Formation of CrSi$_2$ nanoislands on Si(111)7 $\times$ 7 and epitaxial growth of silicon overlayers in Si(111)/CrSi$_2$ nanocrystallites/Si heterostructures

Low-energy electron diffraction and differential reflectance spectroscopy are used to study the self-formation of chromium disilicide (CrSi$_2$) nanoislands on a Si(111) surface. The semiconductor properties of the islands show up even early in chromium deposition at a substrate temperature of 500$^\circ$C, and the two-dimensional growth changes to the three-dimensional one when the thickness of the chromium layer exceeds 0.06 nm. The maximal density of the islands and their sizes are determined. The MBE growth of silicon over the CrSi$_2$ nanoislands is investigated, an optimal growth temperature is determined, and 50-nm-thick atomically smooth silicon films are obtained. Ultraviolet photoelectron spectroscopy combined with the ion etching of the specimens with embedded nanocrystallites demonstrates the formation of the valence band, indicating the crystalline structure of the CrSi$_2$. Multilayer epitaxial structures with embedded CrSi$_2$ nanocrystallites are grown.