A new class of materials with ultra small grain size has recently been synthesized by combining the methods of inert gas condensation of metal vapors and in situ powder compaction. These ‘nanocrystalline’ materials, with grain sizes of 5-10 nm, can have over 30% of their atoms lying in the highly disordered interfaces or grain boundaries. Because of their unique atomic structure, nanocrystalline materials often have properties far different from their bulk counterparts. In addition, kinetic processes can be rapidly accelerated due to the short diffusion distances between grains. In this review, we will report on the thermodynamic properties and reaction kinetics of nanocrystalline metals and on such kinetic properties as sintering and grain growth in nanocrystalline ceramics.

Using high resolution electron microscopy, consolidated nanophase palladium samples were examined following electrolytic thinning after a hydriding - dehydriding cycle at 310 K. Due to the small size and random orientations of the individual grains, a large number of grain boundaries were available for examination. Some of these yielded adequate imaging conditions to allow observation of the lattice structure in the grain boundary regions. Image simulations were performed to determine the sensitivity of the technique to lattice disorder. The results of these studies suggest that grain boundary structures in nanophase palladium are similar to those in conventional coarse-grained polycrystals.

Raman spectra have been recorded for as-consolidated nanophase TiO2 samples with differing grain sizes and on samples annealed in air at a variety of temperatures up to 1273 K. The nanophase samples with the smallest grain size, about 12 nm average diameter, could have 15-30% of their atoms in grain boundaries; nevertheless, the strong Raman-active lines representative of the rutile structure were found to dominate all of the observed spectra, independent of grain size and annealing treatment. These lines were quite broad in the as-consolidated nanophase samples, equally in 12 nm and 100 nm grain-size compacts, but sharpened considerably upon annealing at elevated temperatures. The Raman data give no indication of grain-boundary structures in nanophase TiO2 that are significantly different from those in conventional polycrystals. However, defect structures within the grains, which anneal out at elevated temperatures, are evidenced by changes in the Raman spectra.

X-ray diffraction experiments on nanophase Pd have been performed with the primary goal of determining the nature of grain boundary structures in nanophase materials. A kinematical diffraction analysis has been developed to interpret x-ray θ-2θ data by comparing actual scans with scans produced by computer simulation. This simulation program has been used to explore the effects on diffracted intensity of a variety of microstructural and grain boundary structural parameters such as void concentration, grain size, grain boundary width, and changes in interplanar spacing and density in grain boundary regions. It has been found that a reasonable match to experimental data is produced by at least two model structures; in one, the material contains randomly positioned voids or vacancies, while in the other, the interplanar spacings in grain boundary regions are varied with respect to the spacings found in the grain interiors.

It is pointed out that some of the generic physical properties of a nanocrystalline material are similar to those of a grain-boundary superlattice. The structure and elastic properties of a superlattice of twist boundaries on the (110) plane of silicon are calculated as a function of modulation wavelength using a three-body potential. All elastic moduli are found to be softened. This softening is attributed to the relatively small amount of structural disorder at the interfaces.

The characteristics of Cr coverage of Cu surfaces, including determination of tc, the minimum average film thickness required for formation of a continuous film, have been studied in-situ by Auger Electron Spectroscopy (AES). Auger signal intensities of substrate and deposit were monitored during Cr film growth by vapor deposition in UHV. It was shown that substrate surface morphology (roughness) has a dominant effect on coverage rate and tc. Slower coverage rates and larger tc′s were effected by the presence of native oxides, substrate heating (to 330°C) and H2O-vapor rich (5×10−5 Torr) ambient during Cr deposition. Surface oxides seemed to affect more the coverage of a smooth than a rough surface. Conversely, substrate heating affected more the coverage of a rough surface. The combined effect of substrate heating and water vapor rich atmosphere was pronounced for both smooth and rough surface coverages. Some of the main factors controlling these effects are discussed.

In previous work, the phase stability of Fe-Cr-Mn alloys during irradiation was investigated in a study that included simple binaries, simple ternaries and commercially produced alloys. These low activation alloys are being considered for fusion reactor service in the first wall and in other structural applications subject to high neutron doses. In addition to phase instabilities observed within the grains, grain boundaries were susceptible to varying levels of precipitation dependent upon alloy composition, displacement dose and irradiation temperature. This paper describes the grain boundary microstructures that developed in these Fe-Cr-Mn alloys during irradiation.

