质子辐照VO₂薄膜的损伤机理研究

Research on the Damage Mechanism of H⁺ Irradiated VO₂ Films

摘要: VO₂由于其可逆的金属–绝缘体相变(MIT)与可控的红外光学响应能力而被作为一种性能优异的表面智能热控材料应用在航天领域，然而航天环境中的宇宙射线可通过电离与产生位移缺陷改变VO₂薄膜的缺陷谱与晶格结构，进而影响VO₂的性能。本文对于宇宙射线中的主要组分粒子H⁺系统考察了其在20~160 keV能量区间内对外延生长于Al₂O₃ (0001)的VO₂薄膜的辐照影响，首先采用SRIM模拟软件进行入射模拟，结果表明质子的核阻挡功率与空位密度总是与其能量呈负相关。后续的物性表征结果与模拟结果基本一致，质子能量越低，VO₂所受的质子辐照影响越显著。范德堡电阻测试表明辐照能够使得VO₂在升温过程中的相转变发生提前，其MIT温度从347 K最大降低至341 K；XRD结果表明辐照能够使得VO₂的面外晶格发生膨胀，其沿出射方向的晶面间距d (010)从4.502 Å最大提高至4.514 Å；AFM测量表明辐照能够使得VO₂表面不平整度增加，其表面均方根粗糙度从1.257 nm最大提高至1.896 nm；变温拉曼光谱测量的光学与声子表征显示空位增多会削弱VO₂的室温拉曼特征峰并使得峰的升温衰减提前；傅里叶变换红外谱的结果表明辐照能够破坏VO₂的智能热控能力。

Abstract: VO₂ owing to its reversible metal-insulator transition (MIT) and tunable infrared optical response, has been proposed as an attractive surface smart thermal control material for aerospace applications. However, cosmic rays in the space environment can modify the defect spectra and lattice structure of VO₂ via ionization and displacement processes, thereby degrading VO₂ functional properties. This work systematically examines the effects of the dominant cosmic-ray constituent, the proton in the 20~160 keV energy range on epitaxial VO₂ films grown on Al₂O₃ (0001). SRIM simulations of the incident protons indicate that nuclear stopping power and the resulting vacancy density are inversely correlated with ion energy. Subsequent physical characterizations corroborate the simulation results: lower proton energies produce more pronounced irradiation effects in VO₂. Van der Pauw resistivity measurements show that irradiation advances the phase transition on the heating branch, with the MIT temperature decreasing from 347 K to as low as 341 K. X-ray diffraction reveals an out-of-plane lattice expansion. The interplanar spacing along the out-of-plane (010) direction d (010) increases from 4.502 Å to a maximum of 4.514 Å. Atomic force microscopy indicates an increase in surface roughness, with root-mean-square roughness rising from 1.257 nm to 1.896 nm. Temperature-dependent Raman spectroscopy shows that an increased vacancy concentration weakens the characteristic room-temperature Raman modes and causes their thermal attenuation to occur at lower temperatures. Fourier-transform infrared measurements demonstrate that irradiation degrades the infrared switching capability of VO₂.