Thermal reaction of iron with a Si(111) vicinal surface: Surface ordering and growth of CsCl-type iron silicide

The structural evolution of a vicinal silicon surface, developing upon low coverage deposition of Fe [0.33 and 2 monolayers (ML)], has been carefully studied as a function of annealing temperature by means of scanning tunneling microscopy. The reaction between the deposited material and the substrate, which occurs at room temperature, leads to surface amorphization. Successive annealing induces substantial changes of the surface structure. The onset of 2×2 reconstruction expansion of the Si surface, covered with 0.33 ML Fe, is observed after annealing at 400 °C. Complete reconstruction of the whole surface is found at the same temperature for a coverage of 2 ML. Upon annealing at 700 °C three-dimensional iron silicide islands grow epitaxially on the Si substrate. Their size, shape, and location depend on the amount of the deposited material. For 0.33 ML coverage elongated crystallites are distributed randomly on the vicinal substrate surface. Larger crystallites, grown upon deposition of 2 ML of Fe, take the shape of truncated pyramids and show a tendency to nucleate along vicinal surface terrace edges, forming a self-organized array of nanometer size dots. For both Fe coverages studied they are found to grow in a CsCl-type structure, containing an increasing amount of vacancies with increasing crystallite size. The electronic properties of iron silicide surface are probed with a spatial atomic resolution by means of tunneling spectroscopy. The interface between iron silicide crystallite and silicon substrate displays features characteristic of Schottky barriers.