Imaging polished sapphire with atomic force microscopy

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.