Hydrogen Assisted Nano-crystallization in TiO2 Thin Film Prepared by Hot-Wire Chemical Vapor Deposition

概要

論文の詳細を見る
Preparations and structural studies of TiO2 thin films using hot-wire chemical vapor deposition (CVD) (hot-filament CVD) are reported for the first time. Titanium tetra-isopropoxide [Ti(OC3H7)4] was used as a source gas and decomposed on a heated rhenium filament. The film deposited at the filament temperature ($T_{\text{f}}$) of 1300 °C shows amorphous structure with the substrate temperature ($T_{\text{s}}$) of 300 °C, and X-ray diffraction (XRD) peaks originated from nano-crystalline with anatase structure appeared over $T_{\text{s}}$ of 400–700 °C. The optical band gap energies of the nano-crystalline TiO2 films with anatase structure were ${\sim}3.4$ eV. An increase of $T_{\text{s}}$ from 400 to 700 °C enhanced the XRD peak intensity of (112) orientation. Meanwhile, an increase of $T_{\text{f}}$ up to 1500 °C induces nano-crystalline TiO2 with rutile structure. Furthermore, the hydrogen dilution realizes the nano-crystallite growth of rutile structure even in the deposition at $T_{\text{f}} = 1300$ °C. During this deposition, the actual substrate surface temperature ($T_{\text{suf}}$) was 305 °C. In bulk TiO2 materials, the anatase structure changes to the rutile structure by thermal annealing up to about 800 °C. We propose for the first time that atomic hydrogen contributes to the low temperature nucleation of rutile structure in the deposition of oxide system, TiO2 films.
2009-03-25