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Author(s): Kameni Boumenou, C; Elizabeth, A; Babbe, F; Debot, A; Monig, H; Redinger, A | Abstract: In-depth understanding and subsequent optimization of the contact layers in thin film solar cells are of high importance in order to reduce the amount of nonradiative recombination and thereby improve device performance. In this work, the buried MoSe2/CuInSe2 interface of stoichiometric absorbers is investigated with scanning tunneling spectroscopy and Kelvin probe force microscopy combined with compositional measurements acquired via photo-electron spectroscopy after a mechanical lift-offnprocess. We find that the local density of states, as measured with scanning tunneling spectroscopy, is similar to the front-side of ultra-high vacuum annealed CISe absorbers. The grain boundaries exhibit a weak upward band bending, opposite to Cu-poor CuGaSe2, and we measure an increased Cu accumulation at the rear CISe surface compared to the bulk composition and a non-zero concentration of Cu on the Mo-side. Grazing incidence X-ray diffraction measurements corroborate that a small amount of a CuxSe secondary phase is present at the MoSe2/CuInSe2 interface in contrast to reports on Cu-poor material. Our findings shed new light into the complex interface formation of CuInSe2-based thin film solar cells grown under Cu-rich conditions.

All-optical ultrafast signal modulation and routing by low-loss nanodevices is a crucial step towards an ultracompact optical chip with high performance. Here, we propose a specifically designed silicon dimer nanoantenna, which is tunable via photoexcitation of dense electron-hole plasma with ultrafast relaxation rate. On the basis of this concept, we demonstrate the effect of beam steering by up to 20 degrees through simple variation of the intensity of incident light. The effect, which is suitable for ultrafast light routing in an optical chip, is demonstrated both in the visible and near-IR spectral regions for silicon- and germanium-based nanoantennas. We also reveal the effect of electron-hole plasma photoexcitation on the local density of states (LDOS) in the dimer gap and find that the orientation averaged LDOS can be altered by 50%, whereas modification of the projected LDOS can be even more dramatic, almost five-fold for transverse dipole orientation. Moreover, our analytical model sheds light on the transient dynamics of the studied nonlinear nanoantennas, yielding all temporal characteristics of the suggested ultrafast nanodevice. The proposed concept paves the way to the creation of low-loss, ultrafast, and compact devices for optical signal modulation and routing.

Topological defects, with an asymmetric local electronic redistribution, are expected to locally tune the intrinsic catalytic activity of carbon materials. However, it is still challenging to deliberately create high-density homogeneous topological defects in carbon networks due to the high formation energy. Toward this end, an efficient NH3 thermal-treatment strategy is presented for thoroughly removing pyrrolic-N and pyridinic-N dopants from N-enriched porous carbon particles, to create high-density topological defects. The resultant topological defects are systematically investigated by near-edge X-ray absorption fine structure measurements and local density of states analysis, and the defect formation mechanism is revealed by reactive molecular dynamics simulations. Notably, the as-prepared porous carbon materials possess an enhanced electrocatalytic CO2 reduction performance, yielding a current density of 2.84 mA cm-2 with Faradaic efficiency of 95.2% for CO generation. Such a result is among the best performances reported for metal-free CO2 reduction electrocatalysts. Density functional theory calculations suggest that the edge pentagonal sites are the dominating active centers with the lowest free energy (ΔG) for CO2 reduction. This work not only presents deep insights for the defect engineering of carbon-based materials but also improves the understanding of electrocatalytic CO2 reduction on carbon defects.

The current flow along the boundary of graphene stripes in a perpendicular magnetic field is studied theoretically by the nonequilibrium Green's function method. In the case of specular reflections at the boundary, the Hall resistance shows equidistant peaks, which are due to classical cyclotron motion. When the strength of the magnetic field is increased, anomalous resistance oscillations are observed, similar to those found in a nonrelativistic 2D electron gas [New. J. Phys. 15:113047 (2013)]. Using a simplified model, which allows to solve the Dirac equation analytically, the oscillations are explained by the interference between the occupied edge states causing beatings in the Hall resistance. A rule of thumb is given for the experimental observability. Furthermore, the local current flow in graphene is affected significantly by the boundary geometry. A finite edge current flows on armchair edges, while the current on zigzag edges vanishes completely. The quantum Hall staircase can be observed in the case of diffusive boundary scattering. The number of spatially separated edge channels in the local current equals the number of occupied Landau levels. The edge channels in the local density of states are smeared out but can be made visible if only a subset of the carbon atoms is taken into account.

