Charge separation processes in mixed phase TiO{sub 2} photocatalysts are investigated by electron paramagnetic resonance (EPR) spectroscopy. The mechanisms of interfacial electron transfer, subsequent charge migration and recombination at surface sites, and other interfacial effects on chlorophenol/TiO{sub 2} chemistry have been probed. Distorted interfacial sites have been observed and are proposed as catalytically reactive hot spots. This detailed knowledge of charge transfer processes is critical to the nanoscale design of catalysts and subsequent improvement of catalytic efficiency.

Highly exothermic electron transfer rates were measured using semiconductor electrochemical techniques. Experiments demonstrate that the decrease in the electron transfer rates with the exothermicity of the reactions in so-called abnormal regions is much more moderate than predicted classically, and this effect is probably due to intramolecular vibrations. On the basis of these results, we present a new kinetic model for interfacial charge transfer processes. Some preliminary results for the hole transfer rate are included.

Charge transfer at a liquid-liquid interface is the key process in a variety of chemical and biochemical processes. The kinetics of electron and proton transfer was investigated at micro- and macroscopic interfaces. Experimentally, these techniques are very distinct due to different approaches in measuring the interfacial potential. Nevertheless, three processes, i.e. generation of charge carriers, diffusion and interfacial transfer, constitute three principal steps of charge separation, and are similar regardless of the dimensionality of the system. Differences in (1) the thickness of the double electric layer, (2) span of the photoreaction zone, and (3) relative rate of electron-transfer and phase-transfer reactions enable approximations which are quite unique for a particular system. The mathematical models, corresponding experimental results, and computer-simulation techniques resulting from various descriptions of charge transfer are discussed.   

The interfacial transfer terms are the most important aspect of the two-fluid formulation modeling. However, there exist considerable difficulties in this area both in terms of experiments and modeling. The first step in the right direction is to consider that the interfacial transfer terms are proportional to the interfacial area concentration and driving force. This approach effectively separates the first-order geometrical effect on the interfacial transfers from the local driving forces. Hence more mechanistic modeling of the interfacial transfer terms becomes possible. In view of the importance of the interfacial area concentration, the available experimental data, measurement methods and modeling are reviewed and new directions are indicated.

The DOE funded research has focused on the development of novel non-linear optical methods for the in situ study of surface reaction dynamics. In particular, the work has concentrated on interfacial charge transfer processes as this is the simplest of all surface reactions, i.e., no bonds are broken and the reaction is derived from nuclear repolarization. Interfacial charge transfer forms the basis for a number of important solar energy conversion strategies. In these studies, semiconductor liquid junctions provide a convenient system in which the interfacial charge transfer can be optically initiated. The all-optical approach necessitates that the dynamics of the charge transfer event itself be put in the proper context of the operating photophysical processes at the surface. There are at least four dynamical processes that are coupled in determining the overall rate of electron flux across the interface. In the limit that interfacial charge transfer approaches strong coupling, the time scale for transport of even field accelerated carriers within the space charge region becomes comparable to the charge transfer dynamics. The transport component needs to be convolved to probes of the carrier population at the surface. The other two dynamical processes, carrier thermalization and surface state trapping, determine the states which ultimately serve as the donor levels to the solution acceptor distribution. In terms of the hot carrier model, these latter two processes compete with direct unthermalized charge transfer. There is a fifth dynamical process which also needs consideration: the solvent modes that are coupled to the reaction coordinate. Ultimately, the dynamics of solvent relaxation determine the upper limit to the charge transfer process. Different optical techniques have been developed to follow all the above dynamical processes in which a real time view of charge transfer dynamics at semiconductor surfaces is emerging. These results are discussed here.

Single-molecule fluorescence spectroscopy has now been widely used to investigate complex dynamic processes which would normally be obscured in an ensemble-averaged measurement. In this report we studied photophysical behaviors of single fluorophores in proximity to zinc oxide nanostructures by single-molecule fluorescence spectroscopy and time-correlated single-photon counting (TCSPC). Single fluorophores on ZnO surfaces showed enhanced fluorescence brightness to various extents compared with those on glass; the single-molecule time trajectories also illustrated pronounced fluctuations of emission intensities, with time periods distributed from milliseconds to seconds. We attribute fluorescence fluctuations to the interfacial electron transfer (ET) events. The fluorescence fluctuation dynamics were found to be inhomogeneous from molecule to molecule and from time to time, showing significant static and dynamic disorders in the interfacial electron transfer reaction processes. PMID:23109903

Recent reports of multiexciton generation (MEG), a process by which one absorbed photon generates multiple excitons, in lead chalcogenide nanocrystals (NCs) have intensified research interest in using this phenomenon to improve the efficiency of solar energy conversion. Practical implementation of MEG processes in solar cells and solar-to-fuel conversion devices requires the development of materials with higher MEG efficiencies and lower excitation thresholds than are currently available, as well as schemes for efficient multiexciton extraction before the ultrafast exciton-exciton annihilation occurs. This Account focuses on the extraction of multiexcitons by interfacial electron transfer in model NC-molecular acceptor complexes. We provide an overview of multiexciton annihilation and multiexciton dissociation (MED) processes in NC-acceptor complexes of (i) CdSe quantum dots (QDs), (ii) CdSe/CdS quasi-type II core/shell QDs, (iii) CdSe quantum confined nanorods (QRs), and (iv) PbS QDs. We show that ultrafast electron transfer to adsorbed molecular acceptors can efficiently dissociate multiexcitons generated by absorption of multiple photons in (i), (ii), and (iii). Compared to core-only CdSe QDs, the electron hole distributions in CdSe/CdS quasi-type II QDs and CdSe QRs significantly improve their MED efficiencies by simultaneously retarding Auger recombination and facilitating interfacial electron transfer. Finally, in PbS-methylene blue (MB(+)) complexes, we show that the presence of electron acceptors does not affect the MEG efficiency and electron transfer to MB(+) efficiently dissociates the multiple excitons generated in PbS QDs. Our findings demonstrate that ultrafast interfacial charge transfer can be an efficient approach for extracting multiexcitons, and wavefunction engineering in quantum confined NCs can further improve MED efficiency. PMID:23148478

Scanning probe microscopy (SPM) offers access to the structural and material properties of interfaces, and when combined with macroscopic characterization techniques results in a powerful interfacial development tool. However, the relative infancy of SPM techniques has dictated that initial investigations concentrate on model interfacial systems as benchmarks for testing the control and characterization capabilities of SPM. One such family of model interfacial systems results from the spontaneous adsorption of alkyl thiols to gold. This dissertation examines the application of SPM to the investigation of the interfacial properties of these alkyl thiolate monolayers. Structural investigations result in a proposed explanation for counterintuitive correlations between substrate roughness and heterogeneous electron transfer barrier properties. Frictional measurements are used for characterization of the surface free energy of a series of end-group functionalized monolayers, as well as for the material properties of monolayers composed of varying chain length alkyl thiols. Additional investigations used these characterization techniques to monitor the real-time evolution of chemical and electrochemical surface reactions. The results of these investigations demonstrates the value of SPM technology to the compositional mapping of surfaces, elucidation of interfacial defects, creation of molecularly sized chemically heterogeneous architectures, as well as to the monitoring of surface reactions. However, it is the future which will demonstrate the usefulness of SPM technology to the advancement of science and technology.

Ruthenium nanoparticles (2.12 +/- 0.72 nm in diameter) were stabilized by the self-assembly of alkyne molecules (from 1-hexyne to 1-hexadecyne) onto the Ru surface by virtue of the formation of Ru-vinylidene interfacial linkages. Infrared measurements depicted three vibrational bands at 2050 cm-1, 1980 cm-1 and 1950 cm-1, which were ascribed to the vibrational stretches of the terminal triple bonds that were bound onto the nanoparticle surface. Thermogravimetric analysis showed that there were about 65 to 96 alkyne ligands per nanoparticle (depending on the ligand chainlength), corresponding to a molecular footprint of 20 to 15 Å2. This suggests that the ligands likely adopted a head-on configuration on the nanoparticle surface, consistent with a vinylidene bonding linkage due to interfacial tautomeric rearrangements. With this conjugated interfacial bonding interaction, electronic conductivity measurements of the corresponding nanoparticle solid films showed that the nanoparticles all exhibited linear current-potential curves within the potential range of -0.8 V to +0.8 V at varied temperatures (200 to 300 K). The ohmic characters were partly ascribed to the spilling of core electrons into the organic capping layer that facilitated interparticle charge transfer. Furthermore, based on the temperature dependence of the nanoparticle electronic conductivity, the activation energy for interparticle charge transfer was estimated to be in the range of 70 to 90 meV and significantly, the coupling coefficient (?) was found to be 0.31 Å-1 for nanoparticles stabilized by short-chain alkynes (1-hexyne, 1-octyne, and 1-decyne), and 1.44 Å-1 for those with long alkynes such as 1-dodecyne, 1-tetradecyne, and 1-hexadecyne. This may be accounted for by the relative contributions of the conjugated metal-ligand interfacial bonding interactions versus the saturated aliphatic backbones of the alkyne ligands to the control of interparticle charge transfer.Ruthenium nanoparticles (2.12 +/- 0.72 nm in diameter) were stabilized by the self-assembly of alkyne molecules (from 1-hexyne to 1-hexadecyne) onto the Ru surface by virtue of the formation of Ru-vinylidene interfacial linkages. Infrared measurements depicted three vibrational bands at 2050 cm-1, 1980 cm-1 and 1950 cm-1, which were ascribed to the vibrational stretches of the terminal triple bonds that were bound onto the nanoparticle surface. Thermogravimetric analysis showed that there were about 65 to 96 alkyne ligands per nanoparticle (depending on the ligand chainlength), corresponding to a molecular footprint of 20 to 15 Å2. This suggests that the ligands likely adopted a head-on configuration on the nanoparticle surface, consistent with a vinylidene bonding linkage due to interfacial tautomeric rearrangements. With this conjugated interfacial bonding interaction, electronic conductivity measurements of the corresponding nanoparticle solid films showed that the nanoparticles all exhibited linear current-potential curves within the potential range of -0.8 V to +0.8 V at varied temperatures (200 to 300 K). The ohmic characters were partly ascribed to the spilling of core electrons into the organic capping layer that facilitated interparticle charge transfer. Furthermore, based on the temperature dependence of the nanoparticle electronic conductivity, the activation energy for interparticle charge transfer was estimated to be in the range of 70 to 90 meV and significantly, the coupling coefficient (?) was found to be 0.31 Å-1 for nanoparticles stabilized by short-chain alkynes (1-hexyne, 1-octyne, and 1-decyne), and 1.44 Å-1 for those with long alkynes such as 1-dodecyne, 1-tetradecyne, and 1-hexadecyne. This may be accounted for by the relative contributions of the conjugated metal-ligand interfacial bonding interactions versus the saturated aliphatic backbones of the alkyne ligands to the control of interparticle charge transfer. Electronic supplementary information (ESI) available: TEM micrograph, derivative thermogravimetric curves, and UV-vis and fluorescence spectra of the

This work investigates the impingement of a liquid microdroplet onto a glass substrate at different temperatures. A finite-element model is applied to simulate the transient fluid dynamics and heat transfer during the process. Results for impingement under both isothermal and non-isothermal conditions are presented for four liquids: isopropanol, water, dielectric fluid (FC-72) and eutectic tin-lead solder (63Sn-37Pb). The objective of the work is to select liquids for a combined numerical and experimental study involving a high resolution, laser-based interfacial temperature measurement to measure interfacial heat transfer during microdroplet deposition. Applications include spray cooling, micro-manufacturing and coating processes, and electronics packaging. The initial droplet diameter an...

The interaction of papain with peptide immobilized on the Au surface altered the interfacial electron transfer resistant, charge transfer resistance (RCT), by preventing the redox species approaching the electrode was characterized by electrochemical impedance spectroscopy (EIS), AC voltammetry, cyclic voltammetry and surface plasmon resonance techniques (SPR). From cyclic voltammetry a potential shift of 25-30mV was observed after the addition of papain, with decrease in current and the impedance results showed that RCT increased with increasing concentration of papain indicating the interaction of papain with the immobilized film. This change in kinetics was also observed in SPR. The interaction was further confirmed by reflection-absorption infrared spectroscopy (RAIR).

Two photon photoemission was used to investigate the interfacial charge transfer for size-selected Mo(x)S(y) (x/y: 2/6, 4/6, 6/8, 7/10) clusters deposited on an ultrathin alumina film prepared on a NiAl(110) surface. The local work function of the surface increases with increasing cluster coverage, which is unexpected for charge transfer resulting from the formation of Mo-O bonds between the clusters and the alumina surface. By analogy with Au atoms and clusters on metal-supported ultrathin oxide films, we invoke electron tunneling from the NiAl substrate to explain the charge transfer to the Mo(x)S(y) clusters. Electron tunneling is favored by the large electron affinities of the Mo(x)S(y) clusters and the relatively low work function induced by the presence of the alumina film. The interfacial dipole moments derived from coverage-dependent measurements are cluster dependent and reflect differences in Mo(x)S(y) cluster structure and surface bonding. These results extend previous observations of electronic charging to non-metallic clusters, specifically, metal sulfides, and suggest a novel way to modify the electronic structure and reactivity of nanocatalysts for heterogeneous chemistry. PMID:22534692

Interfacial electron transfer (ET) of biological macromolecules such as metalloproteins is the key process in bioelectrochemistry, enzymatic electrocatalysis, artificial ET chains, single-molecule electronic amplification and rectification, and other phenomena associated with the area of bioelectronics. A key challenge in molecular bioelectronics is to improve the efficiency of long-range charge transfer. The present work shows that this can be achieved by nanoparticle (NP) assisted assembly of cytochrome c (cyt c) on macroscopic single-crystalline electrode surfaces. We present the synthesis and characterization of water-soluble gold nanoparticles (AuNPs) with core diameter 3-4 nm and their application for the enhancement of long-range interfacial ET of a heme protein. Gold nanoparticles were electrostatically conjugated with cyt c to form nanoparticle-protein hybrid ET systems with well-defined stoichiometry. The systems were investigated in homogeneous solution and at liquid/solid interface. Conjugation ofcyt c results in a small but consistent broadening of the nanoparticle plasmon band. This phenomenon can be explained in terms of long-range electronic interactions between the gold nanoparticle and the protein molecule. When the nanoparticle-protein conjugates are assembled on Au(111) surfaces, long-range interfacial ET across a physical distance of over 50 A via the nanoparticle becomes feasible. Moreover, significant enhancement of the interfacial ET rate by more than an order of magnitude compared with that of cyt c in the absence of AuNPs is observed. AuNPs appear to serve as excellent ET relays, most likely by facilitating the electronic coupling between the protein redox center and the electrode surface.

The mechanisms of the electron transfer of S-benzyl-N-(ferrocenyl-1-methyl-methylidene)-dithiocarbazate palladium(II)/zinc(II) complexes [Pd(lsb)2]/[Zn(lsb)2] were studied by cyclic voltammetry, differential pulse voltammetry, digital simulation and in-situ subtractively normalized interfacial Fourier transform infrared (SNIFTIR) spectroelectrochemistry. The results indicate that [Pd(lsb)2], which has a square-planar configuration, involved two consecutive one-electron steps in the redox process, while the tetrahedral configuration of Zn(II) involved a two-electron step. The [Pd(lsb)2] complex exhibits a moderately strong electronic communication between the two-ferrocene moieties, which occurs through the skeleton chain of the ligand due to extensive electron delocalization of the whole molecule during the redox process, while the [Zn(lsb)2] complex shows low electron delocalization, and has two almost identical ferrocene moieties.   

This book presents non-equilibrium thermodynamics and interfacial phenomena associated with vaporization and condensation processes, in addition to fundamentals of heat transfer and fluid flow mechanisms in heat transfer equipment. Topics covered include: thermodynamic and mechanical aspects of interfacial phenomena and phase transitions, interfacial tension, wetting and contact angles, boiling and condensation near immersed bodies, heterogeneous nucleation and bubble growth in liquids, pool boiling, external condensation, internal flow convective boiling and condensation, introduction to two-phase flow, and special topics.

Functional quantum dot (QD)-based nanostructures are often constructed through the self-assembly of QDs with binding partners (molecules or other nanoparticles), a process that leads to a statistical distribution of the number of binding partners. Using single QD fluorescence spectroscopy, we probe this distribution and its effect on the function (electron-transfer dynamics) in QD-C60 complexes. Ensemble-averaged transient absorption and fluorescence decay as well as single QD fluorescence decay measurements show that the QD exciton emission was quenched by electron transfer from the QD to C60 molecules and the electron-transfer rate increases with the C60-to-QD ratio. The electron-transfer rate of single QD-C60 complexes fluctuates with time and varies among different QDs. The standard deviation increases linearly with the average of electron-transfer rates of single QD-C60 complexes, and the distributions of both quantities obey Poisson statistics. The observed distributions of single QD-C60 complexes and ensemble-averaged fluorescence decay kinetics can be described by a model that assumes a Poisson distribution of the number of adsorbed C60 molecules per QD. Our findings suggest that, in self-assembled QD nanostructures, the statistical distribution of the number of adsorbed partners can dominate the distributions of the averages and standard deviation of their interfacial dynamical properties. PMID:21190376

Structurally integrated cobalt(III) complexes showing interesting surface affinity in the interfacial electron transfer reactions were synthesized by incorporating alkyl amines into the coordination sphere of cis-[CoIII(en)2(RNH2)Cl]Cl2; (where RNH2 = MeNH2 (1), EtNH2 (2), PrnNH2 (3), BunNH2 (4), BuiNH2 (5), PennNH2 (6), HexnNH2 (7) and BzNH2 (8)) through a modified synthetic route. Such complexes are playing important role as electron acceptors in the interfacial electron transfer reactions taking place between metal complex and nanosized semiconductor particles in energy conversion schemes. The complexes were characterized by spectral, 1H NMR and 13C NMR techniques, which indicate the 1,2-diamino ethane site angles are closely similar forming five membered gauche configuration. Single crystal X-ray refinements were made to explore the structures of five complexes (2)-(5) and (7). The complexes under study crystallize either in monoclinic or orthorhombic structure and the space consists; (2) P21/n, (3) P212121, (4) Pbca, (5) P21 and (7) P21/n. The Co(III) ion does not have an electronic preference, however, the structures reflect the conformational preference of RNH2 ligand.

