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Sample records for molecular electronic rectification

  1. Gradients of Rectification: Tuning Molecular Electronic Devices by the Controlled Use of Different-Sized Diluents in Heterogeneous Self-Assembled Monolayers.

    Kong, Gyu Don; Kim, Miso; Cho, Soo Jin; Yoon, Hyo Jae

    2016-08-22

    Molecular electronics has received significant attention in the last decades. To hone performance of devices, eliminating structural defects in molecular components inside devices is usually needed. We herein demonstrate this problem can be turned into a strength for modulating the performance of devices. We show the systematic dilution of a monolayer of an organic rectifier (2,2'-bipyridine-terminated n-undecanethiolate) with electronically inactive diluents (n-alkanethiolates of different lengths), gives remarkable gradients of rectification. Rectification is finely tunable in a range of approximately two orders of magnitude, retaining its polarity. Trends of rectification against the length of the diluent indicate the gradient of rectification is extremely sensitive to the molecular structure of the diluent. Further studies reveal that noncovalent intermolecular interactions within monolayers likely leads to gradients of structural defect and rectification. PMID:27443577

  2. Mechanisms of molecular electronic rectification through electronic levels with strong vibrational coupling

    Kuznetsov, A.M.; Ulstrup, Jens

    2002-01-01

    We present a new view and an analytical formalism of electron flow through a donor-acceptor molecule inserted between a pair of metal electrodes. The donor and acceptor levels are strongly coupled to an environmental nuclear continuum. The formalism applies to molecular donor-acceptor systems bot...

  3. Molecular rectifier composed of DNA with high rectification ratio enabled by intercalation

    Guo, Cunlan; Wang, Kun; Zerah-Harush, Elinor; Hamill, Joseph; Wang, Bin; Dubi, Yonatan; Xu, Bingqian

    2016-05-01

    The predictability, diversity and programmability of DNA make it a leading candidate for the design of functional electronic devices that use single molecules, yet its electron transport properties have not been fully elucidated. This is primarily because of a poor understanding of how the structure of DNA determines its electron transport. Here, we demonstrate a DNA-based molecular rectifier constructed by site-specific intercalation of small molecules (coralyne) into a custom-designed 11-base-pair DNA duplex. Measured current–voltage curves of the DNA–coralyne molecular junction show unexpectedly large rectification with a rectification ratio of about 15 at 1.1 V, a counter-intuitive finding considering the seemingly symmetrical molecular structure of the junction. A non-equilibrium Green's function-based model—parameterized by density functional theory calculations—revealed that the coralyne-induced spatial asymmetry in the electron state distribution caused the observed rectification. This inherent asymmetry leads to changes in the coupling of the molecular HOMO‑1 level to the electrodes when an external voltage is applied, resulting in an asymmetric change in transmission.

  4. Giant rectification in graphene nanoflake molecular devices with asymmetric graphene nanoribbon electrodes

    Ji, Xiao-Li; Xie, Zhen; Zuo, Xi; Zhang, Guang-Ping; Li, Zong-Liang; Wang, Chuan-Kui

    2016-09-01

    By applying density functional theory based nonequilibrium Green's function method, we theoretically investigate the electron transport properties of a zigzag-edged trigonal graphene nanoflake (ZTGNF) sandwiched between two asymmetric zigzag graphene nanoribbon (zGNR) and armchair graphene nanoribbon (aGNR) electrodes with carbon atomic chains (CACs) as the anchoring groups. Significant rectifying effects have been observed for these molecular devices in low bias voltage regions. Interestingly, the rectifying performance of molecular devices can be optimized by changing the width of the aGNR electrode and the number of anchoring CACs. Especially, the molecular device displays giant rectification ratios up to the order of 104 when two CACs are used as the anchoring group between the ZTGNF and the right aGNR electrode. Further analysis indicates that the asymmetric shift of the perturbed molecular energy levels and the spatial parity of the electron wavefunctions in the electrodes around the Fermi level play key roles in determining the rectification performance. And the spatial distributions of tunneling electron wavefunctions under negative bias voltages can be modified to be very localized by changing the number of anchoring CACs, which is found to be the origin of the giant rectification ratios.

  5. Electronic heat current rectification in hybrid superconducting devices

    In this work, we review and expand recent theoretical proposals for the realization of electronic thermal diodes based on tunnel-junctions of normal metal and superconducting thin films. Starting from the basic rectifying properties of a single hybrid tunnel junction, we will show how the rectification efficiency can be largely increased by combining multiple junctions in an asymmetric chain of tunnel-coupled islands. We propose three different designs, analyzing their performance and their potential advantages. Besides being relevant from a fundamental physics point of view, this kind of devices might find important technological application as fundamental building blocks in solid-state thermal nanocircuits and in general-purpose cryogenic electronic applications requiring energy management

  6. Electronic heat current rectification in hybrid superconducting devices

    Antonio Fornieri

    2015-05-01

    Full Text Available In this work, we review and expand recent theoretical proposals for the realization of electronic thermal diodes based on tunnel-junctions of normal metal and superconducting thin films. Starting from the basic rectifying properties of a single hybrid tunnel junction, we will show how the rectification efficiency can be largely increased by combining multiple junctions in an asymmetric chain of tunnel-coupled islands. We propose three different designs, analyzing their performance and their potential advantages. Besides being relevant from a fundamental physics point of view, this kind of devices might find important technological application as fundamental building blocks in solid-state thermal nanocircuits and in general-purpose cryogenic electronic applications requiring energy management.

  7. Electronic heat current rectification in hybrid superconducting devices

    Fornieri, Antonio; Martínez-Pérez, María José; Giazotto, Francesco

    2015-05-01

    In this work, we review and expand recent theoretical proposals for the realization of electronic thermal diodes based on tunnel-junctions of normal metal and superconducting thin films. Starting from the basic rectifying properties of a single hybrid tunnel junction, we will show how the rectification efficiency can be largely increased by combining multiple junctions in an asymmetric chain of tunnel-coupled islands. We propose three different designs, analyzing their performance and their potential advantages. Besides being relevant from a fundamental physics point of view, this kind of devices might find important technological application as fundamental building blocks in solid-state thermal nanocircuits and in general-purpose cryogenic electronic applications requiring energy management.

  8. Heat-pulse rectification in graphene Y junctions: A molecular dynamics simulations

    Pan, Feng; Li, Chenhui; Fu, Xiaonan; Wang, Fei; Sun, Qiang; Jia, Yu

    2016-06-01

    By using molecular-dynamics simulations, we demonstrate the existence of heat-pulse rectification in graphene Y junctions. Our results show that the heat pulse will separate into two parts when it flows from stem to branches. However, when it flows from branches to stem, substantial part of the heat pulse is reflected back into the branches with no separation. Moreover, we discuss rectification in different type of junctions and find that the preferred heat pulse transport direction depends on the structure of the junctions, which enable us to delicately control the heat rectification in graphene based structures.

  9. Thermal rectification of a single-wall carbon nanotube: a molecular dynamics study

    Foulaadvand, M. Ebrahim; Saeedi, Azadeh; Yousefi, Farrokh; Khadesadr, Saeed

    2014-01-01

    We have investigated the thermal rectification phenomenon in a single-wall mass graded carbon nanotube by molecular dynamics simulation. Second generation Brenner potential has been used to model the inter atomic carbon interaction. Fixed boundary condition has been taken into account. We compare our findings to a previous study by Alaghemandi et al which has been done with a different potential and boundary condition. The dependence of the rectification factor $R$ on temperature, nanotube di...

  10. Molecular rectification with identical metal electrodes at low temperatures

    A gold deposition technique for the fabrication of Au/LB/Au structures has been developed. The kinetic energy of evaporated gold atoms is reduced by scattering the gold atoms from argon gas. Moreover, the samples are cooled down below 173K (-100 deg C) to avoid the diffusion of gold atoms into the LB films and to fabricate electrically continuous thin gold electrodes (This technique has since been used in fabrication of Au/LB/Au structures even with monolayer LB films (Metzger, et al. (2001)). To measure the current-voltage characteristics of the Au/LB/Au structures at liquid helium temperatures, new junction geometries have been explored. To avoid the direct contact of the Gallium-Indium eutectic onto the LB films, which is the cause of the breakdown of the junction at lower temperatures, a cross electrode junction geometry is used. The problem of poor Langmuir-Blodgett film deposition at the penumbra region of the base electrode is avoided by covering the penumbra region with an insulating ω-tricosenoic acid LB film. Using modified Au/LB/Au structures, the current-voltage characteristics have been successfully measured down to 8K. From the temperature dependence of the current-voltage characteristics, the possible conduction mechanisms of the Au/C16H33Q-3CNQ LB film/Au structures have been discussed. At lower voltages at which non-linear symmetric current-voltage characteristics occur, the possible conduction mechanisms are found to be ohmic conduction at V <0.05V and space-charge-limited conduction above this voltage. At higher voltages, rectification occurs and the conduction mechanism for the rectification is found to be a mixture of Poole-Frenkel hopping conduction and tunnelling. From the data analysis, the signatures of the possible cause of the rectification have been discussed. (author)

  11. Molecular Electronics

    Heath, James R.

    2009-01-01

    Molecular electronics describes the field in which molecules are utilized as the active (switching, sensing, etc.) or passive (current rectifiers, surface passivants) elements in electronic devices. This review focuses on experimental aspects of molecular electronics that researchers have elucidated over the past decade or so and that relate to the fabrication of molecular electronic devices in which the molecular components are readily distinguished within the electronic properties of the de...

  12. Wave-packet rectification in nonlinear electronic systems: A tunable Aharonov-Bohm diode

    Li, Yunyun; Marchesoni, Fabio; Li, Baowen

    2014-01-01

    Rectification of electron wave-packets propagating along a quasi-one dimensional chain is commonly achieved via the simultaneous action of nonlinearity and longitudinal asymmetry, both confined to a limited portion of the chain termed wave diode. However, it is conceivable that, in the presence of an external magnetic field, spatial asymmetry perpendicular to the direction of propagation suffices to ensure rectification. This is the case of a nonlinear ring-shaped lattice with different upper and lower halves (diode), which is attached to two elastic chains (leads). The resulting device is mirror symmetric with respect to the ring vertical axis, but mirror asymmetric with respect to the chain direction. Wave propagation along the two diode paths can be modeled for simplicity by a discrete Schr\\"odinger equation with cubic nonlinearities. Numerical simulations demonstrate that, thanks to the Aharonov-Bohm effect, such a diode can be operated by tuning the magnetic flux across the ring.

  13. Wave-packet rectification in nonlinear electronic systems: a tunable Aharonov-Bohm diode.

    Li, Yunyun; Zhou, Jun; Marchesoni, Fabio; Li, Baowen

    2014-01-01

    Rectification of electron wave-packets propagating along a quasi-one dimensional chain is commonly achieved via the simultaneous action of nonlinearity and longitudinal asymmetry, both confined to a limited portion of the chain termed wave diode. However, it is conceivable that, in the presence of an external magnetic field, spatial asymmetry perpendicular to the direction of propagation suffices to ensure rectification. This is the case of a nonlinear ring-shaped lattice with different upper and lower halves (diode), which is attached to two elastic chains (leads). The resulting device is mirror symmetric with respect to the ring vertical axis, but mirror asymmetric with respect to the chain direction. Wave propagation along the two diode paths can be modeled for simplicity by a discrete Schrödinger equation with cubic nonlinearities. Numerical simulations demonstrate that, thanks to the Aharonov-Bohm effect, such a diode can be operated by tuning the magnetic flux across the ring. PMID:24691462

  14. Rectification of electronic heat current by a hybrid thermal diode

    Martínez-Pérez, M. J.; Fornieri, A.; Giazotto, F.

    2014-01-01

    We report the realization of an ultra-efficient low-temperature hybrid heat current rectifier, thermal counterpart of the well-known electric diode. Our design is based on a tunnel junction between two different elements: a normal metal and a superconducting island. Electronic heat current asymmetry in the structure arises from large mismatch between the thermal properties of these two. We demonstrate experimentally temperature differences exceeding $60$ mK between the forward and reverse the...

  15. Molecular Electronics

    Jennum, Karsten Stein

    This thesis includes the synthesis and characterisation of organic compounds designed for molecular electronics. The synthesised organic molecules are mainly based on two motifs, the obigo(phenyleneethynylenes) (OPE)s and tetrathiafulvalene (TTF) as shown below. These two scaffolds (OPE and TTF......) are chemically merged together to form cruciform-like structures that are an essential part of the thesis. The cruciform molecules were subjected to molecular conductance measurements to explore their capability towards single-crystal field-effect transistors (Part 1), molecular wires, and single electron......, however, was obtained by a study of a single molecular transistor. The investigated OPE5-TTF compound was captured in a three-terminal experiment, whereby manipulation of the molecule’s electronic spin was possible in different charge states. Thus, we demonstrated how the cruciform molecules could...

  16. Nonlinear electron transport properties and rectification effects in InAs/AlGaSb ballistic devices

    The nonlinear electron transport properties and rectification effects in InAs/AlGaSb ballistic devices are reported. We fabricated InAs/AlGaSb three-terminal ballistic junction devices composed of three quantum wires, and characterised electron transport properties with scanning the voltage on the left branch while keeping the voltage on the right constant at 77 K and 300 K. In these structures, we observed clear nonlinearity in the output voltage measured at the central branch. The nonlinear characteristics agreed well with a theoretical prediction. When the left branch is biased to a finite voltage V and the right to a voltage of -V (push-pull fashion), negative voltages appeared at the central branch regardless of the polarity of V. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. The thermal conductivity and thermal rectification of carbon nanotubes studied using reverse non-equilibrium molecular dynamics simulations

    The thermal conductivity of single-walled and multi-walled carbon nanotubes has been investigated as a function of the tube length L, temperature and chiral index using non-equilibrium molecular dynamics simulations. In the ballistic-diffusive regime the thermal conductivity follows a Lα law. The exponent α is insensitive to the diameter of the carbon nanotube; α∼0.77 has been derived for short carbon nanotubes at room temperature. The temperature dependence of the thermal conductivity shows a peak before falling at higher temperatures (>500 K). The phenomenon of thermal rectification in nanotubes has been investigated by gradually changing the atomic mass in the tube-axial direction as well as by loading extra masses on the terminal sites of the tube. A higher thermal conductivity occurs when heat flows from the low-mass to the high-mass region.

  18. Theory of Rectification in Tour Wires: The Role of Electrode Coupling

    Taylor, Jeremy Philip; Brandbyge, Mads; Stokbro, Kurt

    2002-01-01

    We report first-principles studies of electronic transport and rectification in molecular wires attached to gold electrodes. Our ab initio calculation gives an accurate description of the voltage drop as well as the broadening and alignment of the molecular levels in the metal-molecule-metal comp......We report first-principles studies of electronic transport and rectification in molecular wires attached to gold electrodes. Our ab initio calculation gives an accurate description of the voltage drop as well as the broadening and alignment of the molecular levels in the metal...

  19. Electronic properties of organic monolayers and molecular devices

    D Vuillaume; S Lenfant; D Guerin; C Delerue; C Petit; G Salace

    2006-07-01

    We review some of our recent experimental results on charge transport in organic nanostructures such as self-assembled monolayer and monolayers of organic semiconductors. We describe a molecular rectifying junction made from a sequential self-assembly on silicon. These devices exhibit a marked current–voltage rectification behavior due to resonant transport between the Si conduction band and the molecule highest occupied molecular orbital of the molecule. We discuss the role of metal Fermi level pinning in the current–voltage behavior of these molecular junctions. We also discuss some recent insights on the inelastic electron tunneling behavior of Si/alkyl chain/metal junctions.

  20. Hemichannel composition and electrical synaptic transmission: molecular diversity and its implications for electrical rectification

    Palacios-Prado, Nicolás; Huetteroth, Wolf; Pereda, Alberto E.

    2014-01-01

    Unapposed hemichannels (HCs) formed by hexamers of gap junction proteins are now known to be involved in various cellular processes under both physiological and pathological conditions. On the other hand, less is known regarding how differences in the molecular composition of HCs impact electrical synaptic transmission between neurons when they form intercellular heterotypic gap junctions (GJs). Here we review data indicating that molecular differences between apposed HCs at electrical synaps...

  1. Thermal conductivity and thermal rectification in carbon nanotubes with geometric variations of doped nitrogen: Non-equilibrium molecular dynamics simulations

    The thermal conductivity of carbon nanotubes with geometric variations of doped nitrogen is investigated. The phenomenon of thermal rectification shows that the heat transport is preferably in one direction. The asymmetric heat transport of the triangular single-nitrogen-doped carbon nanotubes (SNDCNTs) is larger than that of the parallel various-nitrogen-doped carbon nanotubes (VNDCNTs).

  2. A potential gradient along the layer-by-layer architecture for electron transfer rectification.

    Imaoka, Takane; Kobayashi, Hiroki; Katsurayama, Makoto; Yamamoto, Kimihisa

    2015-09-14

    Electrochemical and photochemical measurements demonstrated that dendritic phenylazomethines, which can make complexes with SnCl2 by a stepwise process, only permit an outbound electron transfer. The unique dendrimer effect allows efficient production of photo-generated radical ion pairs by suppressing their charge recombination. In sharp contrast, the phenylenevinylene or benzylether dendrimers, which lack a heteroatom or π-conjugation, did not exhibit such non-symmetric characters. PMID:25919437

  3. Current rectification by mediating electroactive polymers

    In this work we briefly review the theoretical basis for the electrochemical rectification in mediated redox reactions at redox polymer modified electrodes. Electrochemical rectification may have two distinct origins. It is either caused by a slow kinetics of the reaction between the external redox couple and the mediator or it is originated by a slow electronic transport within the film under an unfavorable thermodynamic condition. We show experimental results for the redox mediation reaction of poly(o-aminophenol) (POAP) on the Fe2+/3+ and on the Fe(CN)63-/4- redox couples in solution that prove the proposed mechanisms of electrochemical rectification

  4. Protonation effects on electron transport through diblock molecular junctions:A theoretical study

    2008-01-01

    Diblock oligomers are widely used in molecular electronics. Based on fully self-consistent nonequilib-rium Green’s function method and density functional theory, we study the electron transport properties of the molecular junction with a dipyrimidinyl-diphenyl (PMPH) diblock molecule sandwiched between two gold electrodes. Effects of different kinds of molecule-electrode anchoring geometry and protona-tion of the PMPH molecule are studied. Protonation leads to both conductance and rectification en-hancements. However, the experimentally observed rectifying direction inversion is not found in our calculation. The preferential current direction is always from the pyrimidinyl to the phenyl side. Our calculations indicate that the protonation of the molecular wire is not the only reason of the rectification inversion.

  5. Rectification effects in coherent transport through single molecules

    Pump, Florian; Cuniberti, Gianaurelio

    2006-01-01

    A minimal model for coherent transport through a donor/acceptor molecular junction is presented. The two donor and acceptor sites are described by single levels energetically separated by an intramolecular tunnel barrier. In the limit of strong coupling to the electrodes a current rectification for different bias voltage polarities occurs. Contacts with recent experiments of molecular rectification are also given.

  6. Towards graphyne molecular electronics.

    Li, Zhihai; Smeu, Manuel; Rives, Arnaud; Maraval, Valérie; Chauvin, Remi; Ratner, Mark A; Borguet, Eric

    2015-01-01

    α-Graphyne, a carbon-expanded version of graphene ('carbo-graphene') that was recently evidenced as an alternative zero-gap semiconductor, remains a theoretical material. Nevertheless, using specific synthesis methods, molecular units of α-graphyne ('carbo-benzene' macrocycles) can be inserted between two anilinyl (4-NH2-C6H4)-anchoring groups that allow these fragments to form molecular junctions between gold electrodes. Here, electrical measurements by the scanning tunnelling microscopy (STM) break junction technique and electron transport calculations are carried out on such a carbo-benzene, providing unprecedented single molecule conductance values: 106 nS through a 1.94-nm N-N distance, essentially 10 times the conductance of a shorter nanographenic hexabenzocoronene analogue. Deleting a C4 edge of the rigid C18 carbo-benzene circuit results in a flexible 'carbo-butadiene' molecule that has a conductance 40 times lower. Furthermore, carbo-benzene junctions exhibit field-effect transistor behaviour when an electrochemical gate potential is applied, opening the way for device applications. All the results are interpreted on the basis of theoretical calculations. PMID:25699991

  7. Inelastic transport and low-bias rectification in a single-molecule diode.

    Hihath, Joshua; Bruot, Christopher; Nakamura, Hisao; Asai, Yoshihiro; Díez-Pérez, Ismael; Lee, Youngu; Yu, Luping; Tao, Nongjian

    2011-10-25

    Designing, controlling, and understanding rectification behavior in molecular-scale devices has been a goal of the molecular electronics community for many years. Here we study the transport behavior of a single molecule diode, and its nonrectifying, symmetric counterpart at low temperatures, and at both low and high biases to help elucidate the electron-phonon interactions and transport mechanisms in the rectifying system. We find that the onset of current rectification occurs at low biases, indicating a significant change in the elastic transport pathway. However, the peaks in the inelastic electron tunneling (IET) spectrum are antisymmetric about zero bias and show no significant changes in energy or intensity in the forward or reverse bias directions, indicating that despite the change in the elastic transmission probability there is little impact on the inelastic pathway. These results agree with first principles calculations performed to evaluate the IETS, which also allow us to identify which modes are active in the single molecule junction. PMID:21932824

  8. Molecular electronic junction transport

    Solomon, Gemma C.; Herrmann, Carmen; Ratner, Mark

    2012-01-01

    Whenasinglemolecule,oracollectionofmolecules,isplacedbetween two electrodes and voltage is applied, one has a molecular transport junction. We discuss such junctions, their properties, their description, and some of their applications. The discussion is qualitative rather than quantitative......, and focuses on mechanism, structure/function relations, regimes and mechanisms of transport, some molecular regularities, and some substantial challenges facing the field. Because there are many regimes and mechanisms in transport junctions, we will discuss time scales, geometries, and inelastic scattering...

  9. Electron transport through molecular junctions

    At present, metal–molecular tunnel junctions are recognized as important active elements in molecular electronics. This gives a strong motivation to explore physical mechanisms controlling electron transport through molecules. In the last two decades, an unceasing progress in both experimental and theoretical studies of molecular conductance has been demonstrated. In the present work we give an overview of theoretical methods used to analyze the transport properties of metal–molecular junctions as well as some relevant experiments and applications. After a brief general description of the electron transport through molecules we introduce a Hamiltonian which can be used to analyze electron–electron, electron–phonon and spin–orbit interactions. Then we turn to description of the commonly used transport theory formalisms including the nonequilibrium Green’s functions based approach and the approach based on the “master” equations. We discuss the most important effects which could be manifested through molecules in electron transport phenomena such as Coulomb, spin and Frank–Condon blockades, Kondo peak in the molecular conductance, negative differential resistance and some others. Bearing in mind that first principles electronic structure calculations are recognized as the indispensable basis of the theory of electron transport through molecules, we briefly discuss the main equations and some relevant applications of the density functional theory which presently is often used to analyze important characteristics of molecules and molecular clusters. Finally, we discuss some kinds of nanoelectronic devices built using molecules and similar systems such as carbon nanotubes, various nanowires and quantum dots.

  10. Electron scattering on molecular hydrogen

    The author considers scattering phenomena which occur when a beam of electrons interacts with a molecular hydrogen gas of low density. Depending on the energy loss of the scattered electrons one can distinguish elastic scattering, excitation and (auto)ionization of the H2-molecule. The latter processes may also lead to dissociation. These processes are investigated in four experiments in increasing detail. (Auth.)

  11. Single Molecule Rectification Induced by the Asymmetry of a Single Frontier Orbital.

    Ding, Wendu; Negre, Christian F A; Vogt, Leslie; Batista, Victor S

    2014-08-12

    A mechanism for electronic rectification under low bias potentials is elucidated for the prototype molecule HS-phenyl-amide-phenyl-SH. We apply density functional theory (DFT) combined with the nonequilibrium Green's function formalism (NEGF), as implemented in the TranSIESTA computational code to calculate transport properties. We find that a single frontier orbital, the closest to the Fermi level, provides the dominant contribution to the overall transmission and determines the current. The asymmetric distribution of electron density in that orbital leads to rectification in charge transport due to its asymmetric response, shifting toward (or away from) the Fermi level under forward (or reverse) applied bias voltage. These findings provide a simple design principle to suppress recombination in molecular assemblies of dye-sensitized solar cells (DSSCs) where interfacial electron transfer is mediated by frontier orbitals with asymmetric character. PMID:26588307

  12. Automatic input rectification

    Long, Fan; Ganesh, Vijay; Carbin, Michael James; Sidiroglou, Stelios; Rinard, Martin

    2012-01-01

    We present a novel technique, automatic input rectification, and a prototype implementation, SOAP. SOAP learns a set of constraints characterizing typical inputs that an application is highly likely to process correctly. When given an atypical input that does not satisfy these constraints, SOAP automatically rectifies the input (i.e., changes the input so that it satisfies the learned constraints). The goal is to automatically convert potentially dangerous inputs into typical inputs that the ...

  13. Molecular electronic-structure theory

    Helgaker, Trygve; Olsen, Jeppe

    2014-01-01

    Ab initio quantum chemistry has emerged as an important tool in chemical research and is appliced to a wide variety of problems in chemistry and molecular physics. Recent developments of computational methods have enabled previously intractable chemical problems to be solved using rigorous quantum-mechanical methods. This is the first comprehensive, up-to-date and technical work to cover all the important aspects of modern molecular electronic-structure theory. Topics covered in the book include: * Second quantization with spin adaptation * Gaussian basis sets and molecular-integral evaluati

  14. Electron transport in molecular junctions

    Jin, Chengjun

    charge position are in quantitative agreement with the experiments, while pure DFT is not. This is the consequence of the accurate energy level alignment, where the DFT+∑ method corrects the self-interaction error in the standard DFT functional and uses a static image charge model to include the image......This thesis addresses the electron transport in molecular junctions, focusing on the energy level alignment and correlation effects. Various levels of theory have been applied to study the structural and electronic effects in different molecular junctions, starting from the single particle density...... the lowest unoccupied molecular level (LUMO) of the 44BP molecule hybridizes strongly with Ni 3d orbitals, the gating is auxiliary by the so-called spinterface. Finally, the correlation effect of the image charge beyond the energy level renormalization has been studied. It is shown that the finite response...

  15. Electron microscopy at molecular dimensions

    Baumeister, W.; Vogell, W.

    1980-01-01

    This book gives a survey of recent trends and activities in molcular microscopy . This branch of electron microscopy which is aimed at determining the structure of biological macromolecules and supramolecular assemblies has made significant progress during the past few years and promises to play a major role in the future of molecular biology. The thirty nine chapters fall into two general groups: The first group discusses the state-of-the-art illustrated by a wide range of molecular specimens containing new material. The second group reviews recent developments in image recording, low dose microscopy and image processing which are of potential interest to those seeking to overcome present limitations in obtaining more detailed structural information. The final five chapters deal with a subject which will surely emerge as a major area of practical interest in molecular microscopy: the artifical assembly of ordered molecular arrays.

  16. Carbon Nanotube Based Molecular Electronics

    Srivastava, Deepak; Saini, Subhash; Menon, Madhu

    1998-01-01

    Carbon nanotubes and the nanotube heterojunctions have recently emerged as excellent candidates for nanoscale molecular electronic device components. Experimental measurements on the conductivity, rectifying behavior and conductivity-chirality correlation have also been made. While quasi-one dimensional simple heterojunctions between nanotubes with different electronic behavior can be generated by introduction of a pair of heptagon-pentagon defects in an otherwise all hexagon graphene sheet. Other complex 3- and 4-point junctions may require other mechanisms. Structural stability as well as local electronic density of states of various nanotube junctions are investigated using a generalized tight-binding molecular dynamics (GDBMD) scheme that incorporates non-orthogonality of the orbitals. The junctions investigated include straight and small angle heterojunctions of various chiralities and diameters; as well as more complex 'T' and 'Y' junctions which do not always obey the usual pentagon-heptagon pair rule. The study of local density of states (LDOS) reveal many interesting features, most prominent among them being the defect-induced states in the gap. The proposed three and four pointjunctions are one of the smallest possible tunnel junctions made entirely of carbon atoms. Furthermore the electronic behavior of the nanotube based device components can be taylored by doping with group III-V elements such as B and N, and BN nanotubes as a wide band gap semiconductor has also been realized in experiments. Structural properties of heteroatomic nanotubes comprising C, B and N will be discussed.

  17. Theoretical study of rectification in Tour wires with asymmetric coupling to gold contacts

    Taylor, Jeremy; Brandbyge, Mads; Stokbro, Kurt

    2002-03-01

    We report first-principles studies of electronic transport properties (using the TranSIESTA^1,2 package) of a molecular-scale rectifier consisting of a Tour wire^3 connected to two gold electrodes. The relationship between current rectification and coupling to the electrodes is studied. The device consists of a molecule which is thiol-gold bonded to one electrode and weakly coupled to another electrode through a tunnel barrier. One key feature of the TranSIESTA package is that it uses the same model chemistry for the electrodes and the molecule/device region, thus allowing an ab-initio evaluation of the self-energy due to the electrodes and a quantitative measure of the alignment and broadening of molecular levels. We find that the strong thiol-gold bond leads to a broad transmission resonance which follows below the Fermi level of the strongly coupled electrode, leading to rectification of the current. We find that the width of the resonance must be taken into account in order to understand the rectification properties of such devices. ^1 M. Brandbyge, J. Taylor, K. Stokbro, J.L. Mozos, P. Ordejon,http://xxx.lanl.gov/abs/cond-mat/0108257 and references therein ^2 SIESTA: D. Sanchez-Portal, P. Ordejon, E. Artacho, and J. Soler, Int. J. Quantum Chem. 65, 453 (1997). ^3 J. M. Tour, M. Kozoki, and J.M. Seminario, J. Am. Chem. Soc. 120, 8486 (2001).

  18. Electron tunneling between two electrodes mediated by a molecular wire containing a redox center

    Graphical abstract: We present a model for a molecular wire containing a redox center and suspended in an electrolyte solution. Current potential curves can contain plateaus and negative differential resistances. - Abstract: We derive an explicit expression for the quantum conductivity of a molecular wire containing a redox center, which is embedded in an electrochemical environment. The redox center interacts with the solvent, and the average over the solvent configurations is performed numerically. Explicit calculations have been performed for a chain of three atoms. When the redox center interacts strongly with neighboring electronic levels, the current-potential curves show interesting features like rectification, current plateaus and negative differential resistance. Electronic spectroscopy of intermediate states can be performed at constant small bias by varying the electrochemical potential of the wire.

  19. Length dependence of rectification in organic co-oligomer spin rectifiers

    Gui-Chao, Hu; Zhao, Zhang; Ying, Li; Jun-Feng, Ren; Chuan-Kui, Wang

    2016-05-01

    The rectification ratio of organic magnetic co-oligomer diodes is investigated theoretically by changing the molecular length. The results reveal two distinct length dependences of the rectification ratio: for a short molecular diode, the charge-current rectification changes little with the increase of molecular length, while the spin-current rectification is weakened sharply by the length; for a long molecular diode, both the charge-current and spin-current rectification ratios increase quickly with the length. The two kinds of dependence switch at a specific length accompanied with an inversion of the rectifying direction. The molecular ortibals and spin-resolved transmission analysis indicate that the dominant mechanism of rectification suffers a change at this specific length, that is, from asymmetric shift of molecular eigenlevels to asymmetric spatial localization of wave functions upon the reversal of bias. This work demonstrates a feasible way to control the rectification in organic co-oligomer spin diodes by adjusting the molecular length. Project supported by the National Natural Science Foundation of China (Grant No. 11374195), the Natural Science Foundation of Shandong Province, China (Grant No. ZR2014AM017), the Taishan Scholar Project of Shandong Province, China, and the Excellent Young Scholars Research Fund of Shandong Normal University, China.

  20. Electron spectroscopy and molecular structure

    Electron spectroscopy can now be applied to solids, liquids and gases. Some fields of research require ultrahigh vacuum conditions, in particular those directly concerned with surface phenomena on the monolayer level. Liquids have just recently been subject to studies and several improvements and extensions of this technique can be done. Much advance has lately been achieved in the case of gases, where the pressure range presently is 10-5-1 torr. Signal-to-background ratios for core lines can be approximately 1000:1 and the resolution has been increased to the extent that vibrational fine structures of 1s levels in some small molecules have been observed. These improvements are based on the monochromatization of the exciting AlKα radiation. Under such conditions the background is furthermore so much reduced that shake-up structures are more generally accessible for closer studies. ESCA shifts are also much easier to resolve and to measure with higher precision, around 0.02 eV. The photoionization dynamics including atomic and molecular relaxations has been investigated, both experimentally and theoretically. In the valence electron region improvements in energy resolution and in the application of the intensity model based on the MO-LCAO approximation greatly facilitate the assignments of the valence orbitals. Accumulation of empirical evidences gathered from series of similar chemical species and also better methods of calculation, both ab initio and semiempirical, have gradually resulted in a much better understanding of the molecular orbital description. The experience of the latest ESCA instrument with monochromatization has motivated an attempt to design an optimized apparatus according to the general principles of this prototype. A considerable gain in intensity can be made at an improved resolution set by the inherent diffraction pattern of the focussing spherical quartz crystals. (author)

  1. Resonant optical rectification in bacteriorhodopsin.

    Groma, Géza I; Colonna, Anne; Lambry, Jean-Christophe; Petrich, Jacob W; Váró, György; Joffre, Manuel; Vos, Marten H; Martin, Jean-Louis

    2004-05-25

    The relative role of retinal isomerization and microscopic polarization in the phototransduction process of bacteriorhodopsin is still an open question. It is known that both processes occur on an ultrafast time scale. The retinal trans-->cis photoisomerization takes place on the time scale of a few hundred femtoseconds. On the other hand, it has been proposed that the primary light-induced event is a sudden polarization of the retinal environment, although there is no direct experimental evidence for femtosecond charge displacements, because photovoltaic techniques cannot be used to detect charge movements faster than picoseconds. Making use of the known high second-order susceptibility chi(2) of retinal in proteins, we have used a nonlinear technique, interferometric detection of coherent infrared emission, to study macroscopically oriented bacteriorhodopsin-containing purple membranes. We report and characterize impulsive macroscopic polarization of these films by optical rectification of an 11-fs visible light pulse in resonance with the optical transition. This finding provides direct evidence for charge separation as a precursor event for subsequent functional processes. A simple two-level model incorporating the resonant second-order optical properties of retinal, which are known to be a requirement for functioning of bacteriorhodopsin, is used to describe the observations. In addition to the electronic response, long-lived infrared emission at specific frequencies was observed, reflecting charge movements associated with vibrational motions. The simultaneous and phase-sensitive observation of both the electronic and vibrational signals opens the way to study the transduction of the initial polarization into structural dynamics. PMID:15148391

  2. Molecular Programming Pseudo-code Representation to Molecular Electronics

    Pradhan, Manas Ranjan

    2010-01-01

    This research paper is proposing the idea of pseudo code representation to molecular programming used in designing molecular electronics devices. Already the schematic representation of logical gates like AND, OR, NOT etc.from molecular diodes or resonant tunneling diode are available. This paper is setting a generic pseudo code model so that various logic gates can be formulated. These molecular diodes have designed from organic molecules or Bio-molecules. Our focus is on to give a scenario of molecular computation through molecular programming. We have restricted our study to molecular rectifying diode and logic device as AND gate from organic molecules only.

  3. Giant Thermal Rectification from Polyethylene Nanofiber Thermal Diodes

    Zhang, Teng

    2015-01-01

    The realization of phononic computing is held hostage by the lack of high performance thermal devices. Here we show through theoretical analysis and molecular dynamics simulations that unprecedented thermal rectification factors (as large as 1.20) can be achieved utilizing the phase dependent thermal conductivity of polyethylene nanofibers. More importantly, such high thermal rectifications only need very small temperature differences (< 20 oC) across the device, which is a significant advantage over other thermal diodes which need temperature biases on the order of the operating temperature. Taking this into consideration, we show that the dimensionless temperature-scaled rectification factors of the polymer nanofiber diodes range from 12 to 25 - much larger than other thermal diodes (< 8). The polymer nanofiber thermal diode consists of a crystalline portion whose thermal conductivity is highly phase-sensitive and a cross-linked portion which has a stable phase. Nanoscale size effect can be utilized t...

  4. Molecular Programming Pseudo-code Representation to Molecular Electronics

    Pradhan, Manas Ranjan; E G Rajan

    2010-01-01

    This research paper is proposing the idea of pseudo code representation to molecular programming used in designing molecular electronics devices. Already the schematic representation of logical gates like AND, OR, NOT etc.from molecular diodes or resonant tunneling diode are available. This paper is setting a generic pseudo code model so that various logic gates can be formulated. These molecular diodes have designed from organic molecules or Bio-molecules. Our focus is on to give a scenario ...

  5. Electrons in molecules from basic principles to molecular electronics

    Launay, Jean-Pierre

    2014-01-01

    The purpose of this book is to provide the reader with essential keys to a unified understanding of the rapidly expanding field of molecular materials and devices: electronic structures and bonding, magnetic, electrical and photo-physical properties, and the mastering of electrons in molecular electronics. Chemists will discover how basic quantum concepts allow us to understand the relations between structures, electronic structures, and properties of molecular entities and assemblies, and to design new molecules and materials. Physicists and engineers will realize how the molecular world fits in with their need for systems flexible enough to check theories or provide original solutions to exciting new scientific and technological challenges. The non-specialist will find out how molecules behave in electronics at the most minute, sub-nanosize level. The comprehensive overview provided in this book is unique and will benefit undergraduate and graduate students in chemistry, materials science, and engineering, ...

  6. Molecular Electronics of Self-Assembled Monolayers

    Wang, Xintai

    material: graphene, and how such material can be incorporated intothe field of molecular electronics.Chapter 3 is a brief introduction of important instruments used in this thesis.Chapter 4, 5 and 6 describe the major experimental work in this thesis. Chapter 4 introduces two novel anchoring......This thesis deals withmolecular electronic investigations on self-assembledmonolayers. The thesis is divided into seven chapters, as outlined below.Chapter 1 is a general introduction of the history of molecular electronics and its current state.Chapter 2 is separated into three parts. Part I...... providesa brief introduction toself-assembledmonolayers(SAMs), includingits structure, formation, and its role in molecular electronic investigations. Part II is an introduction of different molecular functions, which are interesting for designing real devices. Part III is an introduction of a novel carbon...

  7. Molecular modeling of inelastic electron transport in molecular junctions

    A quantum chemical approach for the modeling of inelastic electron tunneling spectroscopy of molecular junctions based on scattering theory is presented. Within a harmonic approximation, the proposed method allows us to calculate the electron-vibration coupling strength analytically, which makes it applicable to many different systems. The calculated inelastic electron transport spectra are often in very good agreement with their experimental counterparts, allowing the revelation of detailed information about molecular conformations inside the junction, molecule-metal contact structures, and intermolecular interaction that is largely inaccessible experimentally

  8. DNA-based applications in molecular electronics

    Linko, Veikko

    2011-01-01

    This thesis is mainly focused on DNA molecules and especially on self-assembled DNA constructs and their potential applications in nanotechnology and molecular electronics. In the field of molecular electronics the conductivity of DNA is a crucial - yet open - question, and it is of great concern, since DNA is a very promising molecule in a context of bottom-up based nanodevices due to its superior selfassembly characteristics. A key tool in all the experiments presented in ...

  9. Probing molecular chirality via electronic transport

    We investigate electronic molecular transport in several conjugated organic oligomers by means of ab initio calculations and nonequilibrium Green's functions method. We demonstrate that the I-V characteristics of these molecules constitute a direct manifestation of their degree of molecular chirality, which is calculated using group theory and depends exclusively on the atomic positions. This result shows that electronic current through these specific molecules is strongly correlated with their geometrical degree of chirality.

  10. Very large thermal rectification in bulk composites consisting partly of icosahedral quasicrystals

    The bulk thermal rectifiers usable at a high temperature above 300 K were developed by making full use of the unusual electron thermal conductivity of icosahedral quasicrystals. The unusual electron thermal conductivity was caused by a synergy effect of quasiperiodicity and by a narrow pseudogap at the Fermi level. The rectification ratio, defined by TRR = |Jlarge|/|Jsmall|, reached vary large values exceeding 2.0. This significant thermal rectification would lead to new practical applications for the heat management. (paper)

  11. Understanding charge transport in molecular electronics.

    Kushmerick, J J; Pollack, S K; Yang, J C; Naciri, J; Holt, D B; Ratner, M A; Shashidhar, R

    2003-12-01

    For molecular electronics to become a viable technology the factors that control charge transport across a metal-molecule-metal junction need to be elucidated. We use an experimentally simple crossed-wire tunnel junction to interrogate how factors such as metal-molecule coupling, molecular structure, and the choice of metal electrode influence the current-voltage characteristics of a molecular junction. PMID:14976024

  12. Progress in molecular precursors for electronic materials

    Buhro, W.E. [Washington Univ., St. Louis, MO (United States)

    1996-09-01

    Molecular-precursor chemistry provides an essential underpinning to all electronic-materials technologies, including photovoltaics and related areas of direct interest to the DOE. Materials synthesis and processing is a rapidly developing field in which advances in molecular precursors are playing a major role. This article surveys selected recent research examples that define the exciting current directions in molecular-precursor science. These directions include growth of increasingly complex structures and stoichiometries, surface-selective growth, kinetic growth of metastable materials, growth of size-controlled quantum dots and quantum-dot arrays, and growth at progressively lower temperatures. Continued progress in molecular-precursor chemistry will afford precise control over the crystal structures, nanostructures, and microstructures of electronic materials.

  13. Electron and Phonon Transport in Molecular Junctions

    Li, Qian

    transmission at the Fermi energy. We propose and analyze a way of using π   stacking to design molecular junctions to control heat transport. We develop a simple model system to identify optimal parameter regimes and then use density functional theory (DFT) to extract model parameters for a number of specific......Molecular electronics provide the possibility to investigate electron and phonon transport at the smallest imaginable scale, where quantum effects can be investigated and exploited directly in the design. In this thesis, we study both electron transport and phonon transport in molecular junctions...... DFT method. It is found that the thermal conductance of π-stacked systems can be reduced by 95%, compared with that in a single-molecule junction. Phonon transmission of π-stacked systems is reduced dramatically in the whole frequency range and the left transmission mainly remains below 5 THz....

  14. Light and Redox Switchable Molecular Components for Molecular Electronics

    Browne, Wesley R.; Feringa, Bernard

    2010-01-01

    The field of molecular and organic electronics has seen rapid progress in recent years, developing from concept and design to actual demonstration devices in which both single molecules and self-assembled monolayers are employed as light-responsive components. Research in this field has seen numerou

  15. Reversal of Thermal Rectification in Quantum Systems

    Zhang, Lifa; Yan, Yonghong; Wu, Chang-Qin; Wang, Jian-Sheng; Li, Baowen

    2009-01-01

    We study thermal transport in anisotropic Heisenberg spin chains using the quantum master equation. It is found that thermal rectification changes sign when the external homogeneous magnetic field is varied. This reversal also occurs when the magnetic field becomes inhomogeneous. Moreover, we can tune the reversal of rectification by temperatures of the heat baths, the anisotropy and size of the spin chains.

  16. Fullerene based devices for molecular electronics

    G. Cuniberti; R. GUTIERREZ; Fagas, G.; Grossmann, F.; Richter, K; Schmidt, R.

    2001-01-01

    We have investigated the electronic properties of a C_60 molecule in between carbon nanotube leads. This problem has been tackled within a quantum chemical treatment utilizing a density functional theory-based LCAO approach combined with the Landauer formalism. Owing to low-dimensionality, electron transport is very sensitive to the strength and geometry of interfacial bonds. Molecular contact between interfacial atoms and electrodes gives rise to a complex conductance dependence on the elect...

  17. Molecular Dissociation Induced by Electron Collisions

    Wolf, Andreas

    2009-05-01

    Free electrons can efficiently break molecules or molecular ions in low-energy collisions by the processes of dissociative recombination or attachment. These processes make slow electrons efficient chemical agents in many environments. For dissociative recombination, in particular, studies of the underlying reaction paths and mechanisms have become possible on a uniquely elementary level in recent years both for theory and experiment. On the experimental side, collisions can be prepared at resolved collision energies down to the meV (10 Kelvin) level, increasingly gaining control also over the initial molecular quantum level, and individual events are detected and kinematically analyzed by fast-beam coincidence fragment imaging. Experiments are reported from the ion cooler ring TSR in Heidelberg. Stored beams of molecular ions cooled in their external and internal degrees of freedom are collinearly merged with intense and cold electron beams from cryogenic GaAs photocathodes, recently shown to yield fast cooling of the center-of-mass motion also for heavy and correspondingly slow molecular ion beams. To reconstruct the molecular fragmentation events multiparticle imaging can now be used systematically with collision energies set a wide range, especially aiming at specific electron capture resonances. Thus, for CF^+ it is found that the electronic state of the C fragment (^3P or ^1D) switches resonantly when the collision energy is changed by only a small fraction. As a new powerful tool, an energy-sensitive multi-strip surface-barrier detector (EMU) has been set up to measure with near-unity efficiency the masses of all fragments together with their hit positions in high-multiplicity events. Among many uses, this device allows internal molecular excitations to be derived for individual chemical channels in polyatomic fragmentation. New results will be presented in particular on the breakup of the hydronium ion (D3O^+).

  18. Computational Nanotechnology Molecular Electronics, Materials and Machines

    Srivastava, Deepak; Biegel, Bryan A. (Technical Monitor)

    2002-01-01

    This presentation covers research being performed on computational nanotechnology, carbon nanotubes and fullerenes at the NASA Ames Research Center. Topics cover include: nanomechanics of nanomaterials, nanotubes and composite materials, molecular electronics with nanotube junctions, kinky chemistry, and nanotechnology for solid-state quantum computers using fullerenes.

  19. Electronic continuum model for molecular dynamics simulations.

    Leontyev, I V; Stuchebrukhov, A A

    2009-02-28

    A simple model for accounting for electronic polarization in molecular dynamics (MD) simulations is discussed. In this model, called molecular dynamics electronic continuum (MDEC), the electronic polarization is treated explicitly in terms of the electronic continuum (EC) approximation, while the nuclear dynamics is described with a fixed-charge force field. In such a force-field all atomic charges are scaled to reflect the screening effect by the electronic continuum. The MDEC model is rather similar but not equivalent to the standard nonpolarizable force-fields; the differences are discussed. Of our particular interest is the calculation of the electrostatic part of solvation energy using standard nonpolarizable MD simulations. In a low-dielectric environment, such as protein, the standard MD approach produces qualitatively wrong results. The difficulty is in mistreatment of the electronic polarizability. We show how the results can be much improved using the MDEC approach. We also show how the dielectric constant of the medium obtained in a MD simulation with nonpolarizable force-field is related to the static (total) dielectric constant, which includes both the nuclear and electronic relaxation effects. Using the MDEC model, we discuss recent calculations of dielectric constants of alcohols and alkanes, and show that the MDEC results are comparable with those obtained with the polarizable Drude oscillator model. The applicability of the method to calculations of dielectric properties of proteins is discussed. PMID:19256627

  20. Exploiting plasmon-induced hot electrons in molecular electronic devices.

    Conklin, David; Nanayakkara, Sanjini; Park, Tae-Hong; Lagadec, Marie F; Stecher, Joshua T; Chen, Xi; Therien, Michael J; Bonnell, Dawn A

    2013-05-28

    Plasmonic nanostructures can induce a number of interesting responses in devices. Here we show that hot electrons can be extracted from plasmonic particles and directed into a molecular electronic device, which represents a new mechanism of transfer from light to electronic transport. To isolate this phenomenon from alternative and sometimes simultaneous mechanisms of plasmon-exciton interactions, we designed a family of hybrid nanostructure devices consisting of Au nanoparticles and optoelectronically functional porphyin molecules that enable precise control of electronic and optical properties. Temperature- and wavelength-dependent transport measurements are analyzed in the context of optical absorption spectra of the molecules, the Au particle arrays, and the devices. Enhanced photocurrent associated with exciton generation in the molecule is distinguished from enhancements due to plasmon interactions. Mechanisms of plasmon-induced current are examined, and it is found that hot electron generation can be distinguished from other possibilities. PMID:23550717

  1. Fingerprinting Electronic Molecular Complexes in Liquid

    Nirmalraj, Peter; La Rosa, Andrea; Thompson, Damien; Sousa, Marilyne; Martin, Nazario; Gotsmann, Bernd; Riel, Heike

    2016-01-01

    Predicting the electronic framework of an organic molecule under practical conditions is essential if the molecules are to be wired in a realistic circuit. This demands a clear description of the molecular energy levels and dynamics as it adapts to the feedback from its evolving chemical environment and the surface topology. Here, we address this issue by monitoring in real-time the structural stability and intrinsic molecular resonance states of fullerene (C60)-based hybrid molecules in the presence of the solvent. Energetic levels of C60 hybrids are resolved by in situ scanning tunnelling spectroscopy with an energy resolution in the order of 0.1 eV at room-temperature. An ultra-thin organic spacer layer serves to limit contact metal-molecule energy overlap. The measured molecular conductance gap spread is statistically benchmarked against first principles electronic structure calculations and used to quantify the diversity in electronic species within a standard population of molecules. These findings provide important progress towards understanding conduction mechanisms at a single-molecular level and in serving as useful guidelines for rational design of robust nanoscale devices based on functional organic molecules.

  2. Towards reproducible, scalable lateral molecular electronic devices

    Durkan, Colm; Zhang, Qian

    2014-08-01

    An approach to reproducibly fabricate molecular electronic devices is presented. Lateral nanometer-scale gaps with high yield are formed in Au/Pd nanowires by a combination of electromigration and Joule-heating-induced thermomechanical stress. The resulting nanogap devices are used to measure the electrical properties of small numbers of two different molecular species with different end-groups, namely 1,4-butane dithiol and 1,5-diamino-2-methylpentane. Fluctuations in the current reveal that in the case of the dithiol molecule devices, individual molecules conduct intermittently, with the fluctuations becoming more pronounced at larger biases.

  3. Towards reproducible, scalable lateral molecular electronic devices

    Durkan, Colm, E-mail: cd229@eng.cam.ac.uk; Zhang, Qian [Nanoscience Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom)

    2014-08-25

    An approach to reproducibly fabricate molecular electronic devices is presented. Lateral nanometer-scale gaps with high yield are formed in Au/Pd nanowires by a combination of electromigration and Joule-heating-induced thermomechanical stress. The resulting nanogap devices are used to measure the electrical properties of small numbers of two different molecular species with different end-groups, namely 1,4-butane dithiol and 1,5-diamino-2-methylpentane. Fluctuations in the current reveal that in the case of the dithiol molecule devices, individual molecules conduct intermittently, with the fluctuations becoming more pronounced at larger biases.

  4. Functional molecules in electronic circuits.

    Weibel, Nicolas; Grunder, Sergio; Mayor, Marcel

    2007-08-01

    Molecular electronics is a fascinating field of research contributing to both fundamental science and future technological achievements. A promising starting point for molecular devices is to mimic existing electronic functions to investigate the potential of molecules to enrich and complement existing electronic strategies. Molecules designed and synthesized to be integrated into electronic circuits and to perform an electronic function are presented in this article. The focus is set in particular on rectification and switching based on molecular devices, since the control over these two parameters enables the assembly of memory units, likely the most interesting and economic application of molecular based electronics. Both historical and contemporary solutions to molecular rectification are discussed, although not exhaustively. Several examples of integrated molecular switches that respond to light are presented. Molecular switches responding to an electrochemical signal are also discussed. Finally, supramolecular and molecular systems with intuitive application potential as memory units due to their hysteretic switching are highlighted. Although a particularly attractive feature of molecular electronics is its close cooperation with neighbouring disciplines, this article is written from the point of view of a chemist. Although the focus here is largely on molecular considerations, innovative contributions from physics, electro engineering, nanotechnology and other scientific disciplines are equally important. However, the ability of the chemist to correlate function with structure, to design and to provide tailor-made functional molecules is central to molecular electronics. PMID:17637951

  5. Epipolar image rectification through geometric algorithms with unknown parameters

    Herráez Boquera, José; Denia Rios, José Luís; Navarro Esteve, Pablo José; RODRÍGUEZ PEREÑA, JAIME; MARTÍN SÁNCHEZ, MARÍA TERESA

    2013-01-01

    Herráez Boquera, J., Denia Rios, J.L., Navarro Esteve, P.J., Rodríguez Pereña, J., Martín Sánchez M.T."Epipolar image rectification through geometric algorithms with unknown parameters". JJ. Electron. Imaging. 22(4), 043021 (Dec 02, 2013). © (2013) Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or mo...

  6. Current rectification in a single molecule diode: the role of electrode coupling

    Sherif, Siya; Rubio-Bollinger, Gabino; Pinilla-Cienfuegos, Elena; Coronado, Eugenio; Cuevas, Juan Carlos; Agraït, Nicolás

    2015-07-01

    We demonstrate large rectification ratios (\\gt 100) in single-molecule junctions based on a metal-oxide cluster (polyoxometalate), using a scanning tunneling microscope (STM) both at ambient conditions and at low temperature. These rectification ratios are the largest ever observed in a single-molecule junction, and in addition these junctions sustain current densities larger than 105 A cm-2. By following the variation of the I-V characteristics with tip-molecule separation we demonstrate unambiguously that rectification is due to asymmetric coupling to the electrodes of a molecule with an asymmetric level structure. This mechanism can be implemented in other type of molecular junctions using both organic and inorganic molecules and provides a simple strategy for the rational design of molecular diodes.

  7. Current rectification in a single molecule diode: the role of electrode coupling.

    Sherif, Siya; Rubio-Bollinger, Gabino; Pinilla-Cienfuegos, Elena; Coronado, Eugenio; Cuevas, Juan Carlos; Agraït, Nicolás

    2015-07-24

    We demonstrate large rectification ratios (> 100) in single-molecule junctions based on a metal-oxide cluster (polyoxometalate), using a scanning tunneling microscope (STM) both at ambient conditions and at low temperature. These rectification ratios are the largest ever observed in a single-molecule junction, and in addition these junctions sustain current densities larger than 10(5) A cm(-2). By following the variation of the I-V characteristics with tip-molecule separation we demonstrate unambiguously that rectification is due to asymmetric coupling to the electrodes of a molecule with an asymmetric level structure. This mechanism can be implemented in other type of molecular junctions using both organic and inorganic molecules and provides a simple strategy for the rational design of molecular diodes. PMID:26133791

  8. Easy rectification for infrared images

    Usamentiaga, R.

    2016-05-01

    Most applications using infrared thermography only take advantage of one feature in the images: the intensity of the objects in the infrared images, which is mainly a function of its temperature. Many different applications use this feature as an indicator of health, early signs of malfunction or signs of hidden conditions. However, infrared images also contain relevant geometric information that can be used to measure objects or to locate areas of thermal contrast in the scene. The problem is that the extraction of geometric information requires a complex camera calibration procedure that depends upon calibration plates which are difficult to build. In this work, an easy rectification procedure for infrared images is proposed without using calibration plates. The proposed method uses a camera projection model not considering distortions, which greatly simplifies the estimation of the projection parameters while producing very good accuracy. The method estimates the projection parameters iteratively based on features from objects in the image and the knowledge about its geometric properties. The result is a method that provides reliable geometric information about the objects in the scene with a single image. A series of experiments are performed to validate the proposed method. Results show excellent performance, with sub-pixel accuracy.

  9. Modeling ion sensing in molecular electronics

    Chen, Caroline J.; Smeu, Manuel; Ratner, Mark A.

