The certification process for a microanalysis standard can be quite lengthy. In addition to certifying the reference material for composition, the extent of heterogeneity between specimens and within specimens must be determined. NIST (or formerly, NBS) 260 Special Publications have been used in the past to describe procedures used for individual SRM certifications. Some of these publications describe in detail how the extent of microheterogeneity (or, microhomogeneity) as well as the specimen to specimen heterogeneity can be determined. The intent here is to describe a general statistical approach used at NIST to determine and report the extent of heterogeneity. This approach can be readily used by other laboratories either for certification or for evaluation of standards.

When evaluating a material for use as a standard, there are several physical characteristics which must be satisfied. The material must be robust under the electron beam at the voltages and currents to which it will be subjected in its proposed use. When mounted and polished, it should be stable on exposure to the atmosphere. However, if the material will not be mounted and polished in use, it should be in the same physical form as the final certified standard material.

We have used several techniques in the field of scanning electron microscopy (SEM) to examine ceramic pot sherds from a number of archaeological sites in New Mexico in an effort to characterize the ceramic material and determine the origin of some of the vessels. Typical archaeological sites belonging to Pueblo Indian ancestors in New Mexico are littered with numerous fragments of vessels which served different purposes such as cooking, food/water storage, eating, and ceremonial. often different styles of painting and slipping found on these fragments relate to different temporal and cultural influences. An important question that arises during examination of the many types of sherds involves the origin of each of the vessels. Analysis of mineral content and mineral chemistry can help answer these questions.

Thin sections of pot sherds from 4 prehistoric Anasazi sites (A.D. 1150-1250) from south and central New Mexico, a prehistoric Anasazi site in northwestern New Mexico (Chaco Canyon, Pueblo Alto A.D. 1000 -1150), and an historic Pueblo site from the Spanish period (A.D. 1540-1700) were examined.

Bulk chemical characterizaton with techniques such as neutron activation analysis (NAA) has been used for many years to identify sources of archaeological artifacts by comparing bulk chemical profiles of archaeological artifacts to profiles determined for samples of raw material for source identification. The chemical approach to determining the provenance of archaeological pottery is complicated by the paste preparation activities of potters and by post-depositional processes. In a ceramic provenance investigation, the investigator typically identifies a series of relatively homogeneous subgroups, which most often are assumed to represent geographically restricted raw material sources. Although the source-specific interpretation is often the most parsimonious explanation of compositional patterning, it is really only the first of several competing hypotheses which, singly or in combination, might account for patterns of similarity and difference in a compositional data set. In this case, two white firing pottery types (SAWH and Ivory) made during the Late and Terminal Formative periods (300 B.C. - 200 A.D.) in southeastern Mesoamerica (Guatemala) were found to be chemically distinct.

Natural rock-forming minerals and many synthetic materials have traditionally been characterized by electron microprobe analysis (EMPA). However, recent advances in technology have created attractive alternatives to EMPA that focus instead on bulk chemistry and high-resolution surface studies. The purpose of this abstract is to demonstrate the continued usefulness of careful electron microprobe analysis as part of a well-coordinated analytical study. To this end, a brief summary is presented of the role the electron microprobe played in the recent discovery of yoshiokaite, a new Ca, Al-silicate mineral and one of only three new minerals discovered on the Moon.[l]

Regolith breccias returned by several Apollo missions were subjected to extensive bulk chemical studies at the University of California, Los A n geles.[2] These bulk chemical studies focused particularly on key trace elements that might identify exotic regolith breccias.

Is average atomic mass or average atomic number more appropriate to describe backscattered electron (BSE) effects in electron-solid interactions? In electron microprobe literature, either one or both of the terms A and Z may be found utilized in various theoretical models to describe electron backscattering. Physical theory would seem to favor atomic number averaging, because backscattering ultimately represents an electromagnetic interaction between the electron and the nucleus. At this scale, mass and its associated property of gravity, is 10 times less powerful than the electromagnetic force. Nonetheless, some empirical results show a strong relation between atomic mass and electron scattering, thus endorsing mass averaging.

