连续激光辐照下二氧化钒薄膜热致相变实验研究

 介绍了VO₂薄膜的相变原理,用磁控离子溅射法制备了VO₂薄膜,并进行了X射线衍射和不同温度下的光谱透过率测量。在1.319 μm 连续波激光辐照下,实时测量了VO₂薄膜的温度变化,以及由于温度变化引起相变后对激光透过率的变化。结果表明,入射到薄膜表面的平均功率为8.9 W、光斑直径2 mm时,激光出光480 ms后,VO₂的温度从室温上升到约100 ℃,薄膜发生了相变,其对1.319 μm激光的透过率从相变前的48％降为相变后的28％。     

脉冲溅射V2O5薄膜结构和性能研究

V2O5薄膜具有很好的离子注入/退出可逆性,是最有潜力的锂离子储存层的候选材料之一,它的电学特性与制备方法、化学计量比、结构和取向等有直接关系,仔细控制工艺参量是制备出在锂电池上应用的V2O5薄膜关键。研究中采用脉冲磁控反应溅射方法,通过精确地控制氧分压、基底温度等关键工艺参量,在石英玻璃和硅片上制备V2O5薄膜。利用X射线衍射和X射线光电子谱,分析了薄膜的成分、相结构、结晶和价态情况,用原子力显微镜表征了薄膜的微观结构,用分光光度计测量从200—2500nm波段V2O5薄膜纯度高、相结构单一、结晶度好。高低温电阻变化2个量级,薄膜的光学能隙为2.46eV。     

采用泵浦探测技术研究VO2薄膜相变特性

为研究纳秒激光作用下的VO₂薄膜的相变特性,采用泵浦-探测技术进行实验。首先,利用直流磁控溅射法制备VO₂薄膜,经X射线衍射（XRD）和原子力显微镜（AFM）分析表明样品质量较高。然后,测量VO₂薄膜在波长532 nm处的透过率随温度的变化情况,发现透过率随温度升高由32%上升到37%,与红外波段完全相反。在此基础上,选择1 064 nm泵浦光和532 nm探测光研究激光参数中能量密度和重频对VO₂薄膜相变特性的影响,同时结合ANSYS有限元软件对纳秒激光作用下VO₂薄膜的单脉冲温升情况进行分析。结果表明：VO₂薄膜在大于30 mJ/cm²的纳秒激光能量密度作用下,单脉冲温升可达相变温度,最小相变响应时间在14 ns左右。进一步提高纳秒激光能量密度,其相变响应时间略有增加但变化不大。在100 Hz以内改变纳秒激光重频对VO₂薄膜的相变响应基本无影响。VO₂薄膜的相变恢复时间随着纳秒激光能量密度的增大而呈自然指数增加,其变化过程与基底材料和纳秒激光参数密切相关。因此,可以通过优化VO₂薄膜基底材料参数提高其激光防护效果。     

在半导体-金属相变温度附近氧化钒薄膜光学性质的异常变动

在可见光—近红外波段的不同波长下,测量了半导体-金属相变过程中氧化钒薄膜样品的反射率和透射率.在薄膜相变过程中,不同波段的反射率曲线和透射率曲线表现出不同的变化趋势.利用非相干光在薄膜中的多级反射-透射模型,计算了相变过程中不同波长下氧化钒薄膜的折射率n和消光系数k随温度的变化.结果表明,在相变温度附近氧化钒薄膜光学性质的异常变动,其原因既有薄膜的折射率和消光系数随波长的变化趋势不同,也有在吸收性薄膜中存在探测光多次反射和透射的累加效应.     

Low reflectance sputtered vanadium oxide thin films on silicon

Vanadium oxide thin films on silicon (Si) substrate are grown by pulsed radio frequency (RF) magnetron sputtering technique at RF power in the range of 100–700 W at room temperature. Deposited thin films are characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques to investigate microstructural, phase, electronic structure and oxide state characteristics. The reflectance and transmittance spectra of the films and the Si substrate are recorded at the solar region (200–2300 nm) of the spectral window. Substantial reduction in reflectance and increase in transmittance is observed for the films grown beyond 200 W. Further, optical constants viz. absorption coefficient, refractive index and extinction coefficient of the deposited vanadium oxide films are evaluated.     

10.6 μm Infrared light photoinduced insulator-to-metal transition in vanadium dioxide

Vanadium dioxide has excellent phase transition characteristic. Before or after phase transition, its optical, electrical, magnetic characteristic hangs hugely. It has a wide application prospect in many areas. Now, the light which can make vanadium dioxide come to pass photoinduced phase transition range from soft X-ray to medium infrared light (6.9 μm, 180 meV). However, whether 10.6 μm (117 meV) long wave infrared light can make vanadium dioxide generate photoinduced phase transition has been not studied. In this paper, we researched the response characteristic of vanadium dioxide excited by 10.6 μm infrared light. We prepared the vanadium dioxide and test the changes of vanadium dioxide thin film’s transmittance to 632.8 nm infrared light when the thin film is irradiate by CO₂ laser. We also test the resistivity of vanadium dioxide. Excluding the effect of thermal induced phase transition, we find that the transmittance of vanadium dioxide thin film to 632.8 nm light and resistivity both changes when irradiating by 10.6 μm laser. This indicates that 10.6 μm infrared light can make the vanadium dioxide come to pass photoinduced phase transition. The finding makes vanadium has a potential application in recording the long-wave infrared hologram and making infrared detector with high resolution.     

