We compare the ground state energy of the following structures of fcc (110) surfaces: the (1×1) flat surface, the (n×1) reconstruction (2 ≤ n < ∞), and the (∞ × 1) structure where the surface is faceted into macroscopic (111) surfaces. We map out the phase diagram using a lattice model with pair and triplet interactions. We argue that it is unlikely that any realist pair potential will give a reconstructed ground state. We also doubt that including, in addition, three body interactions will stabilize the reconstructed structure for interatomic interactions derived from the embedded atom method.

High-resolution angle-resolved photoemission has been used to investigate the behavior of the Cu(001) surface state as a function of Au coverage and substrate temperature. Binding-energy shifts of this state are dependent on the concentration of Au atoms substituted into the top surface layer of the Cu(001) substrate. The results demonstrate the use of surfacelocalized Tamm states as a specific probe of the chemical environment in the surface plane.

The morphologies of submonolayer films of Ni, Fe, Au, and Ag deposited on Au(111) at room temperature are studied using scanning tunneling microscopy (STM). The structures of steps and islands on length scales up to ˜3000Å are examined to determine processes of atomic motion and island nucleation. In all cases the deposited atoms move rapidly at room temperature and their aggregation is affected by the Au(111) “herringbone” reconstruction. Ni and Fe aggregate to form island arrays with regular spacing, which are nucleated at “elbow” sites of the herringbone pattern. Au forms fewer islands, showing these atoms are less likely to stick at these elbow sites. Ag forms a complex structure of monolayer-high fingers which reflect the interaction of diffusion-controlled aggregation with energetic differences defined by the reconstruction. These studies make it clear that the final structure of an ultrathin metal film can depend sensitively on fine details of atomic structure in the substrate.

A controversy has arisen in the past year over whether or not the growth of Fe on Ag(100) at room temperature occurs by a layer-by-layer mechanism. The present work attempts to address this controversy with an investigation of the issues, primarily by x-ray photoelectron (XPS) and Auger electron forward scattering, but with important supporting data from low-energy electron diffraction (LEED), and reflection high-energy electron diffraction (RHEED) oscillations. The results of this work suggest that the origin of the controversy lies in different substrate preparation techniques which produce different atomic step densities on the Ag(100) surface. The step sites are implicated as being the initiators of major departures from a layer-by-layer growth mode whenever most of the deposited Fe atoms have sufficient mobility to reach these steps. However, even when the Fe atoms cannot reach these steps it appears that atomic place-exchange occurs with ≥25% of the top-layer Ag atoms. Atomic place-exchange mechanisms, which could account for this intermixing, have been observed in recent molecular-dynamics simulations of epitakial growth. Thus it seems probable that under the conditions that appear to produce layer-by-layer growth, the growth begins as layer-by-layer growth of an FeAg alloy, and only becomes layer-by-layer in pure Fe as the segregating Ag atoms gradually get left behind in the growing Fe film.

We present a general procedure for quantitative structural refinement of superlattice structures. To analyze a wide range of superlattices, we have derived a general kinematical diffraction formula that includes random, continuous and discrete fluctuations from the average structure. By implementing a non-linear fitting algorithm to fit the entire x-ray diffraction profile, refined parameters that describe the average superlattice structure, and deviations from this average are obtained. The structural refinement procedure is applied to a crystalline/crystalline Mo/Ni superlattices and crystalline/amorphous Pb/Ge superlattices. Roughness introduced artificially during growth in Mo/Ni superlattices is shown to be accurately reproduced by the refinement.

The existence of the supermodulus effect, an enhancement in the elastic modulus of artificially layered metal films, was discovered more than a dozen years ago. Yet the detailed nature of this effect remains a puzzling phenomena. Implications of the interface structure on the elastic properties of gold-nickel multilayers are investigated using x-ray diffraction and high resolution electron microscopy.

The relationship between atomic structure and elastic properties of grain boundaries is investigated from both discrete and continuum points of view. A heterogeneous continuum model of the boundary is introduced where distinct phases are associated with individual atoms and possess their atomic level elastic moduli determined from the atomistic model. The complete fourth-order tensors of both the atomic-level and the effective elastic moduli are determined, where the latter are defined for sub-blocks from an infinite bicrystal and are calculated here for a relatively small number of atom layers above and below the grain boundary. These effective moduli are determined exactly for the discrete atomistic model, while only estimates from upper and lower bounds can be determined for the continuum model. Comparison between the atomistic results and those for the continuum model establishes the validity of this definition of elastic properties for heterogeneous structures at these scales. Furthermore, these comparisons as well as algebraic properties of the fourth-order tensor of moduli lead to criteria to assess the stability of a given grain boundary structure.

