Dislocations of a/2<110> Burgers vectors lying in {001} and {111} planes in the form of cross-grids are often observed in ion implanted and thermally annealed specimens. In order to asses the mechanism of formation of these dislocations, we have calculated energies and determined atomic core structuresof a/2<110>{001} edge dislocations and their dipoles,and of a/2<110>{111} dislocations in silicon by minimizing the total configurational energy.

The plastic response of deforming crystals of mercury cadmium telluride to light occurs with a time delay that depends on wavelength, temperature, and bias voltage. The time delay exhibits a temperature dependence which increases as the temperature is lowered, andis approximately 60 seconds at 20°C. A detailed examination of a number of measurements of the time delay at constant temperature reveals that the time delay falls into one of four separate peaks. These peaks shift with temperature with an overall activation energy of approximately 0.2 eV. Furthermore, the photoplastic responses of a given crystal indicate that softening is observed roughly 40% of the time and hardening the remaining 60%. It has also been observed that the relative positions of the time delay peaks can be markedly affected by a static bias voltage.

A model which explains these observations involves the coulombic interaction of charged point defects with jogs on dislocations. The model predicts four separate time delay peaks as well as the correct ratio of hardening to softening.

Pulsed nuclear magnetic resonance proved to be a new complementary technique for the study of moving dislocations in Al—base alloys. Spin—lattice relaxation measurements clearly indicate that fluctuations in the quadrupolar field caused by moving dislocations in Al—base alloys are different compared to those in ultra—pure Al. From the motion induced part of the spin—lattice relaxation rate the mean jump distance of mobile dislocations has been determined as a function of strain. Measurements have been performed on Al—Cu, Al—Li and Al—Zn binary alloys. Asa typical illustration of the strength of this technique, this paper reports the resultsobtained of Al—(1—2 at%) Zn solid solution.

The phenomenon of plastic flow in alumina was previously [1 and 2] characterized using sintering models and transmission electron microscopy. Some of the findingsof the work were (a) near equality in the activation energy for volume diffusion and surface area reduction (82 kJ/mol), (b) a higher activation energy (440 kJ/mol) for Coble creep mechanism in the absence of gamma/alpha phase transformation and a lower activation energy (250 kJ/mol) when phase transformation was a part ofthe sintering process and, (c) presence of extended dislocations and deformed electron diffraction spots.

In view of these results it was of interest to follow the effect of solute addition on plastic flow [ 3 ]. The solutes were incorporated in alumina through gel synthesis route and formed solid—solution systems of Cr203— A1203 and MoO3 — A12O3 at 1000°C. In the course of sintering there is partiai vaporization of caromiaand reduction of MoO3. The chromiavacancy and Mo metal thus impart an impurity decoration to the lattice. The scanning electron micrographs seem to show that they are segregated along grain boundaries, sub—grain boundaries and dislocations. With increase in temperature the linear vacancy segregations and the scattered vacancy clusters annihilate to form pores. These pores transform to creep cavities that extend from grain boundary to volume. The clustered occurrence of Mo at grain boundaries and its extended spacing in the subgrain boundary is perhaps indicative of a dislocation pipe model for its segregation. On the basis of these modeling and microstructural results a heuristic argument is presented in favor of kinetic equality among self diffusion, dislocation pipe diffusion and dislocation climb, and in favor of the commencement of Coble and Nabarros—Herring creep with severance of these equalities.

It has been found, using computer simulation techniques, that both edge and screw dislocations can be stably introduced into an amorphous Lennard-Jones solid, and can be moved through the model under an applied shear stress.

High resolution electron microscopy (HREM) is recognised as a powerful technique for thedetermination of atomic structures at crystal defects and interfaces. The application ofHREM to the study of insulator/semiconductor and metal/semiconductor interfaces is of particular technological interest. Correlation of electrical properties withinterface structure has been performed, taking advantage of the resolution available in the JEOL 4000EX. Images are usually obtained in a <110> projection, however in the JEOL 4000EX (point-to point resolution <1.7A). we have imaged semiconductor interfaces in the <100=direction using the (220) planes of 1.92Å spacing revealing all atomic columns in silicon, permitting “structure images” of interfaces to be obtained. Two types of interface have been studied at <1.9Å resolution. The roughness of the important crystalline Si/amorphousSiO2 interface observed in implanted buried oxide layers and after wet and dry oxidation of silicon is relevant for the correlation of carrier mobilities with interface structure. Analysis of both the NiSi2/Si(100) and AI/AIGaAs(100) crystal/crystal interfaces where a periodic structure is observed in the plane of the interface allows the use of rigid shift measurements and multislice image calculations to determine an atomistic model. The influence of the NiSi2/Si interface structure on the Schottky barrier height is discussed.