We report a single-molecule fluorescence study of electrocatalysis by single-walled carbon nanotubes (SWNTs) at single-reaction resolution. Applying super-resolution optical imaging, we find that the electrocatalysis occurs at discrete, nanometer-dimension sites on SWNTs. Single-molecule kinetic analysis leads to an electrocatalytic mechanism, allowing quantification of the reactivity and heterogeneity of individual reactive sites. Combined with conductivity measurements, this approach will be powerful to interrogate how the electronic structure of SWNTs affects the electrocatalytic interfacial charge transfer, a process fundamental to photoelectrochemical cells. PMID:19366213

An electron-transfer (ET) reaction between decamethylferrocene in a single tributyl phosphate (TBP) droplet and hexacyanoferrate(III) in the surrounding water phase was investigated by laser trapping, microspectroscopic, and electrochemical techniques. The interfacial ET rate constant (kobs) was inversely proportional to the droplet radius (r) at > 5 ?m, but deviated from a linear relationship between kobs and r?1 at r < 5 ?m. The characteristic droplet-size effect was independent of the Galvani potential between the TBP and water phases. The results are discussed in terms of the physical properties of the micrometer-sized TBP droplet/water interface.   

The molecular structures and absorption spectra of triphenylamine dyes containing different numbers of anchoring groups (S1-S3) were investigated by density functional theory (DFT) and time-dependent DFT. The calculated geometries indicate that strong conjugation is formed in the dyes. The interfacial charge transfer between the TiO2 electrode and S1-S3 are electron injection processes from the excited dyes to the semiconductor conduction band. The simulated absorption bands are assigned to ?????* transitions according to the qualitative agreement between the experimental and calculated results. The effect of anchoring group number on the molecular structures, absorption spectra and photovoltaic performance were comparatively discussed.

We present a theoretical study of electron transport in tailored zigzag graphene nanoribbons (ZGNRs) with triangular structure using density functional theory together with the nonequilibrium Green's function formalism. We find significant rectification with a favorite electron transfer direction from the vertex to the right edge. The triangular ZGNR connecting to the electrode with one thiol group at each terminal shows an average rectification ratio of 8.4 over the bias range from -1.0 to 1.0 V. This asymmetric electron transport property originates from nearly zero band gap of triangular ZGNR under negative bias, whereas a band gap opens under positive bias. When the molecule is connected to the electrode by multithiol groups, the current is enhanced due to strong interfacial coupling; however, the rectification ratio decreases. The simulation results indicate that the unique electronic states of triangular ZGNR are responsible for rectification, rather than the asymmetric anchoring groups. © 2012 Wiley Periodicals, Inc. PMID:23081769

A unique ability of semiconductor nanocrystals (NCs) is the generation and accommodation of multiple excitons through either optical or electric current pumping. The development and improvement of NC-based optoelectronic devices that utilize multiple excitons requires the understanding of multiple exciton dynamics and their efficient conversion to emitted photons or external charges prior to exciton-exciton annihilation. Here, we demonstrate that significantly enhanced multiexciton dissociation efficiency can be achieved in CdSe quantum rods (QRs) compared to CdSe quantum dots (QDs). Using transient absorption spectroscopy, we reveal the formation of bound one-dimensional exciton states in CdSe QRs and that multiple exciton Auger recombination occurs primarily via exciton-exciton collision. Furthermore, quantum confinement in the QR radial direction facilitates ultrafast exciton dissociation by interfacial electron transfer to adsorbed acceptors. Under high excitation intensity, more than 21 electrons can be transferred from one CdSe QR to adsorbed methylviologen molecules, greatly exceeding the multiexciton dissociation efficiency of CdSe QDs. PMID:22702343

Many types of clay tend to absorb organics via electron transferring interactions between the clay and the organics. This may be utilized to design clay incorporated polymer composites with better interfacial properties. In the present paper, 2,5-bis(2-benzoxazolyl) thiophene (BBT), capable of donating electrons, is selected as the interfacial modifier for polypropylene (PP)/halloysite nanotube (HNTs) composites. The electron transfer between HNTs and BBT are confirmed. The mechanical properties and the unique morphology of the nanocomposites are examined. Formation of fibrils of BBT in the presence of HNTs is found in the nanocomposites. The chemical composition of the fibrils in the nanocomposites is found to be composed of largely BBT and a small amount of HNTs. The formation mechanism of BBT fibrils are elucidated to be the strong interactions between BBT and HNTs under melt shearing. The formation of the BBT fibrils leads to much higher crystallinity compared with previously reported PP nanocomposites. The nanocomposites with BBT show substantially increased tensile and flexural properties, which are attributed to the enhanced crystallinity of the nanocomposites.

The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (inbred reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

The study of photochemical and photophysical processes at various liquid interfaces using second harmonic generation methods is described. Among the topics discussed are the dynamics of photoinduced structure changes, the transport of charge across an interface, the rotational motions of interfacial molecules, intermolecular energy transfer within the interface, interfacial photopolymerization, and photoprocesses at a semiconductor/liquid interface. 107 refs., 12 figs.

Using techniques comprising laser trapping, microcapillary injection/manipulation, fluorescence microspectroscopy and electrochemistry of single microdroplets, we kinetically investigated the electron transfer (ET) reaction between decamethylferrocene in tributyl phosphate and hexacyanoferrate(III) in water. In the oil-microdroplet/water system, the overall ET reaction rate significantly depended on the droplet radius (r(d), 0.5 microm 2 microm)/water system. The rate constant values were extremely small in the Gibbs free energy (DeltaG) range of -10 to -25 kJ mol(-1), with DeltaG consisting of the Galvani potential difference between the water and oil phases and the redox potential difference of the solutes. The characteristic ET reaction was discussed in terms of the ion transfer and the ET across the interfacial mixed layer with nanometer-sized thickness. PMID:19212051

Interfacial reactions between melts of several borate glasses and titanium have been investigated by analytical scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). A thin titanium boride interfacial layer is detected by XPS after short (30 minutes) thermal treatments. ASEM analyses after longer thermal treatments (8--120 hours) reveal boron-rich interfacial layers and boride precipitates in the Ti side of the interface.

While intermolecular hole-hopping along the surface of semiconductors is known, there are no previous examples of electron-hopping between molecules on a surface. Herein, we present the first evidence of electron transfer from the photoreduced sensitizer Coumarin-343 (C343) to complex 1, both bound on the surface of NiO. In solution, 1 has been shown to be a mononuclear Fe-based proton-reducing catalyst. The reduction of 1 is reversible and occurs within 50 ns after excitation of C343. Interfacial recombination between the reduced 1((-)) and NiO hole occurs on a 100 ?s time scale by non-exponential kinetics. The observed process is the first essential step in the photosensitized generation of H(2) from a molecular catalyst in the absence of a sacrificial donor reagent. PMID:23140238

For some years, surface analysis was used in fundamental studies of solid-solid contacts existing in tribological systems. Analysis was used to detect material transfer in sliding contacts. The effects of surface films on the adhesion of contacts was monitored. Finally electron spectroscopic analysis of interfaces has shed some light on the fundamental electronic nature of the interfacial bond. More recently, surface analysis was applied to many tribological engineering problems. In particular, identification of chemical films formed during the sliding contact of lubricated systems and study of the surface chemistry of lubricant additives were active areas of research. One or more of four properties of the analytical technique will be important in determining its utility. The four are: lateral resolution, specimen damage, depth resolution and the availability of chemical information. In each of the applications discussed here, the important factors are brought out.

We report a surface ion transfer method to synthesise ternary alloy CdS(1-x)Se(x) (0 ? x ? 1) quantum dots (QDs) in situ on TiO(2) nanoparticles. By tuning the content of selenium in such quantum dots, the optical absorption spectra can be controllably widened to cover the most of the visible light range. The electron transport of such QDs can be modulated by changing the interfacial electronic energy between CdS(1-x)Se(x) QDs and TiO(2) nanoparticles. The QDs with optimized selenium content (x = 0.72) give a balance between a broad optical absorption and a suitable energy band alignment. The homogenous alloy CdS(1-x)Se(x) QDs achieve a maximum light-harvesting efficiency over 90%, and generate a photocurrent density larger than 10 mA cm(-2), which is 2.6- and 1.4-times that of binary CdS and CdSe QDs sensitized photovoltaic devices. PMID:23123801

Dissimilatory metal-reducing bacteria are microorganisms that gain energy by transferring respiratory electrons to extracellular solid-phase electron acceptors. In addition to its importance for physiology and natural environmental processes, this form of metabolism is being investigated for energy conversion and fuel production in bioelectrochemical systems, where microbes are used as biocatalysts at electrodes. One proposed strategy to accomplish this extracellular charge transfer involves forming a conductive pathway to electrodes by incorporating redox components on outer cell membranes and along extracellular appendages known as microbial nanowires within biofilms. To describe extracellular charge transfer in microbial redox chains, we employed a model based on incoherent hopping between sites in the chain and an interfacial treatment of electrochemical interactions with the surrounding electrodes. Based on this model, we calculated the current-voltage (I-V) characteristics and found the results to be in good agreement with I-V measurements across and along individual microbial nanowires produced by the bacterium Shewanella oneidensis MR-1. Based on our analysis, we propose that multistep hopping in redox chains constitutes a viable strategy for extracellular charge transfer in microbial biofilms. PMID:22797729

Interfacial water has unique properties in various functions. Here, using 4-dimensional (4D), ultrafast electron crystallography with atomic-scale spatial and temporal resolution, we report study of structure and dynamics of interfacial water assembly on a hydrophobic surface. Structurally, vertical...

The combination in hybrid heterojunction of nanocrystals and semiconductor polymers has great potential for light-toenergy conversion devices. For this reason, a great number of different quantum dots/polymer molecular solar cells have been investigated. However, less attention has been paid to the photo-induced charge transfer processes at the interface of these systems. Here we report a time resolved spectroscopic study of the electron injection and recombination transfer steps of CdSe/P3HT bulk heterojunction films. From the data obtained using Time Correlating Single Photon Counting (TCSPC) we have inferred that electron injection from P3HT excited state to CdSe nanocrystal conduction band occurs faster than 250 ps and the electron yield is higher than 85%, independently of the nanocrystal shape. On the other hand, the use of Laser Transient Absorption Spectroscopy allowed us to observe that all the studied interfacial charge transfer process can be fitted to dispersive stretched exponentials kinetics, independently of the QD's concentration and nanocrystal morphology, thereby offering evidence of multiple decay process in CdSe/P3HT bulk heterojunctions.

Highlights: > Gold nanoparticle (AuNP) multilayer films were fabricated via a linker-free layer-by-layer assembly. > Direct electron transfer of horseradish peroxidase (HRP) absorbed on as-prepared AuNP multilayer films was enhanced. > The optimized HRP/AuNP multilayer film had a relatively rapid response and satisfactory selectivity for H{sub 2}O{sub 2} detection. - Abstract: Au nanoparticle (AuNP) multilayer films were fabricated by combining interfacial assembly and layer-by-layer assembly. The key point is that the procedure does not require assistance of organic linker molecules, thus providing a suitable platform for the modification of biological molecules. Direct electron transfer can easily take place between a glassy carbon electrode and horseradish peroxidase (HRP) molecules adsorbed on AuNP films. The current density of direct electron transfer was closely related to the layer number, m, and reached a maximum value for m = 4. The optimized HRP/AuNP multilayer film had a relatively rapid response and satisfactory selectivity for H{sub 2}O{sub 2} detection. The linear range and the detection limit were 9.8 x 10{sup -6} to 6 x 10{sup -3} mol/L and {approx}4.9 x 10{sup -6} mol/L (S/N = 3), respectively.

Solid oxide fuel cells (SOFCs) based on BaCe{sub 0.8}Gd{sub 0.2}O{sub 3} (BCG) electrolyte films are constructed and tested at intermediate temperatures (700 to 800 C) using hydrogen as fuel and air as oxidant. The ionic and electronic conductivities as well as the interfacial properties of the BCG electrolyte films, as deposited on Ni-BCG substrates, are also determined from impedance and open-cell voltage measurements. Results indicate that the performance of the fuel cells is very sensitive to materials selection and to processing. Diffusion of Ni from substrates into the BCG electrolyte films during processing increases not only the bulk and interfacial resistances but also the electronic transference numbers of the electrolyte films, resulting in reduced open-cell voltages and poor power output. The performance of solid oxide fuel cells based on BCG electrolyte films may be substantially improved, however, by avoiding Ni diffusion into BCG electrolyte through proper selection of materials and modifications in processing.

On the basis of rational design principles, template-assisted four-helix-bundle proteins that include two histidines for coordinative binding of a heme were synthesized. Spectroscopic and thermodynamic characterization of the proteins in solution reveals the expected bis-histidine coordinated heme configuration. The proteins possess different binding domains on the top surfaces of the bundles to allow for electrostatic, covalent, and hydrophobic binding to metal electrodes. Electrostatic immobilization was achieved for proteins with lysine-rich binding domains (MOP-P) that adsorb to electrodes covered by self-assembled monolayers of mercaptopropionic acid, whereas cysteamine-based monolayers were employed for covalent attachment of proteins with cysteine. Immobilized residues in the binding domain (MOP-C) proteins were studied by surface-enhanced resonance Roman (SERR) spectroscopy and electrochemical methods. For all proteins, immobilization causes a decrease in protein stability and a loosening of the helixpacking, as reflected by a partial dissociation of a histidine ligand in the ferrous state and very low redox potentials. For the covalently attached MOP-C, the overall interfacial redox process involves the coupling of electron transfer and heme ligand dissociation, which was analyzed by time-resolved SERR spectroscopy. Electron transfer was found to be significantly slower for the mono-histidine-coordinated than for the bis-histidine-coordinated heme. For the latter, the formal heterogeneous electron-transfer rate constant of 13 s(-1) is similar to those reported for natural heme proteins with comparable electron-transfer distances, which indicates that covalently bound synthetic heme proteins provide efficient electronic communication with a metal electrode as a prerequisite for potential biotechnological applications.

Demulsification of water-in-oil emulsions that form during various stages of crude oil production is necessary for transportation and further processing in refineries. One of the most convenient and economical methods for dehydrating water-in-oil emulsions is by chemical demulsification. This study focused on the rupture phenomenon of interfacial films in the demulsification process. Langmuir film studies with bitumen interfacial film with added demulsifier at a toluene-water interface suggest that a good demulsifier can instantaneously alter the physicochemical properties of the interfacial films. Atomic force microscope and scanning electron microscope imaging of the Langmuir-Blodgett films showed that at very low concentrations, the demulsifier completely displaces the existing bitumen interfacial film. In addition, UV-absorption spectroscopy, Auger electron spectroscopy and Auger elemental mapping have revealed that the chemical nature of ruptured interface is similar to that of the demulsifier, thus confirming the displacement of interfacial active material of bitumen by the demulsifier at the toluene-water interface.

The interfacial tensions of several solutions of reversed micellar systems used in lysozyme extraction were measured by drop weight and pendant drop methods. The organic phase was 2,2,4-trimethylpentane containing sodium bis(2-ethylhexyl)sulfosuccinate (AOT), and the aqueous phase was a solution of lysozyme and KCl, NaCl or CaCl2. The effects of salt concentration and salt type on the interfacial tension were studied. The hydration of cation associated with AOT affects interfacial properties to some extent. At the same ionic strength, the interfacial flexibility decreased with type of salt, NaCl > CaCl2 > KCl. This order corresponds to that of the cation's hydration number. Overall mass-transfer coefficients of lysozyme were also measured under various salt concentrations of three salt systems and were expressed by a single curve when plotted against interfacial tension.   

In this review, I will describe our research in the field of molecular engineering of transition metal complexes for use as sensitizers in dye sensitized solar cells (DSC), light emitting agents in organic light-emitting diodides (OLEDs) and self assembled molecular charge transport layers in electronic devices. Thanks to the development of ruthenium complexes acting as very efficient sensitizers the DSC reaches currently conversion efficiencies over 11 percent and excellent stability rendering it a credible alternative to silicon devices. The industrial development is advancing rapidly, commercial manufacturing of the DSC having recently been announced. The cell is a viable contender for large-scale future solar energy conversion systems on the bases of cost, efficiency, stability, availability and environmental compatibility. Heteroleptic ruthenium complexes endowed with ion coordinating ligands have shown unprecedented performance in solid state dye sensitized photovoltaic devices. Electron transfer from the excited ruthenium sensitizer into the conduction band of the nanocrystalline titanium dioxide film occurs within femtoseconds. Rapid cross surface hole transfer within self-assembled monolayer of transition metal complexes [complexes have also been witnessed. The saline kinetic features of these interfacial and cross-surface charge transfer reactions will be discussed. Apart from dye-sensitized solar cells these transition metal complexes offer also great promise for a new generation of electroluminescent systems. Examples of these devices will be presented and their mode of operation will be discussed.   

Heterostructures based on Ag3PO4 nanoparticles and TiO2 nanobelts were prepared by a coprecipitation method. The crystalline structures were characterized by X-ray diffraction measurements. Electron microscopic studies showed that the Ag3PO4 nanoparticles and TiO2 nanobelts were in intimate contact which might be exploited to facilitate charge transfer between the two semiconductor materials. In fact, the heterostructures exhibited markedly enhanced photocatalytic activity as compared with unmodified TiO2 nanobelts or commercial TiO2 colloids in the photodegradation of methyl orange under UV irradiation. This was accounted for by the improved efficiency of interfacial charge separation thanks to the unique alignments of their band structures. Remarkably, whereas the photocatalytic activity of the heterostructure was comparable to that of Ag3PO4 nanoparticles alone, the heterostructures exhibited significantly better stability and reusability in repeated tests than the Ag3PO4 nanoparticles.

