Charge ordering induced by intrinsic defects in Sn/Ge(111) submonolayers with a coverage close to 1/3

Abstract

A thermodynamic model is suggested for a (3×3)-type structure formation with a charge density wave (CDW) arising against the background of a \((\sqrt 3 \times \sqrt 3 )R30^\circ\)-type structure in a Group IV metal (Sn, Pb) submonolayer adsorbed with a coverage of ≈1/3 at the (Ge, Si) semiconductor (111) surface. Calculations are carried out by using a self-consistent theory for static fluctuations of the order parameter amplitude. It is shown that the low-symmetry (3×3) phase can nucleate at point defects of the submonolayer as charge-ordered areas of finite radius. The spatial configuration of the CDW and its temperature dependence are calculated. The results obtained are compared with the experimental data for the Sn/Ge(111) system.