A preliminary survey of the dislocation structures of grain boundaries in Bridgman grownpolycrystalline GaAs suggests that many of the phenomena observed in grain boundaries inface centered cubic metals, silicon and germanium also occur in boundaries of a polar semiconductor. Our experiments show that low angle grain boundaries are comprised of crystal lattice dislocations and deviations from coincidence orientations are accommodated bysecondary dislocations; specifically, in twins, the a-fringe technique reveals that there are multiple structures where the different domains are separated by partial grain boundary dislocations.

Nucleation and growth of GaAs fIlms deposited by Molecular Beam Epitaxy upon Si(l00) substrates are studied by transmission electron microscopy. The initial nucleation of GaAs consists of approximately hemispherical islands associated with steps upon the substratesurface and coherently strained to the substrate lattice. As the island size increases, crystalline defects relax the strain between epilayer and substrate. Island coalescence is a secondary defect generation mechanism. Subsequent growth of the epitaxial GaAs layer reveals a progressive deterioration of the GaAs/Si interface planarity and the growth and eventual dissolution of amorphous or misoriented crystalline regions at the GaAs/Si interface.

Composition modulations with a wavelength of -1-3 nm have been observed by transmission electron microscopy in nominally uniform AlxGa1-x As grown by molecular beam epitaxy. We describe the characterisation of this phenomenon and discuss its possible origins, in the light of the reported existence of a long range ordered structure.

Mismatched InGaAs-GaAs epitaxial layers were grown by molecular beam epitaxy (MBE) on substrates containing 9800 or <100 dislocations/cm2. Cathodoluminescence (CL), transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), and energy dispersive x-ray analysis (EDX) were used to analyze the effect of mismatch and substrate dislocation density on interface morphology. Surface ridges in scanning electron microscopy (SEM) images were found to correlate with areas of high recombination in CL. The spacing of dark recombination lines seen in CL was found to be an order of magnitude larger than the spacing of misfit dislocations seen in TEM. CL/IEM correlation reveals that some areas of the misfit array act more strongly as recombination centers than others. CL of step etched samples show that interface defects propagate into the GaAs buffer layer to depths of 4000 Å below the interface. The substrate dislocation density does not have a major effect on the number or spacing of the dark recombination lines.

Particles are observed at the epitaxial layer-substrate Interface of silicon MBE layers when Improper pre—deposition cleaning methods are used. HRTEM shows that the particles In our material are 5 nm to 10 nm In size, and Molre fringe patterns suggest the material Is crystal line. Using a combination of SIMS, HRTEM, and x-ray microanalysis methods, It Is concluded that the Interfacial particles In our material contain carbon and not oxygen, and are beta-SiC growing epitaxially with the silicon.

In situ kinetic measurements on the rate of solid—phase epitaxial regrowth of silicon in a conventional transmission electron microscope are described. The data compare well with those established for the sane material by high voltage electron microscopy and by Rutherford backscattering spectroscopy. High—resolution imaging at the same time provides direct information on atomic mechanisms. It is anticipated that this will beccme a more highly developed procedure in due course, especially for studies of interface reactions.

Recent progress in the understanding of the atomic structure of grain boundaries in ionic solids is briefly reviewed with emphasis on the application of the HREM technique to observations of tilt grain boundaries in NiO. The new generation of high-resolution electron microscopes which are capable of a point-to-point resolution of better than 2 Å have allowed atomic-scale observations that can be directly compared to theoretical grain boundary models. Agreements and differences between theory and experiment are discussed.The importance and significance of faceting and asymmetrical boundaries is pointedout.

A Nb—Al alloy has been internally oxidized to produce A12O3precipitates. The interface between plate—like AI2O3 precipitates and the Nb matrix has been investigated by diffraction, CTEM, and HREM techniques. Periodic arrays of misfit dislocations were observed which acted as diffraction gratings for the electrons. The location of misfit dislocation cores could be determined from HREM images within an accuracy of a few lattice spacings. It can be concluded that the misfit dislocations lead to a good matching of atomic rows across the interface. The dislocation arrangement at this partially coherent interface is in accordance with theoretical expectations from dislocation theory.