    2014-02-01

    We examine the ability of molecules to sense ions by measuring the change in molecular conductance in the presence of such charged species. The detection of protons (H+), alkali metal cations (M+), calcium ions (Ca2+), and hydronium ions (H3O+) is considered. Density functional theory (DFT) is used within the Keldysh non-equilibrium Green's function framework (NEGF) to model electron transport properties of quinolinedithiol (QDT, C9H7NS2), bridging Al electrodes. The geometry of the transport region is relaxed with DFT. The transport properties of the device are modeled with NEGF-DFT to determine if this device can distinguish among the M+ + QDT species containing monovalent cations, where M+ = H+, Li+, Na+, or K+. Because of the asymmetry of QDT in between the two electrodes, both positive and negative biases are considered. The electron transmission function and conductance properties are simulated for electrode biases in the range from -0.5 V to 0.5 V at increments of 0.1 V. Scattering state analysis is used to determine the molecular orbitals that are the main contributors to the peaks in the transmission function near the Fermi level of the electrodes, and current-voltage relationships are obtained. The results show that QDT can be used as a proton detector by measuring transport through it and can conceivably act as a pH sensor in solutions. In addition, QDT may be able to distinguish among different monovalent species. This work suggests an approach to design modern molecular electronic conductance sensors with high sensitivity and specificity using well-established quantum chemistry.

  10. Electron transfer through rigid organic molecular wires enhanced by electronic and electron-vibration coupling

    Sukegawa, Junpei; Schubert, Christina; Zhu, Xiaozhang; Tsuji, Hayato; Guldi, Dirk M.; Nakamura, Eiichi

    2014-10-01

    Electron transfer (ET) is a fundamental process in a wide range of biological systems, photovoltaics and molecular electronics. Therefore to understand the relationship between molecular structure and ET properties is of prime importance. For this purpose, photoinduced ET has been studied extensively using donor-bridge-acceptor molecules, in which π-conjugated molecular wires are employed as bridges. Here, we demonstrate that carbon-bridged oligo-p-phenylenevinylene (COPV), which is both rigid and flat, shows an 840-fold increase in the ET rate compared with the equivalent flexible molecular bridges. A 120-fold rate enhancement is explained in terms of enhanced electronic coupling between the electron donor and the electron acceptor because of effective conjugation through the COPVs. The remainder of the rate enhancement is explained by inelastic electron tunnelling through COPV caused by electron-vibration coupling, unprecedented for organic molecular wires in solution at room temperature. This type of nonlinear effect demonstrates the versatility and potential practical utility of COPVs in molecular device applications.

  11. Molecular rectification with identical metal electrodes at low temperatures Thin film deposition; Gold; Molecular electronics; Langmuir- Blodgett; Au/LB/Au structures; Fabrication

    Okazaki, N

    2003-01-01

    A gold deposition technique for the fabrication of Au/LB/Au structures has been developed. The kinetic energy of evaporated gold atoms is reduced by scattering the gold atoms from argon gas. Moreover, the samples are cooled down below 173K (-100 deg C) to avoid the diffusion of gold atoms into the LB films and to fabricate electrically continuous thin gold electrodes (This technique has since been used in fabrication of Au/LB/Au structures even with monolayer LB films (Metzger, et al. (2001)). To measure the current-voltage characteristics of the Au/LB/Au structures at liquid helium temperatures, new junction geometries have been explored. To avoid the direct contact of the Gallium-Indium eutectic onto the LB films, which is the cause of the breakdown of the junction at lower temperatures, a cross electrode junction geometry is used. The problem of poor Langmuir-Blodgett film deposition at the penumbra region of the base electrode is avoided by covering the penumbra region with an insulating omega-tricosenoic...

  12. Enhanced oscillatory rectification and negative differential resistance in pentamantane diamondoid-cumulene systems

    Tawfik, Sherif Abdulkader; Cui, X. Y.; Ringer, S. P.; Stampfl, C.

    2016-02-01

    We propose a new functionality for diamondoids in nanoelectronics. Based on the nonequilibrium Green's function formalism and density functional theory, we reveal that when attached to gold electrodes, the pentamantane-cumulene molecular junction exhibits large and oscillatory rectification and negative differential resistance (NDR) - depending on the number of carbon atoms in cumulene (Cn). When n is odd rectification is greatly enhanced where the rectification ratio can reach ~180 and a large negative differential resistance peak current of ~3 μA. This oscillatory behavior is well rationalised in terms of the occupancy of the carbon 2p states in Cn. Interestingly, different layers of C atoms in the pentamantane molecule have different contributions to transmission. The first and third layers of C atoms in pentamantane have a slight contribution to rectification, and the fifth and sixth layers have a stronger contribution to both rectification and NDR. Thus, our results suggest potential avenues for controlling their functions by chemically manipulating various parts of the diamondoid molecule, thus extending the applications of diamondoids in nanoscale integrated circuits.

  13. Energy-Saving in Brew-Rectification

    N. I. Ulyanau

    2008-01-01

    Full Text Available The paper investigates dynamics of rectification process on one plate of a column. The basic channels controlling brew-rectification process are described in the paper.The paper also considers problems pertaining to synthesis of an adaptive system that controls non-stationary objects with delay. Synthesis of adaptive systems that automatically control product quality and saving on power resources and productivity with the help of the second method of Lyapunov has been carried out in the paper.Industrial introduction of the given automatic control system of technological process shall permit to increase productivity of a rectification (10–15 %, to decrease specific power consumption by (5–10 % while preserving the specified quality of rectified ethyl alcohol and decrease alcohol losses with luting water and malt-residue.

  14. Electroosmotic flow rectification in conical nanopores

    Laohakunakorn, Nadanai

    2015-01-01

    Recent experimental work has suggested that electroosmotic flows (EOF) through conical nanopores exhibit rectification in the opposite sense to the well-studied effect of ionic current rectification. A positive bias voltage generates large EOF and small current, while negative voltages generate small EOF and large current. Here we systematically investigate this effect using finite-element simulations. We find that inside the pore, the electric field and salt concentration are inversely correlated, which leads to the inverse relationship between the magnitudes of EOF and current. Rectification occurs when the pore is driven into states characterized by different salt concentrations depending on the sign of the voltage. The mechanism responsible for this behaviour is concentration polarization, which requires the pore to exhibit the properties of permselectivity and asymmetry.

  15. Time rectification system for in-beam TOF-PET

    A time rectification system for a In-Beam TOF-PET was described.It consists of a pair of BaF2(φ40 mm x 45 mm) crystals coupled to Philips photomultipliers XP2020Q and a time coincidence electronic system using standard NIM modules. The best coincidence timing resolution of the system for pairs of 511 keV gamma rays is 576 ps. Some factors affecting the time resolution were primarily discussed, such as the types of photomultiplier tubes (PMT), the model of signal readout, the effects of different discriminators and timing amplifiers. The experiment results show that the signal read from the PMT dynode can get the optimum resolution; the PMT types, especially the rise time and electronic transmit time greatly affect the system performance. The shorter the rise time and electronic transmit time for the PMTs is, the better the timing performance is. The system timing performance is also related to the electronic combination. (authors)

  16. Theory of Vibrationally Inelastic Electron Transport through Molecular Bridges

    Cizek, Martin; Thoss, Michael; Domcke, Wolfgang

    2003-01-01

    Vibrationally inelastic electron transport through a molecular bridge that is connected to two leads is investigated. The study is based on a generic model of vibrational excitation in resonant transmission of electrons through a molecular junction. Employing methods from electron-molecule scattering theory, the transmittance through the molecular bridge can be evaluated numerically exactly. The current through the junction is obtained approximately using a Landauer-type formula. Considering ...

  17. Thermal rectification in nonlinear quantum circuits

    Ruokola, T.; Ojanen, T.; Jauho, Antti-Pekka

    2009-01-01

    We present a theoretical study of radiative heat transport in nonlinear solid-state quantum circuits. We give a detailed account of heat rectification effects, i.e., the asymmetry of heat current with respect to a reversal of the thermal gradient, in a system consisting of two reservoirs at finite...

  18. Short chain molecular junctions: Charge transport versus dipole moment

    Graphical abstract: - Highlights: • The role of dipole moment of organic molecules on molecular junctions has been studied. • Molecular junctions constituted using propargyl molecules of different dipole moments. • The electronic properties of the molecules were calculated using Gaussian software. • Junctions show varying rectification due to their varying dipole moment and orientation. - Abstract: The investigation of the influence of dipole moment of short chain organic molecules having three carbon atoms varying in end group on silicon surface was carried on. Here, we use three different molecules of propargyl series varying in dipole moment and its orientation to constitute molecular junctions. The charge transport mechanism in metal–molecules–semiconductor (MMS) junction obtained from current–voltage (I–V) characteristics shows the rectification behavior for two junctions whereas the other junction shows a weak rectification. The electronic properties of the molecules were calculated using Gaussian software package. The observed rectification behavior of these junctions is examined and found to be accounted to the orientation of dipole moment and electron cloud density distribution inside the molecules

  19. Spin-dependent rectification in the C59N molecule

    Mahvash Arabi Darehdor; Nasser Shahtahmasebi

    2013-02-01

    Coherent spin-dependent electron transport is investigated in three conditions: (1) a C60 molecule is connected to two ferromagnetic (FM) electrodes symmetrically, (2) a C59N molecule is connected to two FM electrodes symmetrically and (3) a C59N molecule is connected to two FM electrodes asymmetrically. This work is based on a single-band tight-binding model Hamiltonian and the Green’s function approach with the Landauer–Buttiker formalism. Electrodes used in this study are semi-infinite FM electrodes with finite cross-section. Obvious rectification effect is observed in the C59 N molecule which is connected to the FM electrodes asymmetrically. This effect is more in the P alignment of FM electrodes than in AP alignment of FM electrodes. This study indicates that the rectification behaviour is due to the asymmetry in molecule and junctions. Also in this investigation tunnel magnetoresistance (TMR) is calculated for these molecules. Asymmetry is observed in TMR of C59N which is coupled to the electrodes asymmetrically due to asymmetric junctions, but TMR of C60 is symmetric.

  20. Molecular ferroelectrics: where electronics meet biology

    Li, Jiangyu; Liu, Yuanming; Zhang, Yanhang; Cai, Hong-Ling; Xiong, Ren-Gen

    2013-01-01

    In the last several years, we have witnessed significant advances in molecular ferroelectrics, with ferroelectric properties of molecular crystals approaching those of barium titanate. In addition, ferroelectricity has been observed in biological systems, filling an important missing link in bioelectric phenomena. In this perspective, we will present short historical notes on ferroelectrics, followed by overview on the fundamentals of ferroelectricity. Latest development in molecular ferroele...

  1. Progresses in organic field-effect transistors and molecular electronics

    Wu Weiping; Xu Wei; Hu Wenping; Liu Yunqi; Zhu Daoben

    2006-01-01

    In the past years,organic semiconductors have been extensively investigated as electronic materials for organic field-effect transistors (OFETs).In this review,we briefly summarize the current status of organic field-effect transistors including materials design,device physics,molecular electronics and the applications of carbon nanotubes in molecular electronics.Future prospects and investigations required to improve the OFET performance are also involved.

  2. Unwrapping and stereo rectification for omnidirectional images

    Jie LEI; Xin DU; Yun-fang ZHU; Ji-lin LIU

    2009-01-01

    Omnidirectional imaging sensors have been used in more and more applications when a very large field of view is required. In this paper, we investigate the unwrapping, epipolar geometry and stereo rectification issues for omnidirectional vision when the particular mirror model and the camera parameters are unknown in priori. First, the omnidirectional camera is calibrated under the Taylor model, and the parameters related to this model are obtained. In order to make the classical computer vision algorithms of conventional perspective cameras applicable, the ring omnidirectional image is unwrapped into two kinds of panoramas: cylinder and cuboid. Then the epipolar geometry of arbitrary camera configuration is analyzed and the essential matrix is deduced with its properties being indicated for ring images. After that, a simple stereo rectification method based on the essential matrix and the conformal mapping is proposed. Simulations and real data experimental results illustrate that our methods are effective for the omnidirectional camera under the constraint of a single view point.

  3. Self-assembled nanogaps for molecular electronics

    Tang, Qingxin; Tong, Yanhong; Jain, Titoo;

    2009-01-01

    A nanogap for molecular devices was realized using solution-based self-assembly. Gold nanorods were assembled to gold nanoparticle-coated conducting SnO2:Sb nanowires via thiol end-capped oligo(phenylenevinylene)s (OPVs). The molecular gap was easily created by the rigid molecule itself during se...

  4. Contactless electronic transport in a bio-molecular junction

    Molecular electronics hold promise for next generation ultra-low power, nano-scale integrated electronics. The main challenge in molecular electronics is to make a reliable interface between molecules and metal electrodes. Interfacing metals and molecules detrimentally affects the characteristics of nano-scale molecular electronic devices. It is therefore essential to investigate alternative arrangements such as contact-less tunneling gaps wherever such configurations are feasible. We conduct ab initio density functional theory and non-equilibrium Green's functions calculations to investigate the transport properties of a biocompatible glycine molecular junction. By analyzing the localized molecular orbital energy distributions and transmission probabilities in the transport-gap, we find a glycine molecule confined between two gold electrodes, without making a contact, is energetically stable and possesses high tunneling current resembling an excellent ohmic-like interface.

  5. Contactless electronic transport in a bio-molecular junction

    Hossain, Faruque M., E-mail: fhossain@unimelb.edu.au; Al-Dirini, Feras; Skafidas, Efstratios [Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville 3010 (Australia); Center for Neural Engineering (CfNE), The University of Melbourne, Parkville 3010 (Australia)

    2014-07-28

    Molecular electronics hold promise for next generation ultra-low power, nano-scale integrated electronics. The main challenge in molecular electronics is to make a reliable interface between molecules and metal electrodes. Interfacing metals and molecules detrimentally affects the characteristics of nano-scale molecular electronic devices. It is therefore essential to investigate alternative arrangements such as contact-less tunneling gaps wherever such configurations are feasible. We conduct ab initio density functional theory and non-equilibrium Green's functions calculations to investigate the transport properties of a biocompatible glycine molecular junction. By analyzing the localized molecular orbital energy distributions and transmission probabilities in the transport-gap, we find a glycine molecule confined between two gold electrodes, without making a contact, is energetically stable and possesses high tunneling current resembling an excellent ohmic-like interface.

  6. Molecular modeling and multiscaling issues for electronic material applications

    Iwamoto, Nancy; Yuen, Matthew; Fan, Haibo

    Volume 1 : Molecular Modeling and Multiscaling Issues for Electronic Material Applications provides a snapshot on the progression of molecular modeling in the electronics industry and how molecular modeling is currently being used to understand material performance to solve relevant issues in this field. This book is intended to introduce the reader to the evolving role of molecular modeling, especially seen through the eyes of the IEEE community involved in material modeling for electronic applications.  Part I presents  the role that quantum mechanics can play in performance prediction, such as properties dependent upon electronic structure, but also shows examples how molecular models may be used in performance diagnostics, especially when chemistry is part of the performance issue.  Part II gives examples of large-scale atomistic methods in material failure and shows several examples of transitioning between grain boundary simulations (on the atomistic level)and large-scale models including an example ...

  7. Electron Interference in Molecular Circular Polarization Attosecond XUV Photoionization

    Kai-Jun Yuan

    2015-01-01

    Full Text Available Two-center electron interference in molecular attosecond photoionization processes is investigated from numerical solutions of time-dependent Schrödinger equations. Both symmetric H\\(_2^+\\ and nonsymmetric HHe\\(^{2+}\\ one electron diatomic systems are ionized by intense attosecond circularly polarized XUV laser pulses. Photoionization of these molecular ions shows signature of interference with double peaks (minima in molecular attosecond photoelectron energy spectra (MAPES at critical angles \\(\\vartheta_c\\ between the molecular \\(\\textbf{R}\\ axis and the photoelectron momentum \\(\\textbf{p}\\. The interferences are shown to be a function of the symmetry of electronic states and the interference patterns are sensitive to the molecular orientation and pulse polarization. Such sensitivity offers possibility for imaging of molecular structure and orbitals.

  8. A New Full Adder Cell for Molecular Electronics

    Mehdi Ghasemi

    2011-09-01

    Full Text Available Due to high power consumption and difficulties with minimizing the CMOS transistor size, molecular electronics has been introduced as an emerging technology. Further, there have been noticeable advances in fabrication of molecular wires and switches and also molecular diodes can be used for designing different logic circuits. Considering this novel technology, we use molecules as the active components of the circuit, for transporting electric charge. In this paper, a full adder cell based on molecular electronics is presented. This full adder is consisted of resonant tunneling diodes and transistors which are implemented via molecular electronics. The area occupied by this kind of full adder would be much times smaller than the conventional designs and it can be used as the building block of more complex molecular arithmetic circuits.

  9. A New Full Adder Cell for Molecular Electronics

    Keivan Navi

    2012-01-01

    Full Text Available Due to high power consumption and difficulties with minimizing the CMOS transistor size, molecular electronics has been introduced as an emerging technology. Further, there have been noticeable advances in fabrication of molecular wires and switches and also molecular diodes can be used for designing different logic circuits. Considering this novel technology, we use molecules as the active components of the circuit, for transporting electric charge. In this paper, a full adder cell based on molecular electronics is presented. This full adder is consisted of resonant tunneling diodes and transistors which are implemented via molecular electronics. The area occupied by this kind of full adder would be much times smaller than the conventional designs and it can be used as the building block of more complex molecular arithmetic circuits.

  10. Electron-phonon scattering in molecular electronics: from inelastic electron tunnelling spectroscopy to heating effects

    Gagliardi, Alessio; Frauenheim, Thomas; Niehaus, Thomas A [Bremen Center for Computational Materials Science, University of Bremen, D-28359 Bremen (Germany); Romano, Giuseppe; Pecchia, Alessandro; Di Carlo, Aldo [CNR-INFM Department of Electronics Engineering, University of Rome ' Tor Vergata' , Via del Politecnico 1, 00133 Rome (Italy)], E-mail: gagliard@bccms.uni-bremen.de, E-mail: Gagliardi@Ing.uniroma2.it

    2008-06-15

    In this paper, we investigate dissipation in molecular electronic devices. Dissipation is a crucial quantity which determines the stability and heating of the junction. Moreover, several experimental techniques which use inelastically scattered electrons as probes to investigate the geometry in the junction are becoming fundamental in the field. In order to describe such physical effects, a non-equilibrium Green's function (NEGF) method was implemented to include scattering events between electrons and molecular vibrations in current simulations. It is well known that the final heating of the molecule depends also on the ability of the molecule to relax vibrational quanta into the contact reservoirs. A semi-classical rate equation has been implemented and integrated within the NEGF formalism to include this relaxation. The model is based on two quantities: (i) the rate of emission of phonons in the junction by electron-phonon scattering and (ii) a microscopic approach for the computation of the phonon decay rate, accounting for the dynamical coupling between the vibrational modes localized on the molecule and the contact phonons. The method is applied to investigate inelastic electron tunnelling spectroscopy (IETS) signals in CO molecules on Cu(110) substrates as well as dissipation in C{sub 60} molecules on Cu(110) and Si(100) surfaces. It is found that the mechanisms of energy relaxation are highly mode-specific and depend crucially on the lead electronic structure and junction geometry.

  11. Electron-phonon scattering in molecular electronics: from inelastic electron tunnelling spectroscopy to heating effects

    In this paper, we investigate dissipation in molecular electronic devices. Dissipation is a crucial quantity which determines the stability and heating of the junction. Moreover, several experimental techniques which use inelastically scattered electrons as probes to investigate the geometry in the junction are becoming fundamental in the field. In order to describe such physical effects, a non-equilibrium Green's function (NEGF) method was implemented to include scattering events between electrons and molecular vibrations in current simulations. It is well known that the final heating of the molecule depends also on the ability of the molecule to relax vibrational quanta into the contact reservoirs. A semi-classical rate equation has been implemented and integrated within the NEGF formalism to include this relaxation. The model is based on two quantities: (i) the rate of emission of phonons in the junction by electron-phonon scattering and (ii) a microscopic approach for the computation of the phonon decay rate, accounting for the dynamical coupling between the vibrational modes localized on the molecule and the contact phonons. The method is applied to investigate inelastic electron tunnelling spectroscopy (IETS) signals in CO molecules on Cu(110) substrates as well as dissipation in C60 molecules on Cu(110) and Si(100) surfaces. It is found that the mechanisms of energy relaxation are highly mode-specific and depend crucially on the lead electronic structure and junction geometry

  12. Molecular tips for scanning tunneling microscopy: intermolecular electron tunneling for single-molecule recognition and electronics.

    Nishino, Tomoaki

    2014-01-01

    This paper reviews the development of molecular tips for scanning tunneling microscopy (STM). Molecular tips offer many advantages: first is their ability to perform chemically selective imaging because of chemical interactions between the sample and the molecular tip, thus improving a major drawback of conventional STM. Rational design of the molecular tip allows sophisticated chemical recognition; e.g., chiral recognition and selective visualization of atomic defects in carbon nanotubes. Another advantage is that they provide a unique method to quantify electron transfer between single molecules. Understanding such electron transfer is mandatory for the realization of molecular electronics. PMID:24420248

  13. Thermal conductivity and thermal rectification in unzipped carbon nanotubes

    We study the thermal transport in completely unzipped carbon nanotubes, which are called graphene nanoribbons, partially unzipped carbon nanotubes, which can be seen as carbon-nanotube-graphene-nanoribbon junctions, and carbon nanotubes by using molecular dynamics simulations. It is found that the thermal conductivity of a graphene nanoribbon is much less than that of its perfect carbon nanotube counterparts because of the localized phonon modes at the boundary. A partially unzipped carbon nanotube has the lowest thermal conductivity due to additional localized modes at the junction region. More strikingly, a significant thermal rectification effect is observed in both partially unzipped armchair and zigzag carbon nanotubes. Our results suggest that carbon-nanotube-graphene-nanoribbon junctions can be used in thermal energy control.

  14. Creating large area molecular electronic junctions using atomic layer deposition

    We demonstrate a technique for creating large area, electrically stable molecular junctions. We use atomic layer deposition to create nanometer thick passivating layers of aluminum oxide on top of self-assembled organic monolayers with hydrophilic terminal groups. This layer acts as a protective barrier and allows simple vapor deposition of the top electrode without short circuits or molecular damage. This method allows nonshorting molecular junctions of up to 9 mm2 to be easily and reliably fabricated. The effect of passivation on molecular monolayers is studied with Auger and x-ray spectroscopy, while electronic transport measurements confirm molecular tunneling as the transport mechanism for these devices

  15. Triazatriangulene as binding group for molecular electronics

    Wei, Zhongming; Wang, Xintai; Borges, Anders;

    2014-01-01

    The triazatriangulene (TATA) ring system was investigated as a binding group for tunnel junctions of molecular wires on gold surfaces. Self-assembled monolayers (SAMs) of TATA platforms with three different lengths of phenylene wires were fabricated, and their electrical conductance was recorded by...... platform displays a contact resistance only slightly larger than the thiols. This surprising finding has not been reported before and was analyzed by theoretical computations of the transmission functions of the TATA anchored molecular wires. The relatively low contact resistance of the TATA platform along...

  16. Photoelectrochemical solar conversion systems molecular and electronic aspects

    Munoz, Andres G

    2012-01-01

    Providing new insights into the molecular and electronic processes involved in the conversion of sunlight into chemical products, Photoelectrochemical Solar Conversion Systems: Molecular and Electronic Aspects begins with an historical overview and a survey of recent developments in the electrochemistry of semiconductors and spectroscopic techniques. It then provides a comprehensive introduction to the science of conversion cells, reviews current issues and potential directions, and covers a wide range of materials from organic to inorganic cells.Employing a tutorial organization with balanced

  17. Novel tailor-made externally triggerable single-molecular switches for molecular electronics

    Harzmann, Gero

    2015-01-01

    Molecular electronics marks a highly interdisciplinary scientific field, in which physicists, chemists, and biologist jointly investigate electronic phenomena on a molecular level. Herein, the foremost task of the chemist is the design and synthesis of novel, tailor-made model compounds bearing externally addressable or controllable functions, which are predominantly of electronic nature. This present PhD thesis mainly focusses on the synthetic aspects towards innovative metalorga...

  18. Electron and molecular ion collisions relevant to divertor plasma

    We introduce the concept of the multi-channel quantum defect theory (MQDT) and show the outline of the MQDT newly extended to include the dissociative states. We investigate some molecular processes relevant to the divertor plasma by using the MQDT: the dissociative recombination, dissociative excitation, and rotation-vibrational transition in the hydrogen molecular ion and electron collisions. (author)

  19. Fabrication of multilayer edge molecular electronics and spintronics devices

    Tyagi, Pawan

    2011-01-01

    Advancement of molecular devices will critically depend on the approach to establish electrical connections to the functional molecule(s). We produced a molecular device strategy which is based on chemically attaching of molecules between the two magnetic/nonmagnetic metallic electrodes along the multilayer edge(s) of a prefabricated tunnel junction. Here, we present the fabrication methodology for producing these multilayer edge molecular electronics/spintronics devices (MEMEDs/MEMSDs) and d...

  20. Molecular alignment dependent electron interference in attosecond ultraviolet photoionization

    Kai-Jun Yuan

    2015-01-01

    Full Text Available We present molecular photoionization processes by intense attosecond ultraviolet laser pulses from numerical solutions of time-dependent Schrödinger equations. Simulations preformed on a single electron diatomic H2+ show minima in molecular photoelectron energy spectra resulting from two center interference effects which depend strongly on molecular alignment. We attribute such sensitivity to the spatial orientation asymmetry of the photoionization process from the two nuclei. A similar influence on photoelectron kinetic energies is also presented.

  1. Site-directed deep electronic tunneling through a molecular network

    Electronic tunneling in a complex molecular network of N(>2) donor/acceptor sites, connected by molecular bridges, is analyzed. The 'deep' tunneling dynamics is formulated using a recursive perturbation expansion, yielding a McConnell-type reduced N-level model Hamiltonian. Applications to models of molecular junctions demonstrate that the donor-bridge contact parameters can be tuned in order to control the tunneling dynamics and particularly to direct the tunneling pathway to either one of the various acceptors

  2. Molecular interfaces for plasmonic hot electron photovoltaics

    Pelayo García de Arquer, F.; Mihi, Agustín; Konstantatos, Gerasimos

    2015-01-01

    The use of self-assembled monolayers (SAMs) to improve and tailor the photovoltaic performance of plasmonic hot-electron Schottky solar cells is presented. SAMs allow the simultaneous control of open-circuit voltage, hot-electron injection and short-circuit current. To that end, a plurality of molecule structural parameters can be adjusted: SAM molecule's length can be adjusted to control plasmonic hot electron injection. Modifying SAMs dipole moment allows for a precise tuning of the open-circuit voltage. The functionalization of the SAM can also be selected to modify short-circuit current. This allows the simultaneous achievement of high open-circuit voltages (0.56 V) and fill-factors (0.58), IPCE above 5% at the plasmon resonance and maximum power-conversion efficiencies of 0.11%, record for this class of devices.The use of self-assembled monolayers (SAMs) to improve and tailor the photovoltaic performance of plasmonic hot-electron Schottky solar cells is presented. SAMs allow the simultaneous control of open-circuit voltage, hot-electron injection and short-circuit current. To that end, a plurality of molecule structural parameters can be adjusted: SAM molecule's length can be adjusted to control plasmonic hot electron injection. Modifying SAMs dipole moment allows for a precise tuning of the open-circuit voltage. The functionalization of the SAM can also be selected to modify short-circuit current. This allows the simultaneous achievement of high open-circuit voltages (0.56 V) and fill-factors (0.58), IPCE above 5% at the plasmon resonance and maximum power-conversion efficiencies of 0.11%, record for this class of devices. Electronic supplementary information (ESI) available: Contact-potential differentiometry measurements, FTIR characterization, performance statistics and gold devices. See DOI: 10.1039/c4nr06356b

  3. Microwave power engineering generation, transmission, rectification

    Okress, Ernest C

    1968-01-01

    Microwave Power Engineering, Volume 1: Generation, Transmission, Rectification considers the components, systems, and applications and the prevailing limitations of the microwave power technology. This book contains four chapters and begins with an introduction to the basic concept and developments of microwave power technology. The second chapter deals with the development of the main classes of high-power microwave and optical frequency power generators, such as magnetrons, crossed-field amplifiers, klystrons, beam plasma amplifiers, crossed-field noise sources, triodes, lasers. The third

  4. Nucleophilicity/Electrophilicity Excess in Analyzing Molecular Electronics

    Roy, D. R.; Subramanian, V; Chattaraj, P. K.

    2005-01-01

    Intramolecular electron transfer capability of all metal aromatic and anti-aromatic aluminum cluster compounds is studied in terms of density functional theory based global and local reactivity descriptors. This study will provide important inputs towards the fabrication of the material required for molecular electronics.

  5. High electronic couplings of single mesitylene molecular junctions

    Yuki Komoto

    2015-12-01

    Full Text Available We report on an experimental analysis of the charge transport properties of single mesitylene (1,3,5-trimethylbenzene molecular junctions. The electronic conductance and the current–voltage characteristics of mesitylene molecules wired into Au electrodes were measured by a scanning tunnelling microscopy-based break-junction method at room temperature in a liquid environment. We found the molecular junctions exhibited two distinct conductance states with high conductance values of ca. 10−1G0 and of more than 10−3G0 (G0 = 2e2/h in the electronic conductance measurements. We further performed a statistical analysis of the current–voltage characteristics of the molecular junctions in the two states. Within a single channel resonant tunnelling model, we obtained electronic couplings in the molecular junctions by fitting the current–voltage characteristics to the single channel model. The origin of the high conductance was attributed to experimentally obtained large electronic couplings of the direct π-bonded molecular junctions (ca. 0.15 eV. Based on analysis of the stretch length of the molecular junctions and the large electronic couplings obtained from the I–V analysis, we proposed two structural models, in which (i mesitylene binds to the Au electrode perpendicular to the charge transport direction and (ii mesitylene has tilted from the perpendicular orientation.

  6. Using circumacenes to improve organic electronics and molecular electronics: design clues

    Perez-Jimenez, Angel J; Sancho-Garcia, Juan C, E-mail: aj.perez@ua.e, E-mail: jc.sancho@ua.e [Departamento de Quimica-Fisica, Universidad de Alicante, E-03080, Alicante (Spain)

    2009-11-25

    Theoretical modeling is used here to ascertain the potential use of circumacenes to improve the transport parameters of {pi}-conjugated materials acting as: (i) the layered molecular constituent for organic electronic devices; and (ii) the molecular component of gold-molecule-gold nanobridges for molecular electronic device use. It is concluded that, to a first approximation, the molecular length or, alternatively, the HOMO-LUMO gap (HOMO: highest occupied molecular orbital; LUMO: lowest unoccupied molecular orbital) can be used to relate the two transport regimes usually found in these two fields, thus serving as a key design parameter for guaranteeing good performance of circumanthracene for both regimes. It is also clearly established that going beyond this simple relationship requires knowledge of the detailed molecule-contact geometry of the molecular nanobridge, and how its tremendous impact on the binding strength and the conductance prevents blind extrapolation of results obtained for molecular nanobridges built by means of different experimental set-ups.

  7. Using circumacenes to improve organic electronics and molecular electronics: design clues

    Theoretical modeling is used here to ascertain the potential use of circumacenes to improve the transport parameters of π-conjugated materials acting as: (i) the layered molecular constituent for organic electronic devices; and (ii) the molecular component of gold-molecule-gold nanobridges for molecular electronic device use. It is concluded that, to a first approximation, the molecular length or, alternatively, the HOMO-LUMO gap (HOMO: highest occupied molecular orbital; LUMO: lowest unoccupied molecular orbital) can be used to relate the two transport regimes usually found in these two fields, thus serving as a key design parameter for guaranteeing good performance of circumanthracene for both regimes. It is also clearly established that going beyond this simple relationship requires knowledge of the detailed molecule-contact geometry of the molecular nanobridge, and how its tremendous impact on the binding strength and the conductance prevents blind extrapolation of results obtained for molecular nanobridges built by means of different experimental set-ups.

  8. Generalization of the electronic susceptibility for arbitrary molecular geometries

    Scherrer, Arne; Dreßler, Christian; Ahlert, Paul; Sebastiani, Daniel

    2016-04-01

    We generalize the explicit representation of the electronic susceptibility χ[R](r, r') for arbitrary molecular geometries R. The electronic susceptibility is a response function that yields the response of the molecular electronic charge density at linear order to an arbitrary external perturbation. We address the dependence of this response function on the molecular geometry. The explicit representation of the molecular geometry dependence is achieved by means of a Taylor expansion in the nuclear coordinates. Our approach relies on a recently developed low-rank representation of the response function χ[R](r, r') which allows a highly condensed storage of the expansion and an efficient application within dynamical chemical environments. We illustrate the performance and accuracy of our scheme by computing the vibrationally induced variations of the response function of a water molecule and its resulting Raman spectrum.

  9. Ion-pair formation in electron recombination with molecular ions

    By studying ion-pair formation in electron recombination with molecular ions, fundamental knowledge on the molecular dynamics can be obtained. In order to study these types of reactions, both the electron recombination as well as the dynamics all the way to the asymptotic limits must be well described. We have used the wave packet technique to study ion-pair formation in electron recombination with HeH+, HD+, H3+ and HF+. We here discuss what will determine the general shape of the ion-pair cross section, the threshold effects, possible interference effects as well as the ratio of the cross sections of ion-pair formation to dissociative recombination

  10. Ballistic thermal rectification in nanoscale three-terminal junctions

    Zhang, Lifa; Wang, Jian-Sheng; Li, Baowen

    2010-03-01

    We study ballistic thermal transport in three-terminal atomic nanojunctions by the nonequilibrium Green’s function method. We find that there is ballistic thermal rectification in asymmetric three-terminal structures because of the incoherent phonon scattering from the control terminal. With spin-phonon interaction, we also find the ballistic thermal rectification even in symmetric three-terminal paramagnetic structures.

  11. Electron Scattering by biomass molecular fragments

    Lima, Marco

    2015-09-01

    The replacement of fossil fuels by biofuels from renewable sources may not be a definite answer for greenhouse gas emissions problems, but it is a good step towards a sustainable energy strategy. Few per cent of ethanol is being mixed to gasoline in many countries and in some of them, like Brazil, a very aggressive program has been developed, using, in large scale, flex fuel engines that can run with any mixture of gasoline and ethanol, including 100% ethanol. Important points are how to produce ethanol in a sustainable way and with which technology? Biomass is a good candidate to enhance the first generation (produced from Corn in USA and from sugarcane in Brazil) production towards the so-called second-generation ethanol, since it has cellulose and hemicellulose as source of sugars. In order to liberate these sugars for fermentation, it is important to learn how to separate the main components. Chemical routes (acid treatment) and biological routes (enzymatic hydrolysis) are combined and used for these purposes. Atmospheric plasmas can be useful for attacking the biomass in a controlled manner and low energy electrons may have an important role in the process. Recently, we have been studying the interaction of electrons with lignin subunits (phenol, guaiacol, p-coumaryl alcohol), cellulose components, β-D-glucose and cellobiose (β(1-4) linked glucose dimer) and hemicellulose components [2] (β-D-xylose). We also obtained results for the amylose subunits α-D-glucose and maltose (α(1-4) linked glucose dimer). Altogether, the resonance spectra of lignin, cellulose and hemicellulose components establish a physical-chemical basis for electron-induced biomass pretreatment that could be applied to biofuel production. In order to describe a more realistic system (where molecules are ``wet''), we have obtained the shape resonance spectra of phenol-water clusters, as obtained previously from elastic electron scattering calculations. Our results, obtained in a simple

  12. Energy Transformation in Molecular Electronic Systems

    Kasha, Michael

    1999-05-17

    This laboratory has developed many new ideas and methods in the electronic spectroscopy of molecules. This report covers the contract period 1993-1995. A number of the projects were completed in 1996, and those papers are included in the report. The DOE contract was terminated at the end of 1995 owing to a reorganizational change eliminating nationally the projects under the Office of Health and Environmental Research, U. S. Department of Energy.

  13. Ballistic thermal rectification in asymmetric three-terminal graphene nanojunctions

    Ouyang, Tao; Chen, Yuanping; Xie, Yuee; Wei, X. L.; Yang, Kaike; Yang, Ping; Zhong, Jianxin

    2010-12-01

    Graphene nanojunctions (GNJs) are important components of future nanodevices and nanocircuits. Using the nonequilibrium Green’s function method, we investigate the phononic properties of three-terminal GNJs (TGNJs). The results show that the heat flux runs preferentially along the direction from narrow to wide terminals, presenting an evident ballistic thermal rectification effect in the asymmetric TGNJs. The rectification efficiency is strongly dependent on the asymmetry of the nanojunctions, which increases rapidly with the width discrepancy between the left and right terminals. Meanwhile, the corner form of the TGNJs also plays an important role in the rectification effect. The mechanism of this thermal rectification is explained by a qualitative analysis. Compared to previous thermal rectifiers based on other materials, the asymmetric nanojunctions based on graphene possess much high rectification ratio which can approach about 200%. These indicate that asymmetric TGNJs might be a promising candidate for excellent ballistic thermal (phononic) devices.

  14. Molecular Models for Conductance in Junctions and Electrochemical Electron Transfer

    Mazinani, Shobeir Khezr Seddigh

    This thesis develops molecular models for electron transport in molecular junctions and intra-molecular electron transfer. The goal is to identify molecular descriptors that afford a substantial simplification of these electronic processes. First, the connection between static molecular polarizability and the molecular conductance is examined. A correlation emerges whereby the measured conductance of a tunneling junction decreases as a function of the calculated molecular polarizability for several systems, a result consistent with the idea of a molecule as a polarizable dielectric. A model based on a macroscopic extension of the Clausius-Mossotti equation to the molecular domain and Simmon's tunneling model is developed to explain this correlation. Despite the simplicity of the theory, it paves the way for further experimental, conceptual and theoretical developments in the use of molecular descriptors to describe both conductance and electron transfer. Second, the conductance of several biologically relevant, weakly bonded, hydrogen-bonded systems is systematically investigated. While there is no correlation between hydrogen bond strength and conductance, the results indicate a relation between the conductance and atomic polarizability of the hydrogen bond acceptor atom. The relevance of these results to electron transfer in biological systems is discussed. Hydrogen production and oxidation using catalysts inspired by hydrogenases provides a more sustainable alternative to the use of precious metals. To understand electrochemical and spectroscopic properties of a collection of Fe and Ni mimics of hydrogenases, high-level density functional theory calculations are described. The results, based on a detailed analysis of the energies, charges and molecular orbitals of these metal complexes, indicate the importance of geometric constraints imposed by the ligand on molecular properties such as acidity and electrocatalytic activity. Based on model calculations of

  15. Molecular electronics with single molecules in solid-state devices.

    Moth-Poulsen, Kasper; Bjørnholm, Thomas

    2009-09-01

    The ultimate aim of molecular electronics is to understand and master single-molecule devices. Based on the latest results on electron transport in single molecules in solid-state devices, we focus here on new insights into the influence of metal electrodes on the energy spectrum of the molecule, and on how the electron transport properties of the molecule depend on the strength of the electronic coupling between it and the electrodes. A variety of phenomena are observed depending on whether this coupling is weak, intermediate or strong. PMID:19734925

  16. Molecular electronics with single molecules in solid-state devices

    Moth-Poulsen, Kasper; Bjørnholm, Thomas

    2009-01-01

    The ultimate aim of molecular electronics is to understand and master single-molecule devices. Based on the latest results on electron transport in single molecules in solid-state devices, we focus here on new insights into the influence of metal electrodes on the energy spectrum of the molecule......, and how the electron transport properties of the molecule depend on the strength of the electronic coupling between it and the electrodes. A variety of phenomena are observed depending on whether this coupling is weak, intermediate or strong....

  17. TranSIESTA: a spice for molecular electronics.

    Stokbro, Kurt; Taylor, Jeremy; Brandbyge, Mads; Ordejón, Pablo

    2003-12-01

    Our recently developed method, TranSIESTA, enables modelling of molecular electronic devices under operation conditions. The method is based on density functional theory, and calculates the self-consistent electronic structure of a nanostructure coupled to three-dimensional electrodes with different electrochemical potentials. It uses a full atomistic ab initio description of both the electrodes and the nanoscale device. The calculations reveal information about the scattering states, transmission coefficients, electron current, and non-equilibrium forces in the systems. In this paper we use the method to investigate the electrical properties of three ring phenyl-ethynylene oligomers (OPE). We present results for the electrical effect of side groups and molecular conformations of the molecules. The calculations indicate that molecular switching and negative differential conductance (NDC) are related to rotations of the middle phenyl ring. PMID:14976020

  18. Modeling Polymorphic Molecular Crystals with Electronic Structure Theory.

    Beran, Gregory J O

    2016-05-11

    Interest in molecular crystals has grown thanks to their relevance to pharmaceuticals, organic semiconductor materials, foods, and many other applications. Electronic structure methods have become an increasingly important tool for modeling molecular crystals and polymorphism. This article reviews electronic structure techniques used to model molecular crystals, including periodic density functional theory, periodic second-order Møller-Plesset perturbation theory, fragment-based electronic structure methods, and diffusion Monte Carlo. It also discusses the use of these models for predicting a variety of crystal properties that are relevant to the study of polymorphism, including lattice energies, structures, crystal structure prediction, polymorphism, phase diagrams, vibrational spectroscopies, and nuclear magnetic resonance spectroscopy. Finally, tools for analyzing crystal structures and intermolecular interactions are briefly discussed. PMID:27008426

  19. Inelastic electron tunneling spectroscopy of molecular transport junctions

    Inelastic electron tunneling spectroscopy (IETS) has become a premier analytical tool in the investigation of nano scale and molecular junctions. The IETS spectrum provides invaluable information about the structure, bonding, and orientation of component molecules in the junctions. One of the major advantages of IETS is its sensitivity and resolution at the level of single molecules. This review discusses how IETS is used to study molecular transport junctions and presents an overview of recent experimental studies.

  20. First-principles modelling of molecular single-electron transistors

    Stokbro, Kurt

    2010-01-01

    We present a first-principles method for calculating the charging energy of a molecular single-electron transistor operating in the Coulomb blockade regime. The properties of the molecule are modeled using density-functional theory, the environment is described by a continuum model, and the interaction between the molecule and the environment are included through the Poisson equation. The model is used to calculate the charge stability diagrams of a benzene and C$_{60}$ molecular single-elect...

  1. Single-molecular diodes based on opioid derivatives.

    Siqueira, M R S; Corrêa, S M; Gester, R M; Del Nero, J; Neto, A M J C

    2015-12-01

    We propose an efficient single-molecule rectifier based on a derivative of opioid. Electron transport properties are investigated within the non-equilibrium Green's function formalism combined with density functional theory. The analysis of the current-voltage characteristics indicates obvious diode-like behavior. While heroin presents rectification coefficient R>1, indicating preferential electronic current from electron-donating to electron-withdrawing, 3 and 6-acetylmorphine and morphine exhibit contrary behavior, Rresonant-tunneling diodes. In particular, the rectification rations for heroin diodes show microampere electron current with a maximum of rectification (R=9.1) at very low bias voltage of ∼0.6 V and (R=14.3)∼1.8 V with resistance varying between 0.4 and 1.5 M Ω. Once most of the current single-molecule diodes usually rectifies in nanoampere, are not stable over 1.0 V and present electrical resistance around 10 M. Molecular devices based on opioid derivatives are promising in molecular electronics. PMID:26613894

  2. Effect of interfacial coupling on rectification in organic spin rectifiers

    Hu, Gui-Chao; Zuo, Meng-Ying; Li, Ying; Zhang, Zhao; Ren, Jun-Feng; Wang, Chuan-Kui

    2015-07-01

    The effect of interfacial coupling on rectification in an organic co-oligomer spin diode is investigated theoretically by considering spin-independent and spin-resolved couplings respectively. In the case of spin-independent coupling, an optimal interfacial coupling strength with a significant enhanced rectification ratio is found, whose value depends on the structural asymmetry of the molecule. In the case of spin-resolved coupling, we found that only the variation of the interfacial coupling with specific spin is effective to modulate the rectification, which is due to the spin-filtering property of the central asymmetric magnetic molecule. A transition of the spin-current rectification between parallel spin-current rectification and antiparallel spin-current rectification may be observed with the variation of the spin-resolved interfacial coupling. The interfacial effect on rectification is further analyzed from the spin-dependent transmission spectrum at different biases. Project supported by the National Natural Science Foundation of China (Grant No. 1374195), the Natural Science Foundation of Shandong Province, China (Grant No. ZR2014AM017), and the Excellent Young Scholars Research Fund of Shandong Normal University, China.

  3. Peculiarities of electron excitations decay in ion-molecular crystals

    Ionic-molecular crystals (IMC) have wide application in various optical devices. Its are using in capacity of solid state dosimetric materials and isolators. Peculiarities of chemical and energetic states of IMC lead to following number of features of electron excitation decay in comparison with alkaline-halogen crystals: - both an electrons and a holes simultaneously could be captured and localized either on anion or on cation complexes; - in-molecular forces arising in result of charge capture could conduct to decay of anion or cation complex; - decay products od anion or cation complex could participate in following reaction of new products formation. All these processes and new products of electron excitation decay exert strong effect on optical, magnetic and electrical characteristics of IMC. Knowledge of way and mechanisms of electron excitation decay in IMC could allow to control of radiation stability of crystals with help of impurities participating in different channels of solid state reactions

  4. Heterointerface effects on the nonlinear optical rectification in a laser-dressed graded quantum well

    Niculescu, Ecaterina C.; Eseanu, Nicoleta; Radu, Adrian

    2013-05-01

    An investigation of the laser radiation effects on the nonlinear optical rectification in an AlGaAs inverse parabolic quantum well with asymmetrical barriers is performed within the effective mass approximation, taking into account the dielectric mismatch between the semiconductor and the surrounding medium. Using the accurate dressing effect for the confinement potential and electrostatic self-energy due to the image-charges, we prove that: (i) a spatially dependent effective mass in the laser-dressing parameter definition is required for precise calculations of the energy levels; (ii) the dielectric confinement provides a potential mechanism for controlling electronic states and optical properties of quantum wells. In addition, the laser dependence of the energy where the optical rectification reaches its maximum can be adjusted by external electric fields. The joint action of the intense high-frequency laser and static electric fields may provide tuning of the nonlinear properties in this type of dielectrically modulated heterostructures.

  5. Imaging the molecular dynamics of dissociative electron attachment to water

    Adaniya, Hidihito; Rudek, B.; Osipov, Timur; Haxton, Dan; Weber, Thorsten; Rescigno, Thomas N.; McCurdy, C.W.; Belkacem, Ali

    2009-10-19

    Momentum imaging experiments on dissociative electron attachment to the water molecule are combined with ab initio theoretical calculations of the angular dependence of the quantum mechanical amplitude for electron attachment to provide a detailed picture of the molecular dynamics of dissociation attachment via the two lowest energy Feshbach resonances. The combination of momentum imaging experiments and theory can reveal dissociation dynamics for which the axial recoil approximation breaks down and thus provides a powerful reaction microscope for DEA to polyatomics.

  6. A new parametrizable model of molecular electronic structure

    Laikov, Dimitri N.

    2011-01-01

    A new electronic structure model is developed in which the ground state energy of a molecular system is given by a Hartree-Fock-like expression with parametrized one- and two-electron integrals over an extended (minimal + polarization) set of orthogonalized atom-centered basis functions, the variational equations being solved formally within the minimal basis but the effect of polarization functions being included in the spirit of second-order perturbation theory. It is designed to yield good...

  7. The molecular electronic device and the biochip computer: present status.

    Haddon, R. C.; Lamola, A. A.

    1985-01-01

    The idea that a single molecule might function as a self-contained electronic device has been of interest for some time. However, a fully integrated version--the biochip or the biocomputer, in which both production and assembly of molecular electronic components is achieved through biotechnology-is a relatively new concept that is currently attracting attention both within the scientific community and among the general public. In the present article we draw together some of the approaches bei...

  8. Dynamics of excess electrons in atomic and molecular clusters

    Young, Ryan Michael

    2011-01-01

    Femtosecond time-resolved photoelectron imaging (TRPEI) is applied to the study of excess electrons in clusters as well as to microsolvated anion species. This technique can be used to perform explicit time-resolved as well as one-color (single- or multiphoton) studies on gas phase species. The first part of this dissertation details time-resolved studies done on atomic clusters with an excess electron, the excited-state dynamics of solvated molecular anions, and charge-transfer dynamics to...

  9. Enhanced heat rectification effect in a quantum dot connected to ferromagnetic leads

    Chi, Feng, E-mail: chifeng@semi.ac.cn [School of Physical Science and Technology, Inner Mongolia University, Huhehaote 010023 (China); College of Engineering, Bohai University, Jinzhou 121013 (China); Sun, Lian-Liang [College of Science, North China University of Technology, Beijing 100041 (China); Zheng, Jun; Guo, Yu [College of Engineering, Bohai University, Jinzhou 121013 (China)

    2015-06-15

    We study theoretically the heat generation by electric current in an interacting single level quantum-dot connected to ferromagnetic leads. The heat is transferred between the dot and the lattice vibration of its host material (phonon reservoir). Particular attention is paid on the heat's rectification effect achieved by properly arranging the dot level and the bias voltage. We find that this effect is remarkably enhanced when the two leads' magnetic moments are in antiparallel configuration, i.e., the magnitude of the heat generation is reduced (amplified) in the negative (positive) bias regime as compared to the cases of parallel configuration and nonmagnetic leads. The rectification effect is even enhanced when one of the lead's spin polarization approaches to unit, during which the negative differential of the heat generation is weakened due to the change of the spin-dependent electron occupation numbers on the dot. The found results may be used for thermal transistor in the newly emerged research subject of phononics. - Highlights: • Heat flow between electrons and phonons is controlled by interaction between them. • A thermal diode or rectifier is proposed to work under electrical bias. • The heat rectification effect can be enhanced by the leads' ferromagnetism.

  10. The Molecular Electronic Device and the Biochip Computer: Present Status

    Haddon, R. C.; Lamola, A. A.

    1985-04-01

    The idea that a single molecule might function as a self-contained electronic device has been of interest for some time. However, a fully integrated version--the biochip or the biocomputer, in which both production and assembly of molecular electronic components is achieved through biotechnology--is a relatively new concept that is currently attracting attention both within the scientific community and among the general public. In the present article we draw together some of the approaches being considered for the construction of such devices and delineate the revolutionary nature of the current proposals for molecular electronic devices (MEDs) and biochip computers (BCCs). With the silicon semiconductor industry already in place and in view of the continuing successes of the lithographic process it seems appropriate to ask why the highly speculative MED or BCC has engendered such interest. In some respects the answer is paradigmatic as much as it is real. It is perhaps best stated as the promise of the realm of the molecular. Thus it is envisioned that devices will be constructed by assembly of individual molecular electronic components into arrays, thereby engineering from small upward rather than large downward as do current lithographic techniques. An important corollary of the construction technique is that the functional elements of such an array would be individual molecules rather than macroscopic ensembles. These two aspects of the MED/BCC--assembly of molecular arrays and individually accessible functional molecular units--are truly revolutionary. Both require scientific breakthroughs and the necessary principles, quite apart from the technology, remain essentially unknown. It is concluded that the advent of the MED/BCC still lies well before us. The twin criteria of utilization of individual molecules as functional elements and the assembly of such elements remains as elusive as ever. Biology engineers structures on the molecular scale but biomolecules

  11. The Electron-Pair Repulsion Model for Molecular Geometry

    Gillespie, R. J.

    1970-01-01

    Describes how the electron-pair repulsion model qualitatively explains the size and shape of molecular orbitals. Briefly discusses trigonal bipyramidal molecules, three-center bonds, and transition elements. Describes cluster compounds and finishes with a discussion of the exceptions to the model and effects of ligand-ligand repulsions. (RR)

  12. Fast Electron Repulsion Integrals for Molecular Coulomb Sturmians

    Avery, James Emil

    hyperspherical harmonics. A rudimentary software library has been implemented and preliminary benchmarks indicate very good performance: On average 40 ns, or approximately 80 clock cycles, per electron repulsion integral. This makes molecular Coulomb Sturmians competitive with Gaussian type orbitals in terms of...

  13. Computational Nanotechnology of Molecular Materials, Electronics and Machines

    Srivastava, D.; Biegel, Bryan A. (Technical Monitor)

    2002-01-01

    This viewgraph presentation covers carbon nanotubes, their characteristics, and their potential future applications. The presentation include predictions on the development of nanostructures and their applications, the thermal characteristics of carbon nanotubes, mechano-chemical effects upon carbon nanotubes, molecular electronics, and models for possible future nanostructure devices. The presentation also proposes a neural model for signal processing.

  14. Fullerene-based Anchoring Groups for Molecular Electronics

    Martin, Christian A.; Ding, Dapeng; Sørensen, Jakob Kryger;

    2008-01-01

    We present results on a new fullerene-based anchoring group for molecular electronics. Using lithographic mechanically controllable break junctions in vacuum we have determined the conductance and stability of single-molecule junctions of 1,4-bis(fullero[c]pyrrolidin-1-yl)benzene. The compound can...

  15. Single C59N molecule as a molecular rectifier.

    Zhao, Jin; Zeng, Changgan; Cheng, Xin; Wang, Kedong; Wang, Guanwu; Yang, Jinlong; Hou, J G; Zhu, Qingshi

    2005-07-22

    We report a new kind of experimental realization of a molecular rectifier, which is based on a single azafullerene C59N molecule in a double-barrier tunnel junction via the single electron tunneling effect. An obvious rectifying effect is observed. The positive onset voltage is about 0.5-0.7 V, while the negative onset voltage is about 1.6-1.8 V. Theoretical analyses show that the half-occupied molecular orbital of the C59N molecule and the asymmetric shift of the molecular Fermi level when the molecule is charged are responsible for the molecular rectification. PMID:16090819

  16. Theory and Application of Dissociative Electron Capture in Molecular Identification

    Havey, C D; Jones, T; Voorhees, K J; Laramee, J A; Cody, R B; Clougherty, D P; Eberhart, Mark; Voorhees, Kent J.; Laramee, James A.; Cody, Robert B.; Clougherty, Dennis P.

    2006-01-01

    The coupling of an electron monochromator (EM) to a mass spectrometer (MS) has created a new analytical technique, EM-MS, for the investigation of electrophilic compounds. This method provides a powerful tool for molecular identification of compounds contained in complex matrices, such as environmental samples. EM-MS expands the application and selectivity of traditional MS through the inclusion of a new dimension in the space of molecular characteristics--the electron resonance energy spectrum. However, before this tool can realize its full potential, it will be necessary to create a library of resonance energy scans from standards of the molecules for which EM-MS offers a practical means of detection. Here, an approach supplementing direct measurement with chemical inference and quantum scattering theory is presented to demonstrate the feasibility of directly calculating resonance energy spectra. This approach makes use of the symmetry of the transition-matrix element of the captured electron to discriminat...

  17. Bonding in Molecular Crystals from the Local Electronic Pressure Viewpoint

    Tsirelson, Vladimir G; Tokatly, Ilya V

    2015-01-01

    The spatial distribution of the internal pressure of an electron fluid, which spontaneously arises at the formation of a molecule or a crystal, is linked to the main features of chemical bonding in molecular crystals. The local pressure is approximately expressed in terms of the experimental electron density and its derivatives using the density functional formalism and is applied to identify the bonding features in benzene, formamide and chromium hexacarbonyl. We established how the spatial regions of compression and stretching of the electron fluid in these solids reflect the typical features of chemical bonds of different types. Thus, the internal electronic pressure can serve as a bonding descriptor, which has a clear physical meaning and reveals the specific features of variety of the chemical bonds expressing them in terms of the electron density.

