Effect Of Surface Reconstruction Research Articles

Growth mechanisms of diamond crystals and films prepared by chemical vapor deposition

Diamond crystals and films were prepared either by hot-filament-assisted or microwave-plasma-assisted CVD techniques. Depending on the technique used and on the synthesis parameters, modifications of diamond crystal habit were observed and are analyzed by considering the growth mechanisms of (111) and (100) faces. Consequently, film surfaces with either predominantly (111) faces or only (100) faces were obtained. Effects of surface reconstruction, defect inclusions and etching are considered in view of modifying the relative 〈111〉 and 〈100〉 growth rates and thus the crystal and film surface morphologies.

The effect of surface reconstruction on the capacitance of Au(100) surfaces

The effect of reconstruction of the Au(100) surface on the double-layer capacity was measured using standard ac methods combined with UHV surface preparation and ex situ structure analysis. The (5 × 20) reconstruction present on the UHV-prepared surface was found to be stable in dilute HClO 4 over a wide range of electrode potential. In dilute H 2SO 4, the (5 × 20) reconstruction was lifted at potentials near the pzc by specific adsorption of HSO − 4 even when the anion was present at very low concentrations, eg 10 −5 M. In 0.01 M HClO 4, the reconstruction was lifted only at potentials 0.2 V positive of the pzc, and was restored when the potential was made ca 0.1 V negative of the pzc for the (1 × 1) surface, ie the (5 × 20) ⇋ (1 × 1) transformation was quasi-reversible in dilute HClO 4. Atomic scale roughness, eg steps, appeared to lower the stability of the (5 × 20) structure. The capacity curve for the (5 × 20) reconstructed surface was dramatically different from that of the (1 × 1) surface, with a negative shift in the pzc of ca 0.2 V following the transformation (5 × 20) → (1 × 1), and a decrease in the capacitance of 20–25%, approximately equal to the change in atomic density of the surface. The vacuum work functions (Φ) of the emersed (5 × 20) and (1 × 1) suraces were measured using photoemission spectroscopy, and found to be 5.30 ± 0.05, and 5.05 ± 0.05 eV, respectively, which gives a ΔΦ consistent with the relative values of the pzcs. Our results were consistent in every respect with the previous findings of Kolb and co-workers on the effect of reconstruction on the double-layer capacity of Au(100) surfaces.

Use of surface grooves to control ordering in GaAsP

GaAs1−xPx with 0.4≤x≤0.85 forms the CuPt ordered structure during organometallic vapor phase epitaxy (OMVPE). Only the (1̄11) and (11̄1) variants are observed for growth on (001)-oriented substrates. The mechanism by which ordering occurs is only now being discovered. Total energy calculations, including the effects of surface reconstruction, indicate that the phenomenon can be explained purely on the basis of energy considerations. Indirect evidence indicates that kinetic factors, including processes occurring at steps propagating across the surface in the two-dimensional growth mode, control ordering. In this work, GaAs1−xPx layers have been grown by OMVPE on (001)-oriented GaAs0.6P0.4‘‘substrates.’’ In order to examine the effects of surface kinetic factors, the substrates were first patterned with [110]-oriented grooves 5 μm wide and a fraction of a micron deep. The groove is used to provide a source of steps moving in opposite directions from the two edges. Transmission electron diffraction reveals the formation of large domains of the two variants that meet in the center of the groove. A surprising feature is the presence of a region in the groove with absolutely no ordering. Tracing the surface shape during growth using a superlattice structure indicates that the disordered region is due to growth on {511} facets. The domains formed after the groove is filled are very large, several square microns in cross-sectional area and extending along the entire length of the groove. These results demonstrate that natural ordering in GaAsP, an alloy with mixing on the group V sublattice, can be controlled by regulating the propagation of steps during growth, exactly as for GaInP where mixing is on the group III sublattice.

Anomalous surface phonons of the reconstructed Au(111): A molecular-dynamics simulation.

