Ammonium perchlorate (NH4ClO4 or AP) is an insulating energetic material and is hygroscopic; the surface degrades easily by absorbing moisture in ambient conditions. An ultrahigh vacuum (UHV) atomic-force microscope (AFM) has been designed and built to study the (210) surface of AP in a moisture-free environment. Large-scale images from this apparatus show nanocracks and grains; cracks are mainly aligned with the direction that matches the main crystal steps and grains are plastically deformed by raster scans. Molecular scale images are taken on grains with a constant frictional force. Popping signals are observed in the frictional-force mode which are about ten times larger than the topography of the surrounding intrinsic surface structure. These signals are intermittent and increase in intensity and abundance as the same area is scanned repeatedly. It is speculated that these signals are caused by local reactions initiated by the increased pressure from the tip as it turns around at the end of each line scan.