The atomistic structure of the coherent regions of Nb/A12O3-interfaces of various substrate orientations have been determined by high-resolution electron microscopy (HREM). The substrate surfaces were parallel to (0001)A12O3, (0110)A12O3, (2110)A12O3 and (0112)A12O3. In all cases, the Al sublattice of the A12O3 substrate is continued in the first Nb layer at the interface. This principle results in the unique orientation relationship.

The Burgers vectors of the misfit dislocations and the geometry of the dislocation network of all Nb/A12O3-interfaces have been determined by HREM. All Burgers vectors are lattice vectors. Thus no coherent regions with different atomistic structures are found. The Burgers vectors are of the type 1/2<111>. These Burgers vectors correspond to the Burgers vector of bulk dislocations. All Burgers vector components which do not accommodate the lattice mismatch are compensated in the networks. The network geometry is rectangular for the following interface planes: (0110)A12O3||(112)Nb (orientation 2) and (0112)A12O3||(001)Nb. If the interface is parallel to (0001)A12O3 and (111)Nb the geometry is rhombic.

The core structure of misfit dislocations of orientation 2 with line direction ξ1=[110] are calculated with an atomistic model and a continuum approach. The calculated core structures are in good agreement with the experimental HREM-micrographs of misfit dislocations of orientation 2.

A metal-ceramic interface was produced by depositing Al on a {100} MgO substrate in a MBE system. The interface was studied with High Resolution Electron Microscopy. Results of some image simulations are shown, raising the question if effects of ionicity and charging should be taken into account.

A novel process was developed to firmly coat an aluminium alloy, A16061, with α-A12O3 by means of laser processing. In this approach a mixture of SiO2 and Al powder was used to inject in the laser melted surface of aluminium. A reaction product α-A12O3 layer of a thickness of 100 μm was created which was well bonded to the aluminium surface.Various interfaces, A1/α-A12O3, Al/mullite and α-A12O3/;mullite, were studied by conventional transmission electron microscopy (CTEM) and high resolution electron microscope (HREM). It turns out that the presence of the A1/;muilite interface may be essential to form a well bonded oxide layer and the high Si-content α-A12O3 intermediate layer may be wetted better by liquid Al.

The structural evolution of Au/Ni multilayers (with an increasing number of Ni monolayers (MLs)) has been investigated by HREM. As soon as the thickness of Ni becomes larger than 5 MLs, a structural change occurs which in fact has been predicted by numerical simulations. The deformation in the multilayer has been characterised by HREM image processing and has been related to the Ni profile. This profile has been compared to the chemical profile obtained by scanning PEELS analysis through the multilayer.

An atomistic model for a Ni/Zr hetero-interface formed between closed packed atomic planes is constructed and simulated using energy minimization techniques. The results show how misfit dislocations are introduced in the system and form an hexagonal array, and that the strain field in Ni can reach values two times larger than those in Zr. Calculated values for antisite defect energies are positive and are a strong function of position at the interface, reflecting the role of the dislocation network.

Previous investigations into the nature of polytypoid structures in the A1N-A12O3 and A1NSiO2 systems have concluded that these structures are comprised of ordered stacking faults which accommodate oxygen (and silicon) in the basic wurtzite (2H) AIN structure. The polytypoids are distinct chemical phases intimately related to the pure 2H AIN. More recent work in low oxygen content (<6 at.%) A1N has elucidated the evolution of oxygen-related point defects, and transformation of these defects into extended structures. These studies have shown that all oxygenrelated extended defects in the A1N-A12O3 system are inversion domain boundaries (IDBs).

We present here extensions of the concepts developed from low oxygen content studies which lead to direct application in understanding the polytypoid structures. High resolution electron microscopy (HREM), specific electron diffraction experiments, and structural models are utilized to prove that the polytypoid structures are not based on stacking faults, but, in fact are based on IDBs.

The microstructural and chemical characteristics of silicon carbide whisker/calcium phosphate and carbon fiber/calcium phosphate composites were studied using analytical transmission electron microscopy. The interface at these calcium phosphate-based composites was studied, with particular attention to finding evidence of a chemical reaction at the interface. Structural observations made on these composites explain the fact that their mechanical properties may be strongly affected by the structural properties.

A thin-film substrate geometry is described for the study of enhanced or seeded solid-state phase transformations. As an example of this approach, thin films of hematite have been used as substrates for the study of the seeded phase transformation of a boehmite-derived transition-alumina to α-A12O3. The hematite films were grown on bulk (0001) α-A12O3 single crystal substrates by pulsed-laser ablation. A layer of a boehmite sol was then spin-coated onto the thin film. The assemblages were then heated to 950°C, or 1000°C in order to induce the phase transformation. Specimens were imaged in cross section by transmission electron microscopy. No transformation was observed for specimens heated to 950°C. In specimens heated to 1000°C, the transition alumina was found to transform to alpha-alumina, starting at the surface of the hematite film, via solid-state heteroepitaxy. In this case, islands, growing out from the hematite film into the transition alumina layer, were observed.

