Transmission electron microscopy has been used to study the atomic and dislocation structure of deformed and undeformed Σ13 {510} boundary in Si. It is shown that there are several alternative structures for this boundary, which may be separated by imperfect and partial grain boundary dislocations. It is also shown that the dissociation of crystal lattice dislocations which interact with the boundary during deformation results is far more complicated than simple geometrical models applicable in monatomic materials predicts.

High resolution electron microscopy and high spatial resolution analytical electron microscopy were used to analyze the structure and chemistry of a Σ3 {111} twin boundary in cast polysilicon and a Σ13 (510), [001] tilt boundary in a Si bicrystal. Twin boundaries in cast polysilicon were associated with lattice defects and discrete second phase precipitates. The precipitate was single phase amorphous and faceted on the Si {111} planes. Nanospectroscopy showed mem to be substoichiometric oxide. Similar oxide precipitates, but with different morphology, were also observed on the Σ13 tilt boundary in Si bicrystal, indicating that tilt grain boundaries and steps on twin boundaries were effective heterogeneous sites for nucleation of oxygen containing precipitates. The observed Σ13 tilt boundary exhibited a coincident site lattice periodicity but had an aperiodic interface dislocation core structure. Oxygen that diffused into the boundary in regions where precipitation did not occur may have played a role in modifying the GB core structures, resulting in aperiodicity. For both cases, a detailed analysis of grain boundary atomic structure and precipitate morphology is presented.

A (310) twin boundary in Nb has been fabricated by diffusion bonding oriented single crystals and characterized using high resolution electron microscopy. Atomic structures for the boundary have been predicted using different interatomic potentials. Comparison of the theoretical models to the high resolution images has been performed through image simulation. On the basis of this comparison, one of the low energy structures predicted by theory can be ruled out.

The structure and morphology of 30° <100> tilt grain boundaries in tricrystal films of Al have been investigated by conventional and high resolution electron microscopy. By inducing heteroepitaxial growth on single crystal (111) Si substrates, Al formed polycrystalline thin films made of grains in three symmetry-related (100) orientations. The grain boundaries were well-faceted and a number of symmetric and asymmetric tilt boundaries and triple junctions were observed. Their morphology, topology and preferred faceting was related to the 12mm two-dimensional point symmetry of the tricrystal.

In a combined theoretical and experimental study, the energies and structures of Σ3 [011] twin boundaries in Cu were investigated. The atomic structures and the grain boundary energies were calculated using the Embedded Atom Method (EAM). Grain boundary energies of welded Cu bicrystals of the same boundary orientations were also obtained by the thermal grooving technique. The atomic structure of the symmetric {211} incoherent twin boundary (SITB) was investigated by High Resolution Transmission Electron Microscopy (HRTEM). Calculated grain boundary energies γb plotted against the inclination angle Φ of the boundary plane relative to the {111} coherent twin boundary (CTB) plane show a mininmm for the CTB (Φ = 0°) and a second minimum at Φ = 82°. This dependence on the inclination is also confirmed by the measured energies. Common to all calculated boundary structures is a microface 11 ing into CTB and SITB segments with a symmetric orientation of the adjacent crystals. Additionally, strong relaxations occur for the grain boundaries near the second energy minimum. This relaxation can be interpreted as a sequence of stacking faults located almost perpendicular to the mean boundary plane. They are terminated by partial dislocations which form a small angle boundary. The most apparent feature of these structures is a bending of the {111} planes running across the boundary. The structural properties were confirmed by HRTEM.

A formalism for obtaining the zero-temperature structure of mono-component solids by simulated quenching in the grand-canonical ensemble is outlined. The structure of a high-angle twist grain boundary on the (110) plane of an fee metal is investigated. The lowest energy structure is found to have a density approximately 20% higher than the structure obtained from canonical-ensemble energy-minimization.