A number of tilt grain boundaries prepared from evaporated gold thin films have been investigated by high resolution transmission microscopy. When the grain boundary is parallel to the electron beam and the beam is parallel to a low index rotation axis such as [110] or [001]it is possible to identify atomic positions at the cores of these boundaries as demonstrated here by a Σ = 3 70.5°/[110], (112) growth twin. In many cases it is not possible to make a full atomistic structure determination because the specimen does not have translational periodicity in the beam direction. This may be because the boundary plane is not parallel to the beam or the specimen contains dislocations which have a component of Burgers vector parallel to the beam. Examples are given of various low angle boundary structures in goldwhere there are complications because of the three dimensional nature of their structure.

Solute-atom segregation effects to individual stacking faults (SFs) in Co-0.96 at.% Nb and Co-0.98 at.% Fe alloys were studied employing the atom-probe field-ion microscope (FIM) and transmission electron diffraction techniques. The mean composition of individual SFs was measured for bulk specimens which had been equilibrated in the range 450-575°C. In addition, the composition was measured with a spatial resolution, within the plane of the SFs, of ~1 Å and with a spatial resolution of <4 Å perpendicular to the SFs. These measurements demonstrated the following: (a) The meancompostion of the SFs increased with decreasing temperature according to an Arrhenius-like expression; (b) The Nb or Fe concentrations fall off very quickly with distance--within <4 Å from the plane of the SF the bulk concentation is achieved; (c) The SFs equilibrated above 4500 C contained solute-atom fluctuations (≈5 to 20 \ diameter) which correspond to compositions with stoichiometries of ≈Co2Nb or ≈Co3Fe. In the case of the Co(Nb) alloy, a transmission electron diffraction pattern was obtained ofa SF--with the electron beam normal to the SF--which exhibited superlattice reflections with six-fold symmetry around the hcp matrix reflections. This latter result is consistent with a two-dimensional phase in the SF plane with the composition Co2 Nb. Both the atom-probe FIM and the electron diffraction studies are consistent with two dimensional (2D) ordered phases in the SFs.

The behavior of oxidation—induced stacking faults(OSFs) during the O2 /NF3 oxidation of silicon has been investigated in the temperature range of 850–1100°C with varying concentration of NF 3 (0.011—0.044 vol%). In this study, we report the rapid and non-linear shrinkage of pregrown OSFs with time by a new oxidation process including small(ppm) additions of fluorine compound to the oxidant. It is also found that the shrinkage rate of OSF decreases as the oxidation time is increased. It is proposed that the fast OSF shrinkage is due to excessive vacancy flux as a result of the reaction of fluorine at the Si/SiO2 interface during the initial transient state, and subsequently the shrinkage rate is reduced as the steady—state condition of vacancy—interstitial recombination is approached.

High resolution electron microscopy has been employed to elucidate fault defects and structural details of the δ1 and δ2-Y2Si2O7 crystalline phases. From this study δ1 and δ2-Y2Si2O7 have been found to be orthorhombic having the same cell parameters but different atomic arrangements due to a change in their space groups. Computer simulations were necessary for interpreting details from the high resolution electron micrographs.

Vanadium pentoxide films were grown by sputtering a V target in O2-bearing atmospheres containing 0 to 98% Ar. The interlayer spacing was siudied as a function of sputtering gas 02 content. The results are discussed in terms of defects in thevanadyl 0 layir and correlated with target surface oxidation.

Dopants in ferroelectric materials affect the dielectric constant and the shape of the hysteresis loop. To understand and quantify these effects it is necessary to calculate the interaction between dopant and domain wall. In the following the dopant ion is modelled as an elastic dipole. The stresses surrounding a 180° domain wall are calculated in analogy to calculations in the magnetic case for Bloch walls. It is assumed that electrostrictive effects control the strains and that the spontaneous polarization does not rotate but decreases to zero at the center of the domain wall and increases in the opposite direction on the other side of the domain wall. The calculations are made assumingisotropic elastic constants. It is found that only elastic dipoles oriented in the planeof the domain wall interact with it. The interaction forces as a function of perpendicular distance between wall and dipole show an antisymmetric characteristic.