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中文摘要：
基于太赫兹（THz）时域频谱技术研究了飞秒激光激发下氧化钒纳米薄膜的光致绝缘体金属相变特性。利用直流磁控溅射法在不同条件下制备了一系列蓝宝石基底上的氧化钒薄膜，通过测量薄膜发生光致相变后太赫兹波的透射率来评估成膜质量，得出在溅射时间60 min不变的情况下，退火时间和退火温度分别为60 s和560 ℃时可以得到性能非常良好的氧化钒薄膜。在上述最佳条件下制备的氧化钒薄膜的相变深度可达80%。利用薄膜近似计算了太赫兹波段氧化钒薄膜在光致相变过程中电导率的变化，计算结果表明电导率实部在103 Ω-1·cm-1 量级，并基于Drude模型得到了金属态氧化钒薄膜的复介电常数以及复折射率。在绝缘衬底上制备的具有明显阈值激发功率且相变深度大的氧化钒薄膜将在太赫兹调制器件中有重要应用。
英文摘要：
The photo-induced insulator-metal phase transition of VO2 nanofilms under femtosecond pulse excitation is investigated using terahertz （THz） time-domain spectroscopy. A number of VO2 films are fabricated on sapphire substrates by direct current （DC） magnetron sputtering under different conditions. The film quality is evaluated by measuring the THz transmissions of the films in which photo-induced phase transition has occured and the results show that for a fixed sputtering time of 60 min VO2 films of high quality can be prepared when the annealing time and temperature are 60 s and 560 ℃, respectively. The degree of phase transition of the film fabricated under those best conditions can be as high as 80%. The conductivity of the film in the process of photo-induced phase transition in the THz range is determined based on thin film approximation, and calculations show that the real part of the conductivity is on the order of 103 Ω-1·cm-1. The complex dielectric constant and complex refractive index of the metallic-state thin film are further calculated based on the Drude model. The VO2 films fabricated on insulator substrates have an obvious threshold for the excitation pulse power and show a high degree of phase transition, which will play an important role in THz modulation devices.
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