The dynamical behavior of the reconstructed Au(111) surface is studied by a molecular-dynamics simulation based on a well-tested many-body force model for gold. By calculating the surface spectral densities through time-dependent correlations of molecular-dynamics trajectories, we have constructed the surface-phonon dispersion curve of the reconstructed Au(111) surface. The results are in excellent agreement with the measured surface vibrational spectra, and yield important information on the effect of surface reconstruction on the observed anomalous surface phonons.

Comment on "Effect of surface reconstruction on stability and reactivity of Si clusters"

A Comment on the Letter by Kaxiras, Phys. Rev. Lett. 64, 551 (1990).Received 10 September 1990DOI:https://doi.org/10.1103/PhysRevLett.66.2686©1991 American Physical Society

Adhesion and bonding of polar and non-polar SiC surfaces to Ti(0001)

The atom superposition and electron delocalization molecular orbital calculations have been performed for studying the interfacial bonding and adhesion of some polar and nonpolar surfaces of α- and β-SiC with the close-packed Ti(0001) surface, using large cluster models and idealized structures. Polar SiC surfaces studied in this work are the Si- and C-terminated (111) and (100) planes and the nonpolar surfaces with equal concentration of Si and C, i.e., β-SiC(110), α-SiC(101̄0) and α-SiC(112̄0). For the unrelaxed polar SiC surfaces, the average Si/Ti and C/Ti interfacial bond strengths are maximum for the β-SiC(110)/Ti(0001) interface due to two dangling surface state orbitals on each surface atom in place of one on the (111) SiC surfaces. The Si- and C-terminated (100) surfaces undergo dimerization. Adhesion energies for the (111) and (100) surfaces to Ti(0001) are comparable when surface relaxation and reconstruction effects are considered. Nonpolar α- and β-SiC surfaces bind comparatively weakly to titanium, and their adhesion energies to Ti(0001) are all approximately equal. In each case of interfacial bonding the sp hybridized dangling orbitals on Si and C surface atoms are stabilized by bond formation with Ti 3d band orbitals.

Surface phenomena in RHEED and REM

Based upon previous results for the Bloch-wave solution in the Bragg case and the consistency between the Bloch-wave solution and multislicing in the Bragg case, a complete numerical solution has been developed for reflection electron diffraction called the Bloch wave and multislice combined for reflection (BMCR) method. Results are presented of applying the BMCR method to several problems in high-energy electron reflection. First, simulations of the effects of surface reconstruction and adsorption on RHEED patterns are reported. Next, the results of simulations of surface steps are shown and their effects on the wave field analyzed numerically. Last, the existence of the surface wave which is related to electron surface resonance phenomena is demonstrated.

Effect of surface reconstruction on the apparent Arrhenius parameters for desorption

The effect of adsorbate-induced surface reconstruction on the apparent pre-exponential factor and activation energy for desorption is analyzed and discussed. The reconstruction is assumed to be a continuous displacive phase transition caused by a Fermi surface instability. The adsorbate-induced changes in the surface are shown to result in a rather strong (of the order of 10 2) coverage dependence of the pre-exponential factor for desorption. The direction of the variation is in accordance with the compensation effect (the pre-exponential factor and activation energy decrease with increasing coverage.

In-situ infrared spectroscopy of CO adsorbed at ordered Pt(110)-aqueous interfaces

