1. Fig. 1. Experimental set-up for optical diffraction studies of surface diffusion of hydrogen atoms on Cu(111) using Xe density gratings as templates.

2. Fig st-order optical diffraction signals from hydrogen adatom density gratings on Cu(111). The decay exponents are related to hydrogen diffusion constants.

3. Fig. 3. Arrhenius plot of hydrogen diffusion constants D(T) on Cu(111) from 140K to 210K. The solid line is a fit to Eq. (3).

4. Fig. 4. Arrhenius plot of Xe diffusion constants on Xe multi-layers on Cu(111) from 46K to 54K.