Applications of Surface Science最新文献

The two-dimensional ordering in second stage alkali-metal-graphite intercalation compounds is investigated. It is shown that all hexagonal incommensurate metal lattices form commensurate superlattices. Using this, the observed orientational ordering is modelled by the simple condition that the experimental structure is a superlattice with a local minimum (varying the incommensurate lattice dimension) of the average distance of the metal atom from its nearest graphite hexagon centre. This approach is used in a detailed study of the diffraction pattern of the low temperature phase of second stage rubidium graphite.

Reduction in the scattering losses of ZrO₂, Al₂O₃, CeO₂ and Ta₂O₅ waveguides fabricated on BK-7 glass substrates using ion-assisted evaporation techniques has been achieved. The lowest losses have been observed for an Al₂O₃ ion-assisted film using 1200 eV O₂¹. These losses are of the order of 2–5 dB cm⁻¹ and compare with > 15–20 dB cm¹ for evaporated guides produced without ion assistance.

The resonant reaction $\text{H}\text{(}{}^{19}\text{F}\text{,αγ)}{}^{16}\text{O}{}^{\mathrm{\ast }}$ was used to study the hydrogen content and distribution with depth in a-Si : H films. The films were prepared in a DC magnetron by glow discharge decomposition of silane at a pressure of 1 Pa. The results showed that a surface hydrogen peak was present for a film prepared at 310°C but disappeared when the films were prepared at 370°C. The total hydrogen content was one half of that calculated using infrared absorption spectroscopy. RBS was used to determine the film density and scanning electron microscopy was used to investigate microstructure.

ZnTe films of about 15 nm thickness were prepared by vacuum deposition from ZnTe power onto NaCl substrates heated to 300°C. Zinc oxide particles with a size of 5 nm which were formed on the surface of ZnTe crystals showed no epitaxial relationship with the latter. Tellurium crystals appeared on certain parts of the ZnTe crystals with specific epitaxial relationships such as $\text{(0}\text{1}\text{1}\text{1}\text{)[10}\text{1}\text{0]}\text{Te}\text{(111)[110]}\text{ZnTe and}\text{(0}\text{1}\text{1}\text{1}\text{)[10}\text{1}\text{0]}\text{Te}\text{(0001)[10}\text{1}\text{0]}\text{ZnTe}$. Oxidation of the (110) surfaces of ZnTe crystals are slower than for any other plane. Images of the (110) films at an initial stage of oxidation contained faint superlattice fringes of about 0.85 nm spacing. On the basis of the matching between the HREM images and computer simulation images, the origin of the fringes was attributed to a periodic array of Zn vacancies introduced by the diffusion of Zn atoms to the surface of the ZnTe crystal.

Adsorption of ethylene on the (110) surface of palladium at 110 K gives rise to two related but clearly distinguishable types of electron energy loss (EEL) spectra corresponding to low and high coverage. Most features in the spectra in both coverage regimes can be interpreted in terms of a π-complex of ethylene with the metal surface. Analysis of the corresponding ethylene-d₄ EEL spectra and comparison with infrared, Raman and inelastic neutron scattering data for the analogous ethylene complex, Zeise's salt, supports this assignment. The selection rules applicable to dipole and impact scattering both on- and off-specular are employed to determine the orientation of the π-complexes with respect to the surface. At higher coverages additional loss features are observed. These are interpreted in terms of the presence of a small proportion of σ-diadsorbed ethylene complexes bonded to pairs of metal atoms.

The two-hole and the two-electron spectra, which are related to the XVV Auger and to the APS spectra, respectively, have been computed for an Fe-Ni alloy of different compositions. A recently proposed theory has been used which, by means of some approximations, is capable of treating the two-particle spectra of a Hubbard-type Hamiltonian in the important case of a not completely filled valence band. In that situation, the role of the Coulomb repulsion between two particles is quite relevant in determining shifts and broadenings of the spectra. The Coulomb correlation results also in a renormalization of the one-particle spectrum. The results show that, while the Auger spectra are contributed to by both spin up and spin down bands, the APS spectra are contributed to only by spin down bands.

