Preservation of the Phase Boundary of $\bf Si(111)7\times 7$ Structure in Air Studied by Force Microscopy

Si(111) surfaces cleaned under ultrahigh vacuum were studied by force microscopy in air. 7 x 7 domain boundaries associated with the phase transition from 1 x 1 to 7 x 7 during cooling were imaged as 1.0 approximately 1.5 angstrom high protrusions. The morphology was quite consistent with results from in situ techniques. For rapidly quenched surfaces, disordered 1 x 1 triangles were also seen in the middle of terraces. These structures may be related to the difference in surface atom densities and the difference in reaction to oxygen.