ABSTRACTMaterials engineers have increasing control over nanoscale chemical composition and nanostructures. The latter can be easily analysed by the scanning electron microscope (SEM) yet nanoscale chemical analysis in the SEM poses challenges. Nevertheless, nanoscale chemical analysis capabilities have been developed in the LV-SEM by secondary electron hyperspectral imaging (SEHI). In this article, the insights that SEHI has provided into well characterised semiconductor, photovoltaic, polymer and hard carbon materials are reviewed. Instrument and experimental considerations for the obtainment of secondary electron hyper-spectra are discussed and recommendations for future analyses in the LV-SEM by SEHI are made. 相似文献
Construction mortars contain a broad variety of both inorganic and organic additives beside the cement powder. Here we present a study of tile mortar systems based on portland cement, quartz, methyl cellulose and different latex additives. As known, the methyl cellulose stabilizes the freshly prepared cement paste, the latex additive enhances final hydrophobicity, flexibility and adhesion. Measurements were performed by solid state nuclear magnetic resonance (NMR) and low voltage scanning electron microscopy (LVSEM) to probe the influence of the latex additives on the hydration, hardening and the final tile mortar properties. While solid state NMR enables monitoring of the bulk composition, scanning electron microscopy affords visualization of particles and textures with respect to their shape and the distribution of the different phases.
Within the alkaline cement paste, the poly(vinyl acetate) (VAc)-based latex dispersions stabilized by poly(vinyl alcohol) (PVA) were found to be relatively stable against hydrolysis. The influence of the combined organic additives methyl cellulose, poly(vinyl alcohol) and latexes stabilized by poly(vinyl alcohol) on the final silicate structure of the cement hydration products is small. But even small amounts of additives result in an increased ratio of ettringite to monosulfate within the final hydrated tile mortar as monitored by 27Al NMR. The latex was found to be adsorbed to the inorganic surfaces, acting as glue to the inorganic components. For similar latex water interfaces built up by poly(vinyl alcohol), a variation in the latex polymer composition results in modified organic textures. In addition to the networks of the inorganic cement and of the latex, there is a weak network build up by thin polymer fibers, most probably originating from poly(vinyl alcohol). Besides the weak network, polymer fibers form well-ordered textures covering inorganic crystals such as portlandite. 相似文献
Four different organofunctional silanes were selected and deposited on chemically pretreated aluminum surfaces by immersion and electrodeposition techniques. The surface morphology, comparison of elemental constituents, and surface free energies of silane-coated aluminum were investigated by low voltage scanning electron microscopy (LVSEM), low voltage X-ray analysis (LVXA), and contact angle measurement, respectively. The initial bond strength and long-term durability were evaluated with epoxy adhesive by lap shear tests. The deposition of silane coupling agents enhanced the bond durability of aluminum/epoxy joints under heat and humidity conditions. Also the performance of silane coupling agents depended on the application method. The electrodeposition technique produced a more uniform coverage of silane on the aluminum surface and, thus, was generally more effective than the immersion technique in improving bond performance. 相似文献
It is well known that the differential Mott cross section for large-angle elastic scattering shows maxima and minima at angles depending on material and electron energy. For electron energies of 10–30 keV, the averaging by frequent elastic scattering processes results in approximate Lambert angular distributions of backscattered electrons (BSE). However, the present Monte Carlo calculations for electron energies E = 1–5 keV and different angles of incidence show strong deviations from a Lambert distribution which increases with decreasing energy. The signals of the BSE detector with five annular segments for different take-off directions show good agreement with the calculations for normal electron incidence. 相似文献
Two commercial instruments that permit a gaseous environment in their specimen chamber have been investigated, namely, a 'FEI Quanta 600 FEG' environmental scanning electron microscope and a 'LEO SUPRA 35VP FESEM' low vacuum scanning electron microscope. The gas flow field is first computed by the direct simulation Monte Carlo method and the gas density gradient, speed, Mach number and temperature are found in the transition region from high pressure to vacuum. The electron beam transfer characteristics are then derived for different accelerating voltages and pressures and a comparison is made among different situations and with some published works. Certain physical parameters are analysed and discussed to establish a figure of merit that can be used as a standard performance specification for commercial environmental scanning electron microscope and low vacuum scanning electron microscope. 相似文献