The lamellar transition metal chalcogeno-phosphates (M2P2S6) form an important family of two-dimensional semiconducting materials. They exhibit highly two-dimensional physical properties and an unusual solid-state chemistry that makes them of interest for new technologies. The lamellar structure is formed by stacking layers along a unique crystallographic axis. Under appropriate conditions, guest molecules can diffuse into the space between the layers to form intercalation compounds. The process of intercalation often creates defects and impurity sites resulting in a dramatic modification of the chemical and physical properties of the host lattice.

Several experimental methods have been utilized to characterize the defect structure produced by intercalation: ESR spectroscopy has revealed the equilibrium structure of intercalated molecules. Photoluminescence studies have shown a broadening of the conduction band due to the insertion of defect levels near the band edges. Optically detected magnetic resonance measurements demonstrated the presence of a strongly coupled donor-acceptor pair in the intercalated lattice.

The microstructure of vapor - deposited diamond films was analyzed by electron diffraction and transmission electron energy - loss spectroscopy. Diffraction results show regions with large numbers of stacking faults and twins. Electron energy - loss spectroscopy has been used to measure local electronic properties which are consistent with previous measurements of natural diamond. Transmission EELS investigations of the distribution of graphitic carbon at film surfaces and within the bulk are discussed.

Subsurface damage and surface roughness is determined on silicon wafers by using thermal wave and lightscattering measurements. A comparison with the dielectric breakdown behaviour of thin oxides proves the deleterious influence of a rough Si/SiO2 interface on the breakdown voltage. Subsurface damage on the other hand lowers the breakdown voltage only in connection with surface roughness.

The infrared (IR) absorption technique concurrent with thermal annealing was used to study the isolated AsGa antisite and an EL2-like defect in thermal neutron irradiated GaAs samples grown by the liquid-encapsulated Czochralski (LEC) technique. The residual absorption (unquenchable component) of the IR absorpion spectrum, after EL2 is completely photoquenched, is interpreted as the photoionization of the isolated ASGa antisite. This interpretation is supported by thermal annealing results at 600 C and by the increase of the unquenchable component as the irradiation dose is increased. A thermally unstable EL2-like defect is observed in heavily irradiated GaAs samples after 6 min annealing at 600 C. Thermal annealing kinetics show that the EL2-like defect is composed of three point defects.

A formulation for the entropy of vacancy migration based on the ballistic model is proposed and applied quantitatively to explain activation entropies which were previously considered abnormal.

A sufficient degree of electron irradiation induced damage in Si, Ge, InSb, and InAs has allowed the observation of hopping conductance having a sublinear frequency dependence of s ∝ ws with s ≤ 1. The dependence of s on both the degree of the induced damage and on temperature is studied and discussed in terms of the quantum mechanical tunnelling and the correlated barrier hopping mechanisms.

This paper reviews some of the new advancements made in solving the structure of planar interfaces in a wide range of materials and interface types. The main contributions of the HREM technique are the determination of the atomic positions at the interface, the detection of additional defects such as dislocations or monoatomic steps and more recently the chemical composition when crossing the interface. It is concluded that quantitative results obtained by image processing and pattern recognition will in the future greatly improve the knowledge of interfacial structures at an atomic scale.

The geometric and electronic structure of metal adsorbates on cleaved GaAs(l10) surfaces is studied with the scanning tunneling microscope. For the metals Sb and Bi, an ordered monolayer is formed, although in the case of Bi a series of misfit dislocations appear in the overlayer. In the case of Au, individual atoms are observed on the surface, forming clusters at higher metal coverage. Spectroscopic measurements reveal the presence of a state within the GaAs band gap. This state is observed near individual metal adsorbates (for Au and Sb), and near the edge of metal terraces (for Sb and Bi). The observed state is responsible for determining the position of the Fermi-level at the surface.

