Scanning Microscopy


Two pairs of diametrically opposed Schottky surface barrier diodes in a modified scanning electron microscope (SEM) are used to reconstruct surface elevations and composition differences. An empirically determined function of difference of signals from opposing diodes is used to calculate slopes, which are then integrated to elevations by an efficient 2-dimensional Fast Fourier Transform. Composition differences are distinguished by variations in the overall backscattered electron (BSE) intensity estimated by the sum of the four diode signals. Arithmetic average roughness measurements from the BSE device are within 10% of stylus surface tracer measurements when surface slopes average less than 6 degrees and maximum slopes are less than 45°; shadowing effects for rough surfaces, aliasing, and averaging effects from Fourier integration are apparent. Composition measurements show distinction of high contrast phases; phase boundary-slope interactions are noted.

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