Facets formation of pyramidal Si nanocrystals selectively grown on Si(001)windows in ultrathin SiO2 films

We have used in situ scanning tunneling microscopy (STM) to study the facet formation in the selective growth of pyramidal Si nanocrystals on Si(001) windows in ultrathin 0.3-nm-thick SiO2 films. Broad (001) surfaces develope d as the top of the crystals, and {1, 1,(2n + 1)} (n = 1-6) facets formed t he sidewalls. As growth continued, the slope angle of sidewall facets incre ased, and {1, 1, 9} and {1, 1,(2m + 1)} (0 < m < 4) facets often came to co exist on the sidewalls. On well-oriented Si(001) surfaces, layer-by-layer g rowth in the [001] direction was dominant. On vicinal Si(001) surfaces, lat eral step growth took place in the initial stage, and the layer-by-layer gr owth was suppressed until after a large (001) surface had formed as the top of the crystal. (C) Elsevier Science B.V. All rights reserved.