We first list, in catalogue form, a number of research subjects which have utilized the fieldion microscope (FIM) and atom-probe field-ion microscope (APFIM) techniques in their solution. Then we present the results of a combined transmission electron microscopy (TEM) and APFIM study of a grain boundary (GB) in a Mo-5.4 at.% Re alloy, which had been annealed in bulk form for 35 hours at 1273 K to induce Re segregation. A GB with an orientation within ≈0.4° of Σ = 9 was studied employing TEM and analyzed in detail using Bollmann's 0-Lattice theory and Frank's formula. A set of secondary GB dislocations was observed with a spacing of 11.4 nm. The APFIM measurements -- on this same GB -- indicate that it has a Re concentration of ≈9.8 at.%; this value is 1.75 times greater than the matrix's measured concentration of 5.6±0.9 at.% Re. Thus this research constitutes direct and quantitative experimental evidence for solute-atom segregation to a high-angle grain boundary with a relatively high degree of coincidence ( ≈Σ1 = 9 ). These results are consistent with our Monte Carlo simulations of high coincidence twist boundaries and a Σ = 5 tilt boundary in Pt-1.0 at.% Au alloys which show that solute-atom segregation occurs mainly to the dislocation cores. The experimental and simulated values of the enhancement factor are approximately the same.

In this paper a new method for high-resolution imaging of a crystal lattice is presented, based on high-angle electron scattering in a scanning transmission electron microscope (STEM). An electron probe of atomic dimensions is scanned over the sample and the electron flux scattered through large angles measured by an annular detector and used to form an image. The detector integrates over a large range of angles and therefore replaces the coherent phase contrast of conventional high resolution TEM with the strong atomic number or Z-contrast characteristic of high angle Rutherford scattering. These characteristics make the image entirely complementary to the conventional image, ideal for studying the atomic structure and chemistry of defects and interfaces. Examples of the high Tc superconductors, epitaxial Ge on Si, and Sil−xGex/Si strained layer superlattices are shown, and a simple approximate method of image simulation is presented.

A position sensitive detector has been added to the Oxford atom probe facility, allowing the microchemistry of field ion specimens to be analysed with excellent chemical specificity and a lateral and depth resolution of better than 0.5nm. This paper presents some recent results obtained with this equipment on the chemistry and morphology of interfaces in multi-quantum well samples, illustrating the power of the technique in obtaining very detailed information on microstructural features with dimensions less than lnm.

A Field Ion Microscope Imaging Atom Probe (FIM-LAP) has been applied to study the atomic structure of the icosahedral phase of the Al-Mn system. A multiple twinning model for icosahedral quasicrystals could be disproved, by calculating its FI image, and comparing it with experimental images. One of the decorations of the three dimensional Penrose packing (3DPP) of which FI images were calculated does compare favourably with experimental images, as far as the relative prominence of the two and fivefold poles, and the interplanar distances along the twofold directions are concerned. In particular an atomic decoration of vertices and two sites in the interior of the thick rhombohedron, which is one of the two building blocks of the 3DPP, turned out to be in agreement with the experimental findings.

Results are presented of direct measurements of the adhesion between two molecularly smooth mica surfaces in water. The results show that the adhesion forces and surface energies strongly depend upon the angle between the two surface lattices (angle of crystallographic misorientation). Apart from a relatively angle-independent “baseline” adhesion, sharp adhesion maxima (corresponding to minimum energy “cusps”) were observed at θ = 0°, ±60°, ±120°, and 180°. These discrete angles coincide with interplanar orientations of maximum crystallographic alignment or dense CSL structure. As little as ±1° away from the energy maxima, the energy decreases by 50%. This is much more dramatic than has previously been obtained with high energy metallic solids and suggest that the peak shapes are determined by the interplay of interlayer (adhesion) forces and intralayer (lattice) forces. For the mica system, the lattice forces are much stronger than the van der Waals adhesion forces, and thus the peaks are very sharp. Adsorption of ions onto the mica surfaces decreases the adhesion as well as the whole longer-range force-law which is also angledependent but to a smaller degree as the distance between the surfaces increases beyond a few molecular layers. The consequence of these findings is that the adhesion of grain boundaries and the equilibrium thicknesses of thin interfacial films and intergranular spaces are determined not only by the properties of the surfaces and the molecular structure of the intervening film but also on the relative crystallographic orientation of the two surfaces.