The study presented in this work deals with the synthesis of graphene/BiOBr composite following hydrothermal reaction between graphene oxide and BiOBr. The results achieved demonstrated that the presence of graphene on the surface of BiOBr significantly improved the photocatalytic activity, under visible light irradiation, owing to the low isoelectric characteristics of graphene and better interfacial electron transfer between BiOBr and graphene. The effect of different amounts of graphene such as 1, 3, 6 and 10 wt% on the photocatalytic and adsorption efficiency was investigated. Our results showed that there exists an optimum concentration of graphene (˜6 wt%) for the best photocatalytic response of BiOBr which could be due to crucial energy dissipation. The photocatalytic and adsorption efficiency of the composites were investigated by studying the removal of Sulforhodamine 640 dye as a probe reaction.

The mechanism of photocurrent generation for organic solar cells with a heterojunction formed between metal phthalocyanine and C60 (or a perylene derivative) was studied. Photocurrent was observed under both reverse and forward biases. Under reverse biases, photocurrent action spectra showed that excitons generated in both organic layers contribute to photocurrent, whereas under forward biases, the excitons generated in only one of them contributed to photocurrent. Forward photocurrent was attributed to the electron transfer reaction between excitons and charge carriers accumulated at the organic/organic junction, the charge carriers depending on the rate of carrier injection from the electrodes. Forward photocurrent showed quantum efficiencies higher than 100% under very weak irradiation, and was attributed to current multiplication at the organic/electrode interface. Since this phenomenon is closely associated with the interfacial structure, it can be used as a measure of interface quality.   

Selenium nanoparticles of 10-20 nm in diameter have been prepared using cellulose nanocrystal (CNXL) as a reducing and structure-directing agent under hydrothermal conditions. Na2SeO3 was reduced to form elemental selenium nanoparticles under hydrothermal conditions. During the hydrothermal process (120-160 oC), CNXL rods were mainly maintained and selenium nanoparticles were interfacially bound to CNXL surface. The reaction temperature affects the sizes of interfacially bound selenium nanoparticles. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and transmission electron microscope (TEM) were employed to characterize interfacially bound selenium nanoparticles on CNXL surface.

This study developed a new type of all-solid-state ion-selective electrode based on a transducing layer of a network of single-walled carbon nanotubes. The extraordinary capacity of carbon nanotubes to promote electron transfer between heterogeneous phases made the presence of electroactive polymers or any other ion-to-electron-transfer promoter unnecessary. The new transducer layer was characterized by environmental scanning electron microscopy and electrochemical impedance spectroscopy. The stability of the electrical potential of the new solid-contact electrode was examined by performing current-reversal chronopotentiometry, and the influence of the interfacial water film was assessed by the potentiometric water layer test. The performance of the new electrode was evaluated by determining K+ with an ion-selective membrane that contained the well-known valinomycin ion carrier. The new electrode had a Nernstian slope (58.4 mV/decade), dynamic ranges of four logarithmic units, and selectivities and limits of detection comparable to other solid-contact electrodes. The short response time (less than 10 s for activities higher than 10(-5.5) M) and the stability of the signal over several days makes these new electrodes very promising candidates for attaining true miniaturization. PMID:18271511

The hydrophobic patch of azurin (AZ) from Pseudomonas aeruginosa is an important recognition surface for electron transfer (ET) reactions. The influence of changing the size of this region, by mutating the C-terminal copper-binding loop, on the ET reactivity of AZ adsorbed on gold electrodes modified with alkanethiol self-assembled monolayers (SAMs) has been studied. The distance-dependence of ET kinetics measured by cyclic voltammetry using SAMs of variable chain length, demonstrates that the activation barrier for short-range ET is dominated by the dynamics of molecular rearrangements accompanying ET at the AZ-SAM interface. These include internal electric field-dependent low-amplitude protein motions and the reorganization of interfacial water molecules, but not protein reorientation. Interfacial molecular dynamics also control the kinetics of short-range ET for electrostatically and covalently immobilized cytochrome c. This mechanism therefore may be utilized for short-distance ET irrespective of the type of metal center, the surface electrostatic potential, and the nature of the protein-SAM interaction. PMID:22788731

The authors attempt to distinguish between two competing models of the photovoltage-determining mechanism in dye-sensitized solar cells. One model does not consider the equilibrium potential difference at the TiO{sub 2}/substrate interface to be a significant factor in determining the photovoltage; the other claims that this potential difference sets the upper limit to the achievable photovoltage. The authors deposit dye-sensitized TiO{sub 2} films on four different substrates that have vacuum work functions spanning a 1.4 eV range and measure the photovoltage obtained from these films in three different redox electrolyte solutions. No significant differences in photovoltage are obtained on the different substrates, not even on Pt where the interfacial potential should oppose electron transfer. The authors suggest that the interfacial potential barrier may be smaller than expected and/or too thin to have a significant influence on cell performance. The authors conclude that the photovoltage is determined by photoinduced chemical potential gradients, not by equilibrium electric fields.

As electronic assemblies become more compact and increase in processing bandwidth, escalating thermal energy has become more difficult to manage. The major limitation has been nonmetallic joining using poor thermal interface materials (TIM). The interfacial, versus bulk, thermal conductivity of an adhesive is the major loss mechanism and normally accounts for an order magnitude loss in conductivity per equivalent thickness. The next generation TIM requires a sophisticated understanding of material and surface sciences, heat transport at submicron scales, and the manufacturing processes used in packaging of microelectronics and other target applications. Only when this relationship between bond line manufacturing processes, structure, and contact resistance is well-understood on a fundamental level will it be possible to advance the development of miniaturized microsystems. This report examines using thermal and squeeze-flow modeling as approaches to formulate TIMs incorporating nanoscience concepts. Understanding the thermal behavior of bond lines allows focus on the interfacial contact region. In addition, careful study of the thermal transport across these interfaces provides greatly augmented heat transfer paths and allows the formulation of very high resistance interfaces for total thermal isolation of circuits. For example, this will allow the integration of systems that exhibit multiple operational temperatures, such as cryogenically cooled detectors.

An interfacial condensation heat transfer phenomenon in a steam/water countercurrent stratified flow in a nearly horizontal pipe has been experimentally investigated. The present study has been focused on the measurement of the temperature and velocity distributions within the water layer. In particular, the water layer thickness used in the present work is large enough so that the turbulent mixing is limited and the thermal stratification is established. As a result, the thermal resistance of the water layer to the condensation heat transfer is increased significantly. An empirical correlation of the interfacial condensation heat transfer has been developed. The present correlation agrees with the data within {+-} 15%. 5 refs., 6 figs. (Author)

Present work analyses the behavior and mass transfer of N-methyldiethanolamine (MDEA) in the removal process of carbon dioxide using a bubble column reactor (BCR) as gas-liquid contactor. The use of this type of equipment requires the interfacial area determination for the following mass transfer coefficient calculation based on absorption kinetics. In this work, a photographic method based on the bubble diameter determination, has been employed. The effect of contactor, operation conditions, liquid-phase nature and chemical reaction upon the mass transfer coefficient and interfacial areas have been analysed.

Interactions between metals and oxides are key factors to determine the performance of metal/oxide heterojunctions, particularly in nanotechnology, where the miniaturization of devices down to the nanoregime leads to an enormous increase in the density of interfaces. One central issue of concern in engineering metal/oxide interfaces is to understand and control the interactions which consist of two fundamental aspects: (i) interfacial charge redistribution — electronic interaction, and (ii) interfacial atom transport — chemical interaction. The present paper focuses on recent advances in both electronic and atomic level understanding of the metal oxide interactions at temperatures below 1000 ?C, with special emphasis on model systems like ultrathin metal overlayers or metal nanoclusters supported on well-defined oxide surfaces. The important factors determining the metal oxide interactions are provided. Guidelines are given in order to predict the interactions in such systems, and methods to desirably tune them are suggested. The review starts with a brief summary of the physics and chemistry of heterophase interface contacts. Basic concepts for quantifying the electronic interaction at metal/oxide interfaces are compared to well-developed contact theories and calculation methods. The chemical interaction between metals and oxides, i.e., the interface chemical reaction, is described in terms of its thermodynamics and kinetics. We review the different chemical driving forces and the influence of kinetics on interface reactions, proposing a strong interplay between the chemical interaction and electronic interaction, which is decisive for the final interfacial reactivity. In addition, a brief review of solid gas interface reactions (oxidation of metal surfaces and etching of semiconductor surfaces) is given, in addition to a comparison of a similar mechanism dominating in solid solid and solid gas interface reactions. The main body of the paper reviews experimental and theoretical results from the literature concerning the interactions between metals and oxides (TiO2, SrTiO3, Al2O3, MgO, SiO2, etc.). Chemical reactions, e.g., redox reactions, encapsulation reactions, and alloy formation reactions, are highlighted for metals in contact with mixed conducting oxides of TiO2 and SrTiO3. The dependence of the chemical interactions on the electronic structure of the contacting metal and oxide phases is demonstrated. This dependence originates from the interplay between interfacial space charge transfer and diffusion of ionic defects across interfaces. Interactions between metals and insulating oxides, such as Al2O3, MgO, and SiO2, are strongly confined to the interfaces. Literature results are cited which discuss how the metal/oxide interactions vary with oxide surface properties (surface defects, surface termination, surface hydroxylation, etc.). However, on the surfaces of thin oxide films grown on conducting supports, the effect of the conducting substrates on metal oxide interactions should be carefully considered. In the summary, we conclude how variations in the electronic structure of the metal/oxide junctions enable one to tune the interfacial reactivity and, furthermore, control the macroscopic properties of the interfaces. This includes strong metal support interactions (SMSI), catalytic performance, electrical, and mechanical properties.

The function and efficiency of organic electronic devices is determined to a significant extent by the electronic properties of organic/organic heterojunctions and interfaces between electrodes and organic semiconductors. The energy level alignment between metal electrodes and active organic layers can be adjusted over wide ranges by employing interlayers of strong molecular acceptors and donors that undergo charge transfer reactions with the metal. It will be shown that such interlayers lead to lower charge injection barriers than pristine metals, even when the work function is the same. It is argued that the molecularly modified electrodes are electronically more rigid than their pristine metal counterparts, i.e., the electron spill-out at the organic-terminated surface is less pronounced compared to metal surfaces. The energy levels at organic/organic heterojunctions comprising donors and acceptors as used in organic photovoltaic cells are essentially independent of deposition sequence, as long as supporting electrodes to not induce energy level pinning. When a high work function electrode is used, the energy levels may become Fermi-level pinned and an electric field drops right at the heterojunction. This effect is exemplified for the donor diindenoperylene and the acceptor C60. The electric field distribution within an organic opto-electronic device may thus be adjusted locally by employing interfacial energy level pinning, even at weakly interacting organic/organic interfaces.

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An electrochemical reaction cell using a solid electrolyte was developed to study the thermodynamic and kinetic behavior of interfacial oxides. Al2O3 and TiO2 existing between the Fe alloy melt and the magnesia stabilized zirconia solid electrolyte could be controlled using an electrochemical method of an external direct current at 1823 K. This novel approach could control the electron density near the interface of the oxides and subsequently the interfacial oxygen.In this study, a direct current of 0.1 ampere resulted in the decomposition of the interfacial oxides and an interfacial oxygen concentration below 3 ppm. Furthermore, morphological observations using EPMA confirmed the interfacial oxide control corresponding to the external electrical potential.   

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.

We review recent advances in aberration-corrected scanning transmission electron microscopy that allow sub-Angstrom beams to be used for imaging and spectroscopy, with enormous improvement in sensitivity for single atom detection and the investigation of interfacial electronic structure. Comparison is made between the electronic and structural width of gate oxides, with interpretation through first-principles theory. Future developments are discussed.

Abstract in english In order to characterize the gas-liquid parameters of a down-flow jet loop reactor, experiments were carried out to study the gas holdup, bubble sizes and their distribution, mass transfer area and mass transfer coefficient. The experiments were performed in the bubbly flow regime because of its stability and uniformity. Analysis of experimental data showed an unambiguous relationship between gas holdup, bubble size, bubble size distribution and interfacial area. It has a (more) lso been found that gas holdup and interfacial area is a strong function of slip velocity. The variation of interfacial area and mass transfer coefficient were also analyzed and expressed as a function of operational and geometric parameters.

Reliable integration of solution processed nanoparticle thin films for next generation low-cost flexible electronics is limited by mechanical damage in the form of delamination and cracking of the films, which has not been investigated quantitatively or systematically. Here, we directly measured the interfacial fracture energy of silver nanoparticle thin films by using double cantilever beam fracture mechanics testing. It was demonstrated that the thermal annealing temperature and period affect the interfacial fracture energy. Also it was found that the interfacial fracture resistance can be maximized with optimized annealing conditions by the formation of organic residual bridges during the annealing process. PMID:23128272

This publication presents a detailed experimental and theoretical study of mass transfer of triethylamine (TEA) across the n-decane/water interface. In preliminary investigations, the partition of TEA between n-decane and water is determined. Based on the experimental finding that the dissociation of TEA takes place in the aqueous and in the organic phase, we assume that the interfacial mass transfer is mainly affected by adsorption and desorption of ionized TEA molecules at the liquid/liquid interface. Due to the amphiphilic structure of the dissociated TEA molecules, a dynamic interfacial tension measurement technique can be used to experimentally determine the interfacial mass transport. A model-based approach, which accounts for diffusive mass transport in the finite liquid bulk phases and for adsorption and desorption of ionized TEA molecules at the interface, is employed to analyze the experimental data. In the equilibrium state, the interfacial tension of dissociated TEA at the n-decane/water interface can be adequately described by the Langmuir isotherm. The comparison between the theoretical and the experimental dynamic interfacial tension data reveals that an additional activation energy barrier for adsorption and desorption at the interface has to be regarded to accurately describe the mass transport of TEA from the n-decane phase into the aqueous phase. Corresponding adsorption rate constants can be obtained by fitting the theoretical predictions to the experimental data. Interfacial tension measurements of mass transfer from the aqueous into the organic phase are characterized by interfacial instabilities caused by Marangoni convection, which result in an enhancement of the transfer rate across the interface. PMID:22475436

The heat transfer in turbulent film condensation of flowing vapour on a horizontal flat plate was investigated by means of the analogy between momentum and heat transfer. To describe the momentum transfer in the film a four-region model was presented. With this model the wavy interfacial surface is treated as a stiff rough wall. A shear Nusselt number has been calculated and represented as a function of film Reynolds number and Prandtl number.

Fluid/fluid interfacial areas are important in controlling the rate of mass and energy transfer between fluid phases in porous media. We present a modified thermodynamically based model (TBM) to predict fluid/fluid interfacial areas in porous media for arbitrary drainage/imbibition sequences. The TBM explicitly distinguishes between interfacial areas associated with continuous (free) and isolated (entrapped) nonwetting fluids. The model is restricted to two-fluid systems in which (1) no significant conversion of mechanical work into heat occurs, (2) the wetting fluid completely wets the porous medium’s solid surfaces, and (3) no changes in interfacial area due to mass transfer between phases occur. We show example calculations for two different drainage/imbibition sequences in two porous media: a highly uniform silica sand and a well-graded silt. The TBM’s predictions for interfacial area associated with free nonwetting-fluid are identical to those of a previously published geometry-based model (GBM). However, predictions for interfacial area associated with entrapped nonwetting-fluid are consistently larger in the TBM than in the GBM. Although a comparison of model predictions with experimental data is currently only possible to a limited extent, good general agreement was found for the TBM. As required model parameters are commonly used as inputs for or tracked during multifluid-flow simulations, the modified TBM may be easily incorporated in numerical codes.

Interfacial tension isotherms were determined for individual palladium(II) extractants and interpreted. The following extractants were considered: 4-alkylphenylamines containing from 6 to 14 carbon atoms in the alkyl group, dihexylsulfide, 2-hydroxyethyldecyl sulfide and its partly fluorinated derivative, decylnicotiniate and N,N-dihexylpyridine-3-carboxamide. 4-Alkylphenylamines exhibited significantly stronger interfacial activity than did the other extractants. They adsorbed at the hydrocarbon/water interfaces already at concentrations 10-5 M and permit to decrease the interfacial tension to 5 mN m-1. As a result, they can be used as a phase transfer catalyst to increase the rate of palladium(II) extraction with other extractants. When used alone, the initial rate of extraction increases with the extractant increasing hydrophobicity, thus in the order of increased interfacial activity.   

In the present work, the interfacial movement resulting from sulfur mass transfer at the slag/metal interface was monitored by X-ray sessile drop method in dynamic mode at temperature 1873 K (1600 °C) under nonequilibrium conditions. The experiments were carried out with pure iron and CaO-SiO2-Al2O3-FeO slag (alumina saturated at the experimental temperature) contained in alumina crucibles with well-controlled partial pressures of oxygen and sulfur. The impact of oxygen potential on the droplet oscillation as sulfur from the gas phase reaches the metal drop through the intermediate slag phase was monitored. The interfacial velocity was investigated. It was found that the increases of interfacial velocity and the maximum oscillation time were mainly attributed to the partial pressure of oxygen increases. The experiment results were explained by previous ab initio calculations. The thermo-physical and thermo-chemical properties of slag were also found to influence interfacial velocity.

Perovskite oxides possess a wide range of technologically relevant functional properties including ferromagnetism, ferroelectricity, and superconductivity. Furthermore, the interfaces of perovskite oxides have been shown to exhibit unexpected functional properties not found in the constituent materials. These functional properties arise due to various structural and chemical changes as well as electronic and/or magnetic interactions occurring over nanometer length scales at the interfaces. In order to understand how these interfacial effects impact the ferromagnetic (FM) properties of the half metal La0.7Sr0.3MnO3 (LSMO), we have examined superlattices composed of LSMO sublayers alternating with either the antiferromagnetic (AFM) insulator La0.7Sr0.3FeO3 (LSFO) or the non-magnetic metal La0.5Sr0.5TiO3 (LSTO). A comprehensive approach consisting of bulk magnetization, magneto-transport measurements, and scanning transmission electron microscopy as well as soft x-ray magnetic spectroscopy and microscopy has been used to fully characterize the properties of the interfaces. We find that the nature of the charge transfer across the interfaces affects the FM properties of LSMO, such that at a given sublayer thickness, the LSMO/LSTO system displays a similar Curie temperature but a higher saturation magnetization than the LSMO/LSFO system. For a specific range of sublayer thicknesses, the LSMO/LSFO system displays a unique spin-flop coupling where the FM moments and the AFM spin axis maintain a perpendicular orientation relative to one another. Through this coupling mechanism, the direction of the AFM spin axis can be reoriented with an applied magnetic field. In this talk, I will discuss how these interfacial phenomena contribute to the types of FM and AFM domain patterns observed in the individual layers in the superlattices.

