METASTABLE RECONSTRUCTIONS ON SI(111)

We report unambiguous atomic scale evidence demonstrating that the ato m density in the high temperature ''1x1'' phase of Si(111) is similar to 6% higher than the 7x7. Such evidence is provided by scanning tunne ling microscopy (STM) observation of excess adatom density, and relate d island formation, on surfaces with very large terraces. The unusuall y large terraces were produced by heating the sample with DC current i n the step-down direction at 1200 degrees C. By trapping adatoms on th e terraces through a quench, we have also created areas of metastable reconstructions, i.e., 9x9, 2x2, c2x4 and root 3x root 3, much larger than previously reported. For the first time, we have demonstrated the existence of metastable 11x11, 13x13 and c2x8 on Si(111). We have fou nd that the c2x8 reconstruction can be stabilized as well as other mem bers of the 2x2/c2x4/c2x8 family of reconstructions. An energetic mode l, based on the idea of atomic conservation, is proposed for the forma tion of the observed high atom density metastable reconstructions.