High-quality NiO thin films have been grown on single-crystal α-A12O3 substrates ((0001) orientation) by pulsed-laser ablation, forming essentially the idealized solid-state reaction geometry-a single-crystal film in intimate contact with a single-crystal substrate. These reaction couples have been characterized by cross-section transmission electron microscopy and scanning electron microscopy both before and after being heated in air to induce the solid-state reaction (i.e., Ni-spinel formation). The NiO films consisted of two twin variants which were found to conform to the underlying substrate surface steps. The substrate surface steps were produced by heat-treating the substrates prior to thin film deposition. Using this reaction geometry, it has been found that the initial reaction of the spinel takes place where twin boundaries in the NiO films meet the substrate. The initial reaction corresponds to the nucleation of the spinel. This interpretation is supported by the fact that the reaction proceeded faster up the NiO twin boundaries than elsewhere along the reaction layer (i.e., nucleation of the spinel is easier at twin boundaries in the NiO film). Scanning electron microscopy has been used with the present thin-film reaction geometry to measure reaction layer width along interfaces up to 2 mm long.

A glass ceramic based on the CaO-A12O3-BaO-MgO-B2O3 system was investigated using transmission electron microscopy in order to understand interactions among multiple oxide phases. The microstructure consisted of various crystalline and amorphous phases with stacking faults and dislocation loops in some of the crystalline phases. The microstructural development and phase assemblage of the complex system appeared to be related to defect-interface interactions during heating and cooling processes.

The microstructural and chemical characteristics of the segregated particles, Ni-(Mg)-Al spinel phases, and K-ß’’’ alumina precipitates in fine-grained alumina co-doped with 0.15 wt % of MgO and 0.10 wt % of NiO were studied using analytical transmission electron microscopy. The segregated Ni particles and second phases were generally found at triple junctions or on grain boundaries. The K-ß’’’ alumina precipitates were found to contain occasionally a high density of stacking faults. These microstructural observations point out the location of the dopants and impurities during the sintering process.

In an effort to improve the uniformity of the threshold voltage, the Schottky barrier height, and the ideality factor, Ti0.29W0.52N0.19 and W0.81N0.19 gate metal depositions have been investigated as a function of annealing conditions for GaAs based MESFET devices. Crosssectional TEM samples were made of each device. The results of these studies indicate there is a systematic and significant reaction occurring between the gate metal and the GaAs upon 850°C and 900°C rapid thermal annealing. These reactions take different forms depending on whether Ti is present or not. If Ti is absent (i.e. WN gates) then the interfacial roughness between the gate and the GaAs is less than 30Å indicating the metallization is very unreactive. The WN contacts for some gates show void formation indicative of GaAs decomposition also for some devices an amorphous layer is observed at the interface. Selected area diffraction patterns indicate only the alpha-W and beta-W2N phases are present. For the TiWN gates the interface roughness is as large as 200Å upon 900°C 10 second RTA. However no voids or interfacial amorphous layers were observed. Again only alpha-W and beta-W2N were observed in the bulk of the gates. For both systems, beta-W2N appears to form at the interface however the morphology of the beta-W2N grains are much larger for the TiWN gates. Electrical results indicate the TiWN gates have a lower ideality factor (near 1.1) and greater uniformity across the wafer compared to the WN gates. It is proposed that the presence of Ti in the gate metal aids in reducing any surface oxides thus improving the ideality and uniformity of the gate metal/GaAs contact.

Metallurgical and electrical properties of β-phase PdAl Schottky metallizations on n-GaAs after rapid thermal annealing for 20 s in the temperature range 500-1000°C have been investigated using x-ray diffraction, transmission electron microscopy, Auger depth profiling and current-voltage measurement. The Al-rich contacts were stable up to 900°C, whereas the Pdrich contacts were less stable. The thermal stability of Pd-rich contacts decreased with increasing Pd composition, and interfacial reaction after high temperature annealing resulted in the formation of PdGa compound. The interface between Al-rich PdAI and GaAs substrate was quite sharp even after 900°C anneal. The Schottky barrier heights of Al-rich PdAl contacts increased with annealing temperature. The barrier height enhancement in the annealed Al-rich contacts can be attributed to the thin AlxGal−xAs layer formed at the interface between PdAl and GaAs.