  18. Photoinduced Phase Transition in Strongly Electron-Lattice and Electron–Electron Correlated Molecular Crystals

    Shin-ya Koshihara

    2012-07-01

    Full Text Available Strongly electron-lattice- and electron-electron-correlated molecular crystals, such as charge transfer (CT complexes, are often sensitive to external stimuli, e.g., photoexcitation, due to the cooperative or competitive correlation of various interactions present in the crystals. These crystals are thus productive targets for studying photoinduced phase transitions (PIPTs. Recent advancements in research on the PIPT of CT complexes, especially Et2Me2Sb[Pd(dmit2]2 and (EDO-TTF2PF6, are reviewed in this report. The former exhibits a photoinduced insulator-to-insulator phase transition with clearly assigned spectral change. We demonstrate how to find the dynamics of PIPT using this system. The latter exhibits a photoinduced hidden state as an initial PIPT process. Wide energy ranged time-resolved spectroscopy can probe many kinds of photo-absorption processes, i.e., intra-molecular and inter-molecular electron excitations and intramolecular and electron-molecular vibrations. The photoinduced spectral changes in these photo-absorption processes reveal various aspects of the dynamics of PIPT, including electronic structural changes, lattice structural changes, and molecular deformations. The complexities of the dynamics of the latter system were revealed by our measurements.

  19. Digital image transformation and rectification of spacecraft and radar images

    Wu, S.S.C.

    1985-01-01

    Digital image transformation and rectification can be described in three categories: (1) digital rectification of spacecraft pictures on workable stereoplotters; (2) digital correction of radar image geometry; and (3) digital reconstruction of shaded relief maps and perspective views including stereograms. Digital rectification can make high-oblique pictures workable on stereoplotters that would otherwise not accommodate such extreme tilt angles. It also enables panoramic line-scan geometry to be used to compile contour maps with photogrammetric plotters. Rectifications were digitally processed on both Viking Orbiter and Lander pictures of Mars as well as radar images taken by various radar systems. By merging digital terrain data with image data, perspective and three-dimensional views of Olympus Mons and Tithonium Chasma, also of Mars, are reconstructed through digital image processing. ?? 1985.

  20. Epipolar rectification method for a stereovision system with telecentric cameras

    Liu, Haibo; Zhu, Zhaokun; Yao, Linshen; Dong, Jin; Chen, Shengyi; Zhang, Xiaohu; Shang, Yang

    2016-08-01

    3D metrology of a stereovision system requires epipolar rectification to be performed before dense stereo matching. In this study, we propose an epipolar rectification method for a stereovision system with two telecentric lens-based cameras. Given the orthographic projection matrices of each camera, the new projection matrices are computed by determining the new camera coordinates system in affine space and imposing some constraints on the intrinsic parameters. Then, the transformation that maps the old image planes on to the new image planes is achieved. Experiments are performed to validate the performance of the proposed rectification method. The test results show that the perpendicular distance and 3D reconstructed deviation obtained from the rectified images is not significantly higher than the corresponding values obtained from the original images. Considering the roughness of the extracted corner points and calibrated camera parameters, we can conclude that the proposed method can provide sufficiently accurate rectification results.

  1. Electronic tunneling currents at optical frequencies

    Faris, S. M.; Fan, B.; Gustafson, T. K.

    1975-01-01

    Rectification characteristics of nonsuperconducting metal-barrier-metal junctions as deduced from electronic tunneling theory have been observed experimentally for optical frequency irradiation of the junction.

  2. Thermal rectification in bulk materials with asymmetric shape

    Sawaki, D.; Kobayashi, W.; Moritomo, Y.; Terasaki, I.

    2011-01-01

    We investigate thermal rectification in a bulk material with a pyramid shape to elucidate shape dependence of the thermal rectification, and find that rectifying coefficient R is 1.35 for this shape, which is smaller than R=1.43 for a rectangular shape. This result is fully duplicated by our numerical calculation based on Fourier's law. We also apply this calculation to a given shape, and show a possible way to increase R depending on the shape.

  3. Patterning molecular scale paramagnets at Au Surface: A root to Magneto-Molecular-Electronics

    Messina, Paolo

    2004-01-01

    Few examples of the exploitation of molecular magnetic properties in molecular electronics are known to date. Here we propose the realization of Self assembled monolayers (SAM) of a particular stable organic radical. This radical is meant to be used as a standard molecule on which to prove the validity of a single spin reading procedure known as ESR-STM. We also discuss a range of possible applications, further than ESR-STM, of magnetic monolayers of simple purely organic magnetic molecule.

  4. A new parametrizable model of molecular electronic structure

    Laikov, Dimitri N

    2011-01-01

    A new electronic structure model is developed in which the ground state energy of a molecular system is given by a Hartree-Fock-like expression with parametrized one- and two-electron integrals over an extended (minimal + polarization) set of orthogonalized atom-centered basis functions, the variational equations being solved formally within the minimal basis but the effect of polarization functions being included in the spirit of second-order perturbation theory. It is designed to yield good dipole polarizabilities and improved intermolecular potentials with dispersion terms. The molecular integrals include up to three-center one-electron and two-center two-electron terms, all in simple analytical forms. A method to extract the effective one-electron Hamiltonian of nonlocal-exchange Kohn-Sham theory from the coupled-cluster one-electron density matrix is designed and used to get its matrix representation in a molecule-intrinsic minimal basis as an input to the paramtrization procedure -- making a direct link...

  5. Electron transport properties of single molecular junctions under mechanical modulations

    Electron transport behaviors of single molecular junctions are very sensitive to the atomic scale molecule-metal electrode contact interfaces, which have been difficult to control. We used a modified scanning probe microscope-break junction technique (SPM-BJT) to control the dynamics of the contacts and simultaneously monitor both the conductance and force. First, by fitting the measured data into a modified multiple tunneling barrier model, the static contact resistances, corresponding to the different contact conformations of single alkanedithiol and alkanediamine molecular junctions, were identified. Second, the changes of contact decay constant were measured under mechanical extensions of the molecular junctions, which helped to classify the different single molecular conductance sets into specific microscopic conformations of the molecule-electrode contacts. Third, by monitoring the changes of force and contact decay constant with the mechanical extensions, the changes of conductance were found to be caused by the changes of contact bond length and by the atomic reorganizations near the contact bond. This study provides a new insight into the understanding of the influences of contact conformations, especially the effect of changes of dynamic contact conformation on electron transport through single molecular junctions. (paper)

  6. Laser induced - tunneling, electron diffraction and molecular orbital imaging

    Full text: Multiphoton ionization in the tunneling limit is similar to tunneling in a scanning tunneling microscope. In both cases an electron wave packet tunnels from a bound (or valence) state to the continuum. I will show that multiphoton ionization provides a route to extend tunneling spectroscopy to the interior of transparent solids. Rotating the laser polarization is the analogue of scanning the STM tip - a means of measuring the crystal symmetry of a solid. In gas phase molecules the momentum spectrum of individual electrons can be measured. I will show that, as we rotate the molecule with respect to the laser polarization, the photoelectron spectrum samples a filter projection of the momentum wave function (the molecular analogue to the band structure) of the ionizing orbital. Some electrons created during multiphoton ionization re-collide with their parent ion. I will show that they diffract, revealing the scattering potential of the ion - the molecular structure. The electron can also interfere with the initial orbital from which it separated, creating attosecond XUV pulses or pulse trains. The amplitude and phase of the radiation contains all information needed to re-construct the image of the orbital (just as a sheared optical interferometer can fully characterize an optical pulse). Strong field methods provide an extensive range of new tools to apply to atomic, molecular and solid-state problems. (author)

  7. Design of Carborane Molecular Architectures via Electronic Structure Computations

    Josep M. Oliva

    2009-01-01

    Full Text Available Quantum-mechanical electronic structure computations were employed to explore initial steps towards a comprehensive design of polycarborane architectures through assembly of molecular units. Aspects considered were (i the striking modification of geometrical parameters through substitution, (ii endohedral carboranes and proposed ejection mechanisms for energy/ion/atom/energy storage/transport, (iii the excited state character in single and dimeric molecular units, and (iv higher architectural constructs. A goal of this work is to find optimal architectures where atom/ion/energy/spin transport within carborane superclusters is feasible in order to modernize and improve future photoenergy processes.

  8. III - V semiconductor structures for biosensor and molecular electronics applications

    Luber, S.M.

    2007-01-15

    The present work reports on the employment of III-V semiconductor structures to biosensor and molecular electronics applications. In the first part a sensor based on a surface-near two dimensional electron gas for a use in biological environment is studied. Such a two dimensional electron gas inherently forms in a molecular beam epitaxy (MBE) grown, doped aluminum gallium arsenide - gallium arsenide (AlGaAs-GaAs) heterostructure. Due to the intrinsic instability of GaAs in aqueous solutions the device is passivated by deposition of a monolayer of 4'-substituted mercaptobiphenyl molecules. The influence of these molecules which bind to the GaAs via a sulfur group is investigated by Kelvin probe measurements in air. They reveal a dependence of GaAs electron affinity on the intrinsic molecular dipole moment of the mercaptobiphenyls. Furthermore, transient surface photovoltage measurements are presented which demonstrate an additional influence of mercaptobiphenyl chemisorption on surface carrier recombination rates. As a next step, the influence of pH-value and salt concentration upon the sensor device is discussed based on the results obtained from sensor conductance measurements in physiological solutions. A dependence of the device surface potential on both parameters due to surface charging is deduced. Model calculations applying Poisson-Boltzmann theory reveal as possible surface charging mechanisms either the adsorption of OH- ions on the surface, or the dissociation of OH groups in surface oxides. A comparison between simulation settings and physical device properties indicate the OH- adsorption as the most probable mechanism. In the second part of the present study the suitability of MBE grown III-V semiconductor structures for molecular electronics applications is examined. In doing so, a method to fabricate nanometer separated, coplanar, metallic electrodes based on the cleavage of a supporting AlGaAs-GaAs heterostructure is presented. This is followed

  9. A new parametrizable model of molecular electronic structure

    Laikov, Dimitri N.

    2011-10-01

    A new electronic structure model is developed in which the ground state energy of a molecular system is given by a Hartree-Fock-like expression with parametrized one- and two-electron integrals over an extended (minimal + polarization) set of orthogonalized atom-centered basis functions, the variational equations being solved formally within the minimal basis but the effect of polarization functions being included in the spirit of second-order perturbation theory. It is designed to yield good dipole polarizabilities and improved intermolecular potentials with dispersion terms. The molecular integrals include up to three-center one-electron and two-center two-electron terms, all in simple analytical forms. A method to extract the effective one-electron Hamiltonian of nonlocal-exchange Kohn-Sham theory from the coupled-cluster one-electron density matrix is designed and used to get its matrix representation in a molecule-intrinsic minimal basis as an input to the parametrization procedure - making a direct link to the correlated wavefunction theory. The model has been trained for 15 elements (H, Li-F, Na-Cl, 720 parameters) on a set of 5581 molecules (including ions, transition states, and weakly bound complexes) whose first- and second-order properties were computed by the coupled-cluster theory as a reference, and a good agreement is seen. The model looks promising for the study of large molecular systems, it is believed to be an important step forward from the traditional semiempirical models towards higher accuracy at nearly as low a computational cost.

  10. Electronic shift register memory based on molecular electron-transfer reactions

    The design of a shift register memory at the molecular level is described in detail. The memory elements are based on a chain of electron-transfer molecules incorporated on a very large scale integrated (VLSI) substrate, and the information is shifted by photoinduced electron-transfer reactions. The design requirements for such a system are discussed, and several realistic strategies for synthesizing these systems are presented. The immediate advantage of such a hybrid molecular/VLSI device would arise from the possible information storage density. The prospect of considerable savings of energy per bit processed also exists. This molecular shift register memory element design solves the conceptual problems associated with integrating molecular size components with larger (micron) size features on a chip

  11. Electron densities and the excitation of CN in molecular clouds

    Black, John H.; Van Dishoeck, Ewine F.

    1991-01-01

    In molecular clouds of modest density and relatively high fractional ionization, the rotational excitation of CN is controlled by a competition among electron impact, neutral impact and the interaction with the cosmic background radiation. The degree of excitation can be measured through optical absorption lines and millimeter-wave emission lines. The available, accurate data on CN in diffuse and translucent molecular clouds are assembled and used to determine electron densities. The derived values, n(e) = roughly 0.02 - 0.5/cu cm, imply modest neutral densities, which generally agree well with determinations by other techniques. The absorption- and emission-line measurements of CN both exclude densities higher than n(H2) = roughly 10 exp 3.5/cu cm on scales varying from 0.001 to 60 arcsec in these clouds.

  12. Electron dopable molecular wires based on the extended viologens

    Kolivoška, Viliam; Gál, Miroslav; Pospíšil, Lubomír; Valášek, Michal; Hromadová, Magdaléna

    2011-01-01

    Roč. 13, č. 23 (2011), s. 11422-11429. ISSN 1463-9076 R&D Projects: GA ČR GA203/08/1157; GA ČR GA203/09/0705; GA AV ČR IAA400400802; GA MŠk(CZ) MEB041006 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z40550506 Keywords : electron transfer * spectroelectrochemistry * molecular wires Subject RIV: CG - Electrochemistry Impact factor: 3.573, year: 2011

  13. Electronic kinetics of molecular nitrogen and molecular oxygen in high-latitude lower thermosphere and mesosphere

    A. S. Kirillov

    2010-01-01

    Full Text Available Total quenching rate coefficients of Herzberg states of molecular oxygen and three triplet states of molecular nitrogen in the collisions with O2 and N2 molecules are calculated on the basis of quantum-chemical approximations. The calculated rate coefficients of electronic quenching of O2* and N2* molecules show a good agreement with available experimental data. An influence of collisional processes on vibrational populations of electronically excited N2 and O2 molecules is studied for the altitudes of high-latitude lower thermosphere and mesosphere during auroral electron precipitation. It is indicated that molecular collisions of metastable nitrogen N2(A3Σu* with O2 molecules are principal mechanism in electronic excitation of both Herzberg states c1Σu&minus, A'3Δu, A3Σu+ and high vibrational levels of singlet states a1Δg and b1Σg+ of molecular oxygen O2 at these altitudes.

  14. Pressure shifts and electron scattering in atomic and molecular gases

    In this work, the authors focus on one aspect of Rydberg electron scattering, namely number density effects in molecular gases. The recent study of Rydberg states of CH3I and C6H6 perturbed by H2 is the first attempt to investigate number density effects of a molecular perturber on Rydberg electrons. Highly excited Rydberg states, because of their ''large orbital'' nature, are very sensitive to the surrounding medium. Photoabsorption or photoionization spectra of CH3I have also been measured as a function of perturber pressure in 11 different binary gas mixtures consisting of CH3I and each one of eleven different gaseous perturbers. Five of the perturbers were rare gases (He, Ne, Ar, Kr, Xe) and six were non-dipolar molecules (H2, CH4, N2, C2H6, C3H8). The goal of this work is to underline similarities and differences between atomic and molecular perturbers. The authors first list some results of the molecular study

  15. A molecularly based theory for electron transfer reorganization energy

    Using field-theoretic techniques, we develop a molecularly based dipolar self-consistent-field theory (DSCFT) for charge solvation in pure solvents under equilibrium and nonequilibrium conditions and apply it to the reorganization energy of electron transfer reactions. The DSCFT uses a set of molecular parameters, such as the solvent molecule’s permanent dipole moment and polarizability, thus avoiding approximations that are inherent in treating the solvent as a linear dielectric medium. A simple, analytical expression for the free energy is obtained in terms of the equilibrium and nonequilibrium electrostatic potential profiles and electric susceptibilities, which are obtained by solving a set of self-consistent equations. With no adjustable parameters, the DSCFT predicts activation energies and reorganization energies in good agreement with previous experiments and calculations for the electron transfer between metallic ions. Because the DSCFT is able to describe the properties of the solvent in the immediate vicinity of the charges, it is unnecessary to distinguish between the inner-sphere and outer-sphere solvent molecules in the calculation of the reorganization energy as in previous work. Furthermore, examining the nonequilibrium free energy surfaces of electron transfer, we find that the nonequilibrium free energy is well approximated by a double parabola for self-exchange reactions, but the curvature of the nonequilibrium free energy surface depends on the charges of the electron-transferring species, contrary to the prediction by the linear dielectric theory

  16. Ion transport and rectification in a charged nanoscale cone

    Yang, Fan; Zhang, Li; Mao, Qian; Stone, Howard

    2015-11-01

    The possibility of rectification for ion transport in nanofluidic systems offers a potential route for developing a nanofluidic diode that mimics a semiconductor diode or captures some features of a biological ion channel. The rectification phenomenon, in which a solution would be enriched in one ion, results from asymmetric effects in ionic transport that can be realized by discontinuities in surface charge, concentration differences across a pore, or an asymmetric pore shape such as a cone. In this paper, we focus on the latter two effects and seek to capture the rectification effect in simple terms with a non-dimensional model representative of the many systems studied to date. Specifically, we analyze the rectification phenomenon in a charged nanoscale cone with a concentration difference and/or an electrical potential difference across the pore. Based on the Poisson-Nernst-Planck model and the assumption of one-dimensional transport, we derive a model based on two coupled ordinary differential equations to determine significant parameters such as ionic current. We identify several dimensionless parameters that have not been recognized previously and study the influence of the dimensionless parameters on the rectification. The authors would like to thank The Center for Combustion Energy (CCE) of Tsinghua University for supporting this project.

  17. Growth, modification and integration of carbon nanotubes into molecular electronics

    Moscatello, Jason P.

    Molecules are the smallest possible elements for electronic devices, with active elements for such devices typically a few Angstroms in footprint area. Owing to the possibility of producing ultra-high density devices, tremendous effort has been invested in producing electronic junctions by using various types of molecules. The major issues for molecular electronics include (1) developing an effective scheme to connect molecules with the present micro- and nano-technology, (2) increasing the lifetime and stabilities of the devices, and (3) increasing their performance in comparison to the state-of-the-art devices. In this work, we attempt to use carbon nanotubes (CNTs) as the interconnecting nanoelectrodes between molecules and microelectrodes. The ultimate goal is to use two individual CNTs to sandwich molecules in a cross-bar configuration while having these CNTs connected with microelectrodes such that the junction displays the electronic character of the molecule chosen. We have successfully developed an effective scheme to connect molecules with CNTs, which is scalable to arrays of molecular electronic devices. To realize this far reaching goal, the following technical topics have been investigated. (1) Synthesis of multi-walled carbon nanotubes (MWCNTs) by thermal chemical vapor deposition (T-CVD) and plasma-enhanced chemical vapor deposition (PECVD) techniques (Chapter 3). We have evaluated the potential use of tubular and bamboo-like MWCNTs grown by T-CVD and PE-CVD in terms of their structural properties. (2) Horizontal dispersion of MWCNTs with and without surfactants, and the integration of MWCNTs to microelectrodes using deposition by dielectrophoresis (DEP) (Chapter 4). We have systematically studied the use of surfactant molecules to disperse and horizontally align MWCNTs on substrates. In addition, DEP is shown to produce impurityfree placement of MWCNTs, forming connections between microelectrodes. We demonstrate the deposition density is tunable by

  18. Electron collisions and internal excitation in stored molecular ion beams

    In storage ring experiments the role, which the initial internal excitation of a molecular ion can play in electron collisions, and the effect of these collisions on the internal excitation are investigated. Dissociative recombination (DR) and inelastic and super-elastic collisions are studied in the system of He+2. The DR rate coefficient at low energies depends strongly on the initial vibrational excitation in this system. Therefore changes in the DR rate coefficient are a very sensitive probe for changes in the vibrational excitation in He+2, which is used to investigate the effects of collisions with electrons and residual gas species. The low-energy DR of HD+ is rich with resonances from the indirect DR process, when certain initial rotational levels in the molecular ion are coupled to levels in neutral Rydberg states lying below the ion state. Using new procedures for high-resolution electron-ion collision spectroscopy developed here, these resonances in the DR cross section can be measured with high energy sensitivity. This allows a detailed comparison with results of a MQDT calculation in an effort to assign some or all of the resonances to certain intermediate Rydberg levels. (orig.)

  19. Electron collisions and internal excitation in stored molecular ion beams

    Buhr, H.

    2006-07-26

    In storage ring experiments the role, which the initial internal excitation of a molecular ion can play in electron collisions, and the effect of these collisions on the internal excitation are investigated. Dissociative recombination (DR) and inelastic and super-elastic collisions are studied in the system of He{sup +}{sub 2}. The DR rate coefficient at low energies depends strongly on the initial vibrational excitation in this system. Therefore changes in the DR rate coefficient are a very sensitive probe for changes in the vibrational excitation in He{sup +}{sub 2}, which is used to investigate the effects of collisions with electrons and residual gas species. The low-energy DR of HD{sup +} is rich with resonances from the indirect DR process, when certain initial rotational levels in the molecular ion are coupled to levels in neutral Rydberg states lying below the ion state. Using new procedures for high-resolution electron-ion collision spectroscopy developed here, these resonances in the DR cross section can be measured with high energy sensitivity. This allows a detailed comparison with results of a MQDT calculation in an effort to assign some or all of the resonances to certain intermediate Rydberg levels. (orig.)

  20. Electron Spin Resonance Study of Electrons Trapped in Solid Molecular Hydrogen Films

    Sheludiakov, S.; Ahokas, J.; Järvinen, J.; Vainio, O.; Lehtonen, L.; Zvezdov, D.; Khmelenko, V.; Lee, D. M.; Vasiliev, S.

    2016-05-01

    We report on the measurements of electrons trapped in solid molecular films of H2, HD, and D2. A narrow ESR line associated with the trapped electrons was detected with g=2.00233(5), which turned out to be shifted by -0.3 G from the free electron resonance. Comparison is made with earlier measurements where a similar line has been seen. In addition, for a text {D}2{:}text {H}2 mixture, after raising the temperature above 1 K, we observe a strong line at the location of the electron cyclotron resonance. The line amplitude is dependent on temperature and has an activation energy of 26 K. We believe that at elevated temperatures, electrons diffuse from the bulk of the film to the surface.

  1. Vibrational excitations in molecular layers probed by ballistic electron microscopy

    Kajen, Rasanayagam Sivasayan; Chandrasekhar, Natarajan [Institute of Materials Research and Engineering, 3 Research Link, 117602 (Singapore); Feng Xinliang; Muellen, Klaus [Max-Planck-Institut fuer Polymerforschung, Postfach 3148, D-55021 Mainz (Germany); Su Haibin, E-mail: n-chandra@imre.a-star.edu.sg, E-mail: muellen@mpip-mainz.mpg.de, E-mail: hbsu@ntu.edu.sg [Division of Materials Science, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore)

    2011-10-28

    We demonstrate the information on molecular vibrational modes via the second derivative (d{sup 2}I{sub B}/dV{sup 2}) of the ballistic electron emission spectroscopy (BEES) current. The proposed method does not create huge fields as in the case of conventional derivative spectroscopy and maintains a zero bias across the device. BEES studies carried out on three different types of large polycyclic aromatic hydrocarbon (PAH) molecular layers show that the d{sup 2}I{sub B}/dV{sup 2} spectra consist of uniformly spaced peaks corresponding to vibronic excitations. The peak spacing is found to be identical for molecules within the same PAH family though the BEES onset voltage varies for different molecules. In addition, injection into a particular orbital appears to correspond to a specific vibrational mode as the manifestation of the symmetry principle.

  2. Ab initio molecular dynamics on the electronic Boltzmann equilibrium distribution

    Alonso, J L; Echenique, P [Departamento de Fisica Teorica, Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza (Spain); Castro, A; Polo, V [Institute for Biocomputation and Physics of Complex Systems (BIFI), University of Zaragoza, Mariano Esquillor s/n, E-50018 Zaragoza (Spain); Rubio, A [Nano-Bio Spectroscopy group and ETSF Scientific Development Centre, Departamento de Fisica de Materiales, Universidad del PaIs Vasco, Centro de Fisica de Materiales, CSIC-UPV/EHU-MPC and DIPC, E-20018 San Sebastian (Spain); Zueco, D, E-mail: dzueco@unizar.e [Instituto de Ciencia de Materiales de Aragon and Departamento de Fisica de la Materia Condensada, CSIC-Universidad de Zaragoza, E-50009 Zaragoza (Spain)

    2010-08-15

    We prove that for a combined system of classical and quantum particles, it is possible to describe a dynamics for the classical particles that incorporates in a natural way the Boltzmann equilibrium population for the quantum subsystem. In addition, these molecular dynamics (MD) do not need to assume that the electrons immediately follow the nuclear motion (in contrast to any adiabatic approach) and do not present problems in the presence of crossing points between different potential energy surfaces (conical intersections or spin-crossings). A practical application of this MD to the study of the effect of temperature on molecular systems presenting (nearly) degenerate states-such as the avoided crossing in the ring-closure process of ozone-is presented.

  3. Electron transport through catechol-functionalized molecular rods

    The charge transport properties of a catechol-type dithiol-terminated oligo-phenylene-ethynylene was investigated by cyclic voltammetry (CV) and by the scanning tunnelling microscopy break junction technique (STM-BJ). Single molecule charge transport experiments demonstrated the existence of high and low conductance regions. The junction conductance is rather weakly dependent on the redox state of the bridging molecule. However, a distinct dependence of junction formation probability and of relative stretching distances of the catechol- and quinone-type molecular junctions is observed. Substitution of the central catechol ring with alkoxy-moieties and the combination with a topological analysis of possible π-electron pathways through the respective molecular skeletons lead to a working hypothesis, which could rationalize the experimentally observed conductance characteristics of the redox-active nanojunctions

  4. Electron-phonon interaction within classical molecular dynamics

    Tamm, A.; Samolyuk, G.; Correa, A. A.; Klintenberg, M.; Aabloo, A.; Caro, A.

    2016-07-01

    We present a model for nonadiabatic classical molecular dynamics simulations that captures with high accuracy the wave-vector q dependence of the phonon lifetimes, in agreement with quantum mechanics calculations. It is based on a local view of the e -ph interaction where individual atom dynamics couples to electrons via a damping term that is obtained as the low-velocity limit of the stopping power of a moving ion in a host. The model is parameter free, as its components are derived from ab initio-type calculations, is readily extended to the case of alloys, and is adequate for large-scale molecular dynamics computer simulations. We also show how this model removes some oversimplifications of the traditional ionic damped dynamics commonly used to describe situations beyond the Born-Oppenheimer approximation.

  5. Fulleropyrrolidine end-capped molecular wires for molecular electronics--synthesis, spectroscopic, electrochemical, and theoretical characterization

    Sørensen, Jakob Kryger; Fock, Jeppe; Pedersen, Anders Holmen;

    2011-01-01

    synthetic protocols for derivatives terminated with one or two fullero[c]pyrrolidine "electrode anchoring" groups were developed. An aryl-substituted aziridine could in some cases be employed directly as the azomethine ylide precursor for the Prato reaction without the need of having an electron...... state. However, the fluorescence of C(60) was quenched by charge transfer from the wire to C(60). Quantum chemical calculations predict and explain the collapse of coherent electronic transmission through one of the fulleropyrrolidine-terminated molecular wires....

  6. From Molecular Meccano to Nano-Functional Materials for Molecular Electronics Applications

    Sue, Chi-Hau

    Mechanically interlocked molecules (MIMs), such as bistable catenanes and rotaxanes, have found technological applications in fields as disparate as those involving molecular switches and machines, nanoelectromechanical systems (NEMS), and molecular electronic devices. All these multifarious applications of MIMs require that the synthesis of these molecular components be straightforward and efficient. Furthermore, the elaboration of the structural features of MIMs into metal-organic frameworks (MOFs) provides a way of bringing MIMs from solution into solid state in a systematic and hierarchical manner. This dissertation describes successful attempts in realizing such concepts. The pi-electron deficient tetracationic cyclophane, namely cyclobis(paraquat-p-phenylene) (CBQPT4+), which is a key component in the MIMs for molecular electronics applications, now can be synthesized by a new "template-trading" protocol. The time taken to synthesize CBPQT4+ has been halved as a result of using a pH-responsive derivative of 1,5-diaminonaphthalene to displace the template employed during its synthesis, instead of the time-consuming and energy-wasteful liquid-liquid extraction. By utilizing the considerable sophistication of organic synthesis methods, a series of rigid organic dicarboxylic acids containing crown ethers and [2]catenanes moieties are designed and synthesized. These novel dicarboxylic crown ethers not only retain the characteristics of their parent crown ethers since they can bind cationic guests and serve as templates for making MIMs, but they also present coordination sites to connect with secondary building units (SBUs) in MOFs, in which the organic linkers act as "edges" that bridge the metal centers which in turn act as "vertices". This strategy allows the "bottom-up" construction of crystalline MOFs, whose bulk properties in the solid state can be designed and predicted by the characteristics of the molecular building blocks and superstructures. The

  7. Patterning molecular scale paramagnets at Au Surface: A root to Magneto-Molecular-Electronics

    Messina, Paul C; Sorace, L; Rovai, D; Caneschi, A; Gatteschi, Dante; Messina, Paolo; Mannini, Matteo; Sorace, Lorenzo; Rovai, Donella; Caneschi, Andrea; Gatteschi, Dante

    2004-01-01

    Few examples of the exploitation of molecular magnetic properties in molecular electronics are known to date. Here we propose the realization of Self assembled monolayers (SAM) of a particular stable organic radical. This radical is meant to be used as a standard molecule on which to prove the validity of a single spin reading procedure known as ESR-STM. We demonstrate here that the radical is chemically anchored at the surface, preserves its magnetic functionality and can be imaged by STM. STM and ESR investigations of the molecular film is reported. We also discuss a range of possible applications, further than ESR-STM, of magnetic monolayers of simple purely organic magnetic molecule.

  8. Wave packet dynamics in molecular excited electronic states

    We theoretically explore the use of UV pump – UV probe schemes to resolve in time the dynamics of nuclear wave packets in excited electronic states of the hydrogen molecule. The pump pulse ignites the dynamics in singly excited states, that will be probed after a given time delay by a second identical pulse that will ionize the molecule. The field-free molecular dynamics is first explored by analyizing the autocorrelation function for the pumped wave packet and the excitation probabilities. We investigate both energy and angle differential ionization probabilities and demonstrate that the asymmetry induced in the electron angular distributions gives a direct map of the time evolution of the pumped wave packet

  9. IV. Dissociative recombination of electrons and molecular ions

    The present state of the theory of the dissociative recombination of electrons and molecular ions is reviewed and its shortcomings shown. The mechanisms of direct and indirect dissociative processes are described. Several approximative methods employing the analogy with the recombination of atomic ions and electrons are used for the determination of the dissociative recombination factor. Analyzing the derived formulae the temperature dependence of the dissociative recombination factor is determined and the results are compared with experimental data obtained by several authors. The energy levels of atoms created at the dissociative recombination of He2+, Ar2+, and O2+ ions are described. Methods of measuring the recombination factor are listed. The existing experimental data are summarized and the possible explanation of the observed variations is presented. An exhaustive list of references is given. (J.U.)

  10. Resonant Laser Incisions: Molecular Targets Using the Free Electron Laser

    Reinisch, Lou; Bryant, Grady; Ossoff, Robert H.

    1996-03-01

    Laser ablation of tissue for medical incisions is normally concerned with the energy absorption and the subsequent vaporization of intracellular water. Using Fourier transform infrared spectroscopy, we have identified specific non-water resonances within tissues. Then, using the Vanderbilt Free Electron Laser (wavelength tunable from 2 to 10 microns) and our Computer Assisted Surgical Techniques program (to standardize the laser delivery), we have targeted specific molecular resonances for laser incisions and tissue removal. Using both acute and chronic studies, we can map out the resonant action spectrum to improve surgical outcomes. We have modeled these ablation mechanisms and working to establish the link between these ablation mechanisms and wound healing. This work has been supported, in part, by a grant from the Department of Defense, Medical Free Electron Laser Program, ONR Grant #N000149411023.

  11. Fragmentation of molecular ions in slow electron collisions

    Novotny, Steffen

    2008-06-25

    The fragmentation of positively charged hydrogen molecular ions by the capture of slow electrons, the so called dissociative recombination (DR), has been investigated in storage ring experiments at the TSR, Heidelberg, where an unique twin-electron-beam arrangement was combined with high resolution fragment imaging detection. Provided with well directed cold electrons the fragmentation kinematics were measured down to meV collision energies where pronounced rovibrational Feshbach resonances appear in the DR cross section. For thermally excited HD{sup +} the fragmentation angle and the kinetic energy release were studied at variable precisely controlled electron collision energies on a dense energy grid from 10 to 80 meV. The anisotropy described for the first time by Legendre polynomials higher 2{sup nd} order and the extracted rotational state contributions were found to vary on a likewise narrow energy scale as the rotationally averaged DR rate coefficient. Ro-vibrationally resolved DR experiments were performed on H{sub 2}{sup +} produced in distinct internal excitations by a novel ion source. Both the low-energy DR rate as well as the fragmentation dynamics at selected resonances were measured individually in the lowest two vibrational and first three excited rotational states. State-specific DR rates and angular dependences are reported. (orig.)

  12. Fragmentation of molecular ions in slow electron collisions

    The fragmentation of positively charged hydrogen molecular ions by the capture of slow electrons, the so called dissociative recombination (DR), has been investigated in storage ring experiments at the TSR, Heidelberg, where an unique twin-electron-beam arrangement was combined with high resolution fragment imaging detection. Provided with well directed cold electrons the fragmentation kinematics were measured down to meV collision energies where pronounced rovibrational Feshbach resonances appear in the DR cross section. For thermally excited HD+ the fragmentation angle and the kinetic energy release were studied at variable precisely controlled electron collision energies on a dense energy grid from 10 to 80 meV. The anisotropy described for the first time by Legendre polynomials higher 2nd order and the extracted rotational state contributions were found to vary on a likewise narrow energy scale as the rotationally averaged DR rate coefficient. Ro-vibrationally resolved DR experiments were performed on H2+ produced in distinct internal excitations by a novel ion source. Both the low-energy DR rate as well as the fragmentation dynamics at selected resonances were measured individually in the lowest two vibrational and first three excited rotational states. State-specific DR rates and angular dependences are reported. (orig.)

  13. Designing bistable [2]rotaxanes for molecular electronic devices.

    Dichtel, William R; Heath, James R; Stoddart, J Fraser

    2007-06-15

    The development of molecular electronic components has been accelerated by the promise of increased circuit densities and reduced power consumption. Bistable rotaxanes have been assembled into nanowire crossbar devices, where they may be switched between low- and high-conductivity states, forming the basis for a molecular memory. These memory devices have been scaled to densities of 10(11) bits cm(-2), the 2020 node for memory of the International Technology Roadmap for Semiconductors. Investigations of the kinetics and thermodynamics associated with the electromechanical switching processes of several bistable [2]rotaxane derivatives in solution, self-assembled monolayers on gold, polymer electrolyte gels and in molecular switch tunnel junction devices are consistent with a single, universal switching mechanism whose speed is dependent largely on the environment, as well as on the structure of the switching molecule. X-ray reflectometry studies of the bistable rotaxanes assembled into Langmuir monolayers also lend support to an oxidatively driven mechanical switching process. Structural information obtained from Fourier transform reflection absorption infrared spectroscopy of rotaxane monolayers taken before and after evaporation of a Ti top electrode confirmed that the functionality responsible for switching is not affected by the metal deposition process. All the considerable experimental data, taken together with detailed computational work, support the hypothesis that the tunnelling current hysteresis, which forms the basis of memory operation, is a direct result of the electromechanical switching of the bistable rotaxanes. PMID:17430812

  14. Electronic absorption spectra and geometry of organic molecules an application of molecular orbital theory

    Suzuki, Hiroshi

    1967-01-01

    Electronic Absorption Spectra and Geometry of Organic Molecules: An Application of Molecular Orbital Theory focuses on electronic absorption spectra of organic compounds and molecules. The book begins with the discussions on molecular spectra, electronic absorption spectra of organic compounds, and practical measures of absorption intensity. The text also focuses on molecular orbital theory and group theory. Molecular state functions; fundamental postulates of quantum theory; representation of symmetry groups; and symmetry operations and symmetry groups are described. The book also dis

  15. High-Conductive Organometallic Molecular Wires with Delocalized Electron Systems Strongly Coupled to Metal Electrodes

    Schwarz, Florian; Kastlunger, Georg; Lissel, Franziska; Riel, Heike; Venkatesan, Koushik; Berke, Heinz; Stadler, Robert; Lörtscher, Emanuel

    2015-01-01

    Besides active, functional molecular building blocks such as diodes or switches, passive components as, e.g., molecular wires, are required to realize molecular-scale electronics. Incorporating metal centers in the molecular backbone enables the molecular energy levels to be tuned in respect to the Fermi energy of the electrodes. Furthermore, by using more than one metal center and sp-bridging ligands, a strongly delocalized electron system is formed between these metallic "dopants", facilita...

  16. Molecular self-assembly approaches for supramolecular electronic and organic electronic devices

    Yip, Hin-Lap

    Molecular self-assembly represents an efficient bottom-up strategy to generate structurally well-defined aggregates of semiconducting pi-conjugated materials. The capability of tuning the chemical structures, intermolecular interactions and nanostructures through molecular engineering and novel materials processing renders it possible to tailor a large number of unprecedented properties such as charge transport, energy transfer and light harvesting. This approach does not only benefit traditional electronic devices based on bulk materials, but also generate a new research area so called "supramolecular electronics" in which electronic devices are built up with individual supramolecular nanostructures with size in the sub-hundred nanometers range. My work combined molecular self-assembly together with several novel materials processing techniques to control the nucleation and growth of organic semiconducting nanostructures from different type of pi-conjugated materials. By tailoring the interactions between the molecules using hydrogen bonds and pi-pi stacking, semiconducting nanoplatelets and nanowires with tunable sizes can be fabricated in solution. These supramolecular nanostructures were further patterned and aligned on solid substrates through printing and chemical templating methods. The capability to control the different hierarchies of organization on surface provides an important platform to study their structural-induced electronic properties. In addition to using molecular self-assembly to create different organic nanostructures, functional self-assembled monolayer (SAM) formed by spontaneous chemisorption on surfaces was used to tune the interfacial property in organic solar cells. Devices showed dramatically improved performance when appropriate SAMs were applied to optimize the contact property for efficiency charge collection.

  17. Rigorous theory of molecular orientational nonlinear optics

    Chong Hoon Kwak

    2015-01-01

    Full Text Available Classical statistical mechanics of the molecular optics theory proposed by Buckingham [A. D. Buckingham and J. A. Pople, Proc. Phys. Soc. A 68, 905 (1955] has been extended to describe the field induced molecular orientational polarization effects on nonlinear optics. In this paper, we present the generalized molecular orientational nonlinear optical processes (MONLO through the calculation of the classical orientational averaging using the Boltzmann type time-averaged orientational interaction energy in the randomly oriented molecular system under the influence of applied electric fields. The focal points of the calculation are (1 the derivation of rigorous tensorial components of the effective molecular hyperpolarizabilities, (2 the molecular orientational polarizations and the electronic polarizations including the well-known third-order dc polarization, dc electric field induced Kerr effect (dc Kerr effect, optical Kerr effect (OKE, dc electric field induced second harmonic generation (EFISH, degenerate four wave mixing (DFWM and third harmonic generation (THG. We also present some of the new predictive MONLO processes. For second-order MONLO, second-order optical rectification (SOR, Pockels effect and difference frequency generation (DFG are described in terms of the anisotropic coefficients of first hyperpolarizability. And, for third-order MONLO, third-order optical rectification (TOR, dc electric field induced difference frequency generation (EFIDFG and pump-probe transmission are presented.

  18. Rigorous theory of molecular orientational nonlinear optics

    Classical statistical mechanics of the molecular optics theory proposed by Buckingham [A. D. Buckingham and J. A. Pople, Proc. Phys. Soc. A 68, 905 (1955)] has been extended to describe the field induced molecular orientational polarization effects on nonlinear optics. In this paper, we present the generalized molecular orientational nonlinear optical processes (MONLO) through the calculation of the classical orientational averaging using the Boltzmann type time-averaged orientational interaction energy in the randomly oriented molecular system under the influence of applied electric fields. The focal points of the calculation are (1) the derivation of rigorous tensorial components of the effective molecular hyperpolarizabilities, (2) the molecular orientational polarizations and the electronic polarizations including the well-known third-order dc polarization, dc electric field induced Kerr effect (dc Kerr effect), optical Kerr effect (OKE), dc electric field induced second harmonic generation (EFISH), degenerate four wave mixing (DFWM) and third harmonic generation (THG). We also present some of the new predictive MONLO processes. For second-order MONLO, second-order optical rectification (SOR), Pockels effect and difference frequency generation (DFG) are described in terms of the anisotropic coefficients of first hyperpolarizability. And, for third-order MONLO, third-order optical rectification (TOR), dc electric field induced difference frequency generation (EFIDFG) and pump-probe transmission are presented

  19. ADVANCED MATERIALS Communications Molecular Rectification in Oriented Polymer Structures""

    Sentein, Carole; Fiorini, Céline; Lorin, André; Nunzi, Jean-Michel

    1997-01-01

    Polymeric semiconductor devices are receiving increasing attention in view of potential applications requiring low-cost processing over large areas.'"*] In this respect, unlike with evaporated molecules, the wet-processing capability of polymers offers total compatibility with other complemen-tary technologies. The concepts from which organic-semi-conductor devices are designed are mostly derived from in-organic-semiconductor physics and technology.''] In order to build efficient organic-semi...

  20. Machine learning of molecular electronic properties in chemical compound space

    The combination of modern scientific computing with electronic structure theory can lead to an unprecedented amount of data amenable to intelligent data analysis for the identification of meaningful, novel and predictive structure–property relationships. Such relationships enable high-throughput screening for relevant properties in an exponentially growing pool of virtual compounds that are synthetically accessible. Here, we present a machine learning model, trained on a database of ab initio calculation results for thousands of organic molecules, that simultaneously predicts multiple electronic ground- and excited-state properties. The properties include atomization energy, polarizability, frontier orbital eigenvalues, ionization potential, electron affinity and excitation energies. The machine learning model is based on a deep multi-task artificial neural network, exploiting the underlying correlations between various molecular properties. The input is identical to ab initio methods, i.e. nuclear charges and Cartesian coordinates of all atoms. For small organic molecules, the accuracy of such a ‘quantum machine’ is similar, and sometimes superior, to modern quantum-chemical methods—at negligible computational cost. (paper)

  1. Implementing and Improving Automated Electronic Tumor Molecular Profiling.

    Rioth, Matthew J; Staggs, David B; Hackett, Lauren; Haberman, Erich; Tod, Mike; Levy, Mia; Warner, Jeremy

    2016-03-01

    Oncology practice increasingly requires the use of molecular profiling of tumors to inform the use of targeted therapeutics. However, many oncologists use third-party laboratories to perform tumor genomic testing, and these laboratories may not have electronic interfaces with the provider's electronic medical record (EMR) system. The resultant reporting mechanisms, such as plain-paper faxing, can reduce report fidelity, slow down reporting procedures for a physician's practice, and make reports less accessible. Vanderbilt University Medical Center and its genomic laboratory testing partner have collaborated to create an automated electronic reporting system that incorporates genetic testing results directly into the clinical EMR. This system was iteratively tested, and causes of failure were discovered and addressed. Most errors were attributable to data entry or typographical errors that made reports unable to be linked to the correct patient in the EMR. By providing direct feedback to providers, we were able to significantly decrease the rate of transmission errors (from 6.29% to 3.84%; P < .001). The results and lessons of 1 year of using the system and transmitting 832 tumor genomic testing reports are reported. PMID:26813927

  2. Ion Current Rectification Behavior at Novel Borosilicate Glass Capillaries

    Silver, Barry Richard; Holub, Karel; Mareček, Vladimír

    Ústí nad Labem: BEST servis, 2012 - (Navrátil, T.; Fojta, M.), s. 120-124 ISBN 978-80-905221-0-7. [Moderní elektrochemické metody /32./. Jetřichovice (CZ), 21.05.2012-25.05.2012] Institutional support: RVO:61388955 Keywords : ion * rectification * impedance Subject RIV: CG - Electrochemistry

  3. Rectification And Revival Of Muslim World

    M azram

    2012-01-01

    Full Text Available The present doldrums position and state of decadence, internal differences, external aggression (geographical and ideological, lack of self-confidence and dependence, illiteracy, political instability, economic disaster, lack of knowledge and wisdom, back benchers in science and technology, education, medicine, trade and business, banking system and defensive incapability of Muslim Ummah prompted me to write this article.  Although most of the Muslim nations got their independence because of their dedicated struggle and historic events and incidents but the old masters remained active for a remote control over the Muslim Ummah.  Their intellectuals and scholars, individually as well as collectively, have propagated and advised their leadership, the tactics and approaches by which Muslim Ummah can again be enslaved.  Writings of S.P. Huntington and F. Fukuyama are clear examples.  They are actively gearing the international institutions so cleverly that Muslim Ummah does not even realize their ill motives and objectives.  They brought their leadership in a confronting position with Muslim Ummah and hence threatening the world peace.  This situation prompted us to look at our principal sources of inspiration, which are, the Qur’an, Sunnah of the Prophet (SAW, and examples of the “enlightened Caliphs” and see if we could work out a seminal guidelines for our rectification  and revival.  We have gathered together some of these impressions; these are all tentative, nothing final about them, but these are here nonetheless. ABSTRAK: Kehadiran situasi kebelungguan dan  keruntuhan, perbezaan dalaman, pencerobohan luar (geografi dan ideologi, kurang keyakinan diri dan pergantungan, buta huruf, ketidakstabilan politik, bencana ekonomi, kekurangan ilmu dan hikmah, ketinggalan dalam sains dan teknologi, pendidikan, perubatan, perdagangan dan perniagaan, sistem perbankan dan ketidakupayaan pertahanan umat Islam mendorong saya untuk menulis

  4. Electronic transport of molecular nanowires by considering of electron hopping energy between the second neighbors

    H Rabani

    2015-07-01

    Full Text Available In this paper, we study the electronic conductance of molecular nanowires by considering the electron hopping between the first and second neighbors with the help Green’s function method at the tight-binding approach. We investigate three types of structures including linear uniform and periodic chains as well as poly(p-phenylene molecule which are embedded between two semi-infinite metallic leads. The results show that in the second neighbor approximation, the resonance, anti-resonance and Fano phenomena occur in the conductance spectra of these structures. Moreover, a new gap is observed at edge of the lead energy band wich its width depends on the value of the electron hopping energy between the second neighbors. In the systems including intrinsic gap, this hopping energy shifts the gap in the energy spectra.

  5. Mapping molecular motions leading to charge delocalization with ultrabright electrons

    Sciaini, German

    2014-05-01

    Ultrafast diffraction has broken the barrier to atomic exploration by combining the atomic spatial resolution of diffraction techniques with the temporal resolution of ultrafast spectroscopy. X-ray free electron lasers, slicing techniques and femtosecond laser-driven X-ray and electron sources have been successfully applied for the study of ultrafast structural dynamics in a variety of samples. Yet, the application of fs-diffraction to the study of rather sensitive organic molecular crystals remains unexplored. Organic crystals are composed by weak scattering centres, often present low melting points, poor heat conductivity and are, typically, radiation sensitive. Low repetition rates (about tens of Hertz) are therefore required to overcome accumulative heating effects from the laser excitation that can degrade the sample and mask the structural dynamics. This imparts tremendous constraints on source brightness to acquire enough diffraction data before adverse photo-degradation effects have played a non-negligible role in the crystalline structure. We implemented ultra-bright femtosecond electron diffraction to obtain a movie of the relevant molecular motions driving the photo-induced insulator-to-metal phase transition in the organic charge-transfer salt (EDO-TTF)2PF6. On the first few picoseconds (0 - 10 ps) the structural evolution, well-described by three main reaction coordinates, reaches a transient intermediate state (TIS). Model structural refinement calculations indicate that fast sliding of flat EDO-TTF molecules with consecutive motion of PF6 counter-ions drive the formation of TS instead of the expected flattening of initially bent EDO-TTF moieties which seems to evolve through a slower thermal pathway that brings the system into a final high temperature-type state. These findings establish the potential of ultrabright femtosecond electron sources for probing the primary processes governing structural dynamics with atomic resolution in labile systems

  6. Electronic damping of molecular motion at metal surfaces

    Trail, J R; Bird, D M

    2009-01-01

    A method for the calculation of the damping rate due to electron-hole pair excitation for atomic and molecular motion at metal surfaces is presented. The theoretical basis is provided by Time Dependent Density Functional Theory (TDDFT) in the quasi-static limit and calculations are performed within a standard plane-wave, pseudopotential framework. The artificial periodicity introduced by using a super-cell geometry is removed to derive results for the motion of an isolated atom or molecule, rather than for the coherent motion of an ordered over-layer. The algorithm is implemented in parallel, distributed across both ${\\bf k}$ and ${\\bf g}$ space, and in a form compatible with the CASTEP code. Test results for the damping of the motion of hydrogen atoms above the Cu(111) surface are presented.

  7. Millisecond Coherence Time in a Tunable Molecular Electronic Spin Qubit.

    Zadrozny, Joseph M; Niklas, Jens; Poluektov, Oleg G; Freedman, Danna E

    2015-12-23

    Quantum information processing (QIP) could revolutionize areas ranging from chemical modeling to cryptography. One key figure of merit for the smallest unit for QIP, the qubit, is the coherence time (T 2), which establishes the lifetime for the qubit. Transition metal complexes offer tremendous potential as tunable qubits, yet their development is hampered by the absence of synthetic design principles to achieve a long T 2. We harnessed molecular design to create a series of qubits, (Ph4P)2[V(C8S8)3] (1), (Ph4P)2[V(β-C3S5)3] (2), (Ph4P)2[V(α-C3S5)3] (3), and (Ph4P)2[V(C3S4O)3] (4), with T 2s of 1-4 μs at 80 K in protiated and deuterated environments. Crucially, through chemical tuning of nuclear spin content in the vanadium(IV) environment we realized a T 2 of ∼1 ms for the species (d 20-Ph4P)2[V(C8S8)3] (1') in CS2, a value that surpasses the coordination complex record by an order of magnitude. This value even eclipses some prominent solid-state qubits. Electrochemical and continuous wave electron paramagnetic resonance (EPR) data reveal variation in the electronic influence of the ligands on the metal ion across 1-4. However, pulsed measurements indicate that the most important influence on decoherence is nuclear spins in the protiated and deuterated solvents utilized herein. Our results illuminate a path forward in synthetic design principles, which should unite CS2 solubility with nuclear spin free ligand fields to develop a new generation of molecular qubits. PMID:27163013

  8. Synthesis of one-dimensional metal-containing insulated molecular wire with versatile properties directed toward molecular electronics materials.

    Masai, Hiroshi; Terao, Jun; Seki, Shu; Nakashima, Shigeto; Kiguchi, Manabu; Okoshi, Kento; Fujihara, Tetsuaki; Tsuji, Yasushi

    2014-02-01

    We report, herein, the design, synthesis, and properties of new materials directed toward molecular electronics. A transition metal-containing insulated molecular wire was synthesized through the coordination polymerization of a Ru(II) porphyrin with an insulated bridging ligand of well-defined structure. The wire displayed not only high linearity and rigidity, but also high intramolecular charge mobility. Owing to the unique properties of the coordination bond, the interconversion between the monomer and polymer states was realized under a carbon monoxide atmosphere or UV irradiation. The results demonstrated a high potential of the metal-containing insulated molecular wire for applications in molecular electronics. PMID:24428791

  9. Influence of electroosmotic flow on the ionic current rectification in a pH-regulated, conical nanopore

    Lin, Dong-Huei; Lin, Chih-Yuan; Tseng, Shiojenn; Hsu, Jyh-Ping

    2015-08-01

    The ionic current rectification (ICR) is studied theoretically by considering a pH-regulated, conical nanopore. In particular, the effect of electroosmotic flow (EOF), which was often neglected in previous studies, is investigated by solving a set of coupled Poisson, Nernst-Planck, and Navier-Stokes equations. The behaviors of ICR under various conditions are examined by varying solution pH, bulk ionic concentration, and applied electric potential bias. We show that the EOF effect is significant when the bulk ionic concentration is medium high, the pH is far away from the iso-electric point, and the electric potential bias is high. The percentage deviation in the current rectification ratio arising from neglecting the EOF effect can be on the order of 100%. In addition, the behavior of the current rectification ratio at a high pH taking account of EOF is different both qualitatively and quantitatively from that without taking account of EOF.The ionic current rectification (ICR) is studied theoretically by considering a pH-regulated, conical nanopore. In particular, the effect of electroosmotic flow (EOF), which was often neglected in previous studies, is investigated by solving a set of coupled Poisson, Nernst-Planck, and Navier-Stokes equations. The behaviors of ICR under various conditions are examined by varying solution pH, bulk ionic concentration, and applied electric potential bias. We show that the EOF effect is significant when the bulk ionic concentration is medium high, the pH is far away from the iso-electric point, and the electric potential bias is high. The percentage deviation in the current rectification ratio arising from neglecting the EOF effect can be on the order of 100%. In addition, the behavior of the current rectification ratio at a high pH taking account of EOF is different both qualitatively and quantitatively from that without taking account of EOF. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03433g

  10. Ionic fragmentation channels in electron collisions of small molecular ions

    Dissociative Recombination (DR) is one of the most important loss processes of molecular ions in the interstellar medium (IM). Ion storage rings allow to investigate these processes under realistic conditions. At the Heidelberg test storage ring TSR a new detector system was installed within the present work in order to study the DR sub-process of ion pair formation (IPF). The new detector expands the existing electron target setup by the possibility to measure strongly deflected negative ionic fragments. At the TSR such measurements can be performed with a uniquely high energy resolution by independently merging two electron beams with the ion beam. In this work IPF of HD+, H3+ and HF+ has been studied. In the case of HD+ the result of the high resolution experiment shows quantum interferences. Analysis of the quantum oscillations leads to a new understanding of the reaction dynamics. For H3+ it was for the first time possible to distinguish different IPF channels and to detect quantum interferences in the data. Finally the IPF of HF+ was investigated in an energy range, where in previous experiments no conclusive results could be obtained. (orig.)

  11. Structural and electronic properties of Diisopropylammonium bromide molecular ferroelectric crystal

    Alsaad, A.; Qattan, I. A.; Ahmad, A. A.; Al-Aqtash, N.; Sabirianov, R. F.

    2015-10-01

    We report the results of ab-initio calculations based on Generalized Gradient Approximation (GGA) and hybrid functional (HSE06) of electronic band structure, density of states and partial density of states to get a deep insight into structural and electronic properties of P21 ferroelectric phase of Diisopropylammonium Bromide molecular crystal (DIPAB). We found that the optical band gap of the polar phase of DIPAB is ∼ 5 eV confirming it as a good dielectric. Examination of the density of states and partial density of states reveal that the valence band maximum is mainly composed of bromine 4p orbitals and the conduction band minimum is dominated by carbon 2p, carbon 2s, and nitrogen 2s orbitals. A unique aspect of P21 ferroelectric phase is the permanent dipole within the material. We found that P21 DIPAB has a spontaneous polarization of 22.64 consistent with recent findings which make it good candidate for the creation of ferroelectric tunneling junctions (FTJs) which have the potential to be used as memory devices.

