE was determined by best fit of experimental parameters, comparing the different IMFPs and surface excitation correction factors of Chen and Werner et al. The criteria of best fit are the RMS deviations from the different corrections. The total backscattering spectra (elastic and inelastic) of PE, C and Cu resulted in indirect observation of H.

  6. Quantum state resolved gas-surface reaction dynamics experiments: a tutorial review.

    Science.gov (United States)

    Chadwick, Helen; Beck, Rainer D

    2016-07-07

    We present a tutorial review of our quantum state resolved experiments designed to study gas-surface reaction dynamics. The combination of a molecular beam, state specific reactant preparation by infrared laser pumping, and ultrahigh vacuum surface analysis techniques make it possible to study chemical reactivity at the gas-surface interface in unprecedented detail. We describe the experimental techniques used for state specific reactant preparation and for detection of surface bound reaction products developed in our laboratory. Using the example of the reaction of methane on Ni and Pt surfaces, we show how state resolved experiments uncovered clear evidence for vibrational mode specificity and bond selectivity, as well as steric effects in chemisorption reactions. The state resolved experimental data provides valuable benchmarks for comparison with theoretical models for gas-surface reactivity aiding in the development of a detailed microscopic understanding of chemical reactivity at the gas-surface interface.

  7. One-dimensional description of multidimensional electron transfer reactions in condensed phase.

    Science.gov (United States)

    Dhole, Kajal; Samanta, Alok; Ghosh, Swapan K

    2008-06-05

    We derive a one-dimensional energy diffusion equation for describing the dynamics of multidimensional electron transfer reactions in condensed phase, which is conceptually simpler and computationally more economic than the conventional approaches. We also obtain an analytical expression for the rate of electron transfer reactions for a general one-dimensional effective potential as well as an energy dependent diffusitivity. As an illustrative example, we consider application to electron transfer in a contact ion pair system modeled through harmonic potentials consisting of two slow classical modes and a high frequency vibrational mode for which the numerical results calculated using the proposed one-dimensional approach are shown to be in good agreement with experimental results. The energy diffusion equation and the rate expression for electron transfer obtained from the present theory, therefore, open up the possibility of describing the dynamics of electron transfer in complex systems, through a simpler approach.

  8. Electron Scattering at Surfaces and Interfaces of Transition Metals

    Science.gov (United States)

    Zheng, Pengyuan

    The effect of surfaces on the electron transport at reduced scales is attracting continuous interest due to its broad impact on both the understanding of materials properties and their application for nanoelectronics. The size dependence of for conductor's electrical resistivity rho due to electron surface scattering is most commonly described within the framework of Fuchs and Sondheimer (FS) and their various extensions, which uses a phenomenological scattering parameter p to define the probability of electrons being elastically (i.e. specularly) scattered by the surface without causing an increase of rho at reduced size. However, a basic understanding of what surface chemistry and structure parameters determine the specularity p is still lacking. In addition, the assumption of a spherical Fermi surface in the FS model is too simple for transition metals to give accurate account of the actual surface scattering effect. The goal of this study is to develop an understanding of the physics governing electron surface/interface scattering in transition metals and to study the significance of their Fermi surface shape on surface scattering. The advancement of the scientific knowledge in electron surface and interface scattering of transition metals can provide insights into how to design high-conductivity nanowires that will facilitate the viable development of advanced integrated circuits, thermoelectric power generation and spintronics. Sequential in situ and ex situ transport measurements as a function of surface chemistry demonstrate that electron surface/interface scattering can be engineered by surface doping, causing a decrease in the rho. For instance, the rho of 9.3-nm-thick epitaxial and polycrystalline Cu is reduced by 11--13% when coated with 0.75 nm Ni. This is due to electron surface scattering which exhibits a specularity p = 0.7 for the Cu-vacuum interface that transitions to completely diffuse (p = 0) when exposed to air. In contrast, Ni-coated surfaces

  9. High throughput engineering to revitalize a vestigial electron transfer pathway in bacterial photosynthetic reaction centers.

    Science.gov (United States)

    Faries, Kaitlyn M; Kressel, Lucas L; Wander, Marc J; Holten, Dewey; Laible, Philip D; Kirmaier, Christine; Hanson, Deborah K

    2012-03-09

    Photosynthetic reaction centers convert light energy into chemical energy in a series of transmembrane electron transfer reactions, each with near 100% yield. The structures of reaction centers reveal two symmetry-related branches of cofactors (denoted A and B) that are functionally asymmetric; purple bacterial reaction centers use the A pathway exclusively. Previously, site-specific mutagenesis has yielded reaction centers capable of transmembrane charge separation solely via the B branch cofactors, but the best overall electron transfer yields are still low. In an attempt to better realize the architectural and energetic factors that underlie the directionality and yields of electron transfer, sites within the protein-cofactor complex were targeted in a directed molecular evolution strategy that implements streamlined mutagenesis and high throughput spectroscopic screening. The polycistronic approach enables efficient construction and expression of a large number of variants of a heteroligomeric complex that has two intimately regulated subunits with high sequence similarity, common features of many prokaryotic and eukaryotic transmembrane protein assemblies. The strategy has succeeded in the discovery of several mutant reaction centers with increased efficiency of the B pathway; they carry multiple substitutions that have not been explored or linked using traditional approaches. This work expands our understanding of the structure-function relationships that dictate the efficiency of biological energy-conversion reactions, concepts that will aid the design of bio-inspired assemblies capable of both efficient charge separation and charge stabilization.

  10. Electronic structure, molecular bonding and potential energy surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Ruedenberg, K. [Ames Laboratory, IA (United States)

    1993-12-01

    By virtue of the universal validity of the generalized Born-Oppenheimer separation, potential energy surfaces (PES`) represent the central conceptual as well as quantitative entities of chemical physics and provide the basis for the understanding of most physicochemical phenomena in many diverse fields. The research in this group deals with the elucidation of general properties of PES` as well as with the quantitative determination of PES` for concrete systems, in particular pertaining to reactions involving carbon, oxygen, nitrogen and hydrogen molecules.

  11. Electronic pathway in reaction centers from Rhodobacter sphaeroides and Chloroflexus aurantiacus.

    Science.gov (United States)

    Pudlak, Michal; Pincak, Richard

    2010-06-01

    The reaction centers (RC) of Chloroflexus aurantiacus and Rhodobacter sphaeroidesH(M182)L mutant were investigated. Prediction for electron transfer (ET) at very low temperatures was also performed. To describe the kinetics of the C. aurantiacus RCs, the incoherent model of electron transfer was used. It was shown that the asymmetry in electronic coupling parameters must be included to explain the experiments. For the description of R. sphaeroidesH(M182)L mutant RCs, the coherent and incoherent models of electron transfer were used. These two models are discussed with regard to the observed electron transfer kinetics. It seems likely that the electron transfer asymmetry in R. sphaeroides RCs is caused mainly by the asymmetry in the free energy levels of L- and M-side cofactors. In the case of C. aurantiacus RCs, the unidirectionality of the charge separation can be caused mainly by the difference in the electronic coupling parameters in two branches.

  12. Wave packet motions coupled to electron transfer in reaction centers of Chloroflexus aurantiacus.

    Science.gov (United States)

    Yakovlev, Andrei G; Shkuropatova, Tatiana A; Vasilieva, Lyudmila G; Shkuropatov, Anatoli Ya; Shuvalov, Vladimir A

    2008-08-01

    Transient absorption difference spectroscopy with approximately 20 femtosecond (fs) resolution was applied to study the time and spectral evolution of low-temperature (90 K) absorbance changes in isolated reaction centers (RCs) of Chloroflexus (C.) aurantiacus. In RCs, the composition of the B-branch chromophores is different with respect to that of purple bacterial RCs by occupying the B(B) binding site of accessory bacteriochlorophyll by bacteriopheophytin molecule (Phi(B)). It was found that the nuclear wave packet motion induced on the potential energy surface of the excited state of the primary electron donor P* by approximately 20 fs excitation leads to a coherent formation of the states P+Phi(B)(-) and P+B(A)(-) (B(A) is a bacteriochlorophyll monomer in the A-branch of cofactors). The processes were studied by measuring coherent oscillations in kinetics of the absorbance changes at 900 nm and 940 nm (P* stimulated emission), at 750 nm and 785 nm (Phi(B) absorption bands), and at 1,020-1028 nm (B(A)(-) absorption band). In RCs, the immediate bleaching of the P band at 880 nm and the appearance of the stimulated wave packet emission at 900 nm were accompanied (with a small delay of 10-20 fs) by electron transfer from P* to the B-branch with bleaching of the Phi(B) absorption band at 785 nm due to Phi(B)(-) formation. These data are consistent with recent measurements for the mutant HM182L Rb. sphaeroides RCs (Yakovlev et al., Biochim Biophys Acta 1757:369-379, 2006). Only at a delay of 120 fs was the electron transfer from P* to the A-branch observed with a development of the B(A)(-) absorption band at 1028 nm. This development was in phase with the appearance of the P* stimulated emission at 940 nm. The data on the A-branch electron transfer in C. aurantiacus RCs are consistent with those observed in native RCs of Rb. sphaeroides. The mechanism of charge separation in RCs with the modified B-branch pigment composition is discussed in terms of coupling between

  13. Positron Spur Reactions with Excess Electrons and Anions in Liquid Organic Mixtures of Electron Acceptors

    DEFF Research Database (Denmark)

    Lévay, B.; Mogensen, O. E.

    1980-01-01

    By means of the positron lifetime technique we have measured positronium (Ps) yields in mixtures of nonpolar liquids with various electron scavengers which bind the electron fairly weakly (1–2 eV) in stable anions. The results are discussed with reference to recent excess electron works, and new...... curve. Alcohol clusters did not show antiinhibition in 0.05 M CCl4/neopentane system. Weak electron scavengers (C6F6, naphthalene, biphenyl, benzene) which generally act as antiinhibitors were added to pure non-polar solvents (hexane, isooctane, cyclohexane) and caused Ps enhancement. This can...... to the system, indicating that antirecombination and antiinhibition took place simultaneously. On addition of hexane, isooctane, CS2 or 0.8 M CS2/hexane to pure C6F6 the Ps yield drastically decreased. This correlates well with the drastic decrease of the electron mobility by adding similar additives to C6F6...

  14. Decoupling diffusion from the bimolecular photoinduced electron transfer reaction: a combined ultrafast spectroscopic and kinetic analysis.

    Science.gov (United States)

    Mukherjee, Puspal; Sen, Pratik

    2017-05-10

    We have studied the bimolecular photoinduced electron transfer (PET) reaction between benzophenone (Bp) and DABCO using femtosecond broadband transient absorption spectroscopy in different compositions of acetonitrile/1-butanol binary solvent mixtures. With the increase in the 1-butanol percentage in the mixture, we have observed an increase in the onset delay time of Bp˙(-), which is the product of the reaction. As 1-butanol is more viscous than acetonitrile, we related the onset time to the change in medium viscosity. Moreover, we undertook a complete kinetic analysis of the bimolecular PET reaction under different conditions to show that from transient absorption spectroscopy, we can get the exact rate of electron transfer. This kind of kinetic analysis along with the experimental data is the first of its kind to prove that transient absorption spectroscopy is probably the most useful tool in studying the PET reaction.

  15. Low-energy electron scattering from molecules, biomolecules and surfaces

    CERN Document Server

    Carsky, Petr

    2011-01-01

    Since the turn of the 21st century, the field of electron molecule collisions has undergone a renaissance. The importance of such collisions in applications from radiation chemistry to astrochemistry has flowered, and their role in industrial processes such as plasma technology and lighting are vital to the advancement of next generation devices. Furthermore, the development of the scanning tunneling microscope highlights the role of such collisions in the condensed phase, in surface processing, and in the development of nanotechnology.Low-Energy Electron Scattering from Molecules, Biomolecule

  16. Surface morphology of Trichinella spiralis by scanning electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kim, C.W. (State Univ. of New York, Stony Brook); Ledbetter, M.C.

    1980-02-01

    The surface morphology of larval and adult Trichinella spiralis was studied by scanning electron microscopy (SEM) of fixed, dried, and metal-coated specimens. The results are compared with those found earlier by various investigators using light and transmission electron microscopy. Some morphological features reported here are revealed uniquely by SEM. These include the pores of the cephalic sense organs, the character of secondary cuticular folds, variations of the hypodermal gland cell openings or pores, and the presence of particles on the copulatory bell.

  17. Harvesting the loss: surface plasmon-based hot electron photodetection

    Science.gov (United States)

    Li, Wei; Valentine, Jason G.

    2017-01-01

    Although the nonradiative decay of surface plasmons was once thought to be only a parasitic process within the plasmonic and metamaterial communities, hot carriers generated from nonradiative plasmon decay offer new opportunities for harnessing absorption loss. Hot carriers can be harnessed for applications ranging from chemical catalysis, photothermal heating, photovoltaics, and photodetection. Here, we present a review on the recent developments concerning photodetection based on hot electrons. The basic principles and recent progress on hot electron photodetectors are summarized. The challenges and potential future directions are also discussed.

  18. Kinetics and mechanisms of heterogeneous reaction of NO2 on CaCO3 surfaces under dry and wet conditions

    Directory of Open Access Journals (Sweden)

    Z. M. Chen

    2010-01-01

    Full Text Available With increasing NO2 concentration in the troposphere, the importance of NO2 reaction with mineral dust in the atmosphere needs to be evaluated. Until now, little is known about the reaction of NO2 with CaCO3. In this study, the heterogeneous reaction of NO2 on the surface of CaCO3 particles was investigated at 296 K and NO2 concentrations between 4.58×1015 molecules cm−3 to 1.68×1016 molecules cm−3, using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS combined with X-ray photoelectron spectroscopy (XPS and scanning electron microscopy (SEM, under wet and dry conditions. Nitrate formation was observed under both conditions, while nitrite was observed under wet conditions, indicating the reaction of NO2 on the CaCO3 surface produced nitrate and probably nitrous acid (HONO. Relative humidity (RH influences both the initial uptake coefficient and the reaction mechanism. At low RH, surface −OH is formed through dissociation of the surface adsorbed water via oxygen vacancy, thus determining the reaction order. As RH increases, water starts to condense on the surface and the gas-liquid reaction of NO2 with the condensed water begins. With high enough RH (>52% in our experiment, the gas-liquid reaction of NO2 with condensed water becomes dominant, forming HNO3 and HONO. The initial uptake coefficient γ0 was determined to be (4.25±1.18×10−9 under dry conditions and up to (6.56±0.34×10−8 under wet conditions. These results suggest that the reaction of NO2 on CaCO3 particle is unable to compete with that of HNO3 in the atmosphere. Further studies at lower NO2 concentrations and with a more accurate assessment of the surface area for calculating the uptake coefficient of the reaction of NO2 on CaCO3 particle and to examine its importance as a source of HONO in the atmosphere are needed.

  19. Electron transfer reaction of butane -1,3-diol and cr(vi) in aqueous ...

    African Journals Online (AJOL)

    Kinetic and mechanistic studies of electron transfer reaction of butane-1,3-diol and Cr(VI) ion in aqueous acidic medium have been carried out in aqueous medium at 271°C, I = 1.0 mol dm-3 (NaCl), [H +] = 0.5mol dm-3 (HCl). The reaction was inhibited by added anions and showed negative salt effect. Spectroscopic ...

  20. Coupling reaction between electron-rich pyrimidinones and α-amino acids promoted by phosphonium salts.

    Science.gov (United States)

    ElMarrouni, Abdelatif; Fabrellas, Josep M; Heras, Montserrat

    2011-09-07

    Coupling reaction between electron-rich 2-morpholino-4(3H)-pyrimidinone and nucleophilic side chains of several natural α-amino acids promoted by phosphonium salt has been developed to prepare new optically active pyrimidin-4-yl amino acids. The best results were obtained using a two-step method through the easily available benzotriazolyl-1-oxy intermediate. A detailed optimization study of this reaction is discussed.

  1. Study of thermally activated reaction between Mn and GaAs(111) surface

    Energy Technology Data Exchange (ETDEWEB)

    Soares, M.V.; Jurca, H.F.; Zarpellon, J.; Varalda, J.; Schreiner, W.H.; Mosca, D.H.

    2014-11-03

    We investigate the chemical reactivity of ultra-thin films of Mn on As-terminated (111) GaAs surface kept at ultra-high vacuum conditions in the temperature interval ranging from room temperature to 400 °C. The experiments were performed using a customized molecular beam epitaxy system equipped with reflection high energy electron diffraction and X-ray photoelectron spectroscopy techniques. These analyses were complemented with X-ray diffraction measurements to put in evidence the formation of intermediate compounds. Only Ga{sub 1−x}Mn{sub x}As and sub-arsenised MnAs{sub x} compounds are possibly formed below 200 °C. The onset of the reactivity occurs around 200 °C when ordered compounds such as MnAs and MnGa are observed. The formation of compounds more rich in Mn like Mn{sub 3}Ga and Mn{sub 2}As is found for deposition temperatures of 300 and 400 °C. - Highlights: • Surface chemistry of Mn in contact with GaAs surface • Formation of Mn-based compounds • Solid state reactions of Mn on GaAs.

  2. Electron Impact Induced Reactions of Ethyl Acetate and Its Sulphur Analogues

    DEFF Research Database (Denmark)

    Egsgaard, Helge; Larsen, Elfinn; Carlsen, Lars

    1983-01-01

    The electron impact induced reactions of ethyl acetate and its sulphur analogues have been studied by application of collision activation mass spectrometry and isotopic labelling with H-2 and O-18. The [M-C2H4]+·, [M-CH3]+ and [M-H2O]+· were selected for detailed investigations.......The electron impact induced reactions of ethyl acetate and its sulphur analogues have been studied by application of collision activation mass spectrometry and isotopic labelling with H-2 and O-18. The [M-C2H4]+·, [M-CH3]+ and [M-H2O]+· were selected for detailed investigations....

  3. Direct simulation of proton-coupled electron transfer reaction dynamics and mechanisms

    Science.gov (United States)

    Kretchmer, Joshua S.; Miller, Thomas F., III

    2014-03-01

    Proton-coupled electron transfer (PCET) reactions, in which both an electron and an associated proton undergo reactive transfer, play an important role in many chemical and biological systems. Due to the complexity of this class of reactions, a variety of different mechanisms fall under the umbrella of PCET. However, the physical driving forces that determine the preferred mechanism in a given system still remain poorly understood. Towards this end, we extend ring polymer molecular dynamics (RPMD), a path-integral quantum dynamics method, to enable the direct simulation and characterization of PCET reaction dynamics in both fully atomistic and system-bath models of organometallic catalysts. In addition to providing validation for the simulation method via extensive comparison with existing PCET rate theories, we analyze the RPMD trajectories to investigate the competition between the concerted and sequential reaction mechanisms for PCET, elucidating the large role of the solvent in controlling the preferred mechanism. We further employ RPMD to determine the kinetics and mechanistic features of concerted PCET reactions across different regimes of electronic and vibrational coupling, providing evidence for a new and distinct PCET reaction mechanism.

  4. 2013 Chemical reactions at surfaces. Surfaces in Energy and the Environment. Gordon Research Conference and Gordon Research Seminar (April 28 - May 3, 2013 - Les Diablerets, Switzerland)

    Energy Technology Data Exchange (ETDEWEB)

    Stair, Peter C. [Northwestern Univ., Evanston, IL (United States)

    2013-02-03

    presentations on chemistry at solid and liquid surfaces of relevance to catalysis, synthesis, photochemistry, environmental science, and tribology. Topics include: Fundamental Surface Chemistry; Catalysis; Solid Liquid and Aerosol Interfaces; Surface Photochemistry; Synthesis of Surfaces; Environmental Interfaces; Hot Topics in Surface Chemical Reactions; Tribology; Gas-Surface Scattering and Reactions; Novel Materials and Environments.

  5. Picosecond laser studies of the charge-transfer reaction of excited triplet diphenylcarbene with electron donors

    Science.gov (United States)

    Sitzmann, E. V.; Langan, J.; Eisenthal, K. B.

    1983-12-01

    Evidence of a one-electron transfer process in a carbene reaction has been observed for the first time. The example is the quenching of the photoexcited triplet state of diphenylcarbene ( 3*DPC) by electron donors. Measurement of the fluorescence lifetime as a function of donor concentration yielded the bimolecular rate constant, 3* k. An explanation is offered as to why 3* and 1DPC react efficiently with amines as well as alcohols, whereas the ground triplet, 3DPC, does not.

  6. High-pressure catalytic reactions over single-crystal metal surfaces

    Science.gov (United States)

    Rodriguez, JoséA.; Wayne Goodman, D.

    1991-11-01

    Studies dealing with high-pressure catalytic reactions over single-crystal surfaces are reviewed. The coupling of an apparatus for the measurement of reaction kinetics at elevated pressures with an ultrahigh vacuum system for surface analysis allows detailed study of structure sensitivity, the effects of promoters and inhibitors on catalytic activity, and, in certain cases, identification of reaction intermediates by post-reaction surface analysis. Examples are provided which demonstrate the relevance of single-crystal studies for modeling the behaviour of high-surface-area supported catalysts. Studies of CO methanation and CO oxidation over single-crystal surfaces provide convincing evidence that these reactions are structure insensitive. For structure-sensitive reactions (ammonia synthesis, alkane hydrogenolysis, alkane isomerization, water-gas shift reaction, etc.) model single-crystal studies allow correlations to be established between surface structure and catalytic activity. The effects of both electronegative (S and P) and electropositive (alkali metals) impurities upon the catalytic activity of metal single crystals for ammonia synthesis, CO methanation, alkane hydrogenolysis, ethylene epoxidation and water-gas shift are discussed. The roles of "ensemble" and "ligand" effects in bimetallic catalysts are examined in light of data obtained using surfaces prepared by vapor-depositing one metal onto a crystal face of a dissimilar metal.

  7. Apparatus for testing gas-surface reactions for epicatalysis

    Science.gov (United States)

    Sheehan, D. P.; Zawlacki, T. A.; Helmer, W. H.

    2016-07-01

    Recently, a new mode of gas-surface heterogeneous catalysis (epicatalysis) has been identified, having potential applications ranging from industrial and green chemistry to novel forms of power generation. This article describes an inexpensive, easily constructed, vacuum-compatible apparatus by which multiple candidate gas-surface combinations can be rapidly screened for epicatalytic activity. In exploratory experiments, candidate surfaces (teflon, kapton, glass, and gold) and gases (helium, argon, cyclohexane, water, methanol, formic acid, and acetic acid) were tested for epicatalytic activity. Kapton and teflon displayed small but reproducible differences in formic acid and methanol dimer desorption, thereby demonstrating the first examples of room-temperature epicatalysis. Other gas-surface combinations showed smaller or inconclusive evidence for epicatalysis.

  8. Biametallic Clusters: Insights into Reactions of Subnanoscale Surfaces

    National Research Council Canada - National Science Library

    Wagner, Raymond

    1997-01-01

    Reactivities of bimetallic clusters can be controlled by varying their composition, making them potentially useful as catalysts and valuable for use in elucidating the reactivities of such subnanoscale surfaces...

  9. Electronic nonadiabatic effects in low temperature radical-radical reactions. I. C(3P) + OH(2Π).

    Science.gov (United States)

    Maergoiz, A I; Nikitin, E E; Troe, J

    2014-07-28

    The formation of collision complexes, as a first step towards reaction, in collisions between two open-electronic shell radicals is treated within an adiabatic channel approach. Adiabatic channel potentials are constructed on the basis of asymptotic electrostatic, induction, dispersion, and exchange interactions, accounting for spin-orbit coupling within the multitude of electronic states arising from the separated reactants. Suitable coupling schemes (such as rotational + electronic) are designed to secure maximum adiabaticity of the channels. The reaction between C((3)P) and OH((2)Π) is treated as a representative example. The results show that the low temperature association rate coefficients in general cannot be represented by results obtained with a single (generally the lowest) potential energy surface of the adduct, asymptotically reaching the lowest fine-structure states of the reactants, and a factor accounting for the thermal population of the latter states. Instead, the influence of non-Born-Oppenheimer couplings within the multitude of electronic states arising during the encounter markedly increases the capture rates. This effect extends up to temperatures of several hundred K.

  10. Fluctuation-Induced Pattern Formation in a Surface Reaction

    DEFF Research Database (Denmark)

    Starke, Jens; Reichert, Christian; Eiswirth, Markus

    2006-01-01

    Spontaneous nucleation, pulse formation, and propagation failure have been observed experimentally in CO oxidation on Pt(110) at intermediate pressures ($\\approx 10^{-2}$mbar). This phenomenon can be reproduced with a stochastic model which includes temperature effects. Nucleation occurs randomly...... due to fluctuations in the reaction processes, whereas the subsequent damping out essentially follows the deterministic path. Conditions for the occurence of stochastic effects in the pattern formation during CO oxidation on Pt are discussed....

  11. Reaction chemistry and ligand exchange at cadmium selenide nanocrystal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Owen, Jonathan; Park, Jungwon; Trudeau, Paul-Emile; Alivisatos, A. Paul

    2008-12-02

    Chemical modification of nanocrystal surfaces is fundamentally important to their assembly, their implementation in biology and medicine, and greatly impacts their electrical and optical properties. However, it remains a major challenge owing to a lack of analytical tools to directly determine nanoparticle surface structure. Early nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) studies of CdSe nanocrystals prepared in tri-n-octylphosphine oxide (1) and tri-n-octylphosphine (2), suggested these coordinating solvents are datively bound to the particle surface. However, assigning the broad NMR resonances of surface-bound ligands is complicated by significant concentrations of phosphorus-containing impurities in commercial sources of 1, and XPS provides only limited information about the nature of the phosphorus containing molecules in the sample. More recent reports have shown the surface ligands of CdSe nanocrystals prepared in technical grade 1, and in the presence of alkylphosphonic acids, include phosphonic and phosphinic acids. These studies do not, however, distinguish whether these ligands are bound datively, as neutral, L-type ligands, or by X-type interaction of an anionic phosphonate/phosphinate moiety with a surface Cd{sup 2+} ion. Answering this question would help clarify why ligand exchange with such particles does not proceed generally as expected based on a L-type ligand model. By using reagents with reactive silicon-chalcogen and silicon-chlorine bonds to cleave the ligands from the nanocrystal surface, we show that our CdSe and CdSe/ZnS core-shell nanocrystal surfaces are likely terminated by X-type binding of alkylphosphonate ligands to a layer of Cd{sup 2+}/Zn{sup 2+} ions, rather than by dative interactions. Further, we provide spectroscopic evidence that 1 and 2 are not coordinated to our purified nanocrystals.

  12. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    Science.gov (United States)

    Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-12-22

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

  13. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    Science.gov (United States)

    Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov'Yov, Ilia A.

    2015-12-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

  14. [Inelastic electron scattering from surfaces]. [Annual] progress report

    Energy Technology Data Exchange (ETDEWEB)

    1993-10-01

    This program is aimed at the quantitative study of surface dynamical processes (vibrational, magnetic excitations) in crystalline slabs, ultrathin-layered materials, and chemisorbed systems on substrates, and of the geometric structure connected to these dynamical excitations. High-resolution electron-energy loss spectroscopy (HREELS) is a powerful probe. Off-specular excitation cross sections are much larger if electron energies are in the LEED range (50-300 eV). The analyses has been used to study surfaces of ordered alloys (NiAl). Ab-initio surface lattice dynamical results were combined with phonon-loss cross sections to achieve a more accurate microscopic description. First-principles phonon eigenvectors and eigenfrequencies were used as inputs to electron-energy-loss multiple scattering cross-section calculations. The combined microscopic approach was used to analyze EELS data of Cu(0001) and Ag(001) at two points. Positron diffraction is discussed as a structural and imaging tool. The relation between geometric structure of a film and its local magnetic properties will be studied in the future, along with other things.

  15. Biomimetic surface modification of polypropylene by surface chain transfer reaction based on mussel-inspired adhesion technology and thiol chemistry

    Science.gov (United States)

    Niu, Zhijun; Zhao, Yang; Sun, Wei; Shi, Suqing; Gong, Yongkuan

    2016-11-01

    Biomimetic surface modification of polypropylene (PP) is conducted by surface chain transfer reaction based on the mussel-inspired versatile adhesion technology and thiol chemistry, using 2-methacryloyloxyethylphosphorylcholine (MPC) as a hydrophilic monomer mimicking the cell outer membrane structure and 2,2-azobisisobutyronitrile (AIBN) as initiator in ethanol. A layer of polydopamine (PDA) is firstly deposited onto PP surface, which not only offers good interfacial adhesion with PP, but also supplies secondary reaction sites (-NH2) to covalently anchor thiol groups onto PP surface. Then the radical chain transfer to surface-bonded thiol groups and surface re-initiated polymerization of MPC lead to the formation of a thin layer of polymer brush (PMPC) with cell outer membrane mimetic structure on PP surface. X-ray photoelectron spectrophotometer (XPS), atomic force microscopy (AFM) and water contact angle measurements are used to characterize the PP surfaces before and after modification. The protein adsorption and platelet adhesion experiments are also employed to evaluate the interactions of PP surface with biomolecules. The results show that PMPC is successfully grafted onto PP surface. In comparison with bare PP, the resultant PP-PMPC surface exhibits greatly improved protein and platelet resistance performance, which is the contribution of both increased surface hydrophilicity and zwitterionic structure. More importantly, the residue thiol groups on PP-PMPC surface create a new pathway to further functionalize such zwitterion modified PP surface.

  16. Quantifying Fenton reaction pathways driven by self-generated H2O2 on pyrite surfaces

    Science.gov (United States)

    Gil-Lozano, C.; Davila, A. F.; Losa-Adams, E.; Fairén, A. G.; Gago-Duport, L.

    2017-03-01

    Oxidation of pyrite (FeS2) plays a significant role in the redox cycling of iron and sulfur on Earth and is the primary cause of acid mine drainage (AMD). It has been established that this process involves multi-step electron-transfer reactions between surface defects and adsorbed O2 and H2O, releasing sulfoxy species (e.g., S2O32-, SO42-) and ferrous iron (Fe2+) to the solution and also producing intermediate by-products, such as hydrogen peroxide (H2O2) and other reactive oxygen species (ROS), however, our understanding of the kinetics of these transient species is still limited. We investigated the kinetics of H2O2 formation in aqueous suspensions of FeS2 microparticles by monitoring, in real time, the H2O2 and dissolved O2 concentration under oxic and anoxic conditions using amperometric microsensors. Additional spectroscopic and structural analyses were done to track the dependencies between the process of FeS2 dissolution and the degradation of H2O2 through the Fenton reaction. Based on our experimental results, we built a kinetic model which explains the observed trend of H2O2, showing that FeS2 dissolution can act as a natural Fenton reagent, influencing the oxidation of third-party species during the long term evolution of geochemical systems, even in oxygen-limited environments.

  17. High-temperature sensitivity and its acclimation for photosynthetic electron reactions of desert succulents

    Energy Technology Data Exchange (ETDEWEB)

    Chetti, M.B.; Nobel, P.S. (Univ. of California, Los Angeles (USA))

    1987-08-01

    Photosynthetic electron reactions of succulent plants from hot deserts are able to tolerate extremely high temperatures and to acclimate to seasonal increase in temperature. In this study, we report the influence of relatively long, in vivo, high-temperature treatments on electron transport reactions for two desert succulents, Agave deserti and Opuntia ficus-indica, species which can tolerate 60{degree}C. Whole chain electron transport averaged 3{degree}C more sensitive to a 1-hour high-temperature treatment than did PSII (Photosystem II) which in turn averaged 3{degree}C more sensitive than did PSI. For plants maintained at day/night air temperatures of 30{degree}C/20{degree}C, treatment at 50{degree}C cause these reactions to be inhibited an average of 39% during the first hour, an additional 31% during the next 4 hours, and 100% by 12 hours. Upon shifting the plants from 30{degree}C/20{degree}C to 45{degree}C/35{degree}C, the high temperatures where activity was inhibited 50% increased 3{degree}C to 8{degree}C for the three electron transport reactions, the half-times for acclimation averaging 5 days for A. deserti and 4 days for O. ficus-indica. For the 45{degree}C/35{degree}C plants treated at 60{degree}C for 1 hour, PSI activity was reduced by 54% for A. deserti and 36% for O. ficus-indica. Acclimation leads to a toleration of very high temperatures without substantial disruption of electron transport for these desert succulents, facilitating their survival in hot deserts. Indeed, the electron transport reactions of these species tolerate longer periods at higher temperatures than any other vascular plants so far reported.

  18. Olefin metathesis reaction on GaN (0 0 0 1) surfaces

    Science.gov (United States)

    Makowski, Matthew S.; Zemlyanov, Dmitry Y.; Ivanisevic, Albena

    2011-03-01

    Proof-of-concept reactions were performed on GaN (0 0 0 1) surfaces to demonstrate surface termination with desired chemical groups using an olefin cross-metathesis reaction. To prepare the GaN surfaces for olefin metathesis, the surfaces were hydrogen terminated with hydrogen plasma, chlorine terminated with phosphorous pentachloride, and then terminated with an alkene group via a Grignard reaction. The olefin metathesis reaction then bound 7-bromo-1-heptene. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and water contact angle measurements following each step in the reaction scheme. The XPS data was used to qualitatively identify surface chemical species and to quantitatively determine molecular surface coverage. The bromine atom in 7-bromo-1-heptene served as a heteroatom for identification with XPS. The reaction scheme resulted in GaN substrates with a surface coverage of 0.10 monolayers and excellent stability towards oxidation when exposed to oxygen plasma.

  19. Reaction paths of alane dissociation on the Si(001) surface.

    Science.gov (United States)

    Smith, Richard; Bowler, David R

    2018-01-25

    Building on our earlier study, we examine the kinetic barriers to decomposition of alane, AlH3, on the Si(001) surface, using the nudged elastic band (NEB) approach within DFT. We find that the initial decomposition to AlH with two H atoms on the surface proceeds without a significant barrier. There are several pathways available to lose the final hydrogen, though these present barriers of up to 1 eV. Incorporation is more challenging, with the initial structures less stable in several cases than the starting structures, just as was found for phosphorus. We identify a stable route for Al incorporation following selective surface hydrogen desorption (e.g. by STM tip). The overall process parallels PH3, and indicates that atomically precise acceptor doping should be possible. © 2018 IOP Publishing Ltd.

  20. Atomic and electronic structure of surfaces theoretical foundations

    CERN Document Server

    Lannoo, Michel

    1991-01-01

    Surfaces and interfaces play an increasingly important role in today's solid state devices. In this book the reader is introduced, in a didactic manner, to the essential theoretical aspects of the atomic and electronic structure of surfaces and interfaces. The book does not pretend to give a complete overview of contemporary problems and methods. Instead, the authors strive to provide simple but qualitatively useful arguments that apply to a wide variety of cases. The emphasis of the book is on semiconductor surfaces and interfaces but it also includes a thorough treatment of transition metals, a general discussion of phonon dispersion curves, and examples of large computational calculations. The exercises accompanying every chapter will be of great benefit to the student.

  1. Surface spin-electron acoustic waves in magnetically ordered metals

    CERN Document Server

    Andreev, Pavel A

    2015-01-01

    Degenerate plasmas with motionless ions show existence of three surface waves: the Langmuir wave, the electromagnetic wave, and the zeroth sound. Applying the separated spin evolution quantum hydrodynamics to half-space plasma we demonstrate the existence of the surface spin-electron acoustic wave (SSEAW). We study dispersion of the SSEAW. We show that there is hybridization between the surface Langmuir wave and the SSEAW at rather small spin polarization. In the hybridization area the dispersion branches are located close to each other. In this area there is a strong interaction between these waves leading to the energy exchange. Consequently, generating the Langmuir waves with the frequencies close to hybridization area we can generate the SSEAWs. Thus, we report a method of creation of the SEAWs.

  2. Quantum non-equilibrium approach for fast electron transport in open systems: photosynthetic reaction centers

    CERN Document Server

    Pudlak, M; Nazmitdinov, R G; Pincak, R

    2011-01-01

    Creation of electron or exciton by external fields in a system with initially statistically independent unrelaxed vibrational modes leads to an initial condition term. The contribution of this term in the time convolution generalized master equation approach is studied in second order of the perturbation theory for electron-phonon coupling in the parth integral formalism. The developed approach, applied for analysis of dynamics in the photosynthetic reaction center, exhibits the key role of the initial condition term at the primary stage of electron transfer.

  3. Reactions on the surface and inside of neutron stars

    Directory of Open Access Journals (Sweden)

    Rehm K. E.

    2016-01-01

    Full Text Available Measurements from orbiting X-ray satellites during the last decades have provided us with a wealth of information about nuclear reactions thought to occur in the extreme, highdensity environment of neutron stars. With radioactive ion beams from first-generation facilities we have begun to study some of these processes in the laboratory. In this contribution I report on experiments performed with radioactive beams from the ATLAS accelerator at Argonne. I will discuss the nuclear physics of X-ray bursts and super-bursts, the production of in-flight radioactive beams, as well as novel detectors which are used in these experiments.

  4. Marcus Theory: Thermodynamics CAN Control the Kinetics of Electron Transfer Reactions

    Science.gov (United States)

    Silverstein, Todd P.

    2012-01-01

    Although it is generally true that thermodynamics do not influence kinetics, this is NOT the case for electron transfer reactions in solution. Marcus Theory explains why this is so, using straightforward physical chemical principles such as transition state theory, Arrhenius' Law, and the Franck-Condon Principle. Here the background and…

  5. On the nuclear $(n;t)-$reaction in the three-electron ${}^{6}$Li atom

    CERN Document Server

    Frolov, Alexei M

    2012-01-01

    The nuclear $(n;t)-$reaction of the three-electron ${}^{6}$Li atom with thermal/slow neutrons is considered. An effective method has been developed for determining the probabilities of formation of various atoms and ions in different bound states. We discuss a number of fundamental questions directly related to numerical computations of the final state atomic probabilities. A few appropriate variational expansions for atomic wave functions of the incident lithium atom and final helium atom and/or tritium negatively charged ion are discussed. It appears that the final ${}^4$He atom arising during the nuclear $(n,{}^{6}$Li; ${}^4$He$,t)$-reaction in the three-electron Li atom can also be created in its triplet states. The formation of the quasi-stable three-electron $e^{-}_3$ during the nuclear $(n; t)-$reaction at the Li atom is briefly discussed. Bremsstrahlung emitted by atomic electrons accelerated by the rapidly moving fragments from this reaction is analyzed. The frequency spectrum of the emitted radiatio...

  6. Exciplex mediated photoinduced electron transfer reactions of phthalocyanine-fullerene dyads

    NARCIS (Netherlands)

    Niemi, Marja; Tkachenko, Nikolai V.; Efimov, Alexander; Lehtivuori, Heli; Ohkubo, Kei; Fukuzumi, Shunichi; Lemmetyinen, Helge

    2008-01-01

    Evidences of an intramolecular exciplex intermediate in a photoinduced electron transfer (ET) reaction of double-linked free-base and zinc phthalocyanine-C-60 dyads were found. This was the first time for a dyad with phthalocyanine donor. Excitation of the phthalocyanine moiety of the dyads results

  7. Electron transfer reactions, cyanide and O2 binding of truncated hemoglobin from Bacillus subtilis

    DEFF Research Database (Denmark)

    Fernandez, Esther; Larsson, Jonas T.; McLean, Kirsty J.

    2013-01-01

    The truncated hemoglobin from Bacillus subtilis (trHb-Bs) possesses a surprisingly high affinity for oxygen and resistance to (auto)oxidation; its physiological role in the bacterium is not understood and may be connected with its very special redox and ligand binding reactions. Electron transfer...

  8. Catalytic reaction of cytokinin dehydrogenase : preference for quinones as electron acceptors

    NARCIS (Netherlands)

    Frébortová, Jitka; Fraaije, Marco W.; Galuszka, Petr; Šebela, Marek; Peč, Pavel; Hrbáč, Jan; Novák, Ondřej; Bilyeu, Kristin D.; English, James T.; Frébort, Ivo; Sebela, M.; Pec, P.; Hrbac, J.; Frebort, [No Value

    2004-01-01

    The catalytic reaction of cytokinin oxidase/dehydrogenase (EC 1.5.99.12) was studied in detail using the recombinant flavoenzyme from maize. Determination of the redox potential of the covalently linked flavin cofactor revealed a relatively high potential dictating the type of electron acceptor that

  9. Modifying surface resistivity and liquid moisture management property of keratin fibers through thiol-ene click reactions.

    Science.gov (United States)

    Yu, Dan; Cai, Jackie Y; Church, Jeffrey S; Wang, Lijing

    2014-01-22

    This paper reports on a new method for improving the antistatic and liquid moisture management properties of keratinous materials. The method involves the generation of thiols by controlled reduction of cystine disulfide bonds in keratin with tris(2-carboxyethyl) phosphine hydrochloride and subsequent grafting of hydrophilic groups onto the reduced keratin by reaction with an acrylate sulfonate or acrylamide sulfonate through thiol-ene click chemistry. The modified substrates were characterized with Raman spectroscopy and scanning electron microscopy and evaluated for their performance changes in liquid moisture management, surface resistivity, and wet burst strength. The results have revealed that the thiol-acrylate reaction is more efficient than the thiol-acrylamide reaction, and the keratinous substrate modified with an acrylate sulfonate salt exhibits significantly improved antistatic and liquid moisture management properties.

  10. Electronic properties of semiconductor surfaces and metal/semiconductor interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Tallarida, M.

