Single-phase anatase structure and dominant metallic Ge in Ge/TiO ₂ multi-layer films using a differential pumping co-sputtering system

This study investigates the preparation of Ge/TiO₂ multi-layer films using a differential-pumping co-sputtering system (DPCS). This system has two chambers with different atmospheres, pure Ar for the Ge target and 0.5%O₂ in Ar for the TiO₂ ceramic target. The optical absorption spectra of the multi-layer films obviously shift to visible and near-infrared regions with increasing Ge layer thickness, while keeping O/Ti composition ratios of 2.3 ± 0.1 in TiO₂. X-ray diffraction results indicate that the TiO₂ layer forms a single-phase anatase structure in the multi-layer films. X-ray photoelectron spectroscopy also indicates that metallic Ge is dominant in the multi-layer film with negligible Ge-oxide. Therefore, DPCS provides a multi-layer film with a single-phase anatase structure in the TiO₂ layer and a dominant metallic element in the Ge layer.