  12. Determination of molecular parameters by electron collisions and laser techniques

    In this work a general procedure to study diatomic molecules in intermediate coupling scheme has been developed. This study allows to obtain expressions to calculate molecular line strengths and rotational transition intensities. These results are used in a numerical program to synthetize vibrational and rotational band spectra of any diatomic molecule. With this technique the experimental spectra of the first negative system of N2+ and the fist positive system of N2 are reproduced theoretically and it is possible to deduce its electronic transition moments values by comparison. Also the method has been applied to compare the synthetized bands with the experimental spectra of the B Ou+-- x1Σg+ system of Au2 and the A2Σ--- x 2π system of OH. From these comparison band intensities and electronic moments can be deduced. The branching ratio method to measure the relative spectral response in the 1100-1560 Ao=wavelength range of a vacuum uv monochromator has been used. Relative intensity of rotational lines with origine in a common upper vibrational-rotational level of Warner and Lyman systems of H2, have been measured. Also in this work, the deexcitation of the B3π+(0+u), v'=14 level of I2 after pulsed laser excitation has been studied. The quenching cross sections by collisions with I2, H2, CO2 and CH4 have been determin-ed. (Author)

  13. First principles modelling of contact resistance in molecular electronic devices.

    Stokbro, Kurt; Taylor, Jeremy; Brandbyge, Mads

    2002-03-01

    We have used the TranSIESTA package[1,2] to investigate the contact resistance of gold-thiol bonds. The TranSIESTA package is a new density functional code employing local basis sets[3], combined with a non-equilibrium Greens function transport scheme. With this package we can calculate the selfconsistent electronic structure of a nanostructure coupled to 3-dimensional electrodes with different electrochemical potentials, using the same level of model chemistry for the electrodes as for the nanostructure. We have used the method to calculate the electron transport through DiThiol-Benzene (DTB) connected to gold electrodes. The transport properties have been calculated for a range of different molecule-electrode couplings, and I will discuss the influence of the coupling on the molecular conductance, and compare with experimental data. [1] M. Brandbyge, K. Stokbro, J. Taylor, J. L. Mozos, P. Ordejon, Material Research Society symposium proceedings volume 636, D9.25 (2000). [2] M. Brandbyge, K. Stokbro, J. Taylor, J. L. Mozos, P. Ordejon, Condmat 0110650 [3] SIESTA: D. Sanchez-Portal, P. Ordejon, E. Artacho and J. Soler, Int. J. Quantum Chem. 65, 453 (1997).

  14. Elastic electron scattering cross sections for molecular hydrogen

    Khakoo, M. A.; Trajmar, S.

    1986-01-01

    Using an electron-beam - molecular-beam apparatus and employing the relative flow technique, ratios of the differential elastic scattering cross sections (DCSs of H2 to He were measured at incident electron energies of 15-100 eV and over the angular range of 10-125 degrees. From these ratios, the absolute elastic DCSs for H2 were determined by normalization to accurate, available elastic DCSs of He. Since pure rotational structure was not resolved in this work, the DCSs reported are the sum of elastic and rotational excitations of H2 at room temperature. The reliability of the relative flow normalization to He was checked at each energy and angle by performing similar elastic DCS measurements on Ne (for which the cross sections are known). The resulting absolute Ne DCSs were found to be in good agreement (within 10 percent with the Ne elastic DCSs measured previously (Register and Trajmar, 1984). From the DCSs, integral and momentumtransfer cross sections were calculated. The present results are compared with other recent measurements.

  15. Electronic Structure and Molecular Dynamics Calculations for KBH4

    Papaconstantopoulos, Dimitrios; Shabaev, Andrew; Hoang, Khang; Mehl, Michael; Kioussis, Nicholas

    2012-02-01

    In the search for hydrogen storage materials, alkali borohydrides MBH4 (M=Li, Na, K) are especially interesting because of their light weight and the high number of hydrogen atoms per metal atom. Electronic structure calculations can give insights into the properties of these complex hydrides and provide understanding of the structural properties and of the bonding of hydrogen. We have performed first-principles density-functional theory (DFT) and tight-binding (TB) calculations for KBH4 in both the high temperature (HT) and low temperature (LT) phases to understand its electronic and structural properties. Our DFT calculations were carried out using the VASP code. The results were then used as a database to develop a tight-binding Hamiltonian using the NRL-TB method. This approach allowed for computationally efficient calculations of phonon frequencies and elastic constants using the static module of the NRL-TB, and also using the molecular dynamics module to calculate mean-square displacements and formation energies of hydrogen vacancies.

  16. Ionic fragmentation channels in electron collisions of small molecular ions

    Hoffmann, Jens

    2009-01-28

    Dissociative Recombination (DR) is one of the most important loss processes of molecular ions in the interstellar medium (IM). Ion storage rings allow to investigate these processes under realistic conditions. At the Heidelberg test storage ring TSR a new detector system was installed within the present work in order to study the DR sub-process of ion pair formation (IPF). The new detector expands the existing electron target setup by the possibility to measure strongly deflected negative ionic fragments. At the TSR such measurements can be performed with a uniquely high energy resolution by independently merging two electron beams with the ion beam. In this work IPF of HD{sup +}, H{sub 3}{sup +} and HF{sup +} has been studied. In the case of HD{sup +} the result of the high resolution experiment shows quantum interferences. Analysis of the quantum oscillations leads to a new understanding of the reaction dynamics. For H{sub 3}{sup +} it was for the first time possible to distinguish different IPF channels and to detect quantum interferences in the data. Finally the IPF of HF{sup +} was investigated in an energy range, where in previous experiments no conclusive results could be obtained. (orig.)

  17. Poly(3-hexylthiophene)/multiwalled carbon hybrid coaxial nanotubes: nanoscale rectification and photovoltaic characteristics.

    Kim, Kihyun; Shin, Ji Won; Lee, Yong Baek; Cho, Mi Yeon; Lee, Suk Ho; Park, Dong Hyuk; Jang, Dong Kyu; Lee, Cheol Jin; Joo, Jinsoo

    2010-07-27

    We fabricate hybrid coaxial nanotubes (NTs) of multiwalled carbon nanotubes (MWCNTs) coated with light-emitting poly(3-hexylthiophene) (P3HT). The p-type P3HT material with a thickness of approximately 20 nm is electrochemically deposited onto the surface of the MWCNT. The formation of hybrid coaxial NTs of the P3HT/MWCNT is confirmed by a transmission electron microscope, FT-IR, and Raman spectra. The optical and structural properties of the hybrid NTs are characterized using ultraviolet and visible absorption, Raman, and photoluminescence (PL) spectra where, it is shown that the PL intensity of the P3HT materials decreases after the hybridization with the MWCNTs. The current-voltage (I-V) characteristics of the outer P3HT single NT show the semiconducting behavior, while ohmic behavior is observed for the inner single MWCNT. The I-V characteristics of the hybrid junction between the outer P3HT NT and the inner MWCNT, for the hybrid single NT, exhibit the characteristics of a diode (i.e., rectification), whose efficiency is clearly enhanced with light irradiation. The rectification effect of the hybrid single NT has been analyzed in terms of charge tunneling models. The quasi-photovoltaic effect is also observed at low bias for the P3HT/MWCNT hybrid single NT. PMID:20533839

  18. In Vivo Demonstration of Addressable Microstimulators Powered by Rectification of Epidermically Applied Currents for Miniaturized Neuroprostheses.

    Becerra-Fajardo, Laura; Ivorra, Antoni

    2015-01-01

    Electrical stimulation is used in order to restore nerve mediated functions in patients with neurological disorders, but its applicability is constrained by the invasiveness of the systems required to perform it. As an alternative to implantable systems consisting of central stimulation units wired to the stimulation electrodes, networks of wireless microstimulators have been devised for fine movement restoration. Miniaturization of these microstimulators is currently hampered by the available methods for powering them. Previously, we have proposed and demonstrated a heterodox electrical stimulation method based on electronic rectification of high frequency current bursts. These bursts can be delivered through textile electrodes on the skin. This approach has the potential to result in an unprecedented level of miniaturization as no bulky parts such as coils or batteries are included in the implant. We envision microstimulators designs based on application-specific integrated circuits (ASICs) that will be flexible, thread-like (diameters electro-stimulation. We demonstrate that addressable microstimulators powered by rectification of epidermically applied currents are feasible. PMID:26147771

  19. In Vivo Demonstration of Addressable Microstimulators Powered by Rectification of Epidermically Applied Currents for Miniaturized Neuroprostheses

    2015-01-01

    Electrical stimulation is used in order to restore nerve mediated functions in patients with neurological disorders, but its applicability is constrained by the invasiveness of the systems required to perform it. As an alternative to implantable systems consisting of central stimulation units wired to the stimulation electrodes, networks of wireless microstimulators have been devised for fine movement restoration. Miniaturization of these microstimulators is currently hampered by the available methods for powering them. Previously, we have proposed and demonstrated a heterodox electrical stimulation method based on electronic rectification of high frequency current bursts. These bursts can be delivered through textile electrodes on the skin. This approach has the potential to result in an unprecedented level of miniaturization as no bulky parts such as coils or batteries are included in the implant. We envision microstimulators designs based on application-specific integrated circuits (ASICs) that will be flexible, thread-like (diameters electro-stimulation. We demonstrate that addressable microstimulators powered by rectification of epidermically applied currents are feasible. PMID:26147771

  20. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    Mingsen Deng

    2015-01-01

    Full Text Available The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS. Based on a model molecule of Bis-(4-mercaptophenyl-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices.

  1. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS). Based on a model molecule of Bis-(4-mercaptophenyl)-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices

  2. Surface electron density models for accurate ab initio molecular dynamics with electronic friction

    Novko, D.; Blanco-Rey, M.; Alducin, M.; Juaristi, J. I.

    2016-06-01

    Ab initio molecular dynamics with electronic friction (AIMDEF) is a valuable methodology to study the interaction of atomic particles with metal surfaces. This method, in which the effect of low-energy electron-hole (e-h) pair excitations is treated within the local density friction approximation (LDFA) [Juaristi et al., Phys. Rev. Lett. 100, 116102 (2008), 10.1103/PhysRevLett.100.116102], can provide an accurate description of both e-h pair and phonon excitations. In practice, its applicability becomes a complicated task in those situations of substantial surface atoms displacements because the LDFA requires the knowledge at each integration step of the bare surface electron density. In this work, we propose three different methods of calculating on-the-fly the electron density of the distorted surface and we discuss their suitability under typical surface distortions. The investigated methods are used in AIMDEF simulations for three illustrative adsorption cases, namely, dissociated H2 on Pd(100), N on Ag(111), and N2 on Fe(110). Our AIMDEF calculations performed with the three approaches highlight the importance of going beyond the frozen surface density to accurately describe the energy released into e-h pair excitations in case of large surface atom displacements.

  3. On-chip molecular electronic plasmon sources based on self-assembled monolayer tunnel junctions

    Du, Wei; Wang, Tao; Chu, Hong-Son; Wu, Lin; Liu, Rongrong; Sun, Song; Phua, Wee Kee; Wang, Lejia; Tomczak, Nikodem; Nijhuis, Christian A.

    2016-04-01

    Molecular electronic control over plasmons offers a promising route for on-chip integrated molecular plasmonic devices for information processing and computing. To move beyond the currently available technologies and to miniaturize plasmonic devices, molecular electronic plasmon sources are required. Here, we report on-chip molecular electronic plasmon sources consisting of tunnel junctions based on self-assembled monolayers sandwiched between two metallic electrodes that excite localized plasmons, and surface plasmon polaritons, with tunnelling electrons. The plasmons originate from single, diffraction-limited spots within the junctions, follow power-law distributed photon statistics, and have well-defined polarization orientations. The structure of the self-assembled monolayer and the applied bias influence the observed polarization. We also show molecular electronic control of the plasmon intensity by changing the chemical structure of the molecules and by bias-selective excitation of plasmons using molecular diodes.

  4. Micro- and Nanostructured Materials for Active Devices and Molecular Electronics

    Martin, Peter M.; Graff, Gordon L.; Gross, Mark E.; Burrows, Paul E.; Bennett, Wendy D.; Mast, Eric S.; Hall, Michael G.; Bonham, Charles C.; Zumhoff, Mac R.; Williford, Rick E.

    2003-10-01

    Traditional single layer barrier coatings are not adequate in preventing degradation of the performance of organic molecular electronic and other active devices. Most advanced devices used in display technology now consist of micro and nanostructured small molecule, polymer and inorganic coatings with thin high reactive group 1A metals. This includes organic electronics such as organic light emitting devices (OLED). The lifetimes of these devices rapidly degrades when they are exposed to atmospheric oxygen and water vapor. Thin film photovoltaics and batteries are also susceptible to degradation by moisture and oxygen. Using in-line coating techniques we apply a composite nanostructured inorganic/polymer thin film barrier that restricts moisture and oxygen permeation to undetectable levels using conventional permeation test equipment. We describe permeation mechanisms for this encapsulation coating and flat panel display and other device applications. Permeation through the multilayer barrier coating is defect and pore limited and can be described by Knudsen diffusion involving a long and tortuous path. Device lifetime is also enhanced by the long lag times required to reach the steady state flux regime. Permeation rates in the range of 10-6 cc,g/m2/d have been achieved and OLED device lifetimes. The structure is robust, yet flexible. The resulting device performance and lifetimes will also be described. The barrier film can be capped with a thin film of transparent conductive oxide yielding an engineered nanostructured device for next generation, rugged, lightweight or flexible displays. This enables, for the first time, thin film encapsulation of emissive organic displays.

  5. Rectification of energy transport in nonlinear metamaterials via ratchets

    The presence of discrete breathers (DBs) has already been described in nonlinear photonic materials, such as ferroelectrics and metamaterials (MMs) by the Klein–Gordon (K–G) approach. Rectification of energy transport in MMs in the presence of an appropriate external field is studied via symmetry breaking leading to directed energy transport or ratchet behaviour. Based on the earlier development of the K–G equation in a MM system with a split-ring resonator for antenna applications, a theoretical model for current density is worked out by symmetry analysis and its violation to characterize the ratchet effect. The time-averaged current shows interesting results against phase shift in the ac driver. These data are further related to various parameters, such as coupling and damping in the system. For MMs, this opens a new application for rectification using ratchets. (paper)

  6. Probing flexibility in porphyrin-based molecular wires using double electron electron resonance.

    Lovett, Janet E; Hoffmann, Markus; Cnossen, Arjen; Shutter, Alexander T J; Hogben, Hannah J; Warren, John E; Pascu, Sofia I; Kay, Christopher W M; Timmel, Christiane R; Anderson, Harry L

    2009-09-30

    A series of butadiyne-linked zinc porphyrin oligomers, with one, two, three, and four porphyrin units and lengths of up to 75 A, have been spin-labeled at both ends with stable nitroxide TEMPO radicals. The pulsed EPR technique of double electron electron resonance (DEER) was used to probe the distribution of intramolecular end-to-end distances, under a range of conditions. DEER measurements were carried out at 50 K in two types of dilute solution glasses: deutero-toluene (with 10% deutero-pyridine) and deutero-o-terphenyl (with 5% 4-benzyl pyridine). The complexes of the porphyrin oligomers with monodentate ligands (pyridine or 4-benzyl pyridine) principally adopt linear conformations. Nonlinear conformations are less populated in the lower glass-transition temperature solvent. When the oligomers bind star-shaped multidentate ligands, they are forced to bend into nonlinear geometries, and the experimental end-to-end distances for these complexes match those from molecular mechanics calculations. Our results show that porphyrin-based molecular wires are shape-persistent, and yet that their shapes can deformed by binding to multivalent ligands. Self-assembled ladder-shaped 2:2 complexes were also investigated to illustrate the scope of DEER measurements for providing structural information on synthetic noncovalent nanostructures. PMID:19736940

  7. Studies of Ionic Current Rectification Using Polyethyleneimines Coated Glass Nanopipettes

    Liu, Shujuan; Dong, Yitong; Zhao, Wenbo; Xie, Xiang; Ji, Tianrong; Yin, Xiaohong; Liu, Yun; Liang, Zhongwei; Momotenko, Dmitry; Liang, Dehai; Girault, Hubert H.; Shao, Yuanhua

    2012-01-01

    The modification of glass nanopipettes with polyethyleneimines (PEIs) has been successfully achieved by a relatively simple method, and the smallest tip opening is around 3 nm. Thus, in a much wider range of glass pipettes with radii from several nanometers to a few micrometers, the ion current rectification (ICR) phenomenon has been observed. The influences of different KCl concentrations, pH values, and tip radii on the ICR are investigated in detail. The sizes of PEIs have been determined ...

  8. Magnetic and electronic properties of porphyrin-based molecular nanowires

    Jia-Jia Zheng

    2016-01-01

    Full Text Available Using spin-polarized density functional theory calculations, we performed theoretical investigations on the electronic and magnetic properties of transition metal embedded porphyrin-based nanowires (TM-PNWs, TM = Cr, Mn, Co, Ni, Cu, and Zn. Our results indicate that Ni-PNW and Zn-PNW are nonmagnetic while the rest species are magnetic, and the magnetic moments in TM-PNWs and their corresponding isolated monomer structures are found to be the same. In addition, the spin coupling in the magnetic nanowires can be ignored leading to their degenerate AFM and FM states. These results can be ascribed to the weak intermetallic interactions because of the relatively large distances between neighbor TM atoms. Among all TM-PNW structures considered here, only Mn-PNW shows a half-metallic property while the others are predicted to be semiconducting. The present work paves a new way of obtaining ferromagnetic porphyrin-based nanowires with TM atoms distributed separately and orderly, which are expected to be good candidates for catalysts, energy storage and molecular spintronics.

  9. Electron transport in molecular junctions with graphene as protecting layer

    We present ab initio transport calculations for molecular junctions that include graphene as a protecting layer between a single molecule and gold electrodes. This vertical setup has recently gained significant interest in experiment for the design of particularly stable and reproducible devices. We observe that the signals from the molecule in the electronic transmission are overlayed by the signatures of the graphene sheet, thus raising the need for a reinterpretation of the transmission. On the other hand, we see that our results are stable with respect to various defects in the graphene. For weakly physiosorbed molecules, no signs of interaction with the graphene are evident, so the transport properties are determined by offresonant tunnelling between the gold leads across an extended structure that includes the molecule itself and the additional graphene layer. Compared with pure gold electrodes, calculated conductances are about one order of magnitude lower due to the increased tunnelling distance. Relative differences upon changing the end group and the length of the molecule on the other hand, are similar

  10. Electron transport in molecular junctions with graphene as protecting layer

    Hüser, Falco; Solomon, Gemma C.

    2015-12-01

    We present ab initio transport calculations for molecular junctions that include graphene as a protecting layer between a single molecule and gold electrodes. This vertical setup has recently gained significant interest in experiment for the design of particularly stable and reproducible devices. We observe that the signals from the molecule in the electronic transmission are overlayed by the signatures of the graphene sheet, thus raising the need for a reinterpretation of the transmission. On the other hand, we see that our results are stable with respect to various defects in the graphene. For weakly physiosorbed molecules, no signs of interaction with the graphene are evident, so the transport properties are determined by offresonant tunnelling between the gold leads across an extended structure that includes the molecule itself and the additional graphene layer. Compared with pure gold electrodes, calculated conductances are about one order of magnitude lower due to the increased tunnelling distance. Relative differences upon changing the end group and the length of the molecule on the other hand, are similar.

  11. Electron transport in molecular junctions with graphene as protecting layer

    Hüser, Falco; Solomon, Gemma C., E-mail: gsolomon@nano.ku.dk [Nano-Science Center and Department of Chemistry, University of Copenhagen, 2100 København Ø (Denmark)

    2015-12-07

    We present ab initio transport calculations for molecular junctions that include graphene as a protecting layer between a single molecule and gold electrodes. This vertical setup has recently gained significant interest in experiment for the design of particularly stable and reproducible devices. We observe that the signals from the molecule in the electronic transmission are overlayed by the signatures of the graphene sheet, thus raising the need for a reinterpretation of the transmission. On the other hand, we see that our results are stable with respect to various defects in the graphene. For weakly physiosorbed molecules, no signs of interaction with the graphene are evident, so the transport properties are determined by offresonant tunnelling between the gold leads across an extended structure that includes the molecule itself and the additional graphene layer. Compared with pure gold electrodes, calculated conductances are about one order of magnitude lower due to the increased tunnelling distance. Relative differences upon changing the end group and the length of the molecule on the other hand, are similar.

  12. Magnetic and electronic properties of porphyrin-based molecular nanowires

    Using spin-polarized density functional theory calculations, we performed theoretical investigations on the electronic and magnetic properties of transition metal embedded porphyrin-based nanowires (TM-PNWs, TM = Cr, Mn, Co, Ni, Cu, and Zn). Our results indicate that Ni-PNW and Zn-PNW are nonmagnetic while the rest species are magnetic, and the magnetic moments in TM-PNWs and their corresponding isolated monomer structures are found to be the same. In addition, the spin coupling in the magnetic nanowires can be ignored leading to their degenerate AFM and FM states. These results can be ascribed to the weak intermetallic interactions because of the relatively large distances between neighbor TM atoms. Among all TM-PNW structures considered here, only Mn-PNW shows a half-metallic property while the others are predicted to be semiconducting. The present work paves a new way of obtaining ferromagnetic porphyrin-based nanowires with TM atoms distributed separately and orderly, which are expected to be good candidates for catalysts, energy storage and molecular spintronics

  13. Magnetic and electronic properties of porphyrin-based molecular nanowires

    Zheng, Jia-Jia; Li, Qiao-Zhi; Dang, Jing-Shuang; Zhao, Xiang, E-mail: xzhao@mail.xjtu.edu.cn [Institute for Chemical Physics & Department of Chemistry, MOE Key Laboratory for Non-equilibrium Condensed Matter and Quantum Engineering, School of Science, Xi’an Jiaotong University, Xi’an 710049 (China); Wang, Wei-Wei [Research Center for Computational Science, Institute for Molecular Science, Okazaki, Aichi 444-8585 (Japan)

    2016-01-15

    Using spin-polarized density functional theory calculations, we performed theoretical investigations on the electronic and magnetic properties of transition metal embedded porphyrin-based nanowires (TM-PNWs, TM = Cr, Mn, Co, Ni, Cu, and Zn). Our results indicate that Ni-PNW and Zn-PNW are nonmagnetic while the rest species are magnetic, and the magnetic moments in TM-PNWs and their corresponding isolated monomer structures are found to be the same. In addition, the spin coupling in the magnetic nanowires can be ignored leading to their degenerate AFM and FM states. These results can be ascribed to the weak intermetallic interactions because of the relatively large distances between neighbor TM atoms. Among all TM-PNW structures considered here, only Mn-PNW shows a half-metallic property while the others are predicted to be semiconducting. The present work paves a new way of obtaining ferromagnetic porphyrin-based nanowires with TM atoms distributed separately and orderly, which are expected to be good candidates for catalysts, energy storage and molecular spintronics.

  14. Calibration and rectification research for fish-eye lens application

    Feng, Weijia; Zhang, Baofeng; Cao, Zuoliang; Zong, Xiaoning; Röning, Juha

    2011-01-01

    The purpose of this paper aims to promote the application of fish-eye lens. Accurate parameters calibration and effective distortion rectification of an imaging device is of utmost importance in machine vision. Fish-eye lens produces a hemispherical field of view of an environment, which appears definite significant since its advantage of panoramic sight with a single compact visual scene. But fish-eye lens image has an unavoidable inherent severe distortion. The precise optical center is the precondition for other parameters calibration and distortion correction. Therefore, three different optical center calibration methods have been researched for diverse applications. Support Vector Machine (SVM) and Spherical Equidistance Projection Algorithm (SEPA) are integrated to replace traditional rectification methods. SVM is a machine learning method based on the theory of statistics, which have good capabilities of imitating, regression and classification. In this research, SVM provides a mapping table between the fish-eye image and the standard image for human eyes. Two novel training models have been designed. SEPA has been applied to promote the rectification effect of the edge of fish-eye lens image. The validity and effectiveness of our achievements are demonstrated by processing the real images.

  15. Unified framework for automatic image stitching and rectification

    An, Jaehyun; Kim, Beom Su; Koo, Hyung Il; Cho, Nam Ik

    2015-05-01

    Conventional image stitching methods were developed under the assumption or condition that (1) the optical center of a camera is fixed (fixed-optical-center case) or (2) the camera captures a plane target (plane-target case). Hence, users should know or test which condition is more appropriate for the given set of images and then select a right algorithm or try multiple stitching algorithms. We propose a unified framework for the image stitching and rectification problem, which can handle both cases in the same framework. To be precise, we model each camera pose with six parameters (three for the rotation and three for the translation) and develop a cost function that reflects the registration errors on a reference plane. The designed cost function is effectively minimized via the Levenberg-Marquardt algorithm. For the given set of images, when it is found that the relative camera motions between the images are large, the proposed method performs rectification of images and then composition using the rectified images; otherwise, the algorithm simply builds a visually pleasing result by selecting a viewpoint. Experimental results on synthetic and real images show that our method successfully performs stitching and metric rectification.

  16. Molecular shape of Lumbricus terrestris erythrocruorin studied by electron microscopy and image analysis

    Boekema, Egbert J.; Heel, Marin van

    1989-01-01

    The molecular structure of erythrocruorin (hemoglobin) from Lumbricus terrestris has been studied by electron microscopy of negatively stained particles. Over 1000 molecular projections were selected from a number of electron micrographs and were then classified by multivariate statistical image-pro

  17. Exploring coherent transport through π-stacked systems for molecular electronic devices

    Li, Qian; Solomon, Gemma

    2014-01-01

    Understanding electron transport across π-stacked systems can help to elucidate the role of intermolecular tunneling in molecular junctions and potentially with the design of high-efficiency molecular devices. Here we show how conjugation length and substituent groups influence the electron trans...

  18. High Throughput Ab initio Modeling of Charge Transport for Bio-Molecular-Electronics

    Bruque, Nicolas A.

    2009-01-01

    Self-assembled nanostructures, composed of inorganic and organic materials, have multiple applications in the fields of engineering and nanotechnology. Experimental research using nanoscaled materials, such as semiconductor/metallic nanocrystals, nanowires (NW), and carbon nanotube (CNT)-molecular systems have potential applications in next generation nano electronic devices. Many of these molecular systems exhibit electronic device functionality. However, experimental analytical techniques t...

  19. Power spectrum of the rectified EMG: when and why is rectification beneficial for identifying neural connectivity?

    Negro, Francesco; Keenan, Kevin; Farina, Dario

    2015-01-01

    OBJECTIVE: The identification of common oscillatory inputs to motor neurons in the electromyographic (EMG) signal power spectrum is often preceded by EMG rectification for enhancing the low-frequency oscillatory components. However, rectification is a nonlinear operator and its influence on the EMG signal spectrum is not fully understood. In this study, we aim at determining when EMG rectification is beneficial in the study of oscillatory inputs to motor neurons. APPROACH: We provide a f...

  20. Ballistic switching and rectification in single wall carbon nanotube Y junctions

    Transport properties of various semiconducting zig-zag carbon nanotube Y junctions are studied for the investigations of rectification and switching. Our results indicate that such junctions, when symmetric, can support both ballistic rectification and/or the ballistic switching operating modes. Although structural symmetry of the Y junction is found to be a necessary condition for rectification, it may not be sufficient in all cases

  1. Electronic properties of single-molecule junction: Effect of the molecular distortion

    For a model system consisting of a benzenedithio (BDT) molecule sandwiched between two Au plates, the electronic properties as a function of different BDT geometry are investigated using density functional theory. The distorted BDT structures are got through stretching the electrode distance. The corresponding electronic properties, including the spatial distribution of the frontier orbits, the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital levels and density of states at the Fermi energy are determined. It reveals that the molecular distortion essentially determines electronic structures. The result should be beneficial to understand the stress-dependent or structure-dependent transport mechanism of electrons of the BDT junction.

  2. First-Principles Based Matrix-Green's Function Approach to Molecular Electronic Devices: General Formalism

    Xue, Yongqiang; Datta, Supriyo; Ratner, Mark A.

    2001-01-01

    Transport in molecular electronic devices is different from that in semiconductor mesoscopic devices in two important aspects: (1) the effect of the electronic structure and (2) the effect of the interface to the external contact. A rigorous treatment of molecular electronic devices will require the inclusion of these effects in the context of an open system exchanging particle and energy with the external environment. This calls for combining the theory of quantum transport with the theory o...

  3. Resonant electron heating and molecular phonon cooling in single C$_{60}$ junctions

    SCHULZE, G.; Franke, K. J.; Gagliardi, A.; ROMANO, G; Lin, C S; Da Rosa, A.; Niehaus, T. A.; Frauenheim, Th.; A. Di Carlo; Pecchia, A; Pascual, J. I.

    2008-01-01

    We study heating and heat dissipation of a single \\c60 molecule in the junction of a scanning tunneling microscope (STM) by measuring the electron current required to thermally decompose the fullerene cage. The power for decomposition varies with electron energy and reflects the molecular resonance structure. When the STM tip contacts the fullerene the molecule can sustain much larger currents. Transport simulations explain these effects by molecular heating due to resonant electron-phonon co...

  4. THz Generation by Optical Rectification and Competition with Other Nonlinear Processes

    We present a study of the competition between tera-hertz (THz) generation by optical rectification in (110) ZnTe crystals, two-photon absorption, second harmonic generation and free-carrier absorption. The two-photon nonlinear absorption coefficient, second harmonic generation efficiency and free-carrier absorption coefficient in the THz range are measured independently The incident pump field is shown to be depleted by two-photon absorption and the THz radiation is shown to be reduced, upon focusing, by free-carrier absorption. The reduction of the generated THz radiation upon tight focusing is explained, provided that one also takes into account diffraction effects from the sub-wavelength THz source. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  5. Estimation of minimum electron dose necessary to resolve molecular structure of deoxyribonucleic acid by phase transmission electron microscopy

    The minimum electron dose that is necessary to resolve the molecular structure of deoxyribonucleic acid (DNA) was estimated based on experimental measurements of information limits and simulated DNA images, considering conditions of a low electron dose. From these results, a dose of ∼400 e/A2 was found to be necessary to achieve observation of DNA on a molecular scale under the present experimental setup. A DNA molecule was observed by a phase reconstruction method using through-focus images under the limited electron dose. In the reconstructed images, the helical structure and the intervals of the base pairs of DNA were partially resolved

  6. Energy level alignment and electron transport through metal/organic contacts. From interfaces to molecular electronics

    Abad, Enrique

    2013-07-01

    A new calculational approach to describing metal/organic interfaces. A valuable step towards a better understanding of molecular electronics. Nominated as an outstanding contribution by the Autonomous University of Madrid. In recent years, ever more electronic devices have started to exploit the advantages of organic semiconductors. The work reported in this thesis focuses on analyzing theoretically the energy level alignment of different metal/organic interfaces, necessary to tailor devices with good performance. Traditional methods based on density functional theory (DFT), are not appropriate for analyzing them because they underestimate the organic energy gap and fail to correctly describe the van der Waals forces. Since the size of these systems prohibits the use of more accurate methods, corrections to those DFT drawbacks are desirable. In this work a combination of a standard DFT calculation with the inclusion of the charging energy (U) of the molecule, calculated from first principles, is presented. Regarding the dispersion forces, incorrect long range interaction is substituted by a van der Waals potential. With these corrections, the C60, benzene, pentacene, TTF and TCNQ/Au(111) interfaces are analyzed, both for single molecules and for a monolayer. The results validate the induced density of interface states model.

  7. Electron spin resonance study on lignin molecular mobility

    Molecular mobility of grinded wood lignin is studied in the wide temperature range using the recombination-kinetic method. Macroradicals formed during low-temperature γ-radiolysis of lignin, are used as a molecular probe. Analysis of curves of stage-by-stage heating of specimens confirms microheterogeneity of lignin

  8. Infrared rectification in a nanoantenna-coupled metal-oxide-semiconductor tunnel diode.

    Davids, Paul S; Jarecki, Robert L; Starbuck, Andrew; Burckel, D Bruce; Kadlec, Emil A; Ribaudo, Troy; Shaner, Eric A; Peters, David W

    2015-12-01

    Direct rectification of electromagnetic radiation is a well-established method for wireless power conversion in the microwave region of the spectrum, for which conversion efficiencies in excess of 84% have been demonstrated. Scaling to the infrared or optical part of the spectrum requires ultrafast rectification that can only be obtained by direct tunnelling. Many research groups have looked to plasmonics to overcome antenna-scaling limits and to increase the confinement. Recently, surface plasmons on heavily doped Si surfaces were investigated as a way of extending surface-mode confinement to the thermal infrared region. Here we combine a nanostructured metallic surface with a heavily doped Si infrared-reflective ground plane designed to confine infrared radiation in an active electronic direct-conversion device. The interplay of strong infrared photon-phonon coupling and electromagnetic confinement in nanoscale devices is demonstrated to have a large impact on ultrafast electronic tunnelling in metal-oxide-semiconductor (MOS) structures. Infrared dispersion of SiO2 near a longitudinal optical (LO) phonon mode gives large transverse-field confinement in a nanometre-scale oxide-tunnel gap as the wavelength-dependent permittivity changes from 1 to 0, which leads to enhanced electromagnetic fields at material interfaces and a rectified displacement current that provides a direct conversion of infrared radiation into electric current. The spectral and electrical signatures of the nanoantenna-coupled tunnel diodes are examined under broadband blackbody and quantum-cascade laser (QCL) illumination. In the region near the LO phonon resonance, we obtained a measured photoresponsivity of 2.7 mA W(-1) cm(-2) at -0.1 V. PMID:26414194

  9. In Vivo Demonstration of Addressable Microstimulators Powered by Rectification of Epidermically Applied Currents for Miniaturized Neuroprostheses.

    Laura Becerra-Fajardo

    Full Text Available Electrical stimulation is used in order to restore nerve mediated functions in patients with neurological disorders, but its applicability is constrained by the invasiveness of the systems required to perform it. As an alternative to implantable systems consisting of central stimulation units wired to the stimulation electrodes, networks of wireless microstimulators have been devised for fine movement restoration. Miniaturization of these microstimulators is currently hampered by the available methods for powering them. Previously, we have proposed and demonstrated a heterodox electrical stimulation method based on electronic rectification of high frequency current bursts. These bursts can be delivered through textile electrodes on the skin. This approach has the potential to result in an unprecedented level of miniaturization as no bulky parts such as coils or batteries are included in the implant. We envision microstimulators designs based on application-specific integrated circuits (ASICs that will be flexible, thread-like (diameters < 0.5 mm and not only with controlled stimulation capabilities but also with sensing capabilities for artificial proprioception. We in vivo demonstrate that neuroprostheses composed of addressable microstimulators based on this electrical stimulation method are feasible and can perform controlled charge-balanced electrical stimulation of muscles. We developed miniature external circuit prototypes connected to two bipolar probes that were percutaneously implanted in agonist and antagonist muscles of the hindlimb of an anesthetized rabbit. The electronic implant architecture was able to decode commands that were amplitude modulated on the high frequency (1 MHz auxiliary current bursts. The devices were capable of independently stimulating the target tissues, accomplishing controlled dorsiflexion and plantarflexion joint movements. In addition, we numerically show that the high frequency current bursts comply with

  10. Infrared rectification in a nanoantenna-coupled metal-oxide-semiconductor tunnel diode

    Davids, Paul S.; Jarecki, Robert L.; Starbuck, Andrew; Burckel, D. Bruce; Kadlec, Emil A.; Ribaudo, Troy; Shaner, Eric A.; Peters, David W.

    2015-12-01

    Direct rectification of electromagnetic radiation is a well-established method for wireless power conversion in the microwave region of the spectrum, for which conversion efficiencies in excess of 84% have been demonstrated. Scaling to the infrared or optical part of the spectrum requires ultrafast rectification that can only be obtained by direct tunnelling. Many research groups have looked to plasmonics to overcome antenna-scaling limits and to increase the confinement. Recently, surface plasmons on heavily doped Si surfaces were investigated as a way of extending surface-mode confinement to the thermal infrared region. Here we combine a nanostructured metallic surface with a heavily doped Si infrared-reflective ground plane designed to confine infrared radiation in an active electronic direct-conversion device. The interplay of strong infrared photon-phonon coupling and electromagnetic confinement in nanoscale devices is demonstrated to have a large impact on ultrafast electronic tunnelling in metal-oxide-semiconductor (MOS) structures. Infrared dispersion of SiO2 near a longitudinal optical (LO) phonon mode gives large transverse-field confinement in a nanometre-scale oxide-tunnel gap as the wavelength-dependent permittivity changes from 1 to 0, which leads to enhanced electromagnetic fields at material interfaces and a rectified displacement current that provides a direct conversion of infrared radiation into electric current. The spectral and electrical signatures of the nanoantenna-coupled tunnel diodes are examined under broadband blackbody and quantum-cascade laser (QCL) illumination. In the region near the LO phonon resonance, we obtained a measured photoresponsivity of 2.7 mA W-1 cm-2 at -0.1 V.

  11. Development of an electron-temperature-dependent interatomic potential for molecular dynamics simulation of tungsten under electronic excitation

    Irradiation of a metal by lasers or swift heavy ions causes the electrons to become excited. In the vicinity of the excitation, an electronic temperature is established within a thermalization time of 10-100 fs, as a result of electron-electron collisions. For short times, corresponding to less than 1 ps after excitation, the resulting electronic temperature may be orders of magnitude higher than the lattice temperature. During this short time, atoms in the metal experience modified interatomic forces as a result of the excited electrons. These forces can lead to ultrafast nonthermal phenomena such as melting, ablation, laser-induced phase transitions, and modified vibrational properties. We develop an electron-temperature-dependent empirical interatomic potential for tungsten that can be used to model such phenomena using classical molecular dynamics simulations. Finite-temperature density functional theory calculations at high electronic temperatures are used to parametrize the model potential

  12. Substrate and head group modifications for enhanced stability in molecular electronic devices

    Ferrato, Michael-Anthony

    Poor Self-Assembled Monolayer (SAM) stability is a barrier which impedes the incorporation of molecular layers as functional components in electronic device architectures. Here we investigate the molecular electronic characteristics of two well established approaches to enhancing SAM stability. In Chapter 2 we investigate the electrochemical modification of Au substrates by the underpotential deposition of silver monolayers (AgUPD). In Chapter 3 we study chelating dithiophosphinic acid (DTPA) head groups to anchor SAM molecules to substrates. Based on molecular electronic characterization using EGaIn Tip testbeds, we observed that AgUPD substrates maintained the inherent electronic character of n-alkanethiolate SAMs, but reduced charge transport by almost 1 order of magnitude as compared with the same SAMs on bulk Au substrates. Similar molecular electronic characterization of (diphenyl)dithiophosphinic acid SAMs on Au substrates revealed that the DTPA head group induced a ~3 order of magnitude drop in charge transport as compared with analogous thiophenol SAMs.

  13. Rectification of aerial images using piecewise linear transformation

    Aerial images are widely used in various activities by providing visual records. This type of remotely sensed image is helpful in generating digital maps, managing ecology, monitoring crop growth and region surveying. Such images could provide insight into areas of interest that have lower altitude, particularly in regions where optical satellite imaging is prevented due to cloudiness. Aerial images captured using a non-metric cameras contain real details of the images as well as unexpected distortions. Distortions would affect the actual length, direction and shape of objects in the images. There are many sources that could cause distortions such as lens, earth curvature, topographic relief and the attitude of the aircraft that is used to carry the camera. These distortions occur differently, collectively and irregularly in the entire image. Image rectification is an essential image pre-processing step to eliminate or at least reduce the effect of distortions. In this paper, a non-parametric approach with piecewise linear transformation is investigated in rectifying distorted aerial images. The non-parametric approach requires a set of corresponding control points obtained from a reference image and a distorted image. The corresponding control points are then applied with piecewise linear transformation as geometric transformation. Piecewise linear transformation divides the image into regions by triangulation. Different linear transformations are employed separately to triangular regions instead of using a single transformation as the rectification model for the entire image. The result of rectification is evaluated using total root mean square error (RMSE). Experiments show that piecewise linear transformation could assist in improving the limitation of using global transformation to rectify images

  14. Self-assembled and electrochemically deposited mono/multilayers for molecular electronics applications

    For the development of molecular electronics, it is desirable to investigate characteristics of organic molecules with electronic device functionalities. In near future, such molecular devices could be integrated with silicon to prepare hybrid nanoelectronic devices. In this paper, we review work done in our laboratory on study of characteristics of some functional molecules. For these studies molecular mono and multilayers have been deposited on silicon surface by self-assembly and electrochemical deposition techniques. Both commercially available and specially designed and synthesized molecules have been utilized for these investigations. We demonstrate dielectric layers, memory, switching, rectifier and negative differential resistance devices based on molecular mono and multilayers.

  15. Study of rectification at the metal-cadmium telluride contact

    The barrier heights at the contact between metals and N or P type cadmium telluride have been determined. Various surface treatments have been used for the semiconductor: lapping, polishing and etching in a bromine in methanol solution. Depending on these preparation differences of about 0.1 eV have been observed for the barrier height which in any case was no more than 0.9 - 1.0 eV. These results can not be explained by only considering the Schottky theory of rectification

  16. Resonant electron heating and molecular phonon cooling in single C60 junctions.

    Schulze, G; Franke, K J; Gagliardi, A; Romano, G; Lin, C S; Rosa, A L; Niehaus, T A; Frauenheim, Th; Di Carlo, A; Pecchia, A; Pascual, J I

    2008-04-01

    We study heating and heat dissipation of a single C(60) molecule in the junction of a scanning tunneling microscope by measuring the electron current required to thermally decompose the fullerene cage. The power for decomposition varies with electron energy and reflects the molecular resonance structure. When the scanning tunneling microscope tip contacts the fullerene the molecule can sustain much larger currents. Transport simulations explain these effects by molecular heating due to resonant electron-phonon coupling and molecular cooling by vibrational decay into the tip upon contact formation. PMID:18517981

  17. Electron-Vibration Coupling in Molecular Materials: Assignment of Vibronic Modes from Photoelectron Momentum Mapping

    Graus, M.; Grimm, M.; Metzger, C.; Dauth, M.; Tusche, C.; Kirschner, J.; Kümmel, S.; Schöll, A.; Reinert, F.

    2016-04-01

    Electron-phonon coupling is one of the most fundamental effects in condensed matter physics. We here demonstrate that photoelectron momentum mapping can reveal and visualize the coupling between specific vibrational modes and electronic excitations. When imaging molecular orbitals with high energy resolution, the intensity patterns of photoelectrons of the vibronic sidebands of molecular states show characteristic changes due to the distortion of the molecular frame in the vibronically excited state. By comparison to simulations, an assignment of specific vibronic modes is possible, thus providing unique information on the coupling between electronic and vibronic excitation.

  18. Electron transfer through a molecular wire: Consideration of electron-vibrational coupling within the Liouville space pathway technique

    May, V.

    2002-12-01

    To fully account for electron-vibrational coupling and vibrational relaxation in the course of electron motion through a molecular wire a density operator approach is utilized. If combined with a particular projection operator technique a generalized master equation can be derived which governs the populations of the electronic wire states. The respective memory kernels are determined beyond any perturbation theory with respect to the electron-vibrational coupling and can be classified via so-called Liouville space pathways. An ordering of the different contributions to the current-voltage characteristics becomes possible by introducing an electron transmission coefficient which describes ballistic as well as inelastic electron transport through the wire. The general derivations are illustrated by numerical calculations which demonstrate the drastic influence of the electron-vibrational coupling on the wire transmission coefficient as well as on the current-voltage characteristics.

  19. Vibrational and rotational cooling of electrons by molecular hydrogen. [in Jupiter and Saturn thermosphere

    Waite, J. H., Jr.; Cravens, T. E.

    1981-01-01

    It is noted that the cooling of electrons by vibrational and rotational excitation of molecular hydrogen plays an important role in the thermal balance of electrons in atmospheres containing significant amounts of H2. Calculations are described of vibrational and rotational cooling rates of electrons by H2. Results for a wide range of electron and neutral temperatures are presented, and analytical formulas for some to the cooling rates are given.

  20. Effects of electronic coupling and electrostatic potential on charge transport in carbon-based molecular electronic junctions

    2016-01-01

    Summary Molecular junctions consisting of 2–20 nm thick layers of organic oligomers oriented between a conducting carbon substrate and a carbon/gold top contact have proven to be reproducible and reliable, and will soon enter commercial production in audio processing circuits. The covalent, conjugated bond between one or both sp2-hybridized carbon contacts and an aromatic molecular layer is distinct from the more common metal/molecule or silicon/molecule structures in many reported molecular junctions. Theoretical observations based on density functional theory are presented here, which model carbon-based molecular junctions as single molecules and oligomers between fragments of graphene. Electronic coupling between the molecules and the contacts is demonstrated by the formation of hybrid orbitals in the model structure, which have significant electron density on both the graphene and the molecule. The energies of such hybrid orbitals correlate with tunneling barriers determined experimentally, and electronic coupling between the two graphene fragments in the model correlates with experimentally observed attenuation of transport with molecular layer thickness. Electronic coupling is affected significantly by the dihedral angle between the planes of the graphene and the molecular π-systems, but is absent only when the two planes are orthogonal. Coupling also results in partial charge transfer between the graphene contacts and the molecular layer, which results in a shift in electrostatic potential which affects the observed tunneling barrier. Although the degree of partial charge transfer is difficult to calculate accurately, it does provide a basis for the “vacuum level shift” observed in many experiments, including transport and ultraviolet photoelectron spectroscopy of molecular layers on conductors. PMID:26925350

  1. Effects of electronic coupling and electrostatic potential on charge transport in carbon-based molecular electronic junctions

    Richard L. McCreery

    2016-01-01

    Full Text Available Molecular junctions consisting of 2–20 nm thick layers of organic oligomers oriented between a conducting carbon substrate and a carbon/gold top contact have proven to be reproducible and reliable, and will soon enter commercial production in audio processing circuits. The covalent, conjugated bond between one or both sp2-hybridized carbon contacts and an aromatic molecular layer is distinct from the more common metal/molecule or silicon/molecule structures in many reported molecular junctions. Theoretical observations based on density functional theory are presented here, which model carbon-based molecular junctions as single molecules and oligomers between fragments of graphene. Electronic coupling between the molecules and the contacts is demonstrated by the formation of hybrid orbitals in the model structure, which have significant electron density on both the graphene and the molecule. The energies of such hybrid orbitals correlate with tunneling barriers determined experimentally, and electronic coupling between the two graphene fragments in the model correlates with experimentally observed attenuation of transport with molecular layer thickness. Electronic coupling is affected significantly by the dihedral angle between the planes of the graphene and the molecular π-systems, but is absent only when the two planes are orthogonal. Coupling also results in partial charge transfer between the graphene contacts and the molecular layer, which results in a shift in electrostatic potential which affects the observed tunneling barrier. Although the degree of partial charge transfer is difficult to calculate accurately, it does provide a basis for the “vacuum level shift” observed in many experiments, including transport and ultraviolet photoelectron spectroscopy of molecular layers on conductors.

  2. EPICEA: Probing high-energy electron emission in the molecular frame

    Electron emission provides an excellent opportunity to probe the electronic structure and the chemical reactivity of materials. For molecules, the most natural way is describing it in the molecular frame. Recently, using the upgraded version of the EPICEA coincidence setup available at PLEIADES beamline at SOLEIL (France), we were able to measure the electron emission in the molecular frame for kinetic energies up to several hundreds of eV. At these high energies the de Broglie wavelength is comparable to or smaller than the inter-nuclear distance, the possibility of observing the intramolecular electron diffraction thus being opened.

  3. Electron loss from multiply protonated lysozyme ions in high energy collisions with molecular oxygen

    Hvelplund, P; Nielsen, SB; Sørensen, M;

    2001-01-01

    We report on the electron loss from multiply protonated lysozyme ions Lys-Hn(n)+ (n = 7 - 17) and the concomitant formation of Lys-Hn(n+1)+. in high-energy collisions with molecular oxygen (laboratory kinetic energy = 50 x n keV). The cross section for electron loss increases with the charge state...... of the precursor from n = 7 to n = 11 and then remains constant when n increases further. The absolute size of the cross section ranges from 100 to 200 A2. The electron loss is modeled as an electron transfer process between lysozyme cations and molecular oxygen....

  4. Rectification of nanopores in aprotic solvents - transport properties of nanopores with surface dipoles

    Plett, Timothy; Shi, Wenqing; Zeng, Yuhan; Mann, William; Vlassiouk, Ivan; Baker, Lane A.; Siwy, Zuzanna S.

    2015-11-01

    Nanopores have become a model system to understand transport properties at the nanoscale. We report experiments and modeling of ionic current in aprotic solvents with different dipole moments through conically shaped nanopores in a polycarbonate film and through glass nanopipettes. We focus on solutions of the salt LiClO4, which is of great importance in modeling lithium based batteries. Results presented suggest ion current rectification observed results from two effects: (i) adsorption of Li+ ions to the pore walls, and (ii) a finite dipole moment rendered by adsorbed solvent molecules. Properties of surfaces in various solvents were probed by means of scanning ion conductance microscopy, which confirmed existence of an effectively positive surface potential in aprotic solvents with high dipole moments.Nanopores have become a model system to understand transport properties at the nanoscale. We report experiments and modeling of ionic current in aprotic solvents with different dipole moments through conically shaped nanopores in a polycarbonate film and through glass nanopipettes. We focus on solutions of the salt LiClO4, which is of great importance in modeling lithium based batteries. Results presented suggest ion current rectification observed results from two effects: (i) adsorption of Li+ ions to the pore walls, and (ii) a finite dipole moment rendered by adsorbed solvent molecules. Properties of surfaces in various solvents were probed by means of scanning ion conductance microscopy, which confirmed existence of an effectively positive surface potential in aprotic solvents with high dipole moments. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06340j

  5. Communication: Electrical rectification of C59N: The role of anchoring and doping sites

    Based on the nonequilibrium Green’s function formalism and density-functional theory, we investigate the onset of electrical rectification in a single C59N molecule in conjunction with gold electrodes. Our calculations reveal that rectification is dependent upon the anchoring of the Au atom on C59N; when the Au electrode is singly bonded to a C atom (labeled here as A), the system does not exhibit rectification, whereas when the electrode is connected to the C–C bridge site between two hexagonal rings (labeled here as B), transmission asymmetry is observed, where the rectification ratio reaches up to 2.62 at ±1 V depending on the N doping site relative to the anchoring site. Our analysis of the transmission mechanism shows that N doping of the B configuration causes rectification because more transmission channels are available for transmission in the B configuration than in the A configuration

  6. Communication: Electrical rectification of C{sub 59}N: The role of anchoring and doping sites

    Tawfik, Sherif Abdulkader, E-mail: sherif.abbas@sydney.edu.au; Stampfl, C. [School of Physics, The University of Sydney, Sydney, New South Wales 2006 (Australia); Cui, X. Y.; Ringer, S. P. [Australian Centre for Microscopy and Microanalysis, and School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, New South Wales 2006 (Australia)

    2016-01-14

    Based on the nonequilibrium Green’s function formalism and density-functional theory, we investigate the onset of electrical rectification in a single C{sub 59}N molecule in conjunction with gold electrodes. Our calculations reveal that rectification is dependent upon the anchoring of the Au atom on C{sub 59}N; when the Au electrode is singly bonded to a C atom (labeled here as A), the system does not exhibit rectification, whereas when the electrode is connected to the C–C bridge site between two hexagonal rings (labeled here as B), transmission asymmetry is observed, where the rectification ratio reaches up to 2.62 at ±1 V depending on the N doping site relative to the anchoring site. Our analysis of the transmission mechanism shows that N doping of the B configuration causes rectification because more transmission channels are available for transmission in the B configuration than in the A configuration.

  7. Communication: Electrical rectification of C59N: The role of anchoring and doping sites.

    Tawfik, Sherif Abdulkader; Cui, X Y; Ringer, S P; Stampfl, C

    2016-01-14

    Based on the nonequilibrium Green's function formalism and density-functional theory, we investigate the onset of electrical rectification in a single C59N molecule in conjunction with gold electrodes. Our calculations reveal that rectification is dependent upon the anchoring of the Au atom on C59N; when the Au electrode is singly bonded to a C atom (labeled here as A), the system does not exhibit rectification, whereas when the electrode is connected to the C-C bridge site between two hexagonal rings (labeled here as B), transmission asymmetry is observed, where the rectification ratio reaches up to 2.62 at ±1 V depending on the N doping site relative to the anchoring site. Our analysis of the transmission mechanism shows that N doping of the B configuration causes rectification because more transmission channels are available for transmission in the B configuration than in the A configuration. PMID:26772547

  8. Manipulation of large molecules by low-temperature STM: model systems for molecular electronics

    The ability of the low-temperature scanning tunneling microscope to manipulate atoms and to build nanostructures with atomic precision can be extended to the manipulation of larger molecules and to selectively modify their internal degrees of freedom. Manipulation experiments on individual molecules show an exciting diversity of physical, chemical, and electronic phenomena. They permit a deeper insight into the quantum electronics of molecular systems and provide important information on the conformational and mechanical properties of single complex molecules. In this article, recent experiments on specially designed molecules will be reviewed, which investigate model systems interesting for the developing of molecular electronics. Starting from the realization of the principle of a molecular switch, going through the possibility of recording the small intramolecular changes inside a complex molecule during its movement, toward the study of the electronic contact between a single molecular wire and a metallic nanoelectrode

  9. Stereo Calibration and Rectification for Omnidirectional Multi-camera Systems

    Yanchang Wang

    2012-10-01

    Full Text Available Stereo vision has been studied for decades as a fundamental problem in the field of computer vision. In recent years, computer vision and image processing with a large field of view, especially using omnidirectional vision and panoramic images, has been receiving increasing attention. An important problem for stereo vision is calibration. Although various kinds of calibration methods for omnidirectional cameras are proposed, most of them are limited to calibrate catadioptric cameras or fish‐eye cameras and cannot be applied directly to multi‐camera systems. In this work, we propose an easy calibration method with closed‐form initialization and iterative optimization for omnidirectional multi‐camera systems. The method only requires image pairs of the 2D target plane in a few different views. A method based on the spherical camera model is also proposed for rectifying omnidirectional stereo pairs. Using real data captured by Ladybug3, we carry out some experiments, including stereo calibration, rectification and 3D reconstruction. Statistical analyses and comparisons of the experimental results are also presented. As the experimental results show, the calibration results are precise and the effect of rectification is promising.

  10. Optically induced transport through semiconductor-based molecular electronics

    A tight binding model is used to investigate photoinduced tunneling current through a molecular bridge coupled to two semiconductor electrodes. A quantum master equation is developed within a non-Markovian theory based on second-order perturbation theory with respect to the molecule-semiconductor electrode coupling. The spectral functions are generated using a one dimensional alternating bond model, and the coupling between the molecule and the electrodes is expressed through a corresponding correlation function. Since the molecular bridge orbitals are inside the bandgap between the conduction and valence bands, charge carrier tunneling is inhibited in the dark. Subject to the dipole interaction with the laser field, virtual molecular states are generated via the absorption and emission of photons, and new tunneling channels open. Interesting phenomena arising from memory are noted. Such a phenomenon could serve as a switch

  11. Molecular-based electronically switchable tunnel junction devices.

    Collier, C P; Jeppesen, J O; Luo, Y; Perkins, J; Wong, E W; Heath, J R; Stoddart, J F

    2001-12-19

    Solid-state tunnel junction devices were fabricated from Langmuir Blodgett molecular monolayers of a bistable [2]catenane, a bistable [2]pseudorotaxane, and a single-station [2]rotaxane. All devices exhibited a (noncapacitive) hysteretic current-voltage response that switched the device between high- and low-conductivity states, although control devices exhibited no such response. Correlations between the structure and solution-phase dynamics of the molecular and supramolecular systems, the crystallographic domain structure of the monolayer film, and the room-temperature device performance characteristics are reported. PMID:11741428

  12. Proceedings of the 2. Latin American Meeting on Atomic, Molecular and Electronic Collisions

    Annals of the II Latin American Meeting on Atomic, Molecular and Electronic Collisions. Over than 50 people from Latin America participated on this meeting giving talks on different subjects (theoretical and experimental), related to atomic and molecular physics, as well as, nuclear physics. (A.C.A.S.)

  13. Computational Nanotechnology of Molecular Materials, Electronics, and Actuators with Carbon Nanotubes and Fullerenes

    Srivastava, Deepak; Menon, Madhu; Cho, Kyeongjae; Biegel, Bryan (Technical Monitor)

    2001-01-01

    The role of computational nanotechnology in developing next generation of multifunctional materials, molecular scale electronic and computing devices, sensors, actuators, and machines is described through a brief review of enabling computational techniques and few recent examples derived from computer simulations of carbon nanotube based molecular nanotechnology.

  14. Electronic Transport in Self-organised Molecular Nanostructured Devices

    Pecchia, A.; Movaghar, B.; Kelsall, R. W.; Bourlange, A.; S. D. Evans; Hickey, B. J.; Boden, N.

