Formation of CaF₂ nanostructures on Si(001)

Initial stages of epitaxial growth and formation of CaF₂ nanostructures on Si(001) were studied. A variety of nanostructures were grown including ultrathin two-dimensional layers at 750 °C, quasi-one-dimensional stripes at 650 °C and well-ordered dots at lower growth temperatures. Atomic force microscopy and reflection high-energy electron diffraction were used to measure the nanostructure shape and lattice orientation. The evolution of the surface electronic structure under different growth conditions was studied by ultraviolet photoelectron spectroscopy and metastable de-excitation spectroscopy. The leading role of the wetting layer in high-temperature formation of the fluorite-silicon interface was established.