The Rayleigh wave velocity of metallic superlattices Ag/Cu, Al/Cu and Co/Cu deposited by ion beam sputtering were measured as a function of layering period Λ using Brillouin scattering method. The VR-Λ relationship can be well interpreted using a phenomenological model consisting of three elastically different layers, i.e. two original and an intermediate layer. We have assumed in this model that the elastic modulus and the thickness of the intermediate layer are independent on the layering period.

The structure and elastic properties of superlattices composed of high-angle twist grain boundaries on (100) planes of copper are investigated as a function of both the modulation wavelength and temperature via molecular dynamics simulations. Comparison is made with zero-temperature results, where a stiffening of the Young's modulus normal to the interfaces and a softening of the modulus for shear parallel to the interfaces has previously been observed. The differences between the effects of homogeneous (temperature-induced) and inhomogeneous (interface-induced) structural disorder on the elastic properties is explored.

A softening of the shear elastic constant c44 has been observed previously in Mo/Ni superlattices as a function of decreasing bilayer thickness below approximately 100 Å.[1] We have prepared a series of Mo/Ni superlattice films by ion beam sputtering doped with varying concentrations of either aluminum or oxygen. The chemical and structural properties of these films were then determined using x-ray diffraction (XRD) and Auger electron spectroscopy (AES). The shear elastic properties were characterized by measuring the surface acoustic wave (SAW) velocity of the deposited films. We demonstrate structural and elastic property effects resulting from Al and O impurity incorporation in Mo/Ni multilayers.

Silver-nickel multilayers were prepared by sputtering at 100 K. X-ray diffraction, electrical resistivity and dimensional variation measurements were performed to structurally characterize these stratified materials, both in the as-prepared state and during the course of annealing cycles. Clearly, polycrystalline superlattices with marked (111) texture perpendicular to the strata are formed. We studied the elastic properties of these superlattices by performing uniaxial tension tests. No deviation from linear elasticity was observed, whatever the period. Young's modulus was found to be 130±15 GPa for all the periods studied. Thus no significant functional dependence of Young's modulus on the stacking periodicity exists in the AgNi superlattice, in the range of periods explored, 2.6 to 18 nm.

Multilayer thin film structures for reflecting soft x-rays are now being fabricated in a number of laboratories. However, understanding of. the optical properties of these structures is presently limited by lack of knowledge of the microstructure of the layers, as well as of the details of the interfaces. In this paper we present results from our studies of multilayers grown by molecular beam epitaxy (MBE), characterized in situ by reflection high energy electron diffraction (RHEED), low energy electron diffraction (LEED), Auger, and x-ray photoelectron spectroscopy (XPS), and characterized ex situ by scanning tunneling microscopy (STM), transmission electron microscopy (TEM), x-ray diffraction, and Rutherford back scattering (RBS). In the case of Mo/Si multilayers, we observe the formation of an amorphous interfacial silicide, which can have a positive effect on the performance of these evaporated multilayer mirrors. We observe a contraction in the period of these multilayers as the deposition temperature is raised from 50 °C to 250 °C, corresponding to an increase in the thickness of the interfacial silicide. This contraction indicates that the silicide is more dense than the average atomic density of its components. We also discuss Ag/B and Pd/B multilayers, which have very similar theoretical performance. However, due to differences in the multilayer structures formed, the actual performance of multilayers made from these materials is radically different. The structural differences originate from different growth modes for Ag and Pd on B.

We report the results of photoelectron forward scattering studies of Co-Pt interfaces during the growth of epitaxial superlattices by MBE. These studies reveal that the interfaces are not atomically abrupt but exhibit limited interdiffusion. The dependence of magnetic anisotropy on growth axis and the strong 2-fold in-plane anisotropy for [110] oriented superlattices suggests that magnetocrystalline anisotropy is a major factor in determining the anisotropy in Co/Pt superlatticcs. The possibility that this anisotropy may arise from a combination of structural defects and local ordering is discussed.

