Surface morphology of yttrium silicides epitaxially grown on Si(1 1 1) by STM

We have studied by means of scanning tunneling microscopy and low energy electron diffraction techniques the surface morphology of very thin layers of yttrium silicide epitaxially grown on a Si(1 1 1) substrate. For an Y coverage of 1 ML a two-dimensional p(1×1) silicide layer is formed. The surface morphology of this phase presents characteristic triangular holes with a typical lateral size of 20 Å and oriented as the faulted half unit cell of the 7×7 reconstruction. Further Y coverage leads to the formation of a three-dimensional (3D) (√3×√3)R30° YSi1.7 film. In particular, for a coverage of 3 ML, a 3D YSi1.7 film grows, covering the whole surface. The topography of this phase is characterized by defects consisting of round shaped holes.