Leem measurements of step energies at the (001) surface of heavily boron-doped silicon

We have used the low energy electron microscope (LEEM) to investigate step faceting and striped phase formation on heavily boron-doped Si(001) surfaces. Measurements of thermal fluctuations along the steps, equilibrium island shapes, and the angle of triangular facets provide quantitative information on the step formation energies. We find that a simple, systematic temperature dependence of the spatial anisotropy of the free energy of isolated steps is sufficient to account for the observed faceting of the B type steps. These results suggest that the proliferation of straight A step edges at lower temperature is caused by the energy of isolated A steps becoming vanishingly small. We show that rapid cooling of the samples leads to the nucleation and growth of a high density of vacancy islands on the surfaces. Based on these results, we propose a qualitative model for mass transport during stripe formation.