Scanning Electron Microscopy


A model was developed to calculate the optical reflectance of an absorbing substrate covered by multiple thin layers of absorbing materials. Both multiple homogeneous thin layers and thin surface layers of mixed phases were modeled. Reflectance versus wavelength was measured for polished chalcopyrite (CuFeS2) and compared to calculated data. The identity and thickness of surface compounds used to calculate reflectance curves were partially determined using X-ray photoelectron and Auger electron spectroscopies. Very good agreement between theoretical and experimental reflectance curves were observed as a function of surface composition. The hue (color) and luminosity (brightness) of the polished surface were also calculated from both experimental and theoretical curves and were found to also be valuable for evaluating surface composition. Contrast in optical photomicrographs resulting from both luminosity and hue was illustrated.

Secondary and backscattered electron microscopy were also used to image chalcopyrite polished surfaces which were naturally oxidized by an exposure before and after ion etching. For a substrate covered with thin layers, the resulting backscattered coefficient was calculated as a function of the backscattered coefficient for the surface and the substrate, respectively.

The variations of the relative difference between the effective backscattered coefficients vs the primary beam energy exhibited a maximum for a critical thickness difference of the surface layer. The dependence of the variations in thickness of the oxidized layer with the crystallographic orientation changes of the substrate as well as the resulting contrasts of the optical and electron images were discussed.

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