LAYERED HEAVY-METAL IODIDES EXAMINED BY ATOMIC-FORCE MICROSCOPY

Atomic force microscopy was used to characterize the surface of semi-i nsulating bismuth tri-iodide, lead iodide, and mercuric iodide crystal s. These heavy metal iodides belong to a unique class of materials tha t provide a wide range of interesting problems that can be studied by atomic force microscopy. They have relatively high vapor pressures and cannot be examined noninvasively in vacuum conditions, such as by ele ctron microscopy. Mercuric, bismuth, and lead iodide are layered mater ials with van der Waals bonding along the c axis acid therefore, like mica, can be easily cleaved to provide fresh atomically flat crystalli ne surfaces to study. These crystals are soft with a high degree of pl asticity and, as a result, the surfaces are easily modified by the can tilever tip. They demonstrate reactivity in ambient air at the surface s as well as within the van der Waals gap. Freshly cleaved surfaces we re examined and it was found that single and multiple atomic layers we re easily displaced on the cleaved surfaces in all of the crystals whe n scanned in both contact and modulated contact mode. The effects of c antilever induced modifications of the surfaces of mercuric, lead, and bismuth iodide were studied by atomic force microscopy and their prop erties are discussed. (C) 1996 American Vacuum Society.