Field emission scanning electron microscope analysis

I was characterized by powder X-ray diffraction (PXRD), energy dispersive analysis of X-rays (EDAX), chemical analysis, thermogravimetric analysis (TGA) and IR spectroscopy. EDAX analysis indicated the ratio of Mn S to be 3 2. The presence of fluorine was confirmed by analysis and the percentage of fluorine estimated by EDAX in a field emission scanning electron microscope was also satisfactory. Thermogravimetric analysis also confirms the stoichiometry of the compound. Bond valence sum calculations6 and the absence of electron density near fluorine in the difference Fourier map also provide evidence for the presence of fluorine. The sulfate content was found to be 30.8% compared to the expected 32% on the basis of the formula. 

After 5 minutes of reaction time in each case, the solution was centrifuged and washed with DI water three times. A few drops of washed solutions were placed on sample holders in each case and left to dry under ambient conditions. The dried sanq>les were either coated by evaporation of gold-palladium alloy or sputter coated with gold and they were further characterised by Field Emission-Scanning Electron Microscope (FE-SEM) for product morphology, which was also equipped with an Energy Dispersive Spectroscopy (EDS) facility for elemental analysis. In the control experiments without using the protein, no silica precipitation was observed even over a 24 hour period, as was described previously [13]. 

Resolution in the STEM is limited by the probe diameter, which is about 1 nm in equipment dedicated to this operating mode, at the cost of using a cold field emission gun requiring an ultravacuum. Because of the high-precision optics and the point-by-point image formation principle, the STEM combines the advantages of scanning electron microscope analysis with resolution performance levels similar to the transmission electron microscope. 

With modern scanning electron microscopes many of the restrictions of the transmission electron microscope have been alleviated. Firstly, thin samples are no longer required. With instruments equipped with a field-emission gun, magnifications as low as 50X and as high as lOOOOOX can be achieved routinely. Imaging the back-scattered electrons gives the distribution of the heavy elements at a high resolution, whereas the secondary electrons are indicative of the shape and the size of the solid particles present in the specimen. Analysis of the emitted X-rays can indicate the elemental composition. 

There are several distinct fields of X-ray analysis used in analytical chemistry and materials characterization, namely, XRA, XRD, XRF, and X-ray emission. The basic principles of each are described in the following. X-ray emission is generally used for microanalysis, with either an electron microprobe (Chapter 14) or a scanning electron microscope (SEM). 

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