Scanning Microscopy


We report unambiguous atomic scale evidence demonstrating that the atom density in the high temperature "1x1" phase of Si(111) is ~6% higher than the 7x7. Such evidence is provided by scanning tunneling microscopy (STM) observation of excess adatom density, and related island formation, on surfaces with very large terraces. The unusually large terraces were produced by heating the sample with DC current in the step-down direction at 1200°C. By trapping adatoms on the terraces through a quench, we have also created areas of metastable reconstructions, i.e., 9x9, 2x2, c2x4 and 3x3, 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 found that the c2x8 reconstruction can be stabilized as well as other members of the 2x2/c2x4/c2x8 family of reconstructions. An energetic model, based on the idea of atomic conservation, is proposed for the formation of the observed high atom density metastable reconstructions.

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