Surface infrared spectra in the terminal CO stretching region are reported for CO adsorbed on ordered Pt(110) in 0.1 M HClO 4 as a function of CO coverage, θ (0.05 ≲ θ ≲ 1.0) and electrode potential, E (−0.25 V ⩽ E < 0.2 V versus SCE), primarily to explor the effects of coverage-dependent surface reconstruction. Substantial differences in the coverage-dependent CO stretching frequency, ν ι CO, were observed for CO adlayers formed directly by dosing from suitably dilute solution concentrations (~ 2 × 10 −5 M), and by partial electrooxidative removal (“stripping”) from saturated irreversibly adsorbed layers. The latter procedure typically yielded only small (≲ 5 cm −1) decreases in ν ι CO and essentially constant bandwidth (FWHM ≈ 11 cm −1) from θ = 1.0 to 0.1, the presence of coadsorbed hydrogen (at −0.25 V) and with coadsorbed water (at 0.05 V). This indicates that large domains (“islands”) of close-packed CO remain on patches of (1 × 1) substrate even down to low average coverages under these conditions. For CO adlayers formed by means of the former (“dosing”) procedure at 0.05 V, however, a separate lower-frequency ν CO band (at 2030–2052 cm −1) appears for θ ≲ 0.6, supplementing the higher-frequency feature (at 2060–2072 cm −1) and supplanting it for θ ≲ 0.4. The lower-frequency ν CO band is attributed tentatively to CO bound within (1 × 2) reconstructed Pt(110) domains, having smaller local coverages (i.e. packing densities). Voltammetric electrooxidation of this low-frequency ν CO form, as deduced from simultaneous infrared and electrochemical measurements, occurs at significantly (0.1–0.15 V) lower overpotentials than for the high-frequency form. The corresponding ν ι CO−θ behavior in the presence of coadsorbed hydrogen (i.e. at −0.25 V) is substantially different, a single ν CO band exhibiting a continuous frequency decrease from 2072 (θ = 1.0) to 2005 cm −1 (θ ≈ 0.1) being obtained. Qualitatively similar ν ι CO−θ behavior was also observed in the presence of adsorbed sulfate or chloride anions. This is attributed to co-adsorption yielding a wider and more θ-dependent distribution of CO island sizes. Significant differences are noted with the corresponding infrared spectra observed for the Pt(110)/CO in UHV at 300 K, with regard to the ν CO frequency-, band intensity-, and bandwidth-θ dependencies. The absolute ν ι CO values for the electrochemical and UHV systems also differ when they are compared at the same surface potential. These differences are attributed both to the effects of the double-layer field and to co-adsorbing components on the structure of the electrochemical CO adlayer.

Resonant raman scattering induced by pressure tuning of bulk and colloidal microcrystallite cadmium sulfide

Abstract We have used Resonant Raman scattering induced by pressure tuning to study the phase transition of bulk and 40–80 A colloidal microcrystallite CdS. The experimental results show that the bulk CdS undergoes a well defined first order phase transition at 27 kbar and the intensity of the Raman scattering increases sharply when the level of the intermediate state (bound exciton I2) is close to the photon energy. After the phase transition no Raman scattering and photoluminescence can be observed. However, the phase transition in the colloidal CdS is quite different from the bulk CdS and the phase transition occurs over a large pressure region up to 50 kbar. We attribute this different pressure behavior in colloidal CdS to the effect of surface reconstruction and large surface distortion energy of the small particles.

The effect of adsorbate-induced surface reconstruction on the apparent Arrhenius parameters for desorption

The effect of adsorbate-induced surface reconstruction on the apparent preexponential factor and activation energy for desorption is analyzed and discussed. The reconstruction is assumed to be a continuous order–disorder phase transition. The adsorbate-induced changes in the surface are shown to result in a rather strong (of the order of 102) coverage dependence of the preexponential factor for desorption. The direction of the variation is in accordance with the compensation effect (the preexponential factor and the activation energy decrease with increasing coverage).

Effect of surface reconstruction on stability and reactivity of Si clusters.

It is proposed that ``magic number'' Si clusters of intermediate size correspond to structures in which exactly all surface atoms participate in reconstructions similar to bulk-Si surfaces. Models are given for the experimentally observed stable clusters of 33 and 45 atoms, which display features similar to the 7\ifmmode\times\else\texttimes\fi{}7 and 2\ifmmode\times\else\texttimes\fi{}1 reconstructions of the Si(111) surface. The nature of bonding in the energy-optimized atomic geometries is revealed, through first-principles electronic structure calculations, to be covalent.

The effect of adsorbate-induced surface reconstruction on the apparent arrhenius parameters for desorption

The effect of adsorbate-induced surface reconstruction on the apparent preexponential factor and activation energy for desorption is discussed. The reconstruction is assumed to be a continuous phase transition. The adsorbate-induced changes in the surface are shown to result in a rather strong (of the order of 10 2) coverage dependence of the preexponential factor for desorption. The direction of the variation is in accordance with the compensation effect (the preexponential factor and the activation energy decrease with increasing coverage).

