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ID 48851
フルテキストURL
著者
Muraoka, Y. Graduate School of Natural Science and Technology, Okayama University
Saeki, K. Graduate School of Natural Science and Technology, Okayama University
Eguchi, R. Graduate School of Natural Science and Technology, Okayama University
Wakita, T. Graduate School of Natural Science and Technology, Okayama University
Hirai, M. Graduate School of Natural Science and Technology, Okayama University
Yokoya, T. Graduate School of Natural Science and Technology, Okayama University
Shin, S. RIKEN/SPring-8
抄録
We have prepared VO2 thin films epitaxially grown on TiO2(001) substrates with thickness systematically varied from 2.5 to 13 nm using a pulsed laser deposition method, and studied the transport property and electronic states of the films by means of resistivity and in situ synchrotron photoemission spectroscopy (SRPES). In resistivity measurements, the 13-nm-thick film exhibits a metal-insulator transition at around 290 K on cooling with change of three orders of magnitudes in resistivity. As the film thickness decreases, the metal-insulator transition broadens and the transition temperature increases. Below 4 nm, the films do not show the transition and become insulators. In situ SRPES measurements of near the Fermi level valence band find that the electronic state of the 2.5-nm-thick film is different than that of the temperature-induced insulator phase of VO2 itself although these two states are insulating. Ti 2p core-level photoemission measurements reveal that Ti ions exist near the interface between the films and TiO2 substrates, with a chemical state similar to that in (V,Ti)O-2 solid solution. These results indicate that insulating (V,Ti)O-2 solid solution is formed in the thinner films. We propose a simple growth model of a VO2 thin film on a TiO2(001) substrate. Near the interface, insulating (V,Ti) O-2 solid solution is formed due to the diffusion of Ti ions from the TiO2 substrate into the VO2 film. The concentration of Ti in (V,Ti) O-2 is relatively high near the interface and decreases toward the surface of the film. Beyond a certain film thickness (about 7 nm in the case of the present 13-nm-thick film), the VO2 thin film without any Ti ions starts to grow. Our work suggests that developing a technique for preparing the sharp interface between the VO2 thin films and TiO2 substrates is a key issue to study the physical property of an ultrathin film of "pure" VO2, especially to examine the presence of the novel electronic state called a semi-Dirac point phase predicted by calculations.
発行日
2011-02-15
出版物タイトル
Journal of Applied Physics
109巻
4号
出版者
American Institute of Physics.
開始ページ
043702-1
終了ページ
043702-6
ISSN
0021-8979
資料タイプ
学術雑誌論文
プロジェクト
エネルギー環境新素材拠点
オフィシャル URL
http://dx.doi.org/10.1063/1.3549835
言語
English
OAI-PMH Set
岡山大学
著作権者
© 2011 American Institute of Physics.
論文のバージョン
publisher
査読
有り
DOI
Web of Sience KeyUT