The periodic table presents an opportunity for distinguishing between these two influences: those pairs of elements for which an increase in Z yields a decrease in average A (e.g., Ar-39.95 and K-39.10; Co-58.93 and Ni-58.71; Te-127.60 and 1-126.90) due to natural isotope abundances.

The use of backscattered electron (BSE) imaging in low voltage scanning electron microscopy (SEM) has increased over the past few years. This appears to be due to several factors including improved performance of SEMs at low voltages, reduced beam penetration, more reliable metrology, improved atomic number (Z) contrast information (for low Z) and reduced charging artefacts over secondary electron (SE) imaging. Understanding the factors involved in low voltage BSE detection may assist in improving the information attainable.

It has been shown that the signal Sdet from a BSE detector, for EB ≫ Ew is given by

where η is the BSE yield, Ω is the solid angle subtended by the detector to the specimen, D is the internal conversion efficiency of the detector, EB is beam accelerating voltage, Ew is the energy barrier of the dead layer on the detector's surface, IB is the beam current, F(Z) and F(Ω) are functions which take into account the variation of BSE energy with atomic number Z and collection angle respectively.

Low voltage scanning electron microscopy with a field emission source allows characterization of materials with high spatial resolution. This high resolution comes from the low incident energy which gives a small interaction volume (about 10 nm in Fe at 1 keV ), from the field emission source which gives a small probe size (about 2.5 nm in the most recent FE-SEM) and from virtual, or through the lens, secondary electron detectors with gives high collection efficiency and eliminates some of the SEII and all the SEIII- For example, it has been shown that 10 nm NbC inclusions in steels can be imaged in such FE-SEM at 2 keV (this work was performed with a HITACHI S-4500). However, quantitative x-ray analysis of such precipitates are difficult because the critical ionization energy of the Nb Lα lines is equal to 2.37 keV, an incident electron energy of at least 5 keV must be used to get significant x-ray counts rates.

The Secondary Electron Detector (SED) is the first link in the chain of image formation after the initial illumination of a specimen in a Scanning Electron Microscope (SEM), therefore it is most crucial that the efficiency of the SED be as great as possible in order to maximize Signal-to- Noise Ratio (S/N) as any imperfections, inadequacies, and noise are then amplified along with the signal by the subsequent electronic amplifiers in the signal chain.

In the Everhart-Thornley SED, matching the scintillator's output spectrum to the photomultiplier tube's photocathode spectral sensitivity is one factor along with other characteristics of the PM tube, like quantum efficiency and noise characteristics. Light-pipe material along with as optical coupling techniques are another factor which determines the overall efficiency of converting SE electron strikes on the scintillator to a video output signal.

Advanced metal coating methods have greatly improved the localization of secondary electrons (SEI) from biological specimens staged in an in-lens field emission SEM. Using these metal coatings, molecular level structural information from cell membranes and isolated bio-molecules have been more accurately recorded from frozen-hydrated samples due to the presence of bound water rather than from chemically fixed and dried samples. Although in-lens cryo-SEM systems have provided images with equivalent resolution to TEM-replicas, several conditions are encountered which require optimizing techniques and hardware.

A drop of hydrated Bakers yeast on a gold Balzers carrier was plunge-frozen in ethane at its melting point. Thermal properties of ethane, such as the large difference between melting and boiling points, and its low viscosity increase the heat transfer coefficient during plunging thereby leading to faster cooling of the sample than with other cryogens. Carriers were transferred to the cryo-workstation of the Oxford CT 3500 system.