    2005-05-15

    This thesis reports investigations of the electronic properties of a semiconductor surface (silicon carbide), a reactive metal/semiconductor interface (manganese/silicon) and a non-reactive metal/semiconductor interface (aluminum-magnesium alloy/silicon). The (2 x 1) reconstruction of the 6H-SiC(0001) surface has been obtained by cleaving the sample along the (0001) direction. This reconstruction has not been observed up to now for this compound, and has been compared with those of similar elemental semiconductors of the fourth group of the periodic table. This comparison has been carried out by making use of photoemission spectroscopy, analyzing the core level shifts of both Si 2p and C 1s core levels in terms of charge transfer between atoms of both elements and in different chemical environments. From this comparison, a difference between the reconstruction on the Si-terminated and the C-terminated surface was established, due to the ionic nature of the Si-C bond. The growth of manganese films on Si(111) in the 1-5 ML thickness range has been studied by means of LEED, STM and photoemission spectroscopy. By the complementary use of these surface science techniques, two different phases have been observed for two thickness regimes (<1 ML and >1 ML), which exhibit a different electronic character. The two reconstructions, the (1 x 1)-phase and the ({radical}3 x {radical}3)R30 -phase, are due to silicide formation, as observed in core level spectroscopy. The growth proceeds via island formation in the monolayer regime, while the thicker films show flat layers interrupted by deep holes. On the basis of STM investigations, this growth mode has been attributed to strain due to lattice mismatch between the substrate and the silicide. Co-deposition of Al and Mg onto a Si(111) substrate at low temperature (100K) resulted in the formation of thin alloy films. By varying the relative content of both elements, the thin films exhibited different electronic properties

  11. Control of chemical reactions with electron beams; Kontrolle chemischer Reaktionen mit Elektronenstrahlung

    Energy Technology Data Exchange (ETDEWEB)

    Boehler, Esther

    2014-03-18

    Interaction between low-energy electrons and molecules can lead to dissociative electron attachment (DEA) or dissociative ionization (DI). In condensed matter, the resulting reactive fragments can attack adjacent molecules to yield larger products. In this thesis, reactions initiated by DEA to acetonitrile in condensed phase have been compared to the known gas phase fragmentation channels. Also, gas phase DEA experiments have been performed on chlorosilanes to study the effect of a variation of the organic ligands on the energy of their molecular orbitals and reactivity in DEA processes. Furthermore, hydroamination reactions induced by DI for different alkenes and amines have been investigated. A similar reaction of ammonia and carbon monoxide was shown to produce formamide (HCONH2), which is the smallest molecule to contain a peptide bond and thus represents an important building block of biologically relevant substances.

  12. Reaction dynamics of small molecules at metal surfaces

    CERN Document Server

    Samson, P A

    1999-01-01

    directed angular distributions suggest the influence of a trapping mechanism, recombining molecules scattering through a molecularly adsorbed state, with a transition state of large d sub N sub N responsible for the product vibrational excitation. Although N sub 2 dissociation on Fe(100) forms a simple overlayer structure, on Fe(110), molecular chemisorption does not occur at or above room temperature and the sticking is extremely small (approx 10 sup - sup 6 to 10 sup - sup 7). Activated nitrogen bombardment can be used to prepare a 'surface nitride' with a structure related to the geometry of bulk Fe sub 4 N. Scanning tunnelling microscopy yields atomic scale features that cannot be explained by simple overlayers. It is proposed that the uppermost iron layer reconstructs to generate quasi-octahedral sites between the top two layers, with sub-surface nitrogen in these sites forming a model for the 'surface nitride' structure. The dissociation-desorption dynamics of D sub 2 upon the Sn/Pt(111) surface alloy a...

  13. Surface reactivity and layer analysis of chemisorbed reaction films in ...

    Indian Academy of Sciences (India)

    Administrator

    MS received 15 October 2008; revised 13 March 2009 ... behaviour during thermal decomposition in the temperature range of 50–800°C when thermally evaluated .... Smith. 38 has recently reviewed the surface analytical science for understanding the structure and composition of anti-wear films formed in tribo- contacts.

  14. Numerical Implementation of Surface Catalysis, Reaction, and Sublimation

    Science.gov (United States)

    2007-07-01

    surface kinetics. In a futuristic mission, one can conceive entry flights into Saturn, Uranus , or Neptune. In such entries, radiative heating will be much...Paper 2002-0909. [22] Park, C. (2005). Overview of Radiation Problems in Planetary Entries. Proceedings of the Intern- ational Workshop on Radiation of

  15. Performing chemical reactions in virtual capillary of surface tension ...

    Indian Academy of Sciences (India)

    poly(dimethyl siloxane) elastomers [11,12]. On the other hand, 2D microchannels are generally designed by chemically altering selective regions of a substrate surface. [13]. The fluid flow is induced and controlled in 3D microfluidic channels by several processes like pumping, electro osmosis, capillarity etc., while that in 2D ...

  16. The exothermic reaction route of a self-heatable conductive ink for rapid processable printed electronics.

    Science.gov (United States)

    Shin, Dong-Youn; Han, Jin Wook; Chun, Sangki

    2014-01-07

    We report the exothermic reaction route and new capability of a self-heatable conductive ink (Ag2O and silver 2,2-dimethyloctanoate) in order to achieve both a low sintering temperature and electrical resistivity within a short sintering time for flexible printed electronics and display appliances. Unlike conventional conductive ink, which requires a costly external heating instrument for rapid sintering, self-heatable conductive ink by itself is capable of generating heat as high as 312 °C when its exothermic reaction is triggered at a temperature of 180 °C. This intensive exothermic reaction is found to result from the recursive reaction of the 2,2-dimethyloctanoate anion, which is thermally dissociated from silver 2,2-dimethyloctanoate, with silver oxide microparticles. Through this recursive reaction, a massive number of silver atoms are supplied from silver oxide microparticles, and the nucleation of silver atoms and the fusion of silver nanoparticles become the major source of heat. This exothermic reaction eventually realizes the electrical resistivity of self-heatable conductive ink as low as 27.5 μΩ cm within just 40 s by combining chemical annealing, which makes it suitable for the roll-to-roll printable electronics such as a flexible touch screen panel.

  17. Presolvated Electron Reactions with Methyl Acetoacetate: Electron Localization, Proton-Deuteron Exchange, and H-Atom Abstraction

    Directory of Open Access Journals (Sweden)

    Alex Petrovici

    2014-09-01

    Full Text Available Radiation-produced electrons initiate various reaction processes that are important to radiation damage to biomolecules. In this work, the site of attachment of the prehydrated electrons with methyl acetoacetate (MAA, CH3-CO-CH2-COOCH3 at 77 K and subsequent reactions of the anion radical (CH3-CO•−-CH2-COOCH3 in the 77 to ca. 170 K temperature range have been investigated in homogeneous H2O and D2O aqueous glasses by electron spin resonance (ESR spectroscopy. At 77 K, the prehydrated electron attaches to MAA forming the anion radical in which the electron is delocalized over the two carbonyl groups. This species readily protonates to produce the protonated electron adduct radical CH3-C(•OH-CH2-COOCH3. The ESR spectrum of CH3-C(•OH-CH2-COOCH3 in H2O shows line components due to proton hyperfine couplings of the methyl and methylene groups. Whereas, the ESR spectrum of CH3-C(•OH-CH2-COOCH3 in D2O glass shows only the line components due to proton hyperfine couplings of CH3 group. This is expected since the methylene protons in MAA are readily exchangeable in D2O. On stepwise annealing to higher temperatures (ca. 150 to 170 K, CH3-C(•OH-CH2-COOCH3 undergoes bimolecular H-atom abstraction from MAA to form the more stable radical, CH3-CO-CH•-COOCH3. Theoretical calculations using density functional theory (DFT support the radical assignments.

  18. How fast is the reaction of hydrated electrons with graphene oxide in aqueous dispersions?

    Science.gov (United States)

    Kahnt, Axel; Flyunt, Roman; Laube, Christian; Knolle, Wolfgang; Eigler, Siegfried; Hermann, Ralf; Naumov, Sergej; Abel, Bernd

    2015-11-01

    Understanding the mechanism of the reduction of graphene oxide (GO) is a key-question in graphene related materials science. Here, we investigate the kinetics of the reaction of radiolytically generated hydrated electrons with GO in water. The electron transfer proceeds on the ns time scale and not on the ps time scale, as recently reported by Gengler et al. (Nat. Commun., 2013, 4, 2560).Understanding the mechanism of the reduction of graphene oxide (GO) is a key-question in graphene related materials science. Here, we investigate the kinetics of the reaction of radiolytically generated hydrated electrons with GO in water. The electron transfer proceeds on the ns time scale and not on the ps time scale, as recently reported by Gengler et al. (Nat. Commun., 2013, 4, 2560). Electronic supplementary information (ESI) available: Absorption spectrum of GO, pulse radiolysis and laser photolysis transient absorption spectra, kinetic simulation, frontier molecular orbitals, and possible reaction pathways induced by photoexcitation. See DOI: 10.1039/c5nr03444b

  19. Biomimetic surface modification of polypropylene by surface chain transfer reaction based on mussel-inspired adhesion technology and thiol chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Niu, Zhijun; Zhao, Yang; Sun, Wei; Shi, Suqing, E-mail: shisq@nwu.edu.cn; Gong, Yongkuan

    2016-11-15

    Highlights: • Biomimetic surface modification of PP was successfully conducted by integrating mussel-inspired technology, thiol chemistry and cell outer membranes-like structures. • The resultant biomimetic surface exhibits good interface and surface stability. • The obvious suppression of protein adsorption and platelet adhesion is also achieved. • The residue thoil groups on the surface could be further functionalized. - Abstract: Biomimetic surface modification of polypropylene (PP) is conducted by surface chain transfer reaction based on the mussel-inspired versatile adhesion technology and thiol chemistry, using 2-methacryloyloxyethylphosphorylcholine (MPC) as a hydrophilic monomer mimicking the cell outer membrane structure and 2,2-azobisisobutyronitrile (AIBN) as initiator in ethanol. A layer of polydopamine (PDA) is firstly deposited onto PP surface, which not only offers good interfacial adhesion with PP, but also supplies secondary reaction sites (-NH{sub 2}) to covalently anchor thiol groups onto PP surface. Then the radical chain transfer to surface-bonded thiol groups and surface re-initiated polymerization of MPC lead to the formation of a thin layer of polymer brush (PMPC) with cell outer membrane mimetic structure on PP surface. X-ray photoelectron spectrophotometer (XPS), atomic force microscopy (AFM) and water contact angle measurements are used to characterize the PP surfaces before and after modification. The protein adsorption and platelet adhesion experiments are also employed to evaluate the interactions of PP surface with biomolecules. The results show that PMPC is successfully grafted onto PP surface. In comparison with bare PP, the resultant PP-PMPC surface exhibits greatly improved protein and platelet resistance performance, which is the contribution of both increased surface hydrophilicity and zwitterionic structure. More importantly, the residue thiol groups on PP-PMPC surface create a new pathway to further functionalize such

  20. Hydrogen collisions with transition metal surfaces: Universal electronically nonadiabatic adsorption

    Science.gov (United States)

    Dorenkamp, Yvonne; Jiang, Hongyan; Köckert, Hansjochen; Hertl, Nils; Kammler, Marvin; Janke, Svenja M.; Kandratsenka, Alexander; Wodtke, Alec M.; Bünermann, Oliver

    2018-01-01

    Inelastic scattering of H and D atoms from the (111) surfaces of six fcc transition metals (Au, Pt, Ag, Pd, Cu, and Ni) was investigated, and in each case, excitation of electron-hole pairs dominates the inelasticity. The results are very similar for all six metals. Differences in the average kinetic energy losses between metals can mainly be attributed to different efficiencies in the coupling to phonons due to the different masses of the metal atoms. The experimental observations can be reproduced by molecular dynamics simulations based on full-dimensional potential energy surfaces and including electronic excitations by using electronic friction in the local density friction approximation. The determining factors for the energy loss are the electron density at the surface, which is similar for all six metals, and the mass ratio between the impinging atoms and the surface atoms. Details of the electronic structure of the metal do not play a significant role. The experimentally validated simulations are used to explore sticking over a wide range of incidence conditions. We find that the sticking probability increases for H and D collisions near normal incidence—consistent with a previously reported penetration-resurfacing mechanism. The sticking probability for H or D on any of these metals may be represented as a simple function of the incidence energy, Ein, metal atom mass, M, and incidence angle, 𝜗i n. S =(S0+a ṡEi n+b ṡM ) *(1 -h (𝜗i n-c ) (1 -cos(𝜗 i n-c ) d ṡh (Ei n-e ) (Ei n-e ) ) ) , where h is the Heaviside step function and for H, S0 = 1.081, a = -0.125 eV-1, b =-8.40 ṡ1 0-4 u-1, c = 28.88°, d = 1.166 eV-1, and e = 0.442 eV; whereas for D, S0 = 1.120, a = -0.124 eV-1, b =-1.20 ṡ1 0-3 u-1, c = 28.62°, d = 1.196 eV-1, and e = 0.474 eV.

  1. Fundamental Studies of Diamond Growth and Surface Reactions

    Science.gov (United States)

    1994-07-01

    the material. In the diamond gem industry, mechanical polishing procedures have been developed to obtain an optical quality finish on small-scale...with unpolished samples. The methodology for the technique is described in two journal articlesl6. 17. I 6.0 Characterization of Spectroscopic...sample. Thedegree of improvement in surface roughness in the diamond films can be seen in the Dektak profiles in Fig. 6. The unpolished film had a

  2. Solventless migratory-insertion reactions of substituted cyclopentadienyl iron complexes induced by electron donor ligands

    Directory of Open Access Journals (Sweden)

    Apollinaire Munyaneza

    2009-12-01

    Full Text Available Reaction between solid (C5H5Fe(CO 2CH3 and a range of solid phosphine ligands, L (L = PPh3, P(m-CH3C6H43, P(p-CH3C6H43, P(p-FC6H43, P(p-ClC6H43, PCy3 occurred in the absence of solvent in the melt phase to give the migratory-insertion products, (C5H5Fe(CO(COCH3(L. The reaction was more rapid with small electron withdrawing ligands. Insertion reaction between (RC5H4Fe(CO 2 R’ (R = H, CH3; R’ = CH3, CH2Ph and gaseous ligands such as SO2 and CO were also studied. The insertion of SO2 occurred readily for all the substrates investigated, but CO insertion did not occur (< 1 % using the solventless reaction condition.

  3. Adsorption and desorption of hydrogen at nonpolar GaN (1 1 ¯ 00 ) surfaces: Kinetics and impact on surface vibrational and electronic properties

    Science.gov (United States)

    Lymperakis, L.; Neugebauer, J.; Himmerlich, M.; Krischok, S.; Rink, M.; Kröger, J.; Polyakov, V. M.

    2017-05-01

    The adsorption of hydrogen at nonpolar GaN (1 1 ¯00 ) surfaces and its impact on the electronic and vibrational properties is investigated using surface electron spectroscopy in combination with density functional theory (DFT) calculations. For the surface mediated dissociation of H2 and the subsequent adsorption of H, an energy barrier of 0.55 eV has to be overcome. The calculated kinetic surface phase diagram indicates that the reaction is kinetically hindered at low pressures and low temperatures. At higher temperatures ab initio thermodynamics show, that the H-free surface is energetically favored. To validate these theoretical predictions experiments at room temperature and under ultrahigh vacuum conditions were performed. They reveal that molecular hydrogen does not dissociatively adsorb at the GaN (1 1 ¯00 ) surface. Only activated atomic hydrogen atoms attach to the surface. At temperatures above 820 K, the attached hydrogen gets desorbed. The adsorbed hydrogen atoms saturate the dangling bonds of the gallium and nitrogen surface atoms and result in an inversion of the Ga-N surface dimer buckling. The signatures of the Ga-H and N-H vibrational modes on the H-covered surface have experimentally been identified and are in good agreement with the DFT calculations of the surface phonon modes. Both theory and experiment show that H adsorption results in a removal of occupied and unoccupied intragap electron states of the clean GaN (1 1 ¯00 ) surface and a reduction of the surface upward band bending by 0.4 eV. The latter mechanism largely reduces surface electron depletion.

  4. Surface-mount electronics meet the military's high reliability needs

    Science.gov (United States)

    Reynolds, R. A.

    1985-08-01

    Surface-mount electronics, as opposed to through-hole mounted electronics, will be dominant board assembly technique in the U.S. for at least the next ten years for weight and space saving and for high reliability. New pin-out and packaging standards have been developed, to the benefit of both military and industrial and commercial users. Reliability rather than standards is, however, the major issue, and design, material selection and manufacturing techniques at the board-component interface determine how well any producer's equipment stands up to demanding applications and environments. Problems of matching thermal coefficients of expansion are dwindling as new chip technologies reduce semiconductor power dissipation drastically. The special soldering methods needed, preparation of the circuit board, and the increasingly widespread use of metal-core circuit boards are treated.

  5. Nanoscale electron transport at the surface of a topological insulator

    Science.gov (United States)

    Bauer, Sebastian; Bobisch, Christian A.

    2016-01-01

    The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role. PMID:27098939

  6. Electronic structure of benzene adsorbed on Ni and Cu surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Weinelt, M.; Nilsson, A.; Wassdahl, N. [Uppsala Univ. (Sweden)] [and others

    1997-04-01

    Benzene has for a long time served as a prototype adsorption system of large molecules. It adsorbs with the molecular plane parallel to the surface. The bonding of benzene to a transition metal is typically viewed to involve the {pi} system. Benzene adsorbs weakly on Cu and strongly on Ni. It is interesting to study how the adsorption strength is reflected in the electronic structure of the adsorbate-substrate complex. The authors have used X-ray Emission (XE) and X-ray Absorption (XA) spectroscopies to selectively study the electronic states localized on the adsorbed benzene molecule. Using XES the occupied states can be studies and with XAS the unoccupied states. The authors have used beamline 8.0 and the Swedish endstation equipped with a grazing incidence x-ray spectrometer and a partial yield absorption detector. The resolution in the XES and XAS were 0.5 eV and 0.05 eV, respectively.

  7. One-pot reaction for the preparation of biofunctionalized self-assembled monolayers on gold surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Raigoza, Annette F.; Fies, Whitney; Lim, Amber; Onyirioha, Kristeen; Webb, Lauren J., E-mail: lwebb@cm.utexas.edu

    2017-02-01

    Highlights: • One-pot synthesis of α-helical-terminated self-assembled monolayers on Au(111). • Synthesis of high density, structured, and covalently bound α-helices on Au(111). • Characterization by surface-averaged and single molecule techniques. • Peptide-terminated surfaces for fabrication of biomaterials and sensors. - Abstract: The Huisgen cycloaddition reaction (“click” chemistry) has been used extensively to functionalize surfaces with macromolecules in a straightforward manner. We have previously developed a procedure using the copper(I)-catalyzed click reaction to tether synthetic α-helical peptides carrying two alkyne groups to a well-ordered azide-terminated alkanethiol self-assembled monolayer (SAM) on a Au(111) surface. While convenient, click-based strategies potentially pose significant problems from reagents, solvents, and reaction temperatures that may irreversibly damage some molecules or substrates. Tuning click chemistry conditions would allow individual optimization of reaction conditions for a wide variety of biomolecules and substrate materials. Here, we explore the utility of simultaneous SAM formation and peptide-attachment chemistry in a one-pot reaction. We demonstrate that a formerly multistep reaction can be successfully carried out concurrently by mixing azide-terminated alkanethiols, CuCl, and a propargylglycine-containing peptide over a bare gold surface in ethanol and reacting at 70 °C. X-ray photoelectron spectroscopy (XPS), surface infrared spectroscopy, surface circular dichroic (CD) spectroscopy, and scanning tunneling microscopy (STM) were used to determine that this one-pot reaction strategy resulted in a high density of surface-bound α-helices without aggregation. This work demonstrates the simplicity and versatility of a SAM-plus-click chemistry strategy for functionalizing Au surfaces with structured biomolecules.

  8. Reactions of water and C1 molecules on carbide and metal-modified carbide surfaces.

    Science.gov (United States)

    Wan, Weiming; Tackett, Brian M; Chen, Jingguang G

    2017-04-03

    The formation of carbides can significantly modify the physical and chemical properties of the parent metals. In the current review, we summarize the general trends in the reactions of water and C1 molecules over transition metal carbide (TMC) and metal-modified TMC surfaces and thin films. Although the primary focus of the current review is on the theoretical and experimental studies of reactions of C1 molecules (CO, CO2, CH3OH, etc.), the reactions of water will also be reviewed because water plays an important role in many of the C1 transformation reactions. This review is organized by discussing separately thermal reactions and electrochemical reactions, which provides insights into the application of TMCs in heterogeneous catalysis and electrocatalysis, respectively. In thermal reactions, we discuss the thermal decomposition of water and methanol, as well as the reactions of CO and CO2 over TMC surfaces. In electrochemical reactions, we summarize recent studies in the hydrogen evolution reaction, electrooxidation of methanol and CO, and electroreduction of CO2. Finally, future research opportunities and challenges associated with using TMCs as catalysts and electrocatalysts are also discussed.

  9. Reaction rates of ozone and terpenes adsorbed to model indoor surfaces.

    Science.gov (United States)

    Springs, M; Wells, J R; Morrison, G C

    2011-08-01

    Reaction rates and reaction probabilities have been quantified on model indoor surfaces for the reaction of ozone with two monoterpenes (Δ(3) -carene and d-limonene). Molar surface loadings were obtained by performing breakthrough experiments in a plug-flow reactor (PFR) packed with beads of glass, polyvinylchloride or zirconium silicate. Reaction rates and probabilities were determined by equilibrating the PFR with both the terpene and the ozone and measuring the ozone consumption rate. To mimic typical indoor conditions, temperatures of 20, 25, and 30°C were used in both types of experiments along with a relative humidity ranging from 10% to 80%. The molar surface loading decreased with increased relative humidity, especially on glass, suggesting that water competed with the terpenes for adsorption sites. The ozone reactivity experiments indicate that higher surface loadings correspond with higher ozone uptake. The reaction probability for Δ(3) -carene with ozone ranged from 2.9 × 10(-6) to 3.0 × 10(-5) while reaction probabilities for d-limonene ranged from 2.8 × 10(-5) to 3.0 × 10(-4) . These surface reaction probabilities are roughly 10-100 times greater than the corresponding gas-phase values. Extrapolation of these results to typical indoor conditions suggests that surface conversion rates may be substantial relative to gas-phase rates, especially for lower volatility terpenoids. At present, it is unclear how important heterogeneous reactions will be in influencing indoor concentrations of terpenes, ozone and their reaction products. We observe that surface reaction probabilities were 10 to 100 times greater than their corresponding gas-phase values. Thus indoor surfaces do enhance effective reaction rates and adsorption of terpenes will increase ozone flux to otherwise low-reactivity surfaces. Extrapolation of these results to typical indoor conditions suggests that surface conversion rates may be substantial relative to gas-phase rates, especially

  10. Process of forming catalytic surfaces for wet oxidation reactions

    Science.gov (United States)

    Jagow, R. B. (Inventor)

    1977-01-01

    A wet oxidation process was developed for oxidizing waste materials, comprising dissolved ruthenium salt in a reactant feed stream containing the waste materials. The feed stream is introduced into a reactor, and the reactor contents are then raised to an elevated temperature to effect deposition of a catalytic surface of ruthenium black on the interior walls of the reactor. The feed stream is then maintained in the reactor for a period of time sufficient to effect at least partial oxidation of the waste materials.

  11. Electron recombination in ionized liquid argon: a computational approach based on realistic models of electron transport and reactions.

    Science.gov (United States)

    Jaskolski, Michal; Wojcik, Mariusz

    2011-05-05

    In this work, we propose a new theoretical approach to modeling the electron-ion recombination processes in ionization tracks in liquid argon at 87 K. We developed a computer simulation method using realistic models of charge transport and electron-ion reactions. By introducing the concept of one-dimensional periodicity in the track, we are able to model very large cylindrical structures of charged particles. We apply our simulation method to calculate the electron escape probability as a function of the initial ionization density in the track. The results are in quantitative agreement with experiment for radiation tracks of relatively high ionization density. At low ionization densities, the simulation results slightly overestimate the experimental data. We discuss possible reasons for this disagreement and conclude that it can be explained by the role of δ tracks (short tracks of secondary electrons) in electron-ion recombination processes. We introduce an approximate model that takes into account the presence of δ tracks and allows the experimental data obtained from a liquid-argon ionization detector to be reproduced over a wide range of ionization density.

  12. The reaction dynamics of alkali dimer molecules and electronically excited alkali atoms with simple molecules

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Hongtao [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1995-12-01

    This dissertation presents the results from the crossed molecular beam studies on the dynamics of bimolecular collisions in the gas phase. The primary subjects include the interactions of alkali dimer molecules with simple molecules, and the inelastic scattering of electronically excited alkali atoms with O2. The reaction of the sodium dimers with oxygen molecules is described in Chapter 2. Two reaction pathways were observed for this four-center molecule-molecule reaction, i.e. the formations of NaO2 + Na and NaO + NaO. NaO2 products exhibit a very anisotropic angular distribution, indicating a direct spectator stripping mechanism for this reaction channel. The NaO formation follows the bond breaking of O2, which is likely a result of a charge transfer from Na2 to the excited state orbital of O2-. The scattering of sodium dimers from ammonium and methanol produced novel molecules, NaNH3 and Na(CH3OH), respectively. These experimental observations, as well as the discussions on the reaction dynamics and the chemical bonding within these molecules, will be presented in Chapter 3. The lower limits for the bond dissociation energies of these molecules are also obtained. Finally, Chapter 4 describes the energy transfer between oxygen molecules and electronically excited sodium atoms.

  13. Surface electronic excitations and dynamic spectral properties of adsorbates

    Science.gov (United States)

    Gumhalter, B.

    Many-body aspects of screening and relaxation mechanisms encountered in spectroscopic studies of the electronic structure of adsorbates have recently attracted considerable attention from both experimental and theoretical physicists. Interest in these phenomena has also been augmented by the rapid improvement of experimental techniques which have enabled better resolution and analysis of various subtile components of the adsorbate spectra. Many of these spectral features have until recently been ascribed to purely chemical and initial state effects. One of the first major advances of the theoretical development in this field was to seek and attribute the origin of these structures to the many-body properties of adsorption systems and, secondly, to predict how the many-body effects would manifest themselves in surface spectroscopies. We start with a rather detailed description of the formalism of the surface electronic response and discuss the properties of the surface excitation spectrum of idealized and real metals. This formalism is then successively applied to set up a model of screening firstly in the nonbonding levels of mainly physisorbed adsorbates and later in the core and valence levels of chemisorbed species. Various modifications of the model enable a dynamic description of the final state relaxation and shake-up effects typical of spectroscopic measurements. To treat the particularly complicated problem of dynamic relaxation in the adsorbate valence levels a special perturbational approach based on Mayer's cluster expansion is developed in §5. The characteristics, and some limitations of this approach, which may also prove useful in other physical problems, are described in detail and discussed within the context of the interaction of localized adsorbate charge fluctuations with bosonic surface excitations. Experimental support for the presented theoretical framework and its applications has been very important. A qualitative comparison with the

  14. Pulsed laser-assisted focused electron-beam-induced etching of titanium with XeF2: enhanced reaction rate and precursor transport.

    Science.gov (United States)

    Noh, J H; Fowlkes, J D; Timilsina, R; Stanford, M G; Lewis, B B; Rack, P D

    2015-02-25

    In order to enhance the etch rate of electron-beam-induced etching, we introduce a laser-assisted focused electron-beam-induced etching (LA-FEBIE) process which is a versatile, direct write nanofabrication method that allows nanoscale patterning and editing. The results demonstrate that the titanium electron stimulated etch rate via the XeF2 precursor can be enhanced up to a factor of 6 times with an intermittent pulsed laser assist. The evolution of the etching process is correlated to in situ stage current measurements and scanning electron micrographs as a function of time. The increased etch rate is attributed to photothermally enhanced Ti-F reaction and TiF4 desorption and in some regimes enhanced XeF2 surface diffusion to the reaction zone.

  15. Production of specific structured lipids by enzymatic interesterification: optimization of the reaction by response surface design

    DEFF Research Database (Denmark)

    Xu, Xuebing; Skands, Anja Rebecca Havegaard; Adler-Nissen, Jens

    1998-01-01

    (DAGs). A five-factor response surface design was used to evaluate the influences of five major factors and their relationships. The five factors were water content (Wc, wt% based on enzyme used), reaction temperature (Te,°C), enzyme load (El, wt% based on substrates), reaction time (Tr, hour....... Thus we conclude that the quadratic response models adequately expressed the reaction. Based on the models, the reaction was optimized for the maximum net incorporation and minimum DAG content. The reaction and the control of water content or water activity (Aw) was also discussed.......Rapeseed oil and capric acid were interesterified in solvent-free media catalyzed by Lipozyme IM (Rhizomucor miehei) to produce specific-structured lipids (SSLs). The process was optimized by response surface design concerning the effects of acyl migration and the by-products of diacylglycerols...

  16. Prediction of Tetraoxygen Reaction Mechanism with Sulfur Atom on the Singlet Potential Energy Surface

    Directory of Open Access Journals (Sweden)

    Ashraf Khademzadeh

    2014-01-01

    Full Text Available The mechanism of S+O4 (D2h reaction has been investigated at the B3LYP/6-311+G(3df and CCSD levels on the singlet potential energy surface. One stable complex has been found for the S+O4 (D2h reaction, IN1, on the singlet potential energy surface. For the title reaction, we obtained four kinds of products at the B3LYP level, which have enough thermodynamic stability. The results reveal that the product P3 is spontaneous and exothermic with −188.042 and −179.147 kcal/mol in Gibbs free energy and enthalpy of reaction, respectively. Because P1 adduct is produced after passing two low energy level transition states, kinetically, it is the most favorable adduct in the 1S+1O4 (D2h atmospheric reactions.

  17. Analysis of the non-Markovianity for electron transfer reactions in an oligothiophene-fullerene heterojunction

    Science.gov (United States)

    Mangaud, E.; Meier, C.; Desouter-Lecomte, M.

    2017-09-01

    The non-Markovianity of the electron transfer in an oligothiophene-fullerene heterojunction described by a spin-boson model is analyzed using the time dependent decoherence canonical rates and the volume of accessible states in the Bloch sphere. The dynamical map of the reduced electronic system is computed by the hierarchical equations of motion methodology (HEOM) providing an exact dynamics. Transitory witness of non-Markovianity is linked to the bath dynamics analyzed from the HEOM auxiliary matrices. The signature of the collective bath mode detected from HEOM in each electronic state is compared with predictions of the effective mode extracted from the spectral density. We show that including this main reaction coordinate in a one-dimensional vibronic system coupled to a residual bath satisfactorily describes the electron transfer by a simple Markovian Redfield equation. Non-Markovianity is computed for three inter fragment distances and compared with a priori criterion based on the system and bath characteristic timescales.

  18. Electrons in strong electromagnetic fields: spin effects and radiation reaction (Conference Presentation)

    Science.gov (United States)

    Bauke, Heiko; Wen, Meng; Keitel, Christoph H.

    2017-05-01

    Various different classical models of electrons including their spin degree of freedom are commonly applied to describe the coupled dynamics of relativistic electron motion and spin precession in strong electromagnetic fields. The spin dynamics is usually governed by the Thomas-Bargmann-Michel-Telegdi equation [1, 2] in these models, while the electron's orbital motion follows the (modified) Lorentz force and a spin-dependent Stern-Gerlach force. Various classical models can lead to different or even contradicting predictions how the spin degree of freedom modifies the electron's orbital motion when the electron moves in strong electromagnetic fields. This discrepancy is rooted in the model-specific energy dependency of the spin induced relativistic Stern-Gerlach force acting on the electron. The Frenkel model [3, 4] and the classical Foldy-Wouthuysen model 5 are compared exemplarily against each other and against the quantum mechanical Dirac equation in order to identify parameter regimes where these classical models make different predictions [6, 7]. Our theoretical results allow for experimental tests of these models. In the setup of the longitudinal Stern-Gerlach effect, the Frenkel model and classical Foldy-Wouthuysen model lead in the relativistic limit to qualitatively different spin effects on the electron trajectory. Furthermore, it is demonstrated that in tightly focused beams in the near infrared the effect of the Stern-Gerlach force of the Frenkel model becomes sufficiently large to be potentially detectable in an experiment. Among the classical spin models, the Frenkel model is certainly prominent for its long history and its wide application. Our results, however, suggest that the classical Foldy-Wouthuysen model is superior as it is qualitatively in better agreement with the quantum mechanical Dirac equation. In ultra strong laser setups at parameter regimes where effects of the Stern-Gerlach force become relevant also radiation reaction effects are

  19. Reactions of 1-Hydroxy-1-methylethyl Radicals with NO2-: Time-Resolved Electron Spin Resonance

    Energy Technology Data Exchange (ETDEWEB)

    Filipiak, Piotr; Camaioni, Donald M.; Fessenden, Richard W.; Carmichael, Ian; Hug, Gordon L.

    2006-09-11

    The reaction of the ?-hydroxyalkyl radical of 2-propanol (1-hydroxy-1-methylethyl radical) with nitrite ions was characterized. A product of the reaction was assigned as the adduct nitro radical anion, [HO-C(CH3)2NO2]??. This radical was identified using time-resolved electron spin resonance (TRESR). The radical?s magnetic parameters, the nitrogen hyperfine coupling constant aN of 26.39 G and its g-factor of 2.0052, are the same as those of the nitro radical anion previously discovered in ?OH spin-trapping experiments with the aci-anion of (CH3)2CHNO2. The rate constant for the decay of the ESR kinetic trace of (CH3)2C?-OH is of the same order of magnitude as the rate constant for the growth of the ESR kinetic trace of [HO-C(CH3)2NO2]??, further confirming the nature of the reaction. The bimolecular rate constant for the reaction at pH 7 is {approx}1.7 ? 106 M?1 s?1 measured by following ESR kinetic traces of (CH3)2C?-OH and 2.4 ? 106 M?1 s?1 following the growth of [HO-C(CH3)2NO2]??. The lack of better match in these two measurements is discussed. The yield of [HO-C(CH3)2NO2]?? was measured to be {approx}27% of the reaction of (CH3)2C?-OH with nitrite. Pulse radiolysis-conductivity experiments at lower pH (4.7) also show that electron transfer or the equivalent formation of [HO-C(CH3)2ONO]?? followed by rapid loss of ?NO represent only part of the reaction. These reactions are discussed with guidance by computations using density functional theory.

  20. Ab initio molecular dynamics calculations on reactions of molecules with metal surfaces

    NARCIS (Netherlands)

    Nattino, Francesco

    2015-01-01

    Reactions on metal surfaces are of scientific interest due to the tremendous relevance of heterogeneous catalysis. Single crystal surfaces under controlled physical conditions are generally employed as a model for the real catalysts, with the aim of improving the fundamental understanding of the

  1. The secondary electron yield of noble metal surfaces

    Directory of Open Access Journals (Sweden)

    L. A. Gonzalez

    2017-11-01

    Full Text Available Secondary electron yield (SEY curves in the 0-1000 eV range were measured on polycrystalline Ag, Au and Cu samples. The metals were examined as introduced in the ultra-high vacuum chamber and after having been cleaned by Ar+ ion sputtering. The comparison between the curves measured on the clean samples and in the presence of contaminants, due to the permanence in atmosphere, confirmed that the SEY behavior is strongly influenced by the chemical state of the metal surface. We show that when using very slow primary electrons the sample work function can be determined with high accuracy from the SEY curves. Moreover we prove that SEY is highly sensitive to the presence of adsorbates even at submonolayer coverage. Results showing the effect of small quantities of CO adsorbed on copper are presented. Our findings demonstrate that SEY, besides being an indispensable mean to qualify technical materials in many technological fields, can be also used as a flexible and advantageous diagnostics to probe surfaces and interfaces.

  2. The secondary electron yield of noble metal surfaces

    Science.gov (United States)

    Gonzalez, L. A.; Angelucci, M.; Larciprete, R.; Cimino, R.

    2017-11-01

    Secondary electron yield (SEY) curves in the 0-1000 eV range were measured on polycrystalline Ag, Au and Cu samples. The metals were examined as introduced in the ultra-high vacuum chamber and after having been cleaned by Ar+ ion sputtering. The comparison between the curves measured on the clean samples and in the presence of contaminants, due to the permanence in atmosphere, confirmed that the SEY behavior is strongly influenced by the chemical state of the metal surface. We show that when using very slow primary electrons the sample work function can be determined with high accuracy from the SEY curves. Moreover we prove that SEY is highly sensitive to the presence of adsorbates even at submonolayer coverage. Results showing the effect of small quantities of CO adsorbed on copper are presented. Our findings demonstrate that SEY, besides being an indispensable mean to qualify technical materials in many technological fields, can be also used as a flexible and advantageous diagnostics to probe surfaces and interfaces.

  3. Electronic system for floor surface type detection in robotics applications

    Science.gov (United States)

    Tarapata, Grzegorz; Paczesny, Daniel; Tarasiuk, Łukasz

    2016-11-01

    The paper reports a recognizing method base on ultrasonic transducers utilized for the surface types detection. Ultra-sonic signal is transmitted toward the examined substrate, then reflected and scattered signal goes back to another ultra-sonic receiver. Thee measuring signal is generated by a piezo-electric transducer located at specified distance from the tested substrate. The detector is a second piezo-electric transducer located next to the transmitter. Depending on thee type of substrate which is exposed by an ultrasonic wave, the signal is partially absorbed inn the material, diffused and reflected towards the receiver. To measure the level of received signal, the dedicated electronic circuit was design and implemented in the presented systems. Such system was designed too recognize two types of floor surface: solid (like concrete, ceramic stiles, wood) and soft (carpets, floor coverings). The method will be applied in electronic detection system dedicated to autonomous cleaning robots due to selection of appropriate cleaning method. This work presents the concept of ultrasonic signals utilization, the design of both the measurement system and the measuring stand and as well number of wide tests results which validates correctness of applied ultrasonic method.

  4. Distance dependence of the reaction rate for the reduction of metal cations by solvated electrons: a picosecond pulse radiolysis study.

    Science.gov (United States)

    Schmidhammer, Uli; Pernot, Pascal; De Waele, Vincent; Jeunesse, Pierre; Demarque, Alexandre; Murata, Shigeo; Mostafavi, Mehran

    2010-11-18

    The decay of the solvated electron generated by picosecond electron pulse radiolysis is studied by broad-band transient absorption measurements in ethylene glycol solutions containing decimolar concentrations of Cu(2+), Ni(2+), and Pb(2+) metal cations. Analysis of the nonexponential kinetics of the decays reveals molecular parameters of the electron transfer reaction. It is found that the reaction occurs at long distance for Cu(2+) solutions and is only limited to contact distance in the case of Ni(2+) solutions. The distribution of reaction distance strongly depends on the free enthalpy change of the reactions.

  5. Electron spin interactions in chemistry and biology fundamentals, methods, reactions mechanisms, magnetic phenomena, structure investigation

    CERN Document Server

    Likhtenshtein, Gertz

    2016-01-01

    This book presents the versatile and pivotal role of electron spin interactions in nature. It provides the background, methodologies and tools for basic areas related to spin interactions, such as spin chemistry and biology, electron transfer, light energy conversion, photochemistry, radical reactions, magneto-chemistry and magneto-biology. The book also includes an overview of designing advanced magnetic materials, optical and spintronic devices and photo catalysts. This monograph appeals to scientists and graduate students working in the areas related to spin interactions physics, biophysics, chemistry and chemical engineering.

  6. Catalytic Asymmetric Inverse-Electron-Demand Hetero-Diels-Alder Reactions.

    Science.gov (United States)

    Xie, Mingsheng; Lin, Lili; Feng, Xiaoming

    2017-12-01

    In this review, the recent developments in catalytic asymmetric inverse-electron-demand hetero-Diels-Alder reaction, which is recognized as one of the most powerful routes to construct highly functionalized and enantioenriched six-membered heterocycles, are described. The article is organized on the basis of different kinds of electron-deficient heterodienes, including α,β-unsaturated ketones/aldehydes, o-benzoquinones, α,β-unsaturated imines, N-aryl imines, o-benzoqinone imides, and other aza-olefins. © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Golden rule kinetics of transfer reactions in condensed phase: the microscopic model of electron transfer reactions in disordered solid matrices.

    Science.gov (United States)

    Basilevsky, M V; Odinokov, A V; Titov, S V; Mitina, E A

    2013-12-21

    The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ0 = ℏω0/k(B)T where ω0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ0 kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T → 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for

  8. "Feathered" fractal surfaces to minimize secondary electron emission for a wide range of incident angles

    Science.gov (United States)

    Swanson, Charles; Kaganovich, Igor D.

    2017-07-01

    Complex structures on a material surface can significantly reduce the total secondary electron emission from that surface. The reduction occurs due to the capture of low-energy, true secondary electrons emitted at one point of the structure and intersecting another. We performed Monte Carlo calculations to demonstrate that fractal surfaces can reduce net secondary electron emission produced by the surface as compared to the flat surface. Specifically, we describe one surface, a "feathered" surface, which reduces the secondary electron emission yield more effectively than other previously considered configurations. Specifically, feathers grown onto a surface suppress secondary electron emission from shallow angles of incidence more effectively than velvet. We find that, for the surface simulated, secondary electron emission yield remains below 20% of its un-suppressed value, even for shallow incident angles, where the velvet-only surface gives reduction factor of only 50%.

  9. Bimolecular electron transfer reactions in coumarin amine systems: Donor acceptor orientational effect on diffusion-controlled reaction rates

    Science.gov (United States)

    Satpati, A. K.; Nath, S.; Kumbhakar, M.; Maity, D. K.; Senthilkumar, S.; Pal, H.

