Computer study of the B-Si exchange in the Si(111)√3x√3-B surface phase

The B-H-3-B-S-5 transfer in the B/Si(111)-(root 3 x root 3) surface phase has been studied using the semi-empirical AM1 method. It has been found that the transfer has two parts. In the first part the B atom transfers from the T-4 adatom position to one of the bridge surface positions situated between a pair of the surface silicon atoms. This bridge state is 0.2 eV higher than the T-4 adatom state, and the barrier height between them is 0.6 eV. The second part of the transfer consists of the boron penetrating into the silicon second layer (S-5 position) and, simultaneously, of a silicon forcing out from the S-5 position to the T-4 adatom position. The height of this second barrier is about 0.5 eV and the energy of the final B-S-5 state is lower than the initial B-H-3 state by 1.1 eV. The total barrier height of the B-H-3-B-S-5 transfer is predicted to be about 0.7 eV.