Influence Of Surface Reconstruction Research Articles

Ru-Mn pair-site triggers key oxygen intermediate for enhanced acidic oxygen evolution reaction kinetics

Charge and spin regulation of electrons are identified as a vital factor in improving the oxygen evolution reaction (OER) catalytic activity. Nevertheless, the influence of surface reconstruction on charge and spin structure under complex catalytic reaction conditions has been unintentionally neglected. Correct understanding and targeted regulation of surface reconstruction are the key to prepare high active catalysts. Herein, variable valence states Mn is adopted to regulate Ru-NC, which serves as a model to reduce the localization of Ru 4d structure and stimulate facile charge transfer, achieving accelerated surface reconstruction to generate Ru-O active ingredient with high active to acidic water oxidation. Doping Mn not only accelerates surface reconstruction, but also improves durability by eliminating Ru peroxidation due to Mn-buffered charge compensation. The enhancement of OER activity results from the Mn and O induced Ru spin states to change from intermediate spin to low spin, thereby weakening the interaction with *O intermediates, and promoting *OH adsorption, which benefits the initial step of OER. This study not only provides a strategy to achieve directional reconstruction with the help of metal site asymmetry, but also provides a thorough comprehension of charge and spin dependent acidic OER kinetics.

Influence of surface reconstruction on elastic properties of nanosized diamond films and nanodiamonds

Investigation of elastic properties of nanosized diamond films reveals, that their elastic properties in the range ±5% significantly depend on the reconstructions of their surfaces. Strong correlation between lateral contraction/dilation of the surface and its layer elastic modulus is observed. In contrast to the recent report of stiffening of nanodiamonds smaller than 2 nm in size, our research suggests more complex influence of crystal morphology on elastic properties of nanodiamonds. We have found, that in accordance with our previous results for nanofilms with (110) and (100) faces, dilatation of nanofilms with amplitude of up to 5% should be expected and 5% contraction of (111) face. This results in corresponding change in values of their elastic moduli, compared to those of bulk single crystal diamonds.

Adsorption of atomic hydrogen on defect sites of graphite: Influence of surface reconstruction and irradiation damage

The influence of surface reconstruction and defects due to irradiation damage on the trapping of hydrogen in nuclear graphite has been investigated at the ab initio level. Several models of defects and surfaces have been studied and compared with previously proposed traps, i.e. the zig zag edge of dislocation loops and reconstructed surfaces of graphite crystallites. The relative stabilities of hydrogen adsorption on the (100), (110), and (001) graphite basic planes have been evaluated for different amounts of hydrogen coverage and various types of reconstruction. The unreconstructed (100) surface adsorbs hydrogen the strongest. The (100) and (110) surface reconstructions result in a decreased stability for H adsorption compared to unrelaxed surfaces. Point defects caused by irradiation, such as mono- and divacancies, also trap hydrogen. We find that extended defects are weaker traps than monovacancies. This is true for surface defects as well as for bulk defects. The obtained results show that the existing hypothesis for trapping at dislocation loops has to be refined. Finally, an agreement with experiments is obtained for trapping on the reconstructed surfaces.

Influence of surface reconstruction on dopant incorporation and transport properties of GaAs(Bi) alloys

We report on the influence of surface reconstruction on silicon dopant incorporation and transport properties during molecular-beam epitaxy of GaAs(Bi) alloys. GaAs(Bi) growth with an (n × 3) reconstruction leads to n-type conductivity, while growth with a (2 × 1) reconstruction leads to p-type conductivity. We hypothesize that the presence or absence of surface arsenic dimers prevents or enables dopant incorporation into arsenic lattice sites. We consider the influence of bismuth anions on arsenic-dimer mediated dopant incorporation and the resulting electronic transport properties, demonstrating the applicability of this mechanism to mixed anion semiconductor alloys.

Glancing ion incidence on Si(100): Influence of surface reconstruction on ion subsurface channeling

We demonstrate that a Si target may exhibit the phenomenon of subsurface channeling for glancing incidence ions. To this end, we perform molecular-dynamics simulations of 3 keV Ar${}^{+}$ ion impact at grazing incidence (${83}^{\ensuremath{\circ}}$ toward the surface normal) on a Si (100) surface. Both an unreconstructed and a ($2\ifmmode\times\else\texttimes\fi{}1$) dimer-reconstructed surface are investigated. In both cases, the ion is reflected from the flat terrace and creates neither damage nor sputtering. The situation changes when a surface step is introduced on the surface; ion incidence in the vicinity of the step induces both damage and sputtering. We find that the phenomenon of subsurface channeling plays a dominant role in damage creation at the step edge. Subsurface channels aligned in the $\ensuremath{\langle}110\ensuremath{\rangle}$ direction are created under the reconstructed surface; they run parallel to the dimer rows. If the ion incidence geometry is favorable---incidence azimuth aligned along $\ensuremath{\langle}110\ensuremath{\rangle}$ and the ion approaching an unbonded B step---the ion can enter these channels. Without surface reconstruction no subsurface channeling can occur. Subsurface-channeled ions generate peculiar surface damage patterns which may allow their identification in experiment.