A new atomistic-simulation method for calculating the full local elastic-constant tensor in terms of local stress and local strain for inhomogeneous systems is described. Results of simulations of an isolated high-angle twist grain boundary are presented. A dramatic reduction in resistance to shear parallel to the grain boundary is observed, and its relation to structural disorder is discussed.

The (0001) face of α-Al2O3 and the initial growth of ultra-thin aluminum, films deposited on this surface were studied by a combination of low energy electron diffraction, angle resolved x-ray photoelectron spectroscopy and thermal desorption techniques. At high temperatures, the (0001) face of α-Al2O3 reconstructs to form a (√31×√31)R±9° structure which remains stable at lower temperatures, as evidenced by IEED. ARXPS shows that the annealed sanple retains its bulk composition up to the solid-vacuum interface.

Thin Al films were deposited on the above surface by in situ evaporation. ARXPS results indicate a uniform growth of the initial monolayer of aluminum. Further growth (<3 A°) deviated fr the layer by layer adsorption mechanism.

The initial stage of formation of the Ni/A12O3 interface under different conditions was studied by various surface science techniques. Nickel was deposited in situ in a UHV system onto the basal plane of a sapphire substrate at various temperatures and oxygen partial pressures. The interfacial reaction processes were simultaneously monitored by XPS. When Ni was deposited at elevated temperatures and in the presence of sufficient oxygen, the NiAl204 spinel was formed epitaxially on the Al2O3 substrate, as confirmed by LEED. While under UHV conditions (<4×10−11 torr) and at elevated temperatures (<800°C), the Al2O3 was partially reduced by Ni, and the evidence of Ni-Al intermetallic alloy formation was observed. Further efforts include the construction of a UHV system capable of preparing interfaces suitable for interfacial structure and adhesion studies.

The interface chemistry and structure of thin Al and Au films deposited on Si3N4 have been studied. In the case of Al/Si3N4 system, an interfacial AIN like layer was observed in the as-deposited state. The thickness of this layer was found to increase with increasing the temperature up to 600°C. This thin AlN layer acts as a diffusion barrier which prevents Al to diffuse into Si3N4 Furthermore, Si released in the reaction between Al and Si3N4 appears to crystallize into small islands dispersed in the interfacial region. In contrast to Al, no reaction between Au and Si3N4 was observed in the as-deposited state. However, after heat treatment at temperatures higher than 400°C gold silicides (Au5Si2,Au2Si,Au3Si) with a very thin Si layer accumulated on the Au surface were observed.

The atomic structure of internal interfaces in dense-packed systems has been investigated by high-resolution electron microscopy (HREM). Similarities between the atomic relaxations in heterophase Interfaces and certain largeangle grain boundaries have been observed. In both types of interfaces localization of misfit leads to regions of good atomic matching within the interface separated by misfit dislocation-like defects. It appears that, whenever possible, the GB structures assume configurations in which the atomic coordination is not too much different from the ideal lattice. It is suggested that these kinds of relaxations primarily occur whenever the translational periods along the GB are large or when the interatomic distances are incommensurate. Incorporation of low index planes into the GB appears to lead to preferred, i.e. low energy structures, that can be quite dense with good atomic matching across a large fraction of the interface.

Adhesion of metals to ceramics is an area of extreme importance for packaging of electronic devices. In one of the several adhesion schemes that can be employed to promote adhesion between metals and ceramics, the metal is preferentially oxidized at the interface and there is solid solution mixing between the substrate and the oxidized metal at the interface. An example is the Ni/MgO system. Estimation of the extent of mixing at the interface is often difficult and time consuming. This work describes a simple non-destructive method to estimate the extent of interdiffusion between the oxides using a standard x-ray diffraction measurement. This technique relies on the changes in the peak shapes and positions as a function of the nature and extent of interdiffusion. The technique is precise enough to allow one to estimate interdiffasion coefficients in some oxide/oxide systems. The diffusion and intermixing phenomena in the NiO/MgO system will be examined as an illustrative example.

