X-ray scattering studies are reviewed of the faceting kinetics of stepped silicon (113) surfaces misoriented towards [001]. Following a quench from the one-phase region of the orientational phase diagram into the coexistence region, initially-uniformly-distributed steps rearrange to form a grooved superstructure. Our measurements reveal the behavior of the grooved surface morphology as a function of time. The surface is found to be self-similar in time, with a characteristic groove size (L) varying as a power-law versus time (t): L = L0tøwith a coarsening exponent of ø = 0.164 ± 0.021 ≃ 1/6, consistent with a theory for the kinetics of faceting which focuses on thermally fluctuating step bunches and their collisions. At later times, the groove size approaches a limiting value which depends on the stepped phase misorientation angle, as expected for faceted surfaces in the case that elastic effects are important.

Recent experimental measurements on the interface stresses in two heteroepitaxial systems have shown that the interface stresses were unexpectedly large. For thin deposited layers, the interface stress can exceed the stress caused by the lattice mismatch by far. Arguments are presented which indicate that the surface stress may be caused by the charge transfer between the deposit and the substrate. The consequences for the critical thickness of pseudomorphic films are discussed and it is shown that depending on the sign of the interface stress and the mismatch the critical thickness can be either reduced or enhanced by a large factor.

The connection between the atomic step distributions and decay modes of modulated surfaces is the focus of this paper. We have examined the arrangements of atomic steps on real 1- and 2-D periodic structures by scanning tunneling microscopy(STM) and low energy electron microscopy(LEEM) and have followed their development at temperature by LEEM. The steps present on the surface due to small ‘miscuts’ from exact singular planes can have major effects on both the mechanisms of shape development and the actual shapes that result. Major differences exist in the modes of development between 1- and 2-D periodic step arrays. Some of these observations have led us to a method for producing arrays of step-free Si(001) regions that may have application in device processing.

The two-dimensional (2D) to three-dimensional (3D) morphology change in the highly strained growth of InAs on GaAs(001) is examined via in-situ, ultra-high vacuum (UHV) scanning tunneling microscopy (STM) and contact-mode atomic force microscopy (C-AFM). The formation of 3D InAs islands (˜2–4nm high) at an InAs delivery, θ˜1.57ML is found to be preceded by the appearance of small quasi-3D clusters (˜0.6–1.2nm high). The 2D to 3D transition is found to occur over a range of θ from ˜1.45ML to 1.74ML, with a varying and gradual mass transfer from 2D to 3D features with increasing θ. The InAs 3D islands are also examined in this study using non-contact AFM (NC-AFM) in order to assess the usefulness of this technique for imaging 3D features. Unlike the constancy observed in the C-AFM images, the NC-AFM images exhibit a marked imaging condition dependence. The variability observed in the NC-AFM images is qualitatively compared to the outcome of the simplest, force-gradient model of NC-AFM in order to extract a guideline for NC-AFM imaging of 3D features.

Interatomic potentials of the embedded atom (EAM) type were used to study the atomistic structure of high index surfaces in metals and ordered alloys. The results show that a structural unit model can be developed to model the structure of the high index surfaces on the basis of the structure of a few low energy surfaces. The model can predict the structural features and give an estimate of the energies of the higher index surfaces. We present examples of Fe, B2 FeAl and NiAl.

We have determined the adsorption site and interlayer spacings of c(2×2) N2/Ni(100),(√3 × √3)R30° and (1.5 × 1.5)R18° CO adsorbed on Cu(111), using ARPEFS and a full Multiple-Scattering, Spherical Wave (MSSW) calculation program. The nitrogen molecule stands upright at an atop site, with a N-Ni bond length of 2.25(1) Å, a N-N bond length of 1.10(7) Å, and a first layer Ni-Ni spacing of 1.76(4) Å. The C-Cu bond length is 1.91 (1) Å in the (√3 × √3)R30° phase and 1.91(2) Å in the (1.5 × 1.5)R18° phase. The first layer Cu-Cu spacing is 2.07(3) Å in the (√3 × √3)R30° phase. The first layer Cu-Cu spacing in the (1.5 × 1.5)R18° phase is 2.01(4) Å, a contraction of 3 % from the clean metal value of 2.07 Å.

Using a new solid-on-solid model that correctly takes into account the diamond-cubic crystal structure, both a roughening transition at temperature TR and a distinct preroughening transition at TPR≈0.43TR are found to exist on {111}surfaces of diamond-cubic materials. Results are presented for height-difference correlation functions, surface specific heats, step energies, etch rates, and a preroughening order parameter. Preroughening appears to arise naturally in our nearest-neighbor bond model from the entropic freedom available in the non-trivial crystal structure suggesting that preroughening may be more common than previously anticipated. Preroughening is shown to dramatically lower step energies and step-energy anisotropy on the {111} surface. Preroughening of Si{111} may have been seen in experiments by Noh et al. [Phys. Rev. B 48, 1612 (1993)].

