Publications

Oriented bicrystals of pure C11_b MoSi₂ have been grown in a tri-arc furnace using the Czochralski technique. Two single crystal seeds were used to initiate the growth. Each seed had the orientation intended for one of the grains of the bicrystals, which resulted in a 60° twist boundary on the (110) plane. Seeds were attached to a water-cooled seed rod, which was pulled at 120 mm/h with the seed rod rotating at 45 rpm. The water- cooled copper hearth was counter-rotated at 160 rpm. Asymmetric growth ridges associated with each seed crystal were observed during growth and confirmed the existence of a bicrystal. It was also found that careful alignment of the seeds was needed to keep the grain boundary from growing out of the boule. The resulting boundary was characterized by imaging and crystallographic techniques in a scanning electron microscope. The boundary was found to be fairly sharp and the misorientation between the grains remained within 2° from the disorientation between the seeds.

In the scanning electron microscope (SEM), using electron backscattered diffraction (EBSD), it is possible to measure the spacing of the layers in the reciprocal lattice. These values are of great use in confirming the identification of phases. The technique derives the layer spacing from the HOLZ rings which appear in patterns from many materials. The method adapts results from convergent-beam electron diffraction (CBED) in the transmission electron microscope (TEM). For many materials the measured layer spacing compares well with the calculated layer spacing. A noted exception is for higher atomic number materials. In these cases an extrapolation procedure is described that requires layer spacing measurements at a range of accelerating voltages. This procedure is shown to improves the accuracy of the technique significantly. The application of layer spacing measurements in EBSD is shown to be of use for the analysis of two polytypes of SiC.

This paper describes the use of backscattered electron Kikuchi patterns (BEKP) for phase identification in the scanning electron microscope (SEM). The origin of BEKP is described followed by a discussion of detectors capable of recording high quality patterns. In this study a new detector based on charge coupled device technology is described. Identification of unknown phases is demonstrated on prepared and as received sample surfaces. Identification through a combination of energy dispersive x-ray spectrometry (EDS) and BEKP of a Laves phase in a weld in an alloy of Fe-Co-Ni-Cr-Nb and the identification of Pb{sub 2}Ru{sub 2}O{sub 6.5} crystals on PZT is demonstrated. Crystallographic phase analysis of micron sized phases in the SEM is a powerful new tool for materials characterization.

The article presents the use of Monte Carlo simulations or incoherent scattering model to calculate profiles from precipitates embedded at different depths in thin specimens and then compared the simulations with experimental data measured from embedded particles. Incoherent scattering models is believed to be the best simulation for spatial resolution for x ray microanalysis in the AEM.

Demonstrated in this study is the phase identification through a combination of backscattered electron Kikuchi patterns (BEKP) and energy dispersive x-ray spectrometry (EDS) by the identification of crystals present on ruthenium oxide thin films on Si. The crystals were identified as RuO2, a tetragonal phase. The charge coupled device (CCD)-based detector is also briefly described. The ability of the CCD-based detector to collect high quality patterns without the use of photographic emulsions enables on-line analysis of the BEKP's.

Short communication

The combination of an energy dispersive x-ray spectrometer (EDS) with the ultrahigh vacuum environment of many modern electron microscopes requires the spectrometer designer to take extra precautions and presents the microscopist with the additional option of utilizing windowless spectrometers for light element detection while not worrying about contamination of the detector. UHV is generally defined as a pressure of better than 10{sup {minus}7} Pa and is necessary to prevent specimen modification by the components of the vacuum. UHV may also be defined as an environment in which the time to form a monolayer on the specimen is equal to or longer than the usual time for a laboratory measurement. This report examines performance of energy dispersion x-ray spectrometers in UHV.

Al with additions of Cu is commonly used as the conductor metallizations for integrated circuits (ICs). As the packing density of ICs increases, interconnect lines are required to carry ever higher current densities. Consequently, reliability due to electromigration failure becomes an increasing concern. Cu has been found to increase the lifetimes of these conductors, but the mechanism by which electromigration is improved is not yet fully understood. In order to evaluate certain theories of electromigration it is necessary to have a detailed description of the Cu distribution in the Al microstructure, with emphasis on the distribution of Cu at the grain boundaries. In this study analytical electron microscopy (AEM) has been used to characterize grain boundary regions in an Al-2 wt.% Cu thin film metallization on Si after a variety of thermal treatments. The results of this study indicate that the Cu distribution is dependent on the thermal annealing conditions. At temperatures near the θ phase (CuAl₂) solvus, the Cu distribution may be modelled by the collector plate mechanism, in which the grain boundary is depleted in Cu relative to the matrix. At lower temperatures, Cu enrichment of the boundaries occurs, perhaps as a precursor to second phase formation. Natural cooling from the single phase field produces only grain boundary depletion of Cu consistent with the collector-plate mechanism. The kinetic details of the elemental segregation behavior derived from this study can be used to describe microstructural evolution in actual interconnect alloys.

This paper is about the spatial resolution of x-ray microanalysis in thin foils. The theory of the scattering of an electron beam with a thin foil is discussed.

Short communication.

Curved and planar inversion domain boundaries (IDB) in aluminum nitride (AIN) form in sintered AIN ceramics containing oxygen, and oxygen is known to segregate to them. A number of interface models shown in Table 1, have been suggested based upon crystallographic constraints, chemical information and observed high resolution electron microscope (HREM) images. Until recently, problems with simulation of HREM images from AIN have made accurate determination of the structure of the IDB interface difficult. The aim of the present study was to use quantitative analytical electron microscopy (AEM) to determine the oxygen concentration at the IDBs, and then to compare the experimental results with calculated oxygen concentrations for each of the IDB models using a Monte Carlo electron trajectory simulation program. A match, if any, between the experimental and calculated oxygen concentrations would indicate the model which best described the IDB structure. The best match was obtained for Youngman's defect model. 14 refs., 5 figs., 3 tabs.