THE MICROSCOPIC MECHANISMS OF DIMER OPENING IN THE EARLY STAGES OF SI DEPOSITION ON SI(100)-(2X1)

Molecular dynamics simulations using the Stillinger-Weber potential show that a thermal Si atom sticking on the Si(100)-(2 x 1) surface is able to open a surface dimer at the very earliest stages of deposition. How this takes place depends on the impact parameter and the coverage. An incident atom that hits an area located around the middle of a dimer bond is trapped there with high probability, and inserts itself into the dimer. The atoms that belonged initially to the dimer move, upon trimerization, into the bulk equilibrium positions. Many of the incident atoms stick between dimers and are not able to open them if they are alone; however the dimers could be opened by the joint action of two adsorbed atoms. Thus, the dimer opening process, which will ultimately force the surface to undergo a transition from the (100)-(2 x 1) structure to the (100) structure, is a local phenomenon rather than a collective effect.