First Stage of Oxygen Aggregation in Silicon: The Oxygen Dimer

The structure and dynamic properties of the interstitial oxygen dimer in silicon are found using a combination of infrared spectroscopy and ab initio modeling. We find that the stable dimer consists of a pair of inequivalent weakly coupled interstitial oxygen atoms separated by a Si-Si bond. Two high frequency modes are decoupled in one ${}^{16}\mathrm{O}{-}^{18}\mathrm{O}$ combination but are strongly mixed in the other combination. A third lower lying mode involves the compression of the Si-Si bond joining the oxygen atoms and gives distinct modes in the mixed ${}^{16}\mathrm{O}{-}^{18}\mathrm{O}$ case.