    2008-04-01

    Electron transfer (ET) reactions between excited coumarin dyes and different aliphatic amine (AlA) and aromatic amine (ArA) donors have been investigated in acetonitrile solution using steady-state (SS) and time-resolved (TR) fluorescence quenching measurements. No ground state complex or emissive exciplex formation has been indicated in these systems. SS and TR measurements give similar quenching constants ( kq) for each of the coumarin-amine pairs, suggesting dynamic nature of interaction in these systems. On correlating kq values with the free energy changes (Δ G0) of the ET reactions show the typical Rehm-Weller type of behavior as expected for bimolecular ET reactions under diffusive condition, where kq increases with -Δ G0 at the lower exergonicity (-Δ G0) region but ultimately saturate to a diffusion-limited value (kqDC) at the higher exergonicity region. It is, however, interestingly observed that the kqDC values vary largely depending on the type of the amines used. Thus, kqDC is much higher with ArAs than AlAs. Similarly, the kqDC for cyclic monoamine 1-azabicyclo-[2,2,2]-octane (ABCO) is distinctly lower and that for cyclic diamine 1,4-diazabicyclo-[2,2,2]-octane (DABCO) is distinctly higher than the kqDC value obtained for other noncyclic AlAs. These differences in the kqDC values have been rationalized on the basis of the differences in the orientational restrictions involved in the ET reactions with different types of amines. As understood, n-type donors (AlAs) introduce large orientational restriction and thus significantly reduces the ET efficiency in comparison to the π-type donors (ArAs). Structural constrains are inferred to be the reason for the differences in the kqDC values involving ABCO, DABCO donors in comparison to other noncyclic AlAs. Supportive evidence for the orientational restrictions involving different types of amines donors has also been obtained from DFT based quantum chemical calculations on the molecular orbitals of

  10. Bimolecular electron transfer in ionic liquids: are reaction rates anomalously high?

    Science.gov (United States)

    Liang, Min; Kaintz, Anne; Baker, Gary A; Maroncelli, Mark

    2012-02-02

    Steady-state and picosecond time-resolved emission spectroscopy are used to monitor the bimolecular electron transfer reaction between the electron acceptor 9,10-dicyanoanthracene in its S(1) state and the donor N,N-dimethylaniline in a variety of ionic liquids and several conventional solvents. Detailed study of this quenching reaction was undertaken in order to better understand why rates reported for similar diffusion-limited reactions in ionic liquids sometimes appear much higher than expected given the viscous nature of these liquids. Consistent with previous studies, Stern-Volmer analyses of steady-state and lifetime data provide effective quenching rate constants k(q), which are often 10-100-fold larger than simple predictions for diffusion-limited rate constants k(D) in ionic liquids. Similar departures from k(D) are also observed in conventional organic solvents having comparably high viscosities, indicating that this behavior is not unique to ionic liquids. A more complete analysis of the quenching data using a model combining approximate solution of the spherically symmetric diffusion equation with a Marcus-type description of electron transfer reveals the reasons for frequent observation of k(q) ≫ k(D). The primary cause is that the high viscosities typical of ionic liquids emphasize the transient component of diffusion-limited reactions, which renders the interpretation of rate constants derived from Stern-Volmer analyses ambiguous. Using a more appropriate description of the quenching process enables satisfactory fits of data in both ionic liquid and conventional solvents using a single set of physically reasonable electron transfer parameters. Doing so requires diffusion coefficients in ionic liquids to exceed hydrodynamic predictions by significant factors, typically in the range of 3-10. Direct, NMR measurements of solute diffusion confirm this enhanced diffusion in ionic liquids.

  11. Quantifying Chemical and Electrochemical Reactions in Liquids by in situ Electron Microscopy

    DEFF Research Database (Denmark)

    Canepa, Silvia

    of electrochemical deposition of copper (Cu) by electrochemical liquid scanning electron microscopy (EC-SEM) was done in order to direct observe the formation of dendritic structures. Finally the shape evolution from solid to hollow structures through galvanic replacement reactions were observed for different silver...... (Ag) nanotemplates (cube, rod, nanowires) and gold chloride solution. Results demonstrated that by combining in situ LTEM and ECSEM microscopy with quantitative analysis and systematic studies, meaningful information about the controllable synthesis of metal NPs is achievable....

  12. Reaction of a hydrated electron with gentamycin and collagen—A pulse radiolysis study

    Science.gov (United States)

    Pietrucha, K.; Góra, L.; Doillon, C. J.

    1996-01-01

    The reactions of a hydrated electron (e aq-) with aminoglycoside anbiotic gentamycin and collagen in aqueous medium at different pH have been investigated employing a pulse radiolysis technique. The pseudo-first order equation of reaction kinetics was used to give an accurate description of the decay of e aq- in gentamycin solutions. The rate constant of the e aq- decay in collagen solution was high and reached 3.2 × 10 10 M -1 s -1. The rate constants for the reaction of the e aq- with gentamycin were found to be influenced by pH, decreasing with the deprotonation of the -NH 3 groups, while for pH > pK a which for gentamycin is equal to 7.8, the rate constant was unchanged. These observations suggest that when the amino groups are protonated, reductive deamination occurs, but for unprotonated non-reactive amino groups, a radical anion is formed on the glycoside moiety.

  13. Plasmonic photocatalytic reactions enhanced by hot electrons in a one-dimensional quantum well

    Directory of Open Access Journals (Sweden)

    H. J. Huang

    2015-11-01

    Full Text Available The plasmonic endothermic oxidation of ammonium ions in a spinning disk reactor resulted in light energy transformation through quantum hot charge carriers (QHC, or quantum hot electrons, during a chemical reaction. It is demonstrated with a simple model that light of various intensities enhance the chemical oxidization of ammonium ions in water. It was further observed that light illumination, which induces the formation of plasmons on a platinum (Pt thin film, provided higher processing efficiency compared with the reaction on a bare glass disk. These induced plasmons generate quantum hot electrons with increasing momentum and energy in the one-dimensional quantum well of a Pt thin film. The energy carried by the quantum hot electrons provided the energy needed to catalyze the chemical reaction. The results indicate that one-dimensional confinement in spherical coordinates (i.e., nanoparticles is not necessary to provide an extra excited state for QHC generation; an 8 nm Pt thin film for one-dimensional confinement in Cartesian coordinates can also provide the extra excited state for the generation of QHC.

  14. In situ Regeneration of NADH via Lipoamide Dehydrogenase-catalyzed Electron Transfer Reaction Evidenced by Spectroelectrochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Tam, Tsz Kin; Chen, Baowei; Lei, Chenghong; Liu, Jun

    2012-08-01

    NAD/NADH is a coenzyme found in all living cells, carrying electrons from one reaction to another. We report on characterizations of in situ regeneration of NADH via lipoamide dehydrogenase (LD)-catalyzed electron transfer reaction to regenerate NADH using UV-vis spectroelectrochemistry. The Michaelis-Menten constant (Km) and maximum velocity (Vmax) of NADH regeneration were measured as 0.80 {+-} 0.15 mM and 1.91 {+-} 0.09 {micro}M s-1 in a 1-mm thin-layer spectroelectrochemical cell using gold gauze as the working electrode at the applied potential -0.75 V (vs. Ag/AgCl). The electrocatalytic reduction of the NAD system was further coupled with the enzymatic conversion of pyruvate to lactate by lactate dehydrogenase to examine the coenzymatic activity of the regenerated NADH. Although the reproducible electrocatalytic reduction of NAD into NADH is known to be difficult compared to the electrocatalytic oxidation of NADH, our spectroelectrochemical results indicate that the in situ regeneration of NADH via LD-catalyzed electron transfer reaction is fast and sustainable and can be potentially applied to many NAD/NADH-dependent enzyme systems.

  15. Graphene surface plasmon polaritons with opposite in-plane electron oscillations along its two surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Liang, Huawei; Ruan, Shuangchen, E-mail: scruan@szu.edu.cn; Zhang, Min; Su, Hong; Li, Irene Ling [Shenzhen Key Laboratory of Laser Engineering, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060 (China); Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen University, Shenzhen 518060 (China)

    2015-08-31

    We predict the existence of a surface plasmon polariton (SPP) mode that can be guided by a graphene monolayer, regardless of the sign of the imaginary part of its conductivity. In this mode, in-plane electron oscillations along two surfaces of graphene are of opposite directions, which is very different from conventional SPPs on graphene. Significantly, coating graphene with dielectric films yields a way to guide the SPPs with both sub-wavelength mode widths and ultra-long propagation distances. In particular, the mode characteristics are very sensitive to the chemical potential of graphene, so the graphene-based waveguide can find applications in many optoelectronic devices.

  16. Two-Electron Reaction without Structural Phase Transition in Nanoporous Cathode Material

    Directory of Open Access Journals (Sweden)

    Tomoyuki Matsuda

    2012-01-01

    Full Text Available We investigated the charge/discharge properties, valence states, and structural properties of a nanoporous cathode material LixMn[Fe(CN6]0.83·3.5H2O. The film-type electrode of LixMn[Fe(CN6]0.83·3.5H2O exhibited a high charge capacity (=128 mAh g-1 and a good cyclability (87% of the initial value after 100 cycles and is one of the promising candidates for Li-ion battery cathode. X-ray absorption spectra near the Fe and Mn K-edges revealed that the charge/discharge process is a two-electron reaction; that is, MnII–NC–FeII, MnII–NC–FeIII, and MnIII–NC–FeIII. We further found that the crystal structure remains cubic throughout the charge/discharge process. The lattice constant slightly increased during the [FeII(CN6]4-/[FeIII(CN6]3- oxidization reaction while decreased during the MnII/MnIII oxidization reaction. The two-electron reaction without structural phase transition is responsible for the high charge capacity and the good cyclability.

  17. Influence of Surface Roughness in Electron Beam Welding

    Science.gov (United States)

    Wiednig, C.; Stiefler, F.; Enzinger, N.

    2016-03-01

    The requirements of welded components are rising continuously through increasing demands in engineering. But in engineering not only the quality of welds is important also an economic and timesaving production is crucial. Especially in welding of large cross sections economization potential is existing and significant. Beside the welding technique itself the joint preparation is a major part of work. Electron beam welding has some major advantages in this area. Due the high energy density a very short welding time as well as a small heat affected zone can be achieved. Furthermore the joint preparation can be held simple. Nevertheless, a careful machining and cleaning of the joint surfaces is recommended in literature. In addition to geometric tolerances a specific surface roughness should be kept. These statements are quite general and unspecific. In this contribution a systematic investigation on the influence of joint preparation on the joint properties is presented. By performing several welding experiments with different surface roughness this study provides empirical conclusions. Beside the microscopic investigation of different cross sections and mechanical tests of the welded samples also the process stability during welding was reviewed.

  18. Final Report: Molecular Basis for Microbial Adhesion and Geochemical Surface Reactions: A Study Across Scales

    Energy Technology Data Exchange (ETDEWEB)

    Dixon, David Adams [The University of Alabama

    2013-06-27

    Computational chemistry was used to help provide a molecular level description of the interactions of Gram-negative microbial membranes with subsurface materials. The goal is to develop a better understanding of the molecular processes involved in microbial metal binding, microbial attachment to mineral surfaces, and, eventually, oxidation/reduction reactions (electron transfer) that can occur at these surfaces and are mediated by the bacterial exterior surface. The project focused on the interaction of the outer microbial membrane, which is dominated by an exterior lipopolysaccharide (LPS) portion, of Pseudomonas aeruginosa with the mineral goethite and with solvated ions in the environment. This was originally a collaborative project with T.P. Straatsma and B. Lowery of the Pacific Northwest National Laboratory. The University of Alabama effort used electronic structure calculations to predict the molecular behavior of ions in solution and the behavior of the sugars which form a critical part of the LPS. The interactions of the sugars with metal ions are expected to dominate much of the microscopic structure and transport phenomena in the LPS. This work, in combination with the molecular dynamics simulations of Straatsma and the experimental electrochemistry and microscopy measurements of Lowry, both at PNNL, is providing new insights into the detailed molecular behavior of these membranes in geochemical environments. The effort at The University of Alabama has three components: solvation energies and structures of ions in solution, prediction of the acidity of the critical groups in the sugars in the LPS, and binding of metal ions to the sugar anions. An important aspect of the structure of the LPS membrane as well as ion transport in the LPS is the ability of the sugar side groups such as the carboxylic acids and the phosphates to bind positively charged ions. We are studying the acidity of the acidic side groups in order to better understand the ability of

  19. Manifestation of Geometric and Electronic Shell Structures of Metal Clusters in Intercluster Reactions.

    Science.gov (United States)

    Krishnadas, K R; Baksi, Ananya; Ghosh, Atanu; Natarajan, Ganapati; Pradeep, Thalappil

    2017-06-27

    Monolayer protected clusters exhibit rich diversity in geometric and electronic structures. However, structure-reactivity relationships in these clusters are rarely explored. In this context, [Ag44(SR)30]4-, where -SR is an alkyl/aryl thiolate, is an interesting system due to its geometrically and electronically closed-shell structures and distinct charge states. We demonstrate that these structural features of [Ag44(SR)30]4- are distinctly manifested in its solution-state reaction with another cluster, [Au25(SR)18]-. Through this reaction, an alloy cluster anion, [Au12Ag32(SR)30]4-, evolves spontaneously as revealed by high-resolution electrospray ionization mass spectrometry. Ultraviolet-visible absorption spectroscopy and density functional theory calculations indicate that [Au12Ag32(SR)30]4- is formed by the substitution of all of the Ag atoms in the innermost icosahedral shell of [Ag44(SR)30]4- and the abundance is attributed to its higher stability due to closed geometric as well as electronic shell structure, similar to the reactant clusters. We further demonstrate that the substitution of metal atoms in the middle dodecahedral shell and the outermost mount sites are also possible, however such substitutions produce AuxAg44-x(SR)30 alloy clusters with geometrically and electronically open shells. Depending on specific sites of substitution, an unexpected superatom-nonsuperatom transition occurs in the distribution of AuxAg44-x(SR)30 alloy clusters formed in this reaction. Our results present a unique example of a structure-reactivity relationship in the metal atom substitution chemistry of monolayer protected clusters, wherein a systematic trend, reflecting the geometric and the electronic shell structures of the reactant as well as the product clusters, was observed.

  20. Signatures of quantum effects on radiation reaction in laser-electron-beam collisions

    Science.gov (United States)

    Ridgers, C. P.; Blackburn, T. G.; Del Sorbo, D.; Bradley, L. E.; Slade-Lowther, C.; Baird, C. D.; Mangles, S. P. D.; McKenna, P.; Marklund, M.; Murphy, C. D.; Thomas, A. G. R.

    2017-10-01

    Two signatures of quantum effects on radiation reaction in the collision of a GeV electron beam with a high intensity ( }3\\times 1020~\\text{W}~\\text{cm}-2$ ) laser pulse have been considered. We show that the decrease in the average energy of the electron beam may be used to measure the Gaunt factor for synchrotron emission. We derive an equation for the evolution of the variance in the energy of the electron beam in the quantum regime, i.e. quantum efficiency parameter . We show that the evolution of the variance may be used as a direct measure of the quantum stochasticity of the radiation reaction and determine the parameter regime where this is observable. For example, stochastic emission results in a 25 % increase in the standard deviation of the energy spectrum of a GeV electron beam, 1 fs after it collides with a laser pulse of intensity 21~\\text{W}~\\text{cm}-2$ . This effect should therefore be measurable using current high-intensity laser systems.

  1. Reversible electron-transfer reactions within a nanoscale metal oxide cage mediated by metallic substrates.

    Science.gov (United States)

    Fleming, Christopher; Long, De-Liang; McMillan, Nicola; Johnston, Jacqueline; Bovet, Nicolas; Dhanak, Vin; Gadegaard, Nikolaj; Kögerler, Paul; Cronin, Leroy; Kadodwala, Malcolm

    2008-04-01

    Transition metal oxides exhibit a rich collection of electronic properties and have many practical applications in areas such as catalysis and ultra-high-density magnetic data storage. Therefore the development of switchable molecular transition metal oxides has potential for the engineering of single-molecule devices and nanoscale electronics. At present, the electronic properties of transition metal oxides can only be tailored through the irreversible introduction of dopant ions, modifying the electronic structure by either injecting electrons or core holes. Here we show that a molybdenum(VI) oxide 'polyoxometalate' molecular nanocluster containing two embedded redox agents is activated by a metallic surface and can reversibly interconvert between two electronic states. Upon thermal activation two electrons are ejected from the active sulphite anions and delocalized over the metal oxide cluster cage, switching it from a fully oxidized state to a two-electron reduced state along with the concomitant formation of an S-S bonding interaction between the two sulphur centres inside the cluster shell.

  2. The Radiation Reaction of a Point Electron as a Planck Vacuum Response Phenomenon

    Directory of Open Access Journals (Sweden)

    Daywitt W. C.

    2010-04-01

    Full Text Available The polarizability of the Planck vacuum (PV transforms the bare Coulomb field e = r 2 of a point charge into the observed field e = r 2 , where e and e are the bare and observed electronic charges respectively [1]. In uniform motion this observed field is transformed into the well-known relativistic electric and magnetic fields [2, p.380] by the interac- tion taking place between the bare-charge field and the PV continuum. Given the in- volvement of the PV in both these transformations, it is reasonable to conclude that the negative-energy PV must also be connected to the radiation reaction or damping force of an accelerated point electron. This short paper examines that conclusion by compar- ing it to an early indication [3] that the point electron problem may involve more than just a massive point charge.

  3. Reaction Mechanisms on Multiwell Potential Energy Surfaces in Combustion (and Atmospheric) Chemistry.

    Science.gov (United States)

    Osborn, David L

    2017-05-05

    Chemical reactions occurring on a potential energy surface with multiple wells are ubiquitous in low-temperature combustion and in the oxidation of volatile organic compounds in Earth's atmosphere. The rich variety of structural isomerizations that compete with collisional stabilization makes characterizing such complex-forming reactions challenging. This review describes recent experimental and theoretical advances that deliver increasingly complete views of their reaction mechanisms. New methods for creating reactive intermediates coupled with multiplexed measurements provide many experimental observables simultaneously. Automated methods to explore potential energy surfaces can uncover hidden reactive pathways, and master equation methods enable a holistic treatment of both sequential and well-skipping pathways. Our ability to probe and understand nonequilibrium effects and reaction sequences is increasing. These advances provide the fundamental science base for predictive models of combustion and the atmosphere that are crucial to address global challenges.

  4. pH-dependent electron transfer reaction and direct bioelectrocatalysis of the quinohemoprotein pyranose dehydrogenase

    Energy Technology Data Exchange (ETDEWEB)

    Takeda, Kouta [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); Matsumura, Hirotoshi; Ishida, Takuya [Department of Biomaterial Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657 (Japan); Yoshida, Makoto [Department of Environmental and Natural Resource Science, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509 (Japan); Igarashi, Kiyohiko; Samejima, Masahiro [Department of Biomaterial Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657 (Japan); Ohno, Hiroyuki [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); Nakamura, Nobuhumi, E-mail: nobu1@cc.tuat.ac.jp [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan)

    2016-08-26

    A pyranose dehydrogenase from Coprinopsis cinerea (CcPDH) is an extracellular quinohemoeprotein, which consists a b-type cytochrome domain, a pyrroloquinoline-quinone (PQQ) domain, and a family 1-type carbohydrate-binding module. The electron transfer reaction of CcPDH was studied using some electron acceptors and a carbon electrode at various pH levels. Phenazine methosulfate (PMS) reacted directly at the PQQ domain, whereas cytochrome c (cyt c) reacted via the cytochrome domain of intact CcPDH. Thus, electrons are transferred from reduced PQQ in the catalytic domain of CcPDH to heme b in the N-terminal cytochrome domain, which acts as a built-in mediator and transfers electron to a heterogenous electron transfer protein. The optimal pH values of the PMS reduction (pH 6.5) and the cyt c reduction (pH 8.5) differ. The catalytic currents for the oxidation of L-fucose were observed within a range of pH 4.5 to 11. Bioelectrocatalysis of CcPDH based on direct electron transfer demonstrated that the pH profile of the biocatalytic current was similar to the reduction activity of cyt c characters. - Highlights: • pH dependencies of activity were different for the reduction of cyt c and DCPIP. • DET-based bioelectrocatalysis of CcPDH was observed. • The similar pH-dependent profile was found with cyt c and electrode. • The present results suggested that IET reaction of CcPDH shows pH dependence.

  5. Non-adiabatic processes in the charge transfer reaction of O{sub 2} molecules with potassium surfaces without dissociation

    Energy Technology Data Exchange (ETDEWEB)

    Krix, David; Nienhaus, Hermann, E-mail: hermann.nienhaus@uni-due.de [Faculty of Physics, University of Duisburg-Essen and Center of Nanointegration Duisburg-Essen (CENIDE), Lotharstr. 1, D-47048 Duisburg (Germany)

    2014-08-21

    Thin potassium films grown on Si(001) substrates are used to measure internal chemicurrents and the external emission of exoelectrons simultaneously during adsorption of molecular oxygen on K surfaces at 120 K. The experiments clarify the dynamics of electronic excitations at a simple metal with a narrow valence band. X-ray photoemission reveals that for exposures below 5 L almost exclusively peroxide K{sub 2}O{sub 2} is formed, i.e., no dissociation of the molecule occurs during interaction. Still a significant chemicurrent and a delayed exoelectron emission are detected due to a rapid injection of unoccupied molecular levels below the Fermi level. Since the valence band width of potassium is approximately equal to the potassium work function (2.4 eV) the underlying mechanism of exoemission is an Auger relaxation whereas chemicurrents are detected after resonant charge transfer from the metal valence band into the injected level. The change of the chemicurrent and exoemission efficiencies with oxygen coverage can be deduced from the kinetics of the reaction and the recorded internal and external emission currents traces. It is shown that the non-adiabaticity of the reaction increases with coverage due to a reduction of the electronic density of states at the surface while the work function does not vary significantly. Therefore, the peroxide formation is one of the first reaction systems which exhibits varying non-adiabaticity and efficiencies during the reaction. Non-adiabatic calculations based on model Hamiltonians and density functional theory support the picture of chemicurrent generation and explain the rapid injection of hot hole states by an intramolecular motion, i.e., the expansion of the oxygen molecule on the timescale of a quarter of a vibrational period.

  6. Colour and surface fluorescence development and their relationship with Maillard reaction markers as influenced by structural changes during cornflakes production.

    Science.gov (United States)

    Farroni, Abel; Buera, María Del Pilar

    2012-12-01

    The aim of this work was to study colour and surface fluorescence development in relation to the chemical markers for the Maillard reaction at the cooking, flaking and toasting stages of cornflake production process. Colour was measured by a calibrated computer vision system. Surface fluorescence was measured on compressed samples. Aqueous extracted Maillard reaction markers (hydroxymethylfurfural, carboxymethyl-lysine, absorbance at 420nm and total fluorescence) were measured on protease hydrolyzed samples. Sample microstructure was observed by scanning electron microscopy. During cooking the colour coordinates L(∗) and b(∗) decreased and a(∗) increased. After flaking, the samples appeared lighter, while the pigment concentration, fluorescence and hydroxymethylfurfural did not change. Toasting generated bubbles in the matrix and L(∗) apparently increased, although brown pigment concentration increased. Pigment concentration did not correlate with surface colour due to the destruction or generation of interfaces. Surface and microstructure effects can be avoided by milling and compressing the samples. Copyright © 2012 Elsevier Ltd. All rights reserved.

  7. Theoretical investigation of the methane cracking reaction pathways on Ni (1 1 1) surface

    Science.gov (United States)

    Li, Jingde; Croiset, Eric; Ricardez-Sandoval, Luis

    2015-10-01

    A comprehensive methane cracking reaction pathway was investigated by performing density functional theory (DFT) calculations. In addition to the sequential dissociation reaction, i.e. CH4 → CHx + (4 - x)H → C + 2H2, a more sophisticated surface reaction network was studied, i.e. CHx + C → CHx - 1 + CH. The results show that CHx dehydrogenation is promoted with a low energy barrier through bimolecular reaction and provide an alternative kinetic favorable route for methane cracking. This study also demonstrates that the production of gas phase C2 hydrocarbon species, e.g. C2H2 and C2H4, in methane cracking reaction is unlikely due to the high barrier energy of C2H3 formation and their strong adsorption energy on Ni (1 1 1).

  8. Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA)

    Science.gov (United States)

    SRD 100 Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA) (PC database for purchase)   This database has been designed to facilitate quantitative interpretation of Auger-electron and X-ray photoelectron spectra and to improve the accuracy of quantitation in routine analysis. The database contains all physical data needed to perform quantitative interpretation of an electron spectrum for a thin-film specimen of given composition. A simulation module provides an estimate of peak intensities as well as the energy and angular distributions of the emitted electron flux.

  9. Time- and angle-resolved photoemission spectroscopy of hydrated electrons near a liquid water surface.

    Science.gov (United States)

    Yamamoto, Yo-ichi; Suzuki, Yoshi-Ichi; Tomasello, Gaia; Horio, Takuya; Karashima, Shutaro; Mitríc, Roland; Suzuki, Toshinori

    2014-05-09

    We present time- and angle-resolved photoemission spectroscopy of trapped electrons near liquid surfaces. Photoemission from the ground state of a hydrated electron at 260 nm is found to be isotropic, while anisotropic photoemission is observed for the excited states of 1,4-diazabicyclo[2,2,2]octane and I- in aqueous solutions. Our results indicate that surface and subsurface species create hydrated electrons in the bulk side. No signature of a surface-bound electron has been observed.

  10. Electronic Noses for Composites Surface Contamination Detection in Aerospace Industry.

    Science.gov (United States)

    Vito, Saverio De; Miglietta, Maria Lucia; Massera, Ettore; Fattoruso, Grazia; Formisano, Fabrizio; Polichetti, Tiziana; Salvato, Maria; Alfano, Brigida; Esposito, Elena; Francia, Girolamo Di

    2017-04-02

    The full exploitation of Composite Fiber Reinforced Polymers (CFRP) in so-called green aircrafts design is still limited by the lack of adequate quality assurance procedures for checking the adhesive bonding assembly, especially in load-critical primary structures. In this respect, contamination of the CFRP panel surface is of significant concern since it may severely affect the bonding and the mechanical properties of the joint. During the last years, the authors have developed and tested an electronic nose as a non-destructive tool for pre-bonding surface inspection for contaminants detection, identification and quantification. Several sensors and sampling architectures have been screened in view of the high Technology Readiness Level (TRL) scenarios requirements. Ad-hoc pattern recognition systems have also been devised to ensure a fast and reliable assessment of the contamination status, by combining real time classifiers and the implementation of a suitable rejection option. Results show that e-noses could be used as first line low cost Non Destructive Test (NDT) tool in aerospace CFRP assembly and maintenance scenarios.

  11. Electron transfer reactions for image and image-derived states in dielectric thin films

    Science.gov (United States)

    Jensen, E. T.; Sanche, L.

    2008-08-01

    We have studied the cross section for electron trapping that occurs at the surfaces and interfaces of a variety of thin dielectric films (n-octane, methanol, n-butanol, and difluoromethane) that are grown on Kr buffer films. When such films are bombarded with electrons of very low incident energies (E<~300 meV), charging cross sections up to the order of 10-14 cm2 are measured for submonolayer quantities of a variety of coadsorbed molecules: CH3I, CH3Br, CH3Cl, and CO2. These huge cross sections are ascribed to the formation of image states at the dielectric film interfaces, which trap incoming electrons and, via coupling to the adsorbate electron affinity levels, dramatically enhance the capture probability. We have also shown that thin film dielectric layer structures can be created which display image-derived states, such as a ``quantum well'' in a sandwich structure with two ``electron barrier'' layers surrounding a Kr and adsorbate spacer film. These phenomena are shown to be of a general nature, occurring for a wide variety of molecular thin films, and depend on the dielectric constant and electron affinity of the selected species. We also report the absolute cross section for dissociative electron attachment of submonolayer CH3I adsorbed on Kr thin films.

  12. Exploring the catalytic activity of pristine T6[100] surface for oxygen reduction reaction: A first-principles study

    Science.gov (United States)

    Banerjee, Paramita; Chakrabarty, Soubhik; Thapa, Ranjit; Das, G. P.

    2017-10-01

    The electrocatalytic activity of T6[100] surface containing both sp3 (C1) and sp2 (C2) hybridized carbon atoms is explored using first-principles density functional theory based approach. The top layered C1 atom of the surface is found to be more active towards the oxygen reduction reaction (ORR), as compared to that of C2 atom. This is attributed to the presence of dangling σ bond in the corresponding C1 atom, leading to the high electron density near the Ferrmi level. Whereas, the π electron in the top layered C2 atom forms a weak out of plane network. As estimated from free energy profile, the overpotential is much lower when C1 is considered as the active site and the final step i.e desorption of final OH- ion is found to be the potential determining step. We have also reported the effect of Si dopant on the catalytic activity of T6[100] surface and explained the origin of high overpotential value in this case. Thus in this report, we propose a new metal-free catalyst i.e T6[100] surface, having both sp2 (maintains the high metallicity needed to reduce ohmic loss) and sp3 (helps in capturing the upcoming molecules) hybridized carbon atoms, as a potential candidate for ORR.

  13. Balancing the Hydrogen Evolution Reaction, Surface Energetics, and Stability of Metallic MoS2 Nanosheets via Covalent Functionalization.

    Science.gov (United States)

    Benson, Eric E; Zhang, Hanyu; Schuman, Samuel A; Nanayakkara, Sanjini U; Bronstein, Noah D; Ferrere, Suzanne; Blackburn, Jeffrey L; Miller, Elisa M

    2018-01-10

    We modify the fundamental electronic properties of metallic (1T phase) nanosheets of molybdenum disulfide (MoS2) through covalent chemical functionalization, and thereby directly influence the kinetics of the hydrogen evolution reaction (HER), surface energetics, and stability. Chemically exfoliated, metallic MoS2 nanosheets are functionalized with organic phenyl rings containing electron donating or withdrawing groups. We find that MoS2 functionalized with the most electron donating functional group (p-(CH3CH2)2NPh-MoS2) is the most efficient catalyst for HER in this series, with initial activity that is slightly worse compared to the pristine metallic phase of MoS2. The p-(CH3CH2)2NPh-MoS2 is more stable than unfunctionalized metallic MoS2 and outperforms unfunctionalized metallic MoS2 for continuous H2 evolution within 10 min under the same conditions. With regards to the entire studied series, the overpotential and Tafel slope for catalytic HER are both directly correlated with the electron donating strength of the functional group. The results are consistent with a mechanism involving ground-state electron donation or withdrawal to/from the MoS2 nanosheets, which modifies the electron transfer kinetics and catalytic activity of the MoS2 nanosheet. The functional groups preserve the metallic nature of the MoS2 nanosheets, inhibiting conversion to the thermodynamically stable semiconducting state (2H) when mildly annealed in a nitrogen atmosphere. We propose that the electron density and, therefore, reactivity of the MoS2 nanosheets are controlled by the attached functional groups. Functionalizing nanosheets of MoS2 and other transition metal dichalcogenides provides a synthetic chemical route for controlling the electronic properties and stability within the traditionally thermally unstable metallic state.

  14. Balancing the Hydrogen Evolution Reaction, Surface Energetics, and Stability of Metallic MoS2 Nanosheets via Covalent Functionalization

    Energy Technology Data Exchange (ETDEWEB)

    Link, Elisa M [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Benson, Eric E [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Zhang, Hanyu [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Nanayakkara, Sanjini U [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Bronstein, Noah [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Blackburn, Jeffrey L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Schuman, Samuel [Formerly NREL; Ferrere, Suzanne [Formerly NREL

    2017-12-27

    We modify the fundamental electronic properties of metallic (1T phase) nanosheets of molybdenum disulfide (MoS2) through covalent chemical functionalization, and thereby directly influence the kinetics of the hydrogen evolution reaction (HER), surface energetics, and stability. Chemically exfoliated, metallic MoS2 nanosheets are functionalized with organic phenyl rings containing electron donating or withdrawing groups. We find that MoS2 functionalized with the most electron donating functional group (p-(CH3CH2)2NPh-MoS2) is the most efficient catalyst for HER in this series, with initial activity that is slightly worse compared to the pristine metallic phase of MoS2. The p-(CH3CH2)2NPh-MoS2 is more stable than unfunctionalized metallic MoS2 and outperforms unfunctionalized metallic MoS2 for continuous H2 evolution within 10 min under the same conditions. With regards to the entire studied series, the overpotential and Tafel slope for catalytic HER are both directly correlated with the electron donating strength of the functional group. The results are consistent with a mechanism involving ground-state electron donation or withdrawal to/from the MoS2 nanosheets, which modifies the electron transfer kinetics and catalytic activity of the MoS2 nanosheet. The functional groups preserve the metallic nature of the MoS2 nanosheets, inhibiting conversion to the thermodynamically stable semiconducting state (2H) when mildly annealed in a nitrogen atmosphere. We propose that the electron density and, therefore, reactivity of the MoS2 nanosheets are controlled by the attached functional groups. Functionalizing nanosheets of MoS2 and other transition metal dichalcogenides provides a synthetic chemical route for controlling the electronic properties and stability within the traditionally thermally unstable metallic state.

  15. Unconventional exo selectivity in thermal normal-electron-demand Diels-Alder reactions

    Science.gov (United States)

    Ho, Guo-Ming; Huang, Ci-Jhang; Li, Elise Yu-Tzu; Hsu, Sheng-Kai; Wu, Ti; Zulueta, Medel Manuel L.; Wu, Kevin Binchia; Hung, Shang-Cheng

    2016-10-01

    The Diels-Alder reaction is a useful tool for generating functionalized chiral molecules through the concerted cycloaddition of dienes and dienophiles leading to six-membered rings. Traditionally, the selective predictions of the products rely heavily on consideration of the secondary orbital interactions that stabilize the endo pathway. However, there remain some basic examples defying this notion and produce the exo-isomer as major product. Here we systematically evaluated of the structural features driving exo selectivity in thermal normal-electron-demand Diels-Alder reactions. Substitution at the Cβ position and the size and electronegativity of the electron-withdrawing group of the dienophile are contributing factors. Experimental and computational studies both point toward the steric and electrostatic forces between the substituents in both the diene and the dienophile that increase the likelihood of the exo pathway. For these substrates, the dominance of the endo pathway is reduced by transition state distortions and poor structural alignments of the reacting partners. We also noted the tilt of the dienophile with respect to the diene causing steric strain on the functionalities at the more advanced bond forming carbon-carbon position of the endo transition state. Insights into such factors may benefit synthetic planning and asserting control over this important named reaction.

  16. Study of the Ne(^3P_2) + CH_3F Electron Transfer Reaction below 1 Kelvin

    CERN Document Server

    Jankunas, Justin; Osterwalder, Andreas

    2014-01-01

    Relatively little is known about the dynamics of electron transfer reactions at low collision energy. We present a study of Penning ionization of ground state methyl fluoride molecules by electronically excited neon atoms in the 13 $\\mu$eV--4.8 meV (150 mK--56 K) collision energy range, using a neutral-neutral merged beam setup. Relative cross sections have been measured for three Ne($^3P_2$)+ CH$_3$F reaction channels by counting the number of CH$_3$F$^+$, CH$_2$F$^+$, and CH$_3^+$ product ions, as a function of relative velocity between the neon and methyl fluoride molecular beams. Experimental cross sections markedly deviate from the Langevin capture model at collision energies above 20 K. The branching ratios are constant. In other words, the chemical shape of the CH$_3$F molecule, as seen by Ne($^3P_2$) atom, appears not to change as the collision energy is varied, in contrast to related Ne($^3P_J$) + CH$_3$X (X=Cl and Br) reactions at higher collision energies.

  17. Disentangling electron- and electric-field-induced ring-closing reactions in a diarylethene derivative on Ag(1 1 1)

    Science.gov (United States)

    Reecht, Gaël; Lotze, Christian; Sysoiev, Dmytro; Huhn, Thomas; Franke, Katharina J.

    2017-07-01

    Using scanning tunneling microscopy and spectroscopy we investigate the adsorption properties and ring-closing reaction of a diarylethene derivative (C5F-4Py) on a Ag(1 1 1) surface. We identify an electron-induced reaction mechanism, with a quantum yield varying from 10-14-10-9 per electron upon variation of the bias voltage from 1-2 V. We ascribe the drastic increase in switching efficiency to a resonant enhancement upon tunneling through molecular orbitals. Additionally, we resolve the ring-closing reaction even in the absence of a current passing through the molecule. In this case the electric-field can modify the reaction barrier, leading to a finite switching probability at 4.8 K. A detailed analysis of the switching events shows that a simple plate-capacitor model for the tip-surface junction is insufficient to explain the distance dependence of the switching voltage. Instead, describing the tip as a sphere is in agreement with the findings. We resolve small differences in the adsorption configuration of the closed isomer, when comparing the electron- and field-induced switching product.

  18. Advanced High Energy Density Secondary Batteries with Multi‐Electron Reaction Materials

    Science.gov (United States)

    Luo, Rui; Huang, Yongxin; Li, Li

    2016-01-01

    Secondary batteries have become important for smart grid and electric vehicle applications, and massive effort has been dedicated to optimizing the current generation and improving their energy density. Multi‐electron chemistry has paved a new path for the breaking of the barriers that exist in traditional battery research and applications, and provided new ideas for developing new battery systems that meet energy density requirements. An in‐depth understanding of multi‐electron chemistries in terms of the charge transfer mechanisms occuring during their electrochemical processes is necessary and urgent for the modification of secondary battery materials and development of secondary battery systems. In this Review, multi‐electron chemistry for high energy density electrode materials and the corresponding secondary battery systems are discussed. Specifically, four battery systems based on multi‐electron reactions are classified in this review: lithium‐ and sodium‐ion batteries based on monovalent cations; rechargeable batteries based on the insertion of polyvalent cations beyond those of alkali metals; metal–air batteries, and Li–S batteries. It is noted that challenges still exist in the development of multi‐electron chemistries that must be overcome to meet the energy density requirements of different battery systems, and much effort has more effort to be devoted to this. PMID:27840796

  19. Advanced High Energy Density Secondary Batteries with Multi-Electron Reaction Materials.

    Science.gov (United States)

    Chen, Renjie; Luo, Rui; Huang, Yongxin; Wu, Feng; Li, Li

    2016-10-01

    Secondary batteries have become important for smart grid and electric vehicle applications, and massive effort has been dedicated to optimizing the current generation and improving their energy density. Multi-electron chemistry has paved a new path for the breaking of the barriers that exist in traditional battery research and applications, and provided new ideas for developing new battery systems that meet energy density requirements. An in-depth understanding of multi-electron chemistries in terms of the charge transfer mechanisms occuring during their electrochemical processes is necessary and urgent for the modification of secondary battery materials and development of secondary battery systems. In this Review, multi-electron chemistry for high energy density electrode materials and the corresponding secondary battery systems are discussed. Specifically, four battery systems based on multi-electron reactions are classified in this review: lithium- and sodium-ion batteries based on monovalent cations; rechargeable batteries based on the insertion of polyvalent cations beyond those of alkali metals; metal-air batteries, and Li-S batteries. It is noted that challenges still exist in the development of multi-electron chemistries that must be overcome to meet the energy density requirements of different battery systems, and much effort has more effort to be devoted to this.

  20. Influence of plastic strain on the hydrogen evolution reaction on nickel (100) single crystal surfaces to improve hydrogen embrittlement

    Energy Technology Data Exchange (ETDEWEB)

    Lekbir, C., E-mail: choukri.lekbir@univ-lr.fr; Creus, J.; Sabot, R.; Feaugas, X.

    2013-08-20

    Hydrogen-induced embrittlement can be accountable for premature failure of structure in relation with physical and/or chemical processes occurring on material's surface or in the bulk of the material. Hydrogen Evolution Reaction (HER) corresponding to the early step of hydrogen ingress in the material is explored in present study in relation with plastic strain. HER on nickel (100) single crystal in sulphuric acid medium can be related by a Volmer–Heyrovsky mechanism. The corresponding elementary kinetic parameters as symmetry coefficients, activation enthalpies, and number of active sites have been identified via a thermokinetic model using experimental data. These parameters can be affected by defects associated with plastic strain. Irreversible plastic strain modifies the density and the distribution of storage dislocations affecting the surface roughness at atomic scale and generating additional active adsorption sites. Furthermore, surface emergence of mobile dislocations induces the formation of slip bands, which modify the surface roughness and the electronic state of the surface and increases the (111) surface density. The consequence of plastic strain on HER is explored and discussed in relation with both processes.

  1. Experimental and trajectory study on the reaction of protonated methionine with electronically excited singlet molecular oxygen (a1Δg): reaction dynamics and collision energy effects.

    Science.gov (United States)

    Fang, Yigang; Liu, Fangwei; Bennett, Andrew; Ara, Shamim; Liu, Jianbo

    2011-03-24

    The reaction of protonated methionine with the lowest electronically excited state of molecular oxygen O(2)(a(1)Δ(g)) was studied in a guided ion beam apparatus, including the measurement of reaction cross sections over a center-of-mass collision energy (E(col)) range of 0.1-2.0 eV. A series of electronic structure and RRKM calculations were used to examine the properties of various complexes and transition states that might be important along the reaction coordinate. Only one product channel is observed, corresponding to generation of hydrogen peroxide via transfer of two hydrogen atoms (H2T) from protonated methionine to singlet oxygen. At low collision energies, the reaction approaches the collision limit and may be mediated by intermediate complexes. The reaction shows strong inhibition by collision energy, and becomes negligible at E(col) > 1.25 eV. A large set of quasi-classical direct dynamics trajectory simulations were calculated at the B3LYP/6-21G level of theory. Trajectories reproduced experimental results and provided insight into the mechanistic origin of the H2T reaction, how the reaction probability varies with impact parameter, and the suppressing effect of collision energy. Analysis of the trajectories shows that at E(col) = 1.0 eV the reaction is mediated by a precursor and/or hydroperoxide complex, and is sharply orientation-dependent. Only 20% of collisions have favorable reactant orientations at the collision point, and of those, less than half form precursor and hydroperoxide complexes which eventually lead to reaction. The narrow range of reactive collision orientations, together with physical quenching of (1)O(2) via intersystem crossing between singlet and triplet electronic states, may account for the low reaction efficiency observed at high E(col). © 2011 American Chemical Society

  2. Radical-Molecule Reaction Mechanisms: Role of Electron Delocalization, Complex Formation, and Intramolecular Energy Transfer.

