RHEED Rocking Curve Analysis of Si(111).RAD.3*.RAD.3-Ag Surface Phase Transition at Low Temperature

Abstract

Si(111)√3×√3-Ag surface structural phase transition from honeycomb chained triangles (HCT) structure to inequivalent triangles (IET) structure is investigated using reflection high-energy electron diffraction (RHEED) rocking curves. Rocking curves are measured during spontaneous heating process of a cooled (∼120K) sample up to room temperature. The rocking curves were analyzed using many-beam dynamical RHEED calculations with three kinds of structural models, HCT (Ag triangle stays at mirror symmetry position), IET (Ag triangle rotates by 6 degrees) and rotating-HCT (r-HCT; Ag atoms are randomly rotating between ±6° which maintains the mirror symmetry) structures. At room and low temperatures, r-HCT and IET structures give the best results respectively. Rocking curves between room and low temperatures are also reproduced by mixing of r-HCT and IET structures and the mixing ratio changes almost linearly with substrate temperature. It is obtained that r-HCT coverage is almost 100 % at room temperature and IET coverage is about 60 % at 120 K. It is also found that mixing ratio of IET/r-HCT structure meets 0.5 at about 150 K which is known as a transition temperature in previous reports. [DOI: 10.1380/ejssnt.2006.414]