The energetics and dynamics of Si ad-dimers on Si(001) were investigated by means of total-energy calculations and scanning tunnelling microscopy. Several dimer configurations, and a thermally activated rotational mode of the dimer on top of a dimer row, were predicted theoretically and identified experimentally. The existence of several possible quasi-stable states for the stable nucleus was expected to be a general phenomenon; especially on surfaces of low symmetry. A recent scanning tunnelling microscopic study of the thermal decomposition of disilane on Si(001) had suggested that H atoms which coexisted on the surface could help to stabilize some of the ad-dimer configurations. It was concluded, on the basis of the present results, that it was also possible to determine the effect of impurities upon nucleation and growth processes.

Z.Zhang, F.Wu, H.J.W.Zandvliet, B.Poelsema, H.Metiu, M.G.Lagally: Physical Review Letters, 1995, 74[18], 3644-7