Reactive epitaxial growth of MnSi ultrathin films on Si(111) by Mn deposition

Manganese (Mn) adsorption on the Si(111)-(7x7) surface followed by annealing at a relatively low temperature of 250 degrees C has been studied by using scanning tunneling microscopy as well as low-energy electron diffraction and Auger-electron spectroscopy. The B20-type structure of a Mn monosilicide (MnSi) of epitaxial ultrathin films is formed with a (root 3 x root 3)R30 degrees periodicity. Morphologies of the crystalline MnSi ultrathin films have been investigated for Mn coverage of 1.5, 3, and 5 monolayers (ML). We found a characteristic mode of crystal growth for compound formation in the solid-on-solid system. At each amount of the Mn deposition, structural features, morphology, and formation processes of the MnSi films can be explained by the mass balance between deposited Mn and usable Si atoms. We found that the epitaxial MnSi ultrathin films can be grown coherently on Si(111) at 3 ML of Mn deposition. At 5 ML, the supply of Si atoms from bulk to surface becomes significant, then many deep holes are formed and the surface morphology becomes rough. It is found that the codeposition of Mn and Si leads to the formation of anomalously smooth MnSi surfaces.