High-resolution secondary electron (SE) imaging was first demonstrated at 100 kV in the STEM a decade ago. High-resolution SE imaging is now routinely obtainable in field-emission SEMs. Although nanometer-scale surface features can be examined at low incident beam voltages we still do not fully understand the factors that affect the contrast of low voltage SE images. At high incident beam voltages, SE1 (SEs generated by the incident probe) and SE2 (SEs generated by backscattered electrons at the sample surface) can be spatially separated. SE1 carries high-resolution detail while SE2 contributes to background. At low incident beam voltages, however, the interaction volume of the incident electrons shrinks rapidly with decreasing incident beam voltage. Thus, both the SE1 and SE2 signals carry high-resolution information. At low incident beam voltages, SE3 (SEs generated by backscattered electrons impinging on the sample chamber, pole pieces and etc.) also carries high-resolution detail and contributes significantly to the collected signal, especially for high atomic number materials and at short working distances.

The elemental composition of polyphosphate bodies (PPB’s) and other components of the cell have previously been determined by using energy dispersive X-ray spectrometers(EDX). In this present study we perform a quantitative analysis or normally grown cells and cells that were grown in the overplus phenomenon.

Cells of Plectonema boryanum were grown in modified Fitzgerald's media and harvested after a logarithmic growth phase of 14 days. The overplus cells were grown as has been previously described2. The cells were exposed to l00ppm of lead, as well as other metals separately, for one hour. The cells were then fixed and embedded in EPON according to Luft's procedure.

For X-ray analysis cells were first located using the TEM mode, and then the microscope was switched to the STEM mode. Analysis of cell components were carried out using the spot mode (75Kv).

Despite the large production and consumption of textile fibers on a global basis, the ability to identify specific types of textile fibers with similar physical-chemical properties is a challenging obstacle for the textile industry. One problem in particular is the identification of specialty animal fibers. Cashmere is a specialty fiber that has a value of 7 to 8 times higher than its similar counterpart wool. It is important, therefore, for textile manufactures to be capable of distinguishing between bails of high value specialty fibers and those containing contamination from lower value products.

Today the universally accepted method of identifying fibers is microscopic analysis. However, the optical microscope is limited because of the subjective nature of the analysis and its limited ability to easily measure different parameters of the fiber such as the fiber diameter, the fiber scale length and the fiber scale thickness.

One of the limitations of microscopy is that only a relatively small area is viewed and that both microscopic and macroscopic information is needed to better understand a process or relationship. Microscopic structures that can only be seen at high magnification may appear insignificant at magnifications required to see macroscopic structures. Montages from the scanning electron microscope (SEM) and optical microscope allow large areas to be displayed at relatively high magnifications revealing both macroscopic and microscopic features.

The use of automated digital microscopy and image software have reduced the barriers for creation of montages and provided new display modes, thereby stimulating their use as an enhanced data acquisition, review, and interpretation technique.

The ability to create digital montages is a valuable tool in the analysis of cement and concrete. It has been used to evaluate the relationship between small scale deleterious phases and their larger scale effects.

The environmental scanning electron microscope (or Environmental SEM) is a powerful tool in the materials science laboratory. The large sample chamber and ability to operate in a very poor vacuum (>5Torr) makes it an ideal device for a wide variety of in-situ studies. A three point bending stage has been used in the ElectroScan E3 environmental SEM at the University of Michigan for over four years. The stage is extremely flexible and can be used to view samples in both planar and transverse views. It also allows for quantitative recording of the stress and strain exerted on the sample via a load cell and a linear variable differential transducer. The output s of the load cell are acquired into an Apple Macintosh computer via a National Instruments analog-to-digital acquisition card. To extend the capability of EMAL's in-situ tensile testing laboratory, a uniaxial tensile stage has been constructed in collaboration with the Department of Mechanical Engineering and Applied Mechanics.

We present a method for directly observing and quantifying the mechanical deformation of cellular foods, such as breadcrumb and Chinese water chestnut, with the aim of identifying the key differences in the nature of cell wall failure and crack propagation. These factors are of importance to the food industry, and this work may enhance our understanding of the changes in behaviour of crisp cellular foods when subjected to a moist environment.

Breadcrumb coatings are commonly applied to a core substrate such as meat, poultry, fish and vegetables. After flash-frying the product is often frozen, but during storage there is a tendency for the coating to absorb water from the substrate. The driving force for this process is the large difference in water activity level aw between the two materials. Incorrect reconstitution of the product, for example by microwave cooking, leads to a significant loss of crispness.

