An x-ray spectrometer is actually a scanning monochromator because two conditions must be satisfied, namely: (1) nλ, = 2d sinθ and (2) θI{= θR to within the rocking curve of the crystal 2Δθ. Before Castaing (B.C.) there were four known types of focussing monochromators, namely: Johann, Johansson, Cauchois, and von Hamos. Castaing was fortunate in having Andre Guinier (well known for his work in x-ray crystallography) as his thesis advisor. Thus, he wisely chose to use a spectrometer of the Johansson type. Had he used a flat crystal spectrometer, the result would have been unsatisfactory and the history of microanalysis would have been significantly different. Many of the spectrometers that were used in the early instruments were either of the Johansson type, in which the crystal planes are curved to a radius of 2R and the surface has a radius of R, the focal circle radius. This is sometimes called exact focussing because rays in the plane of the focal circle converge exactly to a point focus. For simpler construction, the Johann crystal which has the surface parallel to the atomic planes (also curved to a radius of 2R) was sometimes used. While both types provide one-dimensional focussing, the Johansson type is preferred because the effective width of the crystal can be greater.

In addition to the type of geometry used, early instruments developed after Castaing (A.C) also had variations in the mechanism of the crystal movement. Many used a relatively simple mechanism with the crystal and detector moving about a fixed center for the focal circle as shown in Fig. 1A. Some later instruments used curved crystals that were fixed in position, and scanning was accomplished either by rotating the crystal as in Fig. 1B or by a mechanism that flexed the crystal and changed the radius of the focal circle as in Fig. 1C. The most satisfactory arrangement and the one subsequently adopted by most manufacturers of commercial microprobes utilized a linear motion of the crystal carriage with a provision for tilting the crystal so that the focal circle always passed though the x-ray source as shown in Fig. 1D. If the detector moves so that it remains on this focal circle, its motion is along a leaf-shaped curve. With this design it is easy to have a readout proportional to wave length.

Radiation damage in quartz has been of interest to the semiconductor industry, optical fiber industry, and nuclear industry. Cross-section transmission electron microscopy (TEM) is a powerful tool for investigating the irradiation effects since it provides a direct measurement of the ion and the damage distributions, and can also provide detailed microstructural information such as the presence of amorphous regions and the size, density and chemical nature of defect aggregates. The results reported below are from a systematic cross-section TEM study on 1.5 MeV Kr+ ion irradiated quartz.

3-mm discs of quartz (along 010 face) were prepared with 100 μm in thickness. One side for each discs was well polished using a 0.05 μm diamond paste. The well-polished side was irradiated at room temperature with 1.5 MeV Kr ions in the HVEM-Tandem Facility at Argonne National Laboratory. Following irradiation, cross-section TEM specimens were prepared using the so-called T-tool technique, a modified tripot technique

Trace impurities and dopants in sintered ceramics, often at levels below 100 parts per million, can significantly affect the performance of the materials. In alumina (A12O3), it is believed that calcium and silicon, which are the main background impurities, cause abnormal grain growth. The addition of magnesium to alumina produces several beneficial results, including enhanced densification and improved corrosion resistance of the ceramic. For example, LUCALUX®, which is a dense, transparent ceramic, is made by adding a small amount of MgO (<0.25%) to the alumina. Primarily because they are difficult to detect and image, it has not been easy to determine experimentally the mechanisms by which trace constituents influence the sintering of ceramics. Imaging secondary ion mass spectrometry (SIMS) is a valuable analytical technique for the submicrometer characterization of ceramics. Relevant to this study, magnesium and isotopes of silicon, which have largely eluded detection by traditional techniques, can be measured with SIMS.

K0.19Ba3.18Mo22O34is a representative of the quaternary reduced molybdenum oxides in the series Mn±δMo4n+2O6n+4. These compounds contain condensed clusters Mo4n+2O8n+10 with a core of n trans edge-sharing molybdenum octahedra. The general concept of cluster condensation is discussed elsewhere. In the case of n being finite the clusters are designated as ‘oligomeric’. The individual clusters are interconnected via common oxygen atoms and arranged in layers. For the title compound with n = 5, the clusters consist of 5 molybdenum octahedra and are accompanied by 4 counter-cations (potassium and barium).

The real structure of K0.19Ba3.81Mo22O34 has been recently studied with a Philips CM30/ST (Cs = 1.15 mm) by HREM, SAED, and EDXS. Besides chemical intergrowth of oligomeric clusters with n = 2—18 in the matrix consisting of pentameric clusters, polytypism was observed. Three ordered polytypes (modifications) were found, whereas only one of them, lM (Ramsdell notation), was detected and analyzed with x-ray methods.

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

The mineral spinel (MgAl2O4) is a candidate material for proposed fusion reactors because of its resistance to structural damage during irradiation. When irradiated to high damage levels, spinel is eventually driven amorphous. However, at lower fluences the nearly cubic close packed arrangement of the oxygen anions remains intact, as indicated by electron diffraction patterns consistent with a face centered cubic Bravais lattice. in this regime, the damage to the material is manifested primarily in the redistribution of the magnesium and aluminum cations among the interstices of the anion sublattice. For ion irradiation, the study of these early stages of damage is well suited to electron beam characterization methods, because the damage is spatially localized at the nearsurface region. Electron diffraction methods have been used for the characterization of cation disorder, but are notoriously unreliable because the similarity in the elastic scattering cross sections offers little discrimination between the magnesium and aluminum cations.

New EPA regulations limiting the emissions of NOx from diesel engines will require a reduction by 70% in the amount of NOx leaving the tailpipe of diesel powered vehicles by the year 2004. Some form of exhaust aftertreatment will need to be applied to diesel engines to meet the new stricter requirements. One option is to develop a “lean-NOx” catalyst that uses a hydrocarbon reductant (e.g. diesel fuel) to convert NOx into N2 and O2. Two of many constraints on such a catalyst are that it achieve a high degree of conversion over a fairly broad temperature range and that the amount of reductant necessary to reach the 70% goal is sufficiently small as to be cost effective. A number of promising systems comprise either platinum group metals or base metals on oxide supports. Such catalyst systems typically involve near-atomic dispersions, or ultra-fine clusters, of the heavy metal species on the oxide support.

Extended abstract of a paper presented at the Pre-Meeting Congress: Materials Research in an Aberration-Free Environment, at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, July 31 and August 1, 2004.

Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007