A numerical model has been developed to simulate images obtained from the three-dimensional atom probe. This model was used to simulate the artefacts commonly observed in two-phase materials. This model takes into account the dynamic evolution of the atomic-scale shape of the specimen during field evaporation. This article reviews the model and its applications to some specific cases. Local magnification effects were studied as a function of the size, the shape, and the orientation of precipitated phases embedded in the matrix. Small precipitates produce large aberrations in good agreement with experiments. The magnification from such precipitates, as measured from the simulation, is only found to match the theoretical value for mesoscopic scale precipitates (size similar to the specimen size). Orientation effects are also observed in excellent agreement with experiments. The measured thickness of a grain-boundary-segregated film in the simulation is found to decrease with the angle between the normal to the grain boundary and the tip axis. Depth scaling artefacts caused by variation in the evaporation field of atoms in multilayer structures were successfully simulated and again showed good agreement with effects observed experimentally.

We present and review dopant mapping examples in semiconductor device structures by electron holography and outline their potential applications for experimental investigation of two-dimensional (2D) dopant diffusion on the nanometer scale. We address the technical challenges of the method when applied to transistor structures with respect to quantification of the results in terms of the 2D p–n junction potential and critically review experimental boundary conditions, accuracy, and potential pitfalls. By obtaining maps of the inner electrostatic potential before and after anneals typically used in device processing, we demonstrate how the “vertical” and “lateral” redistribution of boron during device fabrication can directly be revealed. Such data can be compared with the results of process simulation to extract the fundamental parameters for dopant diffusion in complex device structures.

Lichens have long been regarded as bioindicators of air pollution, and structural studies typically have indicated negative impacts in highly polluted areas. In this research, Parmelia sulcata and Platismatia glauca were collected from one clean and two polluted sites in the Pacific Northwest forests of the United States to investigate the anatomical and ultrastructural responses of relatively resistant lichens to moderate air pollution. Light microscopy of polluted materials revealed only slight increases in the algal cell proportions of the thallus, and a decrease in the fungal cells of the medulla. Using transmission electron microscopy, increased lipid droplets in the cytoplasm and an increase in the cell wall thickness of the photobionts were found in the polluted lichens. These results were compared with physiological data in which the net carbon uptake did not show any significant differences; however, the total chlorophyll content was heightened in the polluted samples. The increased total chlorophyll content and the absence of any changes in the algal cell proportions of the polluted samples suggest that the photobionts possessed a higher chlorophyll content per unit volume of the photobiont at polluted sites. The results also indicate that lichens have altered their storage allocation in different cellular compartments. This may be a result of symbiotic readjustment(s) between the photobiont and the mycobiont. In comparison with the physiological results from these two species, these changes do not represent damaging effects by low-level air pollution.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

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Heterogeneous catalysis is one of the oldest nanosciences. Although model catalysts can be designed, synthesized, and, to a certain degree, characterized, industrial heterogeneous catalysts are often chemically and physically complex systems that have been developed through many years of catalytic art, technology, and science. The preparation of commercial catalysts is generally not well controlled and is often based on accumulated experiences. Catalyst characterization is thus critical to developing new catalysts with better activity, selectivity, and/or stability. Advanced electron microscopy, among many characterization techniques, can provide useful information for the fundamental understanding of heterogeneous catalysis and for guiding the development of industrial catalysts. In this article, we discuss the recent developments in applying advanced electron microscopy techniques to characterizing model and industrial heterogeneous catalysts. The importance of understanding the catalyst nanostructure and the challenges and opportunities of advanced electron microscopy in developing nanostructured catalysts are also discussed.

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.

Protozoan parasites are fearsome pathogens responsible for a substantial proportion of human mortality, morbidity, and economic hardship. The principal disease agents are members of the orders Apicomplexa (Plasmodium, Toxoplasma, Eimeria) and Kinetoplastida (Trypanosomes, Leishmania). The majority of humans are at risk from infection from one or more of these organisms, with profound effects on the economy, social structure and quality of life in endemic areas; Plasmodium itself accounts for over one million deaths per annum, and an estimated 4 × 107 disability-adjusted life years (DALYs), whereas the Kinetoplastida are responsible for over 100,000 deaths per annum and 4 × 106 DALYs. Current control strategies are failing due to drug resistance and inadequate implementation of existing public health strategies. Trypanosoma brucei, the African Trypanosome, has emerged as a favored model system for the study of basic cell biology in Kinetoplastida, because of several recent technical advances (transfection, inducible expression systems, and RNA interference), and these advantages, together with genome sequencing efforts are widely anticipated to provide new strategies of therapeutic intervention. Here we describe a suite of methods that have been developed for the microscopic analysis of T. brucei at the light and ultrastructural levels, an essential component of analysis of gene function and hence identification of therapeutic targets.

