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.