Low spin moment due to hidden multipole order from spin-orbital ordering in LaFeAsO

This work presents new development and applications of ab-initio simulation tools for material science. Focus lies on materials with strong electronic correlation and strong spin-orbit coupling. Improvements on methods for solving the impurity problem in LDA+DMFT is presented, as well as a reliant method for charge self-consistency in a LMTO based electronic structure code. A new adaptive scheme for Brillouin zone integration is developed, where we show a strong reduction of numerical noise compared to standard techniques. A reformulation of the standard LDA+U method aiming to reduce the number of free parameters is introduced. Fast and realistic reduction of the number of free parameters provides the possibility of high throughput calculations and enabled us to study a large number of compounds. An analysis method for polarization in terms of coupled multipoles, and their corresponding energy contributions is developed and applied. This led to the formulation of Katt's rules, a set of rules complementary to Hund's rules. Katt's rules applies for occupying the orbitals of an electronic shell with strong spin-orbit coupling. The analysis is also used to investigate the unconventional Uranium based superconductors URu2Si2, UPt3, UPd2Al3 and UNi2Al3, as well as the high temperature superconductor LaOFeAs. We also investigate the non-magnetic delta-phase of Plutonium, providing insight to the electronic structure and the branching ratios of 4d to 5f transitions seen in photo emission spectra.The influence of surface reconstruction on the magneto crystalline anisotropy is investigated in multilayer Fe/ZnSe, showing that Fe deposited on an unreconstructed interface strongly reduces the uniaxial component of the MAE. We provide a detailed understanding of the magnetic properties of Fe2P, opening possible routes for enhancing the MAE in this system. A general route to strong MAE in nano-laminates is presented, we apply this to propose a candidate with extremely strong anisotropy energy density, 5Fe/2W1-xReX for x=[0.6-0.8].

Influence of the surface reconstruction on the growth of InP on SrTiO 3(0 0 1)

A study of the epitaxial growth of InP on SrTiO 3(0 0 1) (STO) substrates is presented. Reflection high energy electron diffraction (RHEED) and X-ray diffraction experiments evidence the strong influence of STO surface reconstruction on the InP crystalline orientation. When grown on unreconstructed (0 0 1) STO surfaces, the InP lattice has its [1 1 1] direction perpendicular to the growth plane. When grown on (2×1) reconstructed STO surfaces, InP is (0 0 1) oriented on the (0 0 1) STO substrate. In both cases, at least one [1 1 0] InP in-plane direction is aligned to one of the [1 0 0] STO direction.

The Influence of Surface Reconstruction on Arsenic Incorporation Processes During MBE of GaAs

The incorporation factors of arsenic (SAs) for As2 and As4 molecular flux during GaAs MBE were detected. It has been determined that SAs does not depend on the arsenic molecular forms in incident flux. The correlation between SAs and reconstruction state of GaAs(001) grown surface have been shown. The maximal values of SAs for GaAs(001)-(4×2) and - (2×4) surfaces are characterized by 0.42 and 0.72, respectively. The dependences of arsenic incorporation rate and SAs during GaAs MBE versus substrate temperature (Ts) and incident flux density were obtained

Diffusion of Particles Adsorbed on a Reconstructive Surface

The influence of surface reconstruction on diffusion of particles, adsorbed on the surface, is investigated in the framework of symmetrical four-position model. The analytical expressions for the free energy and chemical and jump diffusion coefficients are obtained assuming the lateral interaction between the particles is negligibly small. The coverage dependencies of the tracer, jump and chemical diffusion coefficients are calculated using the expressions and MC simulations. The results demonstrate clearly a drastic change of the behavior of all diffusion coefficients on the reconstructed surface.

