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To relieve strain, metal surfaces under tensile or compressive stress often develop periodic two-dimensional patterns of dislocations. Recently, we have seen new developments in the characterization of strained layers, their theoretical simulations and their applications for growth of self-assembled cluster arrays. The atomic resolution imaging of clean and adsorbate-covered strained surfaces using scanning tunneling microscopy has allowed the identification of reactive sites and the structural characterization of growing clusters.

We investigate the microstructure and orientation relationships observed in aluminum thin films deposited epitaxially on sapphire (0001). The films consist of grains with three distinct types of orientation relative to the substrate. The primary orientation is such that (0001)Al2O3‖(111)Al and [10 1 0] Al2O3‖ [ 1 10] Al. This configuration, which matches the close-packed planes and directions of the metal film with those of the oxygen ion sublattice in the sapphire substrate, allows for growth of two symmetrically equivalent orientation variants resulting in a film composed of interlocking regions of these two domains. Unexpectedly, two additional orientation types are identified in the films. As in the primary variant, the close-packed aluminum {111} planes remain parallel with the sapphire basal planes. However, these orientations are rotated about the aluminum [111] axis such that [10 1 0] Al2O3 is parallel to directions near either [ 1 2 1 ] Al (30° rotation) or [5 4 1 ] Al (∼11° rotation).

The nucleation and growth behavior of Au films on clean and oxygen-precovered Ru(0001) has been systematically studied by scanning tunneling microscopy (STM). The film morphology and the effects of annealing have been followed as a function of coverage from the submonolayer range up to 3 monolayers (ML). Marked differences in these properties are found on the two types of substrates. These effects can be understood in terms of changes, due to the oxygen adsorption, in both the kinetics and thermodynamics of atomic processes during film growth, such as the Au adatom migration and two-dimensional and three-dimensional condensation.

The two-dimensional growth of Au on Ru(0001) in the submonolayer range has been investigated with scanning tunneling microscopy. Upon deposition at room temperature, highly dendritic islands of one layer thickness grow on large Ru terraces. These irregular island shapes are removed upon annealing to 650 K. The dendritic islands exhibit a fractal character, and a dimensional analysis yields a fractal dimension of 1.72\ifmmode\pm\else\textpm\fi{}0.07. The results are in quantitative agreement with a two-dimensional diffusion-limited-aggregation growth mechanism.

The initial growth of Cu and Au films on Ru(0001) has been studied with STM in the sub-monolayer to several monolayer coverage regime. For both metals our results indicate a layer-by-layer growth at least up to two layers, at lower temperatures kinetic limitations can lead to the population of several coexistent layers. Differences are found, however, in the kinetically limited two-dimensional growth behavior of the two metals. The effects of annealing were investigated.

Previous LEED structural studies of benzene chemisorption on transition metal surfaces have relied on the presence of coadsorbed carbon monoxide to induce ordering in the overlayer. To investigate the effect of CO on the benzene structure, the disordered pure benzene layer chemisorbed on Pt(111) is studied by diffuse LEED intensity analysis. The diffuse LEED intensity has been measured using a digital LEED apparatus and analysed using an extension of the beam set neglect method. The benzene is found to chemisorb in a two-fold bridge site rotated by 30° with respect to the site found for the ordered phase formed in the presence of coadsorbed CO. In addition, the benzene ring is found to be distorted. Parallel distortions are subject to large error bars, but perpendicular spacings have been more accurately determined. These include a buckling distortion not previously seen for benzene chemisorption on transition metal surfaces.

To investigate the effects of multiple film components on the morphology of thin films, the growth of Co and Ag on Ru(0001) has been studied by scanning tunneling microscopy. Two types of growth have been identified. In the first, the Co from the vapor phase is directly incorporated into existing Ag islands. In the second, islands composed of a Co-Ag mixture are formed by etching of the existing pure Ag islands. These two mechanisms, which occur simultaneously, lead to dramatically different morphologies. In the second case, dendritic growth of the alloy is found despite the fact that neither of the component metals alone exhibit this behavior. We attribute the dendritic growth to chemically induced step edge diffusion barriers which must generally exist in multicomponent film growth. {copyright} {ital 1996 The American Physical Society.}

We report on the structure and composition of codeposited thin Ag and Cu films on a Ru(0001) substrate. All three metals are immiscible in their bulk forms, however, monolayer films of Ag and Cu are observed to alloy on Ru(0001). In the dilute Cu case, preferential formation of the alloy is found. With increasing Cu concentration, domains of the alloy are formed with characteristic shapes. These data point to a mechanism of alloy formation driven by strain relief of the overlayer film. Details of the structure and composition of the film can be understood within this picture.