The development of the roughness of the Si (100) surface has been investigated at the initial stage of etching in the molecular flow of F2 and XeF2 gases. It was discovered that roughness grew during etching in XeF2 gas and decreased during etching in F2 gas, that is, F2 gas polishes Si surface unlike XeF2. This difference was explained with the help of ellipsometric study of the kinetics of adsorption layer formation.

Despite the growing use of atomic force microscopy (AFM) for the measurement of silicon wafer microroughness, no generally accepted method has been developed to deal with issues around accuracy and reproducibility. We review problems that affect these AFM studies and demonstrate the effect of probe tip size on AFM microroughness data. Without knowledge of AFM probe tip geometry, it is impossible to quantitatively compare Ra or RMS microroughness data between different measurements. An experimental solution is to characterize tip sizes during imaging and compare data taken with similar size tips. While this will significantly improve quantitation, it is restrictive in that data taken with different size tips cannot be easily compared. We propose a solution to this problem in the use of power spectral density (PSD) to evaluate microroughness with a “cutoff frequency” at the lateral wavelength where tip effects begin to affect the accuracy of the microroughness measurement. An example of this approach is described

The kinetics of vacancy diffusion on Si(111) and (001) surfaces are studied by using scanning reflection electron microscopy (SREM). Two types of layer-by-layer etching (reversal of step-flow growth and two-dimensional vacancy island nucleation) are observed during lowenergy Ar ion irradiation (500 eV) at elevated substrate temperatures. This means that vacancies created by low-energy ion impact diffuse on the surfaces, and are annihilated at the step edges. Although isotropic vacancy diffusion is observed on Si(111), anisotropic vacancy diffusion along the dimer rows and preferential vacancy annihilation at the SB steps are observed on Si(001). This anisotropic vacancy diffusion results in single-domain formation. The diffusion length of vacancies is estimated from the width of the denuded zones, which are formed on both sides of the atomic steps by thermal heating after the introduction of vacancies at room temperature. The activation energy of 3.0±0.2 eV obtained for Si(111) corresponds to the potential barrier both for surface adatom diffusion and for lateral binding energy to release adatoms from the step edges. For Si(001) surfaces, the activation energy obtained for vacancy diffusion along the dimer rows is 2.3±0.2 eV. The vacancy diffusion model mediated by dimer vacancy complexes, rather than by single-dimer vacancies, best accounts for our experimental results.

A microcalorimeter for measuring adsorption heats on clean single-crystal surfaces is described. The principle is similar to that pioneered by David King's group: A pulse of gas from a molecular beam adsorbs on an ultrathin single crystal's surface, causing a measurable transient heat input and temperature rise. Our novel heat detector is a 9 μm pyroelectric polymer ribbon, which is mechanically driven to make a gentle mechanical/thermal contact to the back of the singlecrystal sample during measurements. Advantages include use of thicker samples (>3 microns), sample preparation at very high temperatures, and measurements at 100 K. We have applied this to study the heats of adsorption of metals on clean, well-defined and single-crystalline oxide surfaces as a detailed function of coverage, from which we also extract the metal/oxide adhesion energy. We obtain pulse-to-pulse standard deviations of >2% for pulses containing >0.03 ML of Cu, and absolute accuracy within a few percent.

We deposited low-energy 111 atoms on a vicinal Cu(100) surface at 82K, and measured the atomic sites by means of the perturbed angular correlations technique (PAC). The sites of the as-deposited In atoms were determined for deposition energies ranging from 5 to 100 eV. The results are coinpared to Molecular Dynamics simulations of the deposition process.

The binding energies of gold, silver and copper adatoms and their clusters to each (111) surface have been calculated. The binding energy EN of an N-adatom cluster can be roughly written as EN=3NE1+mE2, where 3E1, is the binding energy of a single adatom to the (111) surface and m is the number of bonds within the cluster and E2 is the binding energy of the bond within the cluster. It was found that E1=0.95eV, E2=0.42–0.49eV for gold, E1=0.62eV, E2=0.38-0.44eV for silver and E1=0.81eV, E2=0.43–0.49eV for copper (by use of a newly determined N-body embedded atom potential). The activation energies of motion of these adatom clusters on each (111) surfaces have been calculated by use of a newly determined N-body embedded atom potential and molecular dynamics method.

