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.

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

Three aspects of radiation damage are of concern to electron microscopists: changes in crystallographic or molecular structure, mass loss and change in chemical composition. Structural change can be monitored from the fading of diffraction patterns or from loss of fine structure in an energy-loss spectrum. Total mass loss, in the form of a reduction in inelastic-scattering power, can be observed from the low-loss spectrum. Mass loss can also be monitored from energy-loss ionization edges, with the advantage that the loss of particular elements can be studied separately. It is possible to assign a characteristic dose De for the disappearance of a particular element.

At room temperature, the amount of damage usually depends on the accumulated dose (exposure) but not on the dose rate (current density). However, cooling the specimen tends to reduce mass loss, probably because of the reduced diffusion coefficients.

GaN is a semiconductor with a direct band-gap of 3.4 eV which has a potential application in optoelectronic devices such as UV-emitting lasers and blue light emitting diodes. Extensive efforts have been made to develop low-resistance, thermally stable and uniform ohmic contacts on GaN. In this study, n-GaN films (Si-doped) with an intermediate A1N buffer layer were grown on 6H-SiC substrates via MOVPE. The contacts were formed by depositing Ti and then Au films on GaN by e-beam evaporation at room temperature. Current-voltage measurements as a function of temperature showed that the ohmicity of the Au/Ti contact improved upon annealing, corresponding to changes in the microstructure of the contact interfaces involving a redistribution of nitrogen and gold.

Fig. 1 shows the microstructure of the as-deposited Au/Ti/GaN films. The nanocrystalline Ti film was about 50 nm thick. Au film was polycrystalline, containing many growth twins. The thickness of Au film varied from 260 to 350 nm.

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.

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

The capabilities of the scanning electron microscope (SEM continue to grow. An understanding of and competency in operating the SEM is a vital asset to researchers in many fields. Acquiring the practical knowledge demands considerable training, which is expensive in terms of instrument time and personnel resources. Moreover confined laboratory environments severely limit the number of operators who can be trained simultaneously.

An alternative training approach is to develop software simulations. For example, the Interactive Microscope Laboratory simulates the optical microscope as part of a computer-based teaching resource for school-level biology courses. The VSEM (Virtual Scanning Electron Microscope) project extends our earlier work on emulating the operation and behaviour of the SEM and combines it with a virtual reality model of the instrument. The aim of the VSEM project has been to develop a microscopy teaching application which can be deployed on multiple platforms without the need for expensive hardware or software support facilities.

Pr-Co permanent magnets have attracted much attention recently due to their excellent magnetic properties and low cost; these properties can be further improved by adding small amount of carbon. In this paper, we describe the mechanism of structural transformation resulting from carbon doping in PrCo2 crystals.

We identified the heavily twinned PrCo2Cx (x=0.05-0.25) as a rhombohedral phase with space group Rm. Fig.1 shows its typical morphology of the (110) and (211) primary twins and (110)(211) secondary twins together with the corresponding diffraction patterns. We note that the Bragg spots split along the [hh0]* direction, and that the splitting increases with distance from the [110]* row. The splitting (or α angle of the rhombohedral lattice) also varies with carbon concentration.

Because PrCo2 is an untwinned FCC phase (Fdm), the formation of a twin in PrCo2Cx caused by adding carbon atoms apparently is driven by a minimization in lattice strain, which also is the origin of the cubic-rhombohedral phase-transformation.

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

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

Digital microscopy, the integration of digital and microscopy technologies, was initiated for quantitative microscopic image analysis, but it is now for almost all microscopy applications. During the past decade, with the advance of digital technologies, digital microscopy imaging is becoming an indispensable technology in drug discovery.

We started establishing state-of-the-art digital microscopy imaging for drug discovery with the investigation of bioimaging applications at our US research site. Our results shown that all the top 5 bioimaging needs require computer-aided microscopy. Based on this investigation and our review of the microscopy imaging applications in the pharmaceutical industry, we determined four directions for microscopy in drug discovery: multidimensional/multimodal microscopy, digitalization, automation, and bioimage informatics.

Multidimensional/multimodal microscopy imaging is required by the nature of biological research, which is fundamental in drug discovery. From genomic imaging to pathology observation, we require biological details and compound activities at the levels from subcellular organelles to organ tissues, from cellular signaling to anatomical locations of compounds.

Micrometer sized particles have been studied to show that a high-quality transmission electron microscope (TEM) specimen can be produced, without the use of embedding media, from a site-specific region of chosen particles using the focused ion beam (FIB) lift-out (LO) technique. The uniqueness of this technique is that site-specific TEM LO specimens may be obtained from particles and from regions which are smaller than the conventional ∼10–20 μm × 5 μm × ∼0.1 μm dimensions of the LO specimen. The innovative FIB LO procedures are described in detail and TEM images of electron transparent specimens obtained from specific micrometer-sized particles are presented.

One of the main goals of automated scanning electron microscopy analysis (ASEM) of particles is to provide macroscopic phase and compositional information on particle populations based on the energy dispersive x-ray spectrometry, EDS, analysis of several hundred to several thousand individual particles from the sample. The selection and identification of the various elemental groupings is often accomplished by applying techniques for grouping data, such as multivariate or cluster analysis methods, to characteristic x-ray intensities or normalized elemental concentrations. Particle groupings are often based on major and minor elements with concentrations greater than about 1-2 wt. percent. At these concentration levels, the peak-to-background ratios for the characteristic x-ray peaks are sufficiently large that in the absence of severe peak overlaps the elements can be easily identified even in spectra with poor counting statistics. Additional refinement in particle groupings may be possible if reliable information can be obtained on the trace elements present in particles at less than about 1-2 wt.%.

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

Deposition of calcium carbonate from groundwater was examined on a moss, Didymodon tophaceus, from a Niagara Escarpment waterfall. A spectrophotometer on a polarizing microscope was used for interferometry. A second-order blue interference with an interference minimum around 620 nm was found when moss cell spaces were fully calcified. Filled cell spaces were often surrounded by empty cell spaces. Complete calcification of whole leaflets resulted in progressively higher orders of interference colors and a positive shift in interference minima. Calcified leaflets finally became cemented together, but each retained a weak extinction when rotated. Small calcareous spherulites (mean diameter 15.7 ± 2.1 μm) were found between leaflets. Spherulites exhibited first-order white interference with a Maltese cross that rotated when the polarizer and analyzer were rotated in tandem. A Nikitin-Berek compensator was tilted at 5.5° to give an interference minimum at 600 nm in the optical axis. Quadrants of spherulites with radii more or less in line with the tilting axis of the compensator had lower (P < 0.001) interference minima (535 ± 27 nm) than quadrants with radii more or less perpendicular to the compensator (659 ± 15 nm), thus indicating a radial internal structure. Spherulites were tentatively identified as vaterite.

Carbon tubes or spheres synthesized by arc-discharge are usually mixed with other byproducts, prohibiting direct measurements of their physical properties by the well established optical techniques because a large quantity of pure specimen is required. Electron energy-loss spectroscopy (EELS) is a unique technique that can be applied to probe the electronic structure of a single carbon tube or sphere. In this paper, the classical dielectric response theory is applied to calculate the EELS spectra acquired from a graphitic carbon sphere at various impact parameters. Graphite is an anisotropic dielectric medium whose dielectric function is described by a tensor. A graphitic carbon sphere is composed of concentric graphitic shells whose dielectric tensor in the spherical geometry, under the local response approximation, is given by (Figure 1)

where are the dielectric function of graphite for an electric field perpendicular and parallel, respectively, to the c axis. In the non-relativistic approximation, the surface excitation is calculated by [1]