    Science.gov (United States)

    Dubey, Manvendra Krishna

    This thesis presents: (1) measurements of the kinetics of the reactions of the OH radical with several molecules by the discharge flow technique, (2) reactivity trend analysis, electronic structure, and transition state calculations, (3) molecular beam electric deflection experiments of hot polyatomics. A synthesis of these studies demonstrates that radical-molecule reactions frequently involve an indirect mechanism and are not necessarily direct, activated, bimolecular processes. Indirect mechanisms arise when the reactant frontier orbitals do not transform to the product configuration. Compact reactivity trends among homologous reaction sets are defined by the difference between the ionization potential of the electron donor and the electron affinity of the electron acceptor and show that charge-transfer stabilizations (rather than thermodynamics) govern radical-molecule reactivity. A multiple transition state model is developed to predict the mixed bimolecular/termolecular kinetics implicit in the indirect mechanism. The fundamental assumption of rapid intramolecular energy redistribution in the energized complex in the model is validated by our electric deflection studies. Model calculations for the rm OH + HNO_3to H_2O + NO_3 reaction reproduce the small A factor, negative activation energy, and pressure dependence of the rate. They elucidate the reaction mechanism in molecular detail. The OH first bonds to either the O or N atom of HNO_3 to form an energized complex, which subsequently suffers one of three fates: dissociation to reactants via a loose transition state, dissociation to products via a tight transition state with a negative threshold, or collisional stabilization. These processes compete to determine the overall kinetics. Isotopic scrambling rates are predicted. Our model predicts faster rates than the NASA recommendation at low temperatures with potential consequences for stratospheric photochemistry. The rate constants of the reactions of OH

  3. Bio-orthogonal Fluorescent Labelling of Biopolymers through Inverse-Electron-Demand Diels-Alder Reactions.

    Science.gov (United States)

    Kozma, Eszter; Demeter, Orsolya; Kele, Péter

    2017-03-16

    Bio-orthogonal labelling schemes based on inverse-electron-demand Diels-Alder (IEDDA) cycloaddition have attracted much attention in chemical biology recently. The appealing features of this reaction, such as the fast reaction kinetics, fully bio-orthogonal nature and high selectivity, have helped chemical biologists gain deeper understanding of biochemical processes at the molecular level. Listing the components and discussing the possibilities and limitations of these reagents, we provide a recent snapshot of the field of IEDDA-based biomolecular manipulation with special focus on fluorescent modulation approaches through the use of bio-orthogonalized building blocks. At the end, we discuss challenges that need to be addressed for further developments in order to overcome recent limitations and to enable researchers to answer biomolecular questions in more detail. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  4. Possible correlation effects of surface state electrons on a solid hydrogen film

    NARCIS (Netherlands)

    Mugele, Friedrich Gunther; Albrecht, Uwe; Leiderer, Paul; Kono, Kimitoshi

    1992-01-01

    We have investigated the transport properties of surface state electrons on thin quench-condensed hydrogen films for various electron densities. The surface state electron mobility showed a continuous dependence on the plasma parameter Gamma in the range from 20 to 130, indicating a strong influence

  5. Surface cracking of soda lime glass under pulsed high-current electron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Paul W. [Department of Physics, Bradley University, Peoria, IL 61625 (United States)]. E-mail: pwang@bradley.edu; Kimberlin, K.R. [Department of Physics, Bradley University, Peoria, IL 61625 (United States); Wang Chengyu [Institute of Glass and Inorganic New Materials, Dalian Institute of Light Industry (China); Tao Ying [Institute of Glass and Inorganic New Materials, Dalian Institute of Light Industry (China); Guo Quianglin [Laboratory of Material Modification by Ion, Electron, and Laser Beam, Dalian University of Technology (China); Wu Aimin [Laboratory of Material Modification by Ion, Electron, and Laser Beam, Dalian University of Technology (China); Xu Jiujun [Institute of Materials and Technology, Dalian Maritime University (China)

    2005-12-15

    Electron beam radiation has been widely used to modify the surface properties of materials such as metals, ceramics, and glasses. However, a few investigations of surface topology of glasses after electron irradiation can be found. In contrast to the surface cracking by bending, indentation, and thermally induced stress in soda lime glasses a 2 {mu}s pulsed high-current electron beam was used to modify the surfaces of soda lime glass. Surface topology of irradiated samples was studied by using traditional optical microscopy and atomic force microscopy. Parallel to and perpendicular to surface cracks were observed. The depth of crack can be obtained by electron penetration, Newton's ring and AFM. The stress to produce the crack by electron radiation was calculated using three obtained depths. The observed surface crack is explained in terms of radiation-induced thermal stress and high local electric field-induced by deposited charges from pulsed electrons.

  6. On the ultrafast kinetics of the energy and electron transfer reactions in photosystem I

    Energy Technology Data Exchange (ETDEWEB)

    Slavov, Chavdar Lyubomirov

    2009-07-09

    The subject of the current work is one of the main participants in the light-dependent phase of oxygenic photosynthesis, Photosystem I (PS I). This complex carries an immense number of cofactors: chlorophylls (Chl), carotenoids, quinones, etc, which together with the protein entity exhibit several exceptional properties. First, PS I has an ultrafast light energy trapping kinetics with a nearly 100% quantum efficiency. Secondly, both of the electron transfer branches in the reaction center are suggested to be active. Thirdly, there are some so called 'red' Chls in the antenna system of PS I, absorbing light with longer wavelengths than the reaction center. These 'red' Chls significantly modify the trapping kinetics of PS I. The purpose of this thesis is to obtain better understanding of the above-mentioned, specific features of PS I. This will not merely cast more light on the mechanisms of energy and electron transfer in the complex, but also will contribute to the future developments of optimized artificial light-harvesting systems. In the current work, a number of PS I complexes isolated from different organisms (Thermosynechococcus elongatus, Chlamydomonas reinhardtii, Arabidopsis thaliana) and possessing distinctive features (different macroorganisation, monomers, trimers, monomers with a semibelt of peripheral antenna attached; presence of 'red' Chls) is investigated. The studies are primarily focused on the electron transfer kinetics in each of the cofactor branches in the PS I reaction center, as well as on the effect of the antenna size and the presence of 'red' Chls on the trapping kinetics of PS I. These aspects are explored with the help of several ultrafast optical spectroscopy methods: (i) time-resolved fluorescence ? single photon counting and synchroscan streak camera; and (ii) ultrafast transient absorption. Physically meaningful information about the molecular mechanisms of the energy trapping in PS I is

  7. Computed Potential Energy Surfaces and Minimum Energy Pathways for Chemical Reactions

    Science.gov (United States)

    Walch, Stephen P.; Langhoff, S. R. (Technical Monitor)

    1994-01-01

    Computed potential energy surfaces are often required for computation of such parameters as rate constants as a function of temperature, product branching ratios, and other detailed properties. For some dynamics methods, global potential energy surfaces are required. In this case, it is necessary to obtain the energy at a complete sampling of all the possible arrangements of the nuclei, which are energetically accessible, and then a fitting function must be obtained to interpolate between the computed points. In other cases, characterization of the stationary points and the reaction pathway connecting them is sufficient. These properties may be readily obtained using analytical derivative methods. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method to obtain accurate energetics, gives usefull results for a number of chemically important systems. The talk will focus on a number of applications including global potential energy surfaces, H + O2, H + N2, O(3p) + H2, and reaction pathways for complex reactions, including reactions leading to NO and soot formation in hydrocarbon combustion.

  8. Test calculations of photoneutrons emission from surface of uranium sphere irradiated by 28 MeV electrons

    CERN Document Server

    Blokhin, A I

    2001-01-01

    In this paper the results of physical verification for the BOFOD photonuclear data files are reported, available for the uranium isotopes U sup 2 sup 3 sup 5 , U sup 2 sup 3 sup 8. These results were compared with calculated data by the parameterization driven model of photonuclear reaction and experimental data. Experimental data of photoneutron yields from surface of uranium sphere irradiated by 28 MeV electrons are used for a verification. Both calculations have been carried out with the RTS and T general purpose Monte Carlo code with detailed electron-photon-nucleon transport simulation using the ENDF/B-VI and EPDL evaluated data libraries.

  9. Ultrafast electron crystallography of the cooperative reaction path in vanadium dioxide

    Directory of Open Access Journals (Sweden)

    Ding-Shyue Yang

    2016-05-01

    Full Text Available Time-resolved electron diffraction with atomic-scale spatial and temporal resolution was used to unravel the transformation pathway in the photoinduced structural phase transition of vanadium dioxide. Results from bulk crystals and single-crystalline thin-films reveal a common, stepwise mechanism: First, there is a femtosecond V−V bond dilation within 300 fs, second, an intracell adjustment in picoseconds and, third, a nanoscale shear motion within tens of picoseconds. Experiments at different ambient temperatures and pump laser fluences reveal a temperature-dependent excitation threshold required to trigger the transitional reaction path of the atomic motions.

  10. Environmental Transmission Electron Microscopy Study of Diesel Carbon Soot Combustion under Simulated Catalytic-Reaction Conditions.

    Science.gov (United States)

    Mori, Kohsuke; Watanabe, Keitaro; Sato, Takeshi; Yamashita, Hiromi

    2015-05-18

    Environmental transmission electron microscopy (ETEM) is used to monitor the catalytic combustion of diesel carbon soot upon exposure to molecular oxygen at elevated temperatures by using a gas-injection specimen heating holder. The reaction conditions simulated in the ETEM experiments reconstruct real conditions effectively. This study demonstrated for the first time that soot combustion occurs at the soot-catalyst interface for both Ag/CeO2 and Cu/BaO/La2 O3 catalysts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Study on the surface electronic properties of Li-containing solids

    Energy Technology Data Exchange (ETDEWEB)

    Matsuura, Fumio; Suzuki, Atsushi; Yamaguchi, Kenji; Yamawaki, M. [Tokyo Univ. (Japan)

    1998-03-01

    The electronic state of Li{sub 2}O surface will be modified by absorption and/or desorption of chemically-active species, such as H{sub 2} and H{sub 2}O. The reactions induced by these species will involve some point defects in the solid. Whereas the high temperature Kelvin probe has proven to be quite effective in obtaining information on the surface reactions between gas and solid, an attempt is being made to incorporate numerical calculation to obtain further information which may not be easily done by experiments. The code employed in the present study is `CRYSTAL`, which employs a self-consistent-field Hartree-Fock method. As a preliminary study, we tried to calculate the change of Fermi Energy as a function of the density of oxygen vacancy. The results revealed that the greater the density of oxygen vacancy, the larger the Fermi Energy of Li{sub 2}O, which was consistent with the experimental results obtained by high temperature Kelvin probe. (author)

  12. Electronic Structure of the Perylene / Zinc Oxide Interface: A Computational Study of Photoinduced Electron Transfer and Impact of Surface Defects

    KAUST Repository

    Li, Jingrui

    2015-07-29

    The electronic properties of dye-sensitized semiconductor surfaces consisting of pery- lene chromophores chemisorbed on zinc oxide via different spacer-anchor groups, have been studied at the density-functional-theory level. The energy distributions of the donor states and the rates of photoinduced electron transfer from dye to surface are predicted. We evaluate in particular the impact of saturated versus unsaturated aliphatic spacer groups inserted between the perylene chromophore and the semiconductor as well as the influence of surface defects on the electron-injection rates.

  13. Quantum-kinetic modeling of electron release in low-energy surface collisions of atoms and molecules

    Energy Technology Data Exchange (ETDEWEB)

    Marbach, Johannes

    2012-09-20

    In this work we present a theoretical description of electron release in the collision of atomic and molecular projectiles with metallic and especially dielectric surfaces. The associated electron yield, the secondary electron emission coefficient, is an important input parameter for numerical simulations of dielectric barrier discharges and other bounded low-temperature gas discharges. The available reference data for emission coefficients is, however, very sparse and often uncertain, especially for molecular projectiles. With the present work we aim to contribute to the filling of these gaps by providing a flexible and easy-to-use model that allows for a convenient calculation of the emission coefficient and related quantities for a wide range of projectile-surface systems and the most dominant reaction channels.

  14. FAST MONTE CARLO SIMULATION METHODS FOR BIOLOGICAL REACTION-DIFFUSION SYSTEMS IN SOLUTION AND ON SURFACES.

    Science.gov (United States)

    Kerr, Rex A; Bartol, Thomas M; Kaminsky, Boris; Dittrich, Markus; Chang, Jen-Chien Jack; Baden, Scott B; Sejnowski, Terrence J; Stiles, Joel R

    2008-10-13

    Many important physiological processes operate at time and space scales far beyond those accessible to atom-realistic simulations, and yet discrete stochastic rather than continuum methods may best represent finite numbers of molecules interacting in complex cellular spaces. We describe and validate new tools and algorithms developed for a new version of the MCell simulation program (MCell3), which supports generalized Monte Carlo modeling of diffusion and chemical reaction in solution, on surfaces representing membranes, and combinations thereof. A new syntax for describing the spatial directionality of surface reactions is introduced, along with optimizations and algorithms that can substantially reduce computational costs (e.g., event scheduling, variable time and space steps). Examples for simple reactions in simple spaces are validated by comparison to analytic solutions. Thus we show how spatially realistic Monte Carlo simulations of biological systems can be far more cost-effective than often is assumed, and provide a level of accuracy and insight beyond that of continuum methods.

  15. Signal Amplification by Enzymatic Reaction in an Immunosensor Based on Localized Surface Plasmon Resonance (LSPR

    Directory of Open Access Journals (Sweden)

    Yong-Beom Shin

    2010-03-01

    Full Text Available An enzymatic reaction was employed as a means to enhance the sensitivity of an immunosensor based on localized surface plasmon resonance (LSPR. The reaction occurs after intermolecular binding between an antigen and an antibody on gold nano-island (NI surfaces. For LSPR sensing, the gold NI surface was fabricated on glass substrates using vacuum evaporation and heat treatment. The interferon-g (IFN-g capture antibody was immobilized on the gold NIs, followed by binding of IFN-g to the antibody. Subsequently, a biotinylated antibody and a horseradish peroxidase (HRP conjugated with avidin were simultaneously introduced. A solution of 4-chloro-1-naphthol (4-CN was then used for precipitation; precipitation was the result of the enzymatic reaction catalyzed the HRP on gold NIs. The LSPR spectra were obtained after each binding process. Using this method, the enzyme-catalyzed precipitation reaction on the gold NI surface was found to effectively amplify the change in the signal of the LSPR immunosensor after intermolecular binding.

  16. Surface Functionalization by Strain-Promoted Alkyne-Azide Click Reactions

    NARCIS (Netherlands)

    Manova, R.K.; Beek, van T.A.; Zuilhof, H.

    2011-01-01

    Clicks without Cu: There is a growing demand for reproducible site-specific functionalization of surfaces with biomolecules without introduction of unwanted groups or catalysts, as they may interfere with later applications. The title reactions (see picture) could fulfill these requirements, and

  17. The Hydrated Electron at the Surface of Neat Liquid Water Appears To Be Indistinguishable from the Bulk Species.

    Science.gov (United States)

    Coons, Marc P; You, Zhi-Qiang; Herbert, John M

    2016-08-31

    Experiments have suggested that the aqueous electron, e(-)(aq), may play a significant role in the radiation chemistry of DNA. A recent measurement of the energy (below vacuum level) of the putative "interfacial" hydrated electron at the water/vacuum interface, performed using liquid microjet photoelectron spectroscopy, has been interpreted to suggest that aqueous electrons at the water/biomolecule interface may possess the appropriate energetics to induce DNA strand breaks, whereas e(-)(aq) in bulk water lies too far below the vacuum level to induce such reactions. Other such experiments, however, find no evidence of a long-lived feature at low binding energy. We employ a variety of computational strategies to demonstrate that the energetics of the hydrated electron at the surface of neat liquid water are not significantly different from those of e(-)(aq) in bulk water and as such are incompatible with dissociative electron attachment reactions in DNA. We furthermore suggest that no stable interfacial species may exist at all, consistent with the interpretation of certain surface-sensitive spectroscopy measurements, and that even if a short-lived, metastable species does exist at the vacuum/water interface, it would be extremely difficult to distinguish, experimentally, from e(-)(aq) in bulk water, using either optical absorption or photoelectron spectroscopy.

  18. The Diels-Alder Cycloaddition Reaction of Substituted Hemifullerenes with 1,3-Butadiene: Effect of Electron-Donating and Electron-Withdrawing Substituents.

    Science.gov (United States)

    Mojica, Martha; Méndez, Francisco; Alonso, Julio A

    2016-02-12

    The Diels-Alder (DA) reaction provides an attractive route to increase the number of six member rings in substituted Polycyclic Aromatic Hydrocarbons (PAHs). The density functional theory (DFT) B3LYP method has been used in this work to inquire if the substitution of H over the edge of triindenetriphenylene (pristine hemifullerene 1) and pentacyclopentacorannulene (pristine hemifullerene 2), could improve the DA cycloaddition reaction with 1,3-butadiene. The substituents tested include electron-donating (NH₂, OMe, OH, Me, i-Pr) and electron-withdrawing groups (F, COOH, CF₃, CHO, CN, NO₂). The electronic, kinetic and thermodynamic parameters of the DA reactions of the substituted hemifullerenes with 1,3-butadiene have been analyzed. The most promising results were obtained for the NO₂ substituent; the activation energy barriers for reactions using this substituent were lower than the barriers for the pristine hemifullerenes. This leads us to expect that the cycloadditions to a starting fullerene fragment will be possible.

  19. Visible-Light-Irradiated Graphitic Carbon Nitride Photocatalyzed Diels-Alder Reactions with Dioxygen as Sustainable Mediator for Photoinduced Electrons.

    Science.gov (United States)

    Zhao, Yubao; Antonietti, Markus

    2017-08-01

    Photocatalytic Diels-Alder (D-A) reactions with electron rich olefins are realized by graphitic carbon nitride (g-C3 N4 ) under visible-light irradiation and aerobic conditions. This heterogeneous photoredox reaction system is highly efficient, and the apparent quantum yield reaches a remarkable value of 47 % for the model reaction. Dioxygen plays a critical role as electron mediator, which is distinct from the previous reports in the homogeneous RuII complex photoredox system. Moreover, the reaction intermediate vinylcyclobutane is captured and monitored during the reaction, serving as a direct evidence for the proposed reaction mechanism. The cycloaddition process is thereby determined to be the combination of direct [4+2] cycloaddition and [2+2] cycloaddition followed by photocatalytic rearrangement of the vinylcyclobutane intermediate. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Changes in the surface electronic states of semiconductor fine particles induced by high energy ion irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Yamaki, Tetsuya; Asai, Keisuke; Ishigure, Kenkichi [Tokyo Univ. (Japan); Shibata, Hiromi

    1997-03-01

    The changes in the surface electronic states of Q-sized semiconductor particles in Langmuir-Blodgett (LB) films, induced by high energy ion irradiation, were examined by observation of ion induced emission and photoluminescence (PL). Various emission bands attributed to different defect sites in the band gap were observed at the initial irradiation stage. As the dose increased, the emissions via the trapping sites decreased in intensity while the band-edge emission developed. This suggests that the ion irradiation would remove almost all the trapping sites in the band gap. The low energy emissions, which show a multiexponential decay, were due to a donor-acceptor recombination between the deeply trapped carriers. It was found that the processes of formation, reaction, and stabilization of the trapping sites would predominantly occur under the photooxidizing conditions. (author)

  1. Faraday efficiency and mechanism of electrochemical surface reactions: CO2 reduction and H2 formation on Pt(111).

    Science.gov (United States)

    Hussain, Javed; Jónsson, Hannes; Skúlason, Egill

    2016-12-22

    An atomic scale model of the electrical double layer is used to calculate the mechanism and rate of electrochemical reduction of CO2 as well as H2 formation at a Pt(111) electrode. The water layer contains solvated protons and the electrode has excess electrons at the surface. Density functional theory within the generalized gradient approximation is used to describe the electronic structure while the mechanism and activation energy of the various elementary reactions is obtained by calculating minimum energy paths using the nudged elastic band method. The applied electrical potential is deduced from the calculated work function. The optimal reaction mechanism for CO2 reduction to either methane or methanol is found and the estimated rate compared with that of the competing reaction, H2 formation. When the free energy of only the intermediates and reactants is taken into account, not the activation energy, Pt(111) would seem to be a good electrocatalyst for CO2 reduction, significantly better than Cu(111). This, however, contradicts experimental findings. Detailed calculations reported here show that the activation energy for CO2 reduction is high for both Heyrovsky and Tafel mechanisms on Pt(111) in the relevant range of applied potential. The rate-limiting step of the Heyrovsky mechanism, *COOH + H+ + e- → *CO + H2O, is estimated to have an activation energy of 0.95 eV at -0.9 V vs. standard hydrogen electrode. Under the same conditions, the activation energy for H2 formation is estimated to be only 0.5 eV. This explains why attempts to reduce CO2 using platinum electrodes have produced only H2. A comparison is made with analogous results for Cu(111) [J. Hussain et al., Procedia Comput. Sci., 2015, 51, 1865] where a reaction mechanism with low activation energy for CO2 electroreduction to methane was identified. The difference between the two electrocatalysts is discussed.

  2. Mechanisms before Reactions: A Mechanistic Approach to the Organic Chemistry Curriculum Based on Patterns of Electron Flow

    Science.gov (United States)

    Flynn, Alison B.; Ogilvie, William W.

    2015-01-01

    A significant redesign of the introductory organic chemistry curriculum at the authors' institution is described. There are two aspects that differ greatly from a typical functional group approach. First, organic reaction mechanisms and the electron-pushing formalism are taught before students have learned a single reaction. The conservation of…

  3. Reaction pathways of model compounds of biomass-derived oxygenates on Fe/Ni bimetallic surfaces

    Science.gov (United States)

    Yu, Weiting; Chen, Jingguang G.

    2015-10-01

    Controlling the activity and selectivity of converting biomass-derivatives to fuels and valuable chemicals is critical for the utilization of biomass feedstocks. There are primarily three classes of non-food competing biomass, cellulose, hemicellulose and lignin. In the current work, glycolaldehyde, furfural and acetaldehyde are studied as model compounds of the three classes of biomass-derivatives. Monometallic Ni(111) and monolayer (ML) Fe/Ni(111) bimetallic surfaces are studied for the reaction pathways of the three biomass surrogates. The ML Fe/Ni(111) surface is identified as an efficient surface for the conversion of biomass-derivatives from the combined results of density functional theory (DFT) calculations and temperature programmed desorption (TPD) experiments. A correlation is also established between the optimized adsorption geometry and experimental reaction pathways. These results should provide helpful insights in catalyst design for the upgrading and conversion of biomass.

  4. Probing the Surface of Platinum during the Hydrogen Evolution Reaction in Alkaline Electrolyte

    Energy Technology Data Exchange (ETDEWEB)

    Stoerzinger, Kelsey A. [Physical; Favaro, Marco [Advanced; Joint; Chemical; Ross, Philip N. [Materials; Yano, Junko [Joint; Molecular; Liu, Zhi [State; Division; Hussain, Zahid [Advanced; Crumlin, Ethan J. [Advanced; Joint Center

    2017-11-02

    Understanding the surface chemistry of electrocatalysts in operando can bring insight into the reaction mechanism, and ultimately the design of more efficient materials for sustainable energy storage and conversion. Recent progress in synchrotron based X-ray spectroscopies for in operando characterization allows us to probe the solid/liquid interface directly while applying an external potential, applied here to the model system of Pt in alkaline electrolyte for the hydrogen evolution reaction (HER). We employ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to identify the oxidation and reduction of Pt-oxides and hydroxides on the surface as a function of applied potential, and further assess the potential for hydrogen adsorption and absorption (hydride formation) during and after the HER. This new window into the surface chemistry of Pt in alkaline brings insight into the nature of the rate limiting step, the extent of H ad/absorption and it’s persistence at more anodic potentials.

  5. Surprisingly Long-Lived Ascorbyl Radicals in Acetonitrile: Concerted Proton-Electron Transfer Reactions and Thermochemistry

    Science.gov (United States)

    Warren, Jeffrey J.; Mayer, James M.

    2008-01-01

    Proton-coupled electron transfer (PCET) reactions and thermochemistry of 5,6-isopropylidene ascorbate (iAscH−) have been examined in acetonitrile solvent.iAscH− is oxidized by 2,4,6-tBu3C6H2O• and by excess TEMPO• to give the corresponding 5,6-isopropylidene ascorbyl radical anion (iAsc•−), which persists for hours at 298 K in dry MeCN solution. The stability of iAsc•− is surprising in light of the transience of the ascorbyl radical in aqueous solutions, and is due to the lack of the protons needed for radical disproportionation. A concerted proton-electron transfer (CPET) mechanism is indicated for the reactions of iAscH−. Redox potential, pKa and equilibrium measurements define the thermochemical landscape for 5,6-isopropylidene ascorbic acid and its derivatives in MeCN. These measurements give an O–H bond dissociation free energy (BDFE) for iAscH−of 65.4 ± 1.5 kcal mol−1 in MeCN. Similar studies on underivatized ascorbate indicate a BDFE of 67.8 ± 1.2 kcal mol−1. These values are much lower than the aqueous BDFE for ascorbate of 74.0 ± 1.5 kcal mol−1 derived from reported data. PMID:18505256

  6. Oxygen dependency of one-electron reactions generating ascorbate radicals and hydrogen peroxide from ascorbic acid.

    Science.gov (United States)

    Boatright, William L

    2016-04-01

    The effect of oxygen on the two separate one-electron reactions involved in the oxidation of ascorbic acid was investigated. The rate of ascorbate radical (Asc(-)) formation (and stability) was strongly dependent on the presence of oxygen. A product of ascorbic acid oxidation was measurable levels of hydrogen peroxide, as high as 32.5 μM from 100 μM ascorbic acid. Evidence for a feedback mechanism where hydrogen peroxide generated during the oxidation of ascorbic acid accelerates further oxidation of ascorbic acid is also presented. The second one-electron oxidation reaction of ascorbic acid leading to the disappearance of Asc(-) was also strongly inhibited in samples flushed with argon. In the range of 0.05-1.2 mM ascorbic acid, maximum levels of measurable hydrogen peroxide were achieved with an initial concentration of 0.2 mM ascorbic acid. Hydrogen peroxide generation was greatly diminished at ascorbic acid levels of 0.8 mM or above. Copyright © 2015 Elsevier Ltd. All rights reserved.

  7. Use of molecular beams for kinetic measurements of chemical reactions on solid surfaces

    Science.gov (United States)

    Zaera, Francisco

    2017-05-01

    In this review we survey the contributions that molecular beam experiments have provided to our understanding of the dynamics and kinetics of chemical interactions of gas molecules with solid surfaces. First, we describe the experimental details of the different instrumental setups and approaches available for the study of these systems under the ultrahigh vacuum conditions and with the model planar surfaces often used in modern surface-science experiments. Next, a discussion is provided of the most important fundamental aspects of the dynamics of chemical adsorption that have been elucidated with the help of molecular beam experiments, which include the development of potential energy surfaces, the determination of the different channels for energy exchange between the incoming molecules and the surface, the identification of adsorption precursor states, the understanding of dissociative chemisorption, the determination of the contributions of corrugation, steps, and other structural details of the surface to the adsorption process, the effect to molecular steering, the identification of avenues for assisting adsorption, and the molecular details associated with the kinetics of the uptake of adsorbates as a function of coverage. We follow with a summary of the work directed at the determination of kinetic parameters and mechanistic details of surface reactions associated with catalysis, mostly those promoted by late transition metals. This discussion we initiate with an overview of what has been learned about simple bimolecular reactions such as the oxidation of CO and H2 with O2 and the reaction of CO with NO, and continue with the review of the studies of more complex systems such as the oxidation of alcohols, the conversion of organic acids, the hydrogenation and isomerization of olefins, and the oxidative activation of alkanes under conditions of short contact times. Sections 6 and 7 of this review deal with the advances made in the use of molecular beams with

  8. Reaction of a hydrated electron with gentamycin and collagen -a pulse radiolysis study

    Energy Technology Data Exchange (ETDEWEB)

    Pietrucha, K. [Technical Univ., Lodz (Poland). Inst. of Applied Radiation Chemistry; Gora, L. [Worcester Poltechnic Inst., MA (United States). Dept. of Chemical Engineering; Doillon, C.J. [Laval Univ., Quebec, PQ (Canada). Dept. of Surgery]|[Saint-Francois d`Assise Hospital, Quebec (Canada)

    1996-01-01

    The reactions of a hydrated electron (e{sub aq}{sup -}) with aminoglycoside antibiotic gentamycin and collagen in aqueous medium at different pH have been investigated employing a pulse radiolysis technique. The pseudo-first order equation of reaction kinetics was used to give an accurate description of the decay of e{sub aq}{sup -} in gentamycin solutions. The rate constant of the e{sub aq}{sup -}decay in collagen solutions was high and reached 3.2 x 10{sup 10} M{sup -1} s{sup -1}. The rate constants for the reaction of the e{sub aq}{sup -}with gentamycin were found to be influenced by pH, decreasing with the deprotonation of the -NH{sub 3} groups, while for pH > pK{sub a} which for gentamycin is equal to 7.8, the rate constant was unchanged. These observations suggest that when the amino groups are protonated, reductive deamination occurs, but for unprotonated non-reactive amino groups, a radical anion is formed on the glycoside moiety. (Author).

  9. Chemical electron-transfer reactions in electrospray mass spectrometry: Effective oxidation potentials of electron-transfer reagents in methylene chloride

    Energy Technology Data Exchange (ETDEWEB)

    Van Berkel, G.J.; Zhou, F. (Oak Ridge National Lab., TN (United States))

    1994-10-15

    Cyclic voltammetry (CV), UV/visible absorption spectroscopy, and electrospray mass spectrometry (ES-MS) are used in conjunction to study the mono- and /or dications produced in solution from the reaction of three model compounds ([beta]-carotene, cobalt(II) octaethylporphyrin (Co[sup II]OEP), nickel(II) octaethylporphyrin (Ni[sup II]OEP), in three different solvent/electron-transfer reagent systems (methylene chloride/0.1% trifluoroacetic acid (TFA) (v/v), methylene chloride/0.1% TFA/2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) v/v/200 [mu]M), methylene chloride/0.1% TFA/0.1% antimony pentafluoride (SbF[sub 5]) (v/v/v)). The reactions were carried out on-line with ES-MS by means of flow injection. Correlation of the CV data for these analytes with the ionic species determined to be in the solution on the basis of UV/visible absorption spectra and/or on the basis of the ionic species observed in the gas phase by ES-MS, along with our previously published data on these solvent/reagent systems, allowed an effective oxidation potential range, E, to be assigned to these solvent/reagent systems: methylene chloride/0.1% TFA (v/v), 0.6V [le] E[sub TFA] < 0.7 V; methylene chloride/0.1% TFA/DDQ (v/v/200 [mu]M), 0.8 [le] E[sub TFA/DDQ] < 1.0 V; methylene chloride/0.1% TFA/0.1% SbF[sub 5] (v/v/v), 1.3 [le] E[sub TFA/SbF(5)] < 1.5. 40 refs., 7 figs.

  10. Room temperature 2D electron gas at the (001)-SrTiO3 surface

    Science.gov (United States)

    Gonzalez, Sara; Mathieu, Claire; Copie, Olivier; Feyer, Vitaliy; Schneider, Claus M.; Barrett, Nicholas

    2017-10-01

    Functional oxides and phenomena such as a 2D electron gas (2DEG) at oxide interfaces represent potential technological breakthroughs for post-CMOS electronics. Non-invasive techniques are required to study the surface chemistry and electronic structure, underlying their often unique electrical properties. The sensitivity of photoemission electron microscopy to chemistry and electronic structure makes it an invaluable tool for probing the near surface region of microscopic regions and domains of functional materials. We present results demonstrating a room temperature 2DEG at the (001)-SrTiO3 surface. The 2DEG is switched on by soft X-ray irradiation.

  11. Microstructure and hardness studies of electron beam melted surface of mild steel

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad, M., E-mail: maqomer@yahoo.com [Physics Division, Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad (Pakistan); Haq, M.A.; Ahmed, Ejaz; Ali, G.; Akhter, J.I. [Physics Division, Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad (Pakistan); Iqbal, M. [National Institute of Lasers and Optronics, Nilore, Islamabad (Pakistan)

    2009-04-15

    Electron beam surface melting of mild steel with the addition of Ni and SiC is carried out to improve its surface properties. Microstructure of the electron beam molten surface is characterized by scanning electron microscope. Phases are determined using energy dispersive spectroscopy and X-ray diffraction techniques. During electron beam melting SiC dissociated partially, interacted with liquid alloy and resulted in martensitic phases after solidification. Maximum hardness is achieved in electron beam molten zone. It is concluded that the formation of martensitic phase and the presence of Si and Ni in the solid solution are responsible for increase in hardness in the molten zone.

  12. Electro-deposition of Pd on carbon paper and Ni foam via surface limited redox-replacement reaction for oxygen reduction reaction

    CSIR Research Space (South Africa)

    Modibedi, RM

    2014-05-01

    Full Text Available Pd nanostructured catalysts were electrodeposited by surface-limited redox replacement reactions usingthe electrochemical atomic layer deposition technique. Carbon paper and Ni foam were used as substratesfor the electrodeposition of the metal...

  13. Secondary electron emission characteristics of ion-textured copper and high-purity isotropic graphite surfaces

    Science.gov (United States)

    Curren, A. N.; Jensen, K. A.

    1984-01-01

    Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield for untreated and ion textured oxygen free high conductivity copper and untreated and ion textured high purity isotropic graphite surfaces are presented for a range of primary electron beam energies and beam impingement angles. This investigation was conducted to provide information that would improve the efficiency of multistage depressed collectors (MDC's) for microwave amplifier traveling wave tubes in space communications and aircraft applications. For high efficiency, MDC electrode surfaces must have low secondary electron emission characteristics. Although copper is a commonly used material for MDC electrodes, it exhibits relatively high levels of secondary electron emission if its surface is not treated for emission control. Recent studies demonstrated that high purity isotropic graphite is a promising material for MDC electrodes, particularly with ion textured surfaces. The materials were tested at primary electron beam energies of 200 to 2000 eV and at direct (0 deg) to near grazing (85 deg) beam impingement angles. True secondary electron emission and relative reflected primary electron yield characteristics of the ion textured surfaces were compared with each other and with those of untreated surfaces of the same materials. Both the untreated and ion textured graphite surfaces and the ion treated copper surface exhibited sharply reduced secondary electron emission characteristics relative to those of untreated copper. The ion treated graphite surface yielded the lowest emission levels.

  14. Asymmetric recombination and electron spin relaxation in the semiclassical theory of radical pair reactions

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, Alan M.; Manolopoulos, David E.; Hore, P. J. [Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ (United Kingdom)

    2014-07-28

    We describe how the semiclassical theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting semiclassical theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene triad containing considerably more nuclear spins which has recently been used to establish a “proof of principle” for the operation of a chemical compass [K. Maeda, K. B. Henbest, F. Cintolesi, I. Kuprov, C. T. Rodgers, P. A. Liddell, D. Gust, C. R. Timmel, and P. J. Hore, Nature (London) 453, 387 (2008)]. We find in particular that the intriguing biphasic behaviour that has been observed in the effect of an Earth-strength magnetic field on the time-dependent survival probability of the photo-excited C{sup ·+}PF{sup ·−} radical pair arises from a delicate balance between its asymmetric recombination and the relaxation of the electron spin in the carotenoid radical.

  15. Productions of Volatile Organic Compounds (VOCs) in Surface Waters from Reactions with Atmospheric Ozone

    Science.gov (United States)

    Hopkins, Frances; Bell, Thomas; Yang, Mingxi

    2017-04-01

    Ozone (O3) is a key atmospheric oxidant, greenhouse gas and air pollutant. In marine environments, some atmospheric ozone is lost by reactions with aqueous compounds (e.g. dissolved organic material, DOM, dimethyl sulfide, DMS, and iodide) near the sea surface. These reactions also lead to formations of volatile organic compounds (VOCs). Removal of O3 by the ocean remains a large uncertainty in global and regional chemical transport models, hampering coastal air quality forecasts. To better understand the role of the ocean in controlling O3 concentrations in the coastal marine atmosphere, we designed and implemented a series of laboratory experiments whereby ambient surface seawater was bubbled with O3-enriched, VOC-free air in a custom-made glass bubble equilibration system. Gas phase concentrations of a range of VOCs were monitored continuously over the mass range m/z 33 - 137 at the outflow of the bubble equilibrator by a proton transfer reaction - mass spectrometer (PTR-MS). Gas phase O3 was also measured at the input and output of the equilibrator to monitor the uptake due to reactions with dissolved compounds in seawater. We observed consistent productions of a variety of VOCs upon reaction with O3, notably isoprene, aldehydes, and ketones. Aqueous DMS is rapidly removed from the reactions with O3. To test the importance of dissolved organic matter precursors, we added increasing (milliliter) volumes of Emiliania huxleyi culture to the equilibrator filled with aged seawater, and observed significant linear increases in gas phase concentrations of a number of VOCs. Reactions between DOM and O3 at the sea-air interface represent a potentially significant source of VOCs in marine air and a sink of atmospheric O3.

  16. Computed Potential Energy Surfaces and Minimum Energy Pathway for Chemical Reactions

    Science.gov (United States)

    Walch, Stephen P.; Langhoff, S. R. (Technical Monitor)

    1994-01-01

    Computed potential energy surfaces are often required for computation of such observables as rate constants as a function of temperature, product branching ratios, and other detailed properties. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method with the Dunning correlation consistent basis sets to obtain accurate energetics, gives useful results for a number of chemically important systems. Applications to complex reactions leading to NO and soot formation in hydrocarbon combustion are discussed.

  17. Mesospheric removal of very long-lived greenhouse gases SF6 and CFC-115 by metal reactions, Lyman-α photolysis, and electron attachment.

    Science.gov (United States)

    Totterdill, Anna; Kovács, Tamás; Gómez Martín, Juan Carlos; Feng, Wuhu; Plane, John M C

    2015-03-12

    The fluorinated gases SF6 and C2F5Cl (CFC-115) are chemically inert with atmospheric lifetimes of many centuries which, combined with their strong absorption of IR radiation, results in unusually high global warming potentials. Very long lifetimes imply that mesospheric sinks could make important contributions to their atmospheric removal. In order to investigate this, the photolysis cross sections at the prominent solar Lyman-α emission line (121.6 nm), and the reaction kinetics of SF6 and CFC-115 with the neutral meteoric metal atoms Na, K, Mg, and Fe over large temperature ranges, were measured experimentally. The Na and K reactions exhibit significant non-Arrhenius behavior; quantum chemistry calculations of the potential energy surfaces for the SF6 reactions indicate that the Na and K reactions with SF6 are probably activated by vibrational excitation of the F-SF5 (v3) stretching mode. A limited set of kinetic measurements on Na + SF5CF3 are also presented. The atmospheric removal of these long-lived gases by a variety of processes is then evaluated. For SF6, the removal processes in decreasing order of importance are electron attachment, VUV photolysis, and reaction with K, Na, and H. For CFC-115, the removal processes in decreasing order of importance are reaction with O((1)D), VUV photolysis, and reaction with Na, K, and H.

  18. Selected specific rates of reactions of transients from water in aqueous solution. Hydrated electron, supplemental data. [Reactions with transients from water, with inorganic solutes, and with solutes

    Energy Technology Data Exchange (ETDEWEB)

    Ross, A.B.

    1975-06-01

    A compilation of rates of reactions of hydrated electrons with other transients and with organic and inorganic solutes in aqueous solution appeared in NSRDS-NBS 43, and covered the literature up to early 1971. This supplement includes additional rates which have been published through July 1973.

  19. Monte Carlo simulation of heavy ion induced kinetic electron emission from an Al surface

    CERN Document Server

    Ohya, K

    2002-01-01

    A Monte Carlo simulation is performed in order to study heavy ion induced kinetic electron emission from an Al surface. In the simulation, excitation of conduction band electrons by the projectile ion and recoiling target atoms is treated on the basis of the partial wave expansion method, and the cascade multiplication process of the excited electrons is simulated as well as collision cascade of the recoiling target atoms. Experimental electron yields near conventional threshold energies of heavy ions are simulated by an assumption of a lowering in the apparent surface barrier for the electrons. The present calculation derives components for electron excitations by the projectile ion, the recoiling target atoms and the electron cascades, from the calculated total electron yield. The component from the recoiling target atoms increases with increasing projectile mass, whereas the component from the electron cascade decreases. Although the components from the projectile ion and the electron cascade increase with...

  20. Mechanistic insights into the superoxide-cytochrome c reaction by lysine surface scanning.

    Science.gov (United States)

    Wegerich, Franziska; Giachetti, Andrea; Allegrozzi, Marco; Lisdat, Fred; Turano, Paola

    2013-04-01

    This study summarizes results which have been obtained by a mutational study of human cytochrome c. The protein can be used as a recognition element in analytical assays and biosensors for superoxide radicals since ferricytochrome c reacts with superoxide to form ferrocytochrome c and oxygen. Here lysine mutagenesis of the distal surface (i.e., of exposed residues around the Met80 axial ligand) of human cytochrome c was pursued to evaluate the effect of the surface charges on the reaction rate with the superoxide anion radical and on the redox properties of the heme protein. The latter feature is particularly relevant when the protein is immobilized on a negatively charged self-assembled monolayer on an electrode to be used as a biosensor. The observed effects of the mutations are rationalized through structural investigations based on solution NMR spectroscopy and computational analysis of the surface electrostatics. The results suggest the presence of a specific path that guides superoxide toward an efficient reaction site. Localized positive charges at the rim of the entry channel are effective in increasing the reaction rate, whereas diffused positive charges or charges far from this area are not effective or are even detrimental, resulting in a misguided approach of the anion to the protein surface.

  1. Development of a reaction cell for in-situ/operando studies of surface of a catalyst under a reaction condition and during catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Luan; Tao, Franklin, E-mail: franklin.tao.2011@gmail.com [Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, Kansas 66045 (United States)

    2016-06-15

    Tracking surface chemistry of a catalyst during catalysis is significant for fundamental understanding of catalytic performance of the catalyst since it allows for establishing an intrinsic correlation between surface chemistry of a catalyst at its working status and its corresponding catalytic performance. Ambient pressure X-ray photoelectron spectroscopy can be used for in-situ studies of surfaces of different materials or devices in a gas. To simulate the gaseous environment of a catalyst in a fixed-bed a flowing gaseous environment of reactants around the catalyst is necessary. Here, we report the development of a new flowing reaction cell for simulating in-situ study of a catalyst surface under a reaction condition in gas of one reactant or during catalysis in a mixture of reactants of a catalytic reaction. The homemade reaction cell is installed in a high vacuum (HV) or ultrahigh vacuum (UHV) environment of a chamber. The flowing gas in the reaction cell is separated from the HV or UHV environment through well sealings at three interfaces between the reaction cell and X-ray window, sample door and aperture of front cone of an energy analyzer. Catalyst in the cell is heated through infrared laser beam introduced through a fiber optics interfaced with the reaction cell through a homemade feedthrough. The highly localized heating on the sample holder and Au-passivated internal surface of the reaction cell effectively minimizes any unwanted reactions potentially catalyzed by the reaction cell. The incorporated laser heating allows a fast heating and a high thermal stability of the sample at a high temperature. With this cell, a catalyst at 800 °C in a flowing gas can be tracked readily.

