Scanning electron microscopy design

Scanning electron microscopy and replication techniques provide information concerning the outer surfaces of the sample only. Accurate electron microprobe analyses require smooth surfaces. To use these techniques profitably, it is therefore necessary to incorporate these requirements into the experimental design, since the interfaces of interest are often below the external particle boundary. To investigate the zones of interest, two general approaches to sample preparation have been used. 

Scanning electron microscopy and other experimental methods indicate that the void spaces in a typical catalyst particle are not uniform in size, shape, or length. Moreover, they are often highly interconnected. Because of the complexities of most common pore structures, detailed mathematical descriptions of the void structure are not available. Moreover, because of other uncertainties involved in the design of catalytic reactors, the use of elaborate quantitative models of catalyst pore structures is not warranted. What is required, however, is a model that allows one to take into account the rates of diffusion of reactant and product species through the void spaces. Many of the models in common use simulate the void regions as cylindrical pores for such models a knowledge of the distribution of pore radii and the volumes associated therewith is required. 

This chapter summarizes results obtained during the past 5 years, on the design, preparation and study of titanium and vanadium compounds as candidate precursors to TiC, TiN, VC, and VN. The study of the precursor molecules was conducted through several steps. After their synthesis, thermoanalytical studies (TG-DTA), coupled to simultaneous mass spectroscopic (MS) analysis of the decomposition gases, were carried out to determine their suitability as precursors. CVD experiments were then conducted and were followed by characterization of the deposits by scanning electron microscopy (SEM) energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron microprobe analysis with wavelength dispersion spectroscopy (EPMA-WDS). 

---