    2001-01-01

    We analyse the frequency dependent conductivity of a system which is fabricated using the combination of a quasi 2-dimensional MBE grown metal film and an ordered self-assembled overlayer of adsorbed molecules. The molecules can self-assemble to form quasi 1-dimensional conducting columns, in which electrons can be temporarily trapped. Given the short mean free path of conducting electrons, due to surface and impurity scattering, the long range transport is modelled using a diffusion scheme t...

  15. On the distance dependence of electron transfer through molecular bridges and wires

    Skourtis, Spiros; Nitzan, Abraham

    2002-01-01

    The dependence of electron transfer rates and yields in bridged molecular systems on the bridge length, and the dependence of the zero-bias conduction of molecular wires on wire length are discussed. Both phenomena are controlled by tunneling across the molecular bridge and are consequently expected to show exponential decrease with bridge length that is indeed often observed. Deviations from this exponential dependence for long bridges, in particular a crossover to a very weak dependence on ...

  16. Ab initio analysis of electron-phonon coupling in molecular devices

    Sergueev, N.; Roubtsov, D.; Guo, Hong

    2005-01-01

    We report first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. We analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. For a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two leads, t...

  17. A parity function for studying the molecular electronic structure

    Schmider, Hartmut

    1996-01-01

    Sections through the molecular Wigner function with zero momentum variable are shown to provide important information about the off-diagonal regions of the spinless one-particle reduced density matrix. Since these regions are characteristic for the bonding situation in molecules, the sections...

  18. Recent advances in molecular electronics based on carbon nanotubes.

    Bourgoin, Jean-Philippe; Campidelli, Stéphane; Chenevier, Pascale; Derycke, Vincent; Filoramo, Arianna; Goffman, Marcelo F

    2010-01-01

    Carbon nanotubes (CNTs) have exceptional physical properties that make them one of the most promising building blocks for future nanotechnologies. They may in particular play an important role in the development of innovative electronic devices in the fields of flexible electronics, ultra-high sensitivity sensors, high frequency electronics, opto-electronics, energy sources and nano-electromechanical systems (NEMS). Proofs of concept of several high performance devices already exist, usually at the single device level, but there remain many serious scientific issues to be solved before the viability of such routes can be evaluated. In particular, the main concern regards the controlled synthesis and positioning of nanotubes. In our opinion, truly innovative use of these nano-objects will come from: (i) the combination of some of their complementary physical properties, such as combining their electrical and mechanical properties, (ii) the combination of their properties with additional benefits coming from other molecules grafted on the nanotubes, and (iii) the use of chemically- or bio-directed self-assembly processes to allow the efficient combination of several devices into functional arrays or circuits. In this article, we outline the main issues concerning the development of carbon nanotubes based electronics applications and review our recent results in the field. PMID:21137718

  19. Coordination compounds for molecular electronics: Synthesis, characterization and electronic transport properties of copper rotaxanes and molecular complexes

    Ponce González, Julia

    2014-01-01

    Esta tesis se centra en el estudio de compuestos de coordinación de interés en el campo de la electrónica molecular. Este campo tiene como objetivo la utilización de unidades moleculares como componentes activos en circuitos electrónicos. Los dispositivos unimoleculares presentan cualidades únicas, inherentes a la nanoescala, que no poseen equivalencia en los componentes convencionales, actualmente basados en el silicio. Además, la síntesis de moléculas dispone de un altísimo grado de control...

  20. AC-ELECTROKINETICS BASED TOOLS IN NANOENGINEERING AND MOLECULAR ELECTRONICS

    R. Durán

    2005-08-01

    Full Text Available Slllcon-based mlcroeledronics has been following the integration prognosls of MOORE's Law durlng the past decades and posslbly will do so for another decade or two. Physlcal, technological and also flnancialllmlts In the foreseeable future will slow down the contlnued expansiOn of this branch of mlcroeledronlcs and instead wlll force a new technological approach based on molecular-scale eledronics (MOLETRONICS. New tools are needed to allow molecular devlce manufaduring and nanoscale engineering with hlgh precision and produdivlty. One group of methods with the potentlal for use In such a manufaduring process Is based on a.c. eledrokinetlcs effeds, which are descrlbed and discussed in this paper.

  1. Millisecond Coherence Time in a Tunable Molecular Electronic Spin Qubit

    Zadrozny, Joseph M.; Niklas, Jens; Poluektov, Oleg G.; Freedman, Danna E.

    2015-01-01

    Quantum information processing (QIP) could revolutionize areas ranging from chemical modeling to cryptography. One key figure of merit for the smallest unit for QIP, the qubit, is the coherence time (T 2), which establishes the lifetime for the qubit. Transition metal complexes offer tremendous potential as tunable qubits, yet their development is hampered by the absence of synthetic design principles to achieve a long T 2. We harnessed molecular design to create a series of qubits, (Ph4P)2[V...

  2. Coupled electron-phonon transport from molecular dynamics with quantum baths

    Lu, Jing Tao; Wang, J. S.

    2009-01-01

    Based on generalized quantum Langevin equations for the tight-binding wavefunction amplitudes and lattice displacements, electron and phonon quantum transport are obtained exactly using molecular dynamics (MD) in the ballistic regime. The electron-phonon interactions can be handled with a quasi-c...

  3. Electron and phonon drag in thermoelectric transport through coherent molecular conductors

    Lü, Jing-Tao; Wang, Jian-Sheng; Hedegård, Per;

    2016-01-01

    We study thermoelectric transport through a coherent molecular conductor connected to two electron and two phonon baths using the nonequilibrium Green's function method. We focus on the mutual drag between electron and phonon transport as a result of ‘momentum’ transfer, which happens only when t...

  4. Time-dependent electron interference prior to ionization in the hydrogen atom and hydrogen molecular ion

    de la Calle Negro, A.; Dundas, D.; Taylor, K. T.

    2014-01-01

    We investigate electron dynamics in the hydrogen atom and the hydrogen molecular ion when exposed to long wavelength laser pulses yet having intensity insufficient to ionize the system. We find that the field is still able to drive the electron, leading to time-dependent interference effects.

  5. Electron sharing and anion-π recognition in molecular triangular prisms.

    Schneebeli, Severin T; Frasconi, Marco; Liu, Zhichang; Wu, Yilei; Gardner, Daniel M; Strutt, Nathan L; Cheng, Chuyang; Carmieli, Raanan; Wasielewski, Michael R; Stoddart, J Fraser

    2013-12-01

    Stacking on a full belly: Triangular molecular prisms display electron sharing among their triangularly arranged naphthalenediimide (NDI) redox centers. Their electron-deficient cavities encapsulate linear triiodide anions, leading to the formation of supramolecular helices in the solid state. Chirality transfer is observed from the six chiral centers of the filled prisms to the single-handed helices. PMID:24227594

  6. Tunneling of electrons via rotor-stator molecular interfaces: combined ab initio and model study

    Petreska, Irina; Pejov, Ljupco; Kocarev, Ljupco

    2015-01-01

    Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that confirmation dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previ...

  7. Molecular fingerprints in the electronic properties of crystalline organic semiconductors

    Ciuchi, S.; Hatch, R.C.; Höchst, H.;

    2012-01-01

    By comparing photoemission spectroscopy with a non-perturbative dynamical mean field theory extension to many-body ab initio calculations, we show in the prominent case of pentacene crystals that an excellent agreement with experiment for the bandwidth, dispersion and lifetime of the hole carrier...... of electronic interactions cannot reproduce the experimental photoemission data in this important class of materials....

  8. Electron transfer statistics and thermal fluctuations in molecular junctions

    Goswami, Himangshu Prabal; Harbola, Upendra

    2015-02-01

    We derive analytical expressions for probability distribution function (PDF) for electron transport in a simple model of quantum junction in presence of thermal fluctuations. Our approach is based on the large deviation theory combined with the generating function method. For large number of electrons transferred, the PDF is found to decay exponentially in the tails with different rates due to applied bias. This asymmetry in the PDF is related to the fluctuation theorem. Statistics of fluctuations are analyzed in terms of the Fano factor. Thermal fluctuations play a quantitative role in determining the statistics of electron transfer; they tend to suppress the average current while enhancing the fluctuations in particle transfer. This gives rise to both bunching and antibunching phenomena as determined by the Fano factor. The thermal fluctuations and shot noise compete with each other and determine the net (effective) statistics of particle transfer. Exact analytical expression is obtained for delay time distribution. The optimal values of the delay time between successive electron transfers can be lowered below the corresponding shot noise values by tuning the thermal effects.

  9. Electron transfer statistics and thermal fluctuations in molecular junctions

    Goswami, Himangshu Prabal; Harbola, Upendra [Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 (India)

    2015-02-28

    We derive analytical expressions for probability distribution function (PDF) for electron transport in a simple model of quantum junction in presence of thermal fluctuations. Our approach is based on the large deviation theory combined with the generating function method. For large number of electrons transferred, the PDF is found to decay exponentially in the tails with different rates due to applied bias. This asymmetry in the PDF is related to the fluctuation theorem. Statistics of fluctuations are analyzed in terms of the Fano factor. Thermal fluctuations play a quantitative role in determining the statistics of electron transfer; they tend to suppress the average current while enhancing the fluctuations in particle transfer. This gives rise to both bunching and antibunching phenomena as determined by the Fano factor. The thermal fluctuations and shot noise compete with each other and determine the net (effective) statistics of particle transfer. Exact analytical expression is obtained for delay time distribution. The optimal values of the delay time between successive electron transfers can be lowered below the corresponding shot noise values by tuning the thermal effects.

  10. Electron transfer flavoprotein deficiency: Functional and molecular aspects

    Schiff, M; Froissart, R; Olsen, Rikke Katrine Jentoft; Acquaviva, C; Vianey-Saban, C

    2006-01-01

    Multiple acyl-CoA dehydrogenase deficiency (MADD) is a recessively inherited metabolic disorder that can be due to a deficiency of electron transfer flavoprotein (ETF) or its dehydrogenase (ETF-ubiquinone oxidoreductase). ETF is a mitochondrial matrix protein consisting of alpha- (30kDa) and beta...... mutations in the ETFB gene. Nine novel disease-causing ETF mutations are reported....

  11. Continuous electronic spectrum accompanying the β decay of molecular tritium

    The electronic spectrum of the T2→3HeT++nu-bar+e- β decay is obtained by a Stieltjes-imaging method using Slater and trigonometric basis functions. Except for one strong resonance structure at 68 eV the continuum lacks structure

  12. A quantum-defect theory of molecular electronic polarizability

    An algorithm based on the quantum defect theory is proposed for computing the dynamic polarizability tensor for polar molecules. The algorithm makes use of ab initio methods developed for ground and lowlying electronic states. The computed refractive index and scattered-light depolarization coefficient for gaseous nitric oxide are in good agreement with experiment

  13. Measuring the density of a molecular cluster injector via visible emission from an electron beam

    A method to measure the density distribution of a dense hydrogen gas jet is presented. A Mach 5.5 nozzle is cooled to 80 K to form a flow capable of molecular cluster formation. A 250 V, 10 mA electron beam collides with the jet and produces Hα emission that is viewed by a fast camera. The high density of the jet, several 1016 cm-3, results in substantial electron depletion, which attenuates the Hα emission. The attenuated emission measurement, combined with a simplified electron-molecule collision model, allows us to determine the molecular density profile via a simple iterative calculation.

  14. Enhancing rectification of a nano-swimmer system by multi-layered asymmetric barriers

    Chen, Yen-Fu; Xiao, Song; Chen, Hsuan-Yi; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2015-10-01

    The rectification of nano-swimmers in two chambers separated by a strip of funnel gates is explored by dissipative particle dynamics simulations. According to the trajectories of active colloids across the funnel zone, two rectification mechanisms are identified: geometry-assisted diffusion and trap-hindered diffusion. In general, geometry-assisted diffusion dominates at a small active force (Fa) and run time (τ) while trap-hindered diffusion governs at a large Fa and τ. The rectification ratio is affected by the funnel shape and various geometries are considered: open/closed triangular, circular and rectangular funnels. The rectification ratio of open funnels is always greater than that of closed funnels. Moreover, the open circular funnel has the best performance while the triangular one has the worst. Rectification can be enhanced as the number of funnel layers is increased. It is found that the rectification ratio of self-propelled colloids can be dramatically augmented by triple-layered funnels to be as high as 30. Our simulation study offers an efficient approach for rectification enhancement.

  15. Enhancing rectification of a nano-swimmer system by multi-layered asymmetric barriers.

    Chen, Yen-Fu; Xiao, Song; Chen, Hsuan-Yi; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2015-10-21

    The rectification of nano-swimmers in two chambers separated by a strip of funnel gates is explored by dissipative particle dynamics simulations. According to the trajectories of active colloids across the funnel zone, two rectification mechanisms are identified: geometry-assisted diffusion and trap-hindered diffusion. In general, geometry-assisted diffusion dominates at a small active force (Fa) and run time (τ) while trap-hindered diffusion governs at a large Fa and τ. The rectification ratio is affected by the funnel shape and various geometries are considered: open/closed triangular, circular and rectangular funnels. The rectification ratio of open funnels is always greater than that of closed funnels. Moreover, the open circular funnel has the best performance while the triangular one has the worst. Rectification can be enhanced as the number of funnel layers is increased. It is found that the rectification ratio of self-propelled colloids can be dramatically augmented by triple-layered funnels to be as high as 30. Our simulation study offers an efficient approach for rectification enhancement. PMID:26394906

  16. High throughput ab initio modeling of charge transport for bio-molecular-electronics

    Bruque, Nicolas Alexander

    2009-12-01

    Self-assembled nanostructures, composed of inorganic and organic materials, have multiple applications in the fields of engineering and nanotechnology. Experimental research using nanoscaled materials, such as semiconductor/metallic nanocrystals, nanowires (NW), and carbon nanotube (CNT)-molecular systems have potential applications in next generation nano electronic devices. Many of these molecular systems exhibit electronic device functionality. However, experimental analytical techniques to determine how the chemistry and geometry affects electron transport through these devices does not yet exist. Using theory and modeling, one can approximate the chemistry and geometry at the atomic level and also determine how the chemistry and geometry governs electron current. Nanoelectronic devices however, contain several thousand atoms which makes quantum modeling difficult. Popular atomistic modeling approaches are capable of handling small molecular systems, which are of scientific interest, but have little engineering value. The lack of large scale modeling tools has left the scientific and engineering community with a limited ability to understand, explore, and design complex systems of engineering interest. To address these issues, I have developed a high performance general quantum charge transport model based on the non-equilibrium Green function (NEGF) formalism using density functional theory (DFT) as implemented in the FIREBALL software. FIREBALL is a quantum molecular dynamics code which has demonstrated the ability to model large molecular systems. This dissertation project of integrating NEGF into FIREBALL provides researchers with a modeling tool capable of simulating charge current in large inorganic/organic systems. To provide theoretical support for experimental efforts, this project focused on CNT-molecular systems, which includes the discovery of a CNT-molecular resonant tunneling diode (RTD) for electronic circuit applications. This research also

  17. Multimer Radical Ions and Electron/Hole Localization in Polyatomic Molecular Liquids: A critical review

    Shkrob, Ilya A.; Sauer, Jr., Myran C.

    2004-01-01

    While ionization of some polyatomic molecular liquids (such as water and aliphatic alcohols) yields so-called "solvated electrons" in which the excess electron density is localized in the interstices between the solvent molecules, most organic and inorganic liquids yield radical anions and cations in which the electron and spin densities reside on the solvent molecule or, more commonly, a group of such molecules. The resulting multimer ions have many unusual properties, such as high rates of ...

  18. Intense Electron Beams from GaAs Photocathodes as a Tool for Molecular and Atomic Physics

    Krantz, C.

    2009-01-01

    We present cesium-coated GaAs photocathodes as reliable sources of intense, quasi-monoenergetic electron beams in atomic and molecular physics experiments. In long-time operation of the Electron Target of the ion storage ring TSR in Heidelberg, cold electron beams could be realised at steadily improving intensity and reliability. Minimisation of processes degrading the quantum efficiency allowed to increase the extractable current to more than 1mA at stable cathode lifetimes of 24 h or more. ...

  19. Probing electron-phonon excitations in molecular junctions by quantum interference.

    Bessis, C; Della Rocca, M L; Barraud, C; Martin, P; Lacroix, J C; Markussen, T; Lafarge, P

    2016-01-01

    Electron-phonon coupling is a fundamental inelastic interaction in condensed matter and in molecules. Here we probe phonon excitations using quantum interference in electron transport occurring in short chains of anthraquinone based molecular junctions. By studying the dependence of molecular junction's conductance as a function of bias voltage and temperature, we show that inelastic scattering of electrons by phonons can be detected as features in conductance resulting from quenching of quantum interference. Our results are in agreement with density functional theory calculations and are well described by a generic two-site model in the framework of non-equilibrium Green's functions formalism. The importance of the observed inelastic contribution to the current opens up new ways for exploring coherent electron transport through molecular devices. PMID:26864735

  20. Electron Transfer Dynamics in Efficient Molecular Solar Cells

    Meyer, Gerald John

    2014-10-01

    This research provided new mechanistic insights into surface mediated photochemical processes relevant to solar energy conversion. In this past three years our research has focused on oxidation photo-redox chemistry and on the role surface electric fields play on basic spectroscopic properties of molecular-semiconductor interfaces. Although this research as purely fundamental science, the results and their interpretation have relevance to applications in dye sensitized and photogalvanic solar cells as well as in the storage of solar energy in the form of chemical bonds.

  1. Metal–semiconductor nanojunctions and their rectification characteristics

    Anindita Bose; Kuntal Chatterjee; Dipankar Chakravorty

    2009-06-01

    Junctions of silver–copper oxide and silver–zinc oxide, respectively were prepared within the pores of diameters, 20 nm, in anodic aluminium oxide membranes. Voltage–current characteristics were measured over the temperature range 373–573 K which showed rectification behaviour. Using the standard equation the difference between the work functions of the metal and the semiconductor was calculated. This showed a variation with the temperature of measurement. This is explained as arising due to the effect of pressure generated as a result of thermal expansion of the metallic phases concerned between the electrodes. This is consistent with the theoretical prediction of Fermi level shifting of the semiconductor within the bandgap as a function of pressure.

  2. AN INFORMATION FUSION METHOD FOR SENSOR DATA RECTIFICATION

    Zhang Zhen; Xu Lizhong; Harry Hua Li; Shi Aiye; Han Hua; Wang Huibin

    2012-01-01

    In the applications of water regime monitoring,incompleteness,and inaccuracy of sensor data may directly affect the reliability of acquired monitoring information.Based on the spatial and temporal correlation of water regime monitoring information,this paper addresses this issue and proposes an information fusion method to implement data rectification.An improved Back Propagation (BP) neural network is used to perform data fusion on the hardware platform of a stantion unit,which takes Field-Programmable Gate Array (FPGA) as the core component.In order to verify the effectiveness,five measurements including water level,discharge and velocity are selected from three different points in a water regime monitoring station.The simulation results show that this method can recitify random errors as well as gross errors significantly.

  3. Terahertz generation by optical rectification in uniaxial birefringent crystals

    Rowley, J D; Zawilski, K T; Schunemann, P G; Giles, N C; Bristow, A D

    2012-01-01

    The angular dependence of terahertz (THz) emission from birefringent crystals can differ significantly from that of cubic crystals. Here we consider optical rectification in uniaxial birefringent materials, such as chalcopyrite crystals. The analysis is verified in a (110)-cut ZnGeP2 and compared to (zincblende) GaP. Although the structures share the same nonzero second-order tensor elements, birefringence causes the pump pulse polarization to evolve as it propagates through the crystal, resulting in a drastically different angular dependence in chalcopyrite crystals. The analysis is extended to predict the response from {012}- and (114)-cut chalcopyrite crystals, revealing an increase in the maximum emission in comparison to (110)-cut crystals.

  4. Safety considerations for low temperature rectification of fission inert gases

    In a consideration of the risks of low temperature rectification of krypton from waste gas, the main point is the radiolytic formation of ozone, whose boiling point is nearly equal to that of xenon, in which it can be enriched. The explosion limit values of ozone in oxygen or in different dilutants (He, Ar, Kr, Xe, N2 and CCl2F2) and the speed and pressure of the stationary detonation of O3 in inert gases depending on the mol fraction O3/O2 were determined. The propagation of a detonation by a typical column filler, the effect of impurities (CH4, CO, NO2) on explosion and detonation and the phase equilibrium O3/Xe were also examined. (RB)

  5. Oscillating molecular dipoles require strongly correlated electronic and nuclear motion

    To create an oscillating electric dipole in an homonuclear diatomic cation without an oscillating driver one needs (i) to break the symmetry of the system and (ii) to sustain highly correlated electronic and nuclear motion. Based on numerical simulations in H2+ we present results for two schemes. In the first one (i) is achieved by creating a superposition of symmetric and antisymmetric electronic states freely evolving, while (ii) fails. In a second scheme, by preparing the system in a dressed state of a strong static field, both conditions hold. We then analyze the robustness of this scheme with respect to features of the nuclear wave function and its intrinsic sources of decoherence. (tutorial)

  6. Tuning intermetallic electronic coupling in polyruthenium systems via molecular architecture

    Sandeep Ghumaan; Goutam Kumar Lahiri

    2006-11-01

    A large number of polynuclear ruthenium complexes encompassing selective combinations of spacer (bridging ligand, BL) and ancillary (AL) functionalities have been designed. The extent of intermetallic electronic communication in mixed-valent states and the efficacy of the ligand frameworks towards the tuning of coupling processes have been scrutinised via structural, spectroelectrochemical, EPR, magnetic and theoretical investigations. Moreover, the sensitive oxidation state features in the complexes of non-innocent quinonoid bridging moieties have also been addressed.

  7. Multiple-electron removal and molecular fragmentation of CO by fast F4+ impact

    Multiple-electron removal from and molecular fragmentation of carbon monoxide molecules caused by collisions with 1-MeV/amu F4+ ions were studied using the coincidence time-of-flight technique. In these collisions, multiple-electron removal of the target molecule is a dominant process. Cross sections for the different levels of ionization of the CO molecule during the collision were determined. The relative cross sections of ionization decrease with increasing number of electrons removed in a similar way as seen in atomic targets. This behavior is in agreement with a two-step mechanism, where first the molecule is ionized by a Franck-Condon ionization and then the molecular ion dissociates. Most of the highly charged intermediate states of the molecule dissociate rapidly. Only CO+ and CO2+ molecular ions have been seen to survive long enough to be detected as molecular ions. The relative cross sections for the different breakup channels were evaluated for collisions in which the molecule broke into two charged fragments as well as for collisions where only a single charged molecular ion or fragment were produced. The average charge state of each fragment resulting from COQ+→Ci++Oj+ breakup increases with the number of electrons removed from the molecule approximately following the relationship bar i=bar j=Q/2 as long as K-shell electrons are not removed. This does not mean that the charge-state distribution is exactly symmetric, as, in general, removing electrons from the carbon fragment is slightly more likely than removing electrons from the oxygen due to the difference in binding energy. The cross sections for molecular breakup into a charged fragment and a neutral fragment drop rapidly with an increasing number of electrons removed

  8. Molecular control of electron and hole transfer processes: Theory and applications

    Newton, M.D. [Brookhaven National Lab., Upton, NY (United States). Dept. of Chemistry; Cave, R.J. [Harvey Mudd Coll., Claremont, CA (United States). Dept. of Chemistry

    1996-02-01

    Recent decades have seen remarkable advances in microscopic understanding of electron transfer (ET) processes in widely ranging contexts, including solid-state, liquid solution, and complex biological assemblies. The primary goal of this chapter is to report recent advances in the modeling, calculation, and analysis of electronic coupling in complex molecular aggregates, thereby allowing an assessment of current progress toward the goal of molecular-level control and design. The control of electron transfer kinetics (i.e., enhancing desired processes, while inhibiting others) involves, of course, system energetics (especially activation and reorganization energies) as well as electronic coupling, which is most directly relevant only after the system has reached the appropriate point (or region) along the reaction coordinate. Nevertheless, to focus the discussion in this chapter, the authors will consider such energetics, and the associated molecular and solvent coordinates which control then, only to the extent that they bear on the analysis of the electronic coupling. In the following sections they first discuss the formulation of basic ET models, including the definition of initial and final states, the role of orbitals and 1-particle models in a many-electron context, the utility of various effective Hamiltonians, and the role of vibronic as well as purely electronic effects. With these theoretical tools in hand, they then examine very recent applications to complex molecular systems using the techniques of computational quantum chemistry, followed by detailed analysis of the numerical results. They then conclude with some comments regarding the current ``state of the art`` and remaining challenges.

  9. Electronic transport through tape-porphyrin molecular bridges

    We investigated theoretically how molecular conjugation affects current-voltage (I-V) curves through three types of oligoporphyrin molecules, i.e., the tape-porphyrin, the butadiyne-linked porphyrin, and the edge-fused porphyrin molecules. Among these, the tape-porphyrin molecule is found to be the most conductive due to its extremely small HOMO-LUMO energy gap. Furthermore, the I-V curves through this type of molecule are found to depend considerably on atomic sites to which electrodes are connected. In particular, as long as the applied bias is weak, the current is found to flow strongest when both electrodes are connected to the atomic sites referred to as meso sites. This feature is caused by the fact that the HOMO relevant to resonant tunneling has a higher charge density on the meso sites. These findings indicate that designing not only molecules but also contact structures is highly significant for realizing a desirable function in single molecular devices

  10. A two-step rectification algorithm for airborne linear images with POS data

    TUO Hong-ya; LIU Yun-cai

    2005-01-01

    Rectification for airborne linear images is an indispensable preprocessing step. This paper presents in detail a two-step rectification algorithm. The first step is to establish the model of direct georeference position using the data provided by the Positioning and Orientation System (POS) and obtain the mathematical relationships between the image points and ground reference points. The second step is to apply polynomial distortion model and Bilinear Interpolation to get the final precise rectified images.In this step, a reference image is required and some ground control points (GCPs) are selected. Experiments showed that the final rectified images are satisfactory, and that our two-step rectification algorithm is very effective.

  11. Fluctuating-bias controlled electron transport in molecular junctions

    Ridley, Michael; MacKinnon, Angus; Kantorovich, Lev

    2016-05-01

    We consider the problem of transport through a multiterminal molecular junction in the presence of a stochastic bias, which can also be used to describe transport through fluctuating molecular energy levels. To describe these effects, we first make a simple extension of our previous work [Phys. Rev. B 91, 125433 (2015), 10.1103/PhysRevB.91.125433] to show that the problem of tunneling through noisy energy levels can be mapped onto the problem of a noisy driving bias, which appears in the Kadanoff-Baym equations for this system in an analogous manner to the driving term in the Langevin equation for a classical circuit. This formalism uses the nonequilibrium Green's function method to obtain analytically closed formulas for transport quantities within the wide-band limit approximation for an arbitrary time-dependent bias and it is automatically partition free. We obtain exact closed formulas for both the colored and white noise-averaged current at all times. In the long-time limit, these formulas possess a Landauer-Büttiker-type structure which enables the extraction of an effective transmission coefficient for the transport. Expanding the Fermi function into a series of simple poles, we find an exact formal relation between the parameters which characterize the bias fluctuations and the poles of the Fermi function. This enables us to describe the effect of the temperature and the strength of the fluctuations on the averaged current which we interpret as a quantum analog to the classical fluctuation-dissipation theorem. We use these results to convincingly refute some recent results on the multistability of the current through a fluctuating level, simultaneously verifying that our formalism satisfies some well-known theorems on the asymptotic current. Finally, we present numerical results for the current through a molecular chain which demonstrate a transition from nonlinear to linear I -V characteristics as the strength of fluctuations is increased, as well as a

  12. Molecular and electronic structure of osmium complexes confined to Au(111) surfaces using a self-assembled molecular bridge

    Llave, Ezequiel de la; Herrera, Santiago E.; Adam, Catherine; Méndez De Leo, Lucila P.; Calvo, Ernesto J.; Williams, Federico J., E-mail: fwilliams@qi.fcen.uba.ar [INQUIMAE-CONICET, Departamento de Química Inorgánica, Analítica y Química-Física, Facultad Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Buenos Aires C1428EHA (Argentina)

    2015-11-14

    The molecular and electronic structure of Os(II) complexes covalently bonded to self-assembled monolayers (SAMs) on Au(111) surfaces was studied by means of polarization modulation infrared reflection absorption spectroscopy, photoelectron spectroscopies, scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory calculations. Attachment of the Os complex to the SAM proceeds via an amide covalent bond with the SAM alkyl chain 40° tilted with respect to the surface normal and a total thickness of 26 Å. The highest occupied molecular orbital of the Os complex is mainly based on the Os(II) center located 2.2 eV below the Fermi edge and the LUMO molecular orbital is mainly based on the bipyridine ligands located 1.5 eV above the Fermi edge.

  13. Molecular and electronic structure of osmium complexes confined to Au(111) surfaces using a self-assembled molecular bridge

    de la Llave, Ezequiel; Herrera, Santiago E.; Adam, Catherine; Méndez De Leo, Lucila P.; Calvo, Ernesto J.; Williams, Federico J.

    2015-11-01

    The molecular and electronic structure of Os(II) complexes covalently bonded to self-assembled monolayers (SAMs) on Au(111) surfaces was studied by means of polarization modulation infrared reflection absorption spectroscopy, photoelectron spectroscopies, scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory calculations. Attachment of the Os complex to the SAM proceeds via an amide covalent bond with the SAM alkyl chain 40° tilted with respect to the surface normal and a total thickness of 26 Å. The highest occupied molecular orbital of the Os complex is mainly based on the Os(II) center located 2.2 eV below the Fermi edge and the LUMO molecular orbital is mainly based on the bipyridine ligands located 1.5 eV above the Fermi edge.

  14. Molecular and electronic structure of osmium complexes confined to Au(111) surfaces using a self-assembled molecular bridge

    The molecular and electronic structure of Os(II) complexes covalently bonded to self-assembled monolayers (SAMs) on Au(111) surfaces was studied by means of polarization modulation infrared reflection absorption spectroscopy, photoelectron spectroscopies, scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory calculations. Attachment of the Os complex to the SAM proceeds via an amide covalent bond with the SAM alkyl chain 40° tilted with respect to the surface normal and a total thickness of 26 Å. The highest occupied molecular orbital of the Os complex is mainly based on the Os(II) center located 2.2 eV below the Fermi edge and the LUMO molecular orbital is mainly based on the bipyridine ligands located 1.5 eV above the Fermi edge

  15. Electronic energy loss of slow projectiles evaluated by molecular orbital theory

    Based on the Firsov model of electronic excitations in slow atomic collisions, a method for calculations of the electronic energy loss is proposed. In this method, molecular orbital theory is employed in order to obtain the electronic excitation probability of a quasi-molecule between colliding atoms. By this method, the electronic stopping power has been calculated for the case of the Li-B and Li-Ta collision pairs. Using this calculated electronic stopping power, molecular dynamics simulations have been performed in order to analyze the energy loss observed in a recent experiment, in which 1-keV Li+ ions were scattered from a TaB2 (0 0 0 1) surface. These experimental observations are well explained by this theory

  16. Rectification in substituted atomic wires: a theoretical insight.

    Asai, Yoshihiro

    2012-04-25

    Recently, there have been discussions that the giant diode property found experimentally in diblock molecular junctions could be enhanced by the many-body electron correlation effect beyond the mean field theory. In addition, the effect of electron-phonon scattering on an electric current through the diode molecule, measured by inelastic tunneling spectroscopy (IETS), was found to be symmetric with respect to the voltage sign change even though the current is asymmetric. The reason for this behavior is a matter of speculation. In order to clarify whether or not this feature is limited to organic molecules in the off-resonant tunneling region, we discuss the current asymmetry effect on IETS in the resonant region. We introduced heterogeneous atoms into an atomic wire and found that IETS becomes asymmetric in this substituted atomic wire case. Our conclusion gives the other example of intrinsic differences between organic molecules and metallic wires. While the contribution of electron-phonon scattering to IETS is not affected by the current asymmetry in the former case, it is affected in the latter case. The importance of the contribution of the electron-hole excitation to phonon damping in bringing about the current asymmetry effect in IETS in the latter case is discussed. PMID:22466527

  17. Molecular and electronic structure of actinide hexa-cyanoferrates

    The goal of this work is to improve our knowledge on the actinide-ligand bond properties. To this end, the hexacyanoferrate entities have been used as pre-organized ligand. We have synthesized, using mild chemistry, the following series of complexes: AnIV[FeII(CN)6].xH2O (An = Th, U, Np, Pu); AmIII[FeIII(CN)6].xH2O; Pu III[CoIII(CN)6].xH2O and K(H?)AnIII[FeII(CN)6].xH2O (An = Pu, Am). The metal oxidation states have been obtained thanks to the νCN, stretching vibration and to the actinide LIII absorption edge studies. As Prussian Blue, the AnIV[FeII(CN)6].xH2O (An = Np, Pu) are class II of Robin and Day compounds. X-ray Diffraction has shown besides that these complexes crystallize in the P63/m space group, as the isomorphic LaKFe(CN)6.4H2O complex used as structural model. The EXAFS oscillations at the iron K edge and at the An LIII edge allowed to determine the An-N, An-O, Fe-C and Fe-N distances. The display of the multiple scattering paths for both edges explains the actinide contribution absence at the iron edge, whereas the iron signature is present at the actinide edge. We have shown that the actinide coordination sphere in actinides hexa-cyanoferrates is comparable to the one of lanthanides. However, the actinides typical behavior towards the lanthanides is brought to the fore by the AnIV versus LnIII ions presence in this family of complexes. Contrarily to the 4f electrons, the 5f electrons influence the electronic properties of the compounds of this family. However, the gap between the An-N and Ln-N distances towards the corresponding metals ionic radii do not show any covalence bond evolution between the actinide and lanthanide series. (author)

  18. Renormalized molecular levels in a Sc3N@C-80 molecular electronic device

    Larade, Brian; Taylor, Jeremy Philip; Zheng, Q. R.;

    2001-01-01

    We address several general questions about quantum transport through molecular systems by an ab initio analysis of a scandium-nitrogen doped C-80 metallofullerene device. Charge transfer from the Sc3N is found to drastically change the current-voltage characteristics: the current through the Sc3N...

  19. Electronic and transport properties of a molecular junction with asymmetric contacts

    Asymmetric molecular junctions have been shown experimentally to exhibit a dual-conductance transport property with a pulse-like current-voltage characteristic, by Reed and co-workers. Using a recently developed first-principles integrated piecewise thermal equilibrium current calculation method and a gold-benzene-1-olate-4-thiolate-gold model molecular junction, this unusual transport property has been reproduced. Analysis of the electrostatics and the electronic structure reveals that the high-current state results from subtle bias induced charge transfer at the electrode-molecule contacts that raises molecular orbital energies and enhances the current-contributing molecular density of states and the probabilities of resonance tunneling of conduction electrons from one electrode to another.

  20. Giant spatially-resolved self-assembled donor-acceptor molecular heterojunctions

    Guest, Jeffrey R.; Smerdon, Joseph A.; Giebink, Noel C.; Guisinger, Nathan P.; Darancet, Pierre

    Despite theoretical models predicting that rectification ratios (RR) >1000 should be achievable in molecular rectifiers, demonstrations of this have been rare. It has also been extremely challenging to unravel the structure-function relationships on the nanometer length scales that determine their behavior. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we show that RRs >1000 at biases molecule limit for self-assembled donor-acceptor bilayers of pentacene on C60 on Cu. We show that the system behaves as a molecular analog to a Schottky diode due to strong electronic coupling of C60 to the metallic substrate, and electronic transport is dominated by sequential tunneling from semiconducting pentacene to metallic C60. Furthermore, we demonstrate the extreme sensitivity of the low-bias I (V) characteristics to the molecularly-resolved structure of the heterojunction (HJ), which leads to negative differential resistance and ~ 100 × variation in the rectification ratio within 2 nm of the edge of the molecular HJ. Support was provided by the Department of Energy Office of Basic Energy Sciences (SISGR Grant DE-FG02-09ER16109).

  1. NATO Advanced Research Workshop on Vectorization of Advanced Methods for Molecular Electronic Structure

    1984-01-01

    That there have been remarkable advances in the field of molecular electronic structure during the last decade is clear not only to those working in the field but also to anyone else who has used quantum chemical results to guide their own investiga­ tions. The progress in calculating the electronic structures of molecules has occurred through the truly ingenious theoretical and methodological developments that have made computationally tractable the underlying physics of electron distributions around a collection of nuclei. At the same time there has been consider­ able benefit from the great advances in computer technology. The growing sophistication, declining costs and increasing accessibi­ lity of computers have let theorists apply their methods to prob­ lems in virtually all areas of molecular science. Consequently, each year witnesses calculations on larger molecules than in the year before and calculations with greater accuracy and more com­ plete information on molecular properties. We can surel...

  2. NATO Advanced Study Institute on Electronic Structure of Polymers and Molecular Crystals

    Ladik, János

    1975-01-01

    The NATO Advanced Study Institute on "Electronic Structure of Polymers and Molecular Crystals" was held at the Facultes Universi­ taires de Namur (F.U.N.) from September 1st till September 14th, 1974. We wish to express our appreciation to the NATO Scientific Affairs Division whose generous support made this Institute possible and to the Facultes Universitaires de Namur and the Societe Chimique de Belgique which provided fellowships and travel grants to a number of students. This volume contains the main lectures about the basic principles of the field and about different recent developments of the theory of the electronic structure of polymers and molecular crystals. The school started with the presentation of the basic SCF-LCAO theory of the electronic structure of periodic polymers and molecular crystals (contributions by Ladik, Andre & Delhalle) showing how a combination of quantum chemical and solid state physical methods can provide band structures for these systems. The numerical aspects of these ...

  3. Thermal rectification and negative differential thermal conductance in harmonic chains with nonlinear system-bath coupling

    Ming, Yi; Li, Hui-Min; Ding, Ze-Jun

    2016-03-01

    Thermal rectification and negative differential thermal conductance were realized in harmonic chains in this work. We used the generalized Caldeira-Leggett model to study the heat flow. In contrast to most previous studies considering only the linear system-bath coupling, we considered the nonlinear system-bath coupling based on recent experiment [Eichler et al., Nat. Nanotech. 6, 339 (2011), 10.1038/nnano.2011.71]. When the linear coupling constant is weak, the multiphonon processes induced by the nonlinear coupling allow more phonons transport across the system-bath interface and hence the heat current is enhanced. Consequently, thermal rectification and negative differential thermal conductance are achieved when the nonlinear couplings are asymmetric. However, when the linear coupling constant is strong, the umklapp processes dominate the multiphonon processes. Nonlinear coupling suppresses the heat current. Thermal rectification is also achieved. But the direction of rectification is reversed compared to the results of weak linear coupling constant.

  4. Food Safety Detection Methods Applied to National Special Rectification of Product Quality and Food Safety

    2007-01-01

    @@ Afour-month period of national special rectification for product quality and food safety officially started on August 25, and was focused on eight fields, including those of agricultural products and processed foods.

  5. First-Principles Simulations of Inelastic Electron Tunneling Spectroscopyof Molecular Junctions

    Jiang, Jun; Kula, Mathias; Lu, Wei; Luo, Yi

    2005-01-01

    A generalized Green's function theory is developed to simulate the inelastic electron tunneling spectroscopy (IETS) of molecular junctions. It has been applied to a realistic molecular junction with an octanedithiolate embedded between two gold contacts in combination with the hybrid density functional theory calculations. The calculated spectra are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is...

  6. Molecular fragmentation by recombination with cold electrons studied with a mass sensitive imaging detector

    Mendes, M

    2010-01-01

    The recombination of a molecular cation with a low-energy electron, followed by fragmentation, is a fundamental reaction process in cold and dilute plasmas. For polyatomic ions, it can yield molecular fragments in ro-vibrationally excited states. The discrimination between decay channels with chemically different fragments and the measurement of their excitation energies pose an experimental challenge. This work discusses a new experimental scheme based on fast beam fragment imaging in a stor...

  7. Electronic transport properties of a molecular switch with carbon nanotube electrodes: A first-principles study

    Zhao, P., E-mail: ss_zhaop@ujn.edu.c [School of Science, University of Jinan, Jinan 250022 (China); School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Wang, P.J.; Zhang, Z. [School of Science, University of Jinan, Jinan 250022 (China); Liu, D.S. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Department of Physics, Jining University, Qufu 273155 (China)

    2010-01-01

    We have studied the electronic transport properties of a new kind of optical molecular switch with two single-walled carbon nanotube (SWCNT) electrodes using first-principles transport calculations. It is shown that the enol form shows an overall higher conductance than the keto form at low-bias voltage, which is independent of the SWCNTs' chirality. Meantime, it is possible to tune the conductance of the molecular switch by changing the chirality of the SWCNTs.

  8. High-conductive organometallic molecular wires with delocalized electron systems strongly coupled to metal electrodes.

    Schwarz, Florian; Kastlunger, Georg; Lissel, Franziska; Riel, Heike; Venkatesan, Koushik; Berke, Heinz; Stadler, Robert; Lörtscher, Emanuel

    2014-10-01

    Besides active, functional molecular building blocks such as diodes or switches, passive components, for example, molecular wires, are required to realize molecular-scale electronics. Incorporating metal centers in the molecular backbone enables the molecular energy levels to be tuned in respect to the Fermi energy of the electrodes. Furthermore, by using more than one metal center and sp-bridging ligands, a strongly delocalized electron system is formed between these metallic "dopants", facilitating transport along the molecular backbone. Here, we study the influence of molecule-metal coupling on charge transport of dinuclear X(PP)2FeC4Fe(PP)2X molecular wires (PP = Et2PCH2CH2PEt2); X = CN (1), NCS (2), NCSe (3), C4SnMe3 (4), and C2SnMe3 (5) under ultrahigh vacuum and variable temperature conditions. In contrast to 1, which showed unstable junctions at very low conductance (8.1 × 10(-7) G0), 4 formed a Au-C4FeC4FeC4-Au junction 4' after SnMe3 extrusion, which revealed a conductance of 8.9 × 10(-3) G0, 3 orders of magnitude higher than for 2 (7.9 × 10(-6) G0) and 2 orders of magnitude higher than for 3 (3.8 × 10(-4) G0). Density functional theory (DFT) confirmed the experimental trend in the conductance for the various anchoring motifs. The strong hybridization of molecular and metal states found in the C-Au coupling case enables the delocalized electronic system of the organometallic Fe2 backbone to be extended over the molecule-metal interfaces to the metal electrodes to establish high-conductive molecular wires. PMID:25233125

  9. Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity.

    Hao, Yajiang; Inhester, Ludger; Hanasaki, Kota; Son, Sang-Kil; Santra, Robin

    2015-07-01

    We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL) pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging. PMID:26798806

  10. Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity

    Hao, Yajiang; Hanasaki, Kota; Son, Sang-Kil; Santra, Robin

    2015-01-01

    We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL) pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging.

  11. Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity

    Yajiang Hao

    2015-07-01

    Full Text Available We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging.

  12. Distant electron tunneling controlled by external fields in molecular nano structures

    The influence of stochastic, periodic, and magnetic fields on a long-range electron tunneling in donor - bridge - acceptor and electrode - molecular wire - electrode structures is studied theoretically. The description of a bridge-mediated electron tunneling between donor and acceptor groups is shown to be possible via the introduction of effective transfer rates. The principal distinction in the dependence of low-temperature elastic and inelastic tunnel currents mediated by a molecular wire with bridging paramagnetic ions on an applied magnetic field is considered. The appearance of the field-induced inversion and suppression effects is widely discussed

  13. Molecular-scale imaging of unstained deoxyribonucleic acid fibers by phase transmission electron microscopy

    The molecular structure of deoxyribonucleic acid (DNA) fibers was observed by a phase reconstruction method called three-dimensional Fourier filtering using a 200 kV transmission electron microscope. The characteristic helical structure and the spacing of adjacent base pairs of DNA were partially resolved due to an improved signal-to-noise ratio and resolution enhancement by the phase reconstruction although the molecular structure was damaged by the electron beam irradiation. In the spherical aberration-free phase images, the arrangements of single atom-sized spots forming sinusoidal curves were sometimes observed, which seem to be the contrast originating in the sulfur atoms along the main chains

  14. Electronic absorption spectra and nonlinear optical properties of CO2 molecular aggregates: A quantum chemical study

    Tarun K Mandal; Sudipta Dutta; Swapan K Pati

    2009-09-01

    We have investigated the structural aspects of several carbon dioxide molecular aggregates and their spectroscopic and nonlinear optical properties within the quantum chemical theory framework. We find that, although the single carbon dioxide molecule prefers to be in a linear geometry, the puckering of angles occur in oligomers because of the intermolecular interactions. The resulting dipole moments reflect in the electronic excitation spectra of the molecular assemblies. The observation of significant nonlinear optical properties suggests the potential application of the dense carbon dioxide phases in opto-electronic devices.

  15. Current rectification in a single molecule diode: the role of electrode coupling

    Sherif, Siya; Rubio-Bollinger, G.; Pinilla-Cienfuegos, E.; Coronado, E.; Cuevas, J. C.; Agrait, Nicolas

    2015-01-01

    We demonstrate large rectification ratios (> 100) in single-molecule junctions based on a metal-oxide cluster (polyoxometalate), using a scanning tunneling microscope (STM) both at ambient conditions and at low temperature. These rectification ratios are the largest ever observed in a single-molecule junction, and in addition these junctions sustain current densities larger than 10^5 A/cm^2. By following the variation of the I-V characteristics with tip-molecule separation we demonstrate unam...

  16. Electronic and magnetic properties of silicon supported organometallic molecular wires: a density functional theory (DFT) study

    Liu, Xia; Tan, Yingzi; Li, Xiuling; Wu, Xiaojun; Pei, Yong

    2015-08-01

    The electronic and magnetic properties of transition metal (TM = Sc, Ti, V, Cr and Mn) atom incorporated single and double one-dimensional (1D) styrene molecular wires confined on the hydrogen-terminated Si(100) surface are explored for the first time by means of spin-polarized density functional theory, denoted as Si-[TM(styrene)]. It is unveiled that TM atoms bind asymmetrically to the adjacent phenyl rings, which leads to novel electronic and magnetic properties in stark contrast to the well-studied gas phase TM-benzene molecular wires. Si-[Mn(styrene)]∞ and Si-[Cr(styrene)]∞ single molecular wires (SMWs) are a ferromagnetic semiconductor and half metal, respectively. Creation of H-atom defects on the silicon surface can introduce an impurity metallic band, which leads to novel half-metallic magnetism of a Si-[Mn(styrene)]∞ system. Moreover, double molecular wires (DMWs) containing two identical or hetero SMWs are theoretically designed. The [Mn(styrene)]∞-[Cr(styrene)]∞ DMW exhibits half-metallic magnetism where the spin-up and spin-down channels are contributed by two single molecular wires. Finally, we demonstrate that introducing a TM-defect may significantly affect the electronic structure and magnetic properties of molecular wires. These studies provide new insights into the structure and properties of surface supported 1-D sandwiched molecular wires and may inspire the future experimental synthesis of substrate confined organometallic sandwiched molecular wires.The electronic and magnetic properties of transition metal (TM = Sc, Ti, V, Cr and Mn) atom incorporated single and double one-dimensional (1D) styrene molecular wires confined on the hydrogen-terminated Si(100) surface are explored for the first time by means of spin-polarized density functional theory, denoted as Si-[TM(styrene)]. It is unveiled that TM atoms bind asymmetrically to the adjacent phenyl rings, which leads to novel electronic and magnetic properties in stark contrast to

  17. Spin-polarized Inelastic Electron Tunneling Spectroscopy of Molecular Magnetic Tunnel Junctions

    In this study, we fabricate molecular magnetic tunnel junctions and demonstrate that inelastic electron tunneling spectroscopy technique can be utilized to inspect such junctions to investigate the existence of desired molecular species in the device area. Tunneling magnetoresistance measurements have been carried out and spin-dependent tunneling transport has been observed. Bias-dependence of the tunneling resistance has also been detected. IETS measurements at different magnetic field suggested that the TMR bias-dependence was likely caused by the inelastic scattering due to the molecular vibrations

  18. Electron induced conformational changes of imine-based molecular switches on a Au(111) surface

    Lotze, Christian; Pascual, Jose Ignacio [Inst. f. Experimentalphysik, Freie Universitaet Berlin (Germany); Luo, Ying; Haag, Rainer [Inst. f. Organische Chemie, Freie Universitaet Berlin (Germany)

    2010-07-01

    Organic molecules exhibiting controllable reversible transitions between isomeric states on surfaces promise an enormous potential in the field of molecular electronics. The reversible cis-trans isomerization of azobenzene-like molecules is often hindered by a strong interaction of the nitrogen lone-pair electrons of the di-azo bridge (-N=N-) with the substrate. In order to improve the isomerization capabilities, the di-azo bridge is substituted by an imine-group (-N=CH-). Here, we use low-temperature scanning tunneling microscopy to investigate a sub-monolayer of the newly designed imine-based molecular switch NPCI on a Au(111) surface. Its carboxylic termination mediates the formation of hydrogen-bonded dimers, which align in rows along the herringbone reconstruction. We were able to induce reversible conformational changes with the tunneling electrons from the STM tip and determine its efficiency as a function of electron energy.

  19. Participation of Low Molecular Weight Electron Carriers in Oxidative Protein Folding

    József Mandl

    2009-03-01

    Full Text Available Oxidative protein folding is mediated by a proteinaceous electron relay system, in which the concerted action of protein disulfide isomerase and Ero1 delivers the electrons from thiol groups to the final acceptor. Oxygen appears to be the final oxidant in aerobic living organisms, although the existence of alternative electron acceptors, e.g. fumarate or nitrate, cannot be excluded. Whilst the protein components of the system are well-known, less attention has been turned to the role of low molecular weight electron carriers in the process. The function of ascorbate, tocopherol and vitamin K has been raised recently. In vitro and in vivo evidence suggests that these redox-active compounds can contribute to the functioning of oxidative folding. This review focuses on the participation of small molecular weight redox compounds in oxidative protein folding.

  20. Rectification of the EMG is an unnecessary and inappropriate step in the calculation of Corticomuscular coherence.

    McClelland, Verity M; Cvetkovic, Zoran; Mills, Kerry R

    2012-03-30

    Corticomuscular coherence (CMC) estimation is a frequency domain method used to detect a linear coupling between rhythmic activity recorded from sensorimotor cortex (EEG or MEG) and the electromyogram (EMG) of active muscles. In motor neuroscience, rectification of the surface EMG is a common pre-processing step prior to calculating CMC, intended to maximize information about action potential timing, whilst suppressing information relating to motor unit action potential (MUAP) shape. Rectification is believed to produce a general shift in the EMG spectrum towards lower frequencies, including those around the mean motor unit discharge rate. However, there are no published data to support the claim that EMG rectification enhances the detection of CMC. Furthermore, performing coherence analysis after the non-linear procedure of rectification, which results in a significant distortion of the EMG spectrum, is considered fundamentally flawed in engineering and digital signal processing. We calculated CMC between sensorimotor cortex EEG and EMG of two hand muscles during a key grip task in 14 healthy subjects. CMC calculated using unrectified and rectified EMG was compared. The use of rectified EMG did not enhance the detection of CMC, nor was there any evidence that MUAP shape information had an adverse effect on the CMC estimation. EMG rectification had inconsistent effects on the power and coherence spectra and obscured the detection of CMC in some cases. We also provide a comprehensive theoretical analysis, which, along with our empirical data, demonstrates that rectification is neither necessary nor appropriate in the calculation of CMC. PMID:22120690

  1. Isomorphic classical molecular dynamics model for an excess electron in a supercritical fluid

    Miller III, Thomas F.

    2009-01-01

    Ring polymer molecular dynamics (RPMD) is used to directly simulate the dynamics of an excess electron in a supercritical fluid over a broad range of densities. The accuracy of the RPMD model is tested against numerically exact path integral statistics through the use of analytical continuation techniques. At low fluid densities, the RPMD model substantially underestimates the contribution of delocalized states to the dynamics of the excess electron. However, with increasing solvent density, ...

  2. Reduced Density Matrix Approach to the Laser-Assisted Electron Transport in Molecular Wires

    Welack, Sven

    2006-01-01

    The electron transport through a molecular wire under the influence of an external laser field is studied using a reduced density matrix formalism. The full system is partitioned into the relevant part, i.e. the wire, electron reservoirs and a phonon bath. An earlier second-order perturbation theory approach of Meier and Tannor for bosonic environments which employs a numerical decomposition of the spectral density is used to describe the coupling to the phonon bath and is ex...

  3. Studies on Electronic Charge of the Hydrogen Bond Proton in Model Molecular Systems

    Henryk Chojnacki

    2003-01-01

    Abstract: The population analysis of the hydrogen bond atoms was analyzed within the different basis sets for model molecular systems for the ground and low-lying excited electronic states. The Mulliken, Lőwdin and Hirshfeld methods were used in our investigations. It has been shown that normally the proton is transferred, however, in some excited electronic states the hydrogen atom displacement might be responsible for the tautomeric interconversion.

  4. The Electronic Structure of Organic Molecular Materials : Theoretical and Spectroscopic Investigations

    Brumboiu, Iulia Emilia

    2014-01-01

    In the present thesis the electronic properties of two organic molecules were studied by means of density functional theory (DFT) in connection to their possible applications in organic photovoltaics and molecular spintronics respectively. The first analysed system is the C60 derivative PCBM extensively used in polymer solar cells for the charge separation process. Since fullerenes have been shown to undergo modifications as a result of light exposure, investigating their electronic structure...

  5. EMBEDDED MOLECULAR CLUSTER APPROACH TO THE ELECTRONIC STRUCTURE OF AMORPHOUS AND LIQUID METALS

    Delley, B.; Ellis, D.; Freeman, A

    1980-01-01

    In this approach to the electronic structure of amorphous and liquid metals, we represent the system by molecular clusters which are embedded in an external potential chosen as a suitable representation of the rest of the system. We have determined the electronic structure of a number of Cu, Zr and Cu-Zr clusters using the self-consistent discrete variational-LCAO approach within local density functional theory. Effects due to deviations from perfect crystalline symmetry are analyzed. Total d...

