yrammuS 要概近年，小型マルチガスセンサは，呼気センサ，排気ガスセンサなど多様な用途に応用でき，安心，安全，健康生活の実現に必要なデバイスである．抵抗温度係数(TCR)が高い有力材料として，注目されているVO2はTCR>10％/Kというガスセンサの仕様要求を満たす物性を有するが，物性制御の困難さゆえ，未だこの要求を達成できていない．VO2等の強相関金属酸化物は，温度変化等の外部刺激により金属-絶縁体転移(MIT)を示し，これに伴い抵抗値が101–104倍以上変わる特異な性質を示す．これらの系では，電子の性質特性は物質中で集合・分離して存在し，相転移の際に数百nmサイズの電子相を形成する．この電子相1つが相転移発現の最小構造であり，単一電子相を抽出（試料をナノ構造化）することで潜在的な高いTCRが達成できる．申請者はこれまで10 nmサイズのVO2ナノ構造を作製し，TCR~100％/Kという原理的最大値を実現してきた．本研究では，面方位の異なるTiO2基板上でのVO2ナノ構造マニピュレーションによるMIT特性制御の実現に取り組んだ．ナノ構造マニピュレーションが導く局所歪み状態の変化からMITの起源に迫り，TCR~100％/Kの高感度センサ性能を広い温度領域で示すVO2ナノ構造集積試料を作製し，高感度ガス検出性能を導く基礎特性を実証した．VO2 has been attracting attention as a promising material with a high temperature coefficient of resistance (TCR). VO2 exhibit a metal-insulator transition (MIT) by temperature-change, of which resistivity change is the magnitude of 101-104, leading to high TCR. The MIT in VO2 is mainly due to the rearrangement of vana-dium atom pairs (V-V dimer) in the crystal, and the differences in local crystal distortion is considered to produce differences in the physical properties of electronic phase with a size of several hundred nanometers, which is minimum structure for MIT. In this study, the local crystal distortion is controlled by changing the size of VO2 micro-samples on TiO2 substrate to control the MIT properties. Micro-sized VO2 samples showed steep resistivity change across the MIT and the MIT temperature and hysteresis width were decreased with downsizing of VO2 micro-sample size. The MIT temperature and the hysteresis width were proportional to the length of V-V dimer, which is oriented in the out of plane direction of VO2 film on TiO2 substrate. The in-plane lattice constant of VO2 is strained due to the lattice mismatch between TiO2 and VO2. The VO2 sample exhibits a state with a relaxed lattice by dislocations in case of the sample size is large and a state with a fully strained in-plane lattice in case of the sample size is small, based on the total energy of the VO2. Therefore, the out-of-plane lattice constant, i.e., V-V dimer length, is enlarged in larger VO2 samples, leading to higher MIT temperature with wide hysteresis width. These results strongly indicate an excellent potential for mul-ti-gas sensors, e.g. integrated micro VO2 samples on same chips.服部 梓19Azusa N. HATTORI高感度相転移特性を持つ金属酸化物立体ナノ構造試料の創製とマルチガスセンサへの応用（2021採択）Fabrication of the metal oxide nanostructures with the enhanced metal-insulator transition properties and their multi-gas sensor application(Project 2021)33Rep. Grant. Res., Asahi Glass Foundation (2023)
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