We analyze the results of scanning near-field infrared spectroscopy performed on thin films of a-SiO2 on Si substrate. The measured near-field signal exhibits surface-phonon resonances whose strength has a strong thickness dependence in the range from 2 to 300 {nm}. These observations are compared with calculations in which the tip of the near-field infrared spectrometer is modeled either as a point dipole or an elongated spheroid. The latter model accounts for the antenna effect of the tip and gives a better agreement with the experiment. Possible applications of the near-field technique for depth profiling of layered nanostructures are discussed.
@article{arxiv.1110.4927,
title = {Near-field spectroscopy of silicon dioxide thin films},
author = {Lingfeng M. Zhang and Gregory O. Andreev and Zhe Fei and Alexander S. McLeod and Gerardo Dominguez and Mark Thiemens and Dimitri N. Basov and Antonio H. Castro Neto and Michael M. Fogler},
journal= {arXiv preprint arXiv:1110.4927},
year = {2012}
}