Si/SiO2 interface structures found in three types of lateral seeding epitaxy (lateral solid phase epitaxy; LSPE, epitaxial lateral over growth; ELO, and laser annealing; LA) were studied with a high resolution transmission electron microscope. The (001) Si/SiO2 interface found in the LSPE was thought to have similar flatness as its initial SiO2 surface. In the twin region of the ELO, where the (221)T plang should be parallel to the substrate, the Si/SiO2 interface was sawtoothed with (111)T and {110)T micro-facets. The (001) Si/SiO2 interface in the LA was flatter than that in the LSPE and nO twins were observed. However, the (115) Si/SiO2 interface was saw-toothed. In this case, both (111) and (111) twin boundaries were observed, and (111) and (110) interfaces were atomically flat. A reaction between the Si and SiO2 is expected to occur at their interface, and the appearance of atomically flat interface or saw-toothed facets with low-index planes (which may be thought to have low interface energy with SiO2 ) may be possibly attributed to such reaction.

This paper discusses two analytical techniques: (i) a high resolution transmission electron microscopy (TEM) technique of imaging Si (111) planes at Si/SiO2 interface, and (ii) an accurate measurement of the stress in silicon (Σsi) just below the interface using x-ray microdiffraction (XRMD) technique. The combination of these two techniques allows us to probe Si/SiO2 interfaces for various oxides (75-250Å) grown by different oxidation processes.

A Transmission Electron Microscopy study of the defect microstructure in Silicon On Sapphire before and after Rapid Thermal Annealing is presented. The annealed material is shown to contain a much lower density of twins and threading dislocations. Comparison with the asgrown microstructure enables possible explanations to be proposed for these observations in terms of the removal of barriers to the introduction and movement of dislocations in response to misfit and thermal expansion strains. A regular array of misfit dislocations is observed in the interface of annealed material. These have non-rational line directions and are consistent with complete misfit accommodation.

Experiments are described in which crystals are grown by molecular beam epitaxy to reveal the character of the forces transmitted through interfaces. Both long range forces carried by the electron liquid in metals, and short range interactions associated with atomic size and misfit, are discussed.

The zero-temperature energies and equilibrium volume expansions of point-defect free asymmetrical grain boundaries (GBs) involving the four densest planes in fcc bicrystals (with some higher-index plane on the other side of the interface) have been determined using an embedded-atom-method potential fitted to Au. It is found that the two asymmetrical tilt GBs at the endpoints of the related GB energy vs. twist misorientation curves give rise to pronounced energy cusps. As for symmetrical GBs, a practically linear relationship between the GB energy and equilibrium volume expansion is observed. The volume expansion and the destruction of the perfectcrystal stacking at the GB are shown to cause a pronounced local decrease in the resistance towards shear parallel to the GB plane.

The energetics of dislocation nucleation mechanisms in strained layers are calculated: for strains below 1% nucleation of new dislocations at the surface seems implausible. An experimental TEM study of the first dislocations in lowmismatch GeSi/Si epilayers suggests that dislocations are appearing through a completely novel type of dislocation source. 1/6<114> stacking faults which we observe in unrelaxed films appear to dissociate to emit a glissile dislocation. This source differs from all previous mechanisms in that it occurs in “dislocation-free” material, and a single fault can generate two distinct types of dislocation.

Ultrathin (>5 nm) films of cobalt have been deposited at room temperature onto silicon (100) and annealed to form CoSi2 in an Ultra High Vacuum (UHV) Transmission Electron Microscope (TEM). We show that there is a critical thickness of cobalt, ∼1 nm, below which CoSi2 is formed directly upon annealing to –400°C and above which CoSi2 is formed via in-situ-CoSi2. The thicker CoSi2 layers which originate from the severely mismatched intermediate phase show many epitaxial orientations while the thinner CoSi2 layers, which form directly, show only three. We relate the suppression of the intermediate phase, and consequent good epitaxy, to the dominance of interface energy in ultra thin films.