In order to achieve a better understanding of hydrogen segregation to interfaces, a combination of techniques is being used in which hydrogen is deliberately introduced into planar interfaces between thin films, then the segregation measured using highenergy ion-beam profiling techniques. Results are given for heterophase interfaces produced by epitaxial deposition on silicon: The AI/Si (111) and CoSi2/Si (001) interfaces. A preliminary study of Au tilt boundaries in thin-film bicrystals shows the presence of a large amount of hydrogen, ∼1016 atoms/cm2, in the boundary after plasma hydrogenation, but also the presence of C impurity (∼ 1.6 × 1015 atoms/cm2 ) and Ag. We conclude that some of the hydrogen in the boundary may have been chemically bound to the carbon.

Discontinuous and continuous interfacial layers at the whisker/matrix and grain boundary interfaces in silicon carbide whisker reinforced silicon nitride based composites were investigated by high resolution electron imaging and analytical microscopy. Wide differences in chemical and structural widths of the interfaces were observed.

The effects of segregation of tramp impurities such as sulfur on metal/ceramic bonding is discussed. Microstructural and chemical information is given for the Fe/sapphire interface. The segregation behavior of the interface is evaluated between 500–800 °C. The interfacial structure is shown to be important to the segregation behavior. A possible link between the segregation of sulfur and interface void formation is presented.

Effects of rare-earth (RE) addition on creep, workability and the scaling behavior of Cr-Si, Cr-Ni and Cr-Ni-N steels were investigated. By RE additions both the creep strength and the workability of the tested steels were increased and the spalling resistance was improved. Analysis snowed that RE atoms segregated to grain boundaries, inhibiting segregation of other harmful impurities, and enhanced the cohesive strength of grain boundaries. SEM, EDX, ICP and X-ray investigations of scales showed that although no RE oxides were formed, RE modified the constituent of the scales, promoted the formation of a dense and protective scale and enhanced the cohesion between the scale and the matrix.

The oxidation behavior of Ni, implanted with either divalent Ce2+ or trivalent Y3+, has been studied to test the general applicability of the grain boundary segregation explanation for the reduction in rate of oxidation resulting from reactive element additions to metals that form protective oxide scales. Oxidation of Ce- and Y-implanted Ni at 900°C resulted in grain boundary segregation of the implanted species in the NiO scales formed. The rate of oxidation of Ni was reduced and there was evidence for a change in oxidation mechanism. Additionally, the grain size of the oxides was much smaller. All the observations were entirely consistent with a reduction in cation transport resulting from segregation of foreign ions at the oxide grain boundaries. These results on Ni are compared with recent studies of Ce- and Y-implanted Cr to draw general conclusions about the relationship between grain boundary segregation in oxides and the reactive element effect on oxidation.

The high resolution analytical technique of Atom Probe Field Ion Microscopy (APFTM) haseen used to characterize grain boundaries and the matrix of a stoichiometric NiAl alloy doped with 0.04 (100 wppm) and 0.12 at. % (300 wppm) boron. Field ion images revealed boron segregation to the grain boundaries. Atom probe elemental analysis of the grain boundaries measured a boron coverage of up to 30% of a monolayer. Extensive atom probe analyses also revealed a fine dispersion of nanoscale boride precipitates in the matrix. The boron segregation to the grain boundaries was found to correlate with the observed suppression of intergranular fracture. However, the decrease in ductility of boron-doped NiAl is attributed in part to the precipitation hardening effect of the boride phases.

The precipitation behavior of cobalt and nickel at grain boundaries in multicrystalline silicon is investigated. The metals are diffused into the specimens from a surface source between 800 -1000 °C and the precipitation after cooling is studied by conventional and high resolution TEM. Cobalt and nickel disilicide precipitates nucleate both in the bulk and at grain boundaries. They form few large (micrometer size) plate-like or three-dimensional precipitates depending on the cooling rate. Cobalt disilicide with a slightly larger lattice mismatch has a higher tendency to nucleate at large angle grain boundaries. Both suicides nucleate preferentially at coherent twin boundaries forming a few atomic layers thick platelet parallel to the {111} twin plane. HREM and image simulations are performed to analyze the Si / MS12 / twin interface structure (M = Co, Ni).

