Atomic-Scale Dynamics of a Two-Dimensional Gas-Solid Interface

S. J. Stranick, M. M. Kamna, P. S. Weiss*

Science 266, 99 (1994).

The interface between a two-dimensional (2D) molecular gas and a 2D molecular solid has been imaged with a low temperature ultrahigh vacuum scanning tunneling microscope. The solid consists of benzene molecules 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 well defined adsorption sites at the 1D edge of the 2D solid. Diffusion of molecules between these sites and exchange between the two phases at the interface are observed. On raised terraces of the Cu surface, the 2D gas is held in a cage of the solid as in a 2D nanometer scale gas bulb.