Ffect of vacancies on the residual resistivity of ordered alloys with the face-centered cubic lattice

The paper permits a theoretical study of the effect of vacancies at the sites of the crystal lattice of a binary ordered substitutional alloy with the face-centered cubic lattice on its residual resistivity. The dependence of the electrical resistivity on the composition of the alloy and the temperature of annealing is studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 10, pp. 84–88, October, 1971.     

Strain hardening of alloys with face-centered cubic lattice

A brief review is given of the peculiarities of the strain hardening of face-centered cubic (fee) alloys as compared with pure metals. The fundamental equations connecting the strain hardening characteristics to the quantitative characteristics of the dislocation structure and the slip trace picture are considered in application to alloys with a high friction stress of a nondislocation nature _F. The shape of the strain hardening curves of alloy mono- and polycrystals is analyzed; it is shown that it depends substantially on the stress level F.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 132–150, August, 1976.     

Electrostatic response and surface electron states of a Ca(001) face-centered cubic film

The electron response of a Ca(001) face-centered cubic film to an external electrostatic field is calculated. The results of calculations are compared with the previously obtained data on the electron response of a Cu(001) film. The energy location of occupied and unoccupied excited surface states of the Ca(001) film is determined.     

Effect of impurities on the surface morphology of Fe(111)

The surface composition and morphology of Fe(111) have been examined through a combined analysis that includes low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and scanning tunneling microscopy (STM). The preferential segregation of sulfur has been clearly identified by AES upon annealing. The STM images exhibit numerous triangular pits of various sizes, and the LEED patterns show diffused n × 1 spots. The triangular pits reveal a Sierpinski gasket fractal. For sulfur-free Fe(111), nitrogen segregates to the surface upon annealing, forming a 4√3 × 4√3 superstructure that is identified by LEED patterns and STM images. The STM images show nanoscale triangular clusters regularly aligned in a hexagonal 4√3 × 4√3 configuration. Ultra-thin chromium film deposited on a nitrogen-segregated Fe(111) surface with post-annealing induces further nitrogen segregation, resulting in the formation of triangular pyramid-shaped CrN nanoclusters.     

Change in the lattice properties and melting temperature of a face-centered cubic iron under compression

All four parameters of the Mie–Lennard-Jones pair interatomic potential have been determined, and the state equation (P) and baric dependences of the lattice properties of an fcc iron are calculated using a previously proposed method. The dependences have been studied for the following properties: Debye temperature; the first, second, and third Gruneisen parameters; isothermal bulk modulus B _T and B′(P); isochoric specific heat C _v and C _v ′(P); isobaric specific heat C _p ; coefficient of thermal expansion α _p and α _p ′(P); specific surface energy σ and σ′(P). Calculations performed along two isotherms (1500 and 3000 K) have shown good agreement with the experimental data. Analytical approximations of the baric dependences for B′(P), α _p (P), C _p (P), and σ′(P) have been obtained, and it is shown that at P → ∞ the functions B _T (P) and σ(P) change linearly, while the functions α _p′(P) and C _p ′(P) tend to zero. The calculated baric dependence of the melting temperature shows good agreement with the experimental data.     

Templating a face-centered cubic (110) termination of C60

Scanning tunneling microscopy has been used to study C₆₀ overlayers on TiO₂(100)-(1 × 3). Initial adsorption preferentially occurs on O vacancies (Ti³⁺), evidencing a site-specific interaction dominated by substrate-adsorbate charge transfer. At saturation coverage the molecules are incommensurate with Ti³⁺ sites along [001], suggesting a delicate balance between intermolecular and substrate interactions. The unit cell of the C₆₀ overlayer is 13.8Å× 10.0 ± 0.5Å, consistent with the first layer of fcc C₆₀(110); molecules also adopt sites in the troughs of the (1 × 3) structure to form the second layer.     

On the spectral frequency distribution of translational vibrations in a face-centered cubic lattice of the C60 fullerite

The spectral frequency distribution g(ω) of translational lattice vibrations in the face-centered cubic phase of the C₆₀ fullerite at T = 300 K is calculated by the superposition method. The contribution from the translational vibrations to the heat capacity C _V of the C₆₀ fullerite and the x-ray characteristic temperature gJ_R entering into the exponent of the Debye-Waller factor are determined using the calculated frequency distribution g(ω). The results of the calculations are in good agreement with experimental data. It is noted that the librational and intramolecular lattice vibrations observed in the C₆₀ fullerite do not contribute significantly to the temperature-induced decrease in the x-ray diffraction intensity at T = 300 K. The Grüneisen parameters γ_mod calculated from the x-ray diffraction data are consistent with the thermodynamic Grüneisen parameters γ_lat at temperatures T ≤ 80 K but substantially exceed those at T ≈ 300 K. New x-ray diffraction experiments are proposed for independently determining the anomalously large negative values of the parameter γ₀, which is actually an orientational analog of the Grüneisen parameter.     

Influence of impurities on the surface structures and fault generation in homoepitaxial Si (111) films

In situ LEED studies of the homoepitaxial growth of Si(111) films by uhv sublimation, indicate a strong correlation between the type of surface structure generated and the metallic impurity content of the silicon substrates as estimated from minority carrier lifetimes. The development of the familiar Si (111)−7 × 7 structure is favored by the presence of lifetime-killing impurities in the substrate. Experiments where Fe is introduced on high lifetime substrates prior to annealing and film growth, suggest that this impurity species plays a role in the generation of the 7 × 7 surface structure. Electron microscopy reveals that homoepitaxial Si(111) layers are generally faulted, the number density of which increases progressively as the growth temperature is lowered and the deposition rate increased. Films deposited on high lifetime silicon contain substantially fewer stacking faults than those grown on low lifetime substrates. These results suggest that the faults originate at the substrate surface at microprecipitates consisting of fast diffusing, low solubility impurity species.     