We report the assembly of nanosized ZnS particles on the 2D platform of a graphene oxide (GO) sheet by a facile two-step wet chemistry process, during which the reduced graphene oxide (RGO, also called GR) and the intimate interfacial contact between ZnS nanoparticles and the GR sheet are achieved simultaneously. The ZnS-GR nanocomposites exhibit visible light photoactivity toward aerobic selective oxidation of alcohols and epoxidation of alkenes under ambient conditions. In terms of structure-photoactivity correlation analysis, we for the first time propose a new photocatalytic mechanism where the role of GR in the ZnS-GR nanocomposites acts as an organic dye-like macromolecular "photosensitizer" for ZnS instead of an electron reservoir. This novel photocatalytic mechanism is distinctly different from all previous research on GR-semiconductor photocatalysts, for which GR is claimed to behave as an electron reservoir to capture/shuttle the electrons photogenerated from the semiconductor. This new concept of the reaction mechanism in graphene-semiconductor photocatalysts could provide a new train of thought on designing GR-based composite photocatalysts for targeting applications in solar energy conversion, promoting our in-depth thinking on the microscopic charge carrier transfer pathway connected to the interface between the GR and the semiconductor. PMID:23106763

Theoretical studies of electron correlations of doubly excited electrons in hyperspherical coordinates, and differential and total electron transfer cross sections in fast ion-atom collisions are reported. (GHT)

The effect of aqueous–gas interfacial transfer of volatile species on the ?-radiolysis of water was studied as a function of gas-to-liquid volume ratio at various solution pHs and cover gas compositions. Water samples with cover-gas headspace were irradiated at an absorbed dose rate of 2.5Gys?1 and the radiolytic productions of H2 in the cover gas and H2O2 in the water phase were monitored as a function of irradiation time. The experimental results were compared with computer simulations using a water radiolysis kinetics model that included primary radiolysis, subsequent reactions of the primary radiolysis products in the aqueous phase, and aqueous–gas interfacial transfer of the volatile species H2 and O2. This study shows that the impact of the interfacial...

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This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

This research project involves the design, synthesis and study of the molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

The structure and electronic properties of a boron subphthalocyanine (SubPc) adsorbed on buckminsterfullerene (C60) and of C60 on SubPc surfaces, mimicking reverse orders of deposition, have been studied using density-functional theory (DFT) including long-van der Waals. Total-energy calculations are used to elucidate the initial adsorption of SubPc on C60 low index surfaces and also C60 on SubPc surfaces. The energetics of crystalline substrates with different surface terminations were mapped out using a single molecule of the partnering species. Accordingly, the interfacial structure and properties are different depending on whether the substrate is SubPc or C60, due to the incongruency between lattices and the disorder that develops in the contact layers of C60 and SubPc, respectively. The dependence of the charge transfer energies on the interface morphology is studied using range separated hybrid functionals. The stabilization of charge transfer states to below the absorbing state, needed to optimize the fill factor, also depends on the order of layer deposition. These results are discussed in the context of experiments performed on organic solar cells, showing trade-offs in the short circuit current and open circuit voltage with varying deposition order of the organic layers.

HgTe/CdTe superlattices (SLs) have been grown on CdZnTe (211)B substrates as interfacial layers to improve the reproducibility and material properties of epitaxial HgCdTe. The interfacial SL layer is found by transmission electron microscopy to be capable of smoothing out the substrate's surface roughness and to bend or block threading dislocations from propagating from the substrate into the functional HgCdTe epilayers. The best etch pit density values of 4×104 cm-2 were achieved in long-wavelength infrared HgCdTe epilayers with such interfacial layers, while typical values were in the low 105 cm-2 range. The recombination mechanisms in such layers were dominated by radiative and Auger intrinsic recombination mechanisms, whereas the contributions from the Shockley-Read-Hall mechanism become negligible, which demonstrated that the use of the SL interfacial layers was beneficial for HgCdTe growth using molecular beam epitaxy or MBE.

We have developed a new method that can quantitatively characterize the correlation length and the asperity height of the roughness at a SiO2/Si interface. This method involves, first, ?110? cross-sectional high-resolution transmission electron microscopy (HREM) of the interfaces in very thin specimens (?5 nm thick). Pairs of closely spaced Si atomic columns appear in the HREM image as black dots. The next step involves measuring the HREM image intensity distribution along each black-dot layer parallel to the interface. Then these intensity distributions, which are affected by interfacial roughness, are examined layer-by-layer by Fourier analysis. Moreover, to enable detailed observation of the interfacial roughness, we developed a specimen-preparation technique in which CF4–O2 plasma etching is used to remove ion-milling artifacts. We demonstrate that this examination can provide quantitative indices of the interfacial roughness. Our method can also detect interfacial roughness that has a correlation length of only a few nanometers.   

Interfaces often dictate heat flow in micro- and nanostructured systems. However, despite the growing importance of thermal management in micro- and nanoscale devices, a unified understanding of the atomic-scale structural features contributing to interfacial heat transport does not exist. Herein, we experimentally demonstrate a link between interfacial bonding character and thermal conductance at the atomic level. Our experimental system consists of a gold film transfer-printed to a self-assembled monolayer (SAM) with systematically varied termination chemistries. Using a combination of ultrafast pump-probe techniques (time-domain thermoreflectance, TDTR, and picosecond acoustics) and laser spallation experiments, we independently measure and correlate changes in bonding strength and heat flow at the gold-SAM interface. For example, we experimentally demonstrate that varying the density of covalent bonds within this single bonding layer modulates both interfacial stiffness and interfacial thermal conductance. We believe that this experimental system will enable future quantification of other interfacial phenomena and will be a critical tool to stimulate and validate new theories describing the mechanisms of interfacial heat transport. Ultimately, these findings will impact applications, including thermoelectric energy harvesting, microelectronics cooling, and spatial targeting for hyperthermal therapeutics.

A small amount of surface active agent in a extraction column has the effect of decreasing mass transfer coefficient, while increasing the mass transfer area. The overall mass transfer efficiency is thus varied complicatedly with the surfactant concentration and the hydrodynamic behavior of the two phase in the extraction columns. In this work, spray-tower and packed-tower are used as extraction columns to obtain the overall performance of the equipment. The effects of surfactant on the mass transfer efficiency and interfacial area in the two apparatuses are studied. The results show that the effects of SLS on the decreasing of mass transfer coefficient is more prominent than that on the increasing of mass transfer area in the both apparatuses. In the packed-tower, a higher efficiency is obtained due to the effect of the packing. However, at the presence of SLS, the dispersion effect can not raise the interfacial area high enough to overcome the simultaneous decrease in mass transfer coefficient. The mechanisms to increase interfacial area by the surfactant are different at various concentrations of SLS and different between the two apparatuses, which are also discussed in the article. (author)

The load response of a rock-socketed steel H-pile can be strongly influenced by the nonlinear interfacial behavior between the grout and the steel H-pile, and between the pile and the rock mass. This paper focuses on the load-transfer mechanism of the former interface through experimental push-out t...

To simulate dispersed two-phase flows CFD tools for predicting the local particle number density and the size distribution are required. These quantities do not only have a significant effect on rates of mixing, heterogeneous chemical reaction rates or interfacial heat and mass transfers, but also a...

Fibre-reinforced plastic (FRP) or steel plates can be bonded to the soffit of a beam as a means of retrofitting the beam. In such plated beams, tensile forces develop in the bonded plate and these have to be transferred to the original beam via interfacial shear and normal stresses. Consequently, de...

Film boiling heat transfer coefficients for a downward-facing hemispherical surface are measured from the quenching tests in DELTA (Downward-boiling Experimental Laminar Transition Apparatus). Two test sections are made of copper to maintain low Biot numbers. The outer diameters of the hemispheres are 120 mm and 294 mm, respectively. The thickness of all the test sections is 30 mm. The effect of diameter on film boiling heat transfer is quantified utilizing results obtained from the test sections. The measured data are compared with the numerical predictions from laminar film boiling analysis. The measured heat transfer coefficients are found to be greater than those predicted by the conventional laminar flow theory on account of the interfacial wavy motion incurred by the Helmholtz instability. Incorporation of the wavy motion model considerably improves the agreement between the experimental and numerical results in terms of heat transfer coefficient. In addition, the interfacial wavy motion and the quenching process are visualized through a digital camera.

A pouch-type lithium-ion cell, with graphite anode and LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} cathode, was cycled at C/2 over 100% depth of discharge (DOD) at ambient temperature. The LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} composite cathode was primarily responsible for the significant impedance rise and capacity fade observed in that cell. The processes that led to this impedance rise were assessed by investigating the cathode surface electronic conductance, surface structure, composition, and state of charge at the microscopic level with the use of local probe techniques. Raman microscopy mapping of the cathode surface provided evidence that the state of charge of individual LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} particles was non-uniform despite the deep discharge at the end of cell testing. Current-sensing atomic force microscopy imaging revealed that the cathode surface electronic conductance diminished significantly in the tested cells. Loss of contact of active material particles with the carbon matrix and thin film formation via electrolyte decomposition not only led to LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} particle isolation and contributed to cathode interfacial charge-transfer impedance but also accounted for the observed cell power and capacity loss.

A new sensor containing MgFe2O4 nanoparticles in modified multiwall carbon nanotubes (MgFe2O4-MWCNTs) was prepared, and its electrochemical behavior was investigated. MgFe2O4-MWCNTs were used as a voltammetric sensor for the electrocatalytic determination of ciprofloxacin. The synthesized materials were characterized by different methods such as transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry, and electrochemical impedance spectroscopy. The MgFe2O4-MWCNTs electrode showed an oxidation peak potential at around 250 mV. The immobilized composite films facilitate interfacial electron transfer and electrocatalytic activity on the oxidation of ciprofloxacin. The oxidation peak current was dependent on the ciprofloxacin concentration, which was linear over the range of 0.10 – 1000 ?mol L?1 with a detection limit and quantification limit of 0.01 and 0.08 ?mol L?1, respectively. The relative standard deviation for the determination of 1.0 ?mol L?1 ciprofloxacin was 1.1%. The repeatability of the sensor was investigated by preparing nine similar electrodes. The proposed sensor is a selective and fast tool for the determination of ciprofloxacin in tablet, plasma, and urine samples.   

Quantitative electron energy-loss spectrometry was applied to a range of ceramic materials at a spatial resolution of <5 nm. Analysis of Fe L{sub 23} white lines indicated a low-spin state with a charge transfer of {approximately}1.5 electrons/atom onto the Fe atoms implanted into (amorphized) silicon carbide. Gradients of 2 to 5% in the Co:O stoichiometry were measured across 100-nm-thick Co{sub 3}O{sub 4} layers in an oxidized directionally solidified CoO-ZrO{sub 2} eutectic, with the highest O levels near the ZrO{sub 2}. The energy-loss near-edge structures were dramatically different for the two cobalt oxides; those for CO{sub 3}O{sub 4} have been incorrectly ascribed to CoO in the published literature. Kinetically stabilized solid solubility occurred in an AlN-SiC film grown by low-temperature molecular beam epitaxy (MBE) on {alpha}(6H)-SiC, and no detectable interdiffusion occurred in couples of MBE-grown AlN on SiC following annealing at up to 1750C. In diffusion couples of polycrystalline AlN on SiC, interfacial 8H sialon (aluminum oxy-nitride) and pockets of Si{sub 3}N{sub 4}-rich {beta}{prime} sialon in the SiC were detected.

Polyaniline (PANI) hybridized ZnO photoanode for dye-sensitized solar cell (DSSC) was primarily prepared via a two-step process which involved hydrothermal growth of ZnO nanograss on the fluorine-doped tin oxide (FTO) substrate and subsequently chemisorption of PANI on the surfaces of the ZnO nanorods. The PANI hybridized ZnO nanograss films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectra (FT-IR), and the results indicated that there were chemical interactions between PANI and ZnO. Both pure ZnO nanograss and PANI hybridized ZnO nanograss were applied to DSSC. The results of photoelectrochemical measurement showed that the photocurrent density of PANI (100 mg/L) hybridized ZnO nanograss photoanode was significantly enhanced, and the overall light-conversion efficiency increased by 60%. The electrochemical impedance spectra (EIS) displayed that the electron densities in photoanodes of PANI hybridized ZnO nanograss were larger than that in pure ZnO nanograss. This is ascribed to more effective charge separation and faster interfacial charge transferring occurred in the hybrid photoanode.

The interfacial, electrical, and magnetic properties of the Heusler alloy Co{sub 2}MnGa grown epitaxially on GaAs(100) are presented with an emphasis on the use of this metal-semiconductor combination for a device that operates on the principles of spin-injection between the two materials. Through systematic growth optimization the stoichiometry in the bulk Co{sub 2}MnGa can be controlled to better than +-2%, although the interface is disordered and limits the spin-injection efficiency in a practical spintronic device irrespective of the half-metallic nature of the bulk metal. Molecular beam epitaxial growth was monitored in situ by reflection high energy electron diffraction and the bulk composition was measured ex situ with inductively coupled plasma optical emission spectroscopy. The Co{sub 2}MnGa L2{sub 1} cubic structure is strained below a thickness of 20 nm on GaAs(100) but relaxed in films thicker than 20 nm. Electrical measurements on the Co{sub 2}MnGa reveal general characteristics of a disordered electron system with insulating behavior for layer thicknesses <4 nm. Thicker layers show a negative magnetoresistance with extraordinary Hall effect constants up to 30 OMEGA T{sup -1}. Spin polarization transfer across the interface between Co{sub 2}MnGa and GaAs is approximately 6.4% at 5 K in the current of a GaAs p-i-n diode even with compositional disorder at the interface.

An analysis is carried out to determine the effects of the diffusional resistance on the rate of the adsorption of ammonia in an aqueous solution. A performance prediction model is developed to calculate the local rate of heat and mass transfer, including physical and thermodynamic property calculations of the mixture. An algorithm is developed for calculating the interfacial conditions. The local heat- and mass-transfer calculation is then incorporated into the performance prediction method for adsorption for a given geometry.

Research carried out at the Notre Dame Radiation Laboratory is briefly described. Research involves areas of electron transfer photoprocesses, photochemistry, pulse radiolysis, and charge transfer reactions. 13 refs.

Abstract Interfacial doping in organic semiconductors (OSs) is an important technique to achieve efficient organic electronic devices. In this paper, we discuss how the charge injection into an OS can be enhanced by the insertion of a thin interfacial layer or an electrically doped OS layer between an electrode and an undoped OS. We present that the vacuum level shift and Fermi level modification by the electrical doping is the origin of the efficient charge injection through a metal-organic junction and an organic-organic junction. Application to organic electronics such as organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs) is briefly summarized.

The closing of the nuclear fuel cycle is an unsolved problem of great importance. Separating radionuclides produced in a nuclear reactor is useful both for the storage of nuclear waste and for recycling of nuclear fuel. These separations can be performed by designing appropriate chelation chemistries and liquid-liquid extraction schemes, such as in the TALSPEAK process (Trivalent Actinide-Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes). However, there are no approved methods for the industrial scale reprocessing of civilian nuclear fuel in the United States. One bottleneck in the design of next-generation solvent extraction-based nuclear fuel reprocessing schemes is a lack of interfacial mass transfer rate constants obtained under well-controlled conditions for lanthanide and actinide ligand complexes; such rate constants are a prerequisite for mechanistic understanding of the extraction chemistries involved and are of great assistance in the design of new chemistries. In addition, rate constants obtained under conditions of known interfacial area have immediate, practical utility in models required for the scaling-up of laboratory-scale demonstrations to industrial-scale solutions. Existing experimental techniques for determining these rate constants suffer from two key drawbacks: either slow mixing or unknown interfacial area. The volume of waste produced by traditional methods is an additional, practical concern in experiments involving radioactive elements, both from disposal cost and experimenter safety standpoints. In this paper, we test a plug-based microfluidic system that uses flowing plugs (droplets) in microfluidic channels to determine absolute interfacial mass transfer rate constants under conditions of both rapid mixing and controlled interfacial area. We utilize this system to determine, for the first time, the rate constants for interfacial transfer of all lanthanides, minus promethium, plus yttrium, under TALSPEAK process conditions, as a first step toward testing the molecular mechanism of this separation process. PMID:21888347

The properties of solutes adsorbed at interfaces can be very different compared to bulk solution limits. This thesis examines how polar, hydrophilic silica surfaces and different solvents systematically change a solute's equilibrium and dynamic solvation environment at solid/liquid interfaces. The primary tools used in these studies are steady state fluorescence spectroscopy and time correlated single photon counting (TCSPC) --a fluorescence method capable resolving fluorescence emission on the picosecond timescale. To sample adsorbed solutes, TCSPC experiments were carried out in total internal reflection (TIR) geometry. These studies used total of six different 7-aminocoumarin dyes to isolate the effects of molecular and electronic structure on solute photophysical behavior. Fluorescence lifetimes measured in the TIR geometry are compared to the lifetimes of coumarins in bulk solution using different solvents to infer interfacial polarity and excited state solute conformation and dynamics. Steady state emission experiments measuring the behavior of the coumarins adsorbed at silica surfaces from bulk methanol solutions show that all coumarins had a similar affinity DeltaG ads ˜ - 25-30 kJ/mole. Despite these similar adsorption energetics solute structure had a very pronounced effect on the tendency of solutes to aggregate and form multilayers. Our finding suggests that hydrogen bonding donating properties of the silica surface plays a dominant role in determining the interfacial behavior of these solutes. The silica surface also had pronounced effects on the time dependent emission of some solutes. In particular, the strong hydrogen bond donating properties of the silica surface inhibit formation of a planar, charge transfer state through hydrogen bond donation to the solute's amine group. A consequence of this interaction is that the time dependent emission from solutes adsorbed at the surface appears to be more similar to emission from solutes in nonpolar solvation environments. To test the role of solvent identity on the photophysical properties of adsorbed solutes, additional experiments were carried out with a nonpolar solvent (decane), a moderately polar solvent (n-decanol) and a polar aprotic solvent (acetonitrile). The results from these studies demonstrated that interfacial solvation depends sensitively on a balance of competing forces including those between the solute and substrate, the solute and solvent and the surface and adjacent solvent.