A solid phase regrowth process on GaAs has been observed in Pd- and Ni- based bi-layer structures, e.g. the Si/Ni, the Ge/Pd, the In/Pd, and the Sb/Pd structures. Due to the regrowth, uniform epitaxial layers of Ge, GaAs, InxGa1-xAs, and GaSbl-xAsx on GaAs substrates by solid phase reactions can achieved. The model of this regrowth process will be presented. Based on this regrowth mechanism, a series of non-spiking planar ohmic contacts on n and p type GaAs have been developed. Low contact resistivity in the range of mid 10−7 Ω-cm2 was obtained. The ohmic contact formation mechanism of these contacts will also be discussed. All the studies suggest that the ohmic behavior is a result of the formation of an n+ or p+ surface layer via solid phase reactions. The regrowth process has also been utilized to achieve compositional disordering of GaAs/AlGaAs superlattices, and low loss AlGaAs/GaAs waveguide has been obtained.

The mechanism of C diffusion through short period GaAs-A1GaAs superlattices has been investigated. The diffusion coefficient of C and the interdiffusion rates of the Ga and Al atoms were estimated by analysing, respectively, SIMS data and TEM image intensity traces. The TEM and SIMS results shows that C diffuses with an activation energy of about 2.8eV in the range 850-1000°C and that interdiffusion of Al and Ga on the group III lattice is enhanced by a factor of 5 or more when the C concentration exceeds about 5 × 1019cm−3.

A molecular beam epitaxy-grown In0.2Ga0.8As/GaAs strained layer structure has been studied by scanning tunneling microscopy in cross-section on the (110) cleavage plane perpendicular to [001] the growth direction. Individual Indium atoms were differentially imaged in the group III sublattice, allowing a direct observation of the interface roughness due to the indium compositional fluctuation. In the In0.2Ga0.8As layers, Indium atoms are found in clusters preferentially along the growth direction with each cluster containing 2-3 indium atoms. Indium segregation induced asymmetrical interface broadening is studied on an atomic scale. The interface of In0.2Ga0.8As grown on GaAs is sharp within 2-4 atomic layers. The interface of GaAs grown on In0.2Ga0.8As is found to be broadened to about 5-10 atomic layers. The atomic scale fluctuation due to indium distribution is about 20 Å along the interface in this case. We conclude that clustering and segregation are the main reason for the In0.2Ga0.8As/GaAs interface roughness.

Defects generated from a thin impurity layer between a CBE-grown epilayer and its GaAs substrate have been studied by TEM. Line defects were observed to emerge randomly from the impurity layer in the various <110> directions either as single lines or as various vshaped dislocation pairs. The origin, frequency and significance of these defects is discussed.

The state of deformation in epitaxial layers of InGaAs grown by MBE on GaAs substrates has been determined using high resolution X-ray diffraction. This method enables the strains and rigid body rotations which occur in the layers to be measured and these are described by means of a tensor. Layers of different thicknesses have been grown on substrates whose dislocation densities differ by three orders of magnitude in order to assess the influence of this parameter on layer relaxation through the motion of misfit dislocations to the interface. Transmission electron microscopy has also been used to provide additional information on the relaxations.

In this study, cross-sectional transmission electron microscopy (XTEM) was used to investigate the defect structure at the interface between CdTe(001) and GaAs(001) as well as CdTe(1 11) and GaAs(001). The heterostructures were fabricated by molecular beam epitaxy on GaAs(001) buffer layers grown in-situ by molecular beam epitaxy. The defect structure at the as-deposited CdTe(001)/GaAs(001) interface consists of both dislocations and planar faults. The planar faults are both microtwins and stacking faults. It is found that annealing of the film ex-situ causes a restructuring of the CdTe near the interface, with the microtwins being completely removed upon annealing to 450°C for 100 hours. The CdTe(111)/GaAs(001) thin film structure consists of a large number of microtwins parallel to the growth direction. This twinned structure is shown to be related to the relaxation of a residual misfit strain normal to the twin direction. Possible mechanisms for the relaxation are discussed.

Two regimes of defect generation have been found in MOVPE GaAs/Ge layers upon changing the V/III ratio between 1.3 and 11.8. For low V/III ratio the layers contained misfit dislocations along with stacking faults that had been generated by dissociation of the misfit dislocations. The stacking fault density increased with decreasing V/III ratio. This might be explained by an enhanced mobility of the dissociated partials due the reduced unintentional doping of the layer caused by reduced Ge outdiffusion from the substrate when V/III is small. The secon regime corresponds to high V/III ratios and is characterized by the absence of misfit dislocations and the presence of a high density of planar defects. This means that breakdown of the 2D layer-by-layer growth occurred and 3D island growth prevailed.