Interfaces often undergo phase transitions even though nothing special is happening to the bulk solid. These transitions are possible in any internal interface, such as a grain boundary, an interphase boundary, a stacking fault, or an antiphase boundary. As for bulk solids, interface transitions may be defined from a thermodynamic point of view. When distinct interfacial phases coexist, interfacial phase diagrams are useful in visualizing thermodynamic data. Various classes of these transitions will be discussed in general and then illustrated with examples from recent work on models and experimental systems.

Bismuth-induced grain boundary faceting in Cu-12 at ppm Bi polycrystals was studied using transmission electron microscopy (TEM). The population of faceted grain boundaries in samples aged at 600°C was observed to increase with heat treatment time from 15min to 24h; aging for 72h resulted in de-faceting, presumably due to loss of Bi from the specimen. The majority of completely faceted boundaries were found between grains with misorientation Σ=3. About 65% of the facets of these boundaries were found to lie parallel to crystal plane pairs of the type {111}1/{111]2- The significance of these findings in light of recent high resolution electron microscopy experiments is discussed.

Ge precipitates in Al-Ge alloys have been observed to undergo a transformation in shape during in-situ temperature cycling in a high voltage electron microscope. Octahedral precipitates with a parallel-cube orientation relationship spheroidized on heating and refaceted to the octahedral shape on cooling. This shape transformation was essentially conservative if the temperature excursions were kept small. These observations are discussed in terms of an interface roughening transformation.

Surface extended x-ray absorption fine structure (SEXAFS) was used to investigate the interfacial conditions of Al/Cu and Al/Ni shallow buried interfaces. Previous studies using glancing angle extended x-ray absorption fine structure, x-ray reflectivity, photoemission, and SEXAFS produced conflicting results as to whether or not the interfaces between Al and Cu and Al and Ni were reacted upon room temperature deposition. In this study polycrystalline bilayers of Al/Cu and Al/Ni and trilayers of Al/Cu/Al and Al/Ni/Al were deposited on tantalum foil at room temperature in ultra high vacuum and analyzed to evaluate the reactivity of these systems on a nanometer scale. It became overwhelming apparent that the interfacial phase reactions were a function of the vacuum conditions. Samples deposited with the optimum vacuum conditions showed reaction products upon deposition at room temperature which were characterized by comparisons to standards and by least squares fitting to be CuAl2 and NiAl3 respectively. The results of this study showed that the reacted zone thicknesses were readily dependent on the deposition parameters. For both Al on Cu and Al on Ni as well as the metal on Al conditions 10A reaction zones were observed. These reaction zones were smaller than that observed for bilayers of Al on Cu (30Å) and Al on Ni (60Å) where deposition rates were much higher and samples were much thicker. The reaction species are evident by SEXAFS, where the previous photoemission studies only indicated that changes had occurred. Improved vacuum conditions as compared to the earlier experiments is primarily the reason reactions on deposition were seen in this study as compared to the earlier SEXAFS studies.

The nucleation and growth of facets on stepped Si(111) have been observed in real time using the newly developed technique of low-energy electron microscopy (LEEM). The results show that the growth of an isolated facet spontaneously stops at a well-defined size. This is a surprise as classical theories of the growth of linear facets predict a continuous growth, which would only be limited by collisions with neighboring facets. We review predictions that elastic interactions between surface regions of different structure can stabilize finite size domains and facets. We show that a model in which elastic relaxations caused by the facet boundaries stabilize a finite facet width is entirely consistent with the experimental observations.

We investigate the surface reconstructions of various faces of gold and platinum theoretically with a number of embedded atom potentials. We find that whereas all potentials examined predict equivalent bulk properties, only those with a relatively steep embedding function at surface electron densities predict the experimentally observed buckled quasihexagonal reconstruction for the (100) faces and surface energies in close agreement with experiment. Almost all embedded atom potentials considered predict the observed 2×1 missing row structure for the (110) faces, and some the observed missing row structure for the (311) face of platinum.

Using a tight-binding, total-energy model, we examine atomic relaxations of the ideal stoichiometric and reduced tin oxide (110) surfaces. In both cases we find a nearly bond-length conserving rumple of the top layer, and a smaller counter-relaxation of the second layer. These calculations show no evidence of surface states in the band gap for either surface.