Whereas energy-dispersive X-ray spectrometry (EDS) has been used for compositional analysis in the scanning electron microscope (SEM) for 30 years, the benefits of using low (<5 kV) operating voltages for such analyses have been explored only during the last few years. This paper couples low-voltage EDS with two other emerging areas of characterization: spectrum imaging and multivariate statistical analysis (MSA). The specimen analyzed for this study was a finished Intel Pentium processor, with the polyimide protective coating stripped o ff to expose the final active layers. Data acquisition was performed with a Philips XL30-FEG SEM operated at 2 kV and equipped with an Oxford super-ATW detector and XP3 pulse processor. The specimen was normal to the electron beam and the take-off angle for acquisition was 35°. The microscope was operated with a 150 μm diameter final aperture at spot size 6, which yielded an X-ray count rate of ∼1000 s-1.

Whereas the spatial resolution for standard secondary electron (SEI) imaging in a scanning electron microscope or electron probe microanalyzer is related to the incident probe diameter, the spatial resolution for x-ray microanalysis is related to the convolution of the probe diameter with the spatial extent of the analyzed volume for a point probe. The latter is determined by electron scattering in the specimen and the subsequent emission of excited x-rays from the specimen. As such, it is possible that “What you see is not what you get”. This is especially true for instruments with high brightness electron sources (field emission). This problem is compounded by probe aberrations which at Gaussian image focus can produce significant electron tails extending tens of microns from the center of the probe.

The ability to reliably and quickly determine the resolution of the scanning electron microscope (SEM) is highly desirable becauseonly then can the level of performance which is being achieved be compared to that which was anticipated or specified. Further, in activities such as automated line width measurements, or in telemicroscopy, the ability to quantify the imaging performance provides the remote operator with the necessary information to monitor, document, and optimize the instrument set-up. However, compared to the equivalent task on the transmission electron microscope (TEM) an analysis of SEM performance is hampered by poor signal to noise ratios, and the absence of ideal ‘white noise’ samples.

The two dimensional Fourier power spectrum of an image provides a readout of the frequency content of the information present in the micrograph. From an analysis of the power spectrum the highest spatial frequency transferred in the image can then be determined and hence the resolution of the micrograph can be specified.

Directionally solidified in-situ composites based on niobium and niobium silicides, such as Nb5Si3 and Nb3Si, are presently under investigation as structural materials [1, 2], Alloying additions of elements such as Hf, Ti and Mo to these silicides are also being explored in order to increase strength and oxidation resistance. The present paper describes the effect of Hf, Mo and Ti additions on microstructure and microtexture of high temperature silcide-based in-situ composites.

Alloys were prepared from high purity elements (>99.9%) using induction levitation melting in a segmented water-cooled copper crucible. The alloys were directionally solidified using the Czochralski method [2], Phase identification was performed using scanning electron microscopy, electron microprobe analysis (EMPA), and automated electron back scattering pattern (EBSP) analysis. Using EBSP, positive phase identification was accomplished by direct comparison of the location and character of the diffraction bands in the experimental pattern with those calculated from simulated patterns generated using the possible structure types.

The speed of automated EBSP orientation gathering has now increased to a point where it is possible to examine large areas of deformed material at a resolution close to the length scale of the dislocation substructures involved (typically <1μm for strains of greater than ∊= l). Investigation of such deformed samples invariably gives rise to diffraction images of low quality and to many double patterns. To assist in a critical selection of the data, it is usual to store a measure of the indexing confidence for each point. Here we describe how deformed samples, which provide the appropriate range of pattern qualities, can be used to calibrate acceptance criteria for unsupervised EBSP measurements on deformation microstructures. An application in the use of such criteria is also described.

Two crystals, chosen with orientations that are known to develop a well defined texture spread during deformation, were channel die deformed to a strain of ∊=1.5 (78% reduction).