Host-isotope effect on the localized vibrational modes of oxygen dimer in isotopically enriched silicon

Local vibrational modes of oxygen dimers in silicon have been investigated using naturally available silicon (^natSi) and isotopically enriched ²⁹Si and ³⁰Si crystals. Infrared absorption spectroscopy of ^natSi revealed two pairs of peaks originated from the oxygen dimers, a pair A at 1012 and 1060 cm^-1 and a pair B at 1105 and 1136 cm^-1, whose frequencies shifted when the mass of the silicon host atoms was changed. The observed frequency shifts of both A and B can be accounted for with a simple linear chain calculation assuming two previously proposed atomic configurations known as staggered and skewed dimers. Further analysis, based on the degree of contribution from the second and beyond nearest neighbor silicon masses, allows us to assign the pair B as the skewed dimer absorption peaks while the pair A as the staggered dimer absorption peaks.