ATOMIC-SCALE DYNAMICS OF A 2-DIMENSIONAL GAS-SOLID INTERFACE

The interface between a two-dimensional (2D) molecular gas and a 2D mo lecular solid has been imaged with a low-temperature, ultrahigh-vacuum scanning tunneling microscope. The solid consists of benzene molecule s strongly bound to step edges on a Cu{111} surface. Benzene molecules on the Cu{111} terraces move freely as a 2D gas at 77 kelvin. Benzene molecules transiently occupy welt-defined adsorption sites at the 1D edge of the 2D solid. Diffusion of molecules between these sites and e xchange between the two phases at the interface are observed. On raise d terraces of the copper surface, the 2D gas is held in a cage of the solid as in a 2D nanometer-scale gas bulb.