Adsorption of atomic oxygen on the Si(100) surface

Previous studies on the oxidation of Si(100) have neglected the effects of surface reconstruction. Using total energy methods within a restricted Hartree-Fock framework the authors explicitly include the effects of reconstruction on the adsorption of atomic oxygen on this surface. A new low-coverage 2*1 structure has been found in which the Si surface-subsurface bonds are tilted by about 12 degrees with respect to the surface normal. This structure reverts to a 1*1 as the oxygen coverage increases in agreement with experimental predictions.

The effect of adsorbate-induced surface reconstruction on the apparent arrhenius parameters for desorption

The surface reconstruction described in terms of the second-order phase transition theory, is shown to result in a decrease in the apparent pre-exponential factor for desorption in comparison with the value predicted on the basis of the standard transition state theory provided that adsorbed particles suppress the phase transition. If adsorbed particles facilitate the phase transition, the reconstruction leads to an increase in the pre-exponential factor. The effect may be strong (of the order of 10 ±4. The pre-exponential factors for CO desorption from the Ni(111), Ru(001) and Ir(110) surfaces are compared and discussed. The low value of the desorption pre-exponential factor for the latter surface is explained by the surface reconstruction.

The effect of adsorbate-induced surface reconstruction on the apparent arrhenius parameters for desorption

The surface reconstruction described in terms of the second-order phase transition theory, is shown to result in a decrease in the apparent pre-exponential factor for desorption in comparison with the value predicted on the basis of the standard transition state theory provided that adsorbed particles suppress the phase transition. If adsorbed particles facilitate the phase transition, the reconstruction leads to an increase in the pre-exponential factor. The effect may be strong (of the order of 10 ±4). The pre-exponential factors for CO desorption from the Ni(111), Ru(001) and Ir(110) surfaces are compared and discussed. The low value of the desorption pre-exponential factor for the latter surface is explained by the surface reconstruction.

Charge State Distributions of MeV He Ions Channeled through Thin Crystals with Atomically Clean Surfaces

Charge state distributions of He ions transmitted through self-supporting SnTe and Au single crystals with atomically clean surfaces are measured for the energy range 0.5–2.0 MeV. Anomalous reduction of He + fraction is observed at planar channeling conditions. This is explained by the position dependent electron-loss and -capture probabilities of channeling He ions calculated from the classical Bohr and Bohr-Lindhard models. The effect of surface reconstruction on the charge state distribution is also discussed.

The effect of adsorbate-induced surface reconstruction on diffusion of adsorbed particles

The effect of adsorbate-induced surface reconstruction on diffusion of adsorbed particles

Effects of strain and surface reconstruction on the kinetics of indium incorporation in MBE growth of InAs

Reflection high-energy electron diffraction and mass-spectrometry were used to study the incorporation behavior of indium (In) in the molecular beam epitaxy of InAs on InAs (001) and GaAs (001) surfaces. For InAs homoepitaxy the activation energy, E a, for In loss is found to be 4.0±0.1 eV; for the initial stages of strained (Δα/α=7%) InAs on GaAs heteroepitaxy, E a varies from 0.9 to 2.6±0.1 eV and depends only on surface reconstruction. These results are discussed in terms of bnding energetics and strain effects.

INVESTIGATION OF SURFACE PHONONS AT IDEAL, RELAXED AND 2×1 RECONSTRUCTED Si(lll) SURFACE

Using the perturbation method to study the influence of the coupling between occupied states and empty states on the electronic band energy, we obtained analytical expressions for semiconductor force constant calculation within the scheme of extended band orbital approximation. The surface phonon dispersion curves and related vibrational amplititude distribution of Si(111) ideal, 1×1 relaxed and 2×1 reconstructed Haneman model surfaces are calculated by means of these expressions. The results for different surfaces show the important effects of surface relaxation and reconstruction on the properties of surface phonons. It is also shown that the Haneman model for Si(111)-2×1 reconstructed surface can not explain the experimental surface phonon measurement very well.