Two-dimensional fractal-like growth on semiconductors: The formation of continuous manganese monosilicide ultrathin films on Si(111)

Continuous crystalline MnSi ultrathin films with atomically flat surfaces, which are highly expected to find an application in Si-based spintronics, are grown on Si(111)-7×7 by solid phase epitaxy method. The interfacial reaction between Mn and Si and the formation processes of the films as well as their morphological variation with annealing temperature are investigated using scanning tunneling microscopy. The MnSi ultrathin films form in a two-dimensional (2D) fractal-like mode only at a Mn coverage above ∼2 ML and at an annealing temperature in the narrow range of ∼250-300 °C. Above ∼300 °C, the growth mode gradually transforms into Volmer-Weber mode and correspondingly, the continuous films transform into 2D compact islands. The films grow with a thickness unit of quadruple layer, which is consistent with the B20-type MnSi structure.