The chemisorptive interaction of the CO/Cu(100) system is studied with a Cu₅(1,4)CO cluster model using the constrained space orbital variation (CSOV) analysis. This analysis has been used previously to examine the origin of the CO-metal bond and to show that the energetic importance of the metal to CO π donation is larger than that of the CO to metal σ donation. In the present work, we use it to determine the origin of the differential CO 5σ ionization potential shift observed in the photoemission spectra of CO/Cu(100). This shift is shown to be largely due to electrostatic, environmental potential effects. It does not indicate the nature of the CO-metal bond but does indicate the CO adsorption geometry.

The backscattering factor is the most important parameter for matrix effect corrections in quantitative Auger analysis. Some of the methods previously published are reviewed. A new method is described for determining the backscattering factor using information provided by the background which is usually ignored in an Auger spectrum. Complicated calculations such as The Monte Carlo method were avoided, and the accuracy might be further improved since both the intensity of Auger electrons and the energy distribution of backscattered electrons were obtained under the same experimental conditions. The results are illustrated by a quantitative analysis of two copper alloys, Au-Cu and Ag-Cu.

Surface and subsurface compositional changes in Au-Cu alloys and thin films sputtered with 2 keV Ar, Xe, Ne and Kr ions were observed with low energy (60 eV for Cu and 69 eV for Au) and high energy (239 eV for Au and 920 eV for Cu) Auger peaks at temperatures between liquid nitrogen and room temperature. For a Au_0.56Cu_0.44 alloy, Au enrichment at the surface and depletion beneath the surface was observed with high energy as well as low energy Auger peaks. But the compositional change assessed with low energy Auger peaks is greater than that assessed with high energy peaks. This was also calculated with the simulation of sputtering including ion radiation-enhanced segregation and diffusion. This shows clearly that the Gibbsian segregation plays an important role in composition changes at the surface and subsurface of the ion-sputtered alloy. Compositional changes of Au-Cu thin film alloys prepared by the co-evaporation technique were also observed following sputtering with Ar, Xe, Ne and Kr. Except in the case of Xe, the coevaporated composition was preserved during sputtering at low temperatures (<-120°C).

C40-type, hexagonal VSi₂, MoSi₂ and WSi₂ have been grown epitaxially on (111)Si. V, Mo or W thin films, 250–300 rA in thickness, were electron gun deposited on (111)Si. Epitaxial growth of metal disilicides were induced by thermal annealing in vacuum. For VSi₂ on (111)Si, epitaxial regions, 1–2 μm in size, were found to grow in samples 400–1000°C two-step annealed. MoSi₂ grains, 0.2–2 μm in size, were observed to grow epitaxially on (111)Si following 1100°C annealing. WSi₂ epitaxy, 0.4–1.2 μm in size, on (111)Si was obtained in samples annealed at 1050–1100°C. The orientation relationships between these metal silicides MSi₂ and substrate Si were determined to be $\text{(0001)}\text{MSi}{}_2\text{(111)}\text{Si}\text{, (22}\text{4}\text{0)}\text{MSi}{}_2\text{(22}\text{4}\text{)}\text{Si}$ and $\text{(20}\text{2}\text{0)}\text{MSi}{}_2\text{(20}\text{2}\text{)}\text{Si}$. Regular interfacial dislocation networks were observed at silicides/Si interfaces. The dislocations were identified to be of edge type with ₆¹〈112〉 Burgers vectors. The average spacings of dislocations are 250, 100 and 40 Å for VSi₂/Si, MoSi₂/Si and WSi₂/Si systems, respectively. The disparities in dislocation spacings are attributed to the differences in lattice mismatches and thermal expansion coefficients among these silicide/Si systems. The discovery of a number of new epitaxial silicides presents the exciting possibilities that novel devices with desirable characteristics may be realized.