Dependence of TO and LO mode frequency of thermally grown silicon dioxide films on annealing temperature

We have investigated the structural properties of oxide films using infrared spectroscopy. The TO mode frequencies depend on the annealing temperature but the LO mode frequencies are constant in the bulk region. It is considered that the TO mode frequencies represent the oxide density. In a densified vitreous silica, both the TO and LO mode frequencies decrease. In our experiment, only the TO mode frequency in the oxide bulk region depended on the annealing temperature. Since this result cannot be explained only by the oxide density, we affirm that to inspect the structural properties of oxide, not only the oxide density but also the LO mode frequencies must be taken into consideration.