ATOMIC-FORCE MICROSCOPY OF AMMONIUM-PERCHLORATE

Ammonium perchlorate (NH4ClO4 or AP) is an insulating energetic materi al and is hygroscopic; the surface degrades easily by absorbing moistu re in ambient conditions. An ultrahigh vacuum (UHV) atomic-force micro scope (AFM) has been designed and built to study the (210) surface of AP in a moisture-free environment. Large-scale images from this appara tus show nanocracks and grains; cracks are mainly aligned with the dir ection that matches the main crystal steps and grains are plastically deformed by raster scans. Molecular scale images are taken on grains w ith a constant frictional force. Popping signals are observed in the f rictional-force mode which are about ten times larger than the topogra phy 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.