The kinetics of aluminum and beryllium extraction by mono(2-ethylhexyl)phosphoric acid (M2EHPA) is studied using a stirred transfer cell. M2EHPA has high surface activity and forms reverse micelles in the organic phase. The formation of a 1:1 complex of the metal ion and the dissociated M2EHPA anion in the aqueous phase is found to be rate-determining. The formation of reverse micelles does not affect the extraction rate, and rapid attainment of the extraction equilibria observed otherwise in the shaking experiments is considered to be caused by the large interfacial area due to the lowering of interfacial tension.   

The surface free energies, interfacial tensions and correlation lengths of the Andrews - Baxter - Forrester models in regimes III and IV are calculated with fixed boundary conditions. The interfacial tensions are calculated between arbitrary phases and are shown to be additive. The associated critical exponents are given by 0305-4470/30/7/017/img5 with 0305-4470/30/7/017/img6 in regime III and 0305-4470/30/7/017/img7 with 0305-4470/30/7/017/img8 in regime IV. Our results are obtained using general commuting transfer matrix and inversion relation methods that may be applied to other solvable lattice models.

Au-interfacial oxide layer (GeO/sub 2/, Sb/sub 2/O/sub 3/, Bi/sub 2/O/sub 3/, SnO/sub 2/ and native oxide mixture of AS/sub 2/O/sub 3/ and Ga/sub 2/O/sub 3/)-semiconductor (GaAs) structures were investigated by the Auger Electron Spectroscopy Method. The results of depth profiling with Ar/sup +/-ion sputtering are presented for all metal-insulator-semiconductor (MIS) structures. ''Metal'' atoms from deposited interfacial oxide layers (Ge from Ge/sub 2/O/sub 3/, Sb from Sb/sub 2/O/sub 3/, Bi from Bi/sub 2/O/sub 3/, and Sn from SnO/sub 2/) were observed on the surface. Only As atoms were observed for the native oxide mixture of As/sub 2/O/sub 3/ and Ga/sub 2/O/sub 3/ interfacial layer. These findings suggest that As/sub 2/O/sub 3/ is the dominating oxide at the metal-oxide interface for native oxide GaAs MIS solar cells. The interfacial reaction takes place between Au and the interfacial layer at room temperature. The ''diffusion'' of metal atoms from the interfacial layer towards the surface is suspected to play a role in degradation effect in GaAs MIS solar cells.

The high chromium cast iron and medium carbon steel bimetal was fabricated by liquid-solid casting technology. The effect of volume ratios of liquid to solid (6:1, 10:1 and 12:1) on the interfacial microstructure and mechanical properties of bimetal was investigated. The interfacial microstructure was analyzed using scanning electron microscope (SEM) and transmission electron microscope (TEM). The shear strength and microhardness in as-cast condition were studied at room temperature. The results show that the volume ratios of liquid to solid affect significantly the interfacial microstructure. When liquid-solid volume ratio was 6:1, the unbonded region was detected in interface region because the imported heat energy cannot support effectively the diffusion of element, whereas, when liquid...

First-principles density functional theory studies have been carried out to investigate the effects of perfect and defective anatase TiO(2) supports on the structural stabilities and electronic properties of Pd(m)Ag(n)(m + n = 2-5) bimetallic clusters. Our results showed that the structures of supported Pd-Ag bimetallic clusters are distorted compared to their structures in the gas phase, which is caused by the balance of the cluster inner-interaction and the metal-support interfacial interaction. In particular, Pd(1)Ag(3) and Pd(1)Ag(4) clusters prefer to form three-dimensional structures on both perfect and defective anatase TiO(2) support while their most stable structures in the gas phase are planar. In the most stable structures of supported Pd(m)Ag(n) bimetallic clusters, Pd atoms always occupy the most active sites of TiO(2)(101) surface, which induced Pd enriched at the interface of TiO(2) support and Ag atoms exposed at the surface of the bimetallic cluster. As Ag% increases, the perfect TiO(2) support gets more electrons from the Pd-Ag bimetallic cluster, which reduced the stability of the supported Pd-Ag cluster. The Mulliken population and electron density difference analysis demonstrated that the co-deposition of Ag induced the charge of adsorbed Pd on the perfect TiO(2) support from positive to negative as a result of charge transfer from the half-filled s-orbital of Ag(5s(1)) to the d-orbit of Pd, and the negative charges of Pd on the defective TiO(2) support were also increased by Pd-Ag charge polarization. Therefore, the selectivity of acetylene hydrogenation is enhanced by anatase-TiO(2) supported Pd-Ag bimetallic catalyst as it serves as an electron donor. PMID:22618199

Using scanning tunneling microscopy we observed quasi-one-dimensional electronic states in two epitaxial phases of iron-silicide thin films. In a semiconducting beta-phase we succeeded to directly visualize formation of 1D Hubbard-like surface electronic chains within narrow energy windows of corresponding delocalized states. A similar phenomenon of 1D electronic transport in a metallic gamma-phase occurs via bulk rather than surface states, making it possible to directly visualize buried (interfacial) side of screw dislocations.

Oscillators and magnetic random-access memories (MRAMs) investigated today rely on spin-transfer torque (STT) carried by an electric current flowing through a magnetic tunnel junction (MTJ) having barrier composition MgO. ootnotetextSee the STT review by D. Ralph and M. Stiles, J. Magn. Magn. Mater. 320, 1190 (2008). Experiments confirm the theoretical upper bound ?e=1/2 on the torque yield (defined as dimensionless torque per unit supplied electric current). This bound limits the performance potential of STT-MRAM in which current supplied by one transistor within each cell switches the information bit. Replacement of electric current with heat flow (supplied by a Joule heater) carried by magnons may provide a greater torque yield ?h. ootnotetextJ. Slonczewski, Phys. Rev. B 82, 054403 (2010). The essential structure for this thermagnonic spin transfer (TMST) comprises a stack of three nano layers: a spontaneously magnetized insulator (ferrite for brevity), a non-magnetic metallic spacer, and the free metallic magnet responding to the transferred torque. Phonons carry most of the heat flowing through the ferrite. But spin-1 magnons also carry a portion of it and deposit pure spin polarization into the spacer whose free electrons transport it to the free magnet. Ferrite-metal interfaces also occur in a spin-Seebeck effect. ootnotetextThe talk by E. Saitoh in this Symposium Principles of spin relaxation provide estimates of ?h based on existing data for sd-exchange, superexchange, and non-magnetic interfacial thermal resistance; ?h may exceed ?e by one order of magnitude. ootnotetextJ. Slonczewski, Phys. Rev. B 82, 054403 (2010). Related results of an FMR spin-pumping experiment ootnotetextB. Heinrich et al, Phys. Rev. Letts. 107, 066604 (2011). and DFT computations ootnotetextThe talk by K. Xia in this Symposium. support the potential of TMST-MRAM. In the case of an oscillator, TMST could increase its efficiency and enable largely independent controls of frequency and output voltage.

The interfacial heat transfer between a rotating roller surface and a melt puddle, and the thermal and fluid-dynamical behaviors of the melt puddle play an important role in the formation of the amorphous alloy ribbon in the Planar Flow Casting (PFC) process. Several parametric studies, including the melt and the roller thermal conductivities, melt inflow temperature, rotating roller speed and melt ejection velocity have been performed to investigate their effect on interfacial heat transfer and on the behavior of the melt puddle by the solution of a conjugated fluid–solid (melt/roller) mathematical model. With the given process parameters, the theoretical interfacial heat transfer and interfacial temperature, puddle shape, velocity and temperature distribution in the melt puddle, temperature profile of the roller and thermal penetration depth underneath the puddle, and the growth and cooling characteristics of solid/liquid interface are presented and discussed. It is found that the upstream and downstream menisci are sensitive to the variations of these parameters. The casting conditions affect the profile of theoretical interfacial heat transfer coefficient and roller surface temperature. However, the flow patterns in the puddle hardly change except the size of two recirculation zones with stagnate flow. As a result of lower roller speed and larger melt ejection velocity, the thermal penetration depth in the roller and the thickness of the ribbon increase, and the solidification rate reduces during the later period of solidification process. The decrease of roller thermal conductivity will lead to a high roller surface temperature and a low thermal penetration depth. The melt with high thermal conductivity has a quicker growth of the solid/liquid interface. The solidification rates of the solid/liquid interface seem to also be slow near the final solidification stage with the decrease of roller thermal conductivity, and with the increase of melt inflow temperature and melt ejection velocity.   

The ultimate objectives of this research are to understand the principles underpinning nano-composite polymer electrolytes (CPEs) and facilitate development of novel CPEs that are low-cost, have high conductivities, large Li+ transference numbers, improved electrolyte-electrode interfacial stability, yield long cycle life, exhibit mechanical stability and are easily processable. Our approach is to use nanoparticulate silica fillers to formulate novel composite electrolytes consisting of surface-modified fumed silica nano-particles in polyethylene oxides (PEO) in the presence of lithium salts. We intend to design single-ion conducting silica nanoparticles which provide CPEs with high Li+ transference numbers. We also will develop low-Mw (molecular weight), high-Mw and crosslinked PEO electrolytes with tunable properties in terms of conductivity, transference number, interfacial stability, processability and mechanical strength

This research focuses on the development of a fracture mechanics based-model that predicts the debonding behavior between FRP composites and reinforced concrete beams. The maximum transferable load for FRP composite externally bonded to concrete substrate was expressed as a function of material properties and the fracture energy. Fracture energy for FRP pull-off test was determined with the maximum interfacial shear stress and the corresponding slip. The interfacial shear stress and the corresponding slip are predicted based on a proposed criterion that shear stress failure initiates adjacent to the FRP-concrete bond interface. With the application of the elasticity theory, the corresponding slip of FRP bond system and the interfacial shear stress are obtained. Comparison between the exper...

A new multi-layered model is developed for the fracture analysis of a functionally graded interfacial zone with arbitrary material properties. It is assumed that the interfacial zone is divided into sub-layers with the material properties of each sub-layer varying in a power-law function. The model is used to study the crack problem in the functionally graded interfacial zone between two homogeneous half-planes under a dynamic anti-plane load. Using Fourier?Laplace transforms and the transfer matrix method, the mixed boundary value problem is reduced to a Cauchy singular integral equation, which is solved numerically in the Laplace transform domain. Laplace numerical inversion transform is employed to obtain the stress intensity factors. The results show that the new model is general and e...

SiCW/SiC composites without an intergranular glassy phase are prepared by the CVI process. The microstructure and high temperature strength of SiCW/SiC composites are investigated. The high temperature strength of SiCW/SiC composites depends on the interfacial bonding strength between matrix and whiskers. The matrix is effectively strengthened and toughened by the whiskers, and SiCW/SiC composites show a constant strength of 475+/-32 MPa below 1000^oC. The flexural strength gradually declines from 475+/-32 MPa to 208+/-15 MPa at the temperature from 1000^oC to 1500^oC due to the decreased whisker-matrix interfacial bonding strength. The interfacial bonding strength is too low to transfer stress from the matrix to the whiskers, and SiCW/SiC composites show a constant strength of 208+/-15 MP...

Carbon NanoTubes(CNTs) have excellent properties for improving mechanical, thermal, and electrical characteristics of nanocomposites as reinforcement materials. To develop successful CNT-reinforced nanocomposites, it is important to transfer the extraordinary properties of CNTs to the matrix. Two main issues are homogeneous distribution and high interfacial strength. We have studied CNT reinforced copper matrix nanocomposites. In this study, CNT was dispersed by the mechanical mixing process and interfacial strength between the CNTs and the copper matrix was controlled by coating the nanotubes with nickel or copper. The sintering process was adapted for the fabrication of nanocomposites specimens. The displacement characteristics of nanocomposites at an elevated temperature were investigated by a Small Punch (SP) creep tester to evaluate the interfacial strength between copper particles and CNTs. The electrical and thermal characteristics of the nanocomposites were also investigated.

This work addresses several important topics of the field of organic electronics. The focus lies on organic/metal interfaces, which exist in all organic electronic devices. Physical properties of such interfaces are crucial for device performance. Four main topics have been covered: (i) the impact of molecular orientation on the energy levels, (ii) energy level tuning with strong electron acceptors, (iii) the role of thermodynamic equilibrium at organic/ organic homo-interfaces and (iv) the correlation of interfacial electronic structure and bonding distance. To address these issues a broad experimental approach was necessary: mainly ultraviolet photoelectron spectroscopy was used, supported by X-ray photoelectron spectroscopy, metastable atom electron spectroscopy, X-ray diffraction and X-ray standing waves, to examine vacuum sublimed thin films of conjugated organic molecules (COMs) in ultrahigh vacuum. (i) A novel approach is presented to explain the phenomenon that the ionization energy in molecular assemblies is orientation dependent. It is demonstrated that this is due to a macroscopic impact of intramolecular dipoles on the ionization energy in molecular assemblies. Furthermore, the correlation of molecular orientation and conformation has been studied in detail for COMs on various substrates. (ii) A new approach was developed to tune hole injection barriers ({delta}{sub h}) at organic/metal interfaces by adsorbing a (sub-) monolayer of an organic electron acceptor on the metal electrode. Charge transfer from the metal to the acceptor leads to a chemisorbed layer, which reduces {delta}{sub h} to the COM overlayer. This concept was tested with three acceptors and a lowering of {delta}{sub h} of up to 1.2 eV could be observed. (iii) A transition from vacuum-level alignment to molecular level pinning at the homo-interface between a lying monolayer and standing multilayers of a COM was observed, which depended on the amount of a pre-deposited acceptor. The measured shift in the vacuum level between monolayer and multilayer coverage was direct evidence for thermodynamically driven charge transfer between molecular layers. (iv) A clear correlation between the strength of chemical bonding of COMs and the bonding distance to metal substrates could be shown. All these findings lead to a better understanding of organic/metal interface physics and may help to enhance performance of organic devices in the future. (orig.)

Thermal resistance between layers impedes effective heat dissipation in electronics packaging applications. Thermal conductance for clean and disordered interfaces between silicon (Si) and aluminum (Al) was computed using realistic Si/Al interfaces and classical molecular dynamics with the modified embedded atom method potential. These realistic interfaces, which include atomically clean as well as disordered interfaces, were obtained using density functional theory. At 300 K, the magnitude of interfacial conductance due to phonon-phonon scattering obtained from the classical molecular dynamics simulations was approximately five times higher than the conductance obtained using analytical elastic diffuse mismatch models. Interfacial disorder reduced the thermal conductance due to increased phonon scattering with respect to the atomically clean interface. Also, the interfacial conductance, due to electron-phonon scattering at the interface, was greater than the conductance due to phonon-phonon scattering. This indicates that phonon-phonon scattering is the bottleneck for interfacial transport at the semiconductor/metal interfaces. The molecular dynamics modeling predictions for interfacial thermal conductance for a 5-nm disordered interface between Si/Al were in-line with recent experimental data in the literature.

Many typical chemical engineering operations are multi-fluid systems. They are carried out in distillation columns (vapor/liquid), liquid-liquid contactors (liquid/liquid) and other similar devices. An important parameter is interfacial area concentration, which determines the rate of interfluid heat, mass and momentum transfer and ultimately, the overall performance of the equipment. In many cases, the models for determining interfacial area concentration are empirical and can only describe the cases for which there is experimental data. In an effort to understand multiphase reactors and the mixing process better, a multi-fluid model has been developed as part of a research effort to calculate interfacial area transport in several different types of in-line static mixers. For this work, the ensemble-averaged property conservation equations have been derived for each fluid and for the mixture. These equations were then combined to derive a transport equation for the interfacial area concentration. The final, one-dimensional model was compared to interfacial area concentration data from two sizes of Kenics in-line mixer, two sizes of concurrent jet and a Tee mixer. In all cases, the calculated and experimental data compared well with the highest scatter being with the Tee mixer comparison.

First-principles calculations based on density-functional theory have been applied to the energies and atomic and electronic structures of various metal/inorganic material interfaces such as metal/Al2O3, Au/TiO2 and metal/SiC interfaces used in thermal barrier coatings, gold catalysts, and high-power electronic devices, respectively, in collaboration with electron microscopy observations. In each system, it has been shown that the interface stoichiometry, namely the features of interfacial termination species of inorganic materials, as well as the metal species, is one of the most important factors to design the interfacial structure and the adhesive, mechanical, chemical and electronic properties. Recent electron microscopy observations of peculiar dynamical structural changes in Au/CeO2 systems are discussed from this view point.   

In this project electron transfer at semiconductor liquid interfaces was examined by ultrafast time-resolved and steady-state optical techniques. The experiments primarily yielded information about the electron transfer from titanium dioxide semiconductor particles to absorbed molecules. The results show that the rate of electron transfer depends on the structure of the molecule, and the crystalline phase of the particle. These results can be qualitatively explained by Marcus theory for electron transfer.

While surfaces have been investigated by scattering techniques and scanning probe microscopies, the major tool for investigating the structure of internal interfaces has been transmission electron microscopy (TEM). Several examples of interfacial structure analysis by TEM are given; they cover Si/Al and Al/Ge.

