DIFFUSION OF SINGLE HYDROGEN-ATOMS ON SI(111)-(7X7) SURFACES

Adsorption and diffusion of single hydrogen atoms on Si(111)-(7 x 7) s urfaces at elevated temperatures have been studied using scanning tunn eling microscopy. Hydrogen atoms adsorb preferentially atop rest atoms . An adsorbed H atom can hop between two neighbor rest atoms via an ad atom, i.e., via a metastable intermediate state. Below 340 degrees C, the hopping is mostly confined within a half-cell, but at higher tempe ratures, they can hop across the cell boundary. The activation energie s for different hopping paths were measured. The binding energy differ ence between rest-atom and adatom sites and that between corner and ed ge adatom sites were also determined to be similar to 0.2 and similar to 0.05 eV, respectively.