Structural and optical studies of nanostructured TiO₂-Ge multi-layer thin films

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• 作者：Abdul Faheem Khan^a ; ^b ; ^{faheem_khan_1977@yahoo.com} ; Mazhar Mehmood^c ; Turab Ali^d ; H. Fayaz^a
• 关键词：TiO2&ndash ; Ge multi-layer thin films ; Quantum confinement effects ; Band gap energy ; Annealing
• 刊名：Thin Solid Films
• 出版年：2013
• 出版时间：1 June, 2013
• 年：2013
• 卷：536
• 期：Complete
• 页码：220-228
• 全文大小：2343 K

文摘

This paper reports the effects of annealing on structural and optical properties of nanostructured multi-layer TiO₂-Ge thin films. These films were characterized using different techniques such as X-ray diffraction, X-ray reflectivity, Rutherford backscattering (RBS), and Fourier Transform Infrared spectroscopy. Annealing was responsible for pronounced changes in structural and optical properties of these films, as associated with changes in their structures, stoichiometry and stress-state.

Three sets of TiO₂-Ge multi-layer films were deposited by electron beam evaporation and resistive heating with different Ge layer thickness (5, 10 and 15 nm), and TiO₂ layer thickness was fixed to 20 nm. The films were annealed in air up to 500 ¡ãC for 2 h. RBS studies showed that the layer structure of TiO₂-Ge multi-layer films had been formed. The absorption spectra and band gap energy showed a blue shift with decrease in Ge layer thickness. The absorption spectra of these films suggest quantum confinement that increases with annealing temperature before the complete oxidation of Ge. Apparently complete oxidation results in sudden or sharp rise in band gap energy that matches with that of TiO₂. RBS study reveals that layered structure of TiO₂-Ge multi-layer films is not destroyed by annealing, which may be due to non-wetting behavior of Ge and its oxide with TiO₂. These results imply that nanostructured TiO₂-Ge multi-layer thin films may be employed as heterojunctions (with tunable band gap energy) based on quantum confinement effects for use in photovoltaics.