  2. Electrostatic calculations of amino acid titration and electron transfer, Q-AQB-->QAQ-B, in the reaction center.

    OpenAIRE

    Beroza, P; Fredkin, D R; Okamura, M Y; Feher, G

    1995-01-01

    The titration of amino acids and the energetics of electron transfer from the primary electron acceptor (QA) to the secondary electron acceptor (QB) in the photosynthetic reaction center of Rhodobacter sphaeroides are calculated using a continuum electrostatic model. Strong electrostatic interactions between titrating sites give rise to complex titration curves. Glu L212 is calculated to have an anomalously broad titration curve, which explains the seemingly contradictory experimental results...

  3. Gadolinium cation (Gd+) reaction with O2: Potential energy surface mapped experimentally and with theory

    Science.gov (United States)

    Demireva, Maria; Armentrout, P. B.

    2017-05-01

    Guided ion beam tandem mass spectrometry is used to measure the kinetic energy dependent cross sections for reactions of the lanthanide metal gadolinium cation (Gd+) and GdO+ with O2 and for collision-induced dissociation (CID) of GdO2+ with Xe. Gd+ reacts with O2 in an exothermic and barrierless reaction to form GdO+ and O. GdO2+ is also formed in this reaction, but this product ion is formed in a sequential reaction, as verified by pressure dependent measurements and comparison with the results for the reaction of GdO+ with O2. The CID experiments of GdO2+ indicate the presence of two GdO2+ precursor ion populations, assigned to a weakly bound oxygen molecule adduct (Gd+-O2) and an inserted cyclic Gd+ dioxide species (O-Gd+-O). Analysis of the resulting product ion cross sections yields bond dissociation energies (BDEs, D0) for Gd+-O2 and OGd+-O, where the latter BDE is also independently measured in an exchange reaction between GdO+ and O2. The CID experiments also provide the energy of the barrier for the rearrangement of the Gd+-O2 adduct to the inserted O-Gd+-O structure (as identified by loss of a single oxygen atom). The thermochemistry measured here yields D0(OGd+-O) = 2.86 ± 0.08 eV, D0(Gd+-O2) = 0.75 ± 0.11 eV, and a barrier height relative to Gd+-O2 of 0.31 ± 0.07 eV. These data are sufficient to characterize in some detail the potential energy surface of the Gd+ reaction with O2 entirely from experiment. Theoretical calculations are performed for comparison with the experimental energetics and for further insight into the reaction mechanisms.

  4. Gadolinium cation (Gd(+)) reaction with O2: Potential energy surface mapped experimentally and with theory.

    Science.gov (United States)

    Demireva, Maria; Armentrout, P B

    2017-05-07

    Guided ion beam tandem mass spectrometry is used to measure the kinetic energy dependent cross sections for reactions of the lanthanide metal gadolinium cation (Gd(+)) and GdO(+) with O2 and for collision-induced dissociation (CID) of GdO2(+) with Xe. Gd(+) reacts with O2 in an exothermic and barrierless reaction to form GdO(+) and O. GdO2(+) is also formed in this reaction, but this product ion is formed in a sequential reaction, as verified by pressure dependent measurements and comparison with the results for the reaction of GdO(+) with O2. The CID experiments of GdO2(+) indicate the presence of two GdO2(+) precursor ion populations, assigned to a weakly bound oxygen molecule adduct (Gd(+)-O2) and an inserted cyclic Gd(+) dioxide species (O-Gd(+)-O). Analysis of the resulting product ion cross sections yields bond dissociation energies (BDEs, D0) for Gd(+)-O2 and OGd(+)-O, where the latter BDE is also independently measured in an exchange reaction between GdO(+) and O2. The CID experiments also provide the energy of the barrier for the rearrangement of the Gd(+)-O2 adduct to the inserted O-Gd(+)-O structure (as identified by loss of a single oxygen atom). The thermochemistry measured here yields D0(OGd(+)-O) = 2.86 ± 0.08 eV, D0(Gd(+)-O2) = 0.75 ± 0.11 eV, and a barrier height relative to Gd(+)-O2 of 0.31 ± 0.07 eV. These data are sufficient to characterize in some detail the potential energy surface of the Gd(+) reaction with O2 entirely from experiment. Theoretical calculations are performed for comparison with the experimental energetics and for further insight into the reaction mechanisms.

  5. Surface analysis of topmost layer of epitaxial layered oxide thin film: Application to delafossite oxide for oxygen evolution reaction

    Science.gov (United States)

    Toyoda, Kenji; Adachi, Hideaki; Miyata, Nobuhiro; Hinogami, Reiko; Orikasa, Yuki; Uchimoto, Yoshiharu

    2018-02-01

    Delafossite oxides (ABO2) have a layered structure with alternating layers of A and B elements, the topmost layer of which appears to determine their performance, such as the oxygen evolution reaction (OER) activity. In this study, we investigated the topmost layer of single-domain (0 0 1)-oriented AgCoO2 epitaxial thin film for potential use as an OER catalyst. The thin film was confirmed to possess OER activity at a level comparable to the catalyst in powder form. Atomic scattering spectroscopy revealed the topmost layer to be composed of CoO6 octahedra. In situ X-ray absorption spectroscopy showed that the oxidation of Co at the surface did not change under different potentials, which suggests that there is no valence fluctuation of Co in the stable CoO6 octahedral structure. However, the oxidation number of Co at the surface was lower than that in the bulk. Our density functional theoretical calculations also showed the Co atoms at the surface to have a slightly higher electron occupancy than those in the bulk, and suggests that the unoccupied t2g states of Co at the surface have an influence on OER activity.

  6. Vibrational Surface Electron-Energy-Loss Spectroscopy Probes Confined Surface-Phonon Modes

    Directory of Open Access Journals (Sweden)

    Hugo Lourenço-Martins

    2017-12-01

    Full Text Available Recently, two reports [Krivanek et al. Nature (London 514, 209 (2014NATUAS0028-083610.1038/nature13870, Lagos et al. Nature (London 543, 529 (2017NATUAS0028-083610.1038/nature21699] have demonstrated the amazing possibility to probe vibrational excitations from nanoparticles with a spatial resolution much smaller than the corresponding free-space phonon wavelength using electron-energy-loss spectroscopy (EELS. While Lagos et al. evidenced a strong spatial and spectral modulation of the EELS signal over a nanoparticle, Krivanek et al. did not. Here, we show that discrepancies among different EELS experiments as well as their relation to optical near- and far-field optical experiments [Dai et al. Science 343, 1125 (2014SCIEAS0036-807510.1126/science.1246833] can be understood by introducing the concept of confined bright and dark surface phonon modes, whose density of states is probed by EELS. Such a concise formalism is the vibrational counterpart of the broadly used formalism for localized surface plasmons [Ouyang and Isaacson Philos. Mag. B 60, 481 (1989PMABDJ1364-281210.1080/13642818908205921, García de Abajo and Aizpurua Phys. Rev. B 56, 15873 (1997PRBMDO0163-182910.1103/PhysRevB.56.15873, García de Abajo and Kociak Phys. Rev. Lett. 100, 106804 (2008PRLTAO0031-900710.1103/PhysRevLett.100.106804, Boudarham and Kociak Phys. Rev. B 85, 245447 (2012PRBMDO1098-012110.1103/PhysRevB.85.245447]; it makes it straightforward to predict or interpret phenomena already known for localized surface plasmons such as environment-related energy shifts or the possibility of 3D mapping of the related surface charge densities [Collins et al. ACS Photonics 2, 1628 (2015APCHD52330-402210.1021/acsphotonics.5b00421].

  7. Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low energy electron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, Joel Glenn [Univ. of California, Berkeley, CA (United States)

    2000-05-01

    The surface structures of NaCl(100), LiF(100) and alpha-MgCl2(0001) adsorbed on various metal single crystals have been determined by low energy electron diffraction (LEED). Thin films of these salts were grown on metal substrates by exposing the heated metal surface to a molecular flux of salt emitted from a Knudsen cell. This method of investigating thin films of insulators (ionic salts) on a conducting substrate (metal) circumvents surface charging problems that plagued bulk studies, thereby allowing the use of electron-based techniques to characterize the surface.

  8. Preparation of ferrocene-functionalized gold nanoparticles by primer extension reaction on the particle surface.

    Science.gov (United States)

    Takada, Tadao; Tochi, Takaaki; Nakamura, Mitsunobu; Yamana, Kazushige

    2014-06-15

    DNA molecules possessing multiple ferrocene (Fc) molecules as a redox active probe were prepared by the primer extension (PEX) reaction using a 2'-deoxyuridine-5'-triphosphate derivative in which Fc was connected to the C5-position of the uridine by a diethylene glycol linker. Gold nanoparticles (AuNP) covered with DNA possessing the Fc molecules were prepared by the PEX reaction on the surface. The AuNP-FcDNA conjugates exhibit a detectable electrochemical signal due to the Fc molecules. Possible application of the PEX reaction on AuNP is demonstrated for the detection of a single nucleotide mutation in the target DNA. Copyright © 2014 Elsevier Ltd. All rights reserved.

  9. Electron-transfer reactions of the reductase component of soluble methane monooxygenase from Methylococcus capsulatus (Bath).

    Science.gov (United States)

    Kopp, D A; Gassner, G T; Blazyk, J L; Lippard, S J

    2001-12-11

    Soluble methane monooxygenase (sMMO) catalyzes the hydroxylation of methane by dioxygen to afford methanol and water, the first step of carbon assimilation in methanotrophic bacteria. This enzyme comprises three protein components: a hydroxylase (MMOH) that contains a dinuclear nonheme iron active site; a reductase (MMOR) that facilitates electron transfer from NADH to the diiron site of MMOH; and a coupling protein (MMOB). MMOR uses a noncovalently bound FAD cofactor and a [2Fe-2S] cluster to mediate electron transfer. The gene encoding MMOR was cloned from Methylococcus capsulatus (Bath) and expressed in Escherichia coli in high yield. Purified recombinant MMOR was indistinguishable from the native protein in all aspects examined, including activity, mass, cofactor content, and EPR spectrum of the [2Fe-2S] cluster. Redox potentials for the FAD and [2Fe-2S] cofactors, determined by reductive titrations in the presence of indicator dyes, are FAD(ox/sq), -176 +/- 7 mV; FAD(sq/hq), -266 +/- 15 mV; and [2Fe-2S](ox/red), -209 +/- 14 mV. The midpoint potentials of MMOR are not altered by the addition of MMOH, MMOB, or both MMOH and MMOB. The reaction of MMOR with NADH was investigated by stopped-flow UV-visible spectroscopy, and the kinetic and spectral properties of intermediates are described. The effects of pH on the redox properties of MMOR are described and exploited in pH jump kinetic studies to measure the rate constant of 130 +/- 17 s(-)(1) for electron transfer between the FAD and [2Fe-2S] cofactors in two-electron-reduced MMOR. The thermodynamic and kinetic parameters determined significantly extend our understanding of the sMMO system.

  10. Influence of Surface and Bulk Water Ice on the Reactivity of a Water-forming Reaction

    Science.gov (United States)

    Lamberts, Thanja; Kästner, Johannes

    2017-09-01

    On the surface of icy dust grains in the dense regions of the interstellar medium, a rich chemistry can take place. Due to the low temperature, reactions that proceed via a barrier can only take place through tunneling. The reaction {{H}}+{{{H}}}2{{{O}}}2\\longrightarrow {{{H}}}2{{O}}+{OH} is such a case with a gas-phase barrier of ˜26.5 kJ mol-1. Still, the reaction is known to be involved in water formation on interstellar grains. Here, we investigate the influence of a water ice surface and of bulk ice on the reaction rate constant. Rate constants are calculated using instanton theory down to 74 K. The ice is taken into account via multiscale modeling, describing the reactants and the direct surrounding at the quantum mechanical level with density functional theory (DFT), while the rest of the ice is modeled on the molecular mechanical level with a force field. We find that H2O2 binding energies cannot be captured by a single value, but rather they depend on the number of hydrogen bonds with surface molecules. In highly amorphous surroundings, the binding site can block the routes of attack and impede the reaction. Furthermore, the activation energies do not correlate with the binding energies of the same sites. The unimolecular rate constants related to the Langmuir-Hinshelwood mechanism increase as the activation energy decreases. Thus, we provide a lower limit for the rate constant and argue that rate constants can have values up to two order of magnitude larger than this limit.

  11. Modification of hydroxylated alumina and silica surfaces using sequential reactions with dimethylzinc and n-alkanethiols

    Science.gov (United States)

    Boiadjiev, Vassil Iordanov

    2000-10-01

    This work demonstrates that it is possible to grow thin organic films chemically bound to hydroxylated alumina and silica surfaces by sequential adsorption of trimethylaluminum (TMA) and alcohols, and dimethylzinc and n-alkanethiols, at room temperature. The presence of the resulting alkoxide and thiolate species is demonstrated using infrared spectroscopy and, in the case of thiolates on silica, by nuclear magnetic resonance spectroscopy. The similarity between the reaction on high-surface area alumina and silica, and on planar surfaces allows the surface species to be identified in vacuo prior to attempting self-assembly on planar surfaces. Almost identical results obtained from chemical vapor deposition in vacuo and from sequential reaction in benzene solutions allow chemical grafting of low-vapor pressure, long-chain n-alkanethiols to the dimethylzinc-modified hydroxylated surfaces from solution. This is first studied on high-surface area silica substrates and then expanded to self-assembly on planar hydroxylated silicon substrate. The major reaction pathway for formation and thermal decomposition of aluminum alkoxide and Zn-bound ethanethiolate surface species on alumina and silica substrates is proposed based on the experimental results. It is suggested that initial adsorption of methanol on TMA-modified alumina covered by Al(CH3)2(ads), rapidly replaces a methyl by methoxy species at room temperature. Further reaction of methanol at ˜400 K replaces the second methyl species leading to Al(OCH3)2(ads) . This thermally decomposes on heating to yield primarily dimethyl ether and surface formate species. It is also very reactive with water and rapidly forms adsorbed alumina and methanol. Dimethylzinc reacts with hydroxylated alumina and silica at room temperature to form adsorbed monomethylzinc surface species and evolve methane. Temperature dependent studies reveal that these species are stable at room temperature and gradually decompose in vacuo. Adsorbed

  12. Combinatorial Density Functional Theory-Based Screening of Surface Alloys for the Oxygen Reduction Reaction

    DEFF Research Database (Denmark)

    Greeley, Jeffrey Philip; Nørskov, Jens Kehlet

    2009-01-01

    A density functional theory (DFT)-based, combinatorial search for improved oxygen reduction reaction (ORR) catalysts is presented. A descriptor-based approach to estimate the ORR activity of binary surface alloys, wherein alloying occurs only in the surface layer, is described, and rigorous......, potential-dependent computational tests of the stability of these alloys in aqueous, acidic environments are presented. These activity and stability criteria are applied to a database of DFT calculations on nearly 750 binary transition metal surface alloys; of these, many are predicted to be active...... for the ORR but, with few exceptions, they are found to be thermodynamically unstable in the acidic environments typical of low-temperature fuel cells. The results suggest that, absent other thermodynamic or kinetic mechanisms to stabilize the alloys, surface alloys are unlikely to serve as useful ORR...

  13. Extracellular Electron Uptake: Among Autotrophs and Mediated by Surfaces

    DEFF Research Database (Denmark)

    Tremblay, Pier-Luc; Angenent, Largus T.; Zhang, Tian

    2017-01-01

    Autotrophic microbes can acquire electrons from solid donors such as steel, other microbial cells, or electrodes. Based on this feature, bioprocesses are being developed for the microbial electrosynthesis (MES) of useful products from the greenhouse gas CO2. Extracellular electron-transfer mechan...

  14. Detection of submonolayer oxygen-18 on a gold surface by nuclear reaction analysis

    Energy Technology Data Exchange (ETDEWEB)

    Wielunski, L.S.; Kenny, M.J.; Wieczorek, L. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), Lindfield, NSW (Australia). Div. of Applied Physics

    1993-12-31

    A gold substrate is the preferred solid surface for formation of an organic self-assembled monolayer ( SAM ). Device fabrication process may require the gold film to be exposed to photolithographic processing and plasma treatment prior to molecular assembly. It has been observed that oxygen plasma treatment prevents the formation of SAMs; however, subsequent treatment with an argon plasma allows assembly of the organic monolayers. To understand the mechanisms involved, a plasma containing 98% {sup 18}O was used and the film surface was analysed using the {sup 18}O (p,{alpha}){sup 15}N nuclear reaction. 5 refs., 1 tab., 3 figs.

  15. Surface flashover performance of epoxy resin microcomposites improved by electron beam irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Yin; Min, Daomin [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China); Li, Shengtao, E-mail: stli@mail.xjtu.edu.cn [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China); Li, Zhen; Xie, Dongri [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China); Wang, Xuan [Key Laboratory of Engineering Dielectric and its Application, Ministry of Education, Harbin University of Science and Technology, Harbin 150040 (China); Lin, Shengjun [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China); Pinggao Group Company Ltd., State Grid High Voltage Switchgear Insulation Materials Laboratory, Pingdingshan 467001 (China)

    2017-06-01

    Highlights: • Epoxy resin microcomposites were irradiated by electron beam with energies of 10 and 20 keV. • Surface flashover voltage increase with the increase of electron beam energy. • Both the untreated and irradiated samples have two trap centers, which are labeled as shallow and deep traps. • Deposition energy in epoxy resin microcomposites increases with electron beam energy, and surface trap properties are determined by deposition energy. • The influence of surface conductivity and trap distribution on flashover voltage is discussed. - Abstract: The influencing mechanism of electron beam irradiation on surface flashover of epoxy resin/Al{sub 2}O{sub 3} microcomposite was investigated. Epoxy resin/Al{sub 2}O{sub 3} microcomposite samples with a diameter of 50 mm and a thickness of 1 mm were prepared. The samples were irradiated by electron beam with energies of 10 and 20 keV and a beam current of 5 μA for 5 min. Surface potential decay, surface conduction, and surface flashover properties of untreated and irradiated samples were measured. Both the decay rate of surface potential and surface conductivity decrease with an increase in the energy of electron beam. Meanwhile, surface flashover voltage increase. It was found that both the untreated and irradiated samples have two trap centers, which are labeled as shallow and deep traps. The increase in the energy and density of deep surface traps enhance the ability to capture primary emitted electrons. In addition, the decrease in surface conductivity blocks electron emission at the cathode triple junction. Therefore, electron avalanche at the interface between gas and an insulating material would be suppressed, eventually improving surface flashover voltage of epoxy resin microcomposites.

  16. Controlled silanization-amination reactions on the Ti6Al4V surface for biomedical applications.

    Science.gov (United States)

    Rodríguez-Cano, Abraham; Cintas, Pedro; Fernández-Calderón, María-Coronada; Pacha-Olivenza, Miguel-Ángel; Crespo, Lara; Saldaña, Laura; Vilaboa, Nuria; González-Martín, María-Luisa; Babiano, Reyes

    2013-06-01

    Formation of thin films on titanium alloys incorporating bioactive small molecules or macromolecules is a route to improve their biocompatibility. Aminoalkylsilanes are commonly employed as interface reagents that combine good adhesion properties with an amino tail group susceptible of further functionalization. This article introduces a reproducible methodology to obtain a cross-linked polymer-type brush structure of covalently-bonded aminoalkylsiloxane chains on Ti6Al4V. The experimental protocol can be fine-tuned to provide a high density of surface-coated amino groups (threshold value: 2.1±0.1×10(-8) mol cm(-2)) as proven by chemical and spectrophotometric analyses. Using a model reaction involving the condensation of 3-aminopropyltrimethoxysilane (APTMS) on Ti6Al4V alloy, we herein show the effects of reaction temperature, reaction time and solvent humidity on the composition and structure of the film. The stability of the resulting coating under physiological-like conditions as well as the possibility of surface re-silanization has also been evaluated. To verify if detrimental effects on the biological performance of the Ti6Al4V alloy were induced by this coverage, human primary osteoblasts behavior, Staphylococci adhesion and biofilm formation have been tested and compared to the Ti6Al4V oxidized surface. Reaction with trans-cinnamaldehyde has used in order to determine useful amino groups at aminosilanized surface, XPS and UV analyses of imino derivatives generated reveal that almost a 50% of these groups are actually available at the siloxane chains. Copyright © 2013 Elsevier B.V. All rights reserved.

  17. Novel reactions of one-electron oxidized radicals of selenomethionine in comparison with methionine.

    Science.gov (United States)

    Mishra, B; Sharma, A; Naumov, S; Priyadarsini, K I

    2009-05-28

    Pulse radiolysis studies on hydroxyl (*OH) radical reactions of selenomethionine (SeM), a selenium analogue of methionine, were carried out, and the resultant transient radical cations and their subsequent reactions have been reported. At pHSe*-OH radical adducts produced on reaction of SeM with *OH radical were converted to selenium centered radical cations (Se*+M), which react with another molecule of SeM to form dimer radical cation M(Se therefore Se)M+. At pH 7, the >Se*-OH radical adducts were converted to a monomer radical of the type (Se therefore N)M+ that acquires intramolecular stability through interaction with the lone pair of the N atom and this radical is denoted as SeM*+. SeM*+ decayed by first order kinetics, and the reduction potential of the couple SeM*+/SeM was determined to be 1.21+/-0.05 V vs NHE at pH 7. SeM*+ oxidized ABTS2- and TMPD with rate constants of (2.5+/-0.1)x10(8) and (6.1+/-0.2)x10(8) M(-1) s(-1), respectively, and reacted with hydroxide ion with a rate constant of (3.8+/-0.9)x10(5) M(-1) s(-1). SeM*+ reacts with molecular oxygen, and the rate constant for this reaction was determined to be (4.3+/-0.2)x10(8) M(-1) s(-1); similar reaction with methionine could not be observed experimentally. Like methionine radical cations, SeM*+ undergoes decarboxylation, although with lesser yield, to produce reducing 3-methyl-selenopropyl amino radicals (referred as alpha-amino radicals). The formation of these radicals was confirmed both by the estimation of the liberated CO2 and by one-electron reduction of MV2+, thionine, and PNAP. These results have been supported by quantum chemical calculations. Implications of these results in the biological role of SeM have also been briefly discussed.

  18. Electron beam processed plasticized epoxy coatings for surface protection

    Energy Technology Data Exchange (ETDEWEB)

    Ibrahim, Mervat S. [National Center for Radiation Research and Technology, Nasr City (Egypt); Mohamed, Heba A., E-mail: hebaamohamed@gmail.com [National Research Center, Dokki (Egypt); Kandile, Nadia G. [University College for Girls, Ain Shams University (Egypt); Said, Hossam M.; Mohamed, Issa M. [National Center for Radiation Research and Technology, Nasr City (Egypt)

    2011-10-17

    Highlights: {center_dot} Coating formulations with EA 70%, HD 20%, and castor oil 10% under 1 Mrad pass{sup -1} irradiation dose showed the best adhesion and passed bending tests. {center_dot} The prepared EP-SF-An adduct improve anti-corrosion properties of coatings without any significant effect on physical, mechanical and chemical properties of the cured film. The optimum amount of aniline adduct as corrosion inhibitor was found to be 0.4 g for 100 g of coating formulation. {center_dot} The corrosion inhibition efficiency of the prepared adduct competed the commercial efficiency. - Abstract: Epoxy acrylate oligomer (EA) was plasticized by adding different plasticizers such as epoxidized soybean oil, glycerol and castor oil and cured by electron beam (EB). Different irradiation doses (1, 2.5 and 5 Mrad pass{sup -1}) were used in the curing process. The effect of both different irradiation doses and plasticizers on the end use performance properties of epoxy acrylate coating namely, pencil hardness, bending test, adhesion test, acid and alkali resistance test were studied. It was observed that incorporation of castor oil in epoxy acrylate diluted by 1,6-hexanediol diacrylate (HD) monomer with a ratio (EA 70%, HD 20%, castor oil 10%) under 1 Mrad pass{sup -1} irradiation dose improved the physical, chemical and mechanical properties of cured films than the other plasticizer. Sunflower free fatty acid was epoxidized in situ under well established conditions. The epoxidized sunflower free fatty acids (ESFA) were subjected to react with aniline in sealed ampoules under inert atmosphere at 140 deg. C. The produced adducts were added at different concentrations to epoxy acrylate coatings under certain EB irradiation dose and then evaluated as corrosion inhibitors for carbon steel surfaces in terms of weight loss measurements and corrosion resistance tests. It was found that, addition of 0.4 g of aniline adduct to 100 g epoxy acrylate formula may give the best corrosion

  19. Terminal Alkyne Coupling on a Corrugated Noble Metal Surface: From Controlled Precursor Alignment to Selective Reactions.

    Science.gov (United States)

    Lin, Tao; Zhang, Liding; Björk, Jonas; Chen, Zhi; Ruben, Mario; Barth, Johannes V; Klappenberger, Florian

    2017-11-07

    Surface-templated covalent coupling of organic precursors currently emerges as a promising route to the atom-precise fabrication of low-dimensional carbon materials. Here, we investigate the adsorption and the coupling reactions of 4,4''-diethynyl-1,1':4',1''-terphenyl on Au(110) under ultra-high vacuum conditions by using scanning tunneling microscopy combined with density functional theory and kinetic Monte Carlo calculations. Temperature treatment induces both 1,2,4-asymmetric cyclotrimerization and homocoupling, resulting in various reaction products, including a previously unreported, surface-templated H-shaped pentamer. Our analysis of the temperature-dependent relative product abundances unravels that 1,2,4-trimerization and homocoupling proceed via identical intermediate species with the final products depending on the competition of coupling to a third monomer versus dehydrogenation. Our study sheds light on the control of coupling reactions by corrugated surfaces and annealing protocols. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Kinetics and energetics of electron transfer in reaction centers of the photosynthetic bacterium Roseiflexus castenholzii.

    Science.gov (United States)

    Collins, Aaron M; Kirmaier, Christine; Holten, Dewey; Blankenship, Robert E

    2011-03-01

    The kinetics and thermodynamics of the photochemical reactions of the purified reaction center (RC)-cytochrome (Cyt) complex from the chlorosome-lacking, filamentous anoxygenic phototroph, Roseiflexus castenholzii are presented. The RC consists of L- and M-polypeptides containing three bacteriochlorophyll (BChl), three bacteriopheophytin (BPh) and two quinones (Q(A) and Q(B)), and the Cyt is a tetraheme subunit. Two of the BChls form a dimer P that is the primary electron donor. At 285K, the lifetimes of the excited singlet state, P*, and the charge-separated state P(+)H(A)(-) (where H(A) is the photoactive BPh) were found to be 3.2±0.3 ps and 200±20 ps, respectively. Overall charge separation P*→→ P(+)Q(A)(-) occurred with ≥90% yield at 285K. At 77K, the P* lifetime was somewhat shorter and the P(+)H(A)(-) lifetime was essentially unchanged. Poteniometric titrations gave a P(865)/P(865)(+) midpoint potential of +390mV vs. SHE. For the tetraheme Cyt two distinct midpoint potentials of +85 and +265mV were measured, likely reflecting a pair of low-potential hemes and a pair of high-potential hemes, respectively. The time course of electron transfer from reduced Cyt to P(+) suggests an arrangement where the highest potential heme is not located immediately adjacent to P. Comparisons of these and other properties of isolated Roseiflexus castenholzii RCs to those from its close relative Chloroflexus aurantiacus and to RCs from the purple bacteria are made. Copyright © 2010 Elsevier B.V. All rights reserved.

  1. The role of surface reactions on the active and selective catalyst design for bioethanol steam reforming

    Energy Technology Data Exchange (ETDEWEB)

    Benito, M. [Instituto de Catalisis y Petroleoquimica (CSIC), C/Marie Curie 2, Campus Cantoblanco, 28049 Madrid (Spain); Ciemat, Av. Complutense 22, 28040 Madrid (Spain); Padilla, R.; Serrano-Lotina, A.; Rodriguez, L.; Daza, L. [Instituto de Catalisis y Petroleoquimica (CSIC), C/Marie Curie 2, Campus Cantoblanco, 28049 Madrid (Spain); Brey, J.J. [Hynergreen Technologies, Av. Buhaira 2, 41018 Sevilla (Spain)

    2009-07-01

    In order to study the role of surface reactions involved in bioethanol steam reforming mechanism, a very active and selective catalyst for hydrogen production was analysed. The highest activity was obtained at 700 C, temperature at which the catalyst achieved an ethanol conversion of 100% and a selectivity to hydrogen close to 70%. It also exhibited a very high hydrogen production efficiency, higher than 4.5 mol H{sub 2} per mol of EtOH fed. The catalyst was operated at a steam to carbon ratio (S/C) of 4.8, at 700 C and atmospheric pressure. No by-products, such as ethylene or acetaldehyde were observed. In order to consider a further application in an ethanol processor, a long-term stability test was performed under the conditions previously reported. After 750 h, the catalyst still exhibited a high stability and selectivity to hydrogen production. Based on the intermediate products detected by temperature programmed desorption and reaction (TPD and TPR) experiments, a reaction pathway was proposed. Firstly, the adsorbed ethanol is dehydrogenated to acetaldehyde producing hydrogen. Secondly, the adsorbed acetaldehyde is transformed into acetone via acetic acid formation. Finally, acetone is reformed to produce hydrogen and carbon dioxide, which were the final reaction products. The promotion of such reaction sequence is the key to develop an active, selective and stable catalyst, which is the technical barrier for hydrogen production by ethanol reforming. (author)

  2. Tuning of electron transfer reactions in pluronic-surfactant supramolecular assemblies.

    Science.gov (United States)

    Verma, Poonam; Pal, Haridas

    2015-06-21

    Photoinduced electron transfer (ET) reaction between an anionic acceptor, coumarin-343 (C343), and a neutral donor, N,N-dimethylaniline (DMAN), has been investigated in composite supramolecular assemblies (mixed micelles) comprised of a pluronic copolymer (P123: EO20-PO70-EO20 or F88: EO103-PO39-EO103 where EO: ethylene oxide and PO: propylene oxide) and a cationic surfactant (CTAC: cetyltrimethylammonium chloride), following fluorescence quenching studies. Systematic increase in the quenching rates for the studied donor-acceptor system with the increasing CTAC to pluronic molar ratio in the mixed micelles demonstrates a large modulation in the ET rates. The mixed micellar systems in the present cases are formed through the incorporation of the hydrocarbon chains of CTAC into the poly-PO core of the pluronic micelles whereby the cationic head groups of CTAC are placed at the periphery of the micellar core, protruded into the hydrated poly-EO corona region, leading to the formation of a positively charged layer deep inside these mixed micelles. Thus, the anionic C343 dye, initially dissolved at the micelle-water interface, experiences a gradually increasing electrostatic attraction and is therefore systematically dragged deeper inside the micellar corona, as the CTAC composition is increased in the mixed micellar systems. Consequently, the ET rate of the C343-DMAN pair undergoes a large enhancement in the studied mixed micellar systems with the increasing CTAC to pluronic molar ratio. The present strategy of modulating ET reactions using such composite supramolecular assemblies can find applications in areas where bimolecular ET is an integral reaction step.

  3. The role of substrate electrons in the wetting of a metal surface.

    Science.gov (United States)

    Schiros, T; Takahashi, O; Andersson, K J; Oström, H; Pettersson, L G M; Nilsson, A; Ogasawara, H

    2010-03-07

    We address how the electronic and geometric structures of metal surfaces determine water-metal bonding by affecting the balance between Pauli repulsion and electrostatic attraction. We show how the rigid d-electrons and the softer s-electrons utilize different mechanisms for the redistribution of charge that enables surface wetting. On open d-shell Pt(111), the ligand field of water alters the distribution of metal d-electrons to reduce the repulsion. The closed-shell Cu d(10) configuration of isostructural Cu(111), however, does not afford this mechanism, resulting in a hydrophobic surface and three-dimensional ice cluster formation. On the geometrically corrugated Cu(110) surface, however, charge depletion involving the mobile sp-electrons at atomic rows reduces the exchange repulsion sufficiently such that formation of a two-dimensional wetting layer is still favored in spite of the d(10) electronic configuration.

  4. Polyurethane-based polymer surface modifiers with alkyl ammonium copolyoxetane soft segments: Reaction engineering, surface morphology and antimicrobial behavior

    Science.gov (United States)

    Brunson, Kennard Marcellus, Jr.

    Concentrating quaternary (positive) charge at polymer surfaces is important for applications including layer-by-layer polyelectrolyte deposition and antimicrobial coatings. Prior techniques to introduce quaternary charge to the surface involve grafting of quaternary ammonium moieties to a substrate or using polyurethanes with modified hard segments however there are impracticalities involved with these techniques. In the case of the materials discussed, the quaternary charge is introduced via polyurethane based polymer surface modifiers (PSMs) with quaternized soft segments. The particular advantage to this method is that it utilizes the intrinsic phase separation between the hard and soft segments of polyurethanes. This phase separation results in the surface concentration of the soft segments. Another advantage is that unlike grafting, where modification has to take place after device fabrication, these PSMs can be incorporated with the matrix material during device fabrication. The soft segments of these quaternized polyurethanes are produced via ring opening co-polymerization of oxetane monomers which possess either a trifluoroethoxy (3FOx) side chains or a quaternary ammonium side chain (C12). These soft segments are subsequently reacted with 4,4'-(methylene bis (p-cyclohexyl isocyanate)), HMDI and butanediol (BD) to form the PSM. It was initially intended to increase the concentration of quaternary ammonium charge by increasing PSM soft segment molecular weight. Unexpectedly, produced blends with surface microscale phase separation. This observation prompted further investigation of the effect of PSM soft segment molecular weight on phase separation in PSM-base polyurethane blends and the subsequent effects of this phase separation on the biocidal activity. Analysis of the surface morphology via tapping mode atomic force microscopy (TM-AFM) and scanning electron microscopy (SEM) revealed varying complexities in surface morphology as a function of the PSM soft

  5. Evaluation of accessible mineral surface areas for improved prediction of mineral reaction rates in porous media

    Science.gov (United States)

    Beckingham, Lauren E.; Steefel, Carl I.; Swift, Alexander M.; Voltolini, Marco; Yang, Li; Anovitz, Lawrence M.; Sheets, Julia M.; Cole, David R.; Kneafsey, Timothy J.; Mitnick, Elizabeth H.; Zhang, Shuo; Landrot, Gautier; Ajo-Franklin, Jonathan B.; DePaolo, Donald J.; Mito, Saeko; Xue, Ziqiu

    2017-05-01

    The rates of mineral dissolution reactions in porous media are difficult to predict, in part because of a lack of understanding of mineral reactive surface area in natural porous media. Common estimates of mineral reactive surface area used in reactive transport models for porous media are typically ad hoc and often based on average grain size, increased to account for surface roughness or decreased by several orders of magnitude to account for reduced surface reactivity of field as opposed to laboratory samples. In this study, accessible mineral surface areas are determined for a sample from the reservoir formation at the Nagaoka pilot CO2 injection site (Japan) using a multi-scale image analysis based on synchrotron X-ray microCT, SEM QEMSCAN, XRD, SANS, and FIB-SEM. This analysis not only accounts for accessibility of mineral surfaces to macro-pores, but also accessibility through connected micro-pores in smectite, the most abundant clay mineral in this sample. While the imaging analysis reveals that most of the micro- and macro-pores are well connected, some pore regions are unconnected and thus inaccessible to fluid flow and diffusion. To evaluate whether mineral accessible surface area accurately reflects reactive surface area a flow-through core experiment is performed and modeled at the continuum scale. The core experiment is performed under conditions replicating the pilot site and the evolution of effluent solutes in the aqueous phase is tracked. Various reactive surface area models are evaluated for their ability to capture the observed effluent chemistry, beginning with parameter values determined as a best fit to a disaggregated sediment experiment (Beckingham et al., 2016) described previously. Simulations that assume that all mineral surfaces are accessible (as in the disaggregated sediment experiment) over-predict the observed mineral reaction rates, suggesting that a reduction of RSA by a factor of 10-20 is required to match the core flood

  6. When big brother is watching: goal orientation shapes reactions to electronic monitoring during online training.

    Science.gov (United States)

    Watson, Aaron M; Foster Thompson, Lori; Rudolph, Jane V; Whelan, Thomas J; Behrend, Tara S; Gissel, Amanda L

    2013-07-01

    Web-based training is frequently used by organizations as a convenient and low-cost way to teach employees new knowledge and skills. As web-based training is typically unproctored, employees may be held accountable to the organization by computer software that monitors their behaviors. The current study examines how the introduction of electronic performance monitoring may provoke negative emotional reactions and decrease learning among certain types of e-learners. Through motivated action theory and trait activation theory, we examine the role of performance goal orientation when e-learners are exposed to asynchronous and synchronous monitoring. We show that some e-learners are more susceptible than others to evaluation apprehension when they perceive their activities are being monitored electronically. Specifically, e-learners higher in avoid performance goal orientation exhibited increased evaluation apprehension if they believed asynchronous monitoring was present, and they showed decreased skill attainment as a result. E-learners higher on prove performance goal orientation showed greater evaluation apprehension if they believed real-time monitoring was occurring, resulting in decreased skill attainment. PsycINFO Database Record (c) 2013 APA, all rights reserved.

  7. Phasic availability of terminal electron acceptor on oxygen reduction reaction in microbial fuel cell.

    Science.gov (United States)

    Shanthi Sravan, J; Butti, Sai Kishore; Verma, Anil; Venkata Mohan, S

    2017-10-01

    Oxygen-reduction reactions (ORR) plays a pivotal role in determining microbial fuel cells (MFC) performance. In this study, an attempt to determine the influence of the phasic availability of terminal electron acceptor (TEA) on ORR was made. Two MFCs operated with dissolved oxygen (MFC-DC) and air (MFC-SC) as TEA were constructed and analyzed in continuous mode under open and closed circuit conditions. The bio-electrochemical analysis showed a marked influence of dissolved oxygen resulting in a maximum power density with MFC-DC (769mW/m2) compared to MFC-SC (684mW/m2). The availability of O2 in dissolved phase has lowered the activation losses during the MFC operation as a result of effective ORR. The cyclic voltammetry analysis revealed the TEA dependent biocatalyst activity of NADH and cytochrome complex which enabled electron transfer kinetics and improved substrate utilization. Finally, the study evidenced the critical role of TEA phasic availability to regulate the bio-electrogenic and substrate degradation potential in MFC. Copyright © 2017 Elsevier Ltd. All rights reserved.

  8. Hot-electron-assisted femtochemistry at surfaces: A time-dependent density functional theory approach

    DEFF Research Database (Denmark)

    Gavnholt, Jeppe; Rubio, Angel; Olsen, Thomas

    2009-01-01

    Using time-evolution time-dependent density functional theory (TDDFT) within the adiabatic local-density approximation, we study the interactions between single electrons and molecular resonances at surfaces. Our system is a nitrogen molecule adsorbed on a ruthenium surface. The surface is modeled...... at two levels of approximation, first as a simple external potential and later as a 20-atom cluster. We perform a number of calculations on an electron hitting the adsorbed molecule from inside the surface and establish a picture, where the resonance is being probed by the hot electron. This enables us...

  9. Magnetic resonance studies of photo-induced electron transfer reactions. Final report, June 1, 1990--May 31, 1993

    Energy Technology Data Exchange (ETDEWEB)

    van Willigen, H.

    1992-11-01

    Fourier Transform Electron Paramagnetic Resonance (FT EPR) is useful in study of photochemical reactions: a microwave pulse rotates the electron spin magnetization vector from z (magnetic field) into xy plane ({pi}/2 pulse); the time evolution of magnetization in xy plane, the free induction decay (FID), is sampled. Fourier transform of FID gives the frequency domain EPR spectrum of the free radicals, and the method is ideal for time-resolved studies of free radicals produced by pulsed-laser excitation. Investigations of electron transfer reactions focused on porphyrin (donor) - quinone (acceptor) systems. First, two hydrogen abstraction reactions were studied with FT EPR: photoreduction of acetone with 2-propanol, yielding the acetone ketyl radical, and the reaction of 2-propanol with t-butoxy radicals. Then, the FT EPR study of benzoquinone or duroquinone anion radicals generated by pulsed-laser induced electron transfer from zinc tetraphenylporphyrin (ZnTPP) or tetrasulfonated Zn(TPP), was carried out in homogeneous solution, micellar solutions, and silica gel. Finally, FT EPR was used to study electron transfer quenching of triplet C{sub 60} by electron donors.

  10. Pressure-driven fast reaction and recovery of peptide receptor for an electronic nose application

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Yong Kyoung [Department of Electrical Engineering, Kwangwoon University, Seoul 139-701 (Korea, Republic of); Center for Biomicrosystems, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Lee, Sang-Myung [Department of Chemical Engineering, Kangwon National University, Kangwon-do 200-701 (Korea, Republic of); Chae, Myung-Sic; Yoon Kang, Ji; Song Kim, Tae; Seon Hwang, Kyo, E-mail: kshwang@kist.re.kr, E-mail: jhlee@kw.ac.kr [Center for Biomicrosystems, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Hoon Lee, Jeong, E-mail: kshwang@kist.re.kr, E-mail: jhlee@kw.ac.kr [Department of Electrical Engineering, Kwangwoon University, Seoul 139-701 (Korea, Republic of)

    2014-02-24

    Combining a highly sensitive sensor platform with highly selective recognition elements is essential for micro/nanotechnology-based electronic nose applications. Particularly, the regeneration sensor surface and its conditions are key issues for practical e-nose applications. We propose a highly sensitive piezoelectric-driven microcantilever array chip with highly selective peptide receptors. By utilizing the peptide receptor, which was discovered by a phase display screening process, we immobilized a dinitrotoluene (DNT) specific peptide as well as a DNT nonspecific peptide on the surface of the cantilever array. The delivery of DNT gas via pressure-driven flow led to a greater instant response of ∼30 Hz, compared to diffusion only (∼15 Hz for 15 h). Using a simple pressure-driven air flow of ∼50 sccm, we confirmed that a ratio of ∼70% of the specific-bounded sites from DNT gas molecules could be regenerated, showing re-usability of the peptide receptor in on-site monitoring for electronic nose applications.

