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).

The most critical technical issue preventing large scale application of ceramic matrix composites is the cost-effective application of stable interface coatings on continuous ceramic fibers. Currently, an alumina-silica ceramic fiber containing up to 14 wt. % boria (Nextel 312TM) is composited at elevated temperatures to form a boron nitride (BN) coating on the fiber surface. This BN coating serves as a compliant layer facilitating crack deflection and producing a non-catastrophic failure mode. Continued development of these ceramic matrix composites requires a more complete understanding of the mechanistic paths involved in composite densification. The objective of this work is to investigate and more clearly describe the role of the BN coating and its relation to composite processing and properties of the densified Nextel 312TM fiber/BlackglasTM (silicon oxycarbide) composites.

Three composites consisting of as-received fibers (coated with an organic sizing), desized fibers (sizing removed by heating), and boron nitride coated fibers were fabricated using BlackglasTM preceramic polymer 489C B-stage resin.

Conventional scanning electron microscopy permits the use of cryogenic techniques, which has led to the examination of ice-containing samples (eg ice cream) at temperatures of -80°C and below. At these temperatures moderate etching of the ice crystals occurs which helps to identify the crystals in the surrounding glassy matrix. However, imaging at higher temperatures - equivalent to those at which most ice-containing systems are actually utilised - is impossible because of rapid sublimation. We have set out to develop a system which will enable us to examine ice crystals at temperatures of -20°C and below, corresponding much more closely to realistic conditions of use.

In the environmental scanning electron microscope (ESEM), a gas can be maintained around the sample. Not only can this be used to maintain the sample in its native state, but the gas is actively involved in the imaging process through its role in signal amplification.

The Environmental Scanning Electron Microscope (ESEM) was used to study film-formation in vinyl latices polymerised in the presence of varying amount and type of starch. An understanding of the effect of native biopolymers on film forming mechanisms in latex has technological and industrial relevance because it can lead to the creation of novel latices with potentially lower cost and improved biosustainability.

Film formation studies were carried out on a range of samples selected by ICI Paints as the most promising candidates for the novel latices. These included vinyl latices polymerised with 2 - 15% of potato and waxy maize starch, taken either in native or modified. Normally, no surfactants were used during latex polymerisation; a few samples were prepared for comparative purposes when polymerisation was carried out both with and without the addition of surfactant. Latex films were spun-cast on glass slides before insertion into the microscope.

Liquid containing specimens can be stabilized for observation in the Environmental Scanning Electron Microscope (ESEM). It is also possible to examine systems that are primarily liquid, such as colloidal suspensions and gels, or even possess a multi-component liquid microstructure as in emulsions.(l) In order for such investigations to be useful, an understanding of the origins of secondary electron contrast in liquids is necessary. Our aim here is not to produce a complete theory of secondary electron emission in these systems, but to provide general guidelines for discriminating between two liquids based on relative contrast.

Secondary electron emission from a substance is determined by three processes: creation, transport through the material, and escape from the surface.(2) Contrast between two regions will be due to differences in one or more of these processes. Initial generation of secondary electrons is primarily a function of the ionization cross-sections of the substance and its density.

“Secondary” or ‘low energy’ electron emission in the environmental SEM is a complex summation of surface and near surface interactions of electron and ions, fields developed within the sample and conventional electron-sample interactions. Little is understood about the first two aspects and recent data has illustrated limitations on our understanding of cathodoluminescence. The recently described Charge Contrast Imaging (CCI) has drawn attention to the fact that the role of ions in the environmental SEM have been largely ignored. Generally the positive ions have been regarded to provide charge cancellation at the specimen surface but otherwise to have little effect. This view has persisted in the face of evidence that even without gas amplification effects, charge neutral conditions are obtained at the sample surface with a chamber gas pressure of 0.1 torr2, a pressure far lower than normal operating conditions for the ESEM (1 -2 0 torr).

Over the past few years there have been occasional reports of unusual secondary electron contrasts in certain nonmetallic materials using conventional (CSEM-Johansen et al, 1997), low voltage (LV-SEM-Harker et al, 1993; Harker et al, 1994) and environmental scanning electron microscopy (ESEM-Griffin, 1997; T. Hardt, personal communication) which have documented novel contrast mechanisms whose origins are not yet well understood. Indeed, similar observations were made over 20 years ago in certain uncoated materials (such as SiC) using conventional SEM (Sawyer and Page, 1978). Aspects of these charge contrast imaging (CCI) phenomena are further documented here in a series of ESEM experiments on polished cross sections of uncoated travertine calcite. What is “old” is the fact that these contrasts have been reported on several occasions. What is “new” is the observation that these unusual contrasts are more readily studied and, in some cases, have been found in a wider range of materials using ESEM.

Standard Reference Material (SRM) 482 of the National Institute of Standards and Technology is a set of 6 gold/copper wires, ranging in concentration from 0 to 100% Cu in 20% steps, intended for calibration studies of electron beam microanalyzers. This is an appropriate standard to test the accuracy of energy dispersive x-ray spectrometry (EDS) in the Environmental Scanning Electron Microscope (ESEM). While the presence of the gas in the sample chamber gives the ESEM its unique capabilities, it also is the source of complications to x-ray spectrometry. The gas can spread the primary electron beam into a wide skirt of electrons with the consequent production of x-rays many micrometers from the target location of the beam. In spite of the difficulties, at least two methods have been proposed to correct high pressure data to that expected at low pressures.

