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).

Ex-situ and in-situ studies were performed for self-assembled monolayers (SAMs) formation on mica. The behavior of two surfactants [octadecylphosphonic acid (OPA) and dodecylphosphonic acid (DPA)] in two different solutions [ethanol or tetrahydrofuran (THF)] were studied at different concentrations. A cross section analysis of the monolayer images at partial coverage showed thickness of 1.8 nm, 0.7 nm, and 1.0 nm for OPA, DPA and mixed OPA/DPA, respectively. These values are similar to the ones presented by Xiao and those expected for a monolayer of mixed surfactants as proposed by Whitesides. Since the topography of a monolayer resembles the substrate, the presence of the monolayer at full coverage was determinated by force-distance curve measurements. It was observed that the solvent had the ability to re-dissolve the OPA monolayer, suggesting that the bonding is of a physisorption nature.

The atomic force microscope (AFM) is now a fairly widely used metrological tool for measuring surfaces with nanometer-scale precision, in 3-D. A number of biologists have noticed that untreated biological cells and molecules deposited onto surfaces can also be analyzed by AFM in air or fluids provided the AFM imaging forces do not greatly excede the compressiblity of the specimen. What has gone largely unnoticed in the biological microscopy community is the fact that AFM provides a wealth of opportunity with regard to 3D, nanometer-scale morphometric and biochemical measurements of biomaterials, cells and molecules. The ability to obtain such precise length-scale measurements on biological structures does open up a whole new branch of biological microscopy- something we have termed, Biometrology. A broad definition of Biometrology is, the science of quantifying biological structures such that the measured quantities give rise to biological or diagnostic information.

The AFM (atomic force microscopy) requires a stable and flat substrate on which a biological sample is readily immobilized. For instance, membrane protein 2D crystals in lipid bilayers have been adsorbed to silanized glass with covalently attachment using a photocrosslinker or to mica by physisorption under appropriate ionic conditions. For the immobilization of 2D crystals of water soluble proteins formed on lipid monolayers, a different approach is required to attach the highly hydrophobic tails of the lipid molecules. To find a suitably hydrophobic substrate, the hydrophobicity of different materials was determined by the sitting drop method. Briefly, a 10 μ1 droplet of deionized and filtered water was deposited on the substrate surface and the diameter measured. Table 1 shows a decrease in droplet diameter with increasing hydrophobicity, indicating that substrates such as silanized glass and HOPG (highly ordered pyrolytic graphite) may be suitable for adsorbing lipid monolayers.

Photoelastic measurement is a sensitive optical technique to map strain fields in otherwise isotropic materials. To extend this method to the submicron scale, we combine dynamic polarimetry with nearfield scanning optical microscopy (NSOM) and construct a polarization modulation NSOM (PMNSOM). The 670 nm laser light passes first through a linear polarizer (oriented at 90°), and then through a photoelastic modulator (PEM), and finally through a quarter wave plate. The PEM introduces a sinusoidally time varying phase shift δ0sin(2πft) into the +45° polarization component, where the modulation frequency/is the resonant frequency (50 kHz) of the PEM quartz element. The quarter wave plate (oriented at 0°) transforms this elliptically polarized light into linearly polarized light with its orientation varying sinusoidally at the modulation frequency. This polarized light is then coupled into a single-mode optical fiber leading to the NSOM tip.

Atomic force microscopy (AFM) was introduced in 1984, and proved to be more versatile than scanning tunneling microscopy (STM) due to the AFM's capabilities to scan non-conductive samples under atmospheric conditions and achieve atomic resolution. Ultra high vacuum (UHV) AFM has been used in surface science applications when control of oxidation and corrosion of a sample's surface are required. Expensive equipment and time consuming sample exchanges are two drawbacks of the UHV AFM system that limit its use. Until recently, no hot/cryo-stage, moderate vacuum, controlled gas environment AFM was commonly available.

We have demonstrated that phase transformations are easily observable in metal alloys and polymers with the use of a moderate vacuum AFM that has in-situ heating/cooling capabilities and quick (within minutes) sample exchange times. This talk will describe the results of experiments involving a wide range of samples designed to make use of the full capabilities of a hot/cryo-stage, controlled gas environment AFM.

Gold is an important mineral whether for its value, properties or its natural beauty. It is expected that in a few years Australia will be the second largest producer of gold. Present gold mining practices, though able to recover minute amounts of gold, can be improved. In the current process, gold is dissolved in an alkaline cyanide solution to form Au(CN)2, which is adsorbed onto activated carbon. Activated carbon has shown a special affinity for the gold complex even in the presence of other metalcyanide complexes at much greater concentrations in the pulp. This process is efficient and is able to recover gold at a concentration of 1 part per million in the auriferous ore. The adoption of the carbon technology has contributed substantially to the increased output of Australian gold. Within 15 years, local production has increased more than ten-fold over.

Nanoindentation is becoming an increasingly important tool for the characterization of the mechanical properties of materials on the nanometer scale. The mechanical response of a material is measured by recording the force acting between an indenter and the material while displacing the indenter into the material. The shape of the recorded load displacement curves is not only dependent on the mechanical properties of the material, but also strongly dependent on indenter geometry. To minimize difficulties in the extraction of quantitative material mechanical property information from the force curve, indenter geometry must be controlled and characterized on the same scale as the indentation, i.e. on the nanometer scale. Diamond, the hardest naturally occurring material, is an obvious choice as the indenter material. Conventional lapping techniques4 do not provide sufficient control to produce indenter geometries of the shapes and to the precision required for optimal nanoindentation measurements.