  11. Electronic state of europium atoms on surface of oxidized tungsten

    CERN Document Server

    Davydov, S Y

    2001-01-01

    The energy scheme of the europium atoms adsorption system on the tungsten surface, coated with the oxygen monolayer, is considered. The evaluations of the europium adatoms charged state on the oxidized tungsten surface are performed. It is established, that europium, adsorbed at the oxidized tungsten surface, is a positive ion with the charge close to the unit. The zonal scheme of the Eu-O/W adsorption system for the europium low and high concentrations is proposed

  12. Electronic, magnetic and structural properties of Co3O4 (100) surface: a DFT+U study

    Science.gov (United States)

    Hashim, Ameerul Hazeeq; Zayed, Ala'Omar Hasan; Zain, Sharifuddin Md; Lee, Vannajan Sanghiran; Said, Suhana Mohd

    2018-01-01

    The three most stable (100), (110), and (111) surfaces exposed by Co3O4 are effective catalysts for various oxidation reactions. Among these surfaces, (100) has not yet received ample attention. In this study, we investigated the structural, electronic and magnetic properties of Co3O4 (100) surface using density functional theory calculations. By considering both stoichiometric and nonstoichiometric surface structures of the two possible terminations, A and B. Besides the greater stability of the newly proposed stoichiometric models compared to nonstoichiometric models reported in previous studies, the results show that the B termination is energetically preferred over the entire range of oxygen chemical potentials. Unlike the bulk, Co3+ octahedral ions become magnetic at the surface, which leads to interesting surface magnetic properties. Density of states (DOS) indicate a small band gap of 1.15 eV for the B-stoichiometric model, due to the presence of surface states in the bulk band gap. More polar surface with a very narrow band gap is found in the A-nonstoichiometric model. These surface states may play an important role in the magnetism and metallicity observed experimentally in several Co3O4 systems.

  13. Electron Conditioning of Technical Aluminium Surfaces: Effect on the Secondary Electron Yield

    Energy Technology Data Exchange (ETDEWEB)

    Le Pimpec, F.

    2004-12-13

    The effect of electron conditioning on commercially aluminium alloys 1100 and 6063 were investigated. Contrary to the assumption that electron conditioning, if performed long enough, can reduce and stabilize the SEY to low values (< 1.3, value of many pure elements [1] ), the SEY of aluminium did not go lower than 1.8. In fact, it reincreases with continued electron exposure dose.

  14. Surface electronic structure of fullerides : effects of correlation, electron-phonon coupling, and polymerization

    NARCIS (Netherlands)

    Macovez, Roberto

    2007-01-01

    The phenomenology of C60 both as isolated molecule and in condensed phases is reviewed. C60 compounds (fullerides) display a wide range of electronic ground states ranging from magnetic insulators to superconductors. The fundamental properties and interactions (electron correlation, electron-phonon

  15. Harnessing surface-bound enzymatic reactions to organize microcapsules in solution.

    Science.gov (United States)

    Shklyaev, Oleg E; Shum, Henry; Sen, Ayusman; Balazs, Anna C

    2016-03-01

    By developing new computational models, we examine how enzymatic reactions on an underlying surface can be harnessed to direct the motion and organization of reagent-laden microcapsules in a fluid-filled microchannel. In the presence of appropriate reagents, surface-bound enzymes can act as pumps, which drive large-scale fluid flows. When the reagents diffuse through the capsules' porous shells, they can react with enzymatic sites on the bottom surface. The ensuing reaction generates fluid density variations, which result in fluid flows. These flows carry the suspended microcapsules and drive them to aggregate into "colonies" on and near the enzyme-covered sites. This aggregation continues until the reagent has been depleted and the convection stops. We show that the shape of the assembled colonies can be tailored by patterning the distribution of enzymes on the surface. This fundamental physicochemical mechanism could have played a role in the self-organization of early biological cells (protocells) and can be used to regulate the autonomous motion and targeted delivery of microcarriers in microfluidic devices.

  16. Charge Transfer Reactions Induce Born-Oppenheimer Breakdown in Surface Chemistry: Applications of Double Resonance Spectroscopy in Molecule-Surface Scattering

    Science.gov (United States)

    Wodtke, Alec M.

    2013-06-01

    Atomic and molecular interactions constitute a many-body quantum problem governed fundamentally only by the Coulomb forces between many electrons and nuclei. While simple to state, computers are simply not fast enough to solve this problem by brute force, except for the simplest examples. Combining the Born-Oppenheimer Approximation (BOA) with Density Functional Theory (DFT), however, allows theoretical simulations of extraordinarily complex chemical systems including molecular interactions at solid metal surfaces, the physical basis of surface chemistry. This lecture describes experiments demonstrating the limits of the BOA/DFT approximation as it relates to molecules interacting with solid metal surfaces. One of the most powerful experimental tools at our disposal is a form of double resonance spectroscopy, which allows us to define the quantum state of the molecule both before and after the collision with the surface, providing a complete picture of the resulting energy conversion processes. With such data, we are able to emphasize quantitative measurements that can be directly compared to first principles theories that go beyond the Born-Oppenheimer approximation. One important outcome of this work is the realization that Born-Oppenheimer breakdown can be induced by simple charge transfer reactions that are common in surface chemistry. J. D. White, J. Chen, D. Matsiev, D. J. Auerbach and A. M. Wodtke Nature {433}(7025), 503-505 (2005) Y. H. Huang, C. T. Rettner, D. J. Auerbach and A. M. Wodtke Science {290}(5489), 111-114 (2000) R. Cooper, I. Rahinov, Z. S. Li, D. Matsiev, D. J. Auerbach and A. M. Wodtke Chemical Science {1}(1), 55-61 (2010) J. Larue, T. Schäfer, D. Matsiev, L. Velarde, N. H. Nahler, D. J. Auerbach and A. M. Wodtke PCCP {13}(1), 97-99 (2011).

  17. Energetics of protein fluctuations: Ligand binding to myoglobin and electron transfer in reaction center

    Science.gov (United States)

    McMahon, Benjamin Hamilton

    We have measured the temperature dependent kinetics of two different protein reactions: Psp+Qsbsp{A}{-}-> PQsb{A} electron transfer (ET) in the photosynthetic reaction (RC), and recombination of carbonmonoxide (CO) to myoglobin (Mb) after flash photolysis. The ET reaction allows determination of the temperature dependence of energy dissipation as RC adapts to charge transfer on the 100 ms, 10sp3 and 10sp4 s time scales at temperatures from 5 to 300 K. The adaptation, or conformational relaxation, of RC is observed in four distinct tiers of conformational substrates, with average apparent Arrhenius activation enthalpies of 17, 50, 78, and 110 kJ/mol and pre-exponential factors of 10sp{13},\\ 10sp{15},\\ 10sp{21}, and 10sp{25}\\ ssp{-1}, respectively. This parameterization provides a prediction of the time course of relaxations at all temperatures. At 300 K, relaxations are expected to occur from 1 ps to 1 ms; at lower temperatures the distribution of relaxation times broaden. We extend this study to samples of different pH, viscosity, and salt composition. We observe kinetics of CO recombination to horse heart myoglobin between 10 ns and 100 s at temperatures from 80 to 320 K. Essentially all recombination is visible in this time window, allowing the effect of relaxations to be observed on the nanosecond time scale at high temperatures, as well as microsecond to second time scales at lower temperatures. Variation of the solvent pH from 5.1 to 8.0 changes the average low temperature enthalpy barrier to recombination from 6 to 13 kJ/mol, shifting the time scale probed by the recombination reaction by an order of magnitude. Addition of 500 mM KCl, KSCN, or (NHsb4)sb2SOsb4 significantly changes the probability of geminate recombination without affecting either the enthalpy barrier to recombination or the energetics of CO entry to and exit from the heme pocket of the protein. We present a model of recombination which emphasizes the role of protein fluctuations in

  18. Electrochemical evaluation of electron transfer kinetics of high and low redox potential laccases on gold electrode surface

    Energy Technology Data Exchange (ETDEWEB)

    Frasconi, Marco [Department of Chemistry and Drug Technologies, Sapienza University of Rome, P.le Aldo Moro, 5 00185 Rome (Italy); Boer, Harry; Koivula, Anu [VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT (Finland); Mazzei, Franco, E-mail: franco.mazzei@uniroma1.i [Department of Chemistry and Drug Technologies, Sapienza University of Rome, P.le Aldo Moro, 5 00185 Rome (Italy)

    2010-12-30

    Laccases and other multicopper oxidases are reported to be able to carry out direct electron transfer reactions when immobilized onto electrode surface. This allows detailed research of their electron transfer mechanisms. We have recently characterized the kinetic properties of four laccases in homogenous solution and immobilized onto an electrode surface with respect to a set of different redox mediators. In this paper we report the direct electron transfer of four purified laccases from Trametes hirsuta (ThL), Trametes versicolor (TvL), Melanocarpus albomyces (r-MaL) and Rhus vernicifera (RvL), by trapping the proteins within an electrochemically inert polymer of tributylmethyl phosphonium chloride coating a gold electrode surface. In particular, we have characterized the steps involved in the laccases electron transfer mechanism as well as the factors limiting each step. During the voltammetric experiments, non-turnover Faradic signals with midpoint potential of about 790 and 400 mV were observed for high potential laccases, ThL and TvL, corresponding to redox transformations of the T1 site and the T2/T3 cluster of the enzyme, respectively, whereas low redox potential laccases r-MaL and RvL shown a redox couple with a midpoint potential around 400 mV. The electrocatalytic properties of these laccase modified electrodes for the reduction of oxygen have been evaluated demonstrating significative direct electron transfer kinetics. The biocatalytic activity of laccases was also monitored in the presence of a well known inhibitor, sodium azide. On the basis of the experimental results, a hypothesis about the electronic pathway for intramolecular electron transfer characterizing laccases has been proposed.

  19. Analysis of low energy electron emission arising during slow multicharged ion-surface interactions

    Energy Technology Data Exchange (ETDEWEB)

    Emmichoven, P.A.Z.v. (Oak Ridge National Laboratory, Oak Ridge, TN 37831-6372 (United States) Joint Institute for Heavy Ion Research, Holified Heavy Ion Research Facility, Oak Ridge, TN 37831-6734 (United States)); Havener, C.C. (Oak Ridge National Laboratory, Oak Ridge, TN 37831-6372 (United States)); Hughes, I.G. (Oak Ridge National Laboratory, Oak Ridge, TN 37831-6372 (United States) Joint Institute for Heavy Ion Research, Holifield Heavy Ion Research Facility, Oak Ridge, TN 37831-6374 (United States)); Zehner, D.M.; Meyer, F.W. (Oak Ridge National Laboratory, Oak Ridge, TN 37831-6732 (United States))

    1993-06-05

    We have undertaken a search for low energy electrons expected to arise in low energy multicharged ion-surface interactions when electrons captured into Rydberg levels of the projectile are promoted to the continuum as the projectile impacts the surface. Measurements are presented for 30--100 keV N[sup 2+] -N[sup 6+] ions incident at 20[degree] with the surface on Cu(001) and Au(011) single crystals, for a series of observation angles.

  20. Analysis of low energy electron emission arising during slow multicharged ion-surface interactions

    Energy Technology Data Exchange (ETDEWEB)

    Zeijlmans van Emmichoven, P.A.; Hughes, I.G. (Oak Ridge National Lab., TN (United States) Joint Institute for Heavy Ion Research, Holifield Heavy Ion Research Facility, Oak Ridge, TN (United States)); Havener, C.C.; Zehner, D.M.; Meyer, F.W. (Oak Ridge National Lab., TN (United States))

    1992-01-01

    We have undertaken a search for low energy electrons expected to arise in low energy multicharged ion-surface interactions when electrons captured into Rydberg levels of the projectile are promoted to the continuum as the projectile impacts the surface. Measurements are presented for 30--100 keV N{sup 2+} -- N{sup 6+} ions incident at 20{sup o} with the surface on Cu(001) and Au(0ll) single crystals, for a series of observation angles.

  1. Communication: Charge transfer dominates over proton transfer in the reaction of nitric acid with gas-phase hydrated electrons

    Science.gov (United States)

    Lengyel, Jozef; Med, Jakub; Slavíček, Petr; Beyer, Martin K.

    2017-09-01

    The reaction of HNO3 with hydrated electrons (H2O)n- (n = 35-65) in the gas phase was studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and ab initio molecular dynamics simulations. Kinetic analysis of the experimental data shows that OH-(H2O)m is formed primarily via a reaction of the hydrated electron with HNO3 inside the cluster, while proton transfer is not observed and NO3-(H2O)m is just a secondary product. The reaction enthalpy was determined using nanocalorimetry, revealing a quite exothermic charge transfer with -241 ± 69 kJ mol-1. Ab initio molecular dynamics simulations indicate that proton transfer is an allowed reaction pathway, but the overall thermochemistry favors charge transfer.

  2. What happens when iron becomes wet? Observation of reactions at interfaces between liquid and metal surfaces

    CERN Document Server

    Kimura, M

    2003-01-01

    Synchrotron-radiation has been applied to investigation of interfaces between liquid and metal surfaces, with a special attention to corrosion. Three topics are shown: (1) nano structures of rusts formed on steel after atmospheric corrosion. Evolution of 'Fe(O, OH) sub 6 network' is the key to understand how the durable rusts prevent from formation of more rusts. (2) In situ observation of reactions at the interface has been carried out for localized corrosion of stainless steel. It is shown that change in states of Cr sup 3 sup + and Br sup - ions near the interface is deeply related with a breakout of the passivation film. (3) A structural phase transformation on a Cu sub 3 Au(001) surface was investigated. Ordering remains even at a temperature higher than the bulk-critical temperature, showing surface-induced ordering. These approaches gives us crucial information for a new steel-product. (author)

  3. Synthesis of metal-semiconductor core-shell nanoparticles using electrochemical surface-limited reactions.

    Science.gov (United States)

    Gu, Chaokang; Xu, Hui; Park, Minseo; Shannon, Curtis

    2009-01-06

    We report the synthesis of Au/CuI and Au/CdS core-shell nanoparticle (NP) thin films using codeposition and electrochemical atomic layer deposition (EC-ALD). Au nanoparticle films were prepared on glassy carbon supports by depositing alternating layers of poly(diallyl dimethylammonium)-stabilized Au nanoparticles and CoP(2)W(17)O(61)(8-) polyoxometallate interlayers. From there, CuI was deposited onto the surface of Au nanoparticles using electrochemical atomic layer deposition, while CdS films were grown by an atom-by-atom codeposition method. The semiconductor-Au core-shell nanoparticles were characterized by electrochemistry, photoluminescence spectroscopy, and Raman spectroscopy. Our results indicate that the semiconductors deposit onto the AuNP surface by surface limited electrochemical reactions.

  4. Improving Density Functional Tight Binding Predictions of Free Energy Surfaces for Slow Chemical Reactions in Solution

    Science.gov (United States)

    Kroonblawd, Matthew; Goldman, Nir

    2017-06-01

    First principles molecular dynamics using highly accurate density functional theory (DFT) is a common tool for predicting chemistry, but the accessible time and space scales are often orders of magnitude beyond the resolution of experiments. Semi-empirical methods such as density functional tight binding (DFTB) offer up to a thousand-fold reduction in required CPU hours and can approach experimental scales. However, standard DFTB parameter sets lack good transferability and calibration for a particular system is usually necessary. Force matching the pairwise repulsive energy term in DFTB to short DFT trajectories can improve the former's accuracy for reactions that are fast relative to DFT simulation times (reactions and the free energy surface are not well-known. We present a force matching approach to improve the chemical accuracy of DFTB. Accelerated sampling techniques are combined with path collective variables to generate the reference DFT data set and validate fitted DFTB potentials. Accuracy of force-matched DFTB free energy surfaces is assessed for slow peptide-forming reactions by direct comparison to DFT for particular paths. Extensions to model prebiotic chemistry under shock conditions are discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  5. Manipulating the Surface Reactions in Lithium Sulfur Batteries Using Hybrid Anode Structures

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Cheng; Xiao, Jie; Shao, Yuyan; Zheng, Jianming; Bennett, Wendy D.; Lu, Dongping; Saraf, Laxmikant V.; Engelhard, Mark H.; Ji, Liwen; Zhang, Jiguang; Li, Xiaolin; Graff, Gordon L.; Liu, Jun

    2014-01-09

    Lithium-sulfur (Li-S) batteries have recently attracted extensive attention due to the high theoretical energy density and potential low cost. Even so, significant challenges prevent widespread adoption, including continuous dissolution and consumption of active sulfur during cycling. Here we present a fundamentally new design using electrically connected graphite and lithium metal as a hybrid anode to control undesirable surface reactions on the anode. The lithiated graphite placed in front of the lithium metal functions as an artificial self-regulated solid electrolyte interface (SEI) layer to actively control the electrochemical reaction while minimizing the deleterious side reactions on the surface and bulk lithium metal. Continuous corrosion and contamination of lithium anode by dissolved polysulfides is largely mitigated. Excellent electrochemical performance has been observed. Li-S cell incorporating the hybrid design retain a capacity of more than 800 mAh g-1 for 400 cycles, corresponding to only 11% fade and a Coulombic efficiency above 99%. This simple hybrid concept may also provide new lessons for protecting metal anodes in other energy storage devices.

  6. Noise-and delay-induced phase transitions of the dimer-monomer surface reaction model

    Energy Technology Data Exchange (ETDEWEB)

    Zeng Chunhua, E-mail: zchh2009@126.com [Faculty of Science, Kunming University of Science and Technology, Kunming 650093 (China) and Center of Metallurgical Energy Conservation and Emission Reduction, Ministry of Education, Kunming University of Science and Technology, Kunming 650093 (China); Wang Hua, E-mail: wanghuaheat@hotmail.com [Center of Metallurgical Energy Conservation and Emission Reduction, Ministry of Education, Kunming University of Science and Technology, Kunming 650093 (China)

    2012-06-19

    Highlights: Black-Right-Pointing-Pointer We study the dimer-monomer surface reaction model. Black-Right-Pointing-Pointer We show that noise induces first-order irreversible phase transition (IPT). Black-Right-Pointing-Pointer Combination of noise and time-delayed feedback induce first- and second-order IPT. Black-Right-Pointing-Pointer First- and second-order IPT is viewed as noise-and delay-induced phase transitions. - Abstract: The effects of noise and time-delayed feedback in the dimer-monomer (DM) surface reaction model are investigated. Applying small delay approximation, we construct a stochastic delayed differential equation and its Fokker-Planck equation to describe the state evolution of the DM reaction model. We show that the noise can only induce first-order irreversible phase transition (IPT) characteristic of the DM model, however the combination of the noise and time-delayed feedback can simultaneously induce first- and second-order IPT characteristics of the DM model. Therefore, it is shown that the well-known first- and second-order IPT characteristics of the DM model may be viewed as noise-and delay-induced phase transitions.

  7. Association of the Chloroplastic Respiratory and Photosynthetic Electron Transport Chains of Chlamydomonas reinhardii with Photoreduction and the Oxyhydrogen Reaction 1

    Science.gov (United States)

    Maione, Theodore E.; Gibbs, Martin

    1986-01-01

    The hydrogenase-dependent processes, photoreduction and the dark oxyhydrogen reaction, both of which can support CO2 assimilation, were compared with aerobic photosynthesis and respiration for their sensitivity to electron transport inhibitors in cells and intact chloroplasts of Chlamydomonas reinhardii 11-32/6. Photoreduction but not photosynthesis was inhibited in chloroplasts and the oxyhydrogen reaction detected only in cells was inhibited up to 75 and 90%, respectively, by 150 micromolar rotenone, indicating the involvement of a NAD(P)H-plastoquinone oxidoreductase in the hydrogen utilizing pathways. The oxyhydrogen reaction coupled to CO2 fixation was inhibited more than 95% by 10 micromolar 2,5 - dibromo - 3 - methyl - 6 - isopropyl - p - benzoquinone (DBMIB), a concentration which did not affect respiratory activity. In cells, both photoreduction and the oxyhydrogen reaction exhibited a similar sensitivity to salicylhydroxamic acid (SHAM) showing approximately 90% inhibition by 7 millimolar concentration. Photosynthesis was inhibited only 30% by the same concentration of SHAM. Antimycin A (18 micromolar, 10 micrograms per milliliter) inhibited both photoreduction (80%) and the oxyhydrogen reaction (92%) in cells with the oxyhydrogen reaction being approximately 10 times more sensitive to lower concentrations of the inhibitor. Antimycin A at 18 micromolar concentration did not inhibit photosynthetic CO2 fixation unless the cells were adapted to an atmosphere of N2 and the reaction conducted anaerobically. Photosynthesis, photoreduction, and the oxyhydrogen reaction coupled to CO2 fixation were all inhibited greater than 90% by 10 micromolar carbonylcyanide-p-trifluoromethoxyphenylhydrazone. ATP added to chloroplasts adapted to an atmosphere of H2 could support CO2 uptake in the dark. These results are interpreted as evidence that photoreduction and the oxyhydrogen reaction involve some common components of thylakoidal electron transport pathways in

  8. Association of the Chloroplastic Respiratory and Photosynthetic Electron Transport Chains of Chlamydomonas reinhardii with Photoreduction and the Oxyhydrogen Reaction.

    Science.gov (United States)

    Maione, T E; Gibbs, M

    1986-02-01

    The hydrogenase-dependent processes, photoreduction and the dark oxyhydrogen reaction, both of which can support CO(2) assimilation, were compared with aerobic photosynthesis and respiration for their sensitivity to electron transport inhibitors in cells and intact chloroplasts of Chlamydomonas reinhardii 11-32/6. Photoreduction but not photosynthesis was inhibited in chloroplasts and the oxyhydrogen reaction detected only in cells was inhibited up to 75 and 90%, respectively, by 150 micromolar rotenone, indicating the involvement of a NAD(P)H-plastoquinone oxidoreductase in the hydrogen utilizing pathways. The oxyhydrogen reaction coupled to CO(2) fixation was inhibited more than 95% by 10 micromolar 2,5 - dibromo - 3 - methyl - 6 - isopropyl - p - benzoquinone (DBMIB), a concentration which did not affect respiratory activity. In cells, both photoreduction and the oxyhydrogen reaction exhibited a similar sensitivity to salicylhydroxamic acid (SHAM) showing approximately 90% inhibition by 7 millimolar concentration. Photosynthesis was inhibited only 30% by the same concentration of SHAM. Antimycin A (18 micromolar, 10 micrograms per milliliter) inhibited both photoreduction (80%) and the oxyhydrogen reaction (92%) in cells with the oxyhydrogen reaction being approximately 10 times more sensitive to lower concentrations of the inhibitor. Antimycin A at 18 micromolar concentration did not inhibit photosynthetic CO(2) fixation unless the cells were adapted to an atmosphere of N(2) and the reaction conducted anaerobically. Photosynthesis, photoreduction, and the oxyhydrogen reaction coupled to CO(2) fixation were all inhibited greater than 90% by 10 micromolar carbonylcyanide-p-trifluoromethoxyphenylhydrazone. ATP added to chloroplasts adapted to an atmosphere of H(2) could support CO(2) uptake in the dark. These results are interpreted as evidence that photoreduction and the oxyhydrogen reaction involve some common components of thylakoidal electron transport

  9. Reaction Heterogeneity in LiNi 0.8 Co 0.15 Al 0.05 O 2 Induced by Surface Layer

    Energy Technology Data Exchange (ETDEWEB)

    Grenier, Antonin [X-ray; Liu, Hao [X-ray; Wiaderek, Kamila M. [X-ray; Lebens-Higgins, Zachary W. [Department; Borkiewicz, Olaf J. [X-ray; Piper, Louis F. J. [Department; Chupas, Peter J. [Energy; Chapman, Karena W. [X-ray

    2017-08-15

    Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air, through reaction with atmospheric CO2. This surface impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact vs an eroded Li2CO3 surface-coating. This reaction heterogeneity, with a bimodal distribution of reaction states, has previously been interpreted as a “two-phase” reaction mechanism for NCA, as an activation step that only occurs during the first cycle. Similar surface layers may impact the reaction mechanism observed in other electrode materials using bulk probes such as operando powder XRD.

  10. The role of substrate electrons in the wetting of a metal surface

    DEFF Research Database (Denmark)

    Schiros, T.; Takahashi, O.; Andersson, Klas Jerker

    2010-01-01

    of charge that enables surface wetting. On open d-shell Pt(111), the ligand field of water alters the distribution of metal d-electrons to reduce the repulsion. The closed-shell Cu d(10) configuration of isostructural Cu(111), however, does not afford this mechanism, resulting in a hydrophobic surface......We address how the electronic and geometric structures of metal surfaces determine water-metal bonding by affecting the balance between Pauli repulsion and electrostatic attraction. We show how the rigid d-electrons and the softer s-electrons utilize different mechanisms for the redistribution...... and three-dimensional ice cluster formation. On the geometrically corrugated Cu(110) surface, however, charge depletion involving the mobile sp-electrons at atomic rows reduces the exchange repulsion sufficiently such that formation of a two-dimensional wetting layer is still favored in spite of the d(10...

  11. Pollen grain surface in Vaccinium myrtillus as seen in scanning electron microscopy

    Directory of Open Access Journals (Sweden)

    Józef Kocoń

    2014-01-01

    Full Text Available Pollen grain surface of Vaccinium myrtillus L. was analyzed by scanning electron microscopy. Pollen grains remain in tetrahedral tetrads. Grain surface is verrucose, consisting of thick, irregularly shaped muri, surrounding small, round or oval lumina. The surface of the muri is fissured, and minute papillae can also be noted.

  12. Secondary electron emission yield from high aspect ratio carbon velvet surfaces

    Science.gov (United States)

    Jin, Chenggang; Ottaviano, Angelica; Raitses, Yevgeny

    2017-11-01

    The plasma electrons bombarding a plasma-facing wall surface can induce secondary electron emission (SEE) from the wall. A strong SEE can enhance the power losses by reducing the wall sheath potential and thereby increasing the electron flux from the plasma to the wall. The use of the materials with surface roughness and the engineered materials with surface architecture is known to reduce the effective SEE by trapping the secondary electrons. In this work, we demonstrate a 65% reduction of SEE yield using a velvet material consisting of high aspect ratio carbon fibers. The measurements of SEE yield for different velvet samples using the electron beam in vacuum demonstrate the dependence of the SEE yield on the fiber length and the packing density, which is strongly affected by the alignment of long velvet fibers with respect to the electron beam impinging on the velvet sample. The results of SEE measurements support the previous observations of the reduced SEE measured in Hall thrusters.

  13. Making it stick: convection, reaction and diffusion in surface-based biosensors.

    Science.gov (United States)

    Squires, Todd M; Messinger, Robert J; Manalis, Scott R

    2008-04-01

    The past decade has seen researchers develop and apply novel technologies for biomolecular detection, at times approaching hard limits imposed by physics and chemistry. In nearly all sensors, the transport of target molecules to the sensor can play as critical a role as the chemical reaction itself in governing binding kinetics, and ultimately performance. Yet rarely does an analysis of the interplay between diffusion, convection and reaction motivate experimental design or interpretation. Here we develop a physically intuitive and practical understanding of analyte transport for researchers who develop and employ biosensors based on surface capture. We explore the qualitatively distinct behaviors that result, develop rules of thumb to quickly determine how a given system will behave, and derive order-of-magnitude estimates for fundamental quantities of interest, such as fluxes, collection rates and equilibration times. We pay particular attention to collection limits for micro- and nanoscale sensors, and highlight unexplained discrepancies between reported values and theoretical limits.

  14. On the Role of Nuclear Surface in Heavy Ion Reaction Cross Section Formation

    CERN Document Server

    Lukyanov, V K; Zemlyanaya, E V

    2000-01-01

    The Glauber-Sitenko approach is developed for calculations of the nucleus-nucleus cross sections at intermediate energies on the basis of the analytic expression of the eikonal phase for the symmetrized Woods-Saxon potential. Calculations show that the differential elastic and total reaction cross sections occur in a good agreement with those obtained by numerical solutions of the wave equation. For the total reaction cross section, an instructive model of the phase is suggested that allows one to separate contributions from internal and peripheral regions of interaction. An important role of the surface is established in formation of the total cross section, and effects of the Coulomb field are studied, too. The nature of the continuous ambiguity of optical potentials is ascertained for interpreting experimental data.

  15. Photoelectron spectroscopy and Auger electron spectroscopy of solids and surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kowalczyk, S.P.

    1976-01-01

    The use of photoelectron spectroscopy, primarily x-ray photoelectron spectroscopy, to obtain information on the electronic structure of a wide variety of solids (especially the bulk electronic structure of solids) is covered. Both valence band and core-level spectra, as well as a few cases of photon excited Auger electron spectroscopy, are employed in the investigations to derive information on N(E). The effect of several modulations inherent in the measured I(E)'s, such as final state band structure, cross section, and relaxation, is discussed. Examples of many-electron interactions in PES are given. Some experimental aspects of PES and AES studies are given with emphasis on sample preparation techniques. Multiple splitting of core levels is examined using the Mn levels in MnF/sub 2/ as a detailed case study. Core level splittings in transition metals, rare earth metals, transition metal halides and several alloys are also reported. The application of PES to the study of the chemical bond in some crystalline semiconductors and insulators, A/sup N/B/sup 8-N/ and A/sup N/B/sup 10-N/ compounds is treated, and a spectroscopic scale of ionicity for these compounds is developed from the measured ''s-band'' splitting in the valence band density of states. (GHT)

  16. Negative plasma potential relative to electron-emitting surfaces.

    Science.gov (United States)

    Campanell, M D

    2013-09-01

    Most works on plasma-wall interaction predict that with strong electron emission, a nonmonotonic "space-charge-limited" (SCL) sheath forms where the plasma potential is positive relative to the wall. We show that a fundamentally different sheath structure is possible where the potential monotonically increases toward a positively charged wall that is shielded by a single layer of negative charge. No ion-accelerating presheath exists in the plasma and the ion wall flux is zero. An analytical solution of the "inverse sheath" regime is demonstrated for a general plasma-wall system where the plasma electrons and emitted electrons are Maxwellian with different temperatures. Implications of the inverse sheath effect are that (a) the plasma potential is negative, (b) ion sputtering vanishes, (c) no charge is lost at the wall, and (d) the electron energy flux is thermal. To test empirically what type of sheath structure forms under strong emission, a full plasma bounded by strongly emitting walls is simulated. It is found that inverse sheaths form at the walls and ions are confined in the plasma. This result differs from past particle-in-cell simulation studies of emission which contain an artificial "source sheath" that accelerates ions to the wall, leading to a SCL sheath at high emission intensity.

  17. Surface reaction of silicon chlorides during atomic layer deposition of silicon nitride

    Science.gov (United States)

    Yusup, Luchana L.; Park, Jae-Min; Mayangsari, Tirta R.; Kwon, Young-Kyun; Lee, Won-Jun

    2018-02-01

    The reaction of precursor with surface active site is the critical step in atomic layer deposition (ALD) process. We performed the density functional theory calculation with DFT-D correction to study the surface reaction of different silicon chloride precursors during the first half cycle of ALD process. SiCl4, SiH2Cl2, Si2Cl6 and Si3Cl8 were considered as the silicon precursors, and an NH/SiNH2*-terminated silicon nitride surface was constructed to model the thermal ALD processes using NH3 as well as the PEALD processes using NH3 plasma. The total energies of the system were calculated for the geometry-optimized structures of physisorption, chemisorption, and transition state. The order of silicon precursors in energy barrier, from lowest to highest, is Si3Cl8 (0.92 eV), Si2Cl6 (3.22 eV), SiH2Cl2 (3.93 eV) and SiCl4 (4.49 eV). Silicon precursor with lower energy barrier in DFT calculation showed lower saturation dose in literature for both thermal and plasma-enhanced ALD of silicon nitride. Therefore, DFT calculation is a promising tool in predicting the reactivity of precursor during ALD process.

  18. Surface engineering of transition metal dichalcogenides for two-dimensional electronic device applications

    Science.gov (United States)

    Azcatl Zacatzi, Angelica

    Two-dimensional transition metal dichalcogenides (TMDs) are considered potential channel materials for emerging electronic devices in the roadmap beyond Si-CMOS technology. Layered TMDs offer intrinsically an ultrathin body without compromising the semiconducting properties. For the implementation of TMDs in electronic device structures, the understanding of their surface properties is essential. This work combines a variety of materials characterization techniques such as in-situ X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, and Raman spectroscopy to investigate the chemistry and structure of TMDs upon different surface treatments. In addition, first-principle calculations are presented to give insights on the mechanism involved in the surface modification of TMD. The impact of the TMDs surface modification on processes for gate-oxide integration by atomic layer deposition and covalent doping are investigated here. This work provides a comprehensive understanding of the surface chemistry of TMDs for two-dimensional electronic device applications.

  19. Isometric graphing and multidimensional scaling for reaction-diffusion modeling on regular and fractal surfaces with spatiotemporal pattern recognition.

    Science.gov (United States)

    Kuriakose, Jainy; Ghosh, Anandamohan; Ravi Kumar, V; Kulkarni, B D

    2004-03-15

    Heterogeneous surface reactions exhibiting complex spatiotemporal dynamics and patterns can be studied as processes involving reaction-diffusion mechanisms. In many realistic situations, the surface has fractal characteristics. This situation is studied by isometric graphing and multidimensional scaling (IGMDS) of fractal surfaces for extracting geodesic distances (i.e., shortest scaled distances that obtain edges of neighboring surface nodes and their interconnections) and the results obtained used to model effects of surface diffusion with nonlinear reactions. Further analysis of evolved spatiotemporal patterns may be carried out by IGMDS because high-dimensional snapshot data can be efficiently projected to a transformed subspace with reduced dimensions. Validation of the IGMDS methodology is carried out by comparing results with reduction capabilities of conventional principal component analysis for simple situations of reaction and diffusion on surfaces. The usefulness of the IGMDS methodology is shown for analysis of complex patterns formed on both regular and fractal surfaces, and using generic nonlinear reaction-diffusion systems following FitzHugh Nagumo and cubic reaction kinetics. The studies of these systems with nonlinear kinetics and noise show that effects of surface disorder due to fractality can become very relevant. The relevance is shown by studying properties of dynamical invariants in IGMDS component space, viz., the Lyapunov exponents and the KS entropy for interesting situations of spiral formation and turbulent patterns. (c) 2004 American Institute of Physics.

  20. Surface plasmon enhanced interfacial electron transfer and resonance Raman, surface-enhanced resonance Raman studies of cytochrome C mutants

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Junwei [Iowa State Univ., Ames, IA (United States)

    1999-11-08

    Surface plasmon resonance was utilized to enhance the electron transfer at silver/solution interfaces. Photoelectrochemical reductions of nitrite, nitrate, and CO2 were studied on electrochemically roughened silver electrode surfaces. The dependence of the photocurrent on photon energy, applied potential and concentration of nitrite demonstrates that the photoelectrochemical reduction proceeds via photoemission process followed by the capture of hydrated electrons. The excitation of plasmon resonances in nanosized metal structures resulted in the enhancement of the photoemission process. In the case of photoelectrocatalytic reduction of CO2, large photoelectrocatalytic effect for the reduction of CO2 was observed in the presence of surface adsorbed methylviologen, which functions as a mediator for the photoexcited electron transfer from silver metal to CO2 in solution. Photoinduced reduction of microperoxidase-11 adsorbed on roughened silver electrode was also observed and attributed to the direct photoejection of free electrons of silver metal. Surface plasmon assisted electron transfer at nanostructured silver particle surfaces was further determined by EPR method.

  1. Plant surface reactions: an opportunistic ozone defence mechanism impacting atmospheric chemistry

    Science.gov (United States)

    Jud, W.; Fischer, L.; Canaval, E.; Wohlfahrt, G.; Tissier, A.; Hansel, A.

    2016-01-01

    Elevated tropospheric ozone concentrations are considered a toxic threat to plants, responsible for global crop losses with associated economic costs of several billion dollars per year. Plant injuries have been linked to the uptake of ozone through stomatal pores and oxidative damage of the internal leaf tissue. But a striking question remains: can surface reactions limit the stomatal uptake of ozone and therefore reduce its detrimental effects to plants?In this laboratory study we could show that semi-volatile organic compounds exuded by the glandular trichomes of different Nicotiana tabacum varieties are an efficient ozone sink at the plant surface. In our experiments, different diterpenoid compounds were responsible for a strongly variety-dependent ozone uptake of plants under dark conditions, when stomatal pores are almost closed. Surface reactions of ozone were accompanied by a prompt release of oxygenated volatile organic compounds, which could be linked to the corresponding precursor compounds: ozonolysis cis-abienol (C20H34O) - a diterpenoid with two exocyclic double bonds - caused emissions of formaldehyde (HCHO) and methyl vinyl ketone (C4H6O). The ring-structured cembratrien-diols (C20H34O2) with three endocyclic double bonds need at least two ozonolysis steps to form volatile carbonyls such as 4-oxopentanal (C5H8O2), which we could observe in the gas phase, too.Fluid dynamic calculations were used to model ozone distribution in the diffusion-limited leaf boundary layer under daylight conditions. In the case of an ozone-reactive leaf surface, ozone gradients in the vicinity of stomatal pores are changed in such a way that the ozone flux through the open stomata is strongly reduced.Our results show that unsaturated semi-volatile compounds at the plant surface should be considered as a source of oxygenated volatile organic compounds, impacting gas phase chemistry, as well as efficient ozone sink improving the ozone tolerance of plants.

  2. Plant surface reactions: an opportunistic ozone defence mechanism impacting atmospheric chemistry

    Directory of Open Access Journals (Sweden)

    W. Jud

    2016-01-01

    Full Text Available Elevated tropospheric ozone concentrations are considered a toxic threat to plants, responsible for global crop losses with associated economic costs of several billion dollars per year. Plant injuries have been linked to the uptake of ozone through stomatal pores and oxidative damage of the internal leaf tissue. But a striking question remains: can surface reactions limit the stomatal uptake of ozone and therefore reduce its detrimental effects to plants?In this laboratory study we could show that semi-volatile organic compounds exuded by the glandular trichomes of different Nicotiana tabacum varieties are an efficient ozone sink at the plant surface. In our experiments, different diterpenoid compounds were responsible for a strongly variety-dependent ozone uptake of plants under dark conditions, when stomatal pores are almost closed. Surface reactions of ozone were accompanied by a prompt release of oxygenated volatile organic compounds, which could be linked to the corresponding precursor compounds: ozonolysis cis-abienol (C20H34O – a diterpenoid with two exocyclic double bonds – caused emissions of formaldehyde (HCHO and methyl vinyl ketone (C4H6O. The ring-structured cembratrien-diols (C20H34O2 with three endocyclic double bonds need at least two ozonolysis steps to form volatile carbonyls such as 4-oxopentanal (C5H8O2, which we could observe in the gas phase, too.Fluid dynamic calculations were used to model ozone distribution in the diffusion-limited leaf boundary layer under daylight conditions. In the case of an ozone-reactive leaf surface, ozone gradients in the vicinity of stomatal pores are changed in such a way that the ozone flux through the open stomata is strongly reduced.Our results show that unsaturated semi-volatile compounds at the plant surface should be considered as a source of oxygenated volatile organic compounds, impacting gas phase chemistry, as well as efficient ozone sink improving the ozone tolerance of plants.

  3. Secondary Electron Yield on Cryogenic Surfaces as a Function of Physisorbed Gases

    CERN Document Server

    Kuzucan, Asena; Taborelli, Mauro

    2011-01-01

    In LHC the electron cloud induced by photoelectrons, gas ionization and secondary electrons emitted from the beam pipe walls could be a limitation of the performance. The electron cloud induce heat load on the cryogenic system, cause pressure rise, emittance growth and beam instabilities, which in the end will limit the beam’s lifetime. Beam- induced multipacting, which can arise through oscillatory motion of photoelectrons and low-energy secondary electrons bouncing back and forth between opposite walls of the vacuum chamber during successive passage of proton bunches, represent therefore a potential problem for the machine. The secondary electron yield (SEY) is one of the key parameters for the electron cloud build up and multipacting phenomenon. An electron cloud occurs if the metal surface secondary electron yield is high enough for electron multiplication. This parameter has been extensively studied on room temperature samples but uncertainties remain for samples at cryogenic temperature. Indeed, at l...

  4. Intensity distributions of reflected surface channeling protons scattered on surfaces of electron-bombarded alkali halide crystals

    Science.gov (United States)

    Fukazawa, Y.; Kihara, K.; Iwamoto, K.; Susuki, Y.

    2013-11-01

    We have examined the surface-channeling of 550 keV protons on electron-bombarded KBr(0 0 1) surfaces at grazing incidence. On the surface, electron-stimulated desorption (ESD) resulting from the irradiation of 5 keV electrons changes the surface morphology. In order to investigate the change of the surface morphology, the luminous intensity distributions observed on a fluorescent screen (scattering patterns) of the reflected protons under the surface-channeling conditions are measured. Normalized specular intensity of the protons oscillates, and the results of computer simulations show that the period of the intensity oscillation agrees with the period of layer-by-layer desorption. The measured period of the oscillation is comparable to the simulated one, i.e., the period of the desorption, however, the measured amplitude of the oscillation is weak. This shows that the layer-by-layer desorption of the experimental surface is observed but is not as remarkable as that of the perfect surface introduced in the simulation.

  5. Intensity distributions of reflected surface channeling protons scattered on surfaces of electron-bombarded alkali halide crystals

    Energy Technology Data Exchange (ETDEWEB)

    Fukazawa, Y., E-mail: yukofu@cc.osaka-kyoiku.ac.jp; Kihara, K.; Iwamoto, K.; Susuki, Y.

    2013-11-15

    We have examined the surface-channeling of 550 keV protons on electron-bombarded KBr(0 0 1) surfaces at grazing incidence. On the surface, electron-stimulated desorption (ESD) resulting from the irradiation of 5 keV electrons changes the surface morphology. In order to investigate the change of the surface morphology, the luminous intensity distributions observed on a fluorescent screen (scattering patterns) of the reflected protons under the surface-channeling conditions are measured. Normalized specular intensity of the protons oscillates, and the results of computer simulations show that the period of the intensity oscillation agrees with the period of layer-by-layer desorption. The measured period of the oscillation is comparable to the simulated one, i.e., the period of the desorption, however, the measured amplitude of the oscillation is weak. This shows that the layer-by-layer desorption of the experimental surface is observed but is not as remarkable as that of the perfect surface introduced in the simulation.