Following is a list of microscopy-related meetings and courses. The editors would greatly appreciate input to this list via the electronic submission form found in the MSA World-Wide Web page at http://www.msa.microscopy.com. We will gladly add hypertext links to the notice on the web and insert a listing of the meeting in the next issue of the Journal. Send comments and questions to JoAn Hudson, [email protected] or Nestor Zaluzec, [email protected].

A signal loss is generally reported in electron probe microanalysis (EPMA) of porous, highly divided materials like heterogeneous catalysts. The hypothesis generally proposed to explain this signal loss refers to porosity, roughness, energy losses at interfaces, or charging effects. In this work we investigate by Monte Carlo simulation all these physical effects and compare the simulated results with measurements obtained on a mesoporous alumina. A program using the PENELOPE package and taking into account these four physical phenomena has been written. Simulation results show clearly that neither porosity nor roughness, nor specific energy losses at interfaces, nor charging effects are responsible for the observed signal loss. Measurements performed with analysis of carbon and oxygen lead to a correct total of concentration. The signal loss is thus explained by a composition effect due to a carbon contamination brought by the sample preparation and to a lesser extent by a stoichiometry of the porous alumina different from a massive alumina. For this kind of high specific surface porous sample, a little surface contamination layer becomes an important volume contamination that can produce large quantification errors if the contaminant is not analyzed.

The following shows the correction to Figure 8 that appeared on page 103 of Microscopy and Microanalysis, 10:1, February 2004, in the article by Own et al. The three sections of Figure 8 were previously labeled as a, c, and c. The corrected figure below has the sections correctly labeled as a, b, and c.

The Editor and Cambridge University Press regret the inconvenience that this inadvertent error may have caused.

Reservosomes are endocytic compartments found in the posterior region of epimastigotes of Trypanosoma cruzi. In the differentiation from trypomastigotes to epimastigotes (reverse metacyclogenesis in vitro), one has the rare opportunity of following the biogenesis of an endocytic compartment. Metacyclic trypomastigotes incubated in LIT medium highly enriched with fetal calf serum differentiated directly to epimastigotes. In recently differentiated epimastigotes, acidic organelles were found in round compartments spread along the cell body, whereas in control epimastigotes they were found in reservosomes located in the posterior region. Ultrastructural analysis of intermediate forms showed that the cytostome and reservosomes appeared before differentiation to epimastigotes was completed. Many polymorphic reservosomes, with or without lipid inclusions, were observed from the anterior portion of the cell body, in close relationship with the Golgi complex, to the posterior region. Endocytic tracers were observed in the cytostome, flagellar pocket, vesicles, and newly formed reservosomes. Cruzipain, the main protease of T. cruzi, was localized in newly formed reservosomes and in vesicles budding from the trans-Golgi network that seem to fuse with reservosomes. Ingested gold-labeled albumin and cruzipain colocalized in recently formed reservosomes. Endocytosis and immunocytochemical analysis suggested that the endocytic and the secretory pathways may contribute to reservosome formation.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Sintering of a palladium catalyst supported on alumina (Al2O3) in an oxidizing environment was studied by in situ transmission electron microscopy (TEM). In the case of a fresh catalyst, sintering of Pd particles on an alumina surface in a 500 mTorr steam environment happened via traditional ripening or migration and coalescence mechanisms and was not significant unless heating above 500°C. After the catalyst was used for the hydrogenation of alkynes, TEM coupled with convergent beam electron diffraction and electron energy loss spectroscopy analysis revealed that most of the Pd particles were lifted from the alumina surface by hydrocarbon buildup. This dramatically different morphology totally changed the sintering mechanism of Pd particles during the regeneration process. Catalytic gasification of hydrocarbon around these particles in an oxidizing environment allowed the Pd particles to move around and coalesce with each other at temperatures as low as 350°C. For catalysts heating under 500 mTorr steam at 350°C, steam stripped hydrocarbon catalytically at the beginning, but the reaction stopped after 4 h. Heating in air resulted in both catalytic and noncatalytic stripping of hydrocarbon.

