采用分子束外延(MBE)技术在单晶蓝宝石衬底上生长了高质量化学计量比二氧化钒(VO2)薄膜,通过该技术实现薄膜厚度15～60 nm精确控制.对于优化条件下VO2薄膜,实现了电阻率变化超过4个数量级的优异金属-绝缘体相变,近似于之前报道高质量单晶VO2相变特性.特别是通过太赫兹时域光谱分析了不同厚度的VO2薄膜在太赫兹波段的光学特性.结果表明:VO2薄膜的厚度对其在太赫兹波段的光学特性有很大影响.因此,为了获得更优的可靠性和重复性能,VO2薄膜的厚度必须得到精确控制.本研究结果对于下一步VO2基太赫兹器件研究具有重要意义.
High quality stoichiometric VO2 films were grown on single crystal sapphire substrates by molecular beam epitaxy (MBE),the film thicknesses were precisely controlled on the nanoscale ranging from 15 nm to 60 nm.For the optimized sample,a distinct reversible metal-insulator transition (MIT) with abrupt resistance change more than four orders of magnitude was observed,which was comparable to the ever reported result for high quality single crystal VO2.Especially,the optical properties in the terahertz (THz) frequency range were characterized with THz time-domain spectroscopy (THz-TDs)measurements for samples with various thicknesses,and the results indicate that the THz properties of VO2 film was significantly affected by the thickness.Therefore,the thickness should to be precisely controlled to obtain reproducible and reliable performance.The THz devices based on VO2 film may benefit significantly from these achievements.
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