Segregation at grain boundaries in austenitic stainless steels sensitized by either thermal annealing or irradiation was studied by analytical electron microscopy. Characterization of grain boundary compositions in both types of materials was performed by high spatial resolution (≥2 nm) X-ray microanalysis. Whereas similar chromium depletion is observed in both processes, there are differences in the behavior of the other alloying elements and in the mechanisms responsible for the segregation. In thermal sensitization, the nickel/iron ratio and the silicon level observed at grain boundaries are similar to those for the matrix. In cases where little or no precipitation occurs, co-segregation of phosphorus, chromium, and molybdenum occurs at boundaries and interfaces. For radiation sensitization, radiation-induced segregation (RIS) results in enrichment of nickel, silicon, and, in certain cases, phosphorus and in depletion of iron at grain boundaries. There appears to be some synergism between segregation of nickel and silicon, which increases the magnitude of RIS effects. Grain boundary precipitation is often observed in both thermally- and irradiation-sensitized materials. However, the nature and origins of the two types of precipitation are different. The formation of chromium-enriched grain boundary carbides is the cause of the chromium depletion in thermal sensitization. In contrast, the precipitates produced by irradiation are enriched in nickel and silicon and depleted in chromium relative to the matrix and therefore are the result of RIS. Results for thermal- and radiation-induced segregation in manganese-stabilized austenites are compared to that for nickel-stabilized austenites.

We have studied the distribution and diffusion of Te, Mg, and Zn dopants in GaAs which was grown by an LPE process. It was found that the distribution of the dopant atoms of Te and Zn in the Te-doped n-type epi-layer on the Zn-doped p-type substrate showed a sharp and clear interface. In contrast, the dopant distribution of Mg and Zn in the Mg-doped p-type epi-layer on the Zn-doped substrate indicated a diffuse interface because of significant interdiffusion. The X-ray diffraction of these epi-layers and substrates revealed that the Mg-doped epi-layer showed rather poorer crystalline quality than the other specimens. These experimental results can be accounted for by a model of charged vacancies in a p-type GaAs.

This work concerns a microanalytical study of CVD heteroepitaxial Si1–xGex/Si junctions with x ranging from 0.05 to 0.22. We observe that rather than being chemically abrupt, the width of the interface ranges between 200nm and 2μm with a band of misfit dislocations occupying the same region. Furthermore, the average separation of the dislocations is 2 or 3 times greater than predicted by b/δ considerations. Close scrutiny at individual dislocations within the interface region reveals a local deficit of several hundred Ge atoms per nanometer of dislocation line. It is proposed that the composition profile is rapidly spread by inter-diffusion along dislocations during the deposition process.

The effective heat of formation model enables heats of formation to be calculated as a function of concentration. By choosing the effective concentration at the growth interface to be that of the liquidus minimum, the model correctly predicL. first phase formation for 14 binary systems for which experimental data was found, except for the Au-Cu system which does not have a well-defined minimum on the liquidus curve.

Impurities, such as H, P, S, B, etc, have a very low solubility in iron, and therefore prefer to segregate at the grain boundaries (GBs). In order to analyze the energetics of the impurities on the iron GB, the LMTO calculations were performed on a simple 8-atom supercel 1 emulating a typical (capped trigonal prism) GB environment. The so-called “environment-sensitive embedding energies” were calculated for H, B, C, N, O, Al, Si, P, and S, as a function of the electron charge density due to the host atoms at the impurity site. It was shown that, at the electron charge density typical of a GB, B and C have the lowest energy among the analyzed impurities, and thus would compete with them for the site on the GB, tending to push the other impurities off the GB. The above energies were then used in a modified Finnis-Sinclair embedded atom approach for calculating the equilibrium interplanar distances in the vicinity of a (111) σ3 tilt GB plane, both for the clean GB and that with an impurity. These distances were found to be oscillating, returning to the equilibrium spacing between (111) planes in bulk BCC iron by the 10th-12th plane off the GB plane. H, B, C, N and O actually dampen the deformation wave (making the oscillation amplitudes less than in the clean GB), while, Al, Si, P and S result in an increase of the oscillations. The effect of B, C, N and O may be interpreted as cohesion enhancement; this conclusion supports our earlier first-principles results [1] on B and C.

We present an atomistic model to study void formation in aluminum interconnects in integrated circuit (1C) chips. Aluminum single and bicrystals were studied with various concentrations of vacancies and strain levels. It was found that either vacancies or tensile strains could lead to void formation. It will be shown that the void formation can be prevented by maintaining compressive strains in the computational cells.