  6. On Cosmic-Ray-Driven Electron Reaction Mechanism for Ozone Hole and Chlorofluorocarbon Mechanism for Global Climate Change

    CERN Document Server

    Lu, Qing-Bin

    2012-01-01

    Numerous laboratory measurements have provided a sound physical basis for the cosmic-ray driven electron-induced reaction (CRE) mechanism of halogen-containing molecules for the ozone hole. And observed spatial and time correlations between polar ozone loss or stratospheric cooling and cosmic rays have shown strong evidence of the CRE mechanism [Q.-B. Lu, Phys. Rep. 487, 141-167(2010)]. Chlorofluorocarbons (CFCs) were also long-known greenhouse gases but were thought to play only a minor role in climate change. However, recent observations have shown evidence of the saturation in greenhouse effect of non-CFC gases. A new evaluation has shown that halocarbons alone (mainly CFCs) could account for the rise of 0.5~0.6 deg C in global surface temperature since 1950, leading to the striking conclusion that not CO2 but CFCs were the major culprit for global warming in the late half of the 20th century [Q.-B. Lu, J. Cosmology 8, 1846-1862(2010)]. Surprizingly, a recent paper [J.-W. Grooss and R. Muller, Atmos. Envir...

  7. Influence of laser induced hot electrons on the threshold for shock ignition of fusion reactions

    Energy Technology Data Exchange (ETDEWEB)

    Colaïtis, A.; Ribeyre, X.; Le Bel, E.; Duchateau, G.; Nicolaï, Ph.; Tikhonchuk, V. [Centre Lasers Intenses et Applications, Université de Bordeaux - CNRS - CEA, UMR 5107,351 Cours de la Libération, 33400 Talence (France)

    2016-07-15

    The effects of Hot Electrons (HEs) generated by the nonlinear Laser-Plasma Interaction (LPI) on the dynamics of Shock Ignition Inertial Confinement Fusion targets are investigated. The coupling between the laser beam, plasma dynamics and hot electron generation and propagation is described with a radiative hydrodynamics code using an inline model based on Paraxial Complex Geometrical Optics [Colaïtis et al., Phys. Rev. E 92, 041101 (2015)]. Two targets are considered: the pure-DT HiPER target and a CH-DT design with baseline spike powers of the order of 200–300 TW. In both cases, accounting for the LPI-generated HEs leads to non-igniting targets when using the baseline spike powers. While HEs are found to increase the ignitor shock pressure, they also preheat the bulk of the imploding shell, notably causing its expansion and contamination of the hotspot with the dense shell material before the time of shock convergence. The associated increase in hotspot mass (i) increases the ignitor shock pressure required to ignite the fusion reactions and (ii) significantly increases the power losses through Bremsstrahlung X-ray radiation, thus rapidly cooling the hotspot. These effects are less prominent for the CH-DT target where the plastic ablator shields the lower energy LPI-HE spectrum. Simulations using higher laser spike powers of 500 TW suggest that the CH-DT capsule marginally ignites, with an ignition window width significantly smaller than without LPI-HEs, and with three quarters of the baseline target yield. The latter effect arises from the relation between the shock launching time and the shell areal density, which becomes relevant in presence of a LPI-HE preheating.

  8. The role of substrate electrons in the wetting of a metal surface

    OpenAIRE

    Schiros, T.; Takahashi, O.; Andersson, Klas Jerker; Ostrom, H.; Pettersson, L.G.M.; Nilsson, A.; Ogasawara, H.

    2010-01-01

    We address how the electronic and geometric structures of metal surfaces determine water-metal bonding by affecting the balance between Pauli repulsion and electrostatic attraction. We show how the rigid d-electrons and the softer s-electrons utilize different mechanisms for the redistribution of charge that enables surface wetting. On open d-shell Pt(111), the ligand field of water alters the distribution of metal d-electrons to reduce the repulsion. The closed-shell Cu d(10) configuration o...

  9. Quantum Nuclear Extension of Electron Nuclear Dynamics on Folded Effective-Potential Surfaces

    DEFF Research Database (Denmark)

    Hall, B.; Deumens, E.; Ohrn, Y.

    2014-01-01

    A perennial problem in quantum scattering calculations is accurate theoretical treatment of low energy collisions. We propose a method of extracting a folded, nonadiabatic, effective potential energy surface from electron nuclear dynamics (END) trajectories; we then perform nuclear wave packet dy...... dynamics on that surface and calculate differential cross sections for two-center, one (active) electron systems.......A perennial problem in quantum scattering calculations is accurate theoretical treatment of low energy collisions. We propose a method of extracting a folded, nonadiabatic, effective potential energy surface from electron nuclear dynamics (END) trajectories; we then perform nuclear wave packet...

  10. Unsteady flow of a Maxwell fluid over a stretching surface in presence of chemical reaction

    Directory of Open Access Journals (Sweden)

    Swati Mukhopadhyay

    2012-10-01

    Full Text Available An analysis is presented for unsteady two-dimensional flow of a Maxwell fluid over a stretching surface in presence of a first order constructive/destructive chemical reaction. Using suitable transformations, the governing partial differential equations are converted to ordinary one and are then solved numerically by shooting method. The flow fields and mass transfer are significantly influenced by the governing parameters. Fluid velocity initially decreases with increasing unsteadiness parameter and concentration decreases significantly due to unsteadiness. The effect of increasing values of the Maxwell parameter is to suppress the velocity field. But the concentration is enhanced with increasing Maxwell parameter.

  11. New insights into the nonadiabatic state population dynamics of model proton-coupled electron transfer reactions from the mixed quantum-classical Liouville approach

    Energy Technology Data Exchange (ETDEWEB)

    Shakib, Farnaz A.; Hanna, Gabriel, E-mail: gabriel.hanna@ualberta.ca [Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2 (Canada)

    2016-01-14

    In a previous study [F. A. Shakib and G. Hanna, J. Chem. Phys. 141, 044122 (2014)], we investigated a model proton-coupled electron transfer (PCET) reaction via the mixed quantum-classical Liouville (MQCL) approach and found that the trajectories spend the majority of their time on the mean of two coherently coupled adiabatic potential energy surfaces. This suggested a need for mean surface evolution to accurately simulate observables related to ultrafast PCET processes. In this study, we simulate the time-dependent populations of the three lowest adiabatic states in the ET-PT (i.e., electron transfer preceding proton transfer) version of the same PCET model via the MQCL approach and compare them to the exact quantum results and those obtained via the fewest switches surface hopping (FSSH) approach. We find that the MQCL population profiles are in good agreement with the exact quantum results and show a significant improvement over the FSSH results. All of the mean surfaces are shown to play a direct role in the dynamics of the state populations. Interestingly, our results indicate that the population transfer to the second-excited state can be mediated by dynamics on the mean of the ground and second-excited state surfaces, as part of a sequence of nonadiabatic transitions that bypasses the first-excited state surface altogether. This is made possible through nonadiabatic transitions between different mean surfaces, which is the manifestation of coherence transfer in MQCL dynamics. We also investigate the effect of the strength of the coupling between the proton/electron and the solvent coordinate on the state population dynamics. Drastic changes in the population dynamics are observed, which can be understood in terms of the changes in the potential energy surfaces and the nonadiabatic couplings. Finally, we investigate the state population dynamics in the PT-ET (i.e., proton transfer preceding electron transfer) and concerted versions of the model. The PT

  12. Study of the Electronic Surface State of 3 - 5 Compounds

    Science.gov (United States)

    1975-09-15

    collaboration with Walter Harrison and Sal im Ciraci proved most fruitful. Making use of the Bond Orbital Model, a first order calculation was made of the...energy level? associated with sur- 2 face as compared to bulk orbitals . The results were striking. They showed that, because of the difference between...enough so that there is appreciable electron emission from the GaAs below the oxide layer. 11 12 In Fig. 3 we show an EDO for an Op

  13. Local electronic properties of graphene flakes on noble metal surfaces

    OpenAIRE

    Leicht, Philipp

    2015-01-01

    This thesis examines possible routes for the preparation of graphene nanostructures on metal substrates and performs structural and electronic characterizations using scanning tunneling microcopy and spectroscopy. Investigations of graphene nanostructures necessitate the use of a suitable graphene-substrate combination, which allows for a controlled in situ preparation of small and well-shaped graphene nanostructures. The choice of a graphene-substrate combination with weak interaction in or...

  14. Near-Surface Electronic Contribution to Semiconductor Elasticity

    Science.gov (United States)

    Lin, J. T.; Shuvra, P. D.; McNamara, S.; Gong, H.; Liao, W.; Davidson, J. L.; Walsh, K. M.; Alles, M. L.; Alphenaar, B. W.

    2017-09-01

    The influence of the carrier concentration on the elasticity is measured for a microscale silicon resonator. UV radiation is used to generate a surface charge that gates the underlying carrier concentration, as indicated by the device resistance. Correlated with the carrier concentration change is a drop in the resonant frequency that persists for 60 h following exposure. Model calculations show that the change in resonant frequency is due to the modification of the elastic modulus in the near-surface region. This effect becomes increasingly important as device dimensions are reduced to the nanometer scale, and contributes an important source of instability for microscale and nanoscale electromechanical devices operating in radiation environments.

  15. Magnetite Fe3O4 (111) Surfaces: Impact of Defects on Structure, Stability, and Electronic Properties

    KAUST Repository

    Noh, Jung Hyun

    2015-08-04

    We present a comprehensive investigation, via first-principles density functional theory (DFT) calculations, of various surface terminations of magnetite, Fe3O4 (111), a major iron oxide which has also a number of applications in electronics and spintronics. We compare the thermodynamic stability and electronic structure among the different surfaces terminations. Interestingly, we find that surfaces modified with point defects and adatoms can be more stable than bulk-like terminations. These surfaces show different surface chemistry, electronic structures and distinctive spin polarization features near the Fermi level from those previously considered in the literature. Our studies provide an atomic level insight for magnetite surfaces, which is a necessary step to understanding their interfaces with organic layers in OLED and spintronic devices.

  16. Electronic and chemical properties of a surface-terminated screw dislocation in MgO.

    Science.gov (United States)

    McKenna, Keith P

    2013-12-18

    Dislocations represent an important and ubiquitous class of topological defect found at the surfaces of metal oxide materials. They are thought to influence processes as diverse as crystal growth, corrosion, charge trapping, luminescence, molecular adsorption, and catalytic activity; however, their electronic and chemical properties remain poorly understood. Here, through a detailed first-principles investigation into the properties of a surface-terminated screw dislocation in MgO we provide atomistic insight into these issues. We show that surface dislocations can exhibit intriguing electron trapping properties which are important for understanding the chemical and electronic characteristics of oxide surfaces. The results presented in this article taken together with recent experimental reports show that surface dislocations can be equally as important as more commonly considered surface defects, such as steps, kinks, and vacancies, but are now just beginning to be understood.

  17. Dynamics and resonances of the H(2S) + CH+(X1Σ+) reaction in the electronic ground state: a detailed quantum wavepacket study.

    Science.gov (United States)

    Sundaram, P; Manivannan, V; Padmanaban, R

    2017-08-02

    Initial state-selected and energy resolved channel-specific reaction probabilities, integral cross sections and thermal rate constants of the H(2S) + CH+(X1Σ+) reaction are calculated within the coupled states approximation by a time-dependent wave packet propagation method. The new ab initio global potential energy surface (PES) of the electronic ground state (1 2A') of the system, recently reported by Li et al. [J. Chem. Phys., 2015, 142, 124302], is employed for this purpose. All partial wave contributions up to the total angular momentum J = 60 are considered to obtain the converged integral reaction cross section up to a collision energy of 1.0 eV. Thermal rate constants are calculated by averaging the reaction cross sections over the Boltzmann distribution of energies and compared with the available theoretical and experimental results for the temperature range 10-1000 K. Investigation of the channel-specific reaction attributes shows that the H abstraction (CH+ destruction) channel is highly favored over the H exchange channel. The effect of rotational and vibrational excitations of the CH+ reagent on the dynamics is also studied. The resonances formed during the course of the reaction are also identified by calculating the transition state spectrum and characterized in terms of the eigenfunctions and lifetimes. More than 260 vibrational levels are obtained and their eigenfunctions are calculated, which are represented in terms of the nodal assignments and the eigenenergies. They reveal both the local and hyperspherical behavior for the bound and quasibound states of the CH2+ complex in the ground 1 2A' surface. The lifetime analysis of the quasibound states indicates that the CH2+ resonances survive for as long as ∼400 fs at high energies (E ∼ 2.0 eV) and are expected to decay faster with further increasing energy. Finally, the type of mechanism for the formation of the product (C+ + H2) is elucidated.

  18. Melatonin: Free Radicals and Metabolites Resulting by Emission and Consumption of Solvated Electrons (eaq-): Reaction Mechanisms.

    Science.gov (United States)

    Kneidinger, Herbert; Mitulovic, Goran; Hartmann, Johannes; Quint, Ruth Maria; Getoff, Nikola

    2015-01-01

    Melatonin not only regulates circadian rhythm, but also induces apoptosis in tumor cells. Hence, elucidation of the basic reaction mechanisms of melatonin and its metabolites is a matter of interest. Melatonin dissolved in a mixture of water/ethanol=40/60 form associates (unstable complexes). For simulation of biological processes, melatonin was excited by UV light into the singlet state. By using monochromatic UV light (λ=254 nm) melatonin ejects solvated electrons (eaq (-)), a part of which is scavenged by melatonin in ground state contained in the associates. Consequently, with increase of melatonin concentration a decrease of the determined quantum yield of emitted eaq (-), Q(eaq (-)), is obtained. The complex molecular structure of melatonin contains functional groups which can emit eaq (-), as well such consuming eaq (-). As a succession of these processes various types of metabolites are generated, as well as degradation products, with lower molecular weight, are formed. Not melatonin per se, but the ejected eaq (-) and thereby resulting various metabolites are responsible for different biological properties of melatonin. Copyright © 2015 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved.

  19. Optically Controlled Electron-Transfer Reaction Kinetics and Solvation Dynamics: Effect of Franck-Condon States.

    Science.gov (United States)

    Gupta, Kriti; Patra, Aniket; Dhole, Kajal; Samanta, Alok Kumar; Ghosh, Swapan K

    2017-09-21

    Experimental results for optically controlled electron-transfer reaction kinetics (ETRK) and nonequilibrium solvation dynamics (NESD) of Coumarin 480 in DMPC vesicle show their dependence on excitation wavelength λex. However, the celebrated Marcus theory and linear-response-theory-based approaches for ETRK and NESD, respectively, predict both of the processes to be independent of λex. The above said lacuna in these theories prompted us to develop a novel theory in 1D space, where the effect of innumerable Franck-Condon states is included through λex. The present theory not only sheds light on the origin of failure of the existing theories but also gives the correct trend for the effect of λex on ETRK and NESD. More importantly, the calculated results of NESD are in excellent agreement with the experimental results for different values of λex. The new theory will therefore advance the knowledge of scientific community on the dynamics of photoinduced nonequilibrium processes.

  20. Accurate ab initio potential energy surface, dynamics, and thermochemistry of the F+CH4-->HF+CH3 reaction.

    Science.gov (United States)

    Czakó, Gábor; Shepler, Benjamin C; Braams, Bastiaan J; Bowman, Joel M

    2009-02-28

    An accurate full-dimensional global potential energy surface (PES) for the F+CH(4)-->HF+CH(3) reaction has been developed based on 19 384 UCCSD(T)/aug-cc-pVTZ quality ab initio energy points obtained by an efficient composite method employing explicit UCCSD(T)/aug-cc-pVDZ and UMP2/aug-cc-pVXZ [X=D,T] computations. The PES contains a first-order saddle point, (CH(4)- -F)(SP), separating reactants from products, and also minima describing the van der Waals complexes, (CH(4)- - -F)(vdW) and (CH(3)- - -HF)(vdW), in the entrance and exit channels, respectively. The structures of these stationary points, as well as those of the reactants and products have been computed and the corresponding energies have been determined using basis set extrapolation techniques considering (a) electron correlation beyond the CCSD(T) level, (b) effects of the scalar relativity and the spin-orbit couplings, (c) diagonal Born-Oppenheimer corrections (DBOC), and (d) zero-point vibrational energies and thermal correction to the enthalpy at 298 K. The resulting saddle point barrier and ground state vibrationally adiabatic barrier heights (V(SP) and V(VAGS)), dissociation energy of (CH(3)- - -HF)(vdW) (D(e) and D(0)), and the reaction enthalpy (DeltaH(e) ( degrees ), DeltaH(0) ( degrees ), and DeltaH(298) ( degrees )) are (240+/-40 and 245+/-200 cm(-1)), (1070+/-10 and 460+/-50 cm(-1)), and (-10000+/-50, -11200+/-80, and -11000+/-80 cm(-1)), respectively. Variational vibrational calculations have been carried out for (CH(3)- - -HF)(vdW) in full (12) dimensions. Quasiclassical trajectory calculations of the reaction using the new PES are reported. The computed HF vibrational and rotational distributions are in excellent agreement with experiment.

  1. Gymnosperms have increased capacity for electron leakage to oxygen (Mehler and PTOX reactions) in photosynthesis compared with angiosperms.

    Science.gov (United States)

    Shirao, Masayoshi; Kuroki, Shu; Kaneko, Kaoru; Kinjo, Yuriko; Tsuyama, Michito; Förster, Britta; Takahashi, Shunichi; Badger, Murray R

    2013-07-01

    Oxygen plays an important role in photosynthesis by participating in a number of O2-consuming reactions. O2 inhibits CO2 fixation by stimulating photorespiration, thus reducing plant production. O2 interacts with photosynthetic electron transport in the chloroplasts' thylakoids in two main ways: by accepting electrons from PSI (Mehler reaction); and by accepting electrons from reduced plastoquinone (PQ) mediated by the plastid terminal oxidase (PTOX). In this study, we show, using 101 plant species, that there is a difference in the potential for photosynthetic electron flow to O2 between angiosperms and gymnosperms. We found, from measurements of Chl fluorescence and leaf absorbance at 830 nm, (i) that electron outflow from PSII, as determined by decay kinetics of Chl fluorescence after application of a saturating light pulse, is more rapid in gymnosperms than in angiosperms; (ii) that the reaction center Chl of PSI (P700) is rapidly and highly oxidized in gymnosperms during induction of photosynthesis; and (iii) that these differences are dependent on oxygen. Finally, rates of O2 uptake measured by mass spectrometry in the absence of photorespiration were significantly promoted by illumination in dark-adapted leaves of gymnosperms, but not in those of angiosperms. The light-stimulated O2 uptake was around 10% of the maximum O2 evolution in gymnosperms and 1% in angiosperms. These results suggest that gymnosperms have increased capacity for electron leakage to oxygen in photosynthesis compared with angiosperms. The involvement of the Mehler reaction and PTOX in the electron flow to O2 is discussed.

  2. Assessment of root surfaces of apicected teeth: A scanning electron ...

    African Journals Online (AJOL)

    2014-05-15

    May 15, 2014 ... Abstract. Objectives: The aim of this study was to determine the apical surface characteristics and presence of dental cracks ... The mean number of cracks per ..... walls.[25] In our study, no statistically significant difference was found between the groups. A total of 105 cracks were identified in 30 roots when.

  3. Scanning electron microscopic evaluation of root canal surfaces ...

    African Journals Online (AJOL)

    2014-07-15

    Jul 15, 2014 ... Root canal preparation for all the teeth was carried out with. 3 different types of rotary instruments. ... which enabled removal of overlapping dentin walls. After completing the preparation of the coronal third of ... on dentine or other surfaces after instrumentation with either rotary instrument or endodontic files, ...

  4. Surface Properties of Titanium dioxide and its Structural Modifications by Reactions with Transition Metals

    Science.gov (United States)

    Halpegamage, Sandamali

    Surfaces of metal oxides play a vital role in many technologically important applications. The surfaces of titanium dioxide, in particular, show quite promising properties that can be utilized in solid-state gas sensing and photocatalysis applications. In the first part of this dissertation we investigate these properties of TiO2 surfaces through a vigorous surface scientific approach. In the second part, we investigate the possibilities of modifying the TiO2 surfaces by depositing multi-component transition metal oxide monolayers so that the properties of bare TiO2 surface can be influenced in a beneficial way. For instance, via formation of new surface sites or cations that have different valance states, the chemisorption and catalytic properties can be modified. We use sophisticated experimental surface science techniques that are compatible with ultra-high vacuum technology for surface characterization. All the experimental results, except for the photocatalysis experiments, were compared to and verified by supporting DFT-based theoretical results produced by our theory collaborators. TiO2 based solid-state gas sensors have been used before for detecting trace amounts of explosives such as 2,4-dinitrololuene (DNT), a toxic decomposition product of the explosive 2,4,6-trinitrotoluene (TNT) that have very low vapor pressure. However, the adsorption, desorption and reaction mechanism were not well- understood. Here, we investigate 2,4-DNT adsorption on rutile-TiO2(110) surface in order to gain insight about these mechanisms in an atomistic level and we propose an efficient way of desorbing DNT from the surface through UV-light induced photoreactions. TiO2 exists in different polymorphs and the photocatalytic activity differs from one polymorph to another. Rutile and anatase are the most famous forms of TiO2 in photocatalysis and anatase is known to show higher activity than rutile. The photoactivity also varies depending on the surface orientation for the same

  5. A simple approach to the solvent reorganisation Gibbs free energy in electron transfer reactions of redox metalloproteins

    DEFF Research Database (Denmark)

    Ulstrup, Jens

    1999-01-01

    We discuss a simple model for the environmental reorganisation Gibbs free energy, E-r, in electron transfer between a metalloprotein and a small reaction partner. The protein is represented as a dielectric globule with low dielectric constant, the metal centres as conducting spheres, all embedded...

  6. Tuning the two-dimensional electron liquid at oxide interfaces by buffer-layer-engineered redox reactions

    DEFF Research Database (Denmark)

    Chen, Yunzhong; Green, Robert J.; Sutarto, Ronny

    2017-01-01

    Polar discontinuities and redox reactions provide alternative paths to create two-dimensional electron liquids (2DELs) at oxide interfaces. Herein, we report high mobility 2DELs at interfaces involving SrTiO3 (STO) achieved using polar La7/8Sr1/8MnO3 (LSMO) buffer layers to manipulate both...

  7. Heterogeneous electron transfer and oxygen reduction reaction at nanostructured iron(II) phthalocyanine and its MWCNTs nanocomposites

    CSIR Research Space (South Africa)

    Mamuru, SA

    2010-05-01

    Full Text Available species within the porous layers of MWCNTs. Electron transfer process is much easier at the EPPGE-MWCNT and EPPGE-MWCNT-nanoFePc compared to the other electrodes. The best response for oxygen reduction reaction was at the EPPGE-MWCNTnanoFePc, yielding a 4...

  8. Work function and surface stability of tungsten-based thermionic electron emission cathodes

    Science.gov (United States)

    Jacobs, Ryan; Morgan, Dane; Booske, John

    2017-11-01

    Materials that exhibit a low work function and therefore easily emit electrons into vacuum form the basis of electronic devices used in applications ranging from satellite communications to thermionic energy conversion. W-Ba-O is the canonical materials system that functions as the thermionic electron emitter commercially used in a range of high-power electron devices. However, the work functions, surface stability, and kinetic characteristics of a polycrystalline W emitter surface are still not well understood or characterized. In this study, we examined the work function and surface stability of the eight lowest index surfaces of the W-Ba-O system using density functional theory methods. We found that under the typical thermionic cathode operating conditions of high temperature and low oxygen partial pressure, the most stable surface adsorbates are Ba-O species with compositions in the range of Ba0.125O-Ba0.25O per surface W atom, with O passivating all dangling W bonds and Ba creating work function-lowering surface dipoles. Wulff construction analysis reveals that the presence of O and Ba significantly alters the surface energetics and changes the proportions of surface facets present under equilibrium conditions. Analysis of previously published data on W sintering kinetics suggests that fine W particles in the size range of 100-500 nm may be at or near equilibrium during cathode synthesis and thus may exhibit surface orientation fractions well described by the calculated Wulff construction.

  9. Modifying Surface Chemistry of Metal Oxides for Boosting Dissolution Kinetics in Water by Liquid Cell Electron Microscopy.

    Science.gov (United States)

    Lu, Yue; Geng, Jiguo; Wang, Kuan; Zhang, Wei; Ding, Wenqiang; Zhang, Zhenhua; Xie, Shaohua; Dai, Hongxing; Chen, Fu-Rong; Sui, Manling

    2017-08-22

    Dissolution of metal oxides is fundamentally important for understanding mineral evolution and micromachining oxide functional materials. In general, dissolution of metal oxides is a slow and inefficient chemical reaction. Here, by introducing oxygen deficiencies to modify the surface chemistry of oxides, we can boost the dissolution kinetics of metal oxides in water, as in situ demonstrated in a liquid environmental transmission electron microscope (LETEM). The dissolution rate constant significantly increases by 16-19 orders of magnitude, equivalent to a reduction of 0.97-1.11 eV in activation energy, as compared with the normal dissolution in acid. It is evidenced from the high-resolution TEM imaging, electron energy loss spectra, and first-principle calculations where the dissolution route of metal oxides is dynamically changed by local interoperability between altered water chemistry and surface oxygen deficiencies via electron radiolysis. This discovery inspires the development of a highly efficient electron lithography method for metal oxide films in ecofriendly water, which offers an advanced technique for nanodevice fabrication.

  10. Conformity of macroscopic behavior to local properties in the catalytic ammonia synthesis and oscillatory reactions on metal surfaces

    OpenAIRE

    Cholach, A. R.

    2016-01-01

    Unique catalytic potential of metal surfaces has encouraged a great number of basic and applied studies. The manuscript highlights the general regularities in a field on the grounds of strong interrelation between catalytic, kinetic and thermodynamic behaviour of the reaction system. The trials of the catalytic NH3 synthesis and the oscillatory NO+H2 reaction have revealed that the thermodynamics of the local structure determines the properties and multiplicity of the reaction intermediates e...

  11. Electronic transport at semiconductor surfaces - from point-contact transistor to micro-four-point probes

    DEFF Research Database (Denmark)

    Hasegawa, S.; Grey, Francois

    2002-01-01

    The electrical properties of semiconductor surfaces have played a decisive role in one of the most important discoveries of the last century, transistors. In the 1940s, the concept of surface states-new electron energy levels characteristic of the surface atoms-was instrumental in the fabrication...... of the first point-contact transistors, and led to the successful fabrication of field-effect transistors. However, to this day, one property of semiconductor surface states remains poorly understood, both theoretically and experimentally. That is the conduction of electrons or holes directly through...

  12. Surface Modification of Polyaniline Film by Plasma-Graft Polymerization and Its Effect on the Redox Reaction

    National Research Council Canada - National Science Library

    Yamada, Kenji; Haraguchi, Toshihide; Kajiyama, Tisato

    1998-01-01

    Poly(vinylsulfonic acid) chains having cation-exchangeable groups are introduced onto a surface of polyaniline film by means of plasma-graft polymerization, and the redox reaction mechanism of the plasma-grafted polyaniline...

  13. Static diode pumped alkali lasers: Model calculations of the effects of heating, ionization, high electronic excitation and chemical reactions

    Science.gov (United States)

    Barmashenko, B. D.; Rosenwaks, S.; Heaven, M. C.

    2013-04-01

    The effects of heating, ionization, high electronic excitation and chemical reactions on the operation of diode pumped alkali lasers (DPALs) with a static, non-flowing gain medium are calculated using a semi-analytical model. Unlike other models, assuming a three-level scheme of the laser and neglecting influence of the temperature on the lasing power, it takes into account the temperature rise and losses of neutral alkali atoms due to ionization and chemical reactions, resulting in decrease of the pump absorption and slope efficiency. Good agreement with measurements in a static DPAL [B.V. Zhdanov, J. Sell, R.J. Knize, Electron. Lett. 44 (2008) 582] is obtained. It is found that the ionization processes have a small effect on the laser operation, whereas the chemical reactions of alkali atoms with hydrocarbons strongly affect the lasing power.

  14. Derivatization reaction-based surface-enhanced Raman scattering (SERS) for detection of trace acetone.

    Science.gov (United States)

    Zheng, Ying; Chen, Zhuo; Zheng, Chengbin; Lee, Yong-Ill; Hou, Xiandeng; Wu, Li; Tian, Yunfei

    2016-08-01

    A facile method was developed for determination of trace volatile acetone by coupling a derivatization reaction to surface-enhanced Raman scattering (SERS). With iodide modified Ag nanoparticles (Ag IMNPs) as the SERS substrate, acetone without obvious Raman signal could be converted to SERS-sensitive species via a chemical derivatization reaction with 2,4-dinitrophenylhydrazine (2,4-DNPH). In addition, acetone can be effectively separated from liquid phase with a purge-sampling device and then any serious interference from sample matrices can be significantly reduced. The optimal conditions for the derivatization reaction and the SERS analysis were investigated in detail, and the selectivity and reproducibility of this method were also evaluated. Under the optimal conditions, the limit of detection (LOD) for acetone was 5mgL(-1) or 0.09mM (3σ). The relative standard deviation (RSD) for 80mgL(-1) acetone (n=9) was 1.7%. This method was successfully used for the determination of acetone in artificial urine and human urine samples with spiked recoveries ranging from 92% to 110%. The present method is convenient, sensitive, selective, reliable and suitable for analysis of trace acetone, and it could have a promising clinical application in early diabetes diagnosis. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. Site-specific growth of Au-Pd alloy horns on Au nanorods: A platform for highly sensitive monitoring of catalytic reactions by surface enhancement raman spectroscopy

    KAUST Repository

    Huang, Jianfeng

    2013-06-12

    Surface-enhanced Raman scattering (SERS) is a highly sensitive probe for molecular detection. The aim of this study was to develop an efficient platform for investigating the kinetics of catalytic reactions with SERS. To achieve this, we synthesized a novel Au-Pd bimetallic nanostructure (HIF-AuNR@AuPd) through site-specific epitaxial growth of Au-Pd alloy horns as catalytic sites at the ends of Au nanorods. Using high-resolution electron microscopy and tomography, we successfully reconstructed the complex three-dimensional morphology of HIF-AuNR@AuPd and identified that the horns are bound with high-index {11l} (0.25 < l < 0.43) facets. With an electron beam probe, we visualized the distribution of surface plasmon over the HIF-AuNR@AuPd nanorods, finding that strong longitudinal surface plasmon resonance concentrated at the rod ends. This unique crystal morphology led to the coupling of high catalytic activity with a strong SERS effect at the rod ends, making HIF-AuNR@AuPd an excellent bifunctional platform for in situ monitoring of surface catalytic reactions. Using the hydrogenation of 4-nitrothiophenol as a model reaction, we demonstrated that its first-order reaction kinetics could be accurately determined from this platform. Moreover, we clearly identified the superior catalytic activity of the rod ends relative to that of the rod bodies, owing to the different SERS activities at the two positions. In comparison with other reported Au-Pd bimetallic nanostructures, HIF-AuNR@AuPd offered both higher catalytic activity and greater detection sensitivity. © 2013 American Chemical Society.

  16. Development of an FTIR in situ reactor for real time study of surface reactions in photocatalysis

    Science.gov (United States)

    Hauchecorne, Birger

    For many years, photocatalysis has been proposed as one of the promising techniques to abate environmental pollutants. To improve the catalytic efficiency, it is vital to know the reaction mechanisms of the photocatalytic degradation. Different methods are therefore described in literature to study these mechanisms at the gaseous phase/photocatalyst interface with Fourier transform infrared (FTIR) spectroscopy as a commonly used method. The reactors described in literature and/or available on the market experience some technical and scientific difficulties. Generally, the catalyst can only be investigated after the reactions have occurred, or it is only possible to look at the changes in the gas phase concentrations while the reactions are taking place. It is thus a major challenge to develop a reactor which makes it possible to detect changes on the catalyst surface at the moment the reactions are happening. In this work, a new reactor is developed that makes it possible to study the catalytic surface at the moment the reactions occur, by means of transmission-absorption FTIR spectroscopy. Moreover, by using UV LEDs, it was possible to install the UV light inside the reactor area, so that no harmful UV light can leave the reactor, inherently making it a safer method. It was also opted to construct the reactor in a modular way, so that every part was interchangeable and could easily be replaced according to the needs of the researcher. A special screw cap is designed to hold the UV LEDs on a printed circuit board and to fit in every standard FTIR spectrometer. This study provides exciting new insights in the photocatalytic degradation mechanism of ethylene and acetaldehyde. It is for instance found that OH radicals are used as the oxidising agents to abate these pollutants. For ethylene it was proven that the molecular orbitals play an important role, resulting in the formation of both formaldehyde and formic acid as intermediates before complete mineralisation

  17. Probing the electronic transport on the reconstructed Au/Ge(001 surface

    Directory of Open Access Journals (Sweden)

    Franciszek Krok

    2014-09-01

    Full Text Available By using scanning tunnelling potentiometry we characterized the lateral variation of the electrochemical potential µec on the gold-induced Ge(001-c(8 × 2-Au surface reconstruction while a lateral current flows through the sample. On the reconstruction and across domain boundaries we find that µec shows a constant gradient as a function of the position between the contacts. In addition, nanoscale Au clusters on the surface do not show an electronic coupling to the gold-induced surface reconstruction. In combination with high resolution scanning electron microscopy and transmission electron microscopy, we conclude that an additional transport channel buried about 2 nm underneath the surface represents a major transport channel for electrons.

  18. Probing the electronic transport on the reconstructed Au/Ge(001) surface

    Science.gov (United States)

    Krok, Franciszek; Kaspers, Mark R; Bernhart, Alexander M; Nikiel, Marek; Jany, Benedykt R; Indyka, Paulina; Wojtaszek, Mateusz; Möller, Rolf

    2014-01-01

    Summary By using scanning tunnelling potentiometry we characterized the lateral variation of the electrochemical potential µec on the gold-induced Ge(001)-c(8 × 2)-Au surface reconstruction while a lateral current flows through the sample. On the reconstruction and across domain boundaries we find that µec shows a constant gradient as a function of the position between the contacts. In addition, nanoscale Au clusters on the surface do not show an electronic coupling to the gold-induced surface reconstruction. In combination with high resolution scanning electron microscopy and transmission electron microscopy, we conclude that an additional transport channel buried about 2 nm underneath the surface represents a major transport channel for electrons. PMID:25247129

  19. Effect of defects on reaction of NiO surface with Pb-contained solution

    Science.gov (United States)

    Kim, Jongjin; Hou, Binyang; Park, Changyong; Bahn, Chi Bum; Hoffman, Jason; Black, Jennifer; Bhattacharya, Anand; Balke, Nina; Hong, Hawoong; Kim, Ji Hyun; Hong, Seungbum

    2017-03-01

    In order to understand the role of defects in chemical reactions, we used two types of samples, which are molecular beam epitaxy (MBE) grown NiO(001) film on Mg(001) substrate as the defect free NiO prototype and NiO grown on Ni(110) single crystal as the one with defects. In-situ observations for oxide-liquid interfacial structure and surface morphology were performed for both samples in water and Pb-contained solution using high-resolution X-ray reflectivity and atomic force microscopy. For the MBE grown NiO, no significant changes were detected in the high-resolution X-ray reflectivity data with monotonic increase in roughness. Meanwhile, in the case of native grown NiO on Ni(110), significant changes in both the morphology and atomistic structure at the interface were observed when immersed in water and Pb-contained solution. Our results provide simple and direct experimental evidence of the role of the defects in chemical reaction of oxide surfaces with both water and Pb-contained solution.

  20. Effect of defects on reaction of NiO surface with Pb-contained solution

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jongjin; Hou, Binyang; Park, Changyong; Bahn, Chi Bum; Hoffman, Jason; Black, Jennifer; Bhattacharya, Anand; Balke, Nina; Hong, Hawoong; Kim, Ji Hyun; Hong, Seungbum

    2017-03-20

    In order to understand the role of defects in chemical reactions, we used two types of samples, which are molecular beam epitaxy (MBE) grown NiO(001) film on Mg(001) substrate as the defect free NiO prototype and NiO grown on Ni(110) single crystal as the one with defects. In-situ observations for oxide-liquid interfacial structure and surface morphology were performed for both samples in water and Pb-contained solution using high-resolution X-ray reflectivity and atomic force microscopy. For the MBE grown NiO, no significant changes were detected in the high-resolution X-ray reflectivity data with monotonic increase in roughness. Meanwhile, in the case of native grown NiO on Ni(110), significant changes in both the morphology and atomistic structure at the interface were observed when immersed in water and Pb-contained solution. Our results provide simple and direct experimental evidence of the role of the defects in chemical reaction of oxide surfaces with both water and Pb-contained solution.

  1. The electronic structure of the primary electron donor of reaction centers of purple bacteria at atomic resolution as observed by photo-CIDNP 13C NMR.

    Science.gov (United States)

    Daviso, Eugenio; Prakash, Shipra; Alia, A; Gast, Peter; Neugebauer, Johannes; Jeschke, Gunnar; Matysik, Jörg

    2009-12-29

    Composed of the two bacteriochlorophyll cofactors, P(L) and P(M), the special pair functions as the primary electron donor in bacterial reaction centers of purple bacteria of Rhodobacter sphaeroides. Under light absorption, an electron is transferred to a bacteriopheophytin and a radical pair is produced. The occurrence of the radical pair is linked to the production of enhanced nuclear polarization called photochemically induced dynamic nuclear polarization (photo-CIDNP). This effect can be used to study the electronic structure of the special pair at atomic resolution by detection of the strongly enhanced nuclear polarization with laser-flash photo-CIDNP magic-angle spinning NMR on the carotenoid-less mutant R26. In the electronic ground state, P(L) is strongly disturbed, carrying a slightly negative charge. In the radical cation state, the ratio of total electron spin densities between P(L) and P(M) is 2:1, although it is 2.5:1 for the pyrrole carbons, 2.2:1 for all porphyrinic carbons, and 4:1 for the pyrrole nitrogen. It is shown that the symmetry break between the electronic structures in the electronic ground state and in the radical cation state is an intrinsic property of the special pair supermolecule, which is particularly attributable to a modification of the structure of P(L). The significant difference in electron density distribution between the ground and radical cation states is explained by an electric polarization effect of the nearby histidine.

  2. Two-dimensional simulation research of secondary electron emission avalanche discharge on vacuum insulator surface

    Science.gov (United States)

    Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui

    2015-01-01

    Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.

  3. Scanning Electron Microscopic Evaluation of the Fractured Surfaces of Canine Calculi from Substrata with Different Surface Free Energy

    OpenAIRE

    Uyen, H. M. W.; Jongebloed, W. L.; Busscher, H. J.

    1991-01-01

    The strength of adhesion between dental calculus and enamel or dentin surfaces determines the ease with which the calculus can be removed by brushing or professional dental treatment. In this study, we examined the adhesion of canine calculi formed on substrata with different surface free energies (sfe) and roughness by means of scanning electron microscopy. In 4 beagle dogs fenestrated crowns were made on the upper fourth premolars. Subsequently, facings of glass (sfe = 120 mJ. m-2), bovine ...

  4. Structural, electronic and mechanical properties of inner surface modified imogolite nanotubes

    Directory of Open Access Journals (Sweden)

    Maurício Chagas Da Silva

    2015-03-01

    Full Text Available The electronic, structural and mechanical properties of the modified imogolites have been investigated using self consistent charge-density functional-tight binding method with a posteriori treatment of the dispersion interaction (SCC-DFTB-D. The zigzag (12,0 imogolite has been used as the initial structure for the calculations. The functionalization of the interior (12,0 imogolite nanotubes by organosilanes and by heat treatment leading to the dehydroxylation of the silanols were investigated. The reaction of the silanols with the trimethylmethoxysilanes is favored and the arrangement of the different substitutions that leads to the most symmetrical structures are preferred. The Young moduli and band gaps are slightly decreased. However, the dehydroxylation of the silanol groups in the inner surface of the imogolite leads to the increase of the Young moduli and a drastic decrease of the band gap of about 4.4 eV. It has been shown that the degree of the dehydroxylation can be controlled by heat treatment and tune the band gap, eventually, leading to a semiconductor material with well defined nanotube structure.

  5. Development of a surface conductivity measurement system for ultrahigh vacuum transmission electron microscope

    Energy Technology Data Exchange (ETDEWEB)

    Minoda, H. [Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012 (Japan); Hatano, K.; Yazawa, H. [Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan)

    2009-11-15

    The surface conductivity measurement system using a micro-four-point probe (M4PP) had been developed for the ultrahigh vacuum transmission electron microscope (UHV-TEM). Since the current distribution in the sample crystals during the current voltage measurement by the M4PP is localized within the depth of several micrometers from the surface, the system is sensitive to the surface conductivity, which is related with the surface superstructure. It was installed in the main chamber of the TEM and the surface conductivity can be measured in situ. The surface structures were observed by reflection electron microscopy and diffraction (REM-RHEED). REM-RHEED enables us to observe the surface superstructures and their structure defects such as surface atomic steps and domain boundaries of the surface superstructure. Thus the effects of the defects on the surface conductivity can be investigated. In the present paper we present the surface conductivity measurement system and its application to the Si(111)-{radical}(3)x{radical}(3)-Ag surface prepared on the Si(111) vicinal surfaces. The result clearly showed that the surface conductivity was affected by step configuration.

  6. Enzymatic Transesterification of Ethyl Ferulate with Fish Oil and Reaction Optimization by Response Surface Methodology

    Directory of Open Access Journals (Sweden)

    Zhiyong Yang

    2012-01-01

    Full Text Available The enzymatic transesterification of ethyl ferulate (EF with fish oil from cod liver was investigated with Novozym® 435 as catalyst under solvent-free conditions. The purpose of the study is to evaluate the synthesis system for the production of feruloyl fish oil in industry. The modified HPLC method was first set up to characterise the reaction products together with liquid chromatography electrospray time-of-flight mass spectrometry (HPLC-ESI-TOF-MS. The influence of the addition of glycerol to the system on the feruloyl acylglycerol profile was investigated in terms of transesterification performance. The bioconversion rate of EF can be significantly increased with the increased formation of feruloyl fish oil products when appropriate amount of glycerol is present in the reaction. Therefore, an equivalent molar amount of glycerol was added to EF for the practical optimization of the system. The mutual effects of temperature (40 to 70 °C, reaction time (1 to 5 days, enzyme load (2 to 20 % and molar ratio of fish oil and EF in the substrate (1 to 5 were thus studied with the assistance of response surface methodology (RSM for the purpose of maximizing the formation of feruloyl fish oil. The models were well fitted and verified. The optimized conditions were found to be: temperature 70 °C, enzyme load 4.3 %, substrate ratio 4.7, and reaction time 5 days. Under these conditions, the maximum conversion of EF reached 92.4 %, and the formation of feruloyl fish oil reached 80.4 %, but the formation of by-product was minimized to 11.4 % only.

