Imaging polished sapphire with atomic force microscopy

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Abstract
The polished faces of c‐ and r‐oriented single‐crystal sapphire have been studied with an optical deflection‐sensed atomic force microscope using microfabricated cantilevers and a fiber optic‐based light source.Images taken with repulsive contact forces reveal equally spaced atomic steps. The spacing between these steps corresponds with the off‐axis angle of polishing (∼10 arc‐min). An unidentified large‐scale periodicity (∼1 micron) is also observed. Attractive‐mode images of the same sample have been obtained using electrostatic forces. This was accomplished by evaporating a thin metal film on the sample side of the cantilever. Charge is deposited on the sample by applying a bias to an electrode attached to the back side of the sample and allowing it to come to equilibrium. These attractive‐mode images reveal the same large‐scale periodicity as with repulsive mode, but with an increased amplitude. This result implies that the features are more than simple topography, and possibly correspond to regions of charge accumulation.

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