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

Direct methanol fuel cells (DMFCs) offer a simpler, safer technology for point-of-use power sources compared to other hydrogen fuel cells, by avoiding the need to store hydrogen fuel or to carry out the reformation of hydrocarbons. The direct methanol oxidation electrocatalyst of choice is a nanoscale black consisting of a 50:50 atom % mixture of Pt and Ru. It has recently become known that these presumed bimetallic alloys in fact contain an array of metal, oxide and hydrous phases, which are easily misidentified in routine x-ray diffraction measurements due to particle size-broadening and poor crystallinity. By combining transmission electron microscopy, electrochemistry and thermogravimetric studies, we demonstrate here that the route to improved catalytic activity is not by phase purification of the bimetallic alloys, but instead phase engineering of hydrous ruthenium oxide and Pt mixtures.

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

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.

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.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

One of the ultimate objectives for energy-dispersive X-ray spectrometry (EDS) in the analytical electron microscope (AEM) is single-atom detection in thin specimens, as well as quantitative microanalysis with high accuracy approaching ±1% relative. In order to realize the single-atom analysis, the design of the AEM has to be optimized with respect to improvements in spatial resolution and detectability limits. The detectability limit, as defined by the minimum mass fraction (MMF), is given by:

where P is the peak intensity of interest, (P/B) is the peak-to-background ratio for that peak, and r is the acquisition time. To improve the sensitivity for analysis, any or all of the variables P, (P/B), and τ should be increased. Intermediate-voltage analytical electron microscopes combined with high brightness field-emission gun (FEG) are expected to improve the MMF, while maintaining high spatial resolution. Additionally, the MMF should also be improved by maximizing the solid angle of X-ray collection.

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.

The active form of platelet derived growth factor (PDGF) is a dimeric combination of two polypeptide chains: PDGF-A and PDGF-B. The protein can exist as a heterodimer (PDGF-AB) or as one of two homodimers (PDGF-AA, PDGF-BB), resulting in three isoforms. Two types of PDGF receptors also exist: PDGFRα and PDGFRß. The PDGFRß binds only the PDGF-B chain, while PDGFRα can bind both PDGF-A and -B chains. Both of these receptors show specific temporal and spatial expression patterns that are related to cellular responses including mitogenesis, cell migration, chemotaxis, adhesion and differentiation in a variety of cell types.

Spontaneous mutants in which the PDGFRα is absent exhibit fatal defects during fetal development in mice. Some of these malformities include cardiac septal, valve, and outflow tract defects. Similar defects occur when the function of PDGF-A is disrupted by blocking antibodies. Disruption of PDGF-B function, results in ventricular and atrial dilation, hyper-trabeculation and reduction of the ventricular wall to the thickness of a single cell layer.

A technique has been developed to provide real-time imaging, with several nanometer resolution, of organometallic chemical vapor deposition (CVD) by scanning electron microscopy under conditions approaching those used in the microelectronics industry. The technique involves modifications to an environmental scanning electron microscope (ESEM) to facilitate organometallic precursor gas handling and sample heating. To demonstrate the usefulness of this technique for studying the microstructural evolution of CVD-grown metal films, results of Al/SiO2 CVD experiments are presented.

A video-rate scanning two-photon excitation microscope (TPEM) has been successfully constructed and tested. The TPEM, based on a Nikon RCM-8000, incorporates a femtosecond pulsed laser, a pre-chirper, and a non-confocal detection box for ratio imaging. Fig. 1 shows the schematic layout of the main components of the instrument, each of which is briefly discussed below.

Laser System: A Tsunami Ti: Sapphire laser (from Spectra-Physics) is optically pumped by a 5 W green laser (Millennia from Spectra-Physics) and is capable of generating 100 fs pulses at a repetition rate of 82 MHz and an average power of 0.8 W. The output wavelength is tunable from 690 to 1050 nm with three optical sets, each covering part of the spectrum with some overlapping.

Pre-chirper: After leaving the Tsunami, the laser beam enters an optic unit known as a pre-chirper which pre-chirps laser pulses to compensate for the group velocity dispersion which will result when the laser beam goes through the microscope optics.

Acquisition of large dynamic range information is important for optimizing the performance of SEM’s, TEM’s, and other microscopies. The majority of digital imaging performed in desktop publishing and other consumer markets today is limited to 8-bit resolution, and these technologies are often modified for use in electron microscopy (EM). The limitations of these techniques are clearly evident in many EM situations despite the fact that human visual system is not equipped to differentiate more than 2^5 gray levels. The most common case is when a user seeks to view information hidden in both the image's dark levels and in the brightest levels. If multiple images at different detection levels are required despite digital processing then the image information is being limited by the digitization resolution.

Digitization is the process of converting a signal from the analog form that originates from our microscope detectors to a digital form that is suitable for processing within computers.