Ceramic coatings on oxides can be studied by high resolution transmission electron microscopy (HRTEM), with minimal sample preparation, if the substrate consists of nonporous particles of simple geometric shape. Interfaces suitable for ‘end-on’ examination by HRTEM can be readily obtained without any necessity for ion-beam thinning. All the interface orientations that are thermodynamically stable are available for examination from a single sample. This technique is of general applicability and can be used for studies of metal-ceramic and ceramic-ceramic interfaces. We have examined the nature of boron nitride interfaces with oxides such as MgO, TiO2 and Al2O3 and find that BN appears to wet the oxide surface and form tough, adherent coatings. The hexagonal crystalline BN grows with the (0001) planes always being locally parallel to the oxide surface in every instance.

Several examples will be given of high resolution electron microscope images of both grain boundaries and interfaces and the methods which have been applied to understanding their atomic structure. Specific expitaxial interfacial structures considered are: Pd2Si/Si used for ohmic contacts, Al on Si overlayers and CaF2/Si where the CaF2, is an attractive possibility as a dielectric material. For the case of grain boundaries specific examples of both twist and tilt boundaries in Au will be given to show the imaging capability with the new generation of medium voltage electron microscopes.

Fracture of iron-doped silicon has been studied using HREM. Fractures were introduced into cross section specimens of oxidized silicon using microhardness indents. A crack is extended using thermal stresses generated by the electron beam. The tip of the advancing crack is made up of two or more parallel sub-cracks. As the crack grows, one of these sub-cracks appears to dominate while the multiple crack front still exists at the tip. Also shear strain has been seen across the crack interface. The process appears to be much more complicated that existing models suggest.

Amorphous hydrogenated carbon films are deposited by direct ion beam deposition onto Si and W substrates at room temperature. Simultaneously, the sample surface composition is measured by Auger electron spectroscopy. The results indicate a sharp interface between film and Si and the formation of a W2C layer between film and W. The in-situ measurements are compared with sputter depth profiles. It is found that the former ones give insight into film growth processes, that is unattainable by sputter profiling.

The predominant application of secondary ion mass spectrometry (SIMS) to organic polymeric solids has been the molecular monolayer analysis of thin films in the “static” mode. The primary emphasis in this paper, however, is the evaluation of SIMS for two or three dimensional compositional mapping studie of spatially modified polymer. This often requires the use of the “dynamic” SIMS mode to provide lateral images, depth profiles, or 3-D image depth profiles. Selected applications are presented including SIMS studies of surface derivatized polymers, metal-doped conductive polymer films, and patterned polymeric materials or fibers. One analytical objective is to assess the extent to which compositional information is limited by primary beam damage. The outlook for SIMS instrumentation combining high lateral spatial resolution with minimal primary beam damage to surface molecules is summarized, for example the combination of microfocused liquid metal ion sources and time-of-flight mass spectrometry.

If a polymer mixture which is in the bulk one-phase region is next to an interface - this may be with another polymer, with a non-polymeric solid, or with the air - the composition of the mixture at the interface will be different from the bulk [1-4]. There are two questions we would like to understand: what determines the composition of the mixture at the interface, and how does that composition increment decay back to the bulk value. This surface or interface segregation has important practical consequences; in the surface case such segregation will profoundly affect wettability, with consequences for the strength of adhesive joints and the biocompatibility of polymeric surgical implants, as well as influencing friction and wear; at interfaces with non-polymers segregation is important for the adhesion of mixed polymer phases to non-polymer phases such as reinforcing fibres or fillers. In this paper we describe some experiments on surface segregation in a very well characterised model system and we describe a recent theory that can be quantitatively tested by our data. We will consider the consequences of this new understanding of surface segregation in polymer mixtures, and we will argue that many of these conclusions may be carried over to the more general case of interface segregation, which opens up a number of interesting technological possibilities.

Diffusion of Cu in polyimide(PI) film was observed after Cu evaporation on PI at room temperature. Annealing treatment significantly enhanced the diffusion of Cu. The diffusion coefficient measured at 200 and 400 C using the Fickian erfc solution are 3 × 10−14 and 1 × 10−13 cm2/sec, respectively. Cu shows the Fickian diffusion behavior. In contrast to Cu, no clearly measurable diffusion had occurred for an as-deposited Cr specimen and a specimen annealed at 400 C for 1 hour. However, for longer annealing times a slight amount of Cr diffused into PI because of the growth of the intermixed region. The diffusion coefficients of Cr at 200 and 400 C for less than 20 hours are 2 × 10−15 and 7 × 10−15 cm2/sec, respectively. The diffusion of Cr in PI shows non-Fickian behavior.