The effects of grain boundaries and substrate interactions with hydrogen on the CVD growth of device-quality copper were investigated by high-resolution x-ray photoelectron spectroscopy (HRXPS), Auger electron spectroscopy (AES), four-point resistivity probe, x-ray diffraction (XRD), and hydrogen profiling techniques. The films were deposited at 200° C in a stainless-steel cold-wall-type CVD reactor in an atmosphere of pure H2 from various β-diketonate precursors, including bis(6,6,7,7,8,8,8-heptafluoro-2,2- dimethyl-3,5-octanediono)copper(II), Cu(fod)2, and bis(2,2,6,6-tetramethyl- 3,5-heptanedionato)copper(II), Cu(tmhd)2. The results of these studies showed that films grown on in-situ plasma-cleaned metallic substrates were uniform, continuous, adherent, and highly pure. Films with grain size larger than 500Å exhibited very low resistivity, as low as 1.7 μΩcm. Preliminary investigations of the mechanisms of selective copper CVD showed that selectivity is independent of precursor chemistry and is a function of the nature and degree of substrate interactions with hydrogen.

We describe the recently developed real-space multiple-scattering theory (RSMST), which is designed for performing first-principles electronic-structure calculations of extended defects, such as surfaces and interfaces including atomic relaxations and with or without impurities, without using artificial periodic boundary conditions. We present the results of non-charge-selfconsistent RSMST calculations of the local electronic densities of states at twist and tilt grain boundaries in fcc Cu and bcc Nb, and report on progress towards the implementation of charge self-consistency and total-energy capabilities.

The results of x-ray diffraction, resistivity and magnetization measurements of Ag/Cr metallic superlattices are presented. Dramatic changes in the interplanar distances of Ag and Cr were found as a function of the number of Cr monolayers in a period. The resistivities of the superlattices increased as the composition of Cr increased. Magnetization measurements show that the superlattice [Ag(10ML)/Cr(2ML)] exibits a maximum magnetic susceptibility.

The in-plane thermal conductivity of Ag/Al multilayered films was measured at room temperature by ac calorimetric method as a function of the modulation wavelength and was compared with the electrical conductivity. The electrical conductivity increases with wavelength, Λ, like other metallic multilayered films. The thermal conductivity also tends to increase with Λ, but the Λ dependence is not similar to that of electrical conductivity. Obtained Lorentz number value of the multilayers are almost 10–30% larger than that given by the free electron theory. The Wiedemann-Franz law did not hold in the Ag/Al films and the phonon contribution is not negligible.

This work studies a (310) θ = 36.86° <001> symmetrical-tilt bicrystal model using an Embedded Atom Method aluminum potential. Based on explicit results obtained from the simulations regarding structural order, energy, and mobility, we find that our bicrystal model shows no evidence of pre-melting (complete melting below Tm). Both the surface and the grain-boundary interface exhibit thermal disorder at temperatures below Tm, with complete melting occurring only at, or very near, Tm. Concerning the details of the onset of melting, the data show considerable disordering in the interfacial region starting at about 0.93 Tm. The interfaces exhibit metastable behavior in this temperature range, and the temperature variation of the interfacial thickness suggests that the disordering induced by the interface is a continuous transition, a behavior that has been predicted by a theoretical analysis.

Relative orientations which correspond to minimum energy can be found by particle rotation methods, both for particles on free surface and particles inside a solid. For common fcc metals (Ni,Ag,Cu,Ag) the minimum energy orientations predicted by Embedded Atom Method calculations correspond well with experimental observations. Epitaxial studies of growth on (001)Cu and (111)Cu show the observed orientation relationships of vapor deposited Ag and Au are consistent with EAM calculations and the limited particle rotation experiments available.

The structure and faceting behavior of near-90° <110> tilt grain boundaries in thin films of aluminum with a unique mazed bicrystal geometry is characterized by conventional, highresolution and high-voltage electron microscopy. In this microstructure the absence of triple junctions allows grain boundaries to facet in optimum orientation (inclination) during annealing. The degree of anisotropy of the boundaries is expressed in the form of a rose plot. Small local deviations in misorientation are shown to be necessary to accommodate optimum boundary segments. The crystallographic symmetry inherent in this microstructure is apparent and utilizedthroughout the analysis.