  6. Atomic and molecular photoelectron and Auger-electron-spectroscopy studies using synchrotron radiation

    Electron spectroscopy, combined with synchrotron radiation, was used to measure the angular distributions of photoelectrons and Auger electrons from atoms and molecules as functions of photon energy. The branching ratios and partial cross sections were also measured in certain cases. By comparison with theoretical calculations, the experimental results are interpreted in terms of the characteristic electronic structure and ionization dynamics of the atomic or molecular sample. The time structure of the synchrotron radiation source was used to record time-of-flight (TOF) spectra of the ejected electrons. The double-angle-TOF method for the measurement of photoelectron angular distributions is discussed. This technique offers the advantages of increased electron collection efficiency and the elimination of certain systematic errors. An electron spectroscopy study of inner-shell photoexcitation and ionization of Xe, photoelectron angular distributions from H2 and D2, and photoionization cross sections and photoelectron asymmetries of the valence orbitals of NO are reported

  7. An electron-accepting molecular unit exhibiting an orientational preference favorable for organic photovoltaic applications

    Control of molecular orientation of organic semiconductor is essential for efficient light absorption and charge-carrier transport in organic optoelectronic devices. We synthesized compound 1 as a fundamental electron-accepting building block for the design of n-type semiconductors and conducting polymers. We found that this molecule, upon evaporation onto a substrate such as SiO2 and electron-donor films, spontaneously assembles with a face-on orientation relative to the substrate surface. This orientation is favorable for thin-film organic photovoltaics. Despite relatively small π-conjugation, 1 showed strong absorption in visible-light region and an appropriate lowest unoccupied molecular orbital energy for electron transfer with electron donors including copper phthalocyanine and poly(3-hexylthiophene). Accordingly, thin-film devices, fabricated using 1 and electron donors, exhibited a clear photovoltaic response. This suggests that compound 1 provides a promising building block for the development of active materials in organic photovoltaics. - Highlights: • An electron acceptor (1) featuring an indacenetetraone core was designed. • Acceptor 1 exhibits strong electronic absorption in visible-light region. • Acceptor 1 spontaneously adopts face-on orientation on SiO2 and organic substrates. • Thin film of 1 shows an n-type semiconducting property. • Electron donor/1 bilayer films display a clear photovoltaic response

  8. An electron-accepting molecular unit exhibiting an orientational preference favorable for organic photovoltaic applications

    Akaike, Kouki, E-mail: kakaike@physik.hu-berlin.de [RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Ando, Shinji; Enozawa, Hideo [RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Kosaka, Atsuko; Kajitani, Takashi [RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8503 (Japan); Fukushima, Takanori, E-mail: fukushima@res.titech.ac.jp [RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8503 (Japan)

    2015-05-29

    Control of molecular orientation of organic semiconductor is essential for efficient light absorption and charge-carrier transport in organic optoelectronic devices. We synthesized compound 1 as a fundamental electron-accepting building block for the design of n-type semiconductors and conducting polymers. We found that this molecule, upon evaporation onto a substrate such as SiO{sub 2} and electron-donor films, spontaneously assembles with a face-on orientation relative to the substrate surface. This orientation is favorable for thin-film organic photovoltaics. Despite relatively small π-conjugation, 1 showed strong absorption in visible-light region and an appropriate lowest unoccupied molecular orbital energy for electron transfer with electron donors including copper phthalocyanine and poly(3-hexylthiophene). Accordingly, thin-film devices, fabricated using 1 and electron donors, exhibited a clear photovoltaic response. This suggests that compound 1 provides a promising building block for the development of active materials in organic photovoltaics. - Highlights: • An electron acceptor (1) featuring an indacenetetraone core was designed. • Acceptor 1 exhibits strong electronic absorption in visible-light region. • Acceptor 1 spontaneously adopts face-on orientation on SiO{sub 2} and organic substrates. • Thin film of 1 shows an n-type semiconducting property. • Electron donor/1 bilayer films display a clear photovoltaic response.

  9. Intense electron beams from GaAs photocathodes as a tool for molecular and atomic physics

    Krantz, Claude

    2009-10-28

    We present cesium-coated GaAs photocathodes as reliable sources of intense, quasi-monoenergetic electron beams in atomic and molecular physics experiments. In long-time operation of the Electron Target of the ion storage ring TSR in Heidelberg, cold electron beams could be realised at steadily improving intensity and reliability. Minimisation of processes degrading the quantum efficiency allowed to increase the extractable current to more than 1mA at usable cathode lifetimes of 24 h or more. The benefits of the cold electron beam with respect to its application to electron cooling and electron-ion recombination experiments are discussed. Benchmark experiments demonstrate the superior cooling force and energy resolution of the photoelectron beam compared to its thermionic counterparts. The long period of operation allowed to study the long-time behaviour of the GaAs samples during multiple usage cycles at the Electron Target and repeated in-vacuum surface cleaning by atomic hydrogen exposure. An electron emission spectroscopy setup has been implemented at the photocathode preparation chamber of the Electron Target. Among others, this new facility opened the way to a novel application of GaAs (Cs) photocathodes as robust, ultraviolet-driven electron emitters. Based on this principle, a prototype of an electron gun, designed for implementation at the HITRAP setup at GSI, has been built and taken into operation successfully. (orig.)

  10. Intense electron beams from GaAs photocathodes as a tool for molecular and atomic physics

    We present cesium-coated GaAs photocathodes as reliable sources of intense, quasi-monoenergetic electron beams in atomic and molecular physics experiments. In long-time operation of the Electron Target of the ion storage ring TSR in Heidelberg, cold electron beams could be realised at steadily improving intensity and reliability. Minimisation of processes degrading the quantum efficiency allowed to increase the extractable current to more than 1mA at usable cathode lifetimes of 24 h or more. The benefits of the cold electron beam with respect to its application to electron cooling and electron-ion recombination experiments are discussed. Benchmark experiments demonstrate the superior cooling force and energy resolution of the photoelectron beam compared to its thermionic counterparts. The long period of operation allowed to study the long-time behaviour of the GaAs samples during multiple usage cycles at the Electron Target and repeated in-vacuum surface cleaning by atomic hydrogen exposure. An electron emission spectroscopy setup has been implemented at the photocathode preparation chamber of the Electron Target. Among others, this new facility opened the way to a novel application of GaAs (Cs) photocathodes as robust, ultraviolet-driven electron emitters. Based on this principle, a prototype of an electron gun, designed for implementation at the HITRAP setup at GSI, has been built and taken into operation successfully. (orig.)

  11. Far-infra-red molecular vibrational spectroscopy by inelastic electron tunneling

    In this paper the far infrared vibrational spectrum of polyvinyl-formate is reported as can be obtained by an inelastic electron tunneling experiment. The results here described as compared with those previously known from the current literature show that the afore mentioned technique can improve molecular spectroscopy data both as the covered energy range and resolution

  12. IR-MALDI OF LOW MOLECULAR WEIGHT COMPOUNDS USING A FREE ELECTRON LASER.

    Initial experiments on infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI) using a free electron laser in the analysis of low-molecular-weight compounds are reported. Mass spectra from samples of ethylenediaminetetraacetic acid (EDTA), nitrilotriacet...

  13. Theory of High Frequency Rectification by Silicon Crystals

    Bethe, H. A.

    1942-10-29

    The excellent performance of British "red dot" crystals is explained as due to the knife edge contact against a polished surface. High frequency rectification depends critically on the capacity of the rectifying boundary layer of the crystal, C. For high conversion efficiency, the product of this capacity and of the "forward" (bulk) resistance R {sub b} of the crystal must be small. For a knife edge, this product depends primarily on the breadth of the knife edge and very little upon its length. The contact can therefore have a rather large area which prevents burn-out. For a wavelength of 10 cm. the computations show that the breadth of the knife edge should be less than about 10 {sup -3} cm. For a point contact the radius must be less than 1.5 x 10 {sup -3} cm. and the resulting small area is conducive to burn-out. The effect of "tapping" is probably to reduce the area of contact. (auth)

  14. High rectification in organic diodes based on liquid crystalline phthalocyanines.

    Apostol, Petru; Eccher, Juliana; Dotto, Marta Elisa Rosso; Costa, Cassiano Batesttin; Cazati, Thiago; Hillard, Elizabeth A; Bock, Harald; Bechtold, Ivan H

    2015-12-28

    The optical and electrical properties of mesogenic metal-free and metalated phthalocyanines (PCs) with a moderately sized and regioregular alkyl periphery were investigated. In solution, the individualized molecules show fluorescence lifetimes of 4-6 ns in THF. When deposited as solid thin films the materials exhibit significantly shorter fluorescence lifetimes with bi-exponential decay (1.4-1.8 ns; 0.2-0.4 ns) that testify to the formation of aggregates viaπ-π intermolecular interactions. In diode structures, their pronounced columnar order outbalances the unfavorable planar alignment and leads to excellent rectification behavior. Field-dependent charge carrier mobilities are obtained from the J-V curves in the trap-limited space-charge-limited current regime and demonstrate that the metalated PCs display an improved electrical response with respect to the metal-free homologue. The excited-state lifetime characterization suggest that the π-π intermolecular interactions are stronger for the metal-free PC, confirming that the metallic centre plays an important role in the charge transport inside these materials. PMID:26585027

  15. Heat flux distribution and rectification of complex networks

    Liu, Zonghua; Wu, Xiang; Yang, Huijie; Gupte, Neelima; Li, Baowen

    2010-02-01

    It was recently found that the heterogeneity of complex networks can enhance transport properties such as epidemic spreading, electric energy transfer, etc. A trivial deduction would be that the presence of hubs in complex networks can also accelerate the heat transfer although no concrete research has been done so far. In the present study, we have studied this problem and have found a surprising answer: the heterogeneity does not favor but prevents the heat transfer. We present a model to study heat conduction in complex networks and find that the network topology greatly affects the heat flux. The heat conduction decreases with the increase of heterogeneity of the network caused by both degree distribution and the clustering coefficient. Its underlying mechanism can be understood by using random matrix theory. Moreover, we also study the rectification effect and find that it is related to the degree difference of the network, and the distance between the source and the sink. These findings may have potential applications in real networks, such as nanotube/nanowire networks and biological networks.

  16. Heat flux distribution and rectification of complex networks

    It was recently found that the heterogeneity of complex networks can enhance transport properties such as epidemic spreading, electric energy transfer, etc. A trivial deduction would be that the presence of hubs in complex networks can also accelerate the heat transfer although no concrete research has been done so far. In the present study, we have studied this problem and have found a surprising answer: the heterogeneity does not favor but prevents the heat transfer. We present a model to study heat conduction in complex networks and find that the network topology greatly affects the heat flux. The heat conduction decreases with the increase of heterogeneity of the network caused by both degree distribution and the clustering coefficient. Its underlying mechanism can be understood by using random matrix theory. Moreover, we also study the rectification effect and find that it is related to the degree difference of the network, and the distance between the source and the sink. These findings may have potential applications in real networks, such as nanotube/nanowire networks and biological networks.

  17. First-principles study of the electronic and molecular structure of protein nanotubes

    Okamoto, Hajime; Takeda, Kyozaburo; Shiraishi, Kenji

    2001-09-01

    The electronic and molecular structures of protein nanotubes (PNT's) have been investigated theoretically by first-principles electronic structure calculations. The results have been discussed in comparison to those of the polypeptide open chains (POC's) and polypeptide closed rings (PCR's) in order to give a systematic understanding. Focusing on the intra-ring and inter-ring hydrogen bonds (HB's), we also investigate the PCR stacking mechanism. The present calculation reveals that PNT's are semiconductors and that an extra proton in the tube interior has the potential to be an electron acceptor.

  18. In vivo demonstration of injectable microstimulators based on charge-balanced rectification of epidermically applied currents

    Ivorra, Antoni; Becerra-Fajardo, Laura; Castellví, Quim

    2015-12-01

    Objective. It is possible to develop implantable microstimulators whose actuation principle is based on rectification of high-frequency (HF) current bursts supplied through skin electrodes. This has been demonstrated previously by means of devices consisting of a single diode. However, previous single diode devices caused dc currents which made them impractical for clinical applications. Here flexible thread-like stimulation implants which perform charge balance are demonstrated in vivo. Approach. The implants weigh 40.5 mg and they consist of a 3 cm long tubular silicone body with a diameter of 1 mm, two electrodes at opposite ends, and, within the central section of the body, an electronic circuit made up of a diode, two capacitors, and a resistor. In the present study, each implant was percutaneously introduced through a 14 G catheter into either the gastrocnemius muscle or the cranial tibial muscle of a rabbit hindlimb. Then stimulation was performed by delivering HF bursts (amplitude intramuscular stimulation implants ever assayed in vertebrates.

  19. Rectification of terahertz radiation in semiconductor superlattices in the absence of domains

    We study theoretically the dynamical rectification of a terahertz AC electric field, i.e. the DC current and voltage response to the incident radiation, in strongly coupled semiconductor superlattices. We address the problem of stability against electric field domains: a spontaneous DC voltage is known to appear exactly for parameters for which a spatially homogeneous electron distribution is unstable. We show that by applying a weak direct current bias the rectifier can be switched from a state with zero DC voltage to one with a finite voltage in full absence of domains. The switching occurs near the conditions of dynamical symmetry breaking of an unbiased semiconductor superlattice. Therefore our scheme allows for the generation of DC voltages that would otherwise be unreachable due to domain instabilities. Furthermore, for realistic, highly doped wide miniband superlattices at room temperature, the generated DC field can be nearly quantized, that is, be approximately proportional to an integer multiple of ħω/ea where a is the superlattice period and ω is the AC field frequency. (paper)

  20. Probing Flexibility in Porphyrin-Based Molecular Wires Using Double Electron Electron Resonance

    Lovett, Janet E.; Hoffmann, Markus; Cnossen, Arjen; Shutter, Alexander T. J.; Hogben, Hannah J.; Warren, John E; Pascu, Sofia I.; Kay, Christopher W. M.; Timmel, Christiane R.; Anderson, Harry L.

    2009-01-01

    A series of butadiyne-linked zinc porphyrin oligomers, with one, two, three, and four porphyrin units and lengths of up to 75 angstrom, have been spin-labeled at both ends with stable nitroxide TEMPO radicals. The pulsed EPR technique of double electron electron resonance (DEER) was used to probe the distribution of intramolecular end-to-end distances, under a range of conditions. DEER measurements were carried out at 50 K in two types of dilute solution glasses: deutero-toluene (with 10% deu...

  1. Photoelectron and UV absorption spectroscopy for determination of electronic configurations of negative molecular ions: Chlorophenols

    Tseplin, E.E. [Institute of Molecular and Crystal Physics, Ufa Research Centre, Russian Academy of Sciences, October Prospect 151, Ufa 450075 (Russian Federation)], E-mail: tzeplin@mail.ru; Tseplina, S.N.; Tuimedov, G.M.; Khvostenko, O.G. [Institute of Molecular and Crystal Physics, Ufa Research Centre, Russian Academy of Sciences, October Prospect 151, Ufa 450075 (Russian Federation)

    2009-04-15

    The photoelectron and UV absorption spectra of p-, m-, and o-chlorophenols in the gas phase have been obtained. On the basis of DFT B3LYP/6-311++G(d, p) calculations, the photoelectron bands have been assigned to occupied molecular orbitals. From the TDDFT B3LYP/6-311++G(d, p) calculation results, the UV absorption bands have been assigned to excited singlet states of the molecules under investigation. For each excited state a dominant transition was found. It has been shown that the energies of these singlet transitions correlate with the energy differences between the ground-state molecular orbitals participating in them. Using the UV spectra interpretation, the electronic states of molecular anions detected earlier for the same compounds by means of the resonant electron capture mass-spectrometry have been determined.

  2. Ab initio analysis of electron-phonon coupling in molecular devices.

    Sergueev, N; Roubtsov, D; Guo, Hong

    2005-09-30

    We report a first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. Using a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two aluminum leads as an example, we analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. We find that the low-lying modes are most important. As a function of bias voltage, the electron-phonon coupling strength can change drastically while the vibrational spectrum changes at a few percent level. PMID:16241682

  3. Carbon Nanotube Based Molecular Electronics and Motors: A View from Classical and Quantum Dynamics Simulations

    Srivastava, Deepak; Saini, Subhash (Technical Monitor)

    1998-01-01

    The tubular forms of fullerenes popularly known as carbon nanotubes are experimentally produced as single-, multiwall, and rope configurations. The nanotubes and nanoropes have shown to exhibit unusual mechanical and electronic properties. The single wall nanotubes exhibit both semiconducting and metallic behavior. In short undefected lengths they are the known strongest fibers which are unbreakable even when bent in half. Grown in ropes their tensile strength is approximately 100 times greater than steel at only one sixth the weight. Employing large scale classical and quantum molecular dynamics simulations we will explore the use of carbon nanotubes and carbon nanotube junctions in 2-, 3-, and 4-point molecular electronic device components, dynamic strength characterization for compressive, bending and torsional strains, and chemical functionalization for possible use in a nanoscale molecular motor. The above is an unclassified material produced for non-competitive basic research in the nanotechnology area.

  4. Ultrafast Electron Transfer at Organic Semiconductor Interfaces: Importance of Molecular Orientation

    Ayzner, Alexander L.

    2015-01-02

    © 2014 American Chemical Society. Much is known about the rate of photoexcited charge generation in at organic donor/acceptor (D/A) heterojunctions overaged over all relative arrangements. However, there has been very little experimental work investigating how the photoexcited electron transfer (ET) rate depends on the precise relative molecular orientation between D and A in thin solid films. This is the question that we address in this work. We find that the ET rate depends strongly on the relative molecular arrangement: The interface where the model donor compound copper phthalocyanine is oriented face-on with respect to the fullerene C60 acceptor yields a rate that is approximately 4 times faster than that of the edge-on oriented interface. Our results suggest that the D/A electronic coupling is significantly enhanced in the face-on case, which agrees well with theoretical predictions, underscoring the importance of controlling the relative interfacial molecular orientation.

  5. Full two-electron calculations of antiproton collisions with molecular hydrogen

    Lühr, Armin Christian; Saenz, Alejandro

    2010-01-01

    Total cross sections for single ionization and excitation of molecular hydrogen by antiproton impact are presented over a wide range of impact energies from 1 keV to 6.5 MeV. A nonperturbative time-dependent close-coupling method is applied to fully treat the correlated dynamics of the electrons...... is demonstrated. The present findings provide benchmark results which might be useful for the development of molecular models........ Good agreement is obtained between the present calculations and experimental measurements of single-ionization cross sections at high energies, whereas some discrepancies with the experiment are found around the maximum. The importance of the molecular geometry and a full two-electron description...

  6. Secondary electron emission from Au by medium energy atomic and molecular ions

    Itoh, A; Obata, F; Hamamoto, Y; Yogo, A

    2002-01-01

    Number distributions of secondary electrons emitted from a Au metal surface have been measured for atomic and molecular ions of H sup + , He sup + , C sup + , N sup + , O sup + , H sup + sub 2 , H sup + sub 3 , HeH sup + , CO sup + and O sup + sub 2 in the energy range 0.3-2.0 MeV. The emission statistics obtained are described fairly well by a Polya function. The Polya parameter b, determining the distribution shape, is found to decrease monotonously with increasing emission yield gamma, revealing a surprising relationship of b gamma approx 1 over the different projectile species and impact energies. This finding supports certainly the electron cascading model. Also we find a strong negative molecular effect for heavier molecular ions, showing a significant reduction of gamma compared to the estimated values using constituent atomic projectile data.

  7. Molecular Conduction through Adlayers: Cooperative Effects can Help or Hamper Electron Transport

    We use a one-electron, tight-binding model of a molecular adlayer sandwiched between two metal electrodes to explore how cooperative effects between molecular wires influence electron transport through the adlayer. When compared to an isolated molecular wire, an adlayer exhibits cooperative effects that generally enhance conduction away from an isolated wire s resonance and diminish conductance near such a resonance. We also find that the interwire distance (related to the adlayer density) is a key quantity. Substrate-mediated coupling induces most of the cooperative effects in dense adlayers, whereas direct, interwire coupling (if present) dominates in sparser adlayers. In this manner, cooperative effects through dense adlayers cannot be removed, suggesting an optimal adlayer density for maximizing conduction.

  8. Charge transmission through a molecular wire: the role of terminal sites for the current-voltage behavior.

    Petrov, E G; Zelinskyy, Ya R; May, V; Hänggi, P

    2007-08-28

    The current-voltage and the conductance-voltage characteristics are analyzed for a particular type of molecular wire embedded between two electrodes. The wire is characterized by internal molecular units where the lowest occupied molecular orbital (LUMO) levels are positioned much above the Fermi energy of the electrodes, as well as above the LUMO levels of the terminal wire units. The latter act as specific intermediate donor and acceptor sites which in turn control the current formation via the superexchange and sequential electron transfer mechanisms. According to the chosen wire structure, intramolecular multiphonon processes may block the superexchange component of the interelectrode current, resulting in a negative differential resistance of the molecular wire. A pronounced current rectification appears if (i) the superexchange component dominates the electron transfer between the terminal sites and if (ii) the multiphonon suppression of distant superexchange charge hopping events between those sites is nonsymmetric. PMID:17764286

  9. Efficient electronic coupling and improved stability with dithiocarbamate-based molecular junctions

    von Wrochem, Florian; Gao, Deqing; Scholz, Frank; Nothofer, Heinz-Georg; Nelles, Gabriele; Wessels, Jurina M.

    2010-08-01

    Molecular electronic devices require stable and highly conductive contacts between the metal electrodes and molecules. Thiols and amines are widely used to attach molecules to metals, but they form poor electrical contacts and lack the robustness required for device applications. Here, we demonstrate that dithiocarbamates provide superior electrical contact and thermal stability when compared to thiols on metals. Ultraviolet photoelectron spectroscopy and density functional theory show the presence of electronic states at 0.6 eV below the Fermi level of Au, which effectively reduce the charge injection barrier across the metal-molecule interface. Charge transport measurements across oligophenylene monolayers reveal that the conductance of terphenyl-dithiocarbamate junctions is two orders of magnitude higher than that of terphenyl-thiolate junctions. The stability and low contact resistance of dithiocarbamate-based molecular junctions represent a significant step towards the development of robust, organic-based electronic circuits.

  10. Measuring the Density of a Molecular Cluster Injector via Visible Emission from an Electron Beam

    Lundberg, D. P.; Kaita, R.; Majeski, R. M.; Stotler, D. P.

    2010-06-28

    A method to measure the density distribution of a dense hydrogen gas jet is pre- sented. A Mach 5.5 nozzle is cooled to 80K to form a flow capable of molecular cluster formation. A 250V, 10mA electron beam collides with the jet and produces Hα emission that is viewed by a fast camera. The high density of the jet, several 1016cm-3, results in substantial electron depletion, which attenuates the Hα emission. The attenuated emission measurement, combined with a simplified electron-molecule collision model, allows us to determine the molecular density profile via a simple iterative calculation.

  11. Synthesis and Studies of Sulfur-Containing Heterocyclic Molecules for Molecular Electronics

    Mazzanti, Virginia

    This work describes the synthesis and studies of sulfur containing π conjugated heterocycles, which are considered interesting motifs in the field of molecular electronics. The first project, which is covered in Chapter 1, concerns the functionalization of tetracycle dibenzo[bc,fg][1,4]dithiapent......This work describes the synthesis and studies of sulfur containing π conjugated heterocycles, which are considered interesting motifs in the field of molecular electronics. The first project, which is covered in Chapter 1, concerns the functionalization of tetracycle dibenzo[bc,fg][1...... the synthesis of dimeric structures of redox active system tetrathiafulvalene (TTF). Molecules with different conjugation pathways bridging two TTFs were synthesized and studied using CV and DPV in order to probe the electronic interaction between these two redox units. The last aspect of this thesis, which...

  12. Transient behaviour of electron exchange between a molecular wire and a metal electrode

    Highlights: → Modeling electron transfer rate to electrode from redox via mediated bridge of atoms. → Redox interaction of solvent modeled as classical harmonic oscillator bath. → Both transient and rate constants are calculated. → Negative differential resistance at high overpotential for thermal electron transfer. → Dependency on chain length is analysed. - Abstract: We consider electron exchange between a metal electrode and an attached molecular wire with a redox center at its end. A model Hamiltonian based on a tight-binding scheme is proposed, which contains the coupling of the redox system to the solvent. The corresponding Green's function is calculated exactly, and the time dependence is derived from its Fourier transform. For the case of photo-exited transfer we calculate current transients for a few representative cases. In addition, we calculate the rate of electron transfer for thermal electron transfer from the redox center to the electrode following a potential step.

  13. VUV diagnostic of electron impact processes in low temperature molecular hydrogen plasma

    Komppula, J

    2015-01-01

    Novel methods for diagnostics of molecular hydrogen plasma processes, such as ionization, production of high vibrational levels, dissociation of molecules via excitation to singlet and triplet states and production of metastable states, are presented for molecular hydrogen plasmas in corona equilibrium. The methods are based on comparison of rate coefficients of plasma processes and optical emission spectroscopy of lowest singlet and triplet transitions, i.e. Lyman-band ($B^1\\Sigma^+_u \\rightarrow X^1\\Sigma^+_g$) and molecular continuum ($a^3\\Sigma^+_g \\rightarrow b^3\\Sigma^+_u$), of the hydrogen molecule in VUV wavelength range. Comparison of rate coefficients of spin-allowed and/or spin-forbidden excitations reduces the uncertainty caused by the non-equilibrium distributions of electron energy and molecular vibrational level, which are typically known poorly in plasma sources. The described methods are applied to estimate the rates of various plasma processes in a filament arc discharge.

  14. Generation of DC electric fields due to vortex rectification in superconducting films

    The introduction of the manuscript reviews different mechanisms of generation of permanent electric fields by AC driven vortex lattices in type-II superconductors due to artificial symmetry breaking. The second part shows that superconducting Pb and Nb films (strips or crosses) with or without symmetric periodic pinning centers, subject to a magnetic field perpendicular to the film plane, also exhibit magnetically tunable AC current rectification. At low drive frequencies, not far below the critical temperature, the superconducting films work as one-dimensional rectifiers (i.e. generate an uniform DC electric field along the direction of the AC current) due to unavoidable small vortex pinning asymmetry. At higher frequencies, above 105 Hz, rectification gradually becomes two-dimensional with a strongly non-uniform generated DC electric field. DC voltages, either longitudinal or transversal to the AC current are tunable with the applied magnetic field. The rectified voltage depends strongly on the temperature and the AC drive intensity. In superconductors with periodic pinning centers the rectified voltage varies periodically with the number of vortices per pinning center. Not far below T c, the generated DC electric field is nearly opposite on the opposite film sides. The unusual two-dimensional character of rectification at high frequencies close to T c could be qualitatively understood in terms of local rectification due the oppositely directed asymmetric edge barriers (Bean-Livingston type) or by slowly relaxing electric fields generated by local critical current excess. Anisotropic pinning effects represent a dominant contribution to the rectification further below T c. Since in experiments on rectification in superconductors this electric field adds to the one due to, e.g., anisotropic vortex pinning, one has to take into account its presence when interpreting the rectification experiments

  15. When electron transfer meets electron transport in redox-active molecular nanojunctions.

    Janin, Marion; Ghilane, Jalal; Lacroix, Jean-Christophe

    2013-02-13

    A scanning electrochemical microscope (SECM) was used to arrange two microelectrodes face-to-face separated by a micrometric gap. Polyaniline (PANI) was deposited electrochemically from the SECM tip side until it bridged the two electrodes. The junctions obtained were characterized by following the current through the PANI as a function of its electrochemical potential measured versus a reference electrode acting as a gate electrode in a solid-state transistor. PANI nanojunctions showed conductances below 100 nS in the oxidized state, indicating control of the charge transport within the whole micrometric gap by a limited number of PANI wires. The SECM configuration makes it possible to observe in the same experiment and in the same current range the electron-transfer and electron-transport processes. These two phenomena are distinguished here and characterized by following the variation of the current with the bias voltage and the scan rate. The electron-transfer current changes with the scan rate, while the charge-transport current varies with the bias voltage. Finally, despite the initially micrometric gap, a junction where the conductance is controlled by a single oligoaniline strand is achieved. PMID:23331168

  16. Tunneling of electrons via rotor-stator molecular interfaces: Combined ab initio and model study

    Petreska, Irina; Ohanesjan, Vladimir; Pejov, Ljupčo; Kocarev, Ljupčo

    2016-07-01

    Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that conformation-dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previous work where we investigated the coherent transport via strongly coupled delocalized orbital by application of Non-equilibrium Green's Function Formalism.

  17. Investigation of Terminal Group Effect on Electron Transport Through Open Molecular Structures

    The effect of terminal groups on the electron transport through metal-molecule-metal system has been investigated using nonequilibrium Green's function (NEGF) formalism combined with extended Huckel theory (EHT). Au-molecule-Au junctions are constructed with borazine and BCN unit structure as core molecule and sulphur (S), oxygen (O), selenium (Se) and cyano-group (CN) as terminal groups. The electron transport characteristics of the borazine and BCN molecular systems are analyzed through the transmission spectra and the current-voltage curve. The results demonstrate that the terminal groups modifying the transport behaviors of these systems in a controlled way. Our result shows that, selenium is the best linker to couple borazine to Au electrode and oxygen is the best one to couple BCN to Au electrode. Furthermore, the results of borazine systems are compared with that of BCN molecular systems and are discussed. Simulation results show that the conductance through BCN molecular systems is four times larger than the borazine molecular systems. Negative differential resistance behavior is observed with borazine-CN system and the saturation feature appears in BCN systems. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  18. Electrical characterization of benzenedithiolate molecular electronic devices with graphene electrodes on rigid and flexible substrates

    Jang, Yeonsik; Jeong, Hyunhak; Kim, Dongku; Hwang, Wang-Taek; Kim, Jun-Woo; Jeong, Inho; Song, Hyunwook; Yoon, Jiyoung; Yi, Gyu-Chul; Jeong, Heejun; Lee, Takhee

    2016-04-01

    We investigated the electrical characteristics of molecular electronic devices consisting of benzenedithiolate self-assembled monolayers and a graphene electrode. We used the multilayer graphene electrode as a protective interlayer to prevent filamentary path formation during the evaporation of the top electrode in the vertical metal-molecule-metal junction structure. The devices were fabricated both on a rigid SiO2/Si substrate and on a flexible poly(ethylene terephthalate) substrate. Using these devices, we investigated the basic charge transport characteristics of benzenedithiolate molecular junctions in length- and temperature-dependent analyses. Additionally, the reliability of the electrical characteristics of the flexible benzenedithiolate molecular devices was investigated under various mechanical bending conditions, such as different bending radii, repeated bending cycles, and a retention test under bending. We also observed the inelastic electron tunneling spectra of our fabricated graphene-electrode molecular devices. Based on the results, we verified that benzenedithiolate molecules participate in charge transport, serving as an active tunneling barrier in solid-state graphene-electrode molecular junctions.

  19. Tuning electron transport through a single molecular junction by bridge modification

    The possibility of controlling electron transport in a single molecular junction represents the ultimate goal of molecular electronics. Here, we report that the modification of bridging group makes it possible to improve the performance and obtain new functions in a single cross-conjugated molecular junction, designed from a recently synthesized bipolar molecule bithiophene naphthalene diimide. Our first principles results show that the bipolar characteristic remains after the molecule was modified and sandwiched between two metal electrodes. Rectifying is the intrinsic characteristic of the molecular junction and its performance can be enhanced by replacing the saturated bridging group with an unsaturated group. A further improvement of the rectifying and a robust negative differential resistance (NDR) behavior can be achieved by the modification of unsaturated bridge. It is revealed that the modification can induce a deviation angle about 4° between the donor and the acceptor π-conjugations, making it possible to enhance the communication between the two π systems. Meanwhile, the low energy frontier orbitals of the junction can move close to the Fermi level and encounter in energy at certain biases, thus a transport channel with a considerable transmission can be formed near the Fermi level only at a narrow bias regime, resulting in the improvement of rectifying and the robust NDR behavior. This finding could be useful for the design of single molecular devices.

  20. Voltage-Induced Switching Dynamics of a Coupled Spin Pair in a Molecular Junction.

    Saygun, T; Bylin, J; Hammar, H; Fransson, J

    2016-04-13

    Molecular spintronics is made possible by the coupling between electronic configuration and magnetic polarization of the molecules. For control and application of the individual molecular states, it is necessary to both read and write their spin states. Conventionally, this is achieved by means of external magnetic fields or ferromagnetic contacts, which may change the intentional spin state and may present additional challenges when downsizing devices. Here, we predict that coupling magnetic molecules together opens up possibilities for all electrical control of both the molecular spin states as well as the current flow through the system. By tuning between the regimes of ferromagnetic and antiferromagnetic exchange interaction, the current can be at least an order of magnitude enhanced or reduced. The effect is susceptible to the tunnel coupling and molecular level alignment that can be used to achieve current rectification. PMID:27010805

  1. When electrons meet molecular ions and what happens next: dissociative recombination from interstellar molecular clouds to internal combustion engines.

    Thomas, Richard D

    2008-01-01

    The interaction of matter with its environment is the driving force behind the evolution of 99% of the observed matter in the universe. The majority of the visible universe exists in a state of weak ionization, the so called fourth state of matter: plasma. Plasmas are ubiquitous, from those occurring naturally; interstellar molecular clouds, cometary comae, circumstellar shells, to those which are anthropic in origin; flames, combustion engines and fusion reactors. The evolution of these plasmas is driven by the interaction of the plasma constituents, the ions, and the electrons. One of the most important subsets of these reactions is electron-molecular ion recombination. This process is significant for two very important reasons. It is an ionization reducing reaction, removing two ionised species and producing neutral products. Furthermore, these products may themselves be reactive radical species which can then further drive the evolution of the plasma. The rate at which the electron reacts with the ion depends on many parameters, for examples the collision energy, the internal energy of the ion, and the structure of the ion itself. Measuring these properties together with the manner in which the system breaks up is therefore critical if the evolution of the environment is to be understood at all. Several techniques have been developed to study just such reactions to obtain the necessary information on the parameters. In this paper the focus will be on one the most recently developed of these, the Ion Storage Ring, together with the detection tools and techniques used to extract the necessary information from the reaction. PMID:18618616

  2. Unexpectedly high pressure for molecular dissociation in liquid hydrogen by a reliable electronic simulation

    Mazzola, Guglielmo; Sorella, Sandro

    2014-01-01

    The study of the high pressure phase diagram of hydrogen has continued with renewed effort for about one century as it remains a fundamental challenge for experimental and theoretical techniques. Here we employ an efficient molecular dynamics based on the quantum Monte Carlo method, which can describe accurately the electronic correlation and treat a large number of hydrogen atoms, allowing a realistic and reliable prediction of thermodynamic roperties. We find that the molecular liquid phase is unexpectedly stable and the transition towards a fully atomic liquid phase occurs at much higher pressure than previously believed. The old standing problem of low temperature atomization is, therefore, still far from experimental reach.

  3. Light quasiparticles dominate electronic transport in molecular crystal field-effect transistors

    Li, Z. Q.; Podzorov, V.; Sai, N.; Martin, Michael C.; Gershenson, M. E.; Di Ventra, M.; Basov, D. N.

    2007-03-01

    We report on an infrared spectroscopy study of mobile holes in the accumulation layer of organic field-effect transistors based on rubrene single crystals. Our data indicate that both transport and infrared properties of these transistors at room temperature are governed by light quasiparticles in molecular orbital bands with the effective masses m[small star, filled]comparable to free electron mass. Furthermore, the m[small star, filled]values inferred from our experiments are in agreement with those determined from band structure calculations. These findings reveal no evidence for prominent polaronic effects, which is at variance with the common beliefs of polaron formation in molecular solids.

  4. Atomic and Molecular Photoelectron and Auger Electron SpectroscopyStudies Using Synchrotron Radiation

    Southworth, Stephen H.

    1982-01-01

    Electron spectroscopy, combined with synchrotron radiation, was used to measure the angular distributions of photoelectrons and Auger electrons from atoms and molecules as functions of photon energy. The branching ratios and partial cross sections were a 130 measured in certain cases. By comparison with theoretical calculations, the experimental results are interpreted in terms of the characteristic electronic structure and ionization dynamics of the atomic or molecular sample. The time structure of the synchrotron radiation source was used to record time-of-flight (TOF) spectra o f the ejected electrons. The ''a double-angle-TOF'' method for the measurement of photoelectron angular distributions is discussed. This technique offers the advantages of increased electron collect ion efficiency and the elimination of certain systematic errors. Several results were obtained for Xe using photon energies in the range hv {approx_equal} 60-190 eV, where excitation and ionization of the inner-subshell 4d electrons dominates. The 4d asymmetry parameter {beta} exhibits strong oscillations with energy, in agreement with several theoretical calculations. As predicted, the 5p asymmetry parameter was observed to deviate strongly from that calculated using the independent-electron model, due to intershell correlation with the 4d electrons.

  5. Modulations of electronic tunneling rates through flexible molecular bridges by a dissipative superexchange mechanism

    Long-range coherent electron transfer between a donor and an acceptor is often assisted by intermediate molecular bridge, via the superexchange tunneling mechanism. The effect of electronic-nuclear coupling intensity on the tunneling rate and mechanism is analyzed using a generalized spin-boson model, in which the two level system, representing the donor and the acceptor is coupled to a dissipative nuclear bath only indirectly, via additional N bridge sites. A Langevin-Schroedinger equation, based on a mean field approximation, is applied in order to study the corresponding many-body dynamics, and the results are supported by numerically exact calculations for a single nuclear bridge mode. At zero temperature and when the electron tunneling is slower than the nuclear motion, the main effect of electronic-nuclear coupling is the dissipation of electronic energy at the bridge into nuclear vibrations. At small coupling intensities, the electronic tunneling rate increases due to this dissipative mechanism, but as the coupling intensity increases the tunneling into the acceptor is suppressed and efficient dissipation leads to electronic trapping (solvation) at the bridge. This analysis agrees with numerous experimental and theoretical studies, emphasizing the importance of the nuclear bridge conformation and the bridge flexibility in controlling the electron transfer rate in donor-bridge-acceptor systems

  6. Applications of the Information Theory to Problems of Molecular Electronic Structure and Chemical Reactivity

    Roman F. Nalewajski

    2002-04-01

    Full Text Available Abstract: Recent studies on applications of the information theoretic concepts to molecular systems are reviewed. This survey covers the information theory basis of the Hirshfeld partitioning of molecular electron densities, its generalization to many electron probabilities, the local information distance analysis of molecular charge distributions, the charge transfer descriptors of the donor-acceptor reactive systems, the elements of a “thermodynamic” description of molecular charge displacements, both “vertical” (between molecular fragments for the fixed overall density and “horizontal” (involving different molecular densities, with the entropic representation description provided by the information theory. The average uncertainty measures of bond multiplicities in molecular “communication” systems are also briefly summarized. After an overview of alternative indicators of the information distance (entropy deficiency, missing information between probability distributions the properties of the “stockholder” densities, which minimize the entropy deficiency relative to the promolecule reference, are summarized. In particular, the surprisal analysis of molecular densities is advocated as an attractive information-theoretic tool in the electronic structure theory, supplementary to the familiar density difference diagrams. The subsystem information density equalization rules satisfied by the Hirshfeld molecular fragments are emphasized: the local values of alternative information distance densities of subsystems are equal to the corresponding global value, characterizing the molecule as a whole. These local measures of the information content are semi-quantitatively related to the molecular density difference function. In the density functional theory the effective external potentials of molecular fragments are defined, for which

  7. Molecular-beam studies of the dynamics of organic electron transfer reactions

    Using crossed molecular beams we have studied the dynamics of several electron transfer reactions, A+B→A++B-, where A is an organic base and B is SnCl4, SbF5, or TiCl4. We propose a simple, modified stripping model whereby the electron jumps at the point where the ionic and covalent surfaces cross to form a pair of ions produced by a vertical, Franck--Condon transition. All initial energy in excess of this vertical threshold appears in the translational energy of the products. This model is verified in one case where the vertical ionization potential and electron affinity are known and is then used to obtain a rough vertical electron affinity of SbF5. Except at the lowest energies all the reactions follow this modified stripping mechanism

  8. Correlation between electron-irradiation defects and applied stress in graphene: A molecular dynamics study

    Kida, Shogo; Yamamoto, Masaya; Kawata, Hiroaki; Hirai, Yoshihiko; Yasuda, Masaaki, E-mail: yasuda@pe.osakafu-u.ac.jp [Department of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka 599-8531 (Japan); Tada, Kazuhiro [Department of Electrical and Control Systems Engineering, National Institute of Technology, Toyama College, Toyama 939-8630 (Japan)

    2015-09-15

    Molecular dynamics (MD) simulations are performed to study the correlation between electron irradiation defects and applied stress in graphene. The electron irradiation effect is introduced by the binary collision model in the MD simulation. By applying a tensile stress to graphene, the number of adatom-vacancy (AV) and Stone–Wales (SW) defects increase under electron irradiation, while the number of single-vacancy defects is not noticeably affected by the applied stress. Both the activation and formation energies of an AV defect and the activation energy of an SW defect decrease when a tensile stress is applied to graphene. Applying tensile stress also relaxes the compression stress associated with SW defect formation. These effects induced by the applied stress cause the increase in AV and SW defect formation under electron irradiation.

  9. Correlation between electron-irradiation defects and applied stress in graphene: A molecular dynamics study

    Molecular dynamics (MD) simulations are performed to study the correlation between electron irradiation defects and applied stress in graphene. The electron irradiation effect is introduced by the binary collision model in the MD simulation. By applying a tensile stress to graphene, the number of adatom-vacancy (AV) and Stone–Wales (SW) defects increase under electron irradiation, while the number of single-vacancy defects is not noticeably affected by the applied stress. Both the activation and formation energies of an AV defect and the activation energy of an SW defect decrease when a tensile stress is applied to graphene. Applying tensile stress also relaxes the compression stress associated with SW defect formation. These effects induced by the applied stress cause the increase in AV and SW defect formation under electron irradiation

  10. Self-assembled molecular rafts at liquid|liquid interfaces for four-electron oxygen reduction.

    Olaya, Astrid J; Schaming, Delphine; Brevet, Pierre-Francois; Nagatani, Hirohisa; Zimmermann, Tomas; Vanicek, Jiri; Xu, Hai-Jun; Gros, Claude P; Barbe, Jean-Michel; Girault, Hubert H

    2012-01-11

    The self-assembly of the oppositely charged water-soluble porphyrins, cobalt tetramethylpyridinium porphyrin (CoTMPyP(4+)) and cobalt tetrasulphonatophenyl porphyrin (CoTPPS(4-)), at the interface with an organic solvent to form molecular "rafts", provides an excellent catalyst to perform the interfacial four-electron reduction of oxygen by lipophilic electron donors such as tetrathiafulvalene (TTF). The catalytic activity and selectivity of the self-assembled catalyst toward the four-electron pathway was found to be as good as that of the Pacman type cofacial cobalt porphyrins. The assembly has been characterized by UV-visible spectroscopy, Surface Second Harmonic Generation, and Scanning Electron Microscopy. Density functional theory calculations confirm the possibility of formation of the catalytic CoTMPyP(4+)/ CoTPPS(4-) complex and its capability to bind oxygen. PMID:22107335

  11. Fabrication of tunnel junction-based molecular electronics and spintronics devices

    Tunnel junction-based molecular devices (TJMDs) are highly promising for realizing futuristic electronics and spintronics devices for advanced logic and memory operations. Under this approach, ∼2.5 nm molecular device elements bridge across the ∼2-nm thick insulator of a tunnel junction along the exposed side edge(s). This paper details the efforts and insights for producing a variety of TJMDs by resolving multiple device fabrication and characterization issues. This study specifically discusses (i) compatibility between tunnel junction test bed and molecular solutions, (ii) optimization of the exposed side edge profile and insulator thickness for enhancing the probability of molecular bridging, (iii) effect of fabrication process-induced mechanical stresses, and (iv) minimizing electrical bias-induced instability after the device fabrication. This research will benefit other researchers interested in producing TJMDs efficiently. TJMD approach offers an open platform to test virtually any combination of magnetic and nonmagnetic electrodes, and promising molecules such as single molecular magnets, porphyrin, DNA, and molecular complexes.

  12. Non-dissociative single ionization of molecular hydrogen by electron and positron impact

    We present experimental results for impact ionization of molecular hydrogen by electrons and positrons for the range of impact energies from threshold to about 2 keV (0.4- 2 keV for e-). Our electron data agree with the most recent one measured by others. When we compare our positron results to earlier published single ionization cross sections we find significant differences for impact energies from threshold to about 100 eV with the new cross sections being substantially smaller. In the present study an effort has been made to discriminate against false signals caused by positronium formation and other effects. (author)

  13. Molecular monolayers and interfacial electron transfer of pseudomonas aeruginosa azurin on Au(111)

    Chi, Qijin; Zhang, Jingdong; Nielsen, Jens Ulrik;

    2000-01-01

    disulfide group to form a monolayer. The adsorption of this protein on Au(111) via a gold-sulfur binding mode is further supported by XPS measurements. In situ STM images with molecular resolution have been recorded and show a dense monolayer organization of adsorbed azurin molecules. Direct electron...... long-range electrochemical electron transfer between the electrode and the copper center. Voltammetry, electrochemical impedance spectroscopy (EIS), in situ scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS) have been employed to disclose features of these issues. Zn...

  14. Amplified spontaneous emission of a molecular nitrogen laser excited by an intense relativistic electron beam

    Report of a study of the shape and length of the output pulse of a molecular nitrogen laser, excited by an intense relativistic electron beam, is described. The rate equations are computer solved, at first ignoring the spontaneous emission during the excitation process. Afterwards the rate equations are solved taking into account excitation functions of various shapes and lengths, related to electron-beam pulses of a few kA and a few nsec. Laser power output, energy, and peak-time, i.e., the time at which the gain reaches its saturated value, are given and discussed as functions of the intensity and rise time of the excitation functions

  15. Microplume model of spatial-yield spectra. [applying to electron gas degradation in molecular nitrogen gas

    Green, A. E. S.; Singhal, R. P.

    1979-01-01

    An analytic representation for the spatial (radial and longitudinal) yield spectra is developed in terms of a model containing three simple 'microplumes'. The model is applied to electron energy degradation in molecular nitrogen gas for 0.1 to 5 keV incident electrons. From the nature of the cross section input to this model it is expected that the scaled spatial yield spectra for other gases will be quite similar. The model indicates that each excitation, ionization, etc. plume should have its individual spatial and energy dependence. Extensions and aeronomical and radiological applications of the model are discussed.

  16. Communication: Reduced density matrices in molecular systems: Grand-canonical electron states

    Grand-canonical like descriptions of many electron atomic and molecular open systems which are characterized by a non-integer number of electrons are presented. Their associated reduced density matrices (RDMs) are obtained by introducing the contracting mapping for this type of distributions. It is shown that there is loss of information when connecting RDMs of different order by partial contractions. The energy convexity property of these systems simplifies the description. Consequently, this formulation opens the possibility to a new look for chemical descriptors such as chemical potential and reactivity among others. Examples are presented to discuss the theoretical aspects of this work

  17. On the path length of an excess electron interacted with optical phonons in a molecular chain

    We show that in a molecular chain with dispersionless phonons at zero temperature, a 'quasistationary' moving soliton state of an excess electron is possible. As the soliton velocity vanishes, the path length of the excess electron exponentially tends to infinity. It is demonstrated that in the presence of dispersion, when the soliton initial velocity exceeds the maximum group velocity of the chain, the soliton slows down until it reaches the maximum group velocity and then moves stationarily at this maximum group velocity. A conclusion is made of the fallacy of some works were the existence of moving polarons in a dispersionless medium is considered infeasible

  18. Quantum chemistry the development of ab initio methods in molecular electronic structure theory

    Schaefer III, Henry F

    2004-01-01

    This guide is guaranteed to prove of keen interest to the broad spectrum of experimental chemists who use electronic structure theory to assist in the interpretation of their laboratory findings. A list of 150 landmark papers in ab initio molecular electronic structure methods, it features the first page of each paper (which usually encompasses the abstract and introduction). Its primary focus is methodology, rather than the examination of particular chemical problems, and the selected papers either present new and important methods or illustrate the effectiveness of existing methods in predi

  19. Dengue virus identification by transmission electron microscopy and molecular methods in fatal dengue hemorrhagic fever.

    Limonta, D; Falcón, V; Torres, G; Capó, V; Menéndez, I; Rosario, D; Castellanos, Y; Alvarez, M; Rodríguez-Roche, R; de la Rosa, M C; Pavón, A; López, L; González, K; Guillén, G; Diaz, J; Guzmán, M G

    2012-12-01

    Dengue virus is the most significant virus transmitted by arthropods worldwide and may cause a potentially fatal systemic disease named dengue hemorrhagic fever. In this work, dengue virus serotype 4 was detected in the tissues of one fatal dengue hemorrhagic fever case using electron immunomicroscopy and molecular methods. This is the first report of dengue virus polypeptides findings by electron immunomicroscopy in human samples. In addition, not-previously-documented virus-like particles visualized in spleen, hepatic, brain, and pulmonary tissues from a dengue case are discussed. PMID:22527878

  20. Systematics in a measurement of the electron's electric dipole moment using trapped molecular ions

    Grau, Matt; Cossel, Kevin; Cairncross, William; Gresh, Dan; Zhou, Yan; Ye, Jun; Cornell, Eric

    2015-05-01

    A precision measurement of the electron's electric dipole moment (EDM) has important implications for physics beyond the Standard Model. Trapped molecular ions offer high sensitivity in such an experiment because of the large effective electric fields and long coherence times that are possible. Our experiment uses Ramsey spectroscopy of HfF+ ions in a linear RF trap with rotating bias fields, achieving coherence times beyond 1 second for 1000 trapped ions. Compared to other electron EDM experiments that use molecular beams, we will be sensitive to a different class of systematic errors. In this work we investigate systematic errors arising from all fields involved in the experiment, including the trapping and polarizing electric fields, magnetic field gradients, and motional effects such as geometric phases. This work was supported by NIST and NSF.

  1. Diffractive imaging of a molecular rotational wavepacket with femtosecond Megaelectronvolt electron pulses

    Yang, Jie; Vecchione, Theodore; Robinson, Matthew S; Li, Renkai; Hartmann, Nick; Shen, Xiaozhe; Coffee, Ryan; Corbett, Jeff; Fry, Alan; Gaffney, Kelly; Gorkhover, Tais; Hast, Carsten; Jobe, Keith; Makasyuk, Igor; Reid, Alexander; Robinson, Joseph; Vetter, Sharon; Wang, Fenglin; Weathersby, Stephen; Yoneda, Charles; Centurion, Martin; Wang, Xijie

    2015-01-01

    Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angstrom spatial precision is one of the critical challenges in the chemical sciences, since the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. We performed a gas-phase electron diffraction experiment using Megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved an unprecedented combination of 100 fs root-mean-squared (RMS) temporal resolution and sub-Angstrom (0.76 {\\AA}) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomical...

  2. Molecular solution approach to synthesize electronic quality Cu2ZnSnS4 thin films.

    Yang, Wenbing; Duan, Hsin-Sheng; Cha, Kitty C; Hsu, Chia-Jung; Hsu, Wan-Ching; Zhou, Huanping; Bob, Brion; Yang, Yang

    2013-05-01

    Successful implementation of molecular solution processing from a homogeneous and stable precursor would provide an alternative, robust approach to process multinary compounds compared with physical vapor deposition. Targeting deposition of chemically clear, high quality crystalline films requires specific molecular structure design and solvent selection. Hydrazine (N2H4) serves as a unique and powerful medium, particularly to incorporate selected metallic elements and chalcogens into a stable solution as metal chalcogenide complexes (MCC). However, not all the elements and compounds can be easily dissolved. In this manuscript, we demonstrate a paradigm to incorporate previously insoluble transitional-metal elements into molecular solution as metal-atom hydrazine/hydrazine derivative complexes (MHHD), as exemplified by dissolving of the zinc constituent as Zn(NH2NHCOO)2(N2H4)2. Investigation into the evolution of molecular structure reveals the hidden roadmap to significantly enrich the variety of building blocks for soluble molecule design. The new category of molecular structures not only set up a prototype to incorporate other elements of interest but also points the direction for other compatible solvent selection. As demonstrated from the molecular precursor combining Sn-/Cu-MCC and Zn-MHHD, an ultrathin film of copper zinc tin sulfide (CZTS) was deposited. Characterization of a transistor based on the CZTS channel layer shows electronic properties comparable to CuInSe2, confirming the robustness of this molecular solution processing and the prospect of earth abundant CZTS for next generation photovoltaic materials. This paradigm potentially outlines a universal pathway, from individual molecular design using selected chelated ligands and combination of building blocks in a simple and stable solution to fundamentally change the way multinary compounds are processed. PMID:23581974

  3. Electronic Transport Properties of a Naphthopyran-Based Optical Molecular Switch:an ab initio Study

    XIA Cai-Juan; LIU De-Sheng; ZHANG Ying-Tang

    2011-01-01

    The electronic transport properties of a. Naphthopyran-based molecular optical switch are investigated by using the nonequilibrium Green's Function formalism combined with first-principles density functional theory. The molecule that comprises the switch can convert between its open and closed forms upon photoexcitation. Theoretical results show that the current through the open form is significantly larger than that through the closed form, which is different from other optical switches based on ring-opening reactions of the molecular bridge. The maximum on-off ratio (about 90) can be obtained at 1.4 V. The physical origin of the switching behavior is interpreted based on the spatial distributions of molecular orbitals and the HOMO-LUMO gap. Our result shows that the naphthopyran-based molecule is a good candidate for optical molecular switches and will be useful in the near future.%@@ ronic transport properties of a naphthopyran-based molecular optical switch are investigated by using the nonequilibrium Green's function formalism combined with first-principles density functional theory.The molecule that comprises the switch can convert between its open and closed forms upon photoexcitation.Theoretical results show that the current through the open form is significantly larger than that through the closed form,which is different from other optical switches based on ring-opening reactions of the molecular bridge.The maximum on-off ratio(about 90)can be obtained at 1.4 V.The physical origin of the switching behavior is interpreted based on the spatial distributions of molecular orbitals and the HOMO-LUMO gap.Our result shows that the naphthopyran-based molecule is a good candidate for optical molecular switches and will be useful in the near future.

  4. Tunneling electron induced molecular electroluminescence from individual porphyrin J-aggregates

    Meng, Qiushi; Zhang, Chao; Zhang, Yang, E-mail: zhyangnano@ustc.edu.cn, E-mail: zcdong@ustc.edu.cn; Zhang, Yao; Liao, Yuan; Dong, Zhenchao, E-mail: zhyangnano@ustc.edu.cn, E-mail: zcdong@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2015-07-27

    We investigate molecular electroluminescence from individual tubular porphyrin J-aggregates on Au(111) by tunneling electron excitations in an ultrahigh-vacuum scanning tunneling microscope (STM). High-resolution STM images suggest a spiral tubular structure for the porphyrin J-aggregate with highly ordered “brickwork”-like arrangements. Such aggregated nanotube is found to behave like a self-decoupled molecular architecture and shows red-shifted electroluminescence characteristics of J-aggregates originated from the delocalized excitons. The positions of the emission peaks are found to shift slightly depending on the excitation sites, which, together with the changes in the observed spectral profiles with vibronic progressions, suggest a limited exciton coherence number within several molecules. The J-aggregate electroluminescence is also found unipolar, occurring only at negative sample voltages, which is presumably related to the junction asymmetry in the context of molecular excitations via the carrier injection mechanism.

  5. Tunneling electron induced molecular electroluminescence from individual porphyrin J-aggregates

    Meng, Qiushi; Zhang, Chao; Zhang, Yang; Zhang, Yao; Liao, Yuan; Dong, Zhenchao

    2015-07-01

    We investigate molecular electroluminescence from individual tubular porphyrin J-aggregates on Au(111) by tunneling electron excitations in an ultrahigh-vacuum scanning tunneling microscope (STM). High-resolution STM images suggest a spiral tubular structure for the porphyrin J-aggregate with highly ordered "brickwork"-like arrangements. Such aggregated nanotube is found to behave like a self-decoupled molecular architecture and shows red-shifted electroluminescence characteristics of J-aggregates originated from the delocalized excitons. The positions of the emission peaks are found to shift slightly depending on the excitation sites, which, together with the changes in the observed spectral profiles with vibronic progressions, suggest a limited exciton coherence number within several molecules. The J-aggregate electroluminescence is also found unipolar, occurring only at negative sample voltages, which is presumably related to the junction asymmetry in the context of molecular excitations via the carrier injection mechanism.

  6. On the distance dependence of electron transfer through molecular bridges and wires

    Skourtis, S; Skourtis, Spiros; Nitzan, Abraham

    2002-01-01

    The dependence of electron transfer rates and yields in bridged molecular systems on the bridge length, and the dependence of the zero-bias conduction of molecular wires on wire length are discussed. Both phenomena are controlled by tunneling across the molecular bridge and are consequently expected to show exponential decrease with bridge length that is indeed often observed. Deviations from this exponential dependence for long bridges, in particular a crossover to a very weak dependence on bridge length were recently observed experimentally and discussed theoretically in terms of thermal relaxation and dephasing on the bridge. Here we discuss two other factors that potentially affect the bridge length dependence of these phenomena. First, in experiments initiated by an initial preparation of a non-stationary "donor" state the initial energy is not well defined. A small contribution from initially populated eigenstates that are of mostly bridge-level character may dominate transmission for long bridges, resu...

