The application of double crystal X-ray diffractometry and computer simulation to the characterization of lattice parameter variations through the thickness of heteroepitaxial layers is reviewed. The sensitivity is demonstrated in studies of graded layers grown by vapour phase epitaxy. Capping layers significantly affect rocking curves from superlattice structures. The use of glancing angle diffraction to characterize thin, low period multilayers is examined.

The electron microscope can be operated in several different modes to provide atomic-level detail about surfaces. The REM technique with glancing-angle incidence permits the topography of bulk surfaces to be characterized with a resolution of better than 10A, and atomic-step-height features are visible. The standard TEM bright- and dark-field modes can also be used with appropriate samples to provide monolayer sensitivity. The profile imaging technique is ideal for following real-time dynamic processes. Typical vacuum levels ( ∼10−7 torr), and the lack of facilities for surface cleaning, currently impose a restriction on the materials which can be usefully studied in most available microscopes. Clean and well-defined environments for the sample, without any compromise of the microscope performance, will become increasingly common in the near future.

Surfaces of crystalline materials generally facet and form steps and ledges on low-index planes to reduce their total energy. A conventional wedge-shaped transmission electron microscope (TEM) thin foil, prepared slightly misoriented with respect to a low-index plane, provides a suitable geometry for the study of surface ledges, steps and facets. This TEM study characterizes the surface features of annealed thin foils prepared from various oxides with a range of nominally low-index orientations. Observations from single-crystal α-A12O3 and MgAl2O4 (spinel) will be included.

The steps and facets typically form along energetically favorable, low-index planes and bound terraces of low-index orientation. The structure of these features are discussed. In addition, surface step movement has been observed and monitored through a series of reannealing experiments on the same foil.

We investigate the energetics of structure changes in small particles, a phenomena recently observed by high resolution electron microscopy. The energy variations during transformations from a single crystal to symmetric and asymmetric decahedral multiply twinned particle (MTP) structures are evaluated. We examine briefly a few possible energy gain mechanisms during the particle-beam interaction which enable the particles to cross the activation energy barriers and fluctuate between various local energy minima of the morphological potential energy surface.

The surface roughness of small metallic particles and thin films is determined using TEM weak beam dark field images (WBDF) combined with image processing techniques. It is shown that the well known sensitivity of WBDF images to monoatomic steps on the sample surface can be largely improved by the use of image processing. The optimum conditions for step imaging and for the processing for small particles of Au, Pt and Pd and thin films of Au and Ag are discussed. It is found that under most conditions the surface of the particles and the films is very rough at the atomic level in agreement with the current theories of crystal growth.

Lithographic techniques have been used to prepare transmission electron microscopy samples of MoS2, allowing examination of the edge surface with single-layer resolution. We observe that these surfaces are easily disordered by chemical treatments common in the catalysis industry. In some cases treatment in H2/H2S leads to an exfoliation of the layered structure, a process which can be observed as it occurs in the microscope.

A systematic study has been made on (110) GaAs grown by molecular beam epitaxy. This work represents the first systematic investigation of commonly observed faceting on the (110) GaAs surface which has led to the consistent elimination of the defects. This study involved the analysis of facet geometry, a kinetic model of initial facet formation, and the electrical and optical analysis of facet free (110) GaAs. The latter was obtained with proper growth conditions and a Ga rich surface exposure from a GaAs substrate angled 6° toward (111)Ga.

Grazing incidence x-ray scattering is emerging to become an important structural probe for surface and interface studies, especially in conjunction with the development of high brilliant synchrotron sources. In this paper, we give a brief review of the experimental principle and examples of how the technique can be applied to study surface defects.

Irradiation at elevated temperatures of V(Cr) alloys is known to create a near-surface layer of nonequilibrium Cr enrichment. Highly reproducible RBS spectra were accumulated from a V-15%Cr alloy irradiated at 750°C, and from unirradiated portions of the same specimen. Differences between these spectra are used to demonstrate the high sensitivity of conventional RBS techniques for determining near-surface segregation behavior. Sensitivities obtained utilizing differences in the acquired spectra are much higher than those typically assumed for RBS measurements. Using 1.8 MeV 4He, and conventional RBS equipment and scattering geometries, segregation of < two atomic layers of 52Cr in 51V- 15at.%Cr over a depth of ∼5 nm has been observed.

In view of material technological developments, studies have been made of the interactive processes involved in irradiation of metals with an excimer laser. These studies involved single-pulse irradiation of Al, Ni, Ti, and Zn at various powers up to about 5 MW. Systematic studies at widely differing, yet reproducible, power densities were facilitated using numerically controlled beam focusing. By changing the incident intensity, different plasma pressures were produced during surface melting. These created various types of unstable ripple patterns which emanated radially from the center of beam incidence and were enhanced by immersion in liquid nitrogen.

The results showed only minor differences between substrates possessing different physical properties and the influence of crystallographic orientation was also found to be minimal. An elliptical disturbance zone was produced on the substrates when the beam was defocused and this is attributed to astigmatic effects associated with a lens system incorporating spherical refracting surfaces.

We have performed a systematic study to evaluate the structural response of a {110} fcc surface to an externally imposed elastic deformation, by Molecular Dynamics at a fixed temperature T=0.48T and T=0.68T (T melting point). For high contractions along the dense axis [110], surface concentration of defects (SCD) and diffusion coefficient increase with respect to the equilibrium values. The resulting surface disorder is similar to the one found, at equilibrium, at higher temperatures.

We have performed a series of simulations to examine the atomistic nature of surface relaxations in pure metals and ordered alloys. The surface relaxations (∆dn, n+1) are shown to be oscillatory and to decay rapidly into the bulk. The period and form of the oscillation may be determined by simple geometrical arguments. The oscillation wavelength is always of the order of an atomic diameter. In pure metals, the surface layer of atoms always displaces inward. However, in the ordered alloys the larger atom may displace outward. On planes composed of more than one atom types, rippling occurs.

The surface of a metallic glass has been characterized at the atomic and microstructural levels. On the atomic scale, the glassy surface hal been previously characterized via a model which allows the calculation of surface coordination numbers and the fractal dimension. Catalytic experiments and LEIS measurements appear to confirm the model's prediction of surface roughness on the atomic scale. In this work, the glassy surface has been characterized on the microstructural level via RHEED patterns. In addition, the fresh glassy surface produced by comminution of Fe-B glass has been characterized with respect to the relative stability of the comminuted glass as compared to as-quenched glass.