DIFFUSION OF ADSORBED SI DIMERS ON SI(001)

The diffusion of adsorbed Si dimers on the Si(001)-2 x 1 surface is st udied with hot scanning tunneling microscopy and a tracking technique in which each diffusive event is resolved. The activation energy for d iffusion of a dimer along the top of a substrate dimer row is found to be 1.09+/-0.05 eV, with an attempt frequency of 10(13.2+/-0.6) Hz. A lower bound of 1.40 eV is placed on the activation energy for dimer di ssociation. The free energy of a dimer is observed to decrease by 32+/ -2 meV at a site adjacent to a type-A step. (C) 1997 Elsevier Science B.V.