  7. Tunneling electron induced molecular electroluminescence from individual porphyrin J-aggregates

    We investigate molecular electroluminescence from individual tubular porphyrin J-aggregates on Au(111) by tunneling electron excitations in an ultrahigh-vacuum scanning tunneling microscope (STM). High-resolution STM images suggest a spiral tubular structure for the porphyrin J-aggregate with highly ordered “brickwork”-like arrangements. Such aggregated nanotube is found to behave like a self-decoupled molecular architecture and shows red-shifted electroluminescence characteristics of J-aggregates originated from the delocalized excitons. The positions of the emission peaks are found to shift slightly depending on the excitation sites, which, together with the changes in the observed spectral profiles with vibronic progressions, suggest a limited exciton coherence number within several molecules. The J-aggregate electroluminescence is also found unipolar, occurring only at negative sample voltages, which is presumably related to the junction asymmetry in the context of molecular excitations via the carrier injection mechanism

  8. Uncovering a law of corresponding states for electron tunneling in molecular junctions

    Bâldea, Ioan; Xie, Zuoti; Frisbie, C. Daniel

    2015-06-01

    Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner in terms of reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws of corresponding states contain numerical factors adjusted empirically. Here, we report a law of corresponding states deduced analytically for charge transport via tunneling in molecular junctions, which we validate against current-voltage measurements for conducting probe atomic force microscope junctions based on benchmark molecular series (oligophenylenedithiols and alkanedithiols) and electrodes (silver, gold, and platinum), as well as against transport data for scanning tunneling microscope junctions. Two salient features distinguish the present law of corresponding states from all those known previously. First, it is expressed by a universal curve free of empirical parameters. Second, it demonstrates that a universal behavior is not necessarily affected by strong stochastic fluctuations often observed in molecular electronics. An important and encouraging message of this finding is that transport behavior across different molecular platforms can be similar and extraordinarily reproducible.Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner in terms of reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws of corresponding states contain numerical factors adjusted empirically. Here, we report a law of corresponding states deduced analytically for charge transport via tunneling in molecular junctions, which we validate against current-voltage measurements for conducting probe atomic force microscope junctions based on benchmark molecular series (oligophenylenedithiols and alkanedithiols) and electrodes (silver, gold, and platinum), as well as against transport data

  9. Molecularly Imprinted Electropolymer for a Hexameric Heme Protein with Direct Electron Transfer and Peroxide Electrocatalysis

    Lei Peng; Aysu Yarman; Jetzschmann, Katharina J.; Jae-Hun Jeoung; Daniel Schad; Holger Dobbek; Ulla Wollenberger; Scheller, Frieder W.

    2016-01-01

    For the first time a molecularly imprinted polymer (MIP) with direct electron transfer (DET) and bioelectrocatalytic activity of the target protein is presented. Thin films of MIPs for the recognition of a hexameric tyrosine-coordinated heme protein (HTHP) have been prepared by electropolymerization of scopoletin after oriented assembly of HTHP on a self-assembled monolayer (SAM) of mercaptoundecanoic acid (MUA) on gold electrodes. Cavities which should resemble the shape and size of HTHP wer...

  10. Superatom spectroscopy and the electronic state correlation between elements and isoelectronic molecular counterparts

    Peppernick, Samuel J.; Gunaratne, K.D. Dasitha; Castleman, A. W.

    2009-01-01

    Detailed in the present investigation are results pertaining to the photoelectron spectroscopy of negatively charged atomic ions and their isoelectronic molecular counterparts. Experiments utilizing the photoelectron imaging technique are performed on the negative ions of the group 10 noble metal block (i.e. Ni-, Pd-, and Pt-) of the periodic table at a photon energy of 2.33 eV (532 nm). The accessible electronic transitions, term energies, and orbital angular momentum components of the bound...

  11. Using Markov models to simulate electron spin resonance spectra from molecular dynamics trajectories

    Sezer, Deniz; Freed, Jack H.; Roux, Benoît

    2008-01-01

    Simulating electron spin resonance (ESR) spectra directly from molecular dynamics simulations of a spin labeled protein necessitates a large number (hundreds or thousands) of relatively long (hundreds of ns) trajectories. To meet this challenge, we explore the possibility of constructing accurate stochastic models of the spin label dynamics from atomistic trajectories. A systematic, two-step procedure, based on the probabilistic framework of hidden Markov models, is developed to build a discr...

  12. Ballistic thermal rectification in asymmetric three-terminal mesoscopic dielectric systems

    Ming, Yi; Xian Wang, Zhe; Ding, Ze Jun; Li, Hui Min

    2010-10-01

    By coupling a temperature probe to the asymmetric three-terminal mesoscopic dielectric system, ballistic thermal rectification at low temperature is analytically studied based on the Landauer formulation of transport theory. It is seen that thermal rectification is a purely quantum effect and the quantum statistics of phonons in thermal reservoirs is necessary. Moreover, when the phonon re-emits into the system from the temperature probe, energy changing is necessary to realize thermal rectification. Another necessary condition is the different asymmetries for phonons with different frequencies, which is reflected by the dependence of the ratio τRC(ω)/τRL(ω) on ω, the phonon's frequency, where τRC(ω) and τRL(ω) are respectively the transmission coefficients from two asymmetric terminals to the temperature probe. The analytical results are confirmed by extensive numerical simulations.

  13. Ballistic thermal rectification in asymmetric three-terminal mesoscopic dielectric systems

    By coupling a temperature probe to the asymmetric three-terminal mesoscopic dielectric system, ballistic thermal rectification at low temperature is analytically studied based on the Landauer formulation of transport theory. It is seen that thermal rectification is a purely quantum effect and the quantum statistics of phonons in thermal reservoirs is necessary. Moreover, when the phonon re-emits into the system from the temperature probe, energy changing is necessary to realize thermal rectification. Another necessary condition is the different asymmetries for phonons with different frequencies, which is reflected by the dependence of the ratio τRC(ω)/τRL(ω) on ω, the phonon's frequency, where τRC(ω) and τRL(ω) are respectively the transmission coefficients from two asymmetric terminals to the temperature probe. The analytical results are confirmed by extensive numerical simulations.

  14. Effect of an electric field on the nonlinear optical rectification of a quantum ring

    Xie, Wenfang, E-mail: xiewf@vip.163.com

    2014-06-15

    We have studied the effects of an external electric field on the nonlinear optical rectification of a semiconductor quantum ring. An electric field applied in the ring plane destroys the rotational invariance. Calculations are performed by using the matrix diagonalization method and the compact density-matrix approach within the effective-mass approximation. The results indicate that an increase of electric field gives the red shift of the peak positions of nonlinear optical rectification. The roles of ring size and magnetic field strength as control parameters on this nonlinear property have been investigated. Our results show rich nonlinear optical rectification for quantum rings in the presence of electric fields, which effectively displays the signature of the Aharonov–Bohm oscillation.

  15. Vertex-Atom-Dependent Rectification in Triangular h-BNC/Triangular Graphene Heterojunctions

    Wang, Lihua; Zhao, Jianguo; Zhang, Zizhen; Ding, Bingjun; Guo, Yong

    2016-08-01

    First-principles calculations have shown dramatically unexpected rectifying regularities in particular heterojunction configurations with triangular hexagonal boron-nitride-carbon ( h-BNC) and triangular graphene (TG) sandwiched between two armchair graphene nanoribbon electrodes. When the triangular h-BNC and TG are linked by vertex atoms of nitrogen and carbon (boron and carbon), forward (reverse) rectifying performance can be observed. Moreover, for a certain linking mode, the larger the elemental proportion p (where p = N_{{{boron}} + {{nitrogen}}} /N_{{{boron}} + {{nitrogen}} + {{carbon}}} ) in the h-BNC, the larger the ratio for forward (reverse) rectification. A mechanism for these rectification behaviors is suggested. The findings provide insights into control of rectification behaviors in TG-based nanodevices.

  16. Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions.

    Yan, Haijun; Bergren, Adam Johan; McCreery, Richard; Della Rocca, Maria Luisa; Martin, Pascal; Lafarge, Philippe; Lacroix, Jean Christophe

    2013-04-01

    In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5-22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d  16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8-22 nm. Transport in the 8-22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8-22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1-5 nm associated with quantum-mechanical tunneling. PMID:23509271

  17. The effect of molecular mobility on electronic transport in carbon nanotube-polymer composites and networks

    A multiscale modeling approach to the prediction of electrical conductivity in carbon nanotube (CNT)–polymer composite materials is developed, which takes into account thermally activated molecular mobility of the matrix and the CNTs. On molecular level, a tight-binding density functional theory and non-equilibrium Green's function method are used to calculate the static electron transmission function in the contact between two metallic carbon nanotubes that corresponds to electron transport at 0 K. For higher temperatures, the statistical distribution of effective contact resistances is considered that originates from thermal fluctuations of intermolecular distances caused by molecular mobility of carbon nanotube and the polymer matrix. Based on this distribution and using effective medium theory, the temperature dependence of macroscopic electrical resistivity for CNT-polymer composites and CNT mats is calculated. The predicted data indicate that the electrical conductivity of the CNT-polymer composites increases linearly with temperature above 50 K, which is in a quantitative agreement with the experiments. Our model predicts a slight nonlinearity in temperature dependence of electric conductivity at low temperatures for percolated composites with small CNT loading. The model also explains the effect of glass transition and other molecular relaxation processes in the polymer matrix on the composite electrical conductivity. The developed multiscale approach integrates the atomistic charge transport mechanisms in percolated CNT-polymer composites with the macroscopic response and thus enables direct comparison of the prediction with the measurements of macroscopic material properties

  18. An analytic approach to 2D electronic PE spectra of molecular systems

    Graphical abstract: The three-pulse photon echo (3P-PE) spectra of finite molecular systems using direct calculation from electronic Hamiltonians allows peak classification from 3P-PE spectra dynamics. Display Omitted Highlights: → RWA approach to electronic photon echo. → A straightforward calculation of 2D electronic spectrograms in finite molecular systems. → Importance of population time dynamics in relation to inter-site coherent coupling. - Abstract: The three-pulse photon echo (3P-PE) spectra of finite molecular systems and simplified line broadening models is presented. The Fourier picture of a heterodyne detected three-pulse rephasing PE signal in the δ-pulse limit of the external field is derived in analytic form. The method includes contributions of one and two-excitonic states and allows direct calculation of Fourier PE spectrogram from corresponding Hamiltonian. As an illustration, the proposed treatment is applied to simple systems, e.g. 2-site two-level system (TLS) and n-site TLS model of photosynthetic unit. The importance of relation between Fourier picture of 3P-PE dynamics (corresponding to nonzero population time, T) and coherent inter-state coupling is emphasized.

  19. Crucial Role of Nuclear Dynamics for Electron Injection in a Dye-Semiconductor Complex.

    Monti, Adriano; Negre, Christian F A; Batista, Victor S; Rego, Luis G C; de Groot, Huub J M; Buda, Francesco

    2015-06-18

    We investigate the electron injection from a terrylene-based chromophore to the TiO2 semiconductor bridged by a recently proposed phenyl-amide-phenyl molecular rectifier. The mechanism of electron transfer is studied by means of quantum dynamics simulations using an extended Hückel Hamiltonian. It is found that the inclusion of the nuclear motion is necessary to observe the photoinduced electron transfer. In particular, the fluctuations of the dihedral angle between the terrylene and the phenyl ring modulate the localization and thus the electronic coupling between the donor and acceptor states involved in the injection process. The electron propagation shows characteristic oscillatory features that correlate with interatomic distance fluctuations in the bridge, which are associated with the vibrational modes driving the process. The understanding of such effects is important for the design of functional dyes with optimal injection and rectification properties. PMID:26266622

  20. Carbon Electrode-Molecule Junctions: A Reliable Platform for Molecular Electronics.

    Jia, Chuancheng; Ma, Bangjun; Xin, Na; Guo, Xuefeng

    2015-09-15

    The development of reliable approaches to integrate individual or a small collection of molecules into electrical nanocircuits, often termed "molecular electronics", is currently a research focus because it can not only overcome the increasing difficulties and fundamental limitations of miniaturization of current silicon-based electronic devices, but can also enable us to probe and understand the intrinsic properties of materials at the atomic- and/or molecular-length scale. This development might also lead to direct observation of novel effects and fundamental discovery of physical phenomena that are not accessible by traditional materials or approaches. Therefore, researchers from a variety of backgrounds have been devoting great effort to this objective, which has started to move beyond simple descriptions of charge transport and branch out in different directions, reflecting the interdisciplinarity. This Account exemplifies our ongoing interest and great effort in developing efficient lithographic methodologies capable of creating molecular electronic devices through the combination of top-down micro/nanofabrication with bottom-up molecular assembly. These devices use nanogapped carbon nanomaterials (such as single-walled carbon nanotubes (SWCNTs) and graphene), with a particular focus on graphene, as point contacts formed by electron beam lithography and precise oxygen plasma etching. Through robust amide linkages, functional molecular bridges terminated with diamine moieties are covalently wired into the carboxylic acid-functionalized nanogaps to form stable carbon electrode-molecule junctions with desired functionalities. At the macroscopic level, to improve the contact interface between electrodes and organic semiconductors and lower Schottky barriers, we used SWCNTs and graphene as efficient electrodes to explore the intrinsic properties of organic thin films, and then build functional high-performance organic nanotransistors with ultrahigh responsivities

  1. Rectification cleaning AsCl3 from the admixture of oxygen

    Maznitska O. V.

    2008-06-01

    Full Text Available The process of the rectification cleaning of three-chlorous arsenic from the admixtures of products of his hydrolysis in the atmosphere of chlorous hydrogen has been considered in the article. Dependence of coefficient of relative volatility a three-chlorous arsenic from his concentration in muriatic solution is explored. The conduct of coefficient of relative volatility with concentrations of HCl and AsCl3 is compared. Saving of equalization of balance and equalization of working curve of column at such conduct of process of rectification is shown.

  2. In-silico bonding schemes to encode chemical bonds involving sharing of electrons in molecular structures.

    Punnaivanam, Sankar; Sathiadhas, Jerome Pastal Raj; Panneerselvam, Vinoth

    2016-05-01

    Encoding of covalent and coordinate covalent bonds in molecular structures using ground state valence electronic configuration is achieved. The bonding due to electron sharing in the molecular structures is described with five fundamental bonding categories viz. uPair-uPair, lPair-uPair, uPair-lPair, vPair-lPair, and lPair-lPair. The involvement of lone pair electrons and the vacant electron orbitals in chemical bonding are explained with bonding schemes namely "target vacant promotion", "source vacant promotion", "target pairing promotion", "source pairing promotion", "source cation promotion", "source pairing double bond", "target vacant occupation", and "double pairing promotion" schemes. The bonding schemes are verified with a chemical structure editor. The bonding in the structures like ylides, PCl5, SF6, IF7, N-Oxides, BF4(-), AlCl4(-) etc. are explained and encoded unambiguously. The encoding of bonding in the structures of various organic compounds, transition metals compounds, coordination complexes and metal carbonyls is accomplished. PMID:27041446

  3. Molecular Tomography of the Quantum State by Time-Resolved Electron Diffraction

    A. A. Ischenko

    2013-01-01

    Full Text Available A procedure is described that can be used to reconstruct the quantum state of a molecular ensemble from time-dependent internuclear probability density functions determined by time-resolved electron diffraction. The procedure makes use of established techniques for evaluating the density matrix and the phase-space joint probability density, that is, the Wigner function. A novel expression for describing electron diffraction intensities in terms of the Wigner function is presented. An approximate variant of the method, neglecting the off-diagonal elements of the density matrix, was tested by analyzing gas electron diffraction data for N2 in a Boltzmann distribution and TRED data obtained from the 193 nm photodissociation of CS2 to carbon monosulfide, CS, at 20, 40, and 120 ns after irradiation. The coherent changes in the nuclear subsystem by time-resolved electron diffraction method determine the fundamental transition from the standard kinetics to the dynamics of the phase trajectory of the molecule and the tomography of molecular quantum state.

  4. Atomic and molecular complex resonances from real eigenvalues using standard (hermitian) electronic structure calculations

    Landau, Arie; Kaprálová-Žďánská, Petra Ruth; Moiseyev, Nimrod

    2015-01-01

    Complex eigenvalues, resonances, play an important role in large variety of fields in physics and chemistry. For example, in cold molecular collision experiments and electron scattering experiments, autoionizing and pre-dissociative metastable resonances are generated. However, the computation of complex resonance eigenvalues is difficult, since it requires severe modifications of standard electronic structure codes and methods. Here we show how resonance eigenvalues, positions and widths, can be calculated using the standard, widely used, electronic-structure packages. Our method enables the calculations of the complex resonance eigenvalues by using analytical continuation procedures (such as Pad\\'{e}). The key point in our approach is the existence of narrow analytical passages from the real axis to the complex energy plane. In fact, the existence of these analytical passages relies on using finite basis sets. These passages become narrower as the basis set becomes more complete, whereas in the exact limit,...

  5. Phonon-Induced Electron-Hole Excitation and ac Conductance in Molecular Junction

    Ueda, Akiko; Utsumi, Yasuhiro; Imamura, Hiroshi; Tokura, Yasuhiro

    2016-04-01

    We investigate the linear ac conductance of molecular junctions under a fixed dc bias voltage in the presence of an interaction between a transporting electron and a single local phonon in a molecule with energy ω0. The electron-phonon interaction is treated by the perturbation expansion. The ac conductance as a function of the ac frequency ωac decreases or increases compared with the noninteracting case depending on the magnitude of the dc bias voltage. Furthermore, a dip emerges at ωac ˜ 2ω0. The dip originates from the modification of electron-hole excitation by the ac field, which cannot be obtained by treating the phonon in the linear regime of a classical forced oscillation.

  6. Electron ionization LC-MS with supersonic molecular beams--the new concept, benefits and applications.

    Seemann, Boaz; Alon, Tal; Tsizin, Svetlana; Fialkov, Alexander B; Amirav, Aviv

    2015-11-01

    A new type of electron ionization LC-MS with supersonic molecular beams (EI-LC-MS with SMB) is described. This system and its operational methods are based on pneumatic spray formation of the LC liquid flow in a heated spray vaporization chamber, full sample thermal vaporization and subsequent electron ionization of vibrationally cold molecules in supersonic molecular beams. The vaporized sample compounds are transferred into a supersonic nozzle via a flow restrictor capillary. Consequently, while the pneumatic spray is formed and vaporized at above atmospheric pressure the supersonic nozzle backing pressure is about 0.15 Bar for the formation of supersonic molecular beams with vibrationally cold sample molecules without cluster formation with the solvent vapor. The sample compounds are ionized in a fly-though EI ion source as vibrationally cold molecules in the SMB, resulting in 'Cold EI' (EI of vibrationally cold molecules) mass spectra that exhibit the standard EI fragments combined with enhanced molecular ions. We evaluated the EI-LC-MS with SMB system and demonstrated its effectiveness in NIST library sample identification which is complemented with the availability of enhanced molecular ions. The EI-LC-MS with SMB system is characterized by linear response of five orders of magnitude and uniform compound independent response including for non-polar compounds. This feature improves sample quantitation that can be approximated without compound specific calibration. Cold EI, like EI, is free from ion suppression and/or enhancement effects (that plague ESI and/or APCI) which facilitate faster LC separation because full separation is not essential. The absence of ion suppression effects enables the exploration of fast flow injection MS-MS as an alternative to lengthy LC-MS analysis. These features are demonstrated in a few examples, and the analysis of the main ingredients of Cannabis on a few Cannabis flower extracts is demonstrated. Finally, the advantages of

  7. Quantum Effects in Nanoantennas and Their Applications in Tunability, Mixing, and Rectification

    Chen, Pai-Yen

    2015-08-04

    It has been recently shown that optical nanoantennas made of single or paired metallic nanoparticles can efficiently couple the propagating light into and from deeply subwavelength volumes. The strong light-matter interaction mediated by surface plasmons in metallic nanostructures allows for localizing optical fields to a subdiffraction-limited region, thereby enhancing emission of nanoemitters and offering the flexible control of nanofocused radiation. Here we theoretically study the nanodipole antennas with submicroscopic gaps, i.e. a few nanometers, for which there exists linear and high-order nonlinear quantum conductivities due to the photon-assisted tunneling effect. Noticeably, these quantum conductivities induced at the nanogap are enhanced by several orders of magnitude, due to the strongly localized optical fields associated with the plasmonic resonance.In this talk, we will show that by tailoring the geometry of nanoantennas and the quantum well structure, a quantum nanodipole antenna with a gap size of few nanometers can induce linear, high-order quantum conductivities that are considerably enhanced by the surface plasmon resonance. We envisage here a number of intriguing nanophotonic applications of these quantum nanoantennas, including (i) modulatable and switchable radiators and metamaterials, with electronic and all-optical tuning (which is related to the two photon absorption), (ii) optical rectification for detection and energy harvesting of infrared and visible light, which are related to the relevant second-order quantum conductivity, (iii) harmonic sensing for the work function and the optical index of nanoparticle, e.g. DNA and molecules, loaded inside the nanogap, and (iv) high harmonic generation and wave mixing with nonlinear quantum conductivities.

  8. Unoccupied electronic structure and molecular orientation of rubrene; from evaporated films to single crystals

    Ueba, T.; Park, J.; Terawaki, R.; Watanabe, Y.; Yamada, T.; Munakata, T.

    2016-07-01

    Two-photon photoemission (2PPE) spectroscopy and ultraviolet photoemission spectroscopy (UPS) have been performed for rubrene single crystals and evaporated thin films on highly oriented pyrolytic graphite (HOPG). The changes in the 2PPE intensity from the single crystals by the polarization of the light and by the angle of the light incident plane against the crystalline axes indicate that the molecular arrangement on the surface is similar to that in the bulk crystal. On the other hand, in the case of evaporated films, the polarization dependence of 2PPE indicates that the tetracene backbone becomes standing upright as the thickness increases. In spite of the alignment of molecules, the broadened 2PPE spectral features for thick films suggest that the films are amorphous and molecules are in largely different environments. The film structures are confirmed by scanning tunneling microscopy (STM). The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) derived levels of the single crystal are shifted by + 0.18 and - 0.20 eV, respectively, from those of the 0.8 ML film. The shifts are attributed to the packing density of molecules. It is shown that the unoccupied electronic structure is more sensitively affected by the film structure than the occupied electronic structure.

  9. Electron scattering by biomass molecular fragments: useful data for plasma applications?*

    Ridenti, Marco A.; Amorim Filho, Jayr; Brunger, Michael J.; da Costa, Romarly F.; Varella, Márcio T. do N.; Bettega, Márcio H. F.; Lima, Marco A. P.

    2016-08-01

    Recent data obtained for electron scattering by biomass molecular fragments, indicated that low-energy resonances may have an important role in the de-lignification of biomass through a plasma pre-treatment. To support these findings, we present new experimental evidence of the predicted dissociation pathways on plasma treatment of biomass. An important question is how accurate must the experimental and/or the theoretical data be in order to indicate that plasma modelings can be really useful in understanding plasma applications? In this paper, we initiate a discussion on the role of data accuracy of experimental and theoretical electron-molecule scattering cross sections in plasma modeling. First we review technological motivations for carrying out electron-molecule scattering studies. Then we point out the theoretical and experimental limitations that prevent us from obtaining more accurate cross sections. We present a few examples involving biomass molecular fragments, to illustrate theoretical inaccuracies on: resonances positions and widths, electronic excitation, superelastic cross sections from metastable states and due to multichannel effects on the momentum transfer cross sections. On the experimental side we briefly describe challenges in making absolute cross sections measurements with biomass species and radicals. And finally, through a simulation of a N2 plasma, we illustrate the impact on the simulation due to inaccuracies on the resonance positions and widths and due to multichannel effects on the momentum transfer cross sections. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.Supplementary material in the form of one pdf and two mp4 files available from the Journal web page at http://dx.doi.org/10.1140/epjd/e2016-70272-8

  10. Orbital Interaction Mechanisms of Conductance Enhancement and Rectification by Dithiocarboxylate Anchoring Group

    Li, Zhenyu; Kosov, D. S.

    2006-01-01

    We study computationally the electron transport properties of dithiocarboxylate terminated molecular junctions. Transport properties are computed self-consistently within density functional theory and nonequilibrium Green's functions formalism. A microscopic origin of the experimentally observed current amplification by dithiocarboxylate anchoring groups is established. For the 4,4'-biphenyl bis(dithiocarboxylate) junction, we find that the interaction of the lowest unoccupied molecular orbit...

  11. Photon-assisted electronic and spin transport in a junction containing precessing molecular spin

    Filipović, Milena; Belzig, Wolfgang

    2016-02-01

    We study the ac charge and -spin transport through an orbital of a magnetic molecule with spin precessing in a constant magnetic field. We assume that the source and drain contacts have time-dependent chemical potentials. We employ the Keldysh nonequilibrium Green's functions method to calculate the spin and charge currents to linear order in the time-dependent potentials. The molecular and electronic spins are coupled via exchange interaction. The time-dependent molecular spin drives inelastic transitions between the molecular quasienergy levels, resulting in a rich structure in the transport characteristics. The time-dependent voltages allow us to reveal the internal precession time scale (the Larmor frequency) by a dc conductance measurement if the ac frequency matches the Larmor frequency. In the low-ac-frequency limit the junction resembles a classical electric circuit. Furthermore, we show that the setup can be used to generate dc-spin currents, which are controlled by the molecular magnetization direction and the relative phases between the Larmor precession and the ac voltage.

  12. Artificial light-harvesting antennae: electronic energy transfer by way of molecular funnels.

    Ziessel, Raymond; Harriman, Anthony

    2011-01-14

    Electronic energy transfer (EET) plays a critical role in many biological processes and is used by nature to direct energy to a site where chemical reactions need to be initiated. Such EET can occur over large distances and can involve many individual molecules of identical, similar or disparate chemical identity. Advances in spectroscopy and data processing have allowed the rates of EET to be measured on extremely fast timescales such that improved mechanistic insight becomes feasible. At the same time, highly sophisticated synthetic operations have been devised that facilitate the isolation and purification of elaborate multi-component molecular arrays. A key feature of these arrays concerns the logical positioning of individual units in a way that favours directed EET along the molecular axis or along some other preferred pathway. The availability of these novel molecular materials allows close examination of popular theoretical models and paves the way for the development of advanced molecular sensors, artificial light harvesters, fluorescent labels and sensitizers. Of particular interest is the spectacular growth in the application of boron dipyrromethene dyes as basic reagents in such artificial photon collectors and these compounds have dominated the market in recent years because of their synthetic versatility and valuable photophysical properties. In this article, recent developments in the field are highlighted in terms of synthesis and subsequent spectroscopic exploration. PMID:20957235

  13. Uncovering a law of corresponding states for electron tunneling in molecular junctions.

    Bâldea, Ioan; Xie, Zuoti; Frisbie, C Daniel

    2015-06-21

    Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner in terms of reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws of corresponding states contain numerical factors adjusted empirically. Here, we report a law of corresponding states deduced analytically for charge transport via tunneling in molecular junctions, which we validate against current-voltage measurements for conducting probe atomic force microscope junctions based on benchmark molecular series (oligophenylenedithiols and alkanedithiols) and electrodes (silver, gold, and platinum), as well as against transport data for scanning tunneling microscope junctions. Two salient features distinguish the present law of corresponding states from all those known previously. First, it is expressed by a universal curve free of empirical parameters. Second, it demonstrates that a universal behavior is not necessarily affected by strong stochastic fluctuations often observed in molecular electronics. An important and encouraging message of this finding is that transport behavior across different molecular platforms can be similar and extraordinarily reproducible. PMID:26008991

  14. Resonanant enhancement of molecular excitation intensity in inelastic electron scattering spectrum owing to interaction with plasmons in metallic nanoshell

    Goliney, I Yu

    2014-01-01

    A quantum-mechanical model to calculate the electron energy-loss spectra (EELS) for the system of a closely located metallic nanoshell and a molecule has been developed. At the resonance between the molecular excitation and plasmon modes in the nanoshell, which can be provided by a proper choice of the ratio of the inner and outer nanoshell radii, the cross-section of inelastic electron scattering at the molecular excitation energy is shown to grow significantly, because the molecular transition borrows the oscillator strength from a plasmon. The enhancement of the inelastic electron scattering by the molecule makes it possible to observe molecular transitions with an electron microscope. The dependences of the EEL spectra on the relative arrangement of the molecule and the nanoshell, the ratio between the inner and outer nanoshell radii, and the scattering angle are plotted and analyzed.

  15. 27 CFR 1.82 - Acquiring or receiving distilled spirits in bulk for redistillation, processing, rectification...

    2010-04-01

    ... distilled spirits in bulk for redistillation, processing, rectification, warehousing, or warehousing and..., NONINDUSTRIAL USE OF DISTILLED SPIRITS AND WINE, BULK SALES AND BOTTLING OF DISTILLED SPIRITS Bulk Sales and Bottling of Distilled Spirits Bulk Sales and Bottling § 1.82 Acquiring or receiving distilled spirits...

  16. Self-assembling monolayers of helical oligopeptides with applications in molecular electronics

    Strong, A E

    1997-01-01

    prepared. Transformation of the two (Trt)Cys residues of the resin-bound peptide to the intramolecular disulphide by iodine was achieved in acetonitrile but not in DMF. CD suggested that the conformation of this peptide was a mixture of helix and random coil. Films of the peptide-disulphide and the peptide-dithiol adsorbed from protic solvents were characterised as multilayers by ellipsometry. However CV and ellipsometry showed that a monolayer was successfully prepared from acetonitrile. Future targets for improving and extending this method to form monolayers of linked disulphides are presented. The aim of this project was to develop a generic method of preparing a 'molecular architecture' containing functional groups on a surface at predetermined relative positions several nm apart. This would be of great utility in molecular electronics, chemical sensors and other fields. It was proposed that such an architecture could be prepared on gold using linked, helical oligopeptides that contained the components o...

  17. A morphological study of molecularly imprinted polymers using the scanning electron microscope

    Molecular imprinting is an emerging technique for producing polymers with applications in affinity-based separation, in biomimetic sensors, in catalysis, etc. This variety of uses relies upon the production of polymers with different affinities, specificities, sensitivities and loading capacities. Research into the development of molecular imprinted polymers (MIPs) with new or improved morphologies - which involves modification of the polymerisation process - is therefore underway. This paper reports a comparative study of non-covalent MIPs synthesised by 'bulk' polymerisation using digoxin as template. These were synthesised under different conditions, i.e., changing the functional monomers employed (methacrylic acid or 2-vinylpyridine), the porogens (acetonitrile or dichloromethane) used, and by altering the volume of the latter. The polymerisation process was allowed to proceed either under UV light or in a thermostat-controlled waterbath. The surface morphology (was determined by scanning electron microscopy) and the ability of the different polymers to selectively rebind the template was then evaluated

  18. Small molecules make big differences: molecular doping effects on electronic and optical properties of phosphorene

    Systematical computations on the density functional theory were performed to investigate the adsorption of three typical organic molecules, tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE) and tetrathiafulvalene (TTF), on the surface of phosphorene monolayers and thicker layers. There exist considerable charge transfer and strong non-covalent interaction between these molecules and phosphorene. In particular, the band gap of phosphorene decreases dramatically due to the molecular modification and can be further tuned by applying an external electric field. Meanwhile, surface molecular modification has proven to be an effective way to enhance the light harvesting of phosphorene in different directions. Our results predict a flexible method toward modulating the electronic and optical properties of phosphorene and shed light on its experimental applications. (paper)

  19. Effects of Contact Atomic Structure on Electronic Transport in Molecular Junction

    Based on nonequilibrium Green's function and first-principles calculations, we investigate the change in molecular conductance caused by different adsorption sites with the presence of additional Au atom around the metal-molecule contact in the system that benzene sandwiched between two Au(111) leads. The motivation is the variable situations that may arise in break junction experiments. Numerical results show that the enhancement of conductance induced by the presence of additional Au is dependent on the adsorption sites of anchoring atom. When molecule is located on top site with the presence of additional Au atoms, it can increase molecular conductance remarkably and present negative differential resistance under applied bias which cannot be found in bridge and hollow sites. Furthermore, the effects of different distance between additional Au and sulfur atoms in these three adsorption sites are also discussed. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  20. A morphological study of molecularly imprinted polymers using the scanning electron microscope

    Paniagua Gonzalez, Gema [Departamento de Ciencias Analiticas, Facultad de Ciencias, Universidad Nacional de Educacion a Distancia (UNED), 28040 Madrid (Spain)]. E-mail: gpaniagua@pas.uned.es; Fernandez Hernando, Pilar [Departamento de Ciencias Analiticas, Facultad de Ciencias, Universidad Nacional de Educacion a Distancia (UNED), 28040 Madrid (Spain); Durand Alegria, J.S. [Departamento de Ciencias Analiticas, Facultad de Ciencias, Universidad Nacional de Educacion a Distancia (UNED), 28040 Madrid (Spain)

    2006-01-31

    Molecular imprinting is an emerging technique for producing polymers with applications in affinity-based separation, in biomimetic sensors, in catalysis, etc. This variety of uses relies upon the production of polymers with different affinities, specificities, sensitivities and loading capacities. Research into the development of molecular imprinted polymers (MIPs) with new or improved morphologies - which involves modification of the polymerisation process - is therefore underway. This paper reports a comparative study of non-covalent MIPs synthesised by 'bulk' polymerisation using digoxin as template. These were synthesised under different conditions, i.e., changing the functional monomers employed (methacrylic acid or 2-vinylpyridine), the porogens (acetonitrile or dichloromethane) used, and by altering the volume of the latter. The polymerisation process was allowed to proceed either under UV light or in a thermostat-controlled waterbath. The surface morphology (was determined by scanning electron microscopy) and the ability of the different polymers to selectively rebind the template was then evaluated.

  1. Coupled electronic and vibrational dynamics of a molecular ion in a strong laser field

    Vence, Nicholas; Harrison, Robert; Krstic, Predrag

    2010-03-01

    We study a response of a hydrogen molecular ion to the strong 2-cycle 800-nm laser pulse, using highly accurate numerical solution of the time-dependent Schrodinger equation in 4 spatial dimension. We use a computational approach which employs an adaptive, discontinuous spectral element basis as well as multiresolution analysis and separated representations of operators for efficient computation in multiple dimensions (MADNESS). The basis (tensor product of Legendre polynomials) automatically adapts to meet the requested precision, while the time--dependent evolution of the system is considered using an efficient Chin-Chen propagator. We vary the laser polarization with respect to the fixed molecular axis, while the coupled electron and vibrational dynamics enables calculation of the ionization, dissociation and high-harmonic generation at the ``same footing''.

  2. Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies

    Franck, John M.; Chandrasekaran, Siddarth; Dzikovski, Boris; Dunnam, Curt R.; Freed, Jack H.

    2015-06-01

    The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with π/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic → nematic → liquid-like smectic → solid-like smectic → crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane

  3. Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies

    Franck, John M.; Chandrasekaran, Siddarth; Dzikovski, Boris; Dunnam, Curt R.; Freed, Jack H., E-mail: jhf3@cornell.edu [Department of Chemistry and Chemical Biology and National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853 (United States)

    2015-06-07

    The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with π/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic → nematic → liquid-like smectic → solid-like smectic → crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane

  4. Selective visualization of point defects in carbon nanotubes at the atomic scale by an electron-donating molecular tip.

    Nishino, Tomoaki; Kanata, Satoshi; Umezawa, Yoshio

    2011-07-14

    Electron-donating molecular tips were used for the observation of single-walled carbon nanotubes (SWNTs). Defects in SWNTs were selectively visualized at the atomic scale on the basis of charge-transfer interaction with the molecular tip. PMID:21629907

  5. Molecular dynamics simulations of the structural, vibrational, and electronic properties of amorphous silicon

    Amorphous silicon models have been computer-generated by melt-quenching and film deposition molecular dynamics simulations, employing classical interatomic Si-potentials. The structural, vibrational and electronic properties of these models is described. Dangling-bond gap states are well localized whereas, floating bonds gap states are considerably less localized with wavefunction amplitudes on the neighbors of the five-coordinated atom. In contrast to melt-quenched models, the a-Si films displayed voids, a 15-28% lower density than c-Si, and no five- coordinated atoms. A-Si:H models with 5 and 22% hydrogen, and both monohydride and dihydride species, have also been developed

  6. Electronic Friction-Based Vibrational Lifetimes of Molecular Adsorbates: Beyond the Independent-Atom Approximation.

    Rittmeyer, Simon P; Meyer, Jörg; Juaristi, J Iñaki; Reuter, Karsten

    2015-07-24

    We assess the accuracy of vibrational damping rates of diatomic adsorbates on metal surfaces as calculated within the local-density friction approximation (LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts for intramolecular contributions and overcomes the systematic underestimation of the nonadiabatic losses obtained within the prevalent independent-atom approximation. The quantitative agreement obtained with theoretical and experimental benchmark data suggests the LDFA-AIM scheme as an efficient and reliable approach to account for electronic dissipation in ab initio molecular dynamics simulations of surface chemical reactions. PMID:26252696

  7. Proton-Coupled Electron Transfer in Molecular Electrocatalysis: Theoretical Methods and Design Principles

    Solis, Brian H.; Hammes-Schiffer, Sharon

    2014-07-07

    Molecular electrocatalysts play an essential role in a wide range of energy conversion processes. The objective of electrocatalyst design is to maximize the turnover frequency and minimize the overpotential for the overall catalytic cycle. Typically the catalytic cycle is dominated by key proton-coupled electron transfer (PCET) processes comprised of sequential or concerted electron transfer and proton transfer steps. A variety of theoretical methods have been developed to investigate the mechanisms, thermodynamics, and kinetics of PCET processes in electrocatalytic cycles. Electronic structure methods can be used to calculate the reduction potentials and pKa’s and to generate thermodynamic schemes, free energy reaction pathways, and Pourbaix diagrams, which indicate the most stable species at each pH and potential. These types of calculations have assisted in identifying the thermodynamically favorable mechanisms under specified experimental conditions, such as acid strength and overpotential. Such calculations have also revealed linear correlations among the thermodynamic properties, which can be used to predict the impact of modifying the ligand, substituents, or metal center. The role of non-innocent ligands, namely ligand protonation or reduction, has also been examined theoretically. In addition, the rate constants for electron and proton transfer reactions, as well as concerted PCET reactions, have been calculated to investigate the kinetics of molecular electrocatalysts. The concerted PCET mechanism is thought to lower the overpotential required for catalysis by avoiding high-energy intermediates. Rate constant calculations have revealed that the concerted mechanism involving intramolecular proton transfer will be favored by designing more flexible ligands that facilitate the proton donor-acceptor motion while also maintaining a sufficiently short equilibrium proton donor-acceptor distance. Overall, theoretical methods have assisted in the interpretation

  8. Deep electron traps in CdTe:In films grown by molecular beam epitaxy

    Zakrzewski, A.K.; Dobaczewski, L.; Karczewski, G.; Wojtowicz, T.; Kossut, J. [Institute of Physics, Polish Academy of Science, Warsaw (Poland)

    1995-12-31

    N-type indium CdTe grown on n{sup +}-GaAs molecular beam epitaxy has been studied by the standard deep level transient spectroscopy and the isothermal Laplace-transform deep level transient spectroscopy. It was found that the Cd/Te flux ratio strongly influences the deep level transient spectroscopy results. The unusual temperature dependence of the electron emission rate in films grown at nearly stoichiometric conditions may point out that the observed defect is resonant with the conduction band. (author). 5 refs, 1 fig.

  9. High electron mobility in Ga(In)NAs films grown by molecular beam epitaxy

    We report the highest mobility values above 2000 cm2/Vs in Si doped GaNAs film grown by molecular beam epitaxy. To understand the feature of the origin which limits the electron mobility in GaNAs, temperature dependences of mobility were measured for high mobility GaNAs and referential low mobility GaInNAs. Temperature dependent mobility for high mobility GaNAs is similar to the GaAs case, while that for low mobility GaInNAs shows large decrease in lower temperature region. The electron mobility of high quality GaNAs can be explained by intrinsic limiting factor of random alloy scattering and extrinsic factor of ionized impurity scattering.

  10. Electron spin resonance studies on reduction process of nitroxyl spin radicals used in molecular imaging

    The Electron spin resonance studies on the reduction process of nitroxyl spin probes were carried out for 1mM 14N labeled nitroxyl radicals in pure water and 1 mM concentration of ascorbic acid as a function of time. The electron spin resonance parameters such as signal intensity ratio, line width, g-value, hyperfine coupling constant and rotational correlation time were determined. The half life time was estimated for 1mM 14N labeled nitroxyl radicals in 1 mM concentration of ascorbic acid. The ESR study reveals that the TEMPONE has narrowest line width and fast tumbling motion compared with TEMPO and TEMPOL. From the results, TEMPONE has long half life time and high stability compared with TEMPO and TEMPOL radical. Therefore, this study reveals that the TEMPONE radical can act as a good redox sensitive spin probe for molecular imaging

  11. Center for Molecular Electronics, University of Missouri, St. Louis. Environmental Assessment

    1994-06-01

    The Department of Energy (DOE) proposes to authorize the University of Missouri, St. Louis to proceed with the detailed design and construction of the proposed Center for Molecular Electronics. The proposed Center would consist of laboratories and offices housed in a three-story building on the University campus. The proposed modular laboratories would be adaptable for research activities principally related to physics, chemistry, and electrical engineering. Proposed research would include the development and application of thin-film materials, semi-conductors, electronic sensors and devices, and high-performance polymers. Specific research for the proposed Center has not yet been formulated, therefore, specific procedures for any particular process or study cannot be described at this time. The proposed construction site is an uncontaminated panel of land located on the University campus. This report contains information about the environmental assessment that was performed in accordance with this project.

  12. Studies of the surface structures of molecular crystals and of adsorbed molecular monolayers on the (111) crystal faces of platinum and silver by low-energy electron diffraction

    The structures of molecular crystal surfaces were investigated for the first time by the use of low-energy electron diffraction (LEED). The experimental results from a variety of molecular crystals were examined and compared as a first step towards understanding the properties of these surfaces on a microscopic level. The method of sample preparation employed, vapor deposition onto metal single-crystal substrates at low temperatures in ultrahigh vacuum, allowed concurrent study of the structures of adsorbed monolayers on metal surfaces and of the growth processes of molecular films on metal substrates. The systems investigated were ice, ammonia, naphthalene, benzene, the n-paraffins (C3 to C8), cyclohexane, trioxane, acetic acid, propionic acid, methanol, and methylamine adsorbed and condensed on both Pt(111) and Ag(111) surfaces. Electron-beam-induced damage of the molecular surfaces was observed after electron exposures of 10-4 A sec cm-2 at 20 eV. Aromatic molecular crystal samples were more resistant to damage than samples of saturated molecules. The quality and orientation of the grown molecular crystal films were influenced by substrate preparation and growth conditions. Forty ordered monolayer structures were observed. 110 figures, 22 tables, 162 references

  13. Electron emission and molecular fragmentation during hydrogen and deuterium ion impact on carbon surfaces

    Qayyum, A.; Schustereder, W.; Mair, C.; Scheier, P.; Märk, T. D.; Cernusca, S.; Winter, HP.; Aumayr, F.

    2003-03-01

    Molecular fragmentation and electron emission during hydrogen ion impact on graphite surfaces has been investigated in the eV to keV impact energy region typical for fusion edge plasma conditions. As a target surface graphite tiles for the Tokamak experiment Tore Supra in CEA-Cadarache/France and highly oriented pyrolytic graphite (HOPG) have been used. For both surfaces studied, the experimentally observed threshold for electron emission is at about 50 eV/amu impact energy. Electron emission from the high conductivity side of the carbon tile is 15-20% less as compared to its low conductivity side, whereas results for HOPG are generally between these two cases. Deuterium and hydrogen ions are almost equally effective in liberating electrons from graphite when comparing results for the same impact velocity. Surface-induced dissociation of deuterium ions D 3+ upon impact on Tore Supra graphite tiles, in the collision energy range of 20-100 eV, produced only atomic fragment ions D +. The other possible fragment ion D 2+ could not be observed.

  14. Calculation of the spectrum of quasiparticle electron excitations in organic molecular semiconductors

    Tikhonov, E. V.; Uspenskii, Yu. A.; Khokhlov, D. R.

    2015-06-01

    A quasiparticle electronic spectrum belongs to the characteristics of nanoobjects that are most important for applications. The following methods of calculating the electronic spectrum are analyzed: the Kohn-Sham equations of the density functional theory (DFT), the hybrid functional method, the GW approximation, and the Lehmann approximation used in the spectral representation of one-electron Green's function. The results of these approaches are compared with the data of photoemission measurements of benzene, PTCDA, and phthalocyanine (CuPc, H2Pc, FePc, PtPc) molecules, which are typical representatives of organic molecular semiconductors (OMS). This comparison demonstrates that the Kohn-Sham equations of DFT incorrectly reproduce the electronic spectrum of OMS. The hybrid functional method correctly describes the spectrum of the valence and conduction bands; however, the HOMO-LUMO gap width is significantly underestimated. The correct gap width is obtained in both the GW approximation and the Lehmann approach, and the total energy in this approach can be calculated in the local density approximation of DFT.

  15. Calculation of the spectrum of quasiparticle electron excitations in organic molecular semiconductors

    Tikhonov, E. V., E-mail: tikhonov@mig.phys.msu.ru [Moscow State University (Russian Federation); Uspenskii, Yu. A. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Khokhlov, D. R. [Moscow State University (Russian Federation)

    2015-06-15

    A quasiparticle electronic spectrum belongs to the characteristics of nanoobjects that are most important for applications. The following methods of calculating the electronic spectrum are analyzed: the Kohn-Sham equations of the density functional theory (DFT), the hybrid functional method, the GW approximation, and the Lehmann approximation used in the spectral representation of one-electron Green’s function. The results of these approaches are compared with the data of photoemission measurements of benzene, PTCDA, and phthalocyanine (CuPc, H{sub 2}Pc, FePc, PtPc) molecules, which are typical representatives of organic molecular semiconductors (OMS). This comparison demonstrates that the Kohn-Sham equations of DFT incorrectly reproduce the electronic spectrum of OMS. The hybrid functional method correctly describes the spectrum of the valence and conduction bands; however, the HOMO-LUMO gap width is significantly underestimated. The correct gap width is obtained in both the GW approximation and the Lehmann approach, and the total energy in this approach can be calculated in the local density approximation of DFT.

  16. Electron emission and molecular fragmentation during hydrogen and deuterium ion impact on carbon surfaces

    Molecular fragmentation and electron emission during hydrogen ion impact on graphite surfaces has been investigated in the eV to keV impact energy region typical for fusion edge plasma conditions. As a target surface graphite tiles for the Tokamak experiment Tore Supra in CEA-Cadarache/France and highly oriented pyrolytic graphite (HOPG) have been used. For both surfaces studied, the experimentally observed threshold for electron emission is at about 50 eV/amu impact energy. Electron emission from the high conductivity side of the carbon tile is 15-20% less as compared to its low conductivity side, whereas results for HOPG are generally between these two cases. Deuterium and hydrogen ions are almost equally effective in liberating electrons from graphite when comparing results for the same impact velocity. Surface-induced dissociation of deuterium ions D3+ upon impact on Tore Supra graphite tiles, in the collision energy range of 20-100 eV, produced only atomic fragment ions D+. The other possible fragment ion D2+ could not be observed

  17. Effect Of Electron Beam Irradiation On The Molecular And Colour Properties Of Chlorinated Polyvinyl Chloride

    Polymeric films of chlorinated polyvinyl chloride (CPVC) of nearly 0.25 mm thickness could be obtained by dissolving one gram of CPVC in 10 ml of freshly distilled tetrahydrofurane. Samples from these films were irradiated with different electron beam doses in the range 5-100 kGy. The structural modifications in the electron beam irradiated CPVC samples have been studied as a function of dose using intrinsic viscosity. The results indicate that the electron beam irradiation of CPVC in the dose range 40-100 kGy resulted in an improvement in its intrinsic viscosity and thus in its average molecular mass. Furthermore, the transmission of these samples in the wavelength range 200-2500 nm, as well as any colour changes, was studied. Using the transmission data, both the tri stimulus and the Commission Internationale de l'Eclairage (CIE) LAB coordinate values were calculated. In addition, the colour differences between the non-irradiated sample and those irradiated with different doses were calculated. The results indicate that the CPVC polymer has more response to colour change by electron beam irradiation and accompanied by a significant increase in the yellow and green colour components.

  18. Effects of electron-phonon interaction on thermal and electrical transport through molecular nano-conductors

    Lü, Jing-Tao, E-mail: jtlu@hust.edu.cn [School of Physics, Huazhong University of Science and Technology, 430074 Wuhan (China); Zhou, Hangbo [Department of Physics and Center for Computational Science and Engineering, National University of Singapore, 117551 Singapore (Singapore); NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 117456 Singapore (Singapore); Jiang, Jin-Wu [Shanghai Institute of Applied Mathematics and Mechanics, Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai University, 200072 Shanghai (China); Wang, Jian-Sheng [Department of Physics and Center for Computational Science and Engineering, National University of Singapore, 117551 Singapore (Singapore)

    2015-05-15

    The topic of this review is the effects of electron-phonon interaction (EPI) on the transport properties of molecular nano-conductors. A nano-conductor connects to two electron leads and two phonon leads, possibly at different temperatures or chemical potentials. The EPI appears only in the nano-conductor. We focus on its effects on charge and energy transport. We introduce three approaches. For weak EPI, we use the nonequilibrium Green’s function method to treat it perturbatively. We derive the expressions for the charge and heat currents. For weak system-lead couplings, we use the quantum master equation approach. In both cases, we use a simple single level model to study the effects of EPI on the system’s thermoelectric transport properties. It is also interesting to look at the effect of currents on the dynamics of the phonon system. For this, we derive a semi-classical generalized Langevin equation to describe the nano-conductor’s atomic dynamics, taking the nonequilibrium electron system, as well as the rest of the atomic degrees of freedom as effective baths. We show simple applications of this approach to the problem of energy transfer between electrons and phonons.

  19. Effects of electron-phonon interaction on thermal and electrical transport through molecular nano-conductors

    The topic of this review is the effects of electron-phonon interaction (EPI) on the transport properties of molecular nano-conductors. A nano-conductor connects to two electron leads and two phonon leads, possibly at different temperatures or chemical potentials. The EPI appears only in the nano-conductor. We focus on its effects on charge and energy transport. We introduce three approaches. For weak EPI, we use the nonequilibrium Green’s function method to treat it perturbatively. We derive the expressions for the charge and heat currents. For weak system-lead couplings, we use the quantum master equation approach. In both cases, we use a simple single level model to study the effects of EPI on the system’s thermoelectric transport properties. It is also interesting to look at the effect of currents on the dynamics of the phonon system. For this, we derive a semi-classical generalized Langevin equation to describe the nano-conductor’s atomic dynamics, taking the nonequilibrium electron system, as well as the rest of the atomic degrees of freedom as effective baths. We show simple applications of this approach to the problem of energy transfer between electrons and phonons

  20. On the dissociative electron attachment as a potential source of molecular hydrogen in irradiated liquid water

    Cobut, V.; Jay-Gerin, J.-P.; Frongillo, Y. [Sherbrooke Univ., PQ (Canada). Faculte de Medecine; Patau, J.P. [Toulouse-3 Univ., 31 (France)

    1996-02-01

    In the radiolysis of liquid water, different mechanisms for the formation of molecular hydrogen (H{sub 2}) are involved at different times after the initial energy disposition. It has been suggested that the contributions of the e{sub aq}{sup -} + e{sub aq}{sup -}, H + e{sub aq}{sup -} and H + H reactions between hydrated electrons (e{sub aq}{sup -}) and hydrogen atoms in the spurs are not sufficient to account for all of the observed H{sub 2} yield (0.45 molecules/100 eV) on the microsecond time scale. Addressing the question of the origin of an unscavengeable H{sub 2} yield of 0.15 molecules/100 eV produced before spur expansion, we suggest that the dissociative capture of the so-called vibrationally-relaxing electrons by H{sub 2}O molecules is a possible pathway for the formation of part of the initial H{sub 2} yield. Comparison of recent dissociative-electron-attachment H{sup -}-anion yield-distribution measurements from amorphous H{sub 2}O films with the energy spectrum of vibrationally-relaxing electrons in irradiated liquid water, calculated by Monte Carlo simulations, plays in favor of this hypothesis. (author).

  1. Effects of electron-phonon interaction on thermal and electrical transport through molecular nano-conductors

    Jing-Tao Lü

    2015-05-01

    Full Text Available The topic of this review is the effects of electron-phonon interaction (EPI on the transport properties of molecular nano-conductors. A nano-conductor connects to two electron leads and two phonon leads, possibly at different temperatures or chemical potentials. The EPI appears only in the nano-conductor. We focus on its effects on charge and energy transport. We introduce three approaches. For weak EPI, we use the nonequilibrium Green’s function method to treat it perturbatively. We derive the expressions for the charge and heat currents. For weak system-lead couplings, we use the quantum master equation approach. In both cases, we use a simple single level model to study the effects of EPI on the system’s thermoelectric transport properties. It is also interesting to look at the effect of currents on the dynamics of the phonon system. For this, we derive a semi-classical generalized Langevin equation to describe the nano-conductor’s atomic dynamics, taking the nonequilibrium electron system, as well as the rest of the atomic degrees of freedom as effective baths. We show simple applications of this approach to the problem of energy transfer between electrons and phonons.

  2. Carrier-envelope phase control of electron dynamics in atomic and molecular systems

    Complete test of publication follows. The availability of laser pulses with a duration down to about hundred attoseconds (= 10-16 seconds) has raised the prospect of studying the motion of electrons on the timescales where this motion occurs in nature and to study how electron motion drives structural dynamics in molecular systems. The type and amount of information that can be extracted from the electrons or ions that leave an atom, molecule or cluster upon irradiation with intense laser light is crucial for an understanding of the processes that led to their release and determined their final properties. Velocity-map imaging (VMI) has shown great promise for sub-femtosecond studies on complex systems, as the full 3D-momentum distribution can be extracted that contains not only spectral but also angular information. In a recent study using VMI it was shown that a suitable interference of attosecond electron wave packets generated in the continuum by ionization may yield information on the wavefunction of the system. Laser light with a controlled evolution of the electric field E(t) = a(t) · cos(ωt + ψ), where in addition to the amplitude a(t) and frequency ω control of the carrier-envelope phase ψ is accomplished, permitted the reliable and reproducible generation of single sub-femtosecond pulses by means of high-order harmonic generation, controlled electron emission from atoms and made possible precision attosecond metrology. These achievements have been a direct consequence of the capability of steering the motion of bound electrons in atoms as well as those having been set free from their atomic bound state. Applications of VMI for the observation of the carrier-envelope phase control of electron dynamics in atomic and molecular systems will be highlighted. Results will be presented on electron emission from above-threshold ionization (ATI) of rare-gases (Xe, Ar and Kr) with phase-stabilized intense few-cycle laser pulses. In particular, the changes in

  3. Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics

    A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed

  4. Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics

    Deyne, Andy Van Yperen-De; Pauwels, Ewald; Ghysels, An; Waroquier, Michel; Van Speybroeck, Veronique; Hemelsoet, Karen, E-mail: karen.hemelsoet@ugent.be [Center for Molecular Modeling (CMM), Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); De Meyer, Thierry [Center for Molecular Modeling (CMM), Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); Department of Textiles, Ghent University, Technologiepark 907, 9052 Zwijnaarde (Belgium); De Clerck, Karen [Department of Textiles, Ghent University, Technologiepark 907, 9052 Zwijnaarde (Belgium)

    2014-04-07

    A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed.

  5. Superluminescence from an optically pumped molecular tunneling junction by injection of plasmon induced hot electrons

    Kai Braun

    2015-05-01

    Full Text Available Here, we demonstrate a bias-driven superluminescent point light-source based on an optically pumped molecular junction (gold substrate/self-assembled molecular monolayer/gold tip of a scanning tunneling microscope, operating at ambient conditions and providing almost three orders of magnitude higher electron-to-photon conversion efficiency than electroluminescence induced by inelastic tunneling without optical pumping. A positive, steadily increasing bias voltage induces a step-like rise of the Stokes shifted optical signal emitted from the junction. This emission is strongly attenuated by reversing the applied bias voltage. At high bias voltage, the emission intensity depends non-linearly on the optical pump power. The enhanced emission can be modelled by rate equations taking into account hole injection from the tip (anode into the highest occupied orbital of the closest substrate-bound molecule (lower level and radiative recombination with an electron from above the Fermi level (upper level, hence feeding photons back by stimulated emission resonant with the gap mode. The system reflects many essential features of a superluminescent light emitting diode.