纳米二氧化钒薄膜的电学与光学相变特性

采用双离子束溅射氧化钒薄膜附加热处理的方式制备了纳米二氧化钒薄膜。在热驱动方式下,分别利用四探针测试技术和傅里叶变换红外光谱技术对纳米二氧化钒薄膜的电学与光学半导体-金属相变特性进行了测试与分析。实验结果表明,电学相变特性与光学相变特性之间存在明显的偏差,电学相变温度为63 ℃,高于光学相变温度,60 ℃;电学相变持续的温度宽度较光学相变持续温度宽度宽;在红外光波段,随着波长的增加,纳米二氧化钒薄膜的光学相变温度逐渐增大,由半导体相向金属相转变的初始温度逐渐升高,相变持续的温度宽度变窄。在红外光波段,纳米二氧化钒薄膜的光学相变特性可以通过光波波长进行调控,电学相变特性更适合表征纳米VO₂薄膜的半导体-金属相变特性。     

Influence of hydrogenation on electrical conductivity of vanadium dioxide thin films

The influence of hydrogenation on electrical conductivity of vanadium dioxide thin films has been investigated. It has been shown using measurements of the electrical conductivity that the hydrogenation of vanadium dioxide thin films leads to a decrease in the temperature of the phase transition from the tetragonal phase (with “metallic” conductivity) to the semiconducting monoclinic phase. It has been found that, upon doping of vanadium dioxide with hydrogen, the electrical conductivity of the monoclinic phase can increase by several orders of magnitude. Nonetheless, the temperature dependence of the electrical conductivity of hydrogenated films exhibits a typical semiconducting behavior in the temperature range where the monoclinic phase is stable.     

基于FTO/VO2/FTO结构的VO2薄膜电压诱导相变光调制特性

采用直流磁控溅射和后退火工艺在掺氟的SnO₂(FTO)导电玻璃衬底上制备VO₂薄膜, 研究了不同退火时间和不同比例的氮氧气氛对VO₂薄膜性能的影响, 对VO₂薄膜的结晶取向、表面形貌、表面元素的相对含量和透过率随波长变化进行了测试分析, 结果表明在最佳工艺条件下制备得到了组分相对单一的VO₂薄膜. 基于FTO/VO₂/FTO结构在VO₂薄膜两侧的透明导电膜上施加电压并达到阈值电压时, 观察到了明显的电流突变. 当接触面积为3 mm×3 mm时, 阈值电压为1.7 V, 阈值电压随接触面积的增大而增大. 与不加电压的情况相比, FTO/VO₂/FTO结构在电压作用下高低温的红外透过率差值可达28%, 经反复施加电压, 该结构仍保持性能稳定, 具有较强的电致调控能力.     

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。     

Influence of Concentration of Vanadium in Zinc Oxide on Structural and Optical Properties with Lower Concentration

ZnO films doped with different vanadium concentrations are deposited onto glass substrates by dc reactive magnetron sputtering using a zinc target doped with vanadium. The vanadium concentrations are examined by energy dispersive spectroscopy （EDS） and the charge state of vanadium in ZnO thin films is characterized by x-ray photoelectron spectroscopy. The results of x-ray diffraction （XRD） show that all the films have a wurtzite structure and grow mainly in the c-axis orientation. The grain size and residual stress in the deposited films are estimated by fitting the XRD results. The optical properties of the films are studied by measuring the transmittance. The optical constants （refractive index and extinction coefficient） and the film thickness are obtained by fitting the transmittance. All the results are discussed in relation with the doping of the vanadium.     

Electrical,optical and structural properties of pure and gold-coated VO2 thin films on quartz substrate

In the present study, vanadium dioxide films were grown on quartz glass substrate by reactive KrF laser ablation technique using a vanadium dioxide target. The gold films of various thicknesses were then deposited on the VO₂ film by sputtering technique. Films were characterized by X-ray diffraction to determine crystallography, by four-point probe to determine the electrical property and by double-beam spectrophotometry to determine optical reflection and transmission behaviour in the 200–2500 nm spectral region. The resistance per square of VO₂ thin film decreases by two orders of magnitude across the metal insulator transition (MIT). The optical transmittance and reflectance exhibits, strong temperature dependence in the infrared region without a significant change in the visible region for VO₂ thin films. The presence of gold layer on VO₂ films significantly reduces the resistance per square, the critical temperature and percentage transmittance of the materials.     

Single-particle plasmon resonance spectroscopy of phase transition in vanadium