We theoretically analyse the possibility to electrostatically confine electrons in circular quantum dot arrays, impressed on contacted graphene nanoribbons by top gates. Utilising exact numerical techniques, we compute the scattering efficiency of a single dot and demonstrate that for small-sized scatterers the cross-sections are dominated by quantum effects, where resonant scattering leads to a series of quasi-bound dot states. Calculating the conductance and the local density of states for quantum dot superlattices, we show that the resonant carrier transport through such graphene-based nanostructures can be easily tuned by varying the gate voltage. Schematic representation of a Dirac electron wave packet impinging on a circular, electrostatically defined quantum dot.

The transport properties of Cu/ZnO-nanobelt/Cu nanostructures under uniaxial strains were studied using first-principles calculations, with emphasis on the interfacial contacts. The conductivity G is very sensitive to strain, and it decreases linearly when strain varied from compression to tension, and the piezoresistive gauge factors (GFs) of ZnO nanobelts in non-polarized direction are 5.66 and 4.29 for compressive (ϵ=−0.05) and tensile strain (ϵ=0.05), respectively. As shown in local density of states (LDOS), the number of carriers nearby the Fermi level decreased obviously when the strains changed from compression to tension, which could be used to explain the linearly decreased conductance. In terms of the transferred interfacial charge and potential profiles, the energy barriers between Cu and ZnO nanobelts could be reduced by strains. These results could help to understand the physics in the strain-induced metal/ZnO contacts and be used to modulate effectively the performances of ZnO nanodevices.

Strong interactions between surface plasmons in ultra-compact nanocavities and excitons in two dimensional materials have attracted wide interests for its prospective realization of polariton devices at room temperature. Here, we propose a continuous transition from weak coupling to strong coupling between excitons in MoS2 monolayer and highly localized plasmons in ultra-compact nanoantenna. The nanoantenna is assembled by a silver nanocube positioned over a gold film and separated by a dielectric spacer layer. We observed a 1570-fold enhancement in the photoluminescence at weak coupling regime in hybrid nanocavities with thick spacer layers. The interaction between excitons and plasmons is then directly prompted to strong coupling regime by shrinking down the thickness of spacer layer. Room temperature formation of polaritons with Rabi splitting up to 190 meV was observed, which is the largest plasmon-exciton Rabi splitting reported in two dimensional materials. Numerical calculations quantified the relation between coupling strength, local density of states and spacer thickness, and revealed the transition between weak coupling and strong coupling in nanocavities. The findings in this work offer a guideline for feasible designs of plasmon-exciton interaction systems with gap plasmonic cavities.

The emission profi le and lifetime dynamics of semiconductor quantum dots can be signifi cantly shaped and altered using dielectric and plasmonic nanostructures based on anodic aluminum oxide templates. Remarkable spectral modifi cation and a large total decay rate enhancement in the photoluminescence of quantum dots are observed when they are deposited on a pristine anodic aluminum oxide template. The modifi ed emission spectral profi le is consistent with the calculated photonic local density of states above the anodic aluminum oxide template surface, suggesting that this interesting spectral tuning phenomenon stems from the surface electromagnetic modes supported by the anodic aluminum oxide template. Furthermore, when the anodic aluminum oxide template is loaded with metallic nanowires that sustain plasmon resonances, the photoluminescence of the quantum dots can be largely enhanced. These unprecedented results suggest that the anodic aluminum oxide template can be used as a versatile platform for tailoring the photoluminescence properties of quantum emitters in future photonic and optoelectronic applications.

The influence of intrinsic point defects on the electronic structure of n-type In2O3 single crystals grown by two methods, namely chemical vapor transport and from the melt, was examined by scanning tunneling spectroscopy. This method is a very surface sensitive technique for measuring the local density of states. So far not resolved states within the fundamental band gap have been observed. The gap states have been studied at different crystals and after several annealing treatments in an oxidizing atmosphere. The spectroscopic results will be compared to state of the art DFT-calculations revealing hints on the origin of the gap states of In2O3 to be due to oxygen vacancies as well as indium and oxygen interstitials.

The adsorption of methanol on flat Au (100) surface with different coverages (θ = 1.0, 0.5 and 0.25 monolayer (ML)) is studied using density functional theory. Among the three sites (top, bridge and hollow) and coverages investigated in the present work, no adsorption is stable for θ = 1.0 ML. The most energetically preferred site of adsorption for CH3OH is found to be the hollow site for coverages of 0.25 ML and 0.50 ML. We also find that for all adsorption sites, an increase in CH3OH coverage triggers a decrease in the adsorption energy. The geometric parameters, local density of states and work function changes are analysed in detail. The coadsorption of methoxy and hydrogen has also investigated. In addition, the dissociation of methanol on Au(100) has been studied, and an activation energy was found to be 1.72 eV. This result compare with existing data in the literature for Au(111) surface. Copyright © 2013 John Wiley & Sons, Ltd.