  6. Superluminescence from an optically pumped molecular tunneling junction by injection of plasmon induced hot electrons.

    Braun, Kai; Wang, Xiao; Kern, Andreas M; Adler, Hilmar; Peisert, Heiko; Chassé, Thomas; Zhang, Dai; Meixner, Alfred J

    2015-01-01

    Here, we demonstrate a bias-driven superluminescent point light-source based on an optically pumped molecular junction (gold substrate/self-assembled molecular monolayer/gold tip) of a scanning tunneling microscope, operating at ambient conditions and providing almost three orders of magnitude higher electron-to-photon conversion efficiency than electroluminescence induced by inelastic tunneling without optical pumping. A positive, steadily increasing bias voltage induces a step-like rise of the Stokes shifted optical signal emitted from the junction. This emission is strongly attenuated by reversing the applied bias voltage. At high bias voltage, the emission intensity depends non-linearly on the optical pump power. The enhanced emission can be modelled by rate equations taking into account hole injection from the tip (anode) into the highest occupied orbital of the closest substrate-bound molecule (lower level) and radiative recombination with an electron from above the Fermi level (upper level), hence feeding photons back by stimulated emission resonant with the gap mode. The system reflects many essential features of a superluminescent light emitting diode. PMID:26171286

  7. Research Update: Molecular electronics: The single-molecule switch and transistor

    Kai Sotthewes

    2014-01-01

    Full Text Available In order to design and realize single-molecule devices it is essential to have a good understanding of the properties of an individual molecule. For electronic applications, the most important property of a molecule is its conductance. Here we show how a single octanethiol molecule can be connected to macroscopic leads and how the transport properties of the molecule can be measured. Based on this knowledge we have realized two single-molecule devices: a molecular switch and a molecular transistor. The switch can be opened and closed at will by carefully adjusting the separation between the electrical contacts and the voltage drop across the contacts. This single-molecular switch operates in a broad temperature range from cryogenic temperatures all the way up to room temperature. Via mechanical gating, i.e., compressing or stretching of the octanethiol molecule, by varying the contact's interspace, we are able to systematically adjust the conductance of the electrode-octanethiol-electrode junction. This two-terminal single-molecule transistor is very robust, but the amplification factor is rather limited.

  8. Electrochemical gate-controlled electron transport of redox-active single perylene bisimide molecular junctions

    We report a scanning tunneling microscopy (STM) experiment in an electrochemical environment which studies a prototype molecular switch. The target molecules were perylene tetracarboxylic acid bisimides modified with pyridine (P-PBI) and methylthiol (T-PBI) linker groups and with bulky tert-butyl-phenoxy substituents in the bay area. At a fixed bias voltage, we can control the transport current through a symmetric molecular wire Au|P-PBI(T-PBI)|Au by variation of the electrochemical 'gate' potential. The current increases by up to two orders of magnitude. The conductances of the P-PBI junctions are typically a factor 3 larger than those of T-PBI. A theoretical analysis explains this effect as a consequence of shifting the lowest unoccupied perylene level (LUMO) in or out of the bias window when tuning the electrochemical gate potential VG. The difference in on/off ratios reflects the variation of hybridization of the LUMO with the electrode states with the anchor groups. IT-ES(T) curves of asymmetric molecular junctions formed between a bare Au STM tip and a T-PBI (P-PBI) modified Au(111) electrode in an aqueous electrolyte exhibit a pronounced maximum in the tunneling current at -0.740, which is close to the formal potential of the surface-confined molecules. The experimental data were explained by a sequential two-step electron transfer process

  9. IR-MALDI of low molecular weight compounds using a free electron laser

    Hess, Wayne P.; Park, Hee K.; Yavas, Oguz; Haglund, R. F.

    1998-05-01

    Initial experiments on infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI) using a free electron laser in the analysis of low-molecular-weight compounds are reported. Mass spectra from samples of ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and a phosphate salt were obtained. Low molecular weight (LMW) compounds are of similar mass as the molecular weight of the matrix compound and interference between matrix and analyte ions can degrade MALDI sensitivity. Under optimal conditions, however, we find little interference and that often the analyte signal exceeds the matrix signal, a result also observed in UV-MALDI of these compounds. In the IR-MALDI of EDTA near 3.0 μm the FEL results are similar to those obtained using a fixed frequency 2.94 μm Er:YAG laser of 200 ns pulse duration. However, the tunable FEL laser can selectively excite particular vibrational modes of the matrix (e.g., an OH or CO stretch) or of residual water contained within the crystalline MALDI sample. This capability was used to explore possible vaporization and ionization mechanisms of IR-MALDI for EDTA.

  10. Electron induced conformational changes of an imine-based molecular switch on a Au(111) surface

    Lotze, Christian; Henningsen, Nils; Franke, Katharina; Schulze, Gunnar; Pascual, Jose Ignacio [Inst. f. Experimentalphysik, Freie Universitaet Berlin (Germany); Luo, Ying; Haag, Rainer [Inst. f. Organische Chemie, Freie Universitaet Berlin (Germany)

    2009-07-01

    Azobenzene-based molecules exhibit a cis-trans configurational photoisomerisation in solution. Recently, the adsorption properties of azobenzene derivatives have been investigated on different metal surfaces in order to explore the possible changes in the film properties induced by external stimuli. In azobenzene, the diazo-bridge is a key group for the isomerization process. Its interaction with a metal surface is dominated through the N lone-pair electrons, which reduces the efficiency of the conformational change. In order to reduce the molecule-surface interaction, we explore an alternative molecular architecture by substituting the diazo-bridge (-N=N-) of azobenzene by an imine-group (-N=CH-). We have investigated the imine-based compound para-carboxyl-di-benzene-imine (PCI) adsorbed on a Au(111) surface. The carboxylic terminations mediates the formation of strongly bonded molecular dimers, which align in ordered rows preferentially following the fcc regions of the Au(111) herringbone reconstruction. Low temperature scanning tunneling microscopy was used to induce conformational changes between trans and cis state of individual molecules in a molecular monolayer.

  11. Contact geometry and electronic transport properties of Ag–benzene–Ag molecular junctions

    Highlights: ► We simulate Ag–benzene–Ag junctions with different contact geometries. ► Moderate benzene–Ag interactions can be realized for adsorptions through Ag adatoms. ► Molecular orbitals dominating the low-bias conductance match the contact symmetry. ► Three contact geometries deliver similar conductance consistent with the experiments. - Abstract: Contact geometry and the electronic transport properties of Ag–benzene–Ag molecular junctions have been investigated by using first-principles quantum transport simulations. Our calculations show that a moderate benzene–silver interaction can be achieved when benzene is adsorbed on the Ag(1 1 1) surface through adatoms. In this case three symmetric Ag–benzene–Ag junction models can be constructed, in which the molecule is connected to the electrodes through one or two Ag adatoms on each side. Although the contribution to the transmission around the Fermi level made by the benzene molecular orbitals depends on the number of Ag adatoms and the detailed binding configuration, the transmission coefficients at the Fermi level of the three junctions are calculated to be respectively 0.20, 0.18 and 0.16. These values are well consistent with the experimental ones of 0.24 ± 0.08. Our results thus demonstrate that the conductance of Ag–benzene–Ag junctions is rather stable regardless of the molecule/electrode contact geometry.

  12. Local-field effects in current transport through molecular electronic devices: Current density profiles and local non-equilibrium electron distributions

    Xue, Yongqiang; Ratner, Mark A.

    2004-01-01

    We analyze non-equilibrium current transport in molecular electronic devices, using as an example devices formed by two terphenyl dithiol molecules attached to gold electrodes. Using a first-principles based self-consistent matrix Green's function method, we show that the spatially resolved current density profiles and local electrochemical potential drops provide valuable information regarding the local field effect on molecular transport, which depend on the internal structure of the molecu...

  13. Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. IV. Coulomb explosion of molecular heteroclusters.

    Last, Isidore; Jortner, Joshua

    2004-11-01

    In this paper we present a theoretical and computational study of the temporal dynamics and energetics of Coulomb explosion of (CD4)(n) and (CH4)(n) (n=55-4213) molecular heteroclusters in ultraintense (I=10(16)-10(19) W cm(-2)) laser fields, addressing the manifestation of electron dynamics, together with nuclear energetic and kinematic effects on the heterocluster Coulomb instability. The manifestations of the coupling between electron and nuclear dynamics were explored by molecular dynamics simulations for these heteroclusters coupled to Gaussian laser fields (pulse width tau=25 fs), elucidating outer ionization dynamics, nanoplasma screening effects (being significant for Icharges and masses. Nonuniform heterocluster Coulomb explosion (eta >1) manifests an overrun effect of the light ions relative to the heavy ions, exhibiting the expansion of two spatially separated subclusters, with the light ions forming the outer subcluster at the outer edge of the spatial distribution. Important features of the energetics of heterocluster Coulomb explosion originate from energetic triggering effects of the driving of the light ions by the heavy ions (C(4+) for I=10(17)-10(18) W cm(-2) and C(6+) for I=10(19) W cm(-2)), as well as for kinematic effects. Based on the CVI assumption, scaling laws for the cluster size (radius R(0)) dependence of the energetics of uniform Coulomb explosion of heteroclusters (eta=1) were derived, with the size dependence of the average (E(j,av)) and maximal (E(j,M)) ion energies being E(j,av)=aR(0) (2) and E(j,M)=(5a/3)R(0) (2), as well as for the ion energy distributions P(E(j)) proportional to E(j) (1/2); E(j)1) result in an isotope effect, predicting the enhancement (by 9%-11%) of E(H,av) for Coulomb explosion of (C(4+)H(4) (+))(eta) (eta=3) relative to E(D,av) for Coulomb explosion of (C(4+)D(4) (+))(eta) (eta=1.5), with the isotope effect being determined by the ratio of the kinematic parameters for the pair of Coulomb exploding clusters

  14. Molecular dynamics and simulations study on the vibrational and electronic solvatochromism of benzophenone

    Solvent plays a key role in diverse physico-chemical and biological processes. Therefore, understanding solute-solvent interactions at the molecular level of detail is of utmost importance. A comprehensive solvatochromic analysis of benzophenone (Bzp) was carried out in various solvents using Raman and electronic spectroscopy, in conjunction with Density Functional Theory (DFT) calculations of supramolecular solute-solvent clusters generated using classical Molecular Dynamics Simulations (c-MDSs). The >C=O stretching frequency undergoes a bathochromic shift with solvent polarity. Interestingly, in protic solvents this peak appears as a doublet: c-MDS and ad hoc explicit solvent ab initio calculations suggest that the lower and higher frequency peaks are associated with the hydrogen bonded and dangling carbonyl group of Bzp, respectively. Additionally, the dangling carbonyl in methanol (MeOH) solvent is 4 cm−1 blue-shifted relative to acetonitrile solvent, despite their similar dipolarity/polarizability. This suggests that the cybotactic region of the dangling carbonyl group in MeOH is very different from its bulk solvent structure. Therefore, we propose that this blue-shift of the dangling carbonyl originates in the hydrophobic solvation shell around it resulting from extended hydrogen bonding network of the protic solvents. Furthermore, the 11nπ∗ (band I) and 11ππ∗ (band II) electronic transitions show a hypsochromic and bathochromic shift, respectively. In particular, these shifts in protic solvents are due to differences in their excited state-hydrogen bonding mechanisms. Additionally, a linear relationship is obtained for band I and the >C=O stretching frequency (cm−1), which suggests that the different excitation wavelengths in band I correspond to different solvation states. Therefore, we hypothesize that the variation in excitation wavelengths in band I could arise from different solvation states leading to varying solvation dynamics. This will

  15. Molecular dynamics and simulations study on the vibrational and electronic solvatochromism of benzophenone

    Ravi Kumar, Venkatraman; Verma, Chandra; Umapathy, Siva

    2016-02-01

    Solvent plays a key role in diverse physico-chemical and biological processes. Therefore, understanding solute-solvent interactions at the molecular level of detail is of utmost importance. A comprehensive solvatochromic analysis of benzophenone (Bzp) was carried out in various solvents using Raman and electronic spectroscopy, in conjunction with Density Functional Theory (DFT) calculations of supramolecular solute-solvent clusters generated using classical Molecular Dynamics Simulations (c-MDSs). The >C=O stretching frequency undergoes a bathochromic shift with solvent polarity. Interestingly, in protic solvents this peak appears as a doublet: c-MDS and ad hoc explicit solvent ab initio calculations suggest that the lower and higher frequency peaks are associated with the hydrogen bonded and dangling carbonyl group of Bzp, respectively. Additionally, the dangling carbonyl in methanol (MeOH) solvent is 4 cm-1 blue-shifted relative to acetonitrile solvent, despite their similar dipolarity/polarizability. This suggests that the cybotactic region of the dangling carbonyl group in MeOH is very different from its bulk solvent structure. Therefore, we propose that this blue-shift of the dangling carbonyl originates in the hydrophobic solvation shell around it resulting from extended hydrogen bonding network of the protic solvents. Furthermore, the 11nπ∗ (band I) and 11ππ∗ (band II) electronic transitions show a hypsochromic and bathochromic shift, respectively. In particular, these shifts in protic solvents are due to differences in their excited state-hydrogen bonding mechanisms. Additionally, a linear relationship is obtained for band I and the >C=O stretching frequency (cm-1), which suggests that the different excitation wavelengths in band I correspond to different solvation states. Therefore, we hypothesize that the variation in excitation wavelengths in band I could arise from different solvation states leading to varying solvation dynamics. This will have

  16. Long-Range Electron Effects upon Irradiation of Molecular Solids and Polymers

    Long-range electron effects are responsible for specific localization and selectivity of the radiation-induced chemical transformations occurring in molecular solids and polymers, when the classic diffusion mobility is essentially restricted. In particullar, understanding of the effects of this kind may be of key significance for establishing new ways to control the radiation sensitivity of macromolecules and organized polymeric systems, nanomaterials and biopolymers. This talk will present an overview of model studies of the long-range electron effects with the characteristic scale from several angstroms to ten nanometers. The following aspects of the problem will be analyzed: (1) Positive hole delocalization in ionized molecules. This phenomenon has been demonstrated experimentally and confirmed by quantum chemical calculations for a number of various-type molecules (alkanes, conjugated polyenes, bifunctional compounds). The effective delocalization length was found to be up to 2 nm (or even larger). The role of this effect in site-selective radiation chemistry will be discussed in the frame of concepts of distributed reactivity and 'switching' between delocalized and localized states. (2) Trap-to-trap positive hole and electron migration between isolated molecules or functional groups. The characteristic distance for this process was estimated to be 2 to 4 nm. Special impact will be made on the possible role of this process in selection of specific isomers or conformers upon irradiation of complex systems and macromolecules. (3) The effects of long-range scavenging of low-energy secondary electrons in polymers and organized polymeric systems. As revealed by model experiments, the radius of electron capture in solid polymers may be in the range of 1 to 10 nm. Possible implications of scavenging effects for controlling the radiation chemistry of polymers and organized polymeric systems will be considered

  17. Electronic structure and partial charge distribution of doxorubicin under different molecular environments

    Poudel, Lokendra

    Doxorubicin (trade name Adriamycin, abbreviated DOX) is a well-known an- thracyclic chemotherapeutic used in treating a variety of cancers including acute leukemia, lymphoma, multiple myeloma, and a range of stomach, lung, bladder, bone, breast, and ovarian cancers. The purpose of the present work is to study electronic structure, partial charge distribution and interaction energy of DOX under different environments. It provides a framework for better understanding of bioactivity of DOX with DNA. While in this work, we focus on DOX -- DNA interactions; the obtained knowledge could be translated to other drug -- target interactions or biomolecular interactions. The electronic structure and partial charge distribution of DOX in three dierent molecular environments: isolated, solvated, and intercalated into a DNA complex,were studied by rst principles density functional methods. It is shown that the addition of solvating water molecules to DOX and the proximity and interaction with DNA has a signicant impact on the electronic structure as well as the partial charge distribution. The calculated total partial charges for DOX in the three models are 0.0, +0.123 and -0.06 electrons for the isolated, solvated, and intercalated state, respectively. Furthermore, by using the more accurate ab initio partial charge values on every atom in the models, signicant improvement in estimating the DOX-DNA interaction energy is obtained in conjunction with the NAnoscale Molecular Dynamics (NAMD) code. The electronic structure of the DOX-DNA is further elucidated by resolving the total density of states (TDOS) into dierent functional groups of DOX, DNA, water, co-crystallized Spermine molecule, and Na ions. The surface partial charge distribution in the DOX-DNA is calculated and displayed graphically. We conclude that the presence of the solvent as well as the details of the interaction geometry matter greatly in the determination of the stability of the DOX complexion. Ab initio

  18. Collisional transfer of electrons to the continuum of atomic and molecular ions

    The aim of this study was the systematic investigation of the differences that appear in the peaks of distribution of doubly differential (in angle an energy) 'convoy' electrons, when comparing spectra obtained by bombarding thin carbon foils with atomic (H+) and molecular (H2+) projectiles of equal velocity. The measurements show that the production yield of such electrons is inversely propotional to the ion dwell time in the solid. For long times, the yield ratio fluctuates around the unity value, and the amplitude of this dispersion decreases for longer times. A higher yield is measured for (H2+), but only near the peak cusp. The double differential cross section (DDCS) for electron capture is calculated in second order Born approximation. A transition from a 1s state to the continuum of two correlated protons as a function of their internuclear distance R is considered. As R decreases from approx. 0.5 atomic units towards zero, the DDCS value increases from that corresponding to the atomic projectil (Z=1) limit to the united atom value (Z=2). It is found that, the higher the projectil velocity, the better is the DDCS value agreement with both limits. The equipment used by the author is described. (M.E.L.)

  19. Atomic and Molecular Complex Resonances from Real Eigenvalues Using Standard (Hermitian) Electronic Structure Calculations.

    Landau, Arie; Haritan, Idan; Kaprálová-Žd'ánská, Petra Ruth; Moiseyev, Nimrod

    2016-05-19

    Complex eigenvalues, resonances, play an important role in a large variety of fields in physics and chemistry. For example, in cold molecular collision experiments and electron scattering experiments, autoionizing and predissociative metastable resonances are generated. However, the computation of complex resonance requires modifications of standard electronic structure codes and methods, which are not always straightforward, in addition, application of complex codes requires more computational efforts. Here we show how resonance eigenvalues, positions and widths, can be calculated using the standard, widely used, electronic-structure packages. Our method enables the calculations of the complex resonance eigenvalues by using analytical continuation procedures (such as Padé). The key point in our approach is the existence of narrow analytical passages from the real axis to the complex energy plane. In fact, the existence of these analytical passages relies on using finite basis sets. These passages become narrower as the basis set becomes more complete, whereas in the exact limit, these passages to the complex plane are closed. As illustrative numerical examples we calculated the autoionization Feshbach resonances of helium, hydrogen anion, and hydrogen molecule. We show that our results are in an excellent agreement with the results obtained by other theoretical methods and with available experimental results. PMID:26677725

  20. Momentum imaging spectrometer for molecular fragmentation dynamics induced by pulsed electron beam

    A momentum imaging spectrometer has been built for studying the electron impact molecular fragmentation dynamics. The setup consists of a pulsed electron gun and a time of flight system as well as a two-dimensional time and position sensitive multi-hit detector. The charged fragments with kinetic energy up to 10 eV can be detected in 4π solid angles and their three-dimensional momentum vectors can be reconstructed. The apparatus is tested by electron impact ionization of Ar and dissociative ionization of CO2. By analyzing the ion-ion coincidence spectra, the complete and incomplete Coulomb fragmentation channels for CO22+ and CO23+ are identified. The kinetic energy release (KER) and angular correlation for the two-body breakup channel CO22+*→ O++ CO+ are reported. The peak value of total KER is found to be 6.8 eV which is consistent with the previous photoion-photoion coincidence studies, and the correlation angle of O+ and CO+ is also explicitly determined to be 172.5°

  1. Making hybrid [n]-rotaxanes as supramolecular arrays of molecular electron spin qubits

    Fernandez, Antonio; Ferrando-Soria, Jesus; Pineda, Eufemio Moreno; Tuna, Floriana; Vitorica-Yrezabal, Iñigo J.; Knappke, Christiane; Ujma, Jakub; Muryn, Christopher A.; Timco, Grigore A.; Barran, Perdita E.; Ardavan, Arzhang; Winpenny, Richard E. P.

    2016-01-01

    Quantum information processing (QIP) would require that the individual units involved--qubits--communicate to other qubits while retaining their identity. In many ways this resembles the way supramolecular chemistry brings together individual molecules into interlocked structures, where the assembly has one identity but where the individual components are still recognizable. Here a fully modular supramolecular strategy has been to link hybrid organic-inorganic [2]- and [3]-rotaxanes into still larger [4]-, [5]- and [7]-rotaxanes. The ring components are heterometallic octanuclear [Cr7NiF8(O2CtBu)16]- coordination cages and the thread components template the formation of the ring about the organic axle, and are further functionalized to act as a ligand, which leads to large supramolecular arrays of these heterometallic rings. As the rings have been proposed as qubits for QIP, the strategy provides a possible route towards scalable molecular electron spin devices for QIP. Double electron-electron resonance experiments demonstrate inter-qubit interactions suitable for mediating two-qubit quantum logic gates.

  2. A multiscale simulation technique for molecular electronics: design of a directed self-assembled molecular n-bit shift register memory device

    Lambropoulos, Nicholas A.; Reimers, Jeffrey R.; Crossley, Maxwell J.; Hush, Noel S.; Silverbrook, Kia

    2013-12-01

    A general method useful in molecular electronics design is developed that integrates modelling on the nano-scale (using quantum-chemical software) and on the micro-scale (using finite-element methods). It is applied to the design of an n-bit shift register memory that could conceivably be built using accessible technologies. To achieve this, the entire complex structure of the device would be built to atomic precision using feedback-controlled lithography to provide atomic-level control of silicon devices, controlled wet-chemical synthesis of molecular insulating pillars above the silicon, and controlled wet-chemical self-assembly of modular molecular devices to these pillars that connect to external metal electrodes (leads). The shift register consists of n connected cells that read data from an input electrode, pass it sequentially between the cells under the control of two external clock electrodes, and deliver it finally to an output device. The proposed cells are trimeric oligoporphyrin units whose internal states are manipulated to provide functionality, covalently connected to other cells via dipeptide linkages. Signals from the clock electrodes are conveyed by oligoporphyrin molecular wires, and μ-oxo porphyrin insulating columns are used as the supporting pillars. The developed multiscale modelling technique is applied to determine the characteristics of this molecular device, with in particular utilization of the inverted region for molecular electron-transfer processes shown to facilitate latching and control using exceptionally low energy costs per logic operation compared to standard CMOS shift register technology.

  3. Electronic transport properties of carbon chains between Au and Ag electrodes: A first-principles study

    We report first-principles calculations of the current-voltage characteristic and the conductance of carbon-based molecular wires with different length capped with sulfur ends between two metallic electrodes made of different metals. The optimized molecular structure of carbon chain in the junction is presented on the structure of polyyne. The conductance of the polyyne wires shows oscillatory behavior depending on the number of carbon atoms (triple bonds). Current rectification is found and rectification direction presents inversion with the odd and even number of carbon atoms. -- Highlights: → Au and Ag as two asymmetric electrodes. → Relaxed carbon chain structure is in the form of polyyne. → Oscillatory conductance behavior with the number of carbon atoms. → Current rectification of carbon chains in the asymmetric electrodes. → Rectification inversion with the number of carbon atoms.

  4. An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

    Hendrickson, Heidi Phillips

    technological design and development. Time dependent perturbation theory, employed by non-equilibrium Green's function formalism, is utilized to study the effect of quantum coherences on electron transport and the effect of symmetry breaking on the electronic spectra of model molecular junctions. The fourth part of this thesis presents the design of a physical chemistry course based on a pedagogical approach called Writing-to-Teach. The nature of inaccuracies expressed in student-generated explanations of quantum chemistry topics, and the ability of a peer review process to engage these inaccuracies, is explored within this context.

  5. Ac electronic tunneling at optical frequencies

    Faris, S. M.; Fan, B.; Gustafson, T. K.

    1974-01-01

    Rectification characteristics of non-superconducting metal-barrier-metal junctions deduced from electronic tunneling have been observed experimentally for optical frequency irradiation of the junction. The results provide verification of optical frequency Fermi level modulation and electronic tunneling current modulation.

  6. A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy.

    Lewis, Nicholas H C; Dong, Hui; Oliver, Thomas A A; Fleming, Graham R

    2015-09-28

    Two dimensional electronic spectroscopy has proved to be a valuable experimental technique to reveal electronic excitation dynamics in photosynthetic pigment-protein complexes, nanoscale semiconductors, organic photovoltaic materials, and many other types of systems. It does not, however, provide direct information concerning the spatial structure and dynamics of excitons. 2D infrared spectroscopy has become a widely used tool for studying structural dynamics but is incapable of directly providing information concerning electronic excited states. 2D electronic-vibrational (2DEV) spectroscopy provides a link between these domains, directly connecting the electronic excitation with the vibrational structure of the system under study. In this work, we derive response functions for the 2DEV spectrum of a molecular dimer and propose a method by which 2DEV spectra could be used to directly measure the electronic site populations as a function of time following the initial electronic excitation. We present results from the response function simulations which show that our proposed approach is substantially valid. This method provides, to our knowledge, the first direct experimental method for measuring the electronic excited state dynamics in the spatial domain, on the molecular scale. PMID:26429003

  7. A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy

    Two dimensional electronic spectroscopy has proved to be a valuable experimental technique to reveal electronic excitation dynamics in photosynthetic pigment-protein complexes, nanoscale semiconductors, organic photovoltaic materials, and many other types of systems. It does not, however, provide direct information concerning the spatial structure and dynamics of excitons. 2D infrared spectroscopy has become a widely used tool for studying structural dynamics but is incapable of directly providing information concerning electronic excited states. 2D electronic-vibrational (2DEV) spectroscopy provides a link between these domains, directly connecting the electronic excitation with the vibrational structure of the system under study. In this work, we derive response functions for the 2DEV spectrum of a molecular dimer and propose a method by which 2DEV spectra could be used to directly measure the electronic site populations as a function of time following the initial electronic excitation. We present results from the response function simulations which show that our proposed approach is substantially valid. This method provides, to our knowledge, the first direct experimental method for measuring the electronic excited state dynamics in the spatial domain, on the molecular scale

  8. A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy

    Lewis, Nicholas H. C.; Dong, Hui; Oliver, Thomas A. A.; Fleming, Graham R., E-mail: grfleming@lbl.gov [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Kavli Energy Nanosciences Institute at Berkeley, Berkeley, California 94720 (United States)

    2015-09-28

    Two dimensional electronic spectroscopy has proved to be a valuable experimental technique to reveal electronic excitation dynamics in photosynthetic pigment-protein complexes, nanoscale semiconductors, organic photovoltaic materials, and many other types of systems. It does not, however, provide direct information concerning the spatial structure and dynamics of excitons. 2D infrared spectroscopy has become a widely used tool for studying structural dynamics but is incapable of directly providing information concerning electronic excited states. 2D electronic-vibrational (2DEV) spectroscopy provides a link between these domains, directly connecting the electronic excitation with the vibrational structure of the system under study. In this work, we derive response functions for the 2DEV spectrum of a molecular dimer and propose a method by which 2DEV spectra could be used to directly measure the electronic site populations as a function of time following the initial electronic excitation. We present results from the response function simulations which show that our proposed approach is substantially valid. This method provides, to our knowledge, the first direct experimental method for measuring the electronic excited state dynamics in the spatial domain, on the molecular scale.

  9. Phenomenological electronic stopping-power model for molecular dynamics and Monte Carlo simulation of ion implantation into silicon

    It is crucial to have a good phenomenological model of electronic stopping power for modeling the physics of ion implantation into crystalline silicon. In the spirit of the Brandt-Kitagawa effective charge theory, we develop a model for electronic stopping power for an ion, which can be factorized into (i) a globally averaged effective charge taking into account effects of close and distant collisions by target electrons with the ion, and (ii) a local charge density dependent electronic stopping power for a proton. This phenomenological model is implemented into both molecular dynamics and Monte Carlo simulations. There is only one free parameter in the model, namely, the one electron radius r0s for unbound electrons. By fine tuning this parameter, it is shown that the model can work successfully for both boron and arsenic implants. We report that the results of the dopant profile simulation for both species are in excellent agreement with the experimental profiles measured by secondary-ion mass spectrometry (SIMS) over a wide range of energies and with different incident directions. We point out that the model has wide applicability, for it captures the correct physics of electronic stopping in ion implantation. This model also provides a good physically based damping mechanism for molecular dynamics simulations in the electronic stopping power regime, as evidenced by the striking agreement of dopant profiles calculated in our molecular dynamics simulations with the SIMS data. copyright 1996 The American Physical Society

  10. Extremely low-loss rectification methodology for low-power vibration energy harvesters

    Tiwari, R.; Ryoo, K.; Schlichting, A.; Garcia, E.

    2013-06-01

    Because of its promise for the generation of wireless systems, energy harvesting technology using smart materials is the focus of significant reported effort. Various techniques and methodologies for increasing power extraction have been tested. One of the key issues with the existing techniques is the use of diodes in the harvesting circuits with a typical voltage drop of 0.7 V. Since most of the smart materials, and other transducers, do not produce large voltage outputs, this voltage drop becomes significant in most applications. Hence, there is a need for designing a rectification method that can convert AC to DC with minimal losses. This paper describes a new mechanical rectification scheme, designed using reed switches, in a full-bridge configuration that shows the capability of working with signals from millivolts to a few hundred volts with extremely low losses. The methodology has been tested for piezoelectric energy harvesters undergoing mechanical excitation.

  11. Theoretical analysis of thermal rectification in a bulk Si/nanoporous Si device

    Criado-Sancho, M., E-mail: mcriado@ccia.uned.es [Departamento de Ciencias y Técnicas Físicoquimicas, Facultad de Ciencias, UNED, Senda del Rey 9, 20040 Madrid (Spain); Castillo, L.F. del, E-mail: felipe@unam.mx [Departamento de Polímeros, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Ap. 70-360 Coyoacán, México DF, 04510 (Mexico); Casas-Vázquez, J., E-mail: Jose.Casas@uab.es [Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia (Spain); Jou, D., E-mail: David.Jou@uab.es [Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia (Spain)

    2012-04-09

    We present a theoretical analysis of thermal rectification in a porous Si/bulk Si device, taking into account ballistic effects in phonon-pore collisions when phonon mean free path is much longer than the radius of the pores. Starting from an approximate analytical expression for the effective thermal conductivity of porous Si, we obtain the thermal rectifying coefficient of the device as a function of porosity, pore size, temperature interval, and relative lengths of porous and bulk samples. -- Highlights: ► Heat conductivity of porous Si depends on the pore size. ► Thermal rectification for nanoporous Si/bulk Si is predicted. ► Thermal rectifying coefficient is calculated. ► It is shown to be comparable or higher to that of systems previously considered.

  12. Theoretical analysis of thermal rectification in a bulk Si/nanoporous Si device

    We present a theoretical analysis of thermal rectification in a porous Si/bulk Si device, taking into account ballistic effects in phonon-pore collisions when phonon mean free path is much longer than the radius of the pores. Starting from an approximate analytical expression for the effective thermal conductivity of porous Si, we obtain the thermal rectifying coefficient of the device as a function of porosity, pore size, temperature interval, and relative lengths of porous and bulk samples. -- Highlights: ► Heat conductivity of porous Si depends on the pore size. ► Thermal rectification for nanoporous Si/bulk Si is predicted. ► Thermal rectifying coefficient is calculated. ► It is shown to be comparable or higher to that of systems previously considered.

  13. Extremely low-loss rectification methodology for low-power vibration energy harvesters

    Because of its promise for the generation of wireless systems, energy harvesting technology using smart materials is the focus of significant reported effort. Various techniques and methodologies for increasing power extraction have been tested. One of the key issues with the existing techniques is the use of diodes in the harvesting circuits with a typical voltage drop of 0.7 V. Since most of the smart materials, and other transducers, do not produce large voltage outputs, this voltage drop becomes significant in most applications. Hence, there is a need for designing a rectification method that can convert AC to DC with minimal losses. This paper describes a new mechanical rectification scheme, designed using reed switches, in a full-bridge configuration that shows the capability of working with signals from millivolts to a few hundred volts with extremely low losses. The methodology has been tested for piezoelectric energy harvesters undergoing mechanical excitation. (fast track communication)

  14. Molecular physics

    Williams, Dudley

    2013-01-01

    Methods of Experimental Physics, Volume 3: Molecular Physics focuses on molecular theory, spectroscopy, resonance, molecular beams, and electric and thermodynamic properties. The manuscript first considers the origins of molecular theory, molecular physics, and molecular spectroscopy, as well as microwave spectroscopy, electronic spectra, and Raman effect. The text then ponders on diffraction methods of molecular structure determination and resonance studies. Topics include techniques of electron, neutron, and x-ray diffraction and nuclear magnetic, nuclear quadropole, and electron spin reson

  15. Efficient preconditioning of the electronic structure problem in large scale ab initio molecular dynamics simulations

    Schiffmann, Florian; VandeVondele, Joost

    2015-06-01

    We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling's iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step.

  16. Structural and electronic properties of iron and cobalt molecular sieve catalysts: Progress report. [Cyclopropane

    Suib, S.L.

    1988-05-14

    During the second year of this research we have focused on the characterization of highly dispersed cobalt and iron particles in zeolites with transmission electron microscopy and spin echo nuclear magnetic resonance techniques. We have continued our studies of the structure sensitivity of cyclopropane craking reaction. In-situ Moessbauer studies of iron catalysts have also been done. In addition, several ultahigh vacuum methods have been used to characterize metal-containing molecular sieves. The most significant discovery is that spin echo nuclear magnetic resonance (SENMR) methods can be used to determine the structure of small (5--40 angstrom) size particles of cobalt. Both hexagonal and cubic metal particles have been prepared and a new alloy of cobalt and iron has been characterized by SENMR. This is the first example of the use of spin echo nuclear magnetic resonance methods done in zero external magnetic field for supported catalysts. With this method the relaxation times of different cobalt species can be determined.

  17. Electron microscopy investigation of interface between carbon fiber and ultra high molecular weight polyethylene

    Stepashkin, A.A.; Chukov, D.I., E-mail: dil_chukov@yahoo.com; Gorshenkov, M.V.; Tcherdyntsev, V.V.; Kaloshkin, S.D.

    2014-02-15

    Highlights: • Effect of the carbon fibers surface treatments on the adhesive interactions in UHMWPE composites was studied. • Air oxidation of carbon filler ensures most significant increase in adhesion interaction in UHMWPE based composites. • Nanosized UHMWPE fibers with 20–40 nm in diameter and with 6–10 μm in length, was observed on the surface of carbon fibers. -- Abstract: Scanning electron microscopy was used to investigate the surface of initial and modified high-strength and high-modulus carbon fibers as well as interfaces in the ultra high molecular weight polyethylene, filled with above-mentioned fibers. Effect of the fibers surface modifying method on the adhesive interactions in composites was studied. It was observed that interaction of matrix with a modified surface of fibers results in a formation of bonds with strength higher than the yield strength of the polymer. It results in a formation of long nanosized polymer wires at tensile fracture of composites.

  18. Blending Determinism with Evolutionary Computing: Applications to the Calculation of the Molecular Electronic Structure of Polythiophene.

    Sarkar, Kanchan; Sharma, Rahul; Bhattacharyya, S P

    2010-03-01

    A density matrix based soft-computing solution to the quantum mechanical problem of computing the molecular electronic structure of fairly long polythiophene (PT) chains is proposed. The soft-computing solution is based on a "random mutation hill climbing" scheme which is modified by blending it with a deterministic method based on a trial single-particle density matrix [P((0))(R)] for the guessed structural parameters (R), which is allowed to evolve under a unitary transformation generated by the Hamiltonian H(R). The Hamiltonian itself changes as the geometrical parameters (R) defining the polythiophene chain undergo mutation. The scale (λ) of the transformation is optimized by making the energy [E(λ)] stationary with respect to λ. The robustness and the performance levels of variants of the algorithm are analyzed and compared with those of other derivative free methods. The method is further tested successfully with optimization of the geometry of bipolaron-doped long PT chains. PMID:26613302

  19. Electron capture by slow highly-charged neon and argon ions from molecular and atomic hydrogen

    Electron capture cross sections for low velocity (106-107 cm/s) highly charged Ne/sup q+/ (2 less than or equal to q less than or equal to 7) and Ar/sup q+/ (2 less than or equal to q less than or equal to 10) projectiles incident on molecular and atomic hydrogen targets have been measured. A recoil ion source that uses the collisions of fast heavy (1 MeV/amu) ions with target gas atoms was utilized to produce slow highly charged ions. Atomic hydrogen was produced by dissociating hydrogen molecules in a thermal oven. Measurements and analysis of the data for the atomic hydrogen oven target are discussed in detail. The measured absolute cross sections were compared with the published data and the predictions of theoretical models

  20. A micro seismometer based on molecular electronic transducer technology for planetary exploration

    This letter describes an implementation of micromachined seismometer based on molecular electronic transducer (MET) technology. As opposed to a solid inertial mass, MET seismometer senses the movement of liquid electrolyte relative to fixed electrodes. The employment of micro-electro-mechanical systems techniques reduces the internal size of the sensing cell to 1μm and improves the reproducibility of the device. For operating bias of 600 mV, a sensitivity of 809 V/(m/s2) was measured under acceleration of 400μg(g≡9.81m/s2) at 0.32 Hz. A −115 dB (relative to (m/s2)/√(Hz)) noise level at 1 Hz was achieved. This work develops an alternative paradigm of seismic sensing device with small size, high sensitivity, low noise floor, high shock tolerance, and independence of installation angle, which is promising for next generation seismometers for planetary exploration.

  1. Surface free energy of ultra-high molecular weight polyethylene modified by electron and gamma irradiation

    Surface free energy of biocompatible polymers is important factor which affects the surface properties such as wetting, adhesion and biocompatibility. In the present work, the change in the surface free energy of ultra-high molecular weight polyethylene (UHMWPE) samples, which is produced by electron beam and gamma ray irradiation were, investigated. Mechanism of the changes in surface free energy induced by irradiations of doses ranging from 25 to 500 kGy was studied. FTIR technique was applied for sample analysis. Contact angle measurements showed that wettability and surface free energy of samples have increased with increasing the irradiation dose, where the values of droplet contact angle of the samples decrease gradually with increasing the radiation dose. The increase in the wettability and surface free energy of the irradiated samples are attributed to formation of hydrophilic groups on the polymer surface by the oxidation, which apparently occurs by exposure of irradiated samples to the air.

  2. Electronic properties of liquid Hg-In alloys : Ab-initio molecular dynamics study

    Sharma, Nalini; Thakur, Anil; Ahluwalia, P. K.

    2016-05-01

    Ab-initio molecular dynamics simulations are performed to study the structural properties of liquid Hg-In alloys. The interatomic interactions are described by ab-initio pseudopotentials given by Troullier and Martins. Three liquid Hg-In alloys (Hg10In90, Hg30In70,. Hg50In50, Hg70In30, and Hg90Pb10) at 299 K are considered. The calculated results for liquid Hg (l-Hg) and lead (l-In) are also drawn. Along with the calculated results of considered five liquid alloys of Hg-In alloy. The results obtained from electronic properties namely total density of state and partial density of states help to find the local arrangement of Hg and In atoms and the presence of liquid state in the considered five alloys.

  3. Surface electronic structure and molecular orientation of poly(9-vinylcarbazole) thin film: ARUPS and NEXAFS

    Okudaira, K K; Hasegawa, S; Ishii, H; Azuma, Y; Imamura, M; Shimada, H; Seki, K; Ueno, N

    2001-01-01

    The molecular orientation at the surfaces of poly(9-vinylcarbazole) (PvCz) thin films was studied by angle-resolved ultraviolet photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The observed take-off angle (theta) dependence of photoelectron intensities from top pi band peaks clearly at larger theta than the calculated one for the three-dimensional isotropic random orientation model. The results indicate that there are more pendant groups with large tilt angles than the three-dimensional isotropic random orientation model, which is in good agreement with the result obtained from NEXAFS spectroscopy. The surface electronic states of PvCz may be rather dominated by sigma(C-H) states at the pendant carbazole group than pi states

  4. Studies on the full vibrational energy spectra for some electronic states of diatomic molecular ions XY+

    LIU Yi-ding; SUN Wei-guo; REN Wei-yi

    2006-01-01

    The first accurate studies on the vibrational spectroscopic constants and the corresponding full vibrational energy spectra of some electronic states of diatomic molecular ions XY+ were performed using algebraic method(AM).The AM is applied on the X1Σ+ state of BeH+,the X2Σ+ state of CO+ , the X21-Π state of F2+ the A2Πu state of O2+ and theX2Σ+g Li2+.The results show that AM can generate accurate vibrational spectroscopic constants as well as accurate full vibrational energy spectra by using some accurate experimental vibrational energies,and that the AM vibrational energies are better than other theoretical data.

  5. Efficient preconditioning of the electronic structure problem in large scale ab initio molecular dynamics simulations

    We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling’s iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step

  6. Efficient preconditioning of the electronic structure problem in large scale ab initio molecular dynamics simulations

    Schiffmann, Florian; VandeVondele, Joost, E-mail: Joost.VandeVondele@mat.ethz.ch [Nanoscale Simulations, Department of Materials, ETH Zürich, Wolfgang-Pauli-Str. 27, CH-8093 Zürich (Switzerland)

    2015-06-28

    We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling’s iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step.

  7. Efficient preconditioning of the electronic structure problem in large scale ab initio molecular dynamics simulations.

    Schiffmann, Florian; VandeVondele, Joost

    2015-06-28

    We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling's iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step. PMID:26133420

  8. Molecular electronic states in charge transfer complex studied by x-ray absorption spectroscopy

    The electronic states of tetrathiafulvalene (TTF: TTF = C6H4S4) molecule in organic ferroelectric TTF-p-bromanil (TTF-BA: BA = C6Br4O2) and TTF crystals have been investigated by x-ray absorption spectroscopy (XAS) measurement at S K-edge. We elucidated that the peak structure at 2470.5 eV directly reflects the existence of hole in the highest occupied molecular orbital (HOMO) state of the TTF molecule in TTF-BA; that is consistent with the ionic TTF molecule (TTF+). The XAS of TTF-BA was evaluated on the basis of first-principles calculations, and the calculated spectra reproduce well the shape of experimental spectrum and the peak energy of the HOMO state.

  9. Design of high power rectification power supply based on digital control

    For typical high power rectification power supply, a design based on digital control is introduced. The feasibility and superiority of the digital control scheme were verified through the design and experimental results of the filament power supply for high current ion source of NBI. The application of digital control scheme, making the filament power supply design is more intelligent and simple, as related applications provide a reference. (authors)

  10. Optical Rectification in Isotropic Thin Film Composed of Chiral Molecules with a Tripod-Like Structure

    WANG Xiao-Ou; GONG Li-Jing; LI Chun-Fei

    2008-01-01

    @@ Optical rectification (OR) effect in the isotropic thin film consisting of chiral molecules with a tripod-like structure is investigated.The expressions of static-electric polarization in the isotropic chiral thin films and the relations between the OR and microscopic parameters of chiral medium are obtaineel by theoretical derivation,Furthermore,the relations of static electric polarization with the wavelength of incident light and parameters of chiral molecules are simulated numerically.

  11. Separating Inverse spin Hall voltage and spin rectification voltage by inverting spin injection direction

    Zhang, Wenxu; Peng, Bin; Han, Fangbin; Wang, Qiuru; Soh, Wee Tee; Ong, C. K.; Zhang, WanLi

    2015-01-01

    We develop a method for universally resolving the important issue of separating the inverse spin Hall effect (ISHE) from spin rectification effect (SRE) signal. This method is based on the consideration that the two effects depend on the spin injection direction: The ISHE is an odd function of the spin injection direction while the SRE is independent on it. Thus, inversion of the spin injection direction changes the ISHE voltage signal, while SRE voltage remains. It applies generally to analy...

  12. Development of a model electronic Hamiltonian for understanding electronic relaxation dynamics of [Fe(bpy)3]2+ through molecular dynamics simulations

    A model electronic Hamiltonian of [Fe(bpy)3]2+, which was recently refined for use in molecular dynamics simulations, is reviewed with some additional results. In particular, the quality of the refined model Hamiltonian is examined in terms of the vibrational frequencies and solvation structures of the lowest singlet and quintet states

  13. Ultraflat Au nanoplates as a new building block for molecular electronics

    Jeong, Wooseok; Lee, Miyeon; Lee, Hyunsoo; Lee, Hyoban; Kim, Bongsoo; Park, Jeong Young

    2016-05-01

    We demonstrate the charge transport properties of a self-assembled organic monolayer on Au nanoplates with conductive probe atomic force microscopy (CP-AFM). Atomically flat Au nanoplates, a few hundred micrometers on each side, that have only (111) surfaces, were synthesized using the chemical vapor transport method; these nanoplates were employed as the substrates for hexadecanethiol (HDT) self-assembled monolayers (SAMs). Atomic-scale high-resolution images show (\\sqrt{3}× \\sqrt{3}){{R}}30^\\circ molecular periodicity, indicating a well-ordered structure of the HDT on the Au nanoplates. We observed reduced friction and adhesion forces on the HDT SAMs on Au nanoplates, compared with Si substrates, which is consistent with the lubricating nature of HDT SAMs. The electrical properties, such as I–V characteristics and current as a function of load, were measured using CP-AFM. We obtained a tunneling decay constant (β) of 0.57 Å‑1, including through-bond ({β }{tb} = 0.99 Å‑1) and through-space ({β }{{ts}} = 1.36 Å‑1) decay constants for the two-pathway model. This indicates that the charge transport properties of HDT SAMs on Au nanoplates are consistent with those on a Au (111) film, suggesting that SAMs on nanoplates can provide a new building block for molecular electronics.

  14. Molecular-Based Theory for Electron-Transfer Reorganization Energy in Solvent Mixtures.

    Zhuang, Bilin; Wang, Zhen-Gang

    2016-07-01

    Using statistical-field techniques, we develop a molecular-based dipolar self-consistent-field theory (DSCFT) for charge solvation in liquid mixtures under equilibrium and nonequilibrium conditions, and apply it to compute the solvent reorganization energy of electron-transfer reactions. In addition to the nonequilibrium orientational polarization, the reorganization energy in liquid mixtures is also determined by the out-of-equilibrium solvent composition around the reacting species due to preferential solvation. Using molecular parameters that are readily available, the DSCFT naturally accounts for the dielectric saturation effect and the spatially varying solvent composition in the vicinity of the reacting species. We identify three general categories of binary solvent mixtures, classified by the relative optical and static dielectric permittivities of the solvent components. Each category of mixture is shown to produce a characteristic local solvent composition profile in the vicinity of the reacting species, which gives rise to the distinctive composition dependence of the reorganization energy that cannot be predicted using the dielectric permittivities of the homogeneous solvent mixtures. PMID:27187110

  15. Hildebrand and Hansen solubility parameters from molecular dynamics with applications to electronic nose polymer sensors.

    Belmares, M; Blanco, M; Goddard, W A; Ross, R B; Caldwell, G; Chou, S-H; Pham, J; Olofson, P M; Thomas, Cristina

    2004-11-30

    We introduce the Cohesive Energy Density (CED) method, a multiple sampling Molecular Dynamics computer simulation procedure that may offer higher consistency in the estimation of Hildebrand and Hansen solubility parameters. The use of a multiple sampling technique, combined with a simple but consistent molecular force field and quantum mechanically determined atomic charges, allows for the precise determination of solubility parameters in a systematic way (sigma = 0.4 hildebrands). The CED method yields first-principles Hildebrand parameter predictions in good agreement with experiment [root-mean-square (rms) = 1.1 hildebrands]. We apply the CED method to model the Caltech electronic nose, an array of 20 polymer sensors. Sensors are built with conducting leads connected through thin-film polymers loaded with carbon black. Odorant detection relies on a change in electric resistivity of the polymer film as function of the amount of swelling caused by the odorant compound. The amount of swelling depends upon the chemical composition of the polymer and the odorant molecule. The pattern is unique, and unambiguously identifies the compound. Experimentally determined changes in relative resistivity of seven polymer sensors upon exposure to 24 solvent vapors were modeled with the CED estimated Hansen solubility components. Predictions of polymer sensor responses result in Pearson R2 coefficients between 0.82 and 0.99. PMID:15389751

  16. Effect of contact interface configuration on electronic transport in (C20)2-based molecular junctions

    Using first-principles calculations, we study the electronic transport properties in Au-(C20)2-Au molecular junctions with different contact interface configurations: point contact and bond contact. We observe that the transmission through the bond contact is considerably higher than that of point contact. Furthermore, the I–V characteristics are rather different. For the bond contact, we get a metallic behavior followed by a varistor-type behavior. While as for the point contact, the current increases very slowly in a nonlinear way and is one order of magnitude smaller than that of bond contact. We attribute these obvious differences to the distinct contact configurations. -- Highlights: ► The I–V properties of (C20)2 molecular devices are affected by contact configuration. ► As for the bond contact, metallic behavior in the low bias is observed. ► Varistor-type behavior and nonlinear I–V characteristic in the high bias are found. ► As for the point contact, the Landauer conductance greatly decreases. ► The current is one order of magnitude smaller than that of bond contact.

  17. Disorder-driven nonequilibrium melting studied by electron diffraction, brillouin scattering, and molecular dynamics

    In the present paper, a brief overview of the electron diffraction, Brillouin scattering and molecular dynamics studies of radiation-induced amorphization of ordered intermetallic compounds is presented. In these studies, measured changes in the velocity of surface acoustic phonons, lattice constant, and the Bragg-Williams long-range order parameter induced by irradiation were compared with the results of computer simulations of defect-induced amorphization. The results indicate that progressive chemical disordering of the superlattice structure during irradiation is accompanied by an expansion of the lattice and a large change in sound velocity corresponding to a ∼ 50% decrease in the average shear modulus. The onset of amorphization occurs when the average shear modulus of the crystalline compound becomes equal to that of the amorphous phase. This elastic softening criterion for the onset of amorphization and the dependence of the average shear modulus on the long-range-order parameter are in excellent agreement with molecular dynamics simulations. Both the experimental observations and computer simulations confirm the predictions of the generalized Lindemann melting criterion which stipulates that thermodynamic melting of a defective crystal occurs when the sum of the dynamic and static mean-square atomic displacements reaches a critical value identical to that for melting of the defect-free crystal. In this broader view of melting, the crystal-to-glass transformation is a disorder-driven nonequilibrium melting process occurring at temperatures below the Kauzmann isentropic glass-transition temperature

  18. Correlation between energy deposition and molecular damage from Auger electrons: A case study of ultra-low energy (5–18 eV) electron interactions with DNA

    Purpose: The present study introduces a new method to establish a direct correlation between biologically related physical parameters (i.e., stopping and damaging cross sections, respectively) for an Auger-electron emitting radionuclide decaying within a target molecule (e.g., DNA), so as to evaluate the efficacy of the radionuclide at the molecular level. These parameters can be applied to the dosimetry of Auger electrons and the quantification of their biological effects, which are the main criteria to assess the therapeutic efficacy of Auger-electron emitting radionuclides. Methods: Absorbed dose and stopping cross section for the Auger electrons of 5–18 eV emitted by125I within DNA were determined by developing a nanodosimetric model. The molecular damages induced by these Auger electrons were investigated by measuring damaging cross section, including that for the formation of DNA single- and double-strand breaks. Nanoscale films of pure plasmid DNA were prepared via the freeze-drying technique and subsequently irradiated with low-energy electrons at various fluences. The damaging cross sections were determined by employing a molecular survival model to the measured exposure–response curves for induction of DNA strand breaks. Results: For a single decay of125I within DNA, the Auger electrons of 5–18 eV deposit the energies of 12.1 and 9.1 eV within a 4.2-nm3 volume of a hydrated or dry DNA, which results in the absorbed doses of 270 and 210 kGy, respectively. DNA bases have a major contribution to the deposited energies. Ten-electronvolt and high linear energy transfer 100-eV electrons have a similar cross section for the formation of DNA double-strand break, while 100-eV electrons are twice as efficient as 10 eV in the induction of single-strand break. Conclusions: Ultra-low-energy electrons (<18 eV) substantially contribute to the absorbed dose and to the molecular damage from Auger-electron emitting radionuclides; hence, they should be considered in

  19. Correlation between energy deposition and molecular damage from Auger electrons: A case study of ultra-low energy (5–18 eV) electron interactions with DNA

    Rezaee, Mohammad, E-mail: Mohammad.Rezaee@USherbrooke.ca; Hunting, Darel J.; Sanche, Léon [Groupe en Sciences des Radiations, Département de Médecine Nucléaire et Radiobiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4 (Canada)

    2014-07-15

    Purpose: The present study introduces a new method to establish a direct correlation between biologically related physical parameters (i.e., stopping and damaging cross sections, respectively) for an Auger-electron emitting radionuclide decaying within a target molecule (e.g., DNA), so as to evaluate the efficacy of the radionuclide at the molecular level. These parameters can be applied to the dosimetry of Auger electrons and the quantification of their biological effects, which are the main criteria to assess the therapeutic efficacy of Auger-electron emitting radionuclides. Methods: Absorbed dose and stopping cross section for the Auger electrons of 5–18 eV emitted by{sup 125}I within DNA were determined by developing a nanodosimetric model. The molecular damages induced by these Auger electrons were investigated by measuring damaging cross section, including that for the formation of DNA single- and double-strand breaks. Nanoscale films of pure plasmid DNA were prepared via the freeze-drying technique and subsequently irradiated with low-energy electrons at various fluences. The damaging cross sections were determined by employing a molecular survival model to the measured exposure–response curves for induction of DNA strand breaks. Results: For a single decay of{sup 125}I within DNA, the Auger electrons of 5–18 eV deposit the energies of 12.1 and 9.1 eV within a 4.2-nm{sup 3} volume of a hydrated or dry DNA, which results in the absorbed doses of 270 and 210 kGy, respectively. DNA bases have a major contribution to the deposited energies. Ten-electronvolt and high linear energy transfer 100-eV electrons have a similar cross section for the formation of DNA double-strand break, while 100-eV electrons are twice as efficient as 10 eV in the induction of single-strand break. Conclusions: Ultra-low-energy electrons (<18 eV) substantially contribute to the absorbed dose and to the molecular damage from Auger-electron emitting radionuclides; hence, they should

  20. Is the analysis of molecular electronic structure of corrosion inhibitors sufficient to predict the trend of their inhibition performance

    Kokalj, Anton, E-mail: tone.kokalj@ijs.s [Department of Physical and Organic Chemistry, Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana (Slovenia)

    2010-12-30

    The often used approach in the corrosion inhibition studies employing quantum chemical calculations that relies on the correlation between molecular electronic structure parameters and inhibition effectiveness is critically examined. It is shown that the inhibition performance of three selected triazole-based corrosion inhibitors for copper - 3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH) - cannot be explained on this basis in a sound manner. As the effectiveness of inhibitors is due to several phenomena, the outcome depends on the interplay between them and although molecular electronic parameters may provide many necessary elements, the involved effects can be estimated only approximately which may not always suffice. This supports the proposition that in general molecular electronic properties cannot be directly related to inhibition effectiveness - the actual relation is more involved - thus emphasizing the importance of a rigorous modeling of the inhibitor-surface interaction in the corrosion inhibition studies.