Trivacancy recovery and formation of a cubic symmetry defect trap on111In impurities in Ni

Using perturbed angular correlations we studied the formation of a cubic symmetry defect trap in Ni near 350 K following plastic deformation at 295 K. The trap has been identified structurally as a trivacancy trap. The evolution of the defect-free and cubic trap site populations in the course of isochronal and isothermal annealing experiments leads to the conclusion that the cubic trap forms by simple trapping, and that the capture radius of the cubic trap for additional defects is very small.     

Effects of harmonic phase on nonlinear surface acoustic waves in the (111) plane of cubic crystals

Spectral evolution equations are used to perform numerical studies of nonlinear surface acoustic waves in the (111) plane of several nonpiezoelectric cubic crystals. Nonlinearity matrix elements which describe the coupling of harmonic interactions are used to characterize velocity waveform distortion. In contrast to isotropic solids and the (001) plane of cubic crystals, the nonlinearity matrix elements usually cannot be written in a real-valued form. As a result, the harmonic components are not necessarily in phase, and dramatic variations in waveforms and propagation curves can be observed. Simulations are performed for initially monofrequency surface waves. In some directions the waveforms distort in a manner similar to nonlinear Rayleigh waves, while in other directions the velocity waveforms distort asymmetrically and the formation of shocks and cusped peaks is less distinct. In some cases, oscillations occur near the shocks and peaks because of phase differences between harmonics. A mathematical transformation based on the phase of the matrix elements is shown to provide a reasonable approximation of asymmetric waveform distortion in cases where the matrix elements have similar phase.     

Hydrogen adsorption on the silicon (001) surface and on a step on the (111) surface

Adsorption of atomic hydrogen on an ideal (001) silicon surface is investigated in the present paper. Saturation of one of the two dangling bonds of a silicon atom on this surface by hydrogen removes the interaction (hybridization) between them, resulting in the appearance of a bonding and an antibonding chemisorption state associated with the attacked dangling bond, and in the shift of the peak of the remaining unsaturated dangling bond to the energy typical of a surface state of the (111) surface. Further saturation leads to the disappearance of this peak from the energy spectrum. An analogous situation occurs for the silicon atom with two dangling bonds on a step on the (111) surface, when hydrogen is chemisorbed. Both examples testify to the local chemical nature of Shockley surface states in silicon.The authors thank A. N. Sorokin for useful discussions.     

Vibrational properties of the adsorbed monolayer on face-centered cubic crystals

Calculations of mean-square displacements 〈u²〉 of the atoms in adsorbed monolayers on fcc crystals are presented and compared with LEED experimental results. This text is restricted to the case of a C(2 × 2) adsorbed layer on a (100) surface [experimental case of Ni(100) with adsorbed sulfur, sodium, cesium or oxygen]. 〈u²〉's perpendicular to and parallel to a (100) surface are calculated for the adsorbed atoms and the atoms of the first surface layer of the crystal. The values obtained are compared with those for a clean (100) surface and the volume of the crystal. Every possibility for force constants between adsorbate and substrate atoms is examined. It is shown that the measurement of 〈u²〉 perpendicular to the (100) surface yields the adsorbate-substrate force constants and that 〈u²〉 parallel to the (100) surface yields the adsorbate-adsorbate force constants.     

The effects of hidden impurities on the reactivity of a Pt(111) crystal

The interaction of water with a Pt(111) surface contaminated with Si has been examined by thermal desorption spectroscopy (TDS), work function (Δφ) and sticking coefficient measurements. Water is found to dissociate on the contaminated surface when all traces of oxide have been removed. When the silicon is oxidized, no water dissociation is observed and desorption order apparently changes from one to zero. A model is discussed which explains observed sticking coefficient changes and thermal desorption spectra in terms of island size.     

Laser-induced graphitization on a diamond (111) surface

We report an atomistic simulation study of laser-induced graphitization on the diamond (111) surface. Our simulation results show that the diamond to graphite transition occurs along different pathways depending on the length of the laser pulse being used. Under nanosecond or longer laser pulses, graphitization propagates vertically into bulk layers, leading to the formation of diamond-graphite interfaces after the laser treatment. By contrast, with femtosecond (0.2-0.5 ps) laser pulses, graphitization of the surface occurs layer by layer, resulting in a clean diamond surface after the ablation. This atomistic picture provides an explanation of recent experimental observations.     

Oxygen adsorption on a Pd(111) surface

The interaction of oxygen with Pd(111) has been studied by means of AES, ELS, thermal desorption (TD), electron stimulated desorption (ESD) and work function measurements. It was found that a very small part ( ～ 2–3%) of the available adsorption sites are contributing to the O⁺ electron stimulated yield, the population of the latter being accompanied by enormously large work function changes (up to ～ 0.9 eV). A mechanism of adsorption and depopulation of these sites involving oxygen bulk and surface diffusion has been proposed.     

The Tamm surface state on Cu(111) and Ag(111)

It is shown, that the well-known d-electron Tamm surface-state emission observed in photoelectron spectra from Cu(111) at the M̄ point in the surface Brillouin zone, is indeed due to such a surface state and not a bulk band transition as recently suggested L. Wallden, Solid State Commun. 59, 205 (1986). A similar surface state on Ag(111) is reported.