It is demonstrated by ultra-high vacuum transmission electron microscopy that subsurface dislocations and stacking faults strongly interact with the Au (001) (5×n) surface reconstruction. This effect is found in both bulk single crystal and thin fílm samples.

Channels with widths in the range from 5 μm to 25 μm were formed in {100} surfaces of LiF single crystals by a photolithographic technique. Specimens annealed at or above 0.90 Tm, where Tm is the melting point, and then quenched showed die channels and the ridges between them develop rounded profiles. Evolution of these profiles was evaluated for the various channel widths and for interchannel ridge spacings of 5 to 100 μm in terms of: a) an accepted theoretical model for a surface diffusion controlled process, and b) a model which assumes that shape changes depend only on the relative energies of attachment of atoms in surface sites with various surface curvatures. Either model is consistent with the experimental observations to within the reproducibility in measurements.

Hg1-xCdxTe epitaxial layers on GaAs substrates grown by Metal Organic Chemical Vapour Deposition (MOCVD) display growth defects resembling pyramidal faceted hillocks which appear to originate from defects originally present on the substrate. For <100> oriented GaAs substrates and normal growth conditions, these growth defects have an areal density of 1–1000 mm-2. The size of the hillocks depends on the layer thickness and they have the potential to degrade performance of optoelectronic devices fabricated in the epitaxial layers. Nuclear microprobe analysis, performed with a 2 MeV He+ beam focused to less than 5 μm in diameter, has allowed the hillocks to be imaged with the technique of Channeling Contrast Microscopy (CCM). Channeling spectra, obtained by Rutherford Backseat tering Spectrometry (RBS) of the hillocks themselves, showed that the χmin was 13 %. This was similar to the χmin of the high quality single crystal surrounding material. The CCM images also revealed extensive regions of poor channeling, with shapes that suggested that the regions originally arose from scratches in the substrate. These poor channeling regions were not readily observable by other techniques.

Silicon (111) surfaces have been etched in-situ in a ultra-high vacuum transmission electron microscope. Surface steps are observed to flow during etching, so that Si atoms are removed only from steps. This is in contrast to the behavior during the formation of an oxide layer reported previously. The nucleation of steps and their interaction with surface impurities is described.

In this paper, we will present a study of the thermal reaction of AsjOs with GaAs at temperatures below 550°C using monochromatic X-ray photoelectron spectroscopy (MXPS). A solid-state interface reaction of 4GaAs + 3AS2O5 → 2Ga2O3 + 3AS2O3 + 4As, which includes the usual native oxide thermal reaction: 2GaAs + AS2O3 → Ga2O3 + 4As, as well as a decomposition reaction AS2O5 → AS2O3 + O2 is responsible for the thermal reaction in this temperature range.

This article discusses some of the changes which can occur at interfaces due to reaction or annealing. For chemically unstable interfaces, the atomic recombinations result in formation of new phases, which can even be amorphous in the initial stages. When no further chemical evolution takes place, physical rearrangement can have important consequences on the structure and properties. Examples are drawn from work on Ti-Si, Pt-GaAs, Ti-Si-O-N, Al-Si and TiSi2-Si.

In this work we describe the interaction of Pd with Si1−xGex layers in terms of structure, composition and electrical properties. Strained epitaxial layers of Si1−xGex with x=0.09 and 0.18 were grown on Si (100) by Molecular Beam Epitaxy (MBE) at a growth temperature of 550°C, to a thickness of 3300Å and 2300Å, respectively, and then capped with a 100Å Si layer. At low temperatures (around 250°C), the formation of a ternary phase Pd2Si1−xGex along with small amounts of PdGe takes place. At high temperatures (around 550°C), the interaction is characterized by the formation of a double layered structure, where a Ge rich Si1−xGex region is formed between the Pd2Si1−xGex compound and the unreacted Si1−xGex. The high temperature treatment results in strain relaxation in the epilayer below the compound region. Electrical characterization of diodes formed from these layers clearly shows they are rectifying, with Schottky barrier heights around 0.65 eV.