Understanding of the growth, stability, and structural properties of coherently strained metal overlayers has achieved considerable importance because of the recent discovery of unique interfacial electronic states and catalytic properties of such systems. The structural stability of coherently strained metal films grown on a substrate composed of a different and lattice-mismatched metal is determined via atomistic calculations. An equilibrium energy balance criterion is used, which is evaluated with a Monte Carlo annealing optimization procedure in which the structural energy of the bimetallic system is obtained using the embedded atom method. The stability of coherently strained (100) bimetallic structures chosen from combinations of the fcc metals Ag, Au, Cu, Ni, Pd, and Pt has been studied. The predicted critical thicknesses agree remarkably well with experimental results, but disagree quantitatively with the continuum models.

Forward scattering of XPS and Auger electrons by atoms in a crystalline lattice produce beams of enhanced intensity radiating out from the surface at angles corresponding to the internuclear axes present in the top few atomic layers. This effect has been applied to analyze the mechanism of surface segregation in ultrathin metal films, to analyze the interdiffusion at the interfaces of ultrathin films, and to assess the effects of substrate contamination on the growth of epitaxial films. The systems studied in this work are Cu, Ni, and Co on Ni(100), however the purpose of this work is not to investigate these particular systems but to use them to illustrate the capabilities of forward scattering.

Oxygen adsorption on and the eventual oxidation of the (100), (110), and (111) surfaces of NiAl was studied extensively using a variety of surface sensitive techniques. While the initial rate of uptake at 22°C varied significantly with orientation and surface composition, in all cases it was possible to form an overlayer region containing the equivalent of several monolayers of oxygen. No ordered overlayers were observed. Information about the chemical bonding was obtained from changes in core-level binding energies. Examination of the Al 2p region showed evidence for two different oxide environments, depending on surface treatment. Comparison of these results with those for both Ni and Al clearly shows effects due to alloying.

Growth of a thin BeO layer on the (111) surface of a dilute Al-Be alloy has been studied under oxidizing condition. At 500°C, in the presence of oxygen, Be atoms diffuse to the surface to form BeO. This oxide grows epitaxially with its (0001) basal plane orientation parallel to Al (111). During room temperature oxygen exposure of the AI(111) surface precovered with a BeO layer, it was found that oxygen diffused through the BeO overlayer and formed amorphous Al2O3 at the AI-BeO interface. The thin BeO film remained well ordered even when separated from the substrate by the amorphous layer. The effect of various coverages of BeO on the kinetics of oxidation of Al (111) at room temperature was studied; the influence of the BeO was found to be small in comparison with the case of a polycrystalline sample with predominantly (001) textures.

We have investigated the surface structure of oxides with low atomic number metallic components (Cu and Al) using two different high resolution electron microscopy techniques. First, using flat-on microscopy normal to the surface, we have studied the epitaxy of vapor deposited Cu on single crystal (110) and (111) surfaces of Au and the subsequent oxidation of the Cu under ambient conditions. Three structural variants of (110) oriented Cu2O were found relative to the underlying ( 11I) Au film and the oxide surface has a shifted, 1/2[110], (1 × 1) surface reconstruction. A (211) Cu2O structure was found for the (110) Au film orientation. This case has two structural variants at 90° to each other where one of these variants exhibits surface roughness of ∼5Å. The second structure has atomic step heights of ∼6Å, and a rectangular surface supercell structure of ∼3.0Å × 7.39Å due to (211) bulk lattice layers.

This paper reports upon a new technique for the formation of epitaxial Pd2Si on (100) silicon using thin predeposited titanium layers. Improvements in the quality of epitaxy in Pd2Si on {111} silicon by this technique will also be shown. A preliminary model for the formation of epitaxy will be given. Discrepancies between this model and results in the literature will be discussed and experiments suggested to resolve the uncertainties.

There has recently been considerable interest in the reaction between Co and a clean Si surface. This interest stems from the epitaxy of CoSi2 and NiSi2 on Si and its potential for the construction of reliable and stable metal-semiconductor structures. In fact, the fabrication of a Si/CoSi2/Si transistor has been recently reported.[l] On a more fundamental side, it has been possible to address the problem of the relation between Schottky barrier height and structure at the NiSi2/Ni interface, which exhibits both a rotated (B-type) and unrotated (A-type) geometry.[2] For CoSi2/Si only the 180° rotated, B-type disilicide is formed. By studying the room temperature interface, we have attempted to describe the nature and physical extent of reaction products; such knowledge is important to understand the formation of interface silicides which ultimately control the nature of the high temperature epitaxial interface.

The reaction between a Au film and an Inp substrate occurs much more readily in vacuo than under an external pressure of an inert ga. At atmospheric pressure, the compounds Au2P3 and the γ intermetallic compound (at times designated Au7In3, Au9In4, or Au2In) are formed at 450 °C and remain fairly stable even when annealed at 500°C for hours. Under ultra-high vacuum conditions, phosphorous readily escapes from the film when a sample is annealed at 300°C for 15 minutes, and the major reaction products are the ψ phase (Au3In2) and another intermetallic compound that is probably AuIn. The presence of an inert gas creates a kinetic barrier for the escape of phosphorous from the surface, and thus Au/InP behaves more like a closed thermodynamic system under pressure than in a vacuum.

Optical second harmonic generation is a new surface diagnostic applicable both in ultra-high vacuum and ambient environments and capable of examining gas-solid, liquid-solid and solid-solid interfaces. Studies of surface segregation of chromium and nitrogen on Fe-18Cr-3Mo(II0) single crystal surfaces in ultra-high vacuum are described. Major increases in second harmonic intensity generated by 700 nm excitation at the surface are seen upon heating to temperatures at which chromium and nitrogen cosegregate. Adsorption of oxygen has also been studied on this surface. Second harmonic generation shows promise in providing structural and electronic information for surfaces and interfaces in a wide variety of environments.

The sensitivity of second harmonic generation at interfaces has been utilized to probe the spatial and frequency dependence of the local field generated near the surface of a nearly free electron metal by an externally imposed electromagnetic field. The longitudinal screening field was found to oscillate with a wavelength on the order of 10Å and to propagate into the bulk several layers deep.