Microscopic examination of the surface of single crystal (111) NiAl during various stages of oxidation at 1100 C in air shows the development of islands composed of rings of different colors.These islands appear to grow in size and eventually impinge with increased exposure. Microscopic fluorescence mapping of the surfaces of three single crystals subjected to varied exposure times provides an identification of the composition of the islands and the surrounding area as two different allotropes of alurninum oxide.Additionally, analysis of the map spectra demonstrates the decrease of intensity of their characteristic fluorescence bands in the island centers with increasing island size, which we refer to as “volcanic” intensity topography. Thus, the observed color variation is an interference effect, due to varied films thicknesses through the islands. Finally, the energies of the fluorescent bands are seen to shift as a function of distance from the island center, indicating the development of strain gradients across the islands.

The rate equation treatment of nucleation and growth on perfect substrates has been extended to cover nucleation on random defect sites, and problems involving 1-dimensional (1D) diffusion to sinks. This paper recaps the results of rate equation treatments on perfect terraces, and sumnarises some new models, including: 1) nucleation on point defects, with application to nm-sized Fe and Co particles grown on various CaF2 substrates; 2) nucleation and diffusion in finite 1D deposits, with application to diffusion over, and the break-up of, multilayer deposits of Ag/Ge(111) and Ag/Fe(110); 3) 1D models developed for nucleation in competition with step capture. Comparison of rate-diffusion equations with experiment can result in values for, or bounds on, the controlling energies, in a way which illuminates the main features of interatomic forces at surfaces. The use of defects to grow thin film arrays for practical application presents some interesting challenges at both the nucleation and growth stages, which are discussed briefly.

Kinetic Monte Carlo simulations with two species (Si and H) have been performed to identify the mechanism behind the H-induced creation of a strongly temperature-dependent high density of Si islands in the temperature range of 300–550 K during molecular-beam epitaxy on Si(001) surface. A model is proposed to explain this effect as a result of an activated exchange between H and Si at Si island edges.

Risers and treads on terraced surfaces of modified-Lely (M-Lely) grown 6H-SiC(0001) bulk crystals are investigated by reflection electron microscopy (REM). On risers we find parallel steps, with a height of one or two unit cells. On treads we find in addition to growth spirals island formation. We take these observations to conclude that two competitive processes operate in parallel, the step-flow mode and the two-dimensional nucleation.

The growth and microstructural evolution of Nb thin films on the basal plane of α-Al2O3 were studied at different growth temperatures. The influence of island orientation, density, and misfit strain energy on the growth behavior of Nb films on (0001)α-Al2O3 at high temperatures has been investigated. The films were grown by MBE at 900°C and 1100°C. At these temperatures the Nb grows in the Volmer-Weber growth mode on the basal plane. In-situ reflection high energy electron diffraction (RHEED), Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) investigations revealed that in the initial growth stage, Nb nuclei with different epitaxial orientations were formed. This leads to different orientations of thicker Nb films at different growth temperatures. At a growth temperature of 900°C the Nb{111} planes are parallel to the sapphire basal plane whereas at 1100°C Nb grows with the {110) planes parallel to the basal plane of sapphire. The formation of two different epitaxial orientations of thick Nb films can only be explained by considering both the change in the total density of Nb islands with temperature and the influence of island size on their total energy.

Monte Carlo simulations of physical and chemical vapor deposition are used to study roughening kinetics of films that grow by nucleation and coalescence of clusters. The effects of interlayer transport, preferential dissociation of molecular precursors and energetic differences between the clusters and the substrate are examined.

The deposition of CaGa2S4:Ce has been accomplished using a commercial liquid delivery system on two substrate surfaces: ZnS and SrS. However, the film deposited on ZnS was not of satisfactory quality because of the formation of an amorphous layer and a high amount of residual porosity within the deposition. The use of a SrS layer on top of the ZnS improved the nucleation by reducing the interfacial energy between the substrate and deposition. It greatly reduced the porosity in the coating and reduced the formation of the amorphous layer. The crystallinity of the CaGa2S4 400 peak was also increased by a factor of ten when a layer of SrS was used. Further, the FWHM of the 400 peaks from the two depositions was not significantly different, indicating that the crystallite size and strain was approximately the same. The B40 was increased by a factor of two, from 1.84 cd/m2 for ZnS to 3.67 cd/m2 for SrS. This increase is an improvement in the performance of the films and is attributable to the increase in the crystallinity. To utilize these improvements, the ability to deposit both the SrS and CaGa2S4:Ce layers within the same reactor has been developed.