The microstructure of a Cu/V nanocomposite wire processed by cold drawing was investigated by high resolution transmission electron microscopy and atom probe tomography. The experimental data clearly reveal some deformation induced interfacial mixing where the vanadium filaments are nanoscaled. The ...

This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. The knowledge gained from the study of synthetic model systems which abstract features of the natural photosynthetic apparatus can be used to design artificial photosynthetic systems which employ the basic physics and chemistry of photosynthesis to help meet mankind's energy needs. More specifically, the proposed models are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties.

A photobioelectrochemical cell was constructed using platinized chloroplasts entrapped on a fiberglass filter pad as the photosensitive material. In this two-electrode device, a platinum gauze electrode made pressure contact with the chloroplasts, and a silver/silver chloride electrode made pressure contact with the electrolyte-impregnated filter paper pad. Upon illumination, an oriented photocurrent was observed that is consistent with the vectorial photochemical model of the reaction centers in photosynthetic membranes. The kinetics of interfacial photoelectron transfer in this cell were studied using the technique of repetitive flash illumination. By driving the photocurrent response into steady state, using multiple flash frequencies and normalizing the photoresponse to the rate of flashing, the frequency response of the photocurrent was determined. As expected, in the low-frequency, linear region, the normalized photocurrent response was constant. However, as the rate of flashing increased (above 100 Hz), the yield of photocurrent per frequency interval decreased. This decrease in yield was interpreted as the inability of the thermally activated electron transport chain of photosynthesis to keep pace with the higher rates of reaction center excitation. The reciprocal of the frequency at which the normalized photocurrent has fallen to one-half is called the turnover time. In these experiments this occurred at {approximately}200 Hz, corresponding to a turnover time of 4 ms. 11 refs., 3 figs.

Amino functionalized boron nitride nanotubes were used as the reinforcement material for the fabrication of Al-matrix composites using powder metallurgy process. It was found that the mechanical properties of these composites were improved significantly as compared to pure Al composites fabricated under similar conditions. The microhardness of these composites was found to improve by five times and compressive strength by 300% as compared to pure Al composites under similar processing conditions. The enhanced mechanical properties of these composites can be attributed to the proper dispersion of boron nitride nanotubes (BNNTs) in Al matrix and the formation of a strong interfacial bonding between BNNTs and Al matrix under the processing conditions. High-resolution transmission electron microscopy studies revealed the formation of transition layer of AlB2 which might lead to a better load transfer from Al matrix to the BNNTs. Further, these composites are believed to withstand high temperatures as compared to Al matrix composites reinforced with carbon nanotubes and, therefore, can be used for applications where lightweight and high strength materials are desired with stability at elevated temperatures. PMID:21770161

Operation of SOFCs at intermediate temperatures (500-800 C) requires new combinations of electrolyte and electrode materials that will provide both rapid ion transport across the electrolyte and electrode--electrolyte interfaces and efficient electrocatalysis of the oxygen reduction and fuel oxidation reactions. This project concentrates on materials and issues associated with cathode performance that are known to become limiting factors as the operating temperature is reduced. The specific objectives of the proposed research are to develop cathode materials that meet the electrode performance targets of 1.0 W/cm{sup 2} at 0.7 V in combination with YSZ at 700 C and with GDC, LSGM or bismuth oxide based electrolytes at 600 C. The performance targets imply an area specific resistance of {approx}0.5 {Omega}cm{sup 2} for the total cell. The research strategy is to investigate both established classes of materials and new candidates as cathodes, to determine fundamental performance parameters such as bulk diffusion, surface reactivity and interfacial transfer, and to couple these parameters to performance in single cell tests. In this report, the oxygen exchange kinetics of a P2 composition are described in detail. The oxygen exchange kinetics of the oxygen deficient double perovskite LnBaCo{sub 2}O{sub 5.5+{delta}} (Ln=Pr and Nd) have been determined by electrical conductivity relaxation. The high electronic conductivity and rapid diffusion and surface exchange kinetics of PBCO suggest its application as cathode material in intermediate temperature solid oxide fuel cells.

We have studied self-assembled molecular monolayers (SAMs) of complexes between Os(ii)/(iii), Fe(ii)/(iii), and Ru(ii)/(iii) and a 2,2',6',2''-terpyridine (terpy) derivative linked to Au(111)-electrode surfaces via a 6-acetylthiohexyloxy substituent at the 4'-position of terpy. The complexes were prepared in situ by first linking the terpy ligand to the surface via the S-atom, followed by addition of suitable metal compounds. The metal-terpy SAMs were studied by cyclic voltammetry (CV), and in situ scanning tunnelling microscopy with full electrochemical potential control of substrate and tip (in situ STM). Sharp CV peaks were observed for the Os- and Fe complexes, with interfacial electrochemical electron transfer rate constants of 6-50 s(-1). Well-defined but significantly broader peaks (up to 300 mV) were observed for the Ru-complex. Addition of 2,2'-bipyridine (bipy) towards completion of the metal coordination spheres induced voltammetric sharpening. In situ STM images of single molecular scale strong structural features were observed for the osmium and iron complexes. As expected from the voltammetric patterns, the surface coverage was by far the highest for the Ru-complex which was therefore selected for scanning tunnelling spectroscopy. These correlations displayed a strong peak around the equilibrium potential with systematic shifts with increasing bias voltage, as expected for a sequential two-step in situ ET mechanism.

We have studied self-assembled molecular monolayers (SAMs) of complexes between Os(II)/(III), Fe(II)/(III), and Ru(II)/(III) and a 2,2',6',2''-terpyridine (terpy) derivative linked to Au(111)-electrode surfaces via a 6-acetylthiohexyloxy substituent at the 4'-position of terpy. The complexes were prepared in situ by first linking the terpy ligand to the surface via the S-atom, followed by addition of suitable metal compounds. The metal-terpy SAMs were studied by cyclic voltammetry (CV), and in situ scanning tunnelling microscopy with full electrochemical potential control of substrate and tip (in situ STM). Sharp CV peaks were observed for the Os- and Fe complexes, with interfacial electrochemical electron transfer rate constants of 6-50 s(-1). Well-defined but significantly broader peaks (up to 300 mV) were observed for the Ru-complex. Addition of 2,2'-bipyridine (bipy) towards completion of the metal coordination spheres induced voltammetric sharpening. In situ STM images of single molecular scale strong structural features were observed for the osmium and iron complexes. As expected from the voltammetric patterns, the surface coverage was by far the highest for the Ru-complex which was therefore selected for scanning tunnelling spectroscopy. These correlations displayed a strong peak around the equilibrium potential with systematic shifts with increasing bias voltage, as expected for a sequential two-step in situ ET mechanism. PMID:21701712

Mesoporous TiO2-graphene nanocomposites are fabricated in high yield via two successive steps: (1) hydrothermal hydrolysis of Ti(SO4)2 in an acidic suspension of graphene oxide to gain TiO2-graphene oxide nanocomposites; (2) UV-assisted photocatalytic reduction of graphene oxide to get the TiO2-graphene nanocomposites. The anatase TiO2 nanocrystals with a crystallite size of 10-20 nm are densely packed and supported on meshy graphene sheets with close interfacial contacts, which is confirmed by transmission electron microscopy (TEM) together with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Although a low graphene loading (0-2 wt%) slightly influences the textural properties (including the crystallite size, specific surface areas, and pore volume etc.), the incorporation of graphene in TiO2-graphene nanocomposites greatly increases the adsorption capacity towards azo dyes such as MO and MB, which is possibly associated with their unique surface properties. Significantly, the incorporated graphene exerts combined effects on the adsorption and charge transfer dynamics in TiO2-graphene nanocomposites, which together endow them with good photocatalytic reactivity and tunable photocatalytic selectivity in decomposing MO and MB in aqueous solution.

Operation of SOFCs at intermediate temperatures (500-800 C) requires new combinations of electrolyte and electrode materials that will provide both rapid ion transport across the electrolyte and electrode-electrolyte interfaces and efficient electrocatalysis of the oxygen reduction and fuel oxidation reactions. This project concentrates on materials and issues associated with cathode performance that are known to become limiting factors as the operating temperature is reduced. The specific objectives of the proposed research are to develop cathode materials that meet the electrode performance targets of 1.0 W/cm{sup 2} at 0.7 V in combination with YSZ at 700 C and with GDC, LSGM or bismuth oxide based electrolytes at 600 C. The performance targets imply an area specific resistance of {approx}0.5 {Omega}cm{sup 2} for the total cell. The research strategy is to investigate both established classes of materials and new candidates as cathodes, to determine fundamental performance parameters such as bulk diffusion, surface reactivity and interfacial transfer, and to couple these parameters to performance in single cell tests. In this report, further measurements of the oxygen deficient double perovskite PrBaCo{sub 2}O{sub 5.5+{delta}} are reported. The high electronic conductivity and rapid diffusion and surface exchange kinetics of PBCO suggest its application as cathode material in intermediate temperature solid oxide fuel cells. Preliminary measurements in symmetric cells have shown low ASR values at 600 C. Here we describe the first complete cell measurements on Ni/CGO/CGO/PBCO/CGO cells.

Engineered inorganic nanoparticles (EINP) are expected to pass the wastewater-river-topsoil-groundwater pathway. Despite their increasing release, the processes governing the EINP aging and the changes in functionality in the environment are up to now largely unknown. The objective of the interdisciplinary research unit INTERNANO funded by the German Research Foundation (DFG) is to identify the processes relevant for the fate of EINP and EINP-associated pollutants in the interfacial zone between aquatic and terrestrial ecosystems. The research unit consists of six subprojects and combines knowledge from aquatic and terrestrial sciences as well as from microbiology, ecotoxicology, physicochemistry, soil chemistry and soil physics. For the identification of key processes we will consider compartment specific flow conditions, physicochemistry and biological activity. Situations representative for a floodplain system are simulated using micromodels (?m scale) as well as incubation, soil column and joint laboratory stream microcosm experiments. These results will be transferred to a joint aquatic-terrestrial model system on EINP aging, transport and functioning across the aquatic-terrestrial transition zone. EINP isolation and characterization will be carried out via a combination of chromatographic, light scattering and microscopic methods including dynamic light scattering, elemental analysis, hydrodynamic radius chromatography, field flow fractionation as well as atomic force microscopy, Raman microscopy, dynamic light scattering methods and electron microscopy. INTERNANO generates fundamental aquatic-terrestrial process knowledge, which will help to evaluate the environmental significance of the EINP at aquatic-terrestrial interfaces. Therefore, INTERNANO serves as a qualitative basis to predict the environmental impact of EINP contamination.

Comparative electrochemical behavior of self-assembled monolayers (SAMs) of three heteroaromatic thiols, 2-mercaptobenzoxazole (MBO), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzimidazole (MBI) are investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The electrochemical characteristics of the electrode/solution interface are considerably and differently affected by thiols constructing the SAMs. The consumed charges for reductive desorption of SAMs, which is criterion for the amount of chemically adsorbed thiol, are significantly different for these three SAMs, specially for MBT, implying that SAM of MBT is formed through both sulfur atoms; the thiol sulfur and skeleton sulfur of the thiazole ring. Desorption potentials of the SAMs have shown the following order for strength of gold-sulfur bond: MBT > MBO > MBI. Activity of the three SAMs as pH-sensitive interfaces was also investigated and their surface-pK {sub a} values derived from the EIS measurements showed this order for acidic strength of SAMs: MBO > MBT > MBI. This is the same order expected due to the difference in electronegativity of the O, S, and N heteroatoms, and confirms that the most electron-rich ring imidazole is attached to the benzene ring of MBI. A comparison of the interfacial charge transfer resistance variation as a function of gold immersion time in thiols solution reveals that kinetics of Au-MBT assembly is different from those of two others and confirms formation of Au-MBT SAM via both sulfur atoms of MBT.

The aim of this paper is to correlate interfacial heat transfer coefficient (IHTC) to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of casting under different pressures were obtained using the inverse heat conduction problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented for correlation between external pressure and heat transfer coefficient. Acceptable agreement with data in literature shows the accuracy of the proposed formula.

The fundamental characteristics of interfacial turbulence in gas-liquid mass transfer were studied by desorbing six surface-active solutes from their aqueous solutions in a liquidjet column and a wetted-wall column, and calculating the liquid-phase mass transfer coefficient from the observed transfer rate using oxygen as a tracer. The enhancement factor R and the Marangoni number Ma were correlated by the general equation R = (Ma/Ma /SUB c/) /SUP n/, where n is a constant equal to 0.4 + 0.1. A graphical method for determining the critical Marangoni number Ma /SUB c/ is proposed.

Electronic coupling Vda is one of the key parameters that determine the rate of charge transfer through DNA. While there have been several computational studies of Vda for hole transfer, estimates of electronic couplings for excess electron transfer (ET) in DNA remain unavailable. In the paper, an e...

A two-phase flow experiment using air and water-based ?-Al2O3 nanofluid was conducted to observe the basic hydraulic phenomenon of nanofluids. The local two-phase flow parameters were measured with a conductivity double-sensor two-phase void meter. The void fraction, interfacial velocity, interfacial area concentration, and mean bubble diameter were evaluated, and all of those results using the nanofluid were compared with the corresponding results for pure water. The void fraction distribution was flattened in the nanofluid case more than it was in the pure water case. The higher interfacial area concentration resulted in a smaller mean bubble diameter in the case of the nanofluid. This was the first attempt to measure the local two-phase flow parameters of nanofluids using a conductivity double-sensor two-phase void meter. Throughout this experimental study, the differences in the internal two-phase flow structure of the nanofluid were identified. In addition, the heat transfer enhancement of the nanofluid can be resulted from the increase of the interfacial area concentration which means the available area of the heat and mass transfer.

Abstract BACKGROUND: Thylakoid stabilised emulsions have been reported to possess satiety promoting effects and inhibit pancreatic lipase colipase activity in vitro, which prompted the investigation of their interfacial properties. RESULTS: Thylakoid membranes isolated from spinach were used as an emulsifier/stabiliser in oil (triglyceride) in water emulsions. Emulsions were characterised with respect to droplet size, interfacial tension, creaming, surface load and electron microscopy. The effects of pH and thylakoid concentration were also considered. Droplet size decreased with increasing thylakoid concentration, reaching a plateau around 15 m beyond concentrations of 2 mg protein mL 1 oil. The resulting emulsions were stable against coalescence but were subject to creaming. The surface ...

The stability of lamellar interfaces in lamellar TiAl by straining at ambient temperatures has been investigated using in-situ straining techniques performed in a transmission electron microscope in order to obtain direct evidence to support the previously proposed creep mechanisms in refined lamellar TiAl based upon the interface sliding in association with the cooperative motion of interfacial dislocations. The results have revealed that both sliding and migration of lamellar interfaces can take place as a result of the cooperative motion of interfacial dislocations.

We report on the interfacial characteristics between solution-processed 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) and gold electrodes through controlling the device annealing temperature (DAT) in the schottky diodes. The interfacial characteristics were quantitatively investigated by the height of charge injection barrier from the gold electrode into the TIPS-pentacene layer using Fowler-Nordheim theory. The barrier height was found to be monotonically increased with increasing the DAT. This implies that the contact resistance between the metal electrode and the solution-processed organic semiconductor layer can be definitely increased with a process temperature when such interface is applied to the organic electronic devices.

A series of quasihomogeneous superconducting powders of YBa/sub 2/Cu/sub 3/O/sub 7-//sub x/ have been prepared by sieving and characterized by electron microscopy and x-ray diffraction. Quantitative size-dependent and temperature-dependent magnetic levitation and susceptibility measurements of random powders and of field-oriented (at Tinterfacial effects. Current models of interfacial superconductivity on high-T/sub c/ materials are evaluated in light of these and other results and found to be lacking.

A mixture of graphene oxide (GO) and TiO2 nanocomposites was reduced photocatalytically by UV-irradiation and applied as interfacial layer between a fluorine doped tin oxide (FTO) layer and a nanocrystalline TiO2 film. Impedance spectra implied a decreased back-transport reaction of electrons. The graphene-TiO2 interfacial layer effectively reduced the contact between Formula Not Shown ions in the electrolyte and FTO layer, which inhibited back-transport reaction. The introduction of graphene-TiO2 increased Voc by 54mV and the photoconversion efficiency was improved from 4.89% to 5.26%.

Solar energy conversion is increasingly being recognized as one of the principal ways to meet future energy needs without causing detrimental environmental impact. Hybrid organic-inorganic solar cells (SCs) are attracting particular interest due to the potential for low cost manufacturing and for use in new applications, such as consumer electronics, architectural integration and light-weight sensors. Key materials advantages of these next generation SCs over conventional semiconductor SCs are in design opportunities--since the different functions of the SCs are carried out by different materials, there are greater materials choices for producing optimized structures. In this project, we explore the hybrid organic-inorganic solar cell system that consists of oxide, primarily ZnO, nanostructures as the electron transporter and poly-(3-hexylthiophene) (P3HT) as the light-absorber and hole transporter. It builds on our capabilities in the solution synthesis of nanostructured semiconducting oxide arrays to this photovoltaic (PV) technology. The three challenges in this hybrid material system for solar applications are (1) achieving inorganic nanostructures with critical spacing that matches the exciton diffusion in the polymer, {approx} 10 nm, (2) infiltrating the polymer completely into the dense nanostructure arrays, and (3) optimizing the interfacial properties to facilitate efficient charge transfer. We have gained an understanding and control over growing oriented ZnO nanorods with sub-50 nm diameters and the required rod-to-rod spacing on various substrates. We have developed novel approaches to infiltrate commercially available P3HT in the narrow spacing between ZnO nanorods. Also, we have begun to explore ways to modify the interfacial properties. In addition, we have established device fabrication and testing capabilities at Sandia for prototype devices. Moreover, the control synthesis of ZnO nanorod arrays lead to the development of an efficient anti-reflection coating for multicrystalline Si solar cells. An important component of this project is the collaboration with Dr. Dave Ginley's group at NREL. The NREL efforts, which are funded by NREL's LDRD program, focus on measuring device performance, external quantum efficiency, photoconductance through highly specialized non-contact time-resolved microwave conductivity (TRMC) measurements, and vapor phase deposition of oxide materials. The close collaboration with NREL enables us to enter this competitive field in such short time. Joint publications and presentations have resulted from this fruitful collaboration. To this date, 5 referred journal papers have resulted from this project, with 2 more in preparation. Several invited talks and numerous contributed presentations in international conferences are also noted. Sandia has gained the reputation of being one of forefront research groups on nanostructured hybrid solar cells.

