Hafnium oxide presents a strong interest either for optical coatings or for microelectronic applications. An important parameter to control is its chen-deal interaction with silicon oxide, since those two materials are usually in direct contact in both applications: For optical coatings, silica is the low refractive index used to make interference filters [see M. R. Kozlowski, Thin Films for Optical Systems (Marcel Dekker, New York)], in microelectronics HfO2 could be used as a gate insulator in metal-oxide semiconductor technology [B. H. Lee, Tech. Dig. Int. Electron Devices C, C Meet. 99, 133]. One interesting characterization method of the created interface is infrared spectroscopy in the so-called multiple internal reflection (MIR) technique. Mono- and bilayers of HfO2 and SiO2 have been deposited on germanium substrates by e-beam evaporation and ion beam sputtering. MIR measurements made on those samples show that when HfO2 is deposited on SiO2, parts of the Si-O-Si bonds are broken and Hf-O-Si bonds, representative of hafnium silicate (HfSiO4), are formed at the interface. Hafnium and silicon oxide have also been coevaporated in a reactive atmosphere to deposit the silicate and confirm the position of the Hf-O-Si bond. The results obtained by MIR are confirmed with x-ray photoelectron spectroscopy and transmission electron microscopy analysis.