Compressive and tensile stress in colloidal CdSe semiconductor quantum dots

Compressive and tensile stress in colloidal CdSe quantum dots (QDs) is examined using resonance Raman spectroscopy. We find that the dispersion of the longitudinal optical phonon mode with size does not follow theoretical calculations based on phonon confinement models. To account for these deviations, the presence of compressive or tensile stress in the QDs is proposed. The influence of surface reconstruction on QD behavior is evidenced by differences in hexadecylamine (HDA) and trioctylphospine oxide (TOP/TOPO) passivation. We find that CdSe QDs passivated by HDA exhibit compressive stress, while CdSe QDs passivated by TOP/TOPO exhibit tensile stress. Evidence is provided that the CdSe-HDA QD stress is directly to a passivant driven surface reconstruction effect.

Formation of Si/Ge nanostructures at surfaces by self-organization

The growth of kinetically self-organized 2D islands in Si/Si(111) epitaxy is described. Theisland size distribution for this system was measured using scanning tunnelling microscopy(STM). The influence of surface reconstructions on growth kinetics is studieddirectly using a method of simultaneous deposition and STM scanning. For the caseof growth of Si islands on Si(111), lateral growth of rows of the width of the7 × 7 reconstruction unit cell at the edges of two-dimensional islands leads to the formation of‘magic’ island sizes. The evolution of the size and shape of individual {105} faceted Geislands (hut clusters) on Si(001) is measured during growth. A slower growth rate isobserved when an island grows to larger sizes. This behaviour can be explained bykinetically self-limiting growth. The potential formation of thermodynamically stablestrained islands of a specific size is discussed. The formation of 2D Si/Ge nanostructures atpre-existing defects is studied. The step flow growth mode is used to fabricate Si and Genanowires with a width of 3.5 nm and a thickness of one atomic layer (0.3 nm) byself-assembly. One atomic layer of Bi terminating the surface is used to distinguish betweenthe elements Si and Ge. A difference in apparent height is measured in STMimages for Si and Ge. Also different kinds of two-dimensional Si/Ge nanostructuresuch as alternating Si and Ge nanorings having a width of 5–10 nm were grown.

Diffusion of particles, adsorbed on a reconstructive surface

The influence of surface reconstruction on diffusion of adsorbed particles is investigated in the framework of simple two-position symmetrical model. Exact expressions for the free energy and diffusion coefficient are obtained neglecting the lateral interaction between the adsorbed particles. The critical behavior of the system is described by an anisotropic Ising spin model. The coverage dependencies of the chemical diffusion coefficient are calculated for different temperatures and interaction parameters. The dependencies show clearly the strong influence of the phase transitions, occurring in the system, on the particle migration. The chemical diffusion coefficient turns to zero at the critical points of the system.

The Influence of Surface Reconstruction and C-impurities on Photocatalytic Water Dissociation by TiO2

ABSTRACTTiO2 is well known as a prototype photocatalyst for water dissociation. To understand the mechanism of its photocatalytic water dissociation we performed first-principles calculations. We find that the surface of the catalytically favorable (TiO) termination is very different from the physically favorable (oxygen) termination. The calculated surface energy of the catalytically favorable (TiO) termination is about 10 times larger than that of the physically favorable (oxygen) termination. Analysis of the surface band structure suggests that while O-vacancies are intrinsic active sites for water dissociation into H2 and O2 gas, they are not essential for photocatalytic water dissociation. We also find that carbon impurities decrease the band-gap of TiO2, in agreement with previously reported experimental results. Moreover, we identify the origin of the arcane “double band gap” in carbon doped TiO2. The two onsets seen in the photoabsorption spectrum result from excitations from two of three C p-states within the band gap, not from domains of different composition.

SYMMETRY IN THE DIAGONAL SELF-ASSEMBLED InAs QUANTUM WIRE ARRAYS ON InP SUBSTRATE

Diagonal self-assembled InAs quantum wire (QWR) arrays with the stacked InAs/In 0.52 Al 0.48 As structure are grown on InP substrates, which are (001)-oriented and misoriented by 6° towards the [100] direction. Both the molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE) techniques are employed. Transmission electron microscopy reveals that whether a diagonal InAs QWR array of the stacked InAs/InAlAs is symmetrical about the growth direction or not depends on the growth method as well as substrate orientation. Asymmetry in the diagonal MEE-grown InAs QWR array can be ascribed to the influence of surface reconstruction on upward migration of adatoms during the self-assembly of the InAs quantum wires.