In this paper we present a model of nonequilibrium point defect generation in the silicon substrate during solid state reactions of the surface suicides formation, resulting from the interaction between the substrate and the thin metal film. The model is based on the following principles. The local stress, which is appearing during each act of the suicide molecule (MexSiy) creation at the suicide - silicon interface, relaxes by the generation of ηv point defects. The point defect generation rate (m is the suicide growth rate) has been defined by the mininimization of the system free energy AG, which includes the enthalpy of chemical reaction ΔG the value of the relaxed elastic energy

μ is the silicon shear modulus, Ω = (xΩMe+yΩSi) is the combined volume of metal and silicon atoms with stoichiometric coefficients, ΔΩ = (ΩMexSiy - Ω), ΩV is the vacancy volume in the matrix; and the term ΔGd = ηVkTln(C/C0) which takes into account the energy of the solid solution of noninteracting point defects, where C° is an equilibrium vacancy concentration and C is the real vacancy concentration. The estimations show that there is not any essential thermodynamic force which may prevent stress relaxation for any reasonable point defect supersaturation. For this case point defect generation rate may be written as jV = m(ΔΩ/ΩV). For the reactions of the initial phase formation in the Me-Si structures the values of ΔG*el, ηV and jV have been calculated and it has been shown that vacancy concentration can reach the values of 1015 - 1016 cm-3 at the regions nearest to the interface even during initial low temperature stages of the Ni, Pt, Cr suicide formation with the metal atoms are predominant moving species.

The possibility of studying grain boundary segregation using X-ray diffraction is explored by performing a computer simulation of the diffraction effects expected from the segregation of solute atoms to grain boundaries in two gold alloy systems, i.e. Au-Ag and Au-Ni. Using atomistic Monte-Carlo and molecular statics methods, equilibrium boundary structures are determined and analyzed by computing the grain boundary structure factors. Various changes in both relative and absolute grain boundary structure factors are found which can be directly related to structural and compositional changes due to segregation. In addition, systematic diffraction effects are found as a function of boundary misorientation. The experimental conditions required for verifying these predictions are discussed.

The surface tension variations of a binary two phases liquid mixture are discussed using the square gradient approximation to the free energy functional. The case of a weakly undersaturated solution at a temperature below the critical point for which we calculate a divergence of the surface tension and the layer thickness is particulary emphasized. Applications of such considerations are proposed to discuss the experimental surface tension isotherm of the liquid Sn-O system we have studied using the sessile drop technic and A.E.S. analysis.

For a given non-reactive metal M- refractory oxide system, the influence of a metallic solute A on interfacial chemistry and wetting depends mainly on the value of εO−A the Wagner interaction parameter which quantifies the solute A-solute oxygen interactions in the liquid matrix M.

For εO−A < 0 (moderate attraction between solutes A and O) additions of A in M enhance dissolution of oxide in the liquid alloy, thereby increasing the dissolved oxygen content. The O-A clusters formed are adsorbed at the metal-oxide interface leading to an increase in both wettability and adhesion energy. For εO−A ≪0 (strong A-O interactions), solute A can also form an oxide by reduction of the substrate. The more metallic in character this oxide is, the more wettable it will be by molten metal.

Discontinuous precipitation involves formation of a two phase aggregate from a supersaturated solid solution behind a migrating boundary. It is established that the solute transport occurs primarily through the migrating boundary, called the reaction front. This report presents a systematic study of discontinuous precipitation in a Zn-Ag alloy and measurement of grain boundary chemical diffusivity of Ag in Zn-Ag using a suitable analytical model for the first time. The necessary kinetic parameters were determined by optical and scanning electron microscopes. The activation energy for boundary chemical diffusion of Ag in Zn-Ag has been estimated to be 65.8 kJ/mol.

Mechanical alloying, MA, is an amorphization technique which involves a solid state reaction below the crystallization temperature. This technique is capable of producing a more homogeneous and fine microstructure with improved mechanical properties. Amorphization of Titanium aluminide binary system, in the range of 45–65 at % Al is possible under optimized milling conditions since in this range the mixture has a large negative heat of mixing. This system is considered suitable for human implant applications for its light-weight, wear resistance, corrosion resistance, strength-to-weight ratio and biocompatibility.

Grain growth occurs during the deposition and subsequent processing of metallic films. Observation of the grain structure by scanning ion probe microscopy and grain growth by in situ transmission electron microscopy using a heating stage serves to define some characteristic grain structures and their evolution in pure metal and alloy films used for metallisation.