We show that the Kubo formula can be used to calculate the nonlocal electrical conductivity of layered systems from first principles. We use the Layer Korringa Kohn Rostoker method to calculate the electronic structure and Green function of Co/Cu/Co trilayers within the local density approximation to density functional theory. This Green function is used to calculate the conductivity through the Kubo formula for both majority and minority spins and for alignment and anti-alignment of the Co moments on either side of the Cu spacer layer. This allows us to determine the giant magnetoresistance from first principles. We investigate three possibilities for the scattering in Co/Cu/Co: (1) equal electron lifetimes for Cu, majority spin Co, and minority spin Co, (2) equal electron lifetimes for majority and minority Co, weaker scattering in Cu and spin dependent interfacial scattering, (3) electron lifetimes for majority and minority spin cobalt proportional to their Fermi energy densities of states and spin dependent interfacial scattering.

Titanium (Ti)/Diamond-like-carbon (DLC) and Chromium (Cr)/Carbon (C) multilayer films were prepared on c-axis oriented single crystal sapphire (Al2O3) substrates using magnetron sputtering. Interfacial properties of the films were analyzed using x-ray reflectivity and scanning electron microscopy. When DLC is sputtered on a layer of Ti, an interfacial layer of titanium carbide (TiC) forms which is reported for the first time. Energy provided by the substrate bias necessary to facilitate DLC sp3 bond formation is suspected of allowing TiC to synthesize in a thin layer before DLC forms. It was also found that DLC has difficulty forming on Cr. These results are relevant to biomedical applications where DLC is applied as a low friction/wear film that can be formed on the surface of implants composed mainly of titanium. Further investigation into the medical and tribological effects of TiC interfacial layers is suggested.

The interfacial oxygen diffusion during film growth often results in the appearance of a thin SiO{sub x} layer in SrTiO{sub 3}/Si films and related heterojunctions. High-resolution TEM investigations on the La{sub 0.9}Sr{sub 0.1}MnO{sub 3}/SrTiO{sub 3}/Si(LSMO/STO/Si) heterojunctions suggested that the thickness and microstructure of the SiO{sub x} interfacial layer change visibly from one sample to another grown under slightly different conditions. Electron diffraction observations demonstrated the epitaxial relationships in the LSMO/STO/Si heterojunction as [001]{sub LSMO} parallel [-110]{sub Si}, [110]{sub LSMO} parallel [001]{sub Si} and [001]{sub STO} parallel [001]{sub Si}, [010]{sub STO} parallel [-110]{sub Si}. The electron energy loss spectroscopy analyses on the LSMO/STO/Si interfacial region indicated that the Si ions are in intermediate oxidation states in the amorphous layer and the interfacial Ti bonding changes slightly. Electron holography measurements indicated that the energy barrier between the Si substrate and the LSMO film is about 0.95{+-}0.16 V, where notable negative charges accumulate in the amorphous SiO{sub x} layer.

We discuss scaling the equivalent oxide thickness (EOT) of Hf-based high-k gate dielectrics by post-deposition annealing (PDA). Thin HfON/SiON gate stacks with EOT=0.57 nm were successfully formed by repeating ultra thin (0.6 nm) HfO2 deposition and high-temperature (950 °C) PDA on a previously formed SiON interfacial layer. Physical and electrical analyses revealed that the reduction in EOT was due to crystallization of HfON to the tetragonal phase which has a higher dielectric constant than the amorphous and other crystalline phases. It was also found that Hf diffusion in the SiON interfacial layer was induced by the high-temperature PDA treatment. This also improved the k-value of the interfacial layer and enabled aggressive scaling even when using a SiO2-based interfacial layer. The electron mobility of the gate stack is higher than those in the previous reports, indicating that a high quality interface is realized using this approach. The reduction in EOT together with the excellent interfacial quality demonstrated in the present study shows that this technique is a promising solution for the 22-nm-node and beyond.   

Interface is the key topic of developing advanced fiber reinforced polymeric composites. Novel advanced glass woven fabric (GF) reinforced composites, coded as GF/mBT, were prepared, of which the matrix resin was hyperbranched polysiloxane (HBPSi) modified maleimide-triazine (mBT) resin. The influence of the composition of the matrix on the interfacial nature of the GF/mBT composites were studied and compared with that of the composite based on GF and BT resin using contact angle, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and dielectric properties over wide frequency and temperature ranges. Results show that the interfacial nature of the composites is dependent on the chemistries of the matrices, mBT matrices have better interfacial adhesion with GF than BT resin owing to the formation of chemical and hydrogen bonds between mBT resin and GF; while in the case of mBT resins, the content of HBPSi also plays an important role on the interfacial feature and thus the macro-performance. Specifically, with increasing the content of HBPSi in the matrix, the interlaminate shear strength of corresponding composites significantly improves, demonstrating that better interfacial adhesion guarantees outstanding integrated properties of the resultant composites.

Abstract in portuguese Avaliaram-se as características da interface fibra/matriz em compósitos de poliéster reforçado com fibra de coco. Esta avaliação foi realizada através de medidas da tensão interfacial de cisalhamento e também por observação microestrutural da área de contato fibra de coco/resina poliéster. A partir de ensaios de arrancamento de fibras de coco embutidas em cápsulas de resina poliéster analisou-se por microscopia eletrônica de varredura regiões das fibras q (more) ue se romperam ou sofreram escorregamento ao serem extraídas da resina. Os resultados revelaram uma tensão de cisalhamento interfacial similar a de outras fibras lignocelulósicas e mostraram também uma razoável adesão interfacial decorrente da natureza heterogênea das fibras de coco, o que facilita a impregnação pela resina. Abstract in english The characteristics of the fiber/matrix interface in polyester composites reinforced with coir fibers have been evaluated. This was carried out both, by measuring the interfacial shear strength and by microstructural observation of the coir fibers/polyester resin contact area. Tests of coir fiber extraction from resin sockets allowed an analysis by scanning electron microscopy of regions where the fibers underwent rupture or suffered pullout during extraction. The results (more) showed interfacial shear strength similar to other lignocellulosic fibers. Moreover, a reasonable interface adhesion was obtained owing to the heterogeneous nature of the coir fibers, which facilitates the resin impregnation.

The report represents the comparative analysis of luminescent properties of Eu(III) complex in colloids of silica-coated and layer-by-layer-fabricated nanoparticles. The diverse morphologies of these nanoparticles greatly affect their photophysical properties. The interfacial binding with d-ions exemplified by Cu(II) and the contributions of the ion exchange and energy transfer processes between Eu(III) ions confined within polymeric coating and Cu(II) ions at the interface of nanoparticles also depend on their morphology. The silica coating of Eu(III) complex does not prevent it from the efficient ion displacement by the interfacial Cu(II) ions, which results in the irreversible quenching of Eu(III)-centered luminescence. The lack of the ion exchange and the predominant energy transfer be...

The remediation of DNAPLs in subsurface environments is often limited by the heterogeneous distribution of the organic fluid. The fraction of DNAPL that is in the high conductivity regions of the subsurface can often be recovered relatively easily, although DNAPL in lower conductivity regions is much more difficult to extract, either through direct pumping or remediation measures based on interface mass transfer. The distribution of DNAPL within the vadose zone is affected by a complex interplay of heterogeneities in the porous matrix and the interfacial properties defining the interactions among all fluid and solid phases. Decreasing the interfacial tension between a DNAPL and water in the vadose zone could change the spreading of the DNAPL, thereby increase the surface area for mass transfer and the effectiveness of soil vapor extraction remediation.

A cooling apparatus, system and like method for an electronic device includes a plurality of heat producing electronic devices affixed to a wiring substrate. A plurality of heat transfer assemblies each include heat spreaders and thermally communicate with the heat producing electronic devices for transferring heat from the heat producing electronic devices to the heat transfer assemblies. The plurality of heat producing electronic devices and respective heat transfer assemblies are positioned on the wiring substrate having the regions overlapping. A heat conduit thermally communicates with the heat transfer assemblies. The heat conduit circulates thermally conductive fluid therethrough in a closed loop for transferring heat to the fluid from the heat transfer assemblies via the heat spreader. A thermally conductive support structure supports the heat conduit and thermally communicates with the heat transfer assemblies via the heat spreader transferring heat to the fluid of the heat conduit from the support structure.

Objective is to perform a new type of measurement for optically excited electron transfer processes that can provide unique experimental insight into the molecular mechanism of electron transfer. Measurements of optically excited electron transfer are done with picosecond infrared (IR) absorption spectroscopy to monitor the vibrational motions of the molecules immediately after electron transfer. Theory and experiment suggest that molecular vibrations and distortions are important controlling elements for electron transfer, and direct information has yet to be obtained on these elements of electron transfer mechanisms. The second period of funding has been dedicated to finishing technique development and performing studies of electron transfer in ion pair systems to identify if vibrational dependent electron transfer rates are present in this system. We have succeeded in measuring, for the first time, electron transfer rates as a function of vibrational state in an ion pair complex in solution. In a different area of electron transfer research we have proposed a new mechanism of solvent gated electron transfer.

By means of the falling soap film tunnel and the Schlieren optical method, the Marangoni convection were observed directly in the immediate interfacial neighborhood during the desorption process of acetone from the falling soap film. Moreover, the hydraulic characteristics of the falling soap film tunnel, the acetone concentration, the surface tension of the soap liquid and the mass transfer has been investigated in details through the experimental or theoretical method.

Data for the kinetics of Cu(II) extraction by P50 (5-nonyl-2-hydroxybenzaldoxime) obtained from the total internal reflectance (TIR) static transfer cell is presented. An interfacial mechanism involving two pararell initial addition steps is proposed and forward rate constants determined. These are discussed in relation to other data available for this system and clearly indicate further work is required in the identification of more general reaction mechanisms.   

Pulsed laser excitation sources provide a convenient means of initiating and probing photophysical and photochemical processes at the semiconductor electrode-electrolyte interface. Both time-resolved optical and electrochemical measurements are used to characterize the dynamics of intra-electrode charge separation and interfacial charge transfer as a function of applied bias, solution composition, and electrode physical properties. The philosophy behind this approach to transient measurements will be illustrated with recent experimental reslts involving single crystal and polycrystaline electrodes.

Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for

The papers in this conference were divided into the following sections: Radiation Heat Transfer in Fires; Computational Fluid Dynamics Methods in Two-Phase Flow; Heat Transfer in Microchannels; Thin Film Heat Transfer; Thermal Design of Electronics; Enhanced Heat Transfer I; Porous Media Convection; Contact Resistance Heat Transfer; Materials Processing in Solidification and Crystal Growth; Fundamentals of Combustion; Challenging Modeling Aspects of Radiative Transfer; Fundamentals of Microscale Transport; Laser Processing and Diagnostics for Manufacturing and Materials Processing; Experimental Studies of Multiphase Flow; Enhanced Heat Transfer II; Heat and Mass Transfer in Porous Media; Heat Transfer in Turbomachinery and Gas Turbine Systems; Conduction Heat Transfer; General Papers; Open Forum on Combustion; Combustion and Instrumentation and Diagnostics I; Radiative Heat Transfer and Interactions in Participating and Nonparticipating Media; Applications of Computational Heat Transfer; Heat Transfer and Fluid Aspects of Heat Exchangers; Two-Phase Flow and Heat Transfer Phenomena; Fundamentals of Natural and Mixed Convection Heat Transfer I; Fundamental of Natural and Mixed Convection Heat Transfer II; Combustion and Instrumentation and Diagnostics II; Computational Methods for Multidimensional Radiative Transfer; Process Heat Transfer; Advances in Computational Heat and Mass Transfer; Numerical Methods for Porous Media; Transport Phenomena in Manufacturing and Materials Processing; Practical Combustion; Melting and Solidification Heat Transfer; Transients in Dynamics of Two-Phase Flow; Basic Aspects of Two-Phase Flow; Turbulent Heat Transfer; Convective Heat Transfer in Electronics; Thermal Problems in Radioactive and Mixed Waste Management; and Transport Phenomena in Oscillatory Flows. Separate abstracts were prepared for most papers in this conference.

The stability of interfaces in lamellar TiAl (or TiAl/Ti{sub 3}Al laminate composite) by straining at ambient temperatures has been investigated using in-situ staining techniques performed in a transmission electron microscope in order to obtain direct evidence to support the previously proposed creep mechanisms in refined lamellar TiAl based upon the interface sliding in association with the cooperative motion of interfacial dislocations. It has been reported previously that the mobility of interfacial dislocations can play a crucial role in the creep deformation behavior of refined lamellar TiAl [1,2]. Since the operation of lattice dislocations within refined {alpha}{sub 2} and {gamma} lamellae is largely restricted, the motion of interfacial dislocations becomes the major strain carrier for plasticity. Results of ex-situ TEM investigation have revealed the occurrence of interface sliding in low-stress (LS) creep regime and deformation twinning in high-stress (HS) creep regime. These results have led us to propose that interface sliding associated with a viscous glide of pre-existing interfacial dislocations is the predominant creep mechanism in LS regime and interface-activated deformation twinning in {gamma} lamellae is the predominant creep mechanism in HS regime. Stress concentration resulted from the pileup of interfacial dislocations is suggested to be the cause for the interface-activated deformation twinning. Accordingly, the creep resistance of refined lamellar TiAl is considered to depend greatly on the cooperative motion of interfacial dislocations, which in turn may solely be controlled and hindered by the interfacial segregation of solute atoms (such as W) or interfacial precipitation. Furthermore, through the in-situ TEM investigation, we also found that the lamellar interfaces could migrate directly through the cooperative motion of interfacial dislocations. That is, the {gamma}/{gamma}and {gamma}/{alpha}{sub 2} interfaces can migrate through interface sliding and lead to the coalescence or shrinkage of constituent lamellae (i.e. microstructural instability), which results in a weakening effect when refined lamellar TiAl is employed for engineering applications. Although it is anticipated that interface sliding and migration are prevalent at elevated temperatures, the present in-situ straining study reveals the instability of lamellar interfaces at ambient temperatures.

Mechanical stirring is widely used for hot metal desulfurization in Japan. In this process, solid lime is added as flux and emulsified into molten iron using a vortex formed by the stirrer. However, in addition to the added solid lime, the liquid top slag on the ladle is emulsified and forms granules. To clarify the roles of the solid lime and liquid slag in hot metal desulfurization, the reaction rates of slag, solid lime, and slag with solid lime are determined and the interfacial layers are observed.The results are summarized as follows:(1) The desulfurization rate is very slow when a solid lime rod is immersed into hot metal without slag. The reason for the slow desulfurization is the formation of an interfacial layer, which inhibits the mass transfer of sulfur.(2) Because sulfur is not detected inside the solid CaO, the mass transfer of sulfur from the liquid slag to the solid CaO does not occur. Therefore, it is believed that solid CaO does not play a direct role in the desulfurization reaction, and thus, the reaction is solely due to the liquid slag. A good relationship between the desulfurization rates and the sulfide capacity of the liquid slag is found.(3) When tricalcium aluminate forms at the interface, the desulfurization rate is increased by the immersion of a CaO rod. This is due to the supply of CaO to the slag because this interfacial layer does not inhibit the mass transfer.   

An FET-based biosensor with a ferrocene-modified gold electrode detects the enzyme-produced electrons by using mediators that transfer the electrons from the enzyme to the sensor. Since an extended-gate FET sensor with a light-shielding mask can be operated without a light-shielding box, a small portable instrument will soon be realised. However, when the FET sensor detected enzyme-catalyzed products with the mediators under light conditions, measurements fluctuated due to photo-reduction of the mediators, resulting in decreased sensitivity. To improve sensitivity by reducing the fluctuation, we developed a procedure for directly detecting enzyme-catalyzed products without using the mediators. The key technique used in this procedure was a measurement technique using our developed potential-keeping method, in which the modified electrode of the FET sensor was oxidised by ferricyanide solution to make its surface the same high potential every time, and this high potential was kept until measurement because of the high input impedance of the FET structure. After this method was applied, the interfacial potential of the gold electrode decreased depending on the amount of enzyme-catalyzed products due to the ferrocene molecules immobilised on the gold electrode directly reacting with the products. The results obtained in light conditions indicated that model compounds of the products were detected from 10 ?M to 10 mM with the Nernstian response of 59.2 mV/decade. Also, this method was applied to pesticide detection by using the enzyme inhibition by pesticide, and 5 ppb of diazinon was successfully detected by using only a sensor chip. PMID:20728332

Hybrid films of donor/acceptor conjugated polymer/metal oxides are considered promising materials for low-cost, solution-processed solar cells. Because device performances depend on the nanoscale film morphologies, most attention and extensive efforts have been invested in improving the nanofabrication of hybrid films. Nevertheless, the reported conjugated polymer/metal oxide device efficiencies are still far poorer than those of all-organic and solid-state dye-sensitized metal oxide solar cells. To decouple the effect of insufficient morphology control from other generic photocurrent-limiting processes, we study the photocurrent generation at conjugated polymer-metal oxide interfaces in self-organized, highly ordered, and uniform hybrid nanostructures. A combination of small-angle X-ray scattering, high-resolution transmission electron microscopy (TEM), and energy-filtered TEM confirms the structure and composition of the highly ordered, high interfacial area hybrid cubic mesostructured films prepared by the coassembly of a titania precursor species, a water-soluble polythiophene derivative, and a block copolymer surfactant. Contactless time-resolved microwave photoconductivity (TRMC) measurements show a moderate 2-fold increase in the photoconductivity of the highly ordered TiO{sub x}/conjugated polymer mesostructured film compared to that of a pristine film of the same polymer, indicating inefficient exciton dissociation at the oxide/polymer interface. Furthermore, strong correlation between the TRMC results and the device performance reveals that most of the photogenerated carriers in the conjugated polymer/TiO{sub x} photovoltaic device originate from exciton dissociation in the polymer bulk, followed by electron transfer from the polymer to the metal oxide, and not at the interface. Therefore, the photovoltaic devices utilizing the highly ordered conjugated polymer/metal oxide mesostructured films are not primarily limited by insufficient morphology control but rather by the inefficient process of exciton dissociation in the polymer. This observation is in agreement with the low photocurrent densities generally observed in photovoltaic devices comprising conjugated polymer/metal oxide active layers.

