It was noted that the epitaxy of Ti on Si(001) involved a marked intermixing of Ti and Si atoms, which gave rise to the formation of the silicide. This behavior differed considerably from typical epitaxial growth and was not clearly understood. By using first-principles total-energy calculations, the reaction of a Ti adatom with the Si(001) surface was examined. It was found that the penetration of the Ti adatom into a near-surface interstitial site, and the subsequent ejection of its neighboring surface Si atoms onto a terrace, was kinematically favored with respect to normal hopping diffusion on a Si surface. These reactive processes provided a microscopic mechanism for the initiation of transition-metal silicide formation.

Unusual Ti adsorption on Si(001) and subsequent activation of Si ejection B.D.Yu, Y.Miyamoto, O.Sugino, T.Sasaki, T.Ohno: Physical Review B, 1998, 58[7], 3549-52