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Three-dimensional relaxation of small crystallites was imaged in real time using variable-temperature scanning tunneling microscopy. The micron-sized Pb crystallites, supported on Ru(0001), were equilibrated at 500– 550 K, and the volume-preserving shape relaxation was induced by a rapid temperature decrease to 353– 423 K. The (111) facet at the top of the crystallite grows by sequential peeling of single atomic layers, which shrink like circular islands. The rate of layer peeling slows dramatically as a new final state is reached.

A new technique, combining a pulsed supersonic molecular-beam source and time-resolved surface infrared spectroscopy, has been devised to measure the microscopic diffusion of molecules at surfaces. Following a rapid dose of a periodically stepped Pt(111) crystal face to a low total coverage of CO (\ensuremath{\sim}0.006 monolayer), the time evolution of CO molecules migrating from terrace to step sites was monitored with a temporal resolution as fast as 5 msec. When compared with a simple kinetic model, the data reveal statistical microscopic hopping rates for CO diffusion on the (111) plane over the $T=95\ensuremath{-}195$ K range investigated.