A semi-empirical model for inverted annular flow film boiling heat transfer was previously developed which incorporates the effects of all relevant independent parameters and agrees well with available experimental data in the pressure range from 0.1 to 2 MPa. In the present work, this model has been modified to extend its applicability to elevated pressures up to 8 MPa. New expressions for the interfacial energy transfer to the subcooled liquid jet, and for the heat transfer enhancement term due to oscillatory interfacial disturbances were derived. Steady-state film boiling heat transfer data for forced upflow of water in a vertical tube were used to determine the unknown coefficients in the new relations. The data used were obtained from steady-state experiments applying different versions of the so-called 'hot-patch' technique. Finally, an explicit film boiling heat transfer correlation has been obtained which approaches Bromley's solution for zero flow and saturated conditions. This correlation has been compared with steady-state data from five different sources which cover mass fluxes ranging from 100 to 1010 kg/(m[sup 2]s) in the pressure range from 0.1 to 8 MPa. Results indicate an rms error of 15.5% and a mean deviation of 12.0% between measured and predicted heat transfer coefficients for 3972 data points. (orig.).

During the past ten years, electron tunneling devices such as Josephson junctions and single electron tunneling devices have been fabricated using organic thin films, where the successful preparation of polyimide Langmuir-Blodgett (PI LB) films has made a significant contribution. The electrical properties of PI LB films were also examined carefully, and electrostatic phenomena, interfacial phenomena, electrical breakdown behaviors and so on have been elucidated. Based on these studies, the effects of space charge and coupling capacitance upon the operation of single electron tunneling (SET) devices using organic molecules have been investigated. The equation of step voltage is derived taking into account space charge and coupling capacitance, using an equivalent circuit model. It was concluded that knowledge of interfacial phenomena is very important for a better understanding of the operation of such devices.   

We study the heat transfer between elastic solids with randomly rough surfaces.We include both the heat transfer from the area of real contact, and the heat transfer between the surfaces in the non-contact regions.We apply a recently developed contact mechanics theory, which accounts for the hierarchical nature of the contact between solids with roughness on many different length scales. For elastic contact, at the highest (atomic) resolution the area of real contact typically consists of atomic (nanometer) sized regions, and we discuss the implications of this for the heat transfer. For solids with very smooth surfaces, as is typical in many modern engineering applications, the interfacial separation in the non-contact regions will be very small, and for this case we show the importance of the radiative heat transfer associated with the evanescent electromagnetic waves which exist outside of all bodies. PMID:20175285

Heat flow in the materials with nanoscopic features is dominated by thermal properties of the interfaces. While thermal properties of the solid-solid and solid-liquid interfaces are well studied, research of the thermal transport properties across soft (liquid-liquid) interfaces is very limited. Such interfaces are, however, plentiful in biological systems. In such systems the temperature control is of a great importance, because biochemical reactions, conformation of biomolecules as well as processes in biological cells and membranes have strong temperature sensitivity. The critical ingredient to temperature control in biological systems is the understanding of heat flow and thermal coupling across soft interfaces. To investigate heat transfer across biological and aqueous interfaces we chose to study a number of soft interfacial systems by means of molecular dynamic simulations. One of the interfaces under our investigation is the interface between protein (specifically green fluorescent protein) and water. Using this model we concentrated on the importance of vibrational frequency on coupling between water and proteins, and on significant differences between the roles of low and high frequency vibrations. Our thermal interfacial analysis allowed us to shed new light on to the issue of protein to water slaving, i.e., the concept of water controlling protein dynamics. Considering that the surface of the protein is composed of a complicated mixture of the hydrophobic and hydrophilic domains, to systematically explore the role of interfacial interactions we studied less complicated models with homogenous interfaces whith interfacial chemistry that could be changed in a controlled manner. We demonstrated that thermal transport measurements can be used to probe interfacial environments and to quantify interfacial bonding strength. Such ability provides a unique opportunity to characterize a variety of interfaces, which can be difficult to achieve with more direct structural characterization tools. We followed up with studies of models of heterogeneous interfaces where we addressed the issue of independent vs. correlated contributions of hydrophobic and hydrophilic interfacial regions to thermal transfer. Finally we simulated heat flow across lipid bilayers which involve hydrophilic interfaces, but are characterized by relatively high surface roughness and non-saturated hydrocarbon chains. We found that roughness of the interface can significantly enhance thermal transport across the lipid membranes.

In the two-phase flow analysis with two-fluid model, interfacial area concentration (IAC) is a dominant factor governing the interfacial transfer of momentum and energy. In order to overcome the shortcomings of experimental correlation for IAC, such as the dependency on the flow regime, multi-dimensional computational fluid dynamics (CFD) code was developed with the interfacial area transport equation. The code is based on two-fluid model and simplified marker and cell (SMAC) algorithm using the finite volume method, and the conventional approach in single-phase flow has been modified in order to consider the term of phase change. Also, instead of a static one-dimensional correlation for IAC, the code adopted the one-group interfacial area transport equation which includes source terms with respect to the coalescence and breakup of bubbles, and the phase change such as evaporation or condensation. As benchmark problems of single-phase flow and two-phase flow, the natural convection in rectangular cavity and the subcooled boiling in vertical annulus channel were analyzed, respectively. In the calculation for single-phase flow, the developed code predicted reasonable behavior of buoyancy-driven flow depending on Rayleigh number, so that the robustness in calculation capability of each phase has been confirmed. In the analysis for the subcooled boiling experiment performed in Seoul National University, the calculation results represented the reasonable capability in predicting the multi-dimensional phenomena such as vapor generation and void propagation. (authors)

Identifying key factors governing the rate of carburisation of liquid iron is important for sustainable developments in blast furnace ironmaking. This study investigated the influence of mineral matter on carburisation rate ‘K’ for two different cokes: coke 1 (K=14.7×10?3 s?1) and coke 2 (K=1.1×10?3 s?1). The sessile drop technique was used to investigate carbon dissolution from coke into molten iron (1450°C, 1550°C) and the nature of interfacial products formed. Examination of the underside of the iron droplets showed the iron/coke interface was markedly different in appearance and composition between the two cokes. The interfacial product formed with coke 2 had a mesh like structure that seemed to wet the iron droplet much better than the interfacial product formed with coke 1. In contrast, Fe globules and discrete interfacial products were observed in coke 1. Interfacial products containing calcium sulfide (CaS) and manganese sulfide (MnS), were observed for both cokes. The presence of MnS could reduce the overall viscosity of the interfacial layer as it's known to lower the liquidus temperature. Electron dispersive X-ray analyses of coke 1 identified iron to be in close association with sulfur. These Fe/S species have atomic ratio similar to pyrrhotite (Fe1?xS) or troilite (FeS). Pyrrhotite in coke can decompose to release gaseous sulfur and metallic iron, which can be carburised to form Fe–C particles. Carburisation of liquid iron can thus occur via Fe–C particles. These factors can have a significant influence on the kinetics of carbon dissolution.   

In this paper the interfacial heat transfer coefficient (IHTC) is correlated to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of the casting under different pressures were obtained using the Inverse Heat Conduction Problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented and compared with data in literature which shows acceptable agreement.

The variation of long-range intermolecular forces near interfaces profoundly affects the performance of change-of-phase heat exchangers. Starting with the fundamental electromagnetic force between molecules (dielectric properties), the effects of shape (Kelvin effect), temperature (Clapeyron effect) and concentration on the heat-transfer characteristics of thin films and larger systems are reviewed and connected. A judicious selection of literature gives a consistent set of models of particular use in heat transfer. Examples of experimental verification of these interfacial models in this rapidly developing field are also presented.

The conductivity at each layer of a spin valve system consisting of a ferromagnet, a spacer, and a ferromagnet was investigated using the tight binding model and the Kubo formula. The interfacial roughness was treated by the coherent locator approximation, in which the coherent potential approximation was extended to enable application to alloys with various transfer integrals. In this system, the giant magnetoresistance (GMR) effect appears to originate from the dependence of conductivity in the spacer on the magnetization configuration. Furthermore, the atom-dependent transfer integral and the atom- and spin-dependent relaxation time strongly affect the conductivity and the GMR effect.   

The effect of the modulation of the electronic wave functions by configurational fluctuations of the molecular environment on the kinetic parameters of electron transfer reactions is discussed. A self-consistent algorithm for the calculation of the potential profile along the reaction coordinate of adiabatic electron transfer reactions is elaborated. A new formula for the transition probability of non-adiabatic electron transfer reactions is obtained in an improved Condon approximation A regular method for the calculation of non-Condon corrections is suggested. The importance of these effects for some specific biological and electrochemical electron transfer systems is discussed.

New technologies for direct solar energy conversion have gained more attention in the last few years. In particular, Dye Sensitized Solar Cells (DSSCs) are promising in terms of efficiency and low cost [1,2]. Benefited from systematic device engineering and continuous material innovation, a state of the art DSC with a ruthenium sensitizer has achieved a validated efficiency of 11.1%[3] measured under the air mass 1.5 global (AM1.5G) conditions. The optimized geometries of the 3, 4-Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile are shown in Fig. 1(a). The frontier molecular orbitals (MO) energies of the dyes 3, 4 Pyridinedicarbonitrile, 3-Nitrophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile are shown in Fig. 1(b). The HOMO-LUMO gap of the dye 3, 4 Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile in vacuum is 5.96 eV, 5.54 eV, 5.57 eV, 5.76 eV respectively. The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of dyes 3, 4-Pyridinedicarbonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile were studied by using density functional theory with hybrid functional B3LYP, and the UV-Vis spectra were investigated by using TDDFT methods. The NBO results suggest that 3, 4-Pyridinedicarbonitrile, 3-Aminophthalonitrile 4-Aminophthalonitrile and 4-Methylphthalonitrile are all (D-pi-A) systems. The calculated isotropic polarizability of 3, 4-Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile is. 85.76, 112.72, 26.63 and 115.13 a.u., respectively. The calculated polarizability anisotropy invariant of 3, 4-Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile is 74.451, 83.533, 62.653 and 88.526 a.u., respectively. The hyperpolarizabilities of 3, 4-Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile is 0.80628, 5.60646, 7.7979 and 1.86216 (in a.u.), respectively. The frequencies of strongest IR absorption for 3, 4-Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile are 1614 cm-1, 290 cm-1, 387 cm-1 and 846 cm-1 and the frequencies of strongest Raman activity for 3, 4-Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile are 2345 cm-1, 2338 cm-1,2329 cm-1, 2337cm-1, respectively. The electronic absorption spectral features in visible and near-UV region were assigned based on the qualitative agreement to TDDFT calculations. The absorptions are all ascribed to ?-->?* transition. The three excited states with the lowest excited energies of 3, 4-Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile are photoinduced electron transfer processes that contributes sensitization of photo-to-current conversion processes. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer 3, 4- Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile is electron injection process from excited dyes as donor to the semiconductor conduction band. Based on the comparative analysis of geometries, electronic structures, and spectrum properties between 3, 4-Pyridinedicarbonitrile, 3-Aminophthalonitrile, 4-Aminophthalonitrile and 4-Methylphthalonitrile the role of amide and methyl groups in phthalonitrile is as follows: it enlarged the distance between electron donor group and semiconductor surface, and decreased the timescale of the electron injection rate, resulted in giving lower conversion efficiency. This indicates that the choice of the appropriate conjugate bridge in dye sensitizer is very important to enhance the performance of DSSC.

Electrochemically modulated liquid chromatography (EMLC) employs a conductive material as both a stationary phase for chromatographic separations and as a working electrode for performing electrochemistry experiments. This dual functionality gives EMLC the capacity to manipulate chromatographic separations by changing the potential applied (E{sub app}) to the stationary phase with respect to an external reference. The ability to monitor retention as a function of E{sub app} provides a means to chromatographically monitor electrosorption processes at solid-liquid interfaces. In this dissertation, the retention mechanism for EMLC is examined from the perspective of electrical double layer theory and interfacial thermodynamics. From the chromatographic data, it is possible to determine the interfacial excess ({Lambda}) of a solute and changes in interfacial tension (d{gamma}) as a function of both E{sub app} and the supporting electrolyte concentration. Taken together, these two experimentally manipulated parameters can be examined within the context of the Gibbs adsorption equation to delineate the contribution of a variety of interfacial properties, including the charge of solute on the stationary phase and the potential of zero charge (PZC), to the mechanism behind EMLC-based retention. The chromatographic probing of interfacial phenomena is complemented by electroanalytical experiments that exploit the ability to monitor the electronic current flowing through an EMLC column. Cyclic voltammetry and chronoamperometry of an EMLC column are used to determine the electronic performance characteristics of an EMLC column. An electrochemical flow injection analysis of a column is provided in which the current required to maintain a constant E{sub app} is monitored and provides a way to examine the influence that acetonitrile and supporting electrolyte composition, flow rate, column backpressure, and ionic strength have on the structure of electrified interfaces.

The subject of the present paper is a novel electron transfer between two atoms. It takes place irreversibly when, for instance, an atom accommodating an electron slowly approaches to another neutral atom under certain conditions. This irreversible process exhibited by a dynamical system is studied in adiabatic approximation. Possible application to the study of electron transfer in photosynthetic reaction center is also discussed.   

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Semiconductor nanowires have been studied using electron microscopy since the early days of nanowire growth, e.g. [1]. A common approach for analysing nanowires using transmission electron microscopy (TEM) involves removing them from their substrate and subsequently transferring them onto carbon films. This sample preparation method is fast and usually results in little structural change in the nanowires [2]. However, it does not provide information about the interface between the nanowires and the substrate, who’s physical and electrical properties are important for many modern applications of nanowires. In particular, strain and crystallographic defects can have a major influence on the electronic structure of the material. In improved method for the characterization of such interfaces would be valuable for optimizing and understanding the transport properties of devices based on nanowires. Here, we systematically investigate the interface between a nanowire and its substrate using three complementary methods for assessing strain. Results obtained using high resolution TEM for geometric phase analysis (GPA), convergent beam elecron diffraction (CBED) and nanobeam electron diffraction (NBED) are compared and contrasted. GPA measurements were acquired at 300kV in an FEI Titan 89-300 while the two diffraction methods were applied in the same microscope at 120kV. The GPA analysis software developed by C.T. Koch and V.B. Özdöl was used [3]. For samples other than nanowires, previous comparisons of GPA with CBED and NBED [4,5] have shown a high degree of consistency. Strain has previously only been measured in nanowires removed from their substrate [6], or only using GPA [7]. The sample used for the present investigation was an InP nanowire grown on a Si substrate using metal organic vapor phase deposition (MOCVD). Lattice missmatch between Si and InP is 8%. The nanowire had a diameter of approximately 100 nm in the interface area. TEM samples were prepared using a tripod polishing technique, with Ar ion milling usedas the final thinning step. The resulting sample was clean and virtually free from defects from sample preparation. Measurements using all three techniques were obtained from the same well defined region of the specimen. Energy dispersive X-ray spectroscopy (EDS) maps were also acquired from the same area. Preliminary results acquired using GPA are shown in Figure 1. Whereas the base of the wire show some strain, little strain is observed in the substrate. The influence of defects, interfacial layers and compositional variations on the GPA will be discussed.

The structural and electronic properties of CnH2n+2/Al(110) interfaces (n=5) have been studied by first-principles calculations using a plane-wave pseudopotential method coupled with an efficient electronic minimization scheme for large systems. We have examined the stability of vertical and parallel adsorption of a C5H12 molecule on an Al(110) surface for various adsorption sites and initial interface distances. It has been found that image interactions between the C-H polar bonds and the metal surface with physorption characters dominate the interfacial interactions for both the vertical and parallel cases of the C5H12/Al interfaces. However, for the C5H11 molecule with a dehydrogenated terminal C atom, we have observed the formation of a strong interfacial C-Al bond with both covalent and ionic characters.   

This research program focuses on an experimental study of the structure and chemistry of metal/metal oxide internal interfaces; the latter are mainly created, although not exclusively, by internal oxidation of binary or ternary metal alloys that are solid-solution phases prior to the internal oxidation treatment. The principal research tools are transmission electron microscopy (TEM), high resolution microscopy (HREM), analytical electron microscopy (AEM) and atom-probe field-ion microscopy (APFIM). The APFIM technique is used to determine the chemical composition of the interfacial region on an atomic scale. Initial studies are foucused on Pd/NiO, Cu/MgO, Cu/Al{sub 2}O{sub 3}, Cu/SiO{sub 2} interfaces, as well as metal oxides in Pt-based alloys. Topics of importance include coherency effects, misfit dislocations, structure of the terminating layer between the metal and the metal oxide, microstoichiometry, dipole space charge effects, and distributions of impurities and point defects at the interfacial region.

The diffusion behavior and microstructure evolution of Cu/Ta/GaAs multilayers after thermal annealing are investigated and the mechanism is proposed. A thin 30 nm tantalum layer was sputtered as a diffusion barrier to block Ga and As diffusion into the Cu layer. From the results of sheet resistance measurement, X-ray diffraction analysis, Auger electron spectroscopy and transmission electron microscopy, the Cu/Ta films on GaAs were found to be very stable up to 500 °C without Cu migration into GaAs. After annealing at 550 °C, the interfacial mixing of Ta with GaAs substrate occurred, resulting in the formation of TaAs2, and the diffusion of Ga through the Ta layer formed the Cu3Ga phase at the Cu/Ta interface. After annealing at 600 °C, the reaction of GaAs with Ta and Cu formed TaAs and Cu3Ga owing to Ga migration and interfacial instability.