  7. Heat treatment induced phase transition and microstructural evolution in electron beam surface melted Nb-Si based alloys

    Science.gov (United States)

    Guo, Yueling; Jia, Lina; Kong, Bin; Peng, Hui; Zhang, Hu

    2017-11-01

    The hardness, phase and microstructural development of Nb-18Si-24Ti-2Cr-2Al (at.%) alloys processed by electron beam surface melting (EBSM) and subsequent heat treatments were investigated. The EBSM experiments were performed using an electron beam based 3D printing system. Results showed that Nbss and Nb3Si phases were obtained via EBSM with a significantly refined microstructure. The eutectoid reaction of Nb3Si → Nbss + αNb5Si3 was triggered by heat treatments (HT) at 1200 °C or 1450 °C for 5 h. The growth and the coarsening of αNb5Si3 grains were promoted with a higher HT temperature. The hardness of the EBSM alloy was remarkably reduced by HT.

  8. The physical and chemical properties of polymerization reaction for contact lens irradiated by electron beam

    Energy Technology Data Exchange (ETDEWEB)

    Sin, Junghyeok; Jun, Jin [Dongshin Univ., Naju (Korea, Republic of)

    2010-07-01

    Can EB irradiation be possible the polymerization of HEMA without the cross-linker and initiator? The physical and chemical properties of the polymers are compared between the two polymerization methods Discuss the effects of the EB irradiation on the polymerization for having a good physical properties for the both hard and soft contact lens. EB irradiation can be used to the polymerization reaction and the EB polymerization take place at a very short period of time without any cross-linker and initiator and initiator above 100 kGy of EB dose. The polymer synthesized by EB irradiation can improve the physical properties of contact lens {yields} increase of the OH group on the surface by EB irradiation, resulting in increase o the water content and oxygen permeability of the contact lens The contact lens synthesized by EB irradiation could improve the physical properties of the contact lens, and specially can apply to a disposable soft contact lens with high water content and oxygen permeability.

  9. The Role of Shewanella oneidensis MR-1 Outer Surface Structures in Extracellular Electron Transfer

    Science.gov (United States)

    2010-01-01

    strains were grown similarly for scanning electron microscopy imaging. Cells were lifted off agar plates onto glass cover slips then fixed and treated...observed differences in electron transfer to ferrihydrite and anode surfaces is not clear. Formation of biominerals, such as magnetite (Fe3O4), during

  10. Electron band bending and surface sensitivity: X-ray photoelectron spectroscopy of polar GaN surfaces

    Science.gov (United States)

    Bartoš, I.; Romanyuk, O.; Paskova, T.; Jiříček, P.

    2017-10-01

    The role of electron band bending and surface sensitivity in determining the core level binding energies by X-ray photoelectron spectroscopy is investigated. A dominating contribution of surface atomic layers to photoemission intensity is confirmed for normal photoemission. The energy of the photoelectron core level peak does not deviate from core level peak energies of electrons photoemitted from the surface atomic layers of the crystal. The higher surface sensitivity regime, achieved e.g. at off-normal photoelectron detection angle, can be used to study the surface potential barrier in just a few topmost atomic layers. In addition, it is demonstrated that core level binding energy measured by angle-resolved X-ray photoelectron spectroscopy reflect the electron attenuation anisotropy. In particular, core level binding energy changes with emission angle and correlates with the forward focusing directions in a crystal. This effect is demonstrated by measuring the polar angle dependence of Ga 3d core levels on clean GaN(0001) and GaN(000 1 bar) surfaces with a higher and a lower band bending, respectively. The effect is explained by variation of emission depth in a crystal for normal and off-normal photoelectron emission angles.

  11. A density functional theory based study of the electron transfer reaction at the cathode-electrolyte interface in lithium-air batteries.

    Science.gov (United States)

    Kazemiabnavi, Saeed; Dutta, Prashanta; Banerjee, Soumik

    2015-05-07

    The unique properties of ionic liquids such as a relatively wide electrochemical stability window and very low vapor pressure have made them promising candidates as electrolytes for improving the cyclic performance of lithium-air batteries. The local current density, which is an important parameter in determining the performance of lithium-air batteries, is a function of the rate constant of the electron transfer reactions at the surface of the cathode. In this study, a novel method based on Marcus theory is presented to investigate the effect of varying the length of the alkyl side chain of model imidazolium based cations and the operating temperature on the rates of electron transfer reactions at the cathode. The necessary free energies of all the species involved in the multi-step reduction of oxygen into the peroxide ion were calculated using density functional theory (DFT). Our results indicate that the magnitude of the Gibbs free energy for the reduction of oxygen into the superoxide ion and also for the reduction of superoxide into the peroxide ion increases with an increase in the static dielectric constant of the ionic liquid. This trend in turn corresponds to the decrease in the length of the alkyl side chain of the ionic liquid cation. Furthermore, the change in Gibbs free energy decreases with increase in the operating temperature. The inner-sphere reorganization energies were evaluated using Nelsen's four point method. The total reorganization energies of all reduction reactions increase with decrease in the length of the alkyl side chain and increase in the operating temperature. Finally, the rate constants of the electron transfer reaction involved in the reduction of oxygen were calculated. The logarithm of the reaction rate constants decreases with increase in the static dielectric constant and increases with increase in the operating temperature. Our results provide fundamental insight into the kinetics and thermodynamics of the electron transfer

  12. Exploring the kinetic and thermodynamic aspects of four-electron electrochemical reactions: electrocatalysis of oxygen evolution by metal oxides and biological systems.

    Science.gov (United States)

    Wang, Vincent C-C

    2016-08-10

    Finding fundamental and general mechanisms for electrochemical reactions, such as the oxygen evolution reaction (OER) from water and reduction of CO2, plays vital roles in developing the desired electrocatalysts for facilitating solar fuel production. Recently, density functional theory (DFT) calculations have shown that there is a universal scaling relation of adsorption energy between key intermediate species, HO(ad) and HOO(ad), on the surface of metal oxides as OER electrocatalysts. In this paper, a kinetic and thermodynamic model for the four-electron electrochemical reaction based on previous OER mechanisms proposed by DFT calculations is developed to further investigate the electrocatalytic properties over a wide range of metal oxides and photosystem II. The OER activity of metal oxides (i.e. electrocatalytic current) calculated from the DFT-calculated equilibrium potentials with kinetic properties, such as the rate constants for interfacial electron transfer and catalytic turnover, can lead to a volcano-shaped trend that agrees with the results observed in experiments. In addition, the kinetic aspects of the impact on the electrocatalysts are evaluated. Finally, comparing the results of metal oxides and photosystem II, and fitting experimental voltammograms give further insights into kinetic and thermodynamic roles. Here, the general guidelines for designing OER electrocatalysts with unified kinetic and thermodynamic properties are presented.

  13. Why are GGAs so accurate for reaction kinetics on surfaces? Systematic comparison of hybrid vs. nonhybrid DFT for representative reactions

    Science.gov (United States)

    Mahler, Andrew; Janesko, Benjamin G.; Moncho, Salvador; Brothers, Edward N.

    2017-06-01

    "Jacob's Ladder" of approximate exchange-correlation (XC) functionals in Kohn-Sham density functional theory are widely accepted to have systematic errors in reaction barriers. The first-rung local spin-density approximation (LDA) typically predicts barriers below generalized gradient approximations, which in turn predict barriers below experiment and below fourth-rung hybrid functionals incorporating a fraction of exact exchange. We show that several reactions from previous literature reports, as well as new simulations of carbon-carbon coupling in the Fischer-Tropsch process, do not follow this conventional picture. We introduce the AB9 test set of nine abnormal reaction barriers, in which density gradient corrections and exact exchange admixture tend to lower rather than to raise predicted barriers. Comparisons of normal and abnormal reactions rationalize this phenomenon in terms of how density gradient and exact-exchange corrections stabilize transition states relative to reaction intermediates. Multireference diagnostics confirm that this behavior is not merely a consequence of multireference character. Benchmarks of the AB9 set, using the best available ab initio reference values, highlight the role of symmetry breaking and show surprisingly good performance from both the LDA and "Rung 3.5" functionals. This motivates benchmarks of the AB9 set in future XC functional development.

  14. Photochemistry of adsorbed molecules. XII. Photoinduced ion-molecule reactions at a metal surface for CH3X/RCl/Ag(111) (X=Br, I)

    Science.gov (United States)

    Dixon-Warren, St. J.; Heyd, D. V.; Jensen, E. T.; Polanyi, J. C.

    1993-04-01

    A photoinduced ion-molecule reaction is reported between superimposed molecular layers of alkyl halides on a metal substrate CH3X/RCl/Ag(111) (where X=Br or I and R=CCl3, CHCl2, or CH2Cl) to form CH3Cl(ad) (wavelengths 193, 248, and 350 nm). The reaction is mediated by charge-transfer (CT) photodissociation, in which photoelectrons from the metal surface transfer to the lower layer of adsorbate RCl to form RCl-. These negative ions then react with the upper layer CH3X in an ion-molecule reaction to form CH3Cl+X-. The yield of product CH3Cl is found to be enhanced at ˜1 ML of adsorbed CH3X (upper layer) due to a decrease in the local potential in the region of the adsorbate-adsorbate interface that enhances the probability of CT to the lower layer. In addition to lowering the local potential at the interface, the adsorbed CH3X also lowers the surface work function; as a result changes in the microscopic local potential correlate (via the CT reaction rate) with changes in the observed macroscopic work function. The yield of CH3Cl decreases at still higher CH3X coverage in the upper layer as the work function increases. The ion-molecule reaction gives evidence of being a concerted process in which the Cl- reacts as it separates from RCl- rather than following separation. The reagent RCl-, as in the surface reaction discussed in the previous paper, is formed by CT from ``hot'' electrons rather than free photoelectrons.

  15. FTIR spectroscopy of the reaction center of Chloroflexus aurantiacus: photooxidation of the primary electron donor.

    Science.gov (United States)

    Zabelin, A A; Shkuropatova, V A; Shuvalov, V A; Shkuropatov, A Ya

    2012-02-01

    Photochemical oxidation of the primary electron donor P in reaction centers (RCs) of the filamentous anoxygenic phototrophic bacterium Chloroflexus (C.) aurantiacus was examined by light-induced Fourier transform infrared (FTIR) difference spectroscopy at 95 K in the spectral range of 4000-1200 cm(-1). The light-induced P(+)Q(A)(-)/PQ(A) IR spectrum of C. aurantiacus RCs is compared to the well-characterized FTIR difference spectrum of P photooxidation in the purple bacterium Rhodobacter (R.) sphaeroides R-26 RCs. The presence in the P(+)Q(A)(-)/PQ(A) FTIR spectrum of C. aurantiacus RCs of specific low-energy electronic transitions at ~2650 and ~2200 cm(-1), as well as of associated vibrational (phase-phonon) bands at 1567, 1481, and 1294-1285 cm(-1), indicates that the radical cation P(+) in these RCs has dimeric structure, with the positive charge distributed between the two coupled bacteriochlorophyll a molecules. The intensity of the P(+) absorbance band at ~1250 nm (upon chemical oxidation of P at room temperature) in C. aurantiacus RCs is approximately 1.5 times lower than that in R. sphaeroides R-26 RCs. This fact, together with the decreased intensity of the absorbance band at ~2650 cm(-1), is interpreted in terms of the weaker coupling of bacteriochlorophylls in the P(+) dimer in C. aurantiacus compared to R. sphaeroides R-26. In accordance with the previous (pre)resonance Raman data, FTIR measurements in the carbonyl stretching region show that in C. aurantiacus RCs (i) the 13(1)-keto C=O groups of P(A) and P(B-) molecules constituting the P dimer are not involved in hydrogen bonding in either neutral or photooxidized state of P and (ii) the 3(1)-acetyl C=O group of P(B) forms a hydrogen bond (probably with tyrosine M187) absorbing at 1635 cm(-1). Differential signals at 1757(+)/1749(-) and 1741(+)/1733(-) cm(-1) in the FTIR spectrum of C. aurantiacus RCs are attributed to the 13(3)-ester C=O groups of P in different environments.

  16. Ionic liquids influence on the surface properties of electron beam irradiated wood

    Energy Technology Data Exchange (ETDEWEB)

    Croitoru, Catalin [“Transilvania” University of Brasov, Product Design and Environment Department, 29 Eroilor Str., 500036, Brasov (Romania); Patachia, Silvia, E-mail: st.patachia@unitbv.ro [“Transilvania” University of Brasov, Product Design and Environment Department, 29 Eroilor Str., 500036, Brasov (Romania); Doroftei, Florica; Parparita, Elena; Vasile, Cornelia [“Petru Poni” Institute of Macromolecular Chemistry, Physical Chemistry of Polymers Department, 41A Gr. Ghica Voda Alley, Iasi (Romania)

    2014-09-30

    Highlights: • Wood veneers impregnated with three imidazolium-based ionic liquids and irradiated with electron beam were studied by FTIR-ATR, SEM/EDX, AFM, contact angle and image analysis. • ILs preserve the surface properties of the wood (surface energy, roughness, color) upon irradiation, in comparison with the reference wood, but the surface composition is changed by treatment with IL-s, mainly with 1-butyl-3-methylimidazolium tetrafluoroborate. • Under electron beam irradiation covalent bonding of the imidazolium moiety to wood determines a higher resistance to water penetration and spreading on the surface. - Abstract: In this paper, the influence of three imidazolium-based ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate and 1-hexyl-3-methylimidazolium chloride) on the structure and surface properties of sycamore maple (Acer pseudoplatanus) veneers submitted to electron beam irradiation with a dose of 50 kGy has been studied by using Fourier transform infrared spectroscopy, as well as image, scanning electron microscopy/SEM/EDX, atomic force microscopy and contact angle analysis. The experimental results have proven that the studied ionic liquids determine a better preservation of the structural features of wood (cellulose crystallinity index and lignin concentration on the surface) as well as some of surface properties such as surface energy, roughness, color upon irradiation with electron beam, in comparison with the reference wood, but surface composition is changed by treatment with imidazolium-based ionic liquids mainly with 1-butyl-3-methylimidazolium tetrafluoroborate. Also, under electron beam irradiation covalent bonding of the imidazolium moiety to wood determines a higher resistance to water penetration and spreading on the surface.

  17. Defect and structural imperfection effects on the electronic properties of BiTeI surfaces

    Science.gov (United States)

    Fiedler, Sebastian; El-Kareh, Lydia; Eremeev, Sergey V.; Tereshchenko, Oleg E.; Seibel, Christoph; Lutz, Peter; Kokh, Konstantin A.; Chulkov, Evgueni V.; Kuznetsova, Tatyana V.; Grebennikov, Vladimir I.; Bentmann, Hendrik; Bode, Matthias; Reinert, Friedrich

    2014-07-01

    The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ˜100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability.

  18. Probing the dynamics of polyatomic multichannel elementary reactions by crossed molecular beam experiments with soft electron-ionization mass spectrometric detection.

    Science.gov (United States)

    Casavecchia, Piergiorgio; Leonori, Francesca; Balucani, Nadia; Petrucci, Raffaele; Capozza, Giovanni; Segoloni, Enrico

    2009-01-07

    environments via computer models. Examples are taken from recent on-going work (partly published) on the reactions of atomic oxygen with acetylene, ethylene and allyl radical, of great importance in combustion. A reaction of relevance in interstellar chemistry, as that of atomic carbon with acetylene, is also discussed briefly. Comparison with theoretical results is made wherever possible, both at the level of electronic structure calculations of the potential energy surfaces and dynamical computations. Recent complementary CMB work as well as kinetic work exploiting soft photo-ionization with synchrotron radiation are noted. The examples illustrated in this article demonstrate that the type of dynamical results now obtainable on polyatomic multichannel radical-molecule and radical-radical reactions might well complement reaction kinetics experiments and hence contribute to bridging the gap between microscopic reaction dynamics and thermal reaction kinetics, enhancing significantly our basic knowledge of chemical reactivity and understanding of the elementary reactions which occur in real-world environments.

  19. Production of Organic Grain Coatings by Surface-Mediated Reactions and the Consequences of This Process for Meteoritic Constituents

    Science.gov (United States)

    Nuth, Joseph A., III; Johnson, Natasha M.

    2011-01-01

    When hydrogen, nitrogen and CO are exposed to amorphous iron silicate surfaces at temperatures between 500 - 900K, a carbonaceous coating forms via Fischer-Tropsch type reactions. Under normal circumstances such a catalytic coating would impede or stop further reaction. However, we find that this coating is a better catalyst than the amorphous iron silicates that initiate these reactions. The formation of a self-perpetuating catalytic coating on grain surfaces could explain the rich deposits of macromolecular carbon found in primitive meteorites and would imply that protostellar nebulae should be rich in organic material. Many more experiments are needed to understand this chemical system and its application to protostellar nebulae.

  20. FTIR spectroscopy of the reaction center of Chloroflexus aurantiacus: photoreduction of the bacteriopheophytin electron acceptor.

    Science.gov (United States)

    Zabelin, Alexej A; Shkuropatova, Valentina A; Shuvalov, Vladimir A; Shkuropatov, Anatoly Ya

    2011-09-01

    Mid-infrared spectral changes associated with the photoreduction of the bacteriopheophytin electron acceptor H(A) in reaction centers (RCs) of the filamentous anoxygenic phototrophic bacterium Chloroflexus (Cfl.) aurantiacus are examined by light-induced Fourier transform infrared (FTIR) spectroscopy. The light-induced H(A)(-)/H(A) FTIR (1800-1200cm(-1)) difference spectrum of Cfl. aurantiacus RCs is compared to that of the previously well characterized purple bacterium Rhodobacter (Rba.) sphaeroides RCs. The most notable feature is that the large negative IR band at 1674cm(-1) in Rba. sphaeroides R-26, attributable to the loss of the absorption of the 13(1)-keto carbonyl of H(A) upon the radical anion H(A)(-) formation, exhibits only a very minor upshift to 1675cm(-1) in Cfl. aurantiacus. In contrast, the absorption band of the 13¹-keto C=O of H(A)(-) is strongly upshifted in the spectrum of Cfl. aurantiacus compared to that of Rba. sphaeroides (from 1588 to 1623cm(-1)). The data are discussed in terms of: (i) replacing the glutamic acid at L104 in Rba. sphaeroides R-26 RCs by a weaker hydrogen bond donor, a glutamine, at the equivalent position L143 in Cfl. aurantiacus RCs; (ii) a strengthening of the hydrogen-bonding interaction of the 13¹-keto C=O of H(A) with Glu L104 and Gln L143 upon H(A)(-) formation and (iii) a possible influence of the protein dielectric environment on the 13¹-keto C=O stretching frequency of neutral H(A). A conformational heterogeneity of the 13³-ester C=O group of H(A) is detected for Cfl. aurantiacus RCs similar to what has been previously described for purple bacterial RCs. 2011 Elsevier B.V. All rights reserved.

  1. Low-Energy Nuclear Reactions Resulting as Picometer Interactions with Similarity to K-Shell Electron Capture

    Science.gov (United States)

    Hora, H.; Miley, G. H.; Li, X. Z.; Kelly, J. C.; Osman, F.

    2006-02-01

    Since the appeal by Brian Josephson at the meeting of the Nobel Laureates July 2004, it seems to be indicated to summarize the following serious, reproducible and confirmed observations on reactions of protons or deuterons incorporated in host metals such as palladium. Some reflections to Rutherford's discovery of nuclear physics, the Cockroft-Oliphant discovery of anomalous low-energy fusion reactions and the chemist Hahn's discovery of fission had to be included. Using gaseous atmosphere or discharges between palladium targets, rather significant results were seen e.g. from the "life after death" heat production of such high values per host atom that only nuclear reactions can be involved. This supports the earlier evaluation of neutron generation in fully reversible experiments with gas discharges hinting that a reasonable screening effect - preferably in the swimming electron layer - may lead to reactions at nuclear distances d of picometers with reaction probability times U of about megaseconds similar to the K-shell capture radioactivity. Further electrolytic experiments led to low-energy nuclear reactions (LENR) where the involvement of pollution could be excluded from the appearance of very seldom rare earth elements. A basically new theory for DD cross-sections is used to confirm the picometer-megasecond reactions of cold fusion. Other theoretical aspects are given from measured heavy element distributions similar to the standard abundance distribution, SAD, in the Universe with consequences on endothermic heavy nuclei generation, magic numbers and to quark-gluon plasmas.

  2. Angular studies of potential electron emission in the interaction of slow ions with Al surfaces

    Science.gov (United States)

    Riccardi; Barone; Bonanno; Oliva; Baragiola

    2000-01-10

    We report energy distributions of electrons emitted from Al surfaces under impact by 1 keV Ar+ and 1-5 keV Ne+ ions. The variation of the energy distributions with the angle of incidence is different for both ions and provides information on the mechanism responsible for electron emission. For Ar+ electron emission results mainly from Auger neutralization, while for Ne+ an important emission mechanism is the decay of plasmon excitations. We find a transition between surface and bulk plasmon excitations as the energy of the ion is increased.

  3. Surface Reaction Kinetics of Steam- and CO2-Reforming as Well as Oxidation of Methane over Nickel-Based Catalysts

    Directory of Open Access Journals (Sweden)

    Karla Herrera Delgado

    2015-05-01

    Full Text Available An experimental and kinetic modeling study on the Ni-catalyzed conversion of methane under oxidative and reforming conditions is presented. The numerical model is based on a surface reaction mechanism consisting of 52 elementary-step like reactions with 14 surface and six gas-phase species. Reactions for the conversion of methane with oxygen, steam, and CO2 as well as methanation, water-gas shift reaction and carbon formation via Boudouard reaction are included. The mechanism is implemented in a one-dimensional flow field description of a fixed bed reactor. The model is evaluated by comparison of numerical simulations with data derived from isothermal experiments in a flow reactor over a powdered nickel-based catalyst using varying inlet gas compositions and operating temperatures. Furthermore, the influence of hydrogen and water as co-feed on methane dry reforming with CO2 is also investigated.

  4. Hot-electron-mediated desorption rates calculated from excited-state potential energy surfaces

    DEFF Research Database (Denmark)

    Olsen, Thomas; Gavnholt, Jeppe; Schiøtz, Jakob

    2009-01-01

    We present a model for desorption induced by (multiple) electronic transitions [DIET (DIMET)] based on potential energy surfaces calculated with the delta self-consistent field extension of density-functional theory. We calculate potential energy surfaces of CO and NO molecules adsorbed on variou...

  5. Direct observation of surface reconstruction and termination on a complex metal oxide catalyst by electron microscopy

    KAUST Repository

    Zhu, Yihan

    2012-03-19

    On the surface: The surface reconstruction of an MoVTeO complex metal oxide catalyst was observed directly by various electron microscopic techniques and the results explain the puzzling catalytic behavior. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Electronic interconnects and devices with topological surface states and methods for fabricating same

    Energy Technology Data Exchange (ETDEWEB)

    Yazdani, Ali; Ong, N. Phuan; Cava, Robert J.

    2017-04-04

    An interconnect is disclosed with enhanced immunity of electrical conductivity to defects. The interconnect includes a material with charge carriers having topological surface states. Also disclosed is a method for fabricating such interconnects. Also disclosed is an integrated circuit including such interconnects. Also disclosed is a gated electronic device including a material with charge carriers having topological surface states.

  7. Reduction of secondary electron yield for E-cloud mitigation by laser ablation surface engineering

    Energy Technology Data Exchange (ETDEWEB)

    Valizadeh, R., E-mail: reza.valizadeh@stfc.ac.uk [ASTeC, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Malyshev, O.B. [ASTeC, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Wang, S. [ASTeC, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Department of Physics, Loughborough University, Loughborough LE11 3TU (United Kingdom); Sian, T. [ASTeC, STFC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); The Photon Science Institute, The University of Manchester, Manchester M13 9PL (United Kingdom); Cropper, M.D. [Department of Physics, Loughborough University, Loughborough LE11 3TU (United Kingdom); Sykes, N. [Micronanics Ltd., Didcot, Oxon OX11 0QX (United Kingdom)

    2017-05-15

    Highlights: • SEY below 1 can be achieved with Laser ablation surface engineering. • SEY <1 surface can be produced with different types of nanosecond lasers. • Both microstructure (groves) and nano-structures are playing a role in reducing SEY. - Abstract: Developing a surface with low Secondary Electron Yield (SEY) is one of the main ways of mitigating electron cloud and beam-induced electron multipacting in high-energy charged particle accelerators. In our previous publications, a low SEY < 0.9 for as-received metal surfaces modified by a nanosecond pulsed laser was reported. In this paper, the SEY of laser-treated blackened copper has been investigated as a function of different laser irradiation parameters. We explore and study the influence of micro- and nano-structures induced by laser surface treatment in air of copper samples as a function of various laser irradiation parameters such as peak power, laser wavelength (λ = 355 nm and 1064 nm), number of pulses per point (scan speed and repetition rate) and fluence, on the SEY. The surface chemical composition was determined by x-ray photoelectron spectroscopy (XPS) which revealed that heating resulted in diffusion of oxygen into the bulk and induced the transformation of CuO to sub-stoichiometric oxide. The surface topography was examined with high resolution scanning electron microscopy (HRSEM) which showed that the laser-treated surfaces are dominated by microstructure grooves and nanostructure features.

  8. Frictional and bone ingrowth properties of engineered surface topographies produced by electron beam technology

    NARCIS (Netherlands)

    Biemond, J. Elizabeth; Aquarius, Rene; Verdonschot, Nicolaas Jacobus Joseph; Buma, Pieter

    2011-01-01

    Background Electron beam melting (E-beam) is a new technology to produce 3-dimensional surface topographies for cementless orthopedic implants. Methods The friction coefficients of two newly developed E-beam produced surface topographies were in vitro compared with sandblasted E-beam and titanium

  9. Micro-Shaping of Nanopatterned Surfaces by Electron Beam Irradiation

    Directory of Open Access Journals (Sweden)

    Carlos Angulo Barrios

    2016-04-01

    Full Text Available We show that planar nanopatterned thin films on standard polycarbonate (PC compact discs (CD can be micro-shaped in a non-contact manner via direct e-beam exposure. The shape of the film can be controlled by proper selection of the e-beam parameters. As an example of application, we demonstrate a two-dimensional (2D array of micro-lenses/reservoirs conformally covered by an Al 2D nanohole array (NHA film on a PC CD substrate. It is also shown that such a curvilinear Al NHA layer can be easily transferred onto a flexible polymeric support. The presented technique provides a new tool for creating lab-on-CD architectures and developing multifunctional (flexible non-planar nanostructured films and surfaces.

  10. Heterogeneous Reactions of Acetic Acid with Oxide Surfaces: Effects of Mineralogy and Relative Humidity.

    Science.gov (United States)

    Tang, Mingjin; Larish, Whitney A; Fang, Yuan; Gankanda, Aruni; Grassian, Vicki H

    2016-07-21

    We have investigated the heterogeneous uptake of gaseous acetic acid on different oxides including γ-Al2O3, SiO2, and CaO under a range of relative humidity conditions. Under dry conditions, the uptake of acetic acid leads to the formation of both acetate and molecularly adsorbed acetic acid on γ-Al2O3 and CaO and only molecularly adsorbed acetic acid on SiO2. More importantly, under the conditions of this study, dimers are the major form for molecularly adsorbed acetic acid on all three particle surfaces investigated, even at low acetic acid pressures under which monomers are the dominant species in the gas phase. We have also determined saturation surface coverages for acetic acid adsorption on these three oxides under dry conditions as well as Langmuir adsorption constants in some cases. Kinetic analysis shows that the reaction rate of acetic acid increases by a factor of 3-5 for γ-Al2O3 when relative humidity increases from 0% to 15%, whereas for SiO2 particles, acetic acid and water are found to compete for surface adsorption sites.

  11. Reactions of Hexa-aquo Transition Metal Ions with the Hydrated Electron up to 300 °C.

    Science.gov (United States)

    Kanjana, Kotchaphan; Courtin, Bruce; MacConnell, Ashley; Bartels, David M

    2015-11-12

    Reactions of the hydrated electron with divalent aqueous transition-metal ions, Cd(2+), Zn(2+), Ni(2+), Cu(2+), Co(2+), Fe(2+), and Mn(2+), were studied using a pulse radiolysis technique. The kinetics study was carried out at a constant pressure of 120 bar with temperatures up to 300 °C. The rate constants at room temperature agree with those reported in the literature. The reaction of Cd(2+) is approximately diffusion-limited, but none of the first-row transition-metal ion reactions are diffusion-controlled at any temperature studied. The activation energies obtained from the Arrhenius plots are in the range 14.5-40.6 kJ/mol. Pre-exponential factors are quite large, between 1 × 10(13) and 7 × 10(15) M(-1) s(-1). There appears to be a large degree of entropy-enthalpy compensation in the activation of Zn(2+), Ni(2+), Co(2+), and Cu(2+), as the larger pre-exponential factors strongly correlate with higher activation energy. Saturation of the ionic strength effect suggests that these reactions could be long-range nonadiabatic electron "jumps", but Marcus theory is incompatible with direct formation of ground state (M(+))aq ions. A self-consistent explanation is that electron transfer occurs to excited states derived from the metal 4s orbitals. The ionic strength effect in the Mn(2+) and Fe(2+) reactions suggests that these proceed by short-range adiabatic electron attachment involving breakdown of the water coordination shell.

  12. Direct vs. indirect pathway for nitrobenzene reduction reaction on a Ni catalyst surface: a density functional study.

    Science.gov (United States)

    Mahata, Arup; Rai, Rohit K; Choudhuri, Indrani; Singh, Sanjay K; Pathak, Biswarup

    2014-12-21

    Density functional theory (DFT) calculations are performed to understand and address the previous experimental results that showed the reduction of nitrobenzene to aniline prefers direct over indirect reaction pathways irrespective of the catalyst surface. Nitrobenzene to aniline conversion occurs via the hydroxyl amine intermediate (direct pathway) or via the azoxybenzene intermediate (indirect pathway). Through our computational study we calculated the spin polarized and dispersion corrected reaction energies and activation barriers corresponding to various reaction pathways for the reduction of nitrobenzene to aniline over a Ni catalyst surface. The adsorption behaviour of the substrate, nitrobenzene, on the catalyst surface was also considered and the energetically most preferable structural orientation was elucidated. Our study indicates that the parallel adsorption behaviour of the molecules over a catalyst surface is preferable over vertical adsorption behaviour. Based on the reaction energies and activation barrier of the various elementary steps involved in direct or indirect reaction pathways, we find that the direct reduction pathway of nitrobenzene over the Ni(111) catalyst surface is more favourable than the indirect reaction pathway.

  13. Electronic structure and solvation of copper and silver ions: a theoretical picture of a model aqueous redox reaction.

    Science.gov (United States)

    Blumberger, Jochen; Bernasconi, Leonardo; Tavernelli, Ivano; Vuilleumier, Rodolphe; Sprik, Michiel

    2004-03-31

    Electronic states and solvation of Cu and Ag aqua ions are investigated by comparing the Cu(2+) + e(-)--> Cu(+) and Ag(2+) + e(-)--> Ag(+) redox reactions using density functional-based computational methods. The coordination number of aqueous Cu(2+) is found to fluctuate between 5 and 6 and reduces to 2 for Cu(+), which forms a tightly bound linear dihydrate. Reduction of Ag(2+) changes the coordination number from 5 to 4. The energetics of the oxidation reactions is analyzed by comparing vertical ionization potentials, relaxation energies, and vertical electron affinities. The model is validated by a computation of the free energy of the full redox reaction Ag(2+) + Cu(+) --> Ag(+) + Cu(2+). Investigation of the one-electron states shows that the redox active frontier orbitals are confined to the energy gap between occupied and empty states of the pure solvent and localized on the metal ion hydration complex. The effect of solvent fluctuations on the electronic states is highlighted in a computation of the UV absorption spectrum of Cu(+) and Ag(+).

  14. Emission of low-energy electrons from multicharged ions interacting with metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Zeijlmans van Emmichoven, P.A. (Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6372 (United States) Joint Institute for Heavy Ion Research, Holifield Heavy Ion Research Facility, Oak Ridge, Tennessee 37831-6374 (United States)); Havener, C.C. (Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6372 (United States)); Hughes, I.G. (Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6372 (United States) Joint Institute for Heavy Ion Research, Holifield Heavy Ion Research Facility, Oak Ridge, Tennessee 37831-6374 (United States)); Zehner, D.M.; Meyer, F.W. (Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6372 (United States))

    1993-05-01

    Low-energy electron spectra are reported for 60- and 100-keV multicharged ions interacting at an incident angle of 20[degree] with Au and Cu surfaces. Analysis of the spectra indicate that at least two features contribute. The first feature represents the major contribution to the total electron yield and consists of 5--10-eV electrons emitted over a wide range of angles. The angular distribution of this component is not symmetric with respect to the surface normal, but shows an increase in the forward direction of the incident ions. It will be shown that this component arises predominantly from below the surface. Possible potential-emission mechanisms which may contribute will be discussed. The second feature, which constitutes a minor part of the overall electron emission, occurs at higher electron energies ([similar to]20 eV), and is peaked at the extreme forward angles. Binary encounters between incident ions and metal electrons at the surface-vacuum interface will be shown to describe the main features of this component. At even higher electron energies ([gt]40 eV) the spectra show a tail whose slope does not depend on either the initial charge state or kinetic energy of the incident ions. The invariance with kinetic energy is in sharp contrast with the corresponding experimental results from ion-atom collisions.

  15. Reactions of Superoxide with Iron Porphyrins in the Bulk and the Near-Surface Region of Ionic Liquids.

    Science.gov (United States)

    Dees, Anne; Jux, Norbert; Tröppner, Oliver; Dürr, Katharina; Lippert, Rainer; Schmid, Martin; Küstner, Bernd; Schlücker, Sebastian; Steinrück, Hans-Peter; Gottfried, J Michael; Ivanović-Burmazović, Ivana

    2015-07-20

    The redox reaction of superoxide (KO2) with highly charged iron porphyrins (Fe(P4+), Fe(P8+), and Fe(P8-)) has been investigated in the ionic liquids (IL) [EMIM][Tf2N] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and [EMIM][B(CN)4] (1-ethyl-3-methylimidazolium tetracyanoborate) by using time-resolved UV/vis stopped-flow, electrochemistry, cryospray mass spectrometry, EPR, and XPS measurements. Stable KO2 solutions in [EMIM][Tf2N] can be prepared up to a 15 mM concentration and are characterized by a signal in EPR spectrum at g = 2.0039 and by the 1215 cm(-1) stretching vibration in the resonance Raman spectrum. While the negatively charged iron porphyrin Fe(P8-) does not react with superoxide in IL, Fe(P4+) and Fe(P8+) do react in a two-step process (first a reduction of the Fe(III) to the Fe(II) form, followed by the binding of superoxide to Fe(II)). In the reaction with KO2, Fe(P4+) and Fe(P8+) show similar rate constants (e.g., in the case of Fe(P4+): k1 = 18.6 ± 0.5 M(-1) s(-1) for the first reaction step, and k2 = 2.8 ± 0.1 M(-1) s(-1) for the second reaction step). Notably, these rate constants are four to five orders of magnitude lower in [EMIM][Tf2N] than in conventional solvents such as DMSO. The influence of the ionic liquid is also apparent during electrochemical experiments, where the redox potentials for the corresponding Fe(III)/Fe(II) couples are much more negative in [EMIM][Tf2N] than in DMSO. This modified redox and kinetic behavior of the positively charged iron porphyrins results from their interactions with the anions of the ionic liquid, while the nucleophilicity of the superoxide is reduced by its interactions with the cations of the ionic liquid. A negligible vapor pressure of [EMIM][B(CN)4] and a sufficient enrichment of Fe(P8+) in a close proximity to the surface enabled XPS measurements as a case study for monitoring direct changes in the electronic structure of the metal centers during redox processes in solution and

  16. Fabrication of surface micro- and nanostructures for superhydrophobic surfaces in electric and electronic applications

    Science.gov (United States)

    Xiu, Yonghao

    In our study, the superhydrophobic surface based on biomimetic lotus leave is explored to maintain the desired properties for self-cleaning. Parameters in controlling bead-up and roll-off characteristics of water droplets were investigated on different model surfaces. The governing equations were proposed. Heuristic study is performed. First, the fundamental understanding of the effect of roughness on superhydrophobicity is performed. The effect of hierarchical roughness, i.e., two scale roughness effect on roughness is investigated using systems of (1) monodisperse colloidal silica sphere (submicron) arrays and Au nanoparticle on top and (2) Si micrometer pyramids and Si nanostructures on top from KOH etching and metal assisted etching of Si. The relation between the contact area fraction and water droplet contact angles are derived based on Wenzel and Cassie-Baxter equation for the systems and the two scale effect is explained regarding the synergistic combination of two scales. Previously the microscopic three-phase-contact line is thought to be the key factor in determining contact angles and hystereses. In our study, Laplace pressure was brought up and related to the three-phase-contact line and taken as a key figure of merit in determining superhydrophobicity. In addition, we are one of the first to study the effect of tapered structures (wall inclination). Combining with a second scale roughness on the tapered structures, stable Cassie state for both water and low surface energy oil may be achieved. This is of great significance for designing both superhydrophobicity and superoleophobicity. Regarding the origin of contact angle hysteresis, study of superhydrophobicity on micrometer Si pillars was performed. The relation between the interface work of function and contact angle hysteresis was proposed and derived mathematically based on the Young-Dupre equation. The three-phase-contact line was further related to a secondary scale roughness induced. Based on

  17. Excitation of surface and volume plasmons in metal nanocluster by fast electrons

    CERN Document Server

    Gildenburg, V B; Pavlichenko, I A

    2015-01-01

    Surface and volume plasmons excited in a metal cluster by moving electron and corresponding inelastic scattering spectra are studied based on the hydrodynamic approach. Along with the bulk losses traditionally taken into account, the surface and radiative ones are also considered as the physical mechanisms responsible for the plasmon damping. The second and third mechanisms are found to be essential for the surface plasmons and depend very differently on the multipole mode order. The differential equations are obtained which describe the temporal evolution of every particular mode as that one of a linear oscillator excited by the given external force, and the electron energy loss spectra are calculated. The changes in spectrum shape with the impact parameter and with the electron passage time are analyzed and found to be in good enough agreement with the data of scanning transmission electron microscopy (STEM) experiments. It is shown that, in the general case, a pronounced contribution to the formation of th...

  18. Primary role of electron work function for evaluation of nanostructured titania implant surface against bacterial infection

    Energy Technology Data Exchange (ETDEWEB)

    Golda-Cepa, M., E-mail: golda@chemia.uj.edu.pl [Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow (Poland); Syrek, K. [Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow (Poland); Brzychczy-Wloch, M. [Department of Bacteriology, Microbial Ecology and Parasitology, Jagiellonian University Medical College, Czysta 18, 31-121 Krakow (Poland); Sulka, G.D. [Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow (Poland); Kotarba, A., E-mail: kotarba@chemia.uj.edu.pl [Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow (Poland)

    2016-09-01

    The electron work function as an essential descriptor for the evaluation of metal implant surfaces against bacterial infection is identified for the first time. Its validity is demonstrated on Staphylococcus aureus adhesion to nanostructured titania surfaces. The established correlation: work function–bacteria adhesion is of general importance since it can be used for direct evaluation of any electrically conductive implant surfaces. - Highlights: • The correlation between work function and bacteria adhesion was discovered. • The discovered correlation is rationalized in terms of electrostatic bacteria–surface repulsion. • The results provide basis for the simple evaluation of implant surfaces against infection.

  19. Formation of Surface Nano- and Textured Austenite Induced by Pulsed Electron Beam Irradiation under Melting Mode

    Directory of Open Access Journals (Sweden)

    K. M. Zhang

    2013-01-01

    Full Text Available We report in this paper an interesting phenomenon associated with low-energy high-current pulsed electron beam (LEHCPEB treatment: surface nanograined and textured austenite formation under the melting treatment mode. The treatment induces superfast heating and melting followed by a rapid solidification and cooling of the material surfaces. As a result, nano-structured surface layers can be achieved quite easily. Examples of nanoaustenite formation with special texture state in the modified surface layer of AISI D2 steel and NiTi alloy will show the potential for surface nanocrystallization of materials with improved properties by LEHCPEB technique.

  20. Chemical, electronic, and magnetic structure of LaFeCoSi alloy: Surface and bulk properties

    Energy Technology Data Exchange (ETDEWEB)

    Lollobrigida, V. [Dipartimento di Scienze, Università Roma Tre, I-00146 Rome (Italy); Dipartimento di Matematica e Fisica, Università Roma Tre, I-00146 Rome (Italy); Basso, V.; Kuepferling, M.; Coïsson, M.; Olivetti, E. S.; Celegato, F. [Istituto Nazionale di Ricerca Metrologica (INRIM), I-10135 Torino (Italy); Borgatti, F. [CNR, Istituto per lo Studio dei Materiali Nanostrutturati (ISMN), I-40129 Bologna (Italy); Torelli, P.; Panaccione, G. [CNR, Istituto Officina dei Materiali (IOM), Lab. TASC, I-34149 Trieste (Italy); Tortora, L. [Laboratorio di Analisi di Superficie, Dipartimento di Matematica e Fisica, Università Roma Tre, I-00146 Rome (Italy); Dipartimento di Ingegneria Meccanica, Università Tor Vergata, I-00133 Rome (Italy); Stefani, G.; Offi, F. [Dipartimento di Scienze, Università Roma Tre, I-00146 Rome (Italy)

    2014-05-28

    We investigate the chemical, electronic, and magnetic structure of the magnetocaloric LaFeCoSi compound with bulk and surface sensitive techniques. We put in evidence that the surface retains a soft ferromagnetic behavior at temperatures higher than the Curie temperature of the bulk due to the presence of Fe clusters at the surface only. This peculiar magnetic surface effect is attributed to the exchange interaction between the ferromagnetic Fe clusters located at the surface and the bulk magnetocaloric alloy, and it is used here to monitor the magnetic properties of the alloy itself.