We have performed a theoretical and experimental study of the signal composition in the Environmental SEM (ESEM) with the intention of forming a set of general guidelines for optimising the signal to background ratio. In the ElectroScan ESEM, a gas ionisation cascade is used to amplify the secondary electron signals emanating from the specimen surface. The presence of gas in the chamber also gives rise to a pressure dependent background signal derived from ionisation events between gas molecules and high energy primary beam and backscattered electrons, as well as secondary electrons generated by the probe skirt.

The signal collected by an environmental secondary detector (ESD) (ElectroScan, 1991) or a gaseous secondary detector (GSED) (ElectroScan, 1994) is an amplified signal which is a composite of at least three contributions. These are the amplified currents arising from the ionisation of the gas by high energy electrons from the primary (Ipe) and backscattered electrons (Ihse).

Knowledge of the magnitude of the scattered electron skirt in the environmental scanning electron microscope (ESEM) or low vacuum scanning electron microscope (LVSEM) is important to the understanding of the analytical spatial resolution of energy dispersive spectrometry (EDS). The extent of beam scattering is a function of the distance from the final aperture to the specimen, composition of the gas present, chamber pressure, accelerating voltage, and beam current. This work compares model predictions of electron scattering to experimental measurements of electron scattering. Several of the popular Monte Carlo programs written for electron-solid interactions were not designed for low vacuum conditions. Joy has developed a model that takes into account the electron scattering which takes place in the chamber before interacting with the specimen; thus it is useful for LVSEM conditions. That model is incorporated in Electron Flight Simulator - E (Small World, Vienna VA)1 and is used in this work.

The ESEM is able to image liquids in their natural state, unlike conventional SEM, and offers significantly better resolution than optical microscopy. The ability to image binary liquid mixtures, such as water-oil emulsions, depends upon sufficient contrast for differentiation of the dispersed and continuous phases. We have made observations of such water-oil emulsions in an Electroscan 2010 Environmental SEM, and have duly obtained images with good contrast. Experiments were carried out on emulsions of vegetable oil-in-water, polybutene-in-water and water-in-polybutene, all emulsified with nonionic polysaccharide surfactants. Each sample was imaged at a temperature of approximately 3°C, in water vapour at a pressure of 4 torr, in order to maintain the liquid state.

From the ESEM micrographs in Figures 1, 2 and 3, it is clear that water exhibits a greater secondary electron emission than an unsaturated hydrocarbon.

The tendency of poly-G oligonucleotides to undergo self-assembly into helical nucleic acid tetramers have been termed G-quartets. Also known as G-wires, these structures retain their crystallographic determined dimensions better than duplex DNA when imaged with the atomic force microscope (AFM). Relative humidity has been known to affect both the resolution and measured height DNA strands on mica. The results below aim to develop a model that can be used to define the mechanical properties of G-wires by scanning probe microscopy investigations. G-wires were examined under a wide range of relative humidity to determine their tolerance to shear forces under the AFM, and to establish imaging conditions for hydration scanning tunneling microscopy (HSTM).

The relative humidity dependence of G-wires were taken with 125 μm long, 20 μm wide silicon nitride cantilevers in contact AFM mode (spring constant ∼ 0.4 N/m) (Fig. 1).

Our group is interested in exploring how functional molecules (e.g. those composed of organic functional groups that do not necessarily lend themselves to an ordered 2D packing arrangement) can form well-ordered adlayers with functional properties. To this end. we have studied the formation of self assembled structures of 5-(N,N-didecyl-amino)-2.4- pentadienal (DAPDA, Figure 1) deposited on a highly ordered pyrolytic graphite (HOPG) surface. This molecule has two distinctive features that should dramatically affect its ordering on a surface. Neither of these have been systematically explored in ordered adlayers. First, the extended conjugation of the molecule gives it a large in-plane dipole moment as well as a high polarizability. Second, it contains two hydrocarbon tails, only one of which can lie coplanar with the conjugated moiety. Both molecularly resolved monolayer and bilayer structures were found using a combination of scanning tunneling microscopy and tapping mode atomic force microscopies.

Langmuir-Blodgett (LB) films of fatty acid salts are inherently unstable due to the fundamental incompatibility of the asymmetric monolayer film transferred from the water surface with the centrosymmetric equilibrium form of the fatty acid bulk crystal. One consequence of this incompatibility is that fatty acid salt films deposited by the LB technique do not remain as flat and uniform films, but reorganize into bilayer step islands. By using mixed chain length films, the islands and holes had distinct heights that suggest this reorganization occurs by a bulk folding of the layers rather than a molecular reorganization of the molecules.

We have studied cadmium arachidate (CdA) LB films, varying the substrate used, the number of layers deposited, and the time the film spends under the aqueous subphase. All films were imaged in air with an Atomic Force Microscope (AFM).