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.

Nb–silicide in situ composites have great potential for high-temperature turbine applications. Nb–silicide composites consist of a ductile Nb-based solid solution together with high-strength silicides, such as Nb5Si3 and Nb3Si. With the appropriate addition of alloying elements, such as Ti, Hf, Cr, and Al, it is possible to achieve a promising balance of room-temperature fracture toughness, high-temperature creep performance, and oxidation resistance. In Nb–silicide composites generated from metal-rich binary Nb-Si alloys, Nb3Si is unstable and experiences eutectoid decomposition to Nb and Nb5Si3. At high Ti concentrations, Nb3Si is stabilized to room temperature, and the eutectoid decomposition is suppressed. However, the effect of both Ti and Hf additions in quaternary alloys has not been investigated previously. The present article describes the discovery of a low-temperature eutectoid phase transformation during which (Nb)3Si decomposes into (Nb) and (Nb)5Si3, where the (Nb)5Si3 possesses the hP16 crystal structure, as opposed to the tI32 crystal structure observed in binary Nb5Si3. The Ti and Hf concentrations were adjusted over the ranges of 21 to 33 (at.%) and 7.5 to 33 (at.%) to understand the effect of bulk composition on the phases present and the eutectoid phase transformation.

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Scanning electron microscopy (SEM) was used to study the endometrium of nine 1-year-old thoroughbred mares after twice intrauterine infusions of gentamicin, on 2 consecutive days. Five mares were infused on 2 consecutive days with 40 ml gentamicin (50 mg/ml) mixed with 80 ml of normal saline. Four mares served as controls and were infused with 120 ml of saline on 2 consecutive days. Endometrial biopsies were obtained from all mares 3 days after the second intrauterine infusion. Each biopsy was processed for SEM by standard methods. The endometrial epithelium of the gentamicin-infused mares had more cellular perforations than the saline-infused mares. The gentamicin-infused mares had less and shorter microvilli. The ciliated cells were fewer and some ciliated cells had disrupted and some had drooping cilia. The endometrial epithelium of the gentamicin-infused mares had a considerable number of endometrial cells that lost their luminal surfaces and some that lost their microvilli, compared to the saline-infused mares. We suggest that the information gathered in this pilot study should be used as basis for further investigation, on a larger scale basis, of the effects of repeated intrauterine infusion of gentamicin on the endometrial mucosa of mares.

Quantitative chemical analysis by energy-dispersive X-ray spectrometry (EDS) in the environmental scanning electron microscope (ESEM) is difficult. This analysis is complicated by the spread of the electron beam by chamber gas molecules and the necessity for surface charge neutralization. Without charge neutralization, errors in quantitative analysis can range up to 15–20% relative. It is possible to achieve the error expected of traditional EDS, ±5% relative error, using a newly developed surface charge neutralization scheme for the ESEM. Estimates of accuracy and precision are based on studies of the National Bureau of Standards (now National Institutes for Science and Technology) Standard Reference Material 482, a series of certified copper–gold alloys. The scheme for charge neutralization requires an independent path to ground at or near the surface of the specimen. The current through the ground path must be maintained at zero by adjusting the voltage on the Gaseous Secondary Electron DetectorTM when the sample chamber is at a gas pressure of 1–2 torr. This procedure forms the exact number of chamber gas positive ions to neutralize negative electrical charge on the specimen surface from electron bombardment.

Results for the X-ray emission efficiency (counts per C per sr) of K-lines for selected elements (C, Al, Si, Ti, Cu, Ge) and for the first time also for compounds and alloys (SiC, GaP, AlCu, TiAlC) are presented. An energy dispersive X-ray spectrometer (EDS) of known detection efficiency (counts per photon) has been used to record the spectra at a takeoff angle of 25° determined by the geometry of the secondary electron microscope's specimen chamber. Overall uncertainty in measurement could be reduced to 5 to 10% in dependence on the line intensity and energy. Measured emission efficiencies have been compared with calculated efficiencies based on models applied in standardless analysis. The widespread XPP and PROZA models give somewhat too low emission efficiencies. The best agreement between measured and calculated efficiencies could be achieved by replacing in the modular PROZA96 model the original expression for the ionization cross section by the formula given by Casnati et al. (1982) A discrepancy remains for carbon, probably due to the high overvoltage ratio.