Theory of anharmonicity on bond-centered hydrogen oscillators in silicon

摘要

An anomalous positive shift when the mass of the Si host isotope is increased has been observed recently [Pereira et a]., Physica B 340342 (2003) 697] for the asymmetric stretch frequency of the bond-centered proton in Si (H-BC(+)). On the other hand, the usual downward isotope shift was observed for the analogous bond-centered deuteron (D-BC(+)). Based on phenomenological and ab initio modeling studies, we explain the observed puzzling effect. We introduce a Si-H-Si linear model that accounts well for the observations when anharmonicity, volumetric effects due to the host-isotope mass change, and the coupling of the Si-H-Si unit to the lattice are taken into account. The positive isotope shift for H-BC(+) results from anharmonic A(2u) + A(1g) mode mixing and volumetric effects. (c) 2005 Elsevier B.V. All rights reserved.