Scanning Electron Microscopy


SIMS routines have been developed for the analysis of oxide materials, with applications particularly in element profiling of corrosion layers on glasses after weathering or leaching. The possibilities of quantification and reproducibility have been found critically sensitive to the buildup of charge on the insulating specimens. With control of constant specimen potential, relative sensitivity factors in the positive mass spectrum have been determined for about 20 elements in 10 different alkali-borosilicate glasses. Secondary ion yields were studied as functions of the energy range of ions admitted to the analyzer. At relatively low energies, including the top of the energy distribution, the formalism of the "local thermal equilibrium" model was found to be very well approximated, strongly favoring the yields of elements with low ionization potentials. For ions with relatively high energies the role of Ei was less pronounced, and there were some indications of atomic binding effects.

With well-defined conditions of energy pass window and of offset in sample voltage, considerable reproducibility of calibration could be obtained. In routine profiling it has been found advantageous to work at rather high offset, which rendered a narrowed range of specific elemental yields, easily interpreted mass spectra, and reduced sensitivity to surface charge effects.

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