Co deposition on Au(111) and Au(100) electrodes: an in situ STM study

The initial stages of Co deposition onto Au(111) and Au(100) electrodes have been investigated by cyclic voltammetry and in situ scanning tunnelling microscopy (STM). Special emphasis was placed on the nucleation behaviour at surface defects such as monoatomic high steps. Depending on the crystallographic orientation of the substrate and on the electrochemical parameters, either three- or two-dimensional growth has been observed. Because Co deposition occurs at potentials, at which gold surfaces are reconstructed normally, the influence of surface reconstruction on the nucleation-and-growth behaviour is addressed briefly.

The influence of surface reconstruction on the collective motion of adsorbed atoms

The effect of adsorbate-induced surface reconstruction on the motion of adsorbed particles is analyzed by means of Monte Carlo modeling. The reconstruction is assumed to be the order–disorder phase transition that is described by the two-position model introduced by A.V. Myshlyavtsev et al. [J. Chem. Phys. 92 (1990) 3909]. The lattice gas model is used to mimic the hydrogen adsorption on the (001) face of tungsten [H/W(001)], which presents a c(2×2) structure below the critical temperature, T c. The phase diagram of the real system is reproduced only at low coverages ( θ<0.25). One of the principal features of the model is that the critical temperature can either increase or decrease with coverage, depending on the relation of the parameters which describe the system. In addition, different ordered phases, such as c(2×2) and (2×1) can be present according to the characteristics of the metal–metal, J NN, adsorbate–adsorbate, ε NN, and adsorbate–metal, λ NN, interactions. Utilizing Monte Carlo simulations we characterize how the behavior of the chemical, D, the jump, D J, and the tracer, D *, diffusion coefficients depend on the different ordered phases predicted by the model. In order to calculate the chemical diffusion coefficient we apply the fluctuation and Kubo–Green methods. Surface diffusion is strongly anisotropic for the (2×1) ordered phase, indicating that it is facilitated in one direction and reduced in another.

The effect of surface reconstructions on the surface morphology during in situ etching of GaAs

The influence of surface reconstructions on the surface morphology during in situ layer-by-layer etching of GaAs(001) has been studied based on the observation of reflection high-energy electron-diffraction measurements. For the etching, AsBr3 is used as a reactive source etchant under solid source molecular beam epitaxy conditions, focusing on a high temperature region in which the etching rate is limited by a supply rate of AsBr3 resulting in a constant value. Despite the fact that the etching starts on a layer-by-layer basis, an initially smooth surface turns considerably rougher depending on the stoichiometry associated with the surface reconstruction. The best morphology after a removal of 250 nm is obtained in the Ga-rich (3×1) reconstruction region close to the phase transition boundary to the As-rich (2×4). This is also verified by the measurement of scanning electron microscopy and atomic force microscopy.

Influence of surface reconstruction on MBE growth of layered GaSe on Si(111) substrates

Very thin GaSe films, about 100 Å thick, have been epitaxially grown by molecular beam epitaxy on differently ordered Si(111) substrates, namely: the clean 7 × 7 reconstructed surface with its dangling bonds, the H-passivated 1 × 1 surface and the Ga-passivated 3 × 3 R30° reconstructed one. For each substrate, the GaSe layer and its interface with Si have been studied by low energy electron diffraction, Auger electron spectroscopy and photoemission yield spectroscopy. Upon sequential removal of the GaSe film by Joule heating in ultrahigh vacuum, it is shown that, (i) the band offsets are not sensitive to the initial surface structure of the substrate, (ii) the uniformity of the GaSe layer and of the Fermi level position is questionable on Si(111) 3 -Ga , (iii) the density of gap states in the GaSe layer increases upon ageing in air.

Exact results for adatom migration on a reconstructive surface

The influence of surface reconstruction on adatom diffusion is investigated in the framework of anisotropic Ising model. The exact expressions for diffusion coefficient are obtained for an ordered and disordered phase of the surface. Dependences of the diffusion coefficient on the adatom concentration and interaction parameters are discussed. It is shown that the region of critical slow down of the diffusion is extremely small. Consequently, it is hard to test predicted dependences experimentally or by numerical simulation. We discuss shortly possible experimental technique for investigation of the critical behaviour of surface diffusion coefficient.

The influence of surface reconstructions on the CO oxidation reaction rate for the [formula omitted] surface

The influence of the oxygen induced surface reconstructions on the CO 2 production rate at the Ag(110)O system will be discussed, based on titration, reactive thermal desorption and LEED measurements. We present evidence that the reactivity of oxygen is reduced in the temperature range of 190–250 K by embedding oxygen in a reconstructed surface as compared to chemisorbed oxygen; above 250 K the coverage dependence of the oxygen induced reconstructions generates an autocatalytic component into the CO 2 formation rate.