MBE法制备VO2薄膜及其中红外调制深度测量

为了给VO₂薄膜在定向红外对抗系统防护方面的应用提供理论依据，我们用透过率调制深度表征VO₂薄膜在中红外波段的相变特性。本实验利用分子束外延法（MBE）制备VO₂外延单晶薄膜，经XRD、AFM表征，发现其具有（020）择优取向、纯度较高，薄膜表面平整、均匀且致密。经VU-Vis-IR测量发现其近红外透过率相变特性显著，但在紫外和可见光范围内透过率相变特性较不明显。然后我们对制备时间为30 min、40 min的两组薄膜分别进行25~70℃的升温和降温实验，观察其对波长为3 459 nm、脉宽50 ns、重频50 kHz、功率密度0.14 W/cm²的中红外激光的透过率变化，并比较两组薄膜的温滞曲线特性。实验发现它们对中红外透过率的调制深度均可达60%以上，前者比后者对中红外的调制深度高出约4%。这说明利用分子束外延法制备的VO₂单晶薄膜具有良好的中红外调制特性，且调制深度和膜厚有关。进一步表明了利用VO₂薄膜实现中红外激光防护具有一定的可行性。

VO2 Thin Films Prepared by MBE and Measurements of Mid-infrared Modulation Depth

In order to provide the theoretical basis for the application of VO₂ thin films to anti-directional infrared countermeasures system, the phase transition characteristics of VO₂ thin films in the infrared band were characterized by the transmittance modulation depth. At first, VO₂ epitaxial mono crystalline thin films were prepared by molecular beam epitaxy(MBE), and then characterized by X-ray diffraction(XRD), atomic force microscope(AFM). It is found that it has (020) preferential orientation, high purity VO₂ in the thin films, the surface of thin films is smooth, uniform and dense. The near infrared transmittance phase transmittance property is found to be outstanding by VU-Vis-IR measurement, however, it is less obvious in ultraviolet and visible light. We took an experiment that transmittance variation for mid-infrared from 25 to 70℃ temperature rising and cooling process based on two groups of VO₂ prepared for 30 min and 40 min, respectively. The mid-infrared laser was used in the experiment with 3 459 nm wavelength, 50 ns pulse width, 50 kHz repetition frequency, and 0.14 W/cm² power density. The two temperature hysteresis curves were compared. It is found that the transmittance modulation depth of mid-infrared of them both can reach over 60%, and the former group is about 4% higher than the latter group in transmittance modulation depth in mid-infrared. This indicates that the VO₂ mono crystalline films prepared by the molecular beam epitaxial method have good mid-infrared transmittance modulation characteristics, and the modulation depth is related to film thickness. It is further demonstrated that it is feasible to put VO₂ thin films into anti-directional infrared countermeasures system.