We study the influence of angular degrees of freedom of magnetic adatoms on metallic surfaces onto scanning tunneling spectra. Kondo scattering of electrons off the adatom changes the local density of states near the Fermi level. The spatial dependence of this correction is set by the orbital structure of the local moment localized on the adatom. By considering a multilevel Anderson model with non-degenerate orbitals of differing orbital structure, we demonstrate that the spatial dependence of the scanning tunneling spectrum contains sufficient information to infer the orbital degrees of freedom of the magnetic adatom.

Electronic and spin transport properties of a benzene molecule connected to semi-infinite armchair and zigzag graphene nano-ribbon leads are calculated using non-equilibrium Green function (NEGF) method at zero bias regime. It is shown that, the molecule is conductive in a specific range of energy for both armchair and zigzag leads. This behavior is similar for both kinds of leads. In presence of Rashba spin–orbit interaction, the molecule shows spin filtering properties for both kinds of leads but these properties are not similar for armchair and zigzag leads. Also, a spin-polarized current is seen in the molecule connected to zigzag leads. The benzene molecule with Rashba spin–orbit interaction can be considered as an excellent candidate for molecular electronic and spintronic devices which can have very small dimensions relative to the conventional semiconductor devices.

We perform the conventional band structure and local density of states (LDOS) calculations in the vicinity of the Fermi level at ab initio molecular orbital level with 6-31G base set for one DNA duplex with repeated mononucleotide sequences and four DNA duplexes with repeated dinucleotide sequences in B form neutralized by Na+. The LDOS of six other DNA duplexes with repeated trinucleotide sequences in the same states are analyzed. The obtained results are compared with those by the band calculations based on periodic boundary condition using screw axis symmetry. The investigations focused on the influence of the base composition and base sequence on the DNA conductivity. The band structure and LDOS calculation results indicated that base guanine is more important for DNA conductivity than the other bases, and DNA conductivity varies with base sequence of DNA. Moreover, poly (dG) • poly (dC) shows the best conductor in our DNA duplex models. © 2012 Wiley Periodicals, Inc.

Electronic transport through a double quantum dot interferometer with Rashba spin–orbit interaction is investigated. By means of the slave-boson mean-field approximation and Green function technique, we calculated the local density of states (DOS) and the linear conductance in the Kondo regime at zero temperature. It is shown that the local DOS and the linear conductance of each spin component can be tuned by the Rashba spin–orbit interaction with help of the magnetic flux. In particular, by modulating the strength of the Rashba spin–orbit interaction properly, only one spin component electron can be allowed to transport through this structure.

The low-energy electronic properties of strained graphene are usually obtained by transforming the bond vectors according to the Cauchy-Born rule. In this work, we derive a new effective Dirac Hamiltonian by assuming a more general transformation rule for the bond vectors under uniform strain, which takes into account the strain-induced relative displacement between the two sublattices of graphene. Our analytical results show that the consideration of such relative displacement yields a qualitatively different Fermi velocity with respect to previous reports. Furthermore, from the derived Hamiltonian, we analyze effects of this relative displacement on the local density of states and the optical conductivity, as well as the implications on the scanning tunneling spectroscopy, including external magnetic field, and optical transmittance experiments of strained graphene., Comment: 5 pages, 2 figures. Published version in Phys. Status Solidi RRL

We discuss the possibility to probe magnetic properties of nanostructures buried beneath a metallic surface by means of local probe techniques. We prove, that those properties can be deduced from the spin-resolved local density of states (LDOS) above the surface. In-plane polarization maps in vacuum above the surface are shown to allow one to simultaneously detect electronic, magnetic, and even geometric properties of subsurface structures. It is argued, that the coupling of buried nanostructures to each other can be deduced from the symmetry of the polarization map. To underline the importance of studying buried nanostructures several possible applications of buried magnetic impurities are pointed out. The exchange coupling of an adatom to a nanostructure or a monolayer (ML) across a paramagnetic spacer is shown to oscillate with the thickness of the latter. This could provide one with reliable means to stabilize the spin of a magnetic adatom in either a ferromagnetic or an antiferromagnetic configuration with respect to the magnetic orientation of the monolayer or nanostructure. The possibility to tailor the exchange coupling between single magnetic impurities on a surface through the adjustment of the overlayer thickness and the interatomic separation in a dimer, is discussed.

We performed first-principle calculations, by employing the ultrasoft pseudopotential plane-wave (UPPW) method, for the multilayer relaxation and the local density of states (LDOS) of Cu(430) and its corresponding flat Cu(110) surfaces. The shift directions of the atoms in the terrace (layers 1–4), sub-terrace (layers 5–7) and third-terrace (layers 8–11) of the Cu(430) surface are similar to the layers 1, 2 and 3 of the Cu(110) surface, respectively. And the stepped surface changes to a flatter version with a thin compacted layer, including the topmost seven atomic layers and separating slightly from the underneath atomic layers. Because of a reduction in the coordination numbers (CNs),there is a sharp rise in the higher energy region and a slight reduction in the lower energy region of the LDOSfor the topmost three layer atoms of the Cu(430) surface and the first layer atom of the Cu(110) surface. The shape of the LDOS of the corresponding layer with the same CN is similar for both the surfaces. Copyright © 2009 John Wiley & Sons, Ltd.

The structures, stabilities, and electronic properties of the single-vacancy-defected fullerenes, C60 and C70, and the single- and double-vacancy-defected single-walled carbon nanotubes (SWCNTs) were studied within density functional theory. The isomerization barriers for the single-vacancy-defected C60 on the triplet potential energy surface (PES) are lower than those on the singlet PES. The symmetric double-vacancy-defected (10,0) SWCNT is the most stable one among the models investigated. According to the analyses of frontier molecular orbitals (FMOs), nature bond orbitals, and local density of states, introduction of vacancy on the SWCNT decreases the band gap of semiconducting SWCNT, increases the band gap of conducting SWCNT, destructs the π conjugation of the FMOs, and gives rise to enhanced chemical activity. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

For a finite-step barrier model of a metal surface, it is shown that structure in the local density of states, around the bulk density of states, is induced deep into the metal. In a non-free-electron metal, it is stressed that the range over which such structure persists into the bulk metal depends on the shape of the Fermi surface. A summary is then given of the way in which chemical bonds are affected by a metal surface in physisorbed and chemisorbed regimes. A bond parallel to a planar metal surface is weakened and lengthened. Polyatomic molecules are discussed, with particular reference to H2O on the (0001) surface of Ru metal. The principle of maximum overlap predicts the center geometry for the O atom, not the overhead site. The spillout of electron density affects the angle of H2O and near the united atom it opens up the angle a little compared with the free space value for a given O—H length. Finally, the linear response function of the infinite-step barrier model, plus a model potential designed to simulate a flat molecule like benzene adsorbed parallel to the surface, is used to calculate the charge density displaced in the metal. Near the surface, this displaced electron density, along an axis through the center of the benzene ring and perpendicular to it, is shown to be sensitive to the dimensions of the adsorbed molecule. It would therefore be of interest if field gradients due to the displaced charge could be measured.

First-principles calculations are performed to explore the CH3 dissociation on Ni(100). The CH2 species bind most strongly to the hollow site with two CH bonds pointing toward the neighboring surface Ni atoms. Through the calculations of local density of states (LDOSs) and partial charge density, the CHNi three-center bond is regarded as the key factor determining the CH3 adsorption. The CH3 dissociation on Ni(100) is investigated along two different reaction pathways. After zero-point energy (ZPE) correction considered, the energy barriers for the CH3 dehydrogenation are calculated to be 0.46 and 0.54 eV. Because these barriers are much lower than that for the CH3 dissociation on Ni(111), the CH3 dehydrogenation is found to be structure-sensitive. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

We report on numerical studies into the interplay of disorder and electron-electron interactions within the integer quantum Hall regime, where the presence of a strong magnetic field and two-dimensional confinement of the electronic system profoundly affects thermodynamic and transport properties. We emphasise the behaviour of the electronic compressibility, the local density of states, and the Kubo conductivity. Our treatment of the electron-electron interactions relies on the Hartree-Fock approximation so as to achieve system sizes comparable to experimental situations. Our results clearly exhibit manifestations of various interaction-mediated features, such as non-linear screening, local charging, and g-factor enhancement, implying the inadequacy of independent-particle models for comparison with experimental results., Comment: 13 Wiley-VCH LaTeX pages with 8 figures, style files included

An anomalous temperature dependence of 115In-NMR spectrum is observed in the newly-discovered high field and low temperature superconducting phase of CeCoIn5. The anomalies near the upper limit of HC 2 are attributed to spatially-distributed local density of states of quasiparticles. From a simulation with the phenomenological model for the sinusoidally-modulated superconducting order parameter, the present NMR study provides a microscopic evidence that the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is realized at the high field phase in CeCoIn5. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Using ab initio pseudopotential calculations, we have investigated the atomic and electronic structure of a c(3√2×√2) striped reconstruction, induced by segregated C impurities, at the Fe(001) surface. The segregated C atoms form zigzag chains, which in turn produce one-dimensional Fe surface states near the Fermi energy. We address the influence of the C chains on the local surface atomic geometry, local electrostatic potential, and local density of states, and discuss the formation mechanism of the one-dimensional surface states.

The local density of states at cleaved cross-sectional surfaces of InAs/GaSb superlattices were investigated by low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) with atomic resolution. Broken-gap energy band profiles (the overlap of the conduction band of InAs and the valence band of GaSb) were clearly seen in the LT-STS spectra as a function of growth direction. Clear images of electron standing waves confined in the superlattice were also obtained. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fourier transformed maps of the local density of states in disordered superconducting Bi 2 Sr 2 CaCu 2 O 8+δ provided important information on the quasiparticle states and their interference in high-temperature superconductors. Neglecting the momentum-dependence of the impurity potential it is possible to disentangle the quasiparticle interference effect from the static structure factor of the scatterers. The k-dependence of the impurity potential makes such a distinction difficult. Here, for the model momentum-dependent potential, we discuss the quasiparticle interference induced by an impurity in an s-wave superconductor.

The Mn3N2 (010) surface has been studied using spin-polarized scanning tunneling microscopy at the atomic scale. The principle objective of this work is to elucidate the properties and potential of this technique to measure atomic-scale magnetic structures. The experimental approach involves the use of a combined molecular beam epitaxy/scanning tunneling microscopy system that allows the study of atomically clean magnetic surfaces. Several key findings have been obtained. First, both magnetic and non-magnetic atomic-scale information has been obtained in a single spin-polarized image. Magnetic modulation of the height profile having an antiferromagnetic super-period of c = 12.14 A (6 atomic rows) together with a non-magnetic superstructure having a period of c/2 = 6.07 A (3 atomic rows) was observed. Methods of separation of magnetic and non-magnetic profiles are presented. Second, bias voltage-dependent spin-polarized images show a reversal of the magnetic modulation at a particular voltage. This reversal is clearly due to a change in the sign of the magnetic term in the tunnel current. Since this term depends on both the tip's as well as the sample's magnetic local density of states, the reversal can be caused by either the sample or the tip. Third, the shape of the line profile was found to vary with the bias voltage, which is related to the energy-dependent spin contribution from the 2 chemically inequivalent Mn sites on the surface. Overall, the results shown here expand the application of the method of spin-polarized scanning tunneling microscopy to measure atomic-scale magnetic structures. Microsc. Res. Tech. 66:72–84, 2005. © 2005 Wiley-Liss, Inc.

A nonperturbative theory of the multiphonon relaxation of a strongly excited local vibration is developed. It is found that for a high initial level, the relaxation first accelerates in time, and later starts to slow down. The experimental evidence of such a non-monotonous relaxation is given by the hot luminescence in solid Xe. A theory of optical transitions in a center with strongly reduced local springs in the final electronic state is also developed. In this case a resonant increase of the local density of states of low-frequency phonons takes place, and a low frequency pseudo-local mode emerges. Appearance of such a mode in the final state means that a strong mode mixing takes place at the transition. This results in strong increase of the mean number of created low-frequency phonons. As a consequence, the zero-phonon transition practically disappears and the long-wave part of the phonon sideband is strongly enhanced, resulting in formation of so-called lambda-shaped spectrum.

Using a recently developed first-principles supercell method that includes the electron and core-hole interaction, the XANES/ELNES spectra of Si-L 2,3 , Si-K, and N-K edges in α-Si 3 N 4 , β-Si 3 N 4 , spinel c-Si 3 N 4 , and Si 2 N 2 O were calculated and compared. The difference in total energies between the initial ground state and the final core-hole state provides the transition energy. The calculated spectra are found to be in good agreement with the experimental measurements on β-Si 3 N 4 and c-Si 3 N 4 . The differences in the XANES/ELNES spectra for the same element in different crystals are explained in terms of differences in local bonding. The use of orbital-decomposed local density of states to explain the measured spectra is shown to be inadequate. These results reaffirm the importance of including the core-hole effect in any XANES/ ELNES spectral calculation.

The influences of different distributions of defects in (5, 5) single-walled carbon nanotube (SWCNT) on the electronic structure of SWCNT are considered. Furthermore, we suggest one way to connect two perfect semi-infinite tubes with different chiralities, such as four different (5, 5)/(n, 0) (n = 8, 9, 10) intramolecular junctions. Their electronic local density of states (LDOS) and quantum conductance are studied. It is found that the conductance gap of the metal/semiconductor heterojunction is not determined only by the electronic structure of semiconductor tube, and the defect distribution mainly change the step behavior of conductance, which is particularly obvious in (5, 5)/(9, 0) metal/metal junctions. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

TUNCUR codes are aimed at a self-consistent calculation of both equilibrated structures and electronic properties of a sample and scanning tunneling microscopy (STM) tip altogether with the tunneling current between them in the framework of the same computational scheme. Both objects are modeled by atomic clusters. Quantum chemical calculations in TUNCUR codes are provided by sequential programs, CLUSTER-Z1 and CLUSTER-Z2, which perform Hartree–Fock self-consistent field semiempirical calculations in the valence sp- and spd-basis, respectively. TUNCUR consists of three main blocks that provide calculations of STM recordings in two modes of operation as well as computing local density of states. All calculations are performed over a grid of variable parameters. There are two additional blocks for calculations of both the current Z-dependence and volt-ampere characteristic of the tunneling gap. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

We have examined a method of direct extraction of accurate tight-binding parameters from an ab-initio band-structure calculation. The linear muffin-tin potential method, in its full-potential implementation, has been used to provide the hamiltonian and overlap matrix elements in the momentum space. These matrix elements are Fourier transformed to real space to produce the tight-binding parameters. The feasibility of this method has been tested on the intermetallic alloy NiAl, using spd orbitals for each atom. The parameters generated for this alloy have been used as input to a real-space calculation of the local density of states using the recursion method., 12 pages, RevTex, 5 figures

Spin polarization is investigated for Cr/Mn systems at T = 0 K using real-space tight-binding approach. The magnetism is described in the Hartree-Fock approximation of Hubbard Hamiltonian and the local density of states is calculated within the recursion technique. The magnetic moments for bulk Cr, and Cr n /Mn interfaces for n = 1-3 overlayers with and without relaxation for low index crystallographic orientations are calculated. The antiferromagnetic ground state is considered for Mn (Cr) structures. The magnetism is most favored in the (111) orientation, whereas it has the least value in (011) orientation in all systems due to the coordination.

We study the electronic states of different GaAs–AlAs Fibonacci quasi-perodic heterostructures grown along the (001) direction. We employ an empirical tight-binding Hamiltonian including spin–orbit coupling together with the surface Green function matching method. We present results for the eighth Fibonacci generation formed from different building blocks. We compare these results with those of the constituent quantum wells and with those of heterostructures containing the same number of GaAs and AlAs slabs after periodic repetition of the building blocks. No Fibonacci spectrum is found in the energy regions near the conduction and valence band edges of GaAs. A selective localization of the local density of states in the GaAs layers is found for many electronic states.

The local density of states of an anisotropic normal metal-superconductor-normal metal and normal metal-insulator-superconductor-normal metal junction is investigated using the Green's function method. The Green's functions are determined by means of the solutions of the Bogoliubov-de Gennes equations for anisotropic superconductors. We find oscillations in the local density of states which in the isotropic case coincide with those found in the Tomasch effect. The local density of states depends on the potential symmetry, the strength of the insulating barrier, and the width of the superconducting region. The influence of different pair potential symmetries on the local density of states is analyzed in detail. In particular, s and d symmetries are considered.

We study the non-interacting two-impurity Anderson model on a lattice using the Green function equation-of-motion method. A case of particular interest is the RKKY limit that is characterized by a small hybridization between impurities and host electrons and the absence of a direct coupling between the impurities. In contrast to the low-density case, at half band-filling and particle-hole symmetry, the RKKY interaction decays as the inverse square of the impurity distance along the axis of a simple cubic lattice. In the RKKY limit, for the spectral function we generically observe a small splitting of the single-impurity resonance into two peaks. For a vanishing density-density correlation function of the host electrons, we find only a broadened single peak in the local density of states.

Using an empirical many-body potential and a genetic algorithm, the geometries of small V 3 to V 19 clusters have been optimized. We find that the clusters do not mimic the bulk structure and undergo significant geometrical changes with size. Based on the optimization geometries, the d electronic structure and magnetic properties of V clusters are studied, by using a Hubbard tight-binding model Hamiltonian in the unrestricted Hartree-Fock approximation. The calculated average magnetic moments for these clusters are consistent with the upper limits obtained from experiments. The total density of states (TDOS) and the local density of states (LDOS) of d electrons shed light on the evolution of the electronic properties.

We study the local density of states in a half metal sandwiched by the two superconductors. The spin-flip scattering at the junction interface opens the Josephson channels of the odd-frequency spin-triplet s-wave Cooper pairs. The penetration of the odd-frequency pairs enhances the quasiparticle density of states near the Fermi energy in a half metal, which is responsible for the unusual nonmonotonic temperature dependence of the Josephson current. On the basis of calculated results, we propose experiments to confirm the odd-frequency Cooper pairs.

Spin-polarized density functional theory (DFT)-based total energy calculations were performed to investigate the electronic structure of Pt monolayer on Fe(001) {Pt ML /Fe(001)} and its effect on O 2 dissociative adsorption. Local density of states (LDOS) at Pt surface shows induced spin polarization on Pt monolayer increasing unoccupied d zz orbital on Pt surface. The potential energy curves (PEC) for the reaction of Pt with O 2 show that the system produces a combination of lower activation barrier for O 2 dissociation and a weaker O binding than that of clean Pt(001). The modification of Pt surface electronic structure led to a favorable 0-Pt d interaction with promotion of O unpaired electron antiparallel spin alignment with Pt spin as verified by the decrease in O and Pt magnetic moments upon O adsorption. Such results render stabilization and a lowering of energy cost for O 2 activation. The weaker O binding, however, may be attributed to the stronger metal-metal interlayer binding in Pt ML /Fe(001) than in Pt(001), which indicates an increased stability of Pt monolayer on Fe(001) than on its corresponding pure metal slab.

Most scanning tunneling microscopy (STM) studies of adsorbed molecules are performed either on molecules that are chemically bound to the surface or are part of a molecular monolayer. In the first case, the chemical reaction with the surface changes the surface local density of states. In the second one, the electrons tunnel through a physisorbed molecule. In the study described in this paper STM imaging is performed on isolated molecules immobilized on a clean semiconductor surface where atomic resolution is observed. This is an intermediate case. The adsorption behavior of diene molecules on Si(111)7 × 7 was investigated. The molecules adsorb by reaction of the double bonds on the surface. In the reaction, the C=C bond is opened to create two neighboring Si-C bonds. Two such C-C bonds are used to immobilize the chain to the surface. The adsorption chemistry is affected not only by the nature of the Si-C bond but also by steric limitations. Performing STM imaging on such systems ensures that the position of the immobilized chemical group (in this case an aliphatic chain) could be clearly identified and that it was possible to image parts of the molecule that are not chemically bound to the surface. STM images of 1,13-tetradecadiene revealed a white protrusion in the location of the aliphatic chain. The increase in transmission is explained by an additional channel for tunneling: through bond tunneling. Long-range electron transfer through molecules is a widely known chemical and biochemical process. This observation opens the possibility to investigate this fundamental phenomenon in large details. The potential applications for molecular electronics are discussed.

Asymmetric metal-dielectric nanostructures are demonstrated superior optical properties arising from the combination of strong enhancement of near-fields and controllable scattering characteristics which originate from plasmonic and high-index dielectric components. Here, being inspired by the recent advances of the asymmetric hybrid nanoparticles fabrication [Dmitry Zuev, et al., Adv. Mater. 28, 3087 (2016)], we suggest and study numerically a novel type of hybrid dimer nanoantennas. The nanoantennas consist of asymmetric metal-dielectric (Au/Si) nanoparticles and allow tuning of the near- and far-field properties via laser induced reshaping of the metal part at the nanoscale. We demonstrate an ability to modification of the scattering properties, near-field distribution profilis, normalized local density of states, and radiation patterns of the nanoantenna upon the laser reshaping. The parameters used to investigate these effects correspond to experimentally demonstrated values.

Effective spin mixing conductance (ESMC) across the nonmagnetic metal (NM)/ferromagnet interface, spin Hall conductivity (SHC), and spin diffusion length (SDL) in the NM layer govern the functionality and performance of pure spin current devices. It is shown that all three parameters can be tuned significantly via the spin orbit coupling (SOC) strength of the NM layer by virtue of the unique Pd1-xPtx/Y3Fe5O12 system. Surprisingly, the ESMC is observed to increase significantly with x changing from 0 to 1.0, due to the enhanced local density of states for Pt-rich alloys. The SHC in PdPt alloys turns out to be dominated by the skew scattering term. In particular, the skew scattering parameter has for the first time been rigorously demonstrated to increase with increasing SOC strength. Meanwhile, the SDL is found to decrease when Pd atoms are replaced by heavier Pt atoms, validating the SOC induced spin flip scattering model in polyvalent PdPt alloys. A thorough grasp of the dependence of these parameters on the SOC strength in the present work can help to develop a better theoretical graph on the physics of SOC and spin orbit torque switching, relevant to next generation spintronic devices.

An LCAO scheme (linear combination of atomic orbitals) taking into account ten atomic orbitals (s-, p-, and d-type) is used to calculate the electronic structure of a vacancy present in the core of the reconstructed 90° partial dislocation in silicon. The levels in the band gap are extracted using Lanczos' algorithm and a continued fraction representation of the local density of states. The three-fold degenerate state of the ideal vacancy is split into three levels with energies 0.26, 1.1, and 1.9 eV measured from the valence band edge.

We present a microscopic investigation of frequently observed impurity-induced states in stoichiometric LiFeAs using low-temperature scanning tunneling microscopy and spectroscopy (STM/STS). Our data reveal seven distinct well-defined defects which are discernible in topographic measurements. Depending on their local topographic symmetry, we are able to assign five defect types to specific lattice sites at the Li, Fe, and As positions. The most prominent result is that two different defect types have a remarkably different impact on the superconducting state. A specific and quite abundant Fe-defect with -symmetry generates significant impurity-induced additional states primarily at positive bias voltage with pronounced peaks in the on-site local density of states (LDOS) at about 4 and 12 mV. On the other hand, a -symmetric As-defect causes a significantly enhanced LDOS at both positive and negative bias voltages. We expect that these findings provide fresh input for further experimental and theoretical studies on elucidating the nature of superconductivity in LiFeAs.

The influence of rings on the electronic structure of open and closed lattices, like the Bethe and Husimi lattices, respectively, is studied. In both lattices topological defects are introduced changing, in alternating form, the number of nearest neighbors on each site. In the Bethe lattice with or without topological defects the local density of states has the symmetry of a central ring, but topological defects generate a gap in the electronic structure and some bound states in between. In the Husimi model formed with rings of two different numbers of sides, it is found that the electronic bands are symmetrical, if and only if, combinations of rings with even number of sides, independent of the presence of topological defects, are considered. In addition, gaps appear when alternating topological defects are introduced.

The pseudospin model for the G 1−x P x semiconductor alloy is considered in the coherent potential approximation. The phonon density of states in ultraheavily doped semiconductor thin films is investigated as a function of impurity concentration and the position of a monatomic layer inside the film. The obtained results show the dependence of the local density of states on the surface conditions

An elongation method, which had already been proposed to calculate the electronic structure of aperiodic polymer efficiently, was applied to atactic polypropylene, with the approximation level of the extended Huckel method. The atomic populations thus calculated were found to be dependent sensitively on the tacticity of the polymer. Next, this elongation method was applied to the π-electron stacking system composed of ethylene and butadiene, etc. Excellent agreement was found between the elongation method and the usual extended Huckel calculations. Thus, the elongation method can confidently be applied to π-electron molecular crystal systems. Finally, the local density of states of polyacetylene with both cis–transoid and trans–cisoid structures was calculated. We found that the site with large local density of state in the valence band of a polymer chain gives large electron transfer to the site with large local density of state in the conduction band of another polymer chain. © 1994 John Wiley & Sons, Inc.

The nature of the contact layer of water on surfaces is of relevance for many practical fields, including corrosion, electrochemistry, environmental science and heterogeneous catalysis. Here we focus on the geometric and electronic structure of the water contact layer on transition metal surfaces and the interaction between the water monolayer and the surface. By combining synchrotron radiation-based X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) techniques with density functional theory (DFT) computational methods we obtain element-specific information on the partial local density of states, local atomic structure, geometrical parameters and molecular orientation, allowing general principles for water–metal interaction to be derived.

The electronic structure of a hexagonal Husumi cactus with a finite number of substitutional impurities in essentially two different cases is studied: (i) one impure hexagon in a pure Husumi cactus system and (ii) a Husumi cactus formed by infinite repetition of a contaminated hexagon (heterocactus). The tight-binding Hamiltonian is used considering interaction to nearest neighbors and one orbital per site, with diagonal and off-diagonal disorder. The Dyson equation describing the electron dynamics is solved using two types of effective transfer matrices. Localized states appear in the electronic gap for the heterocactus formed by infinite repetition of a hexagon with two impurities on sites 1. All genuine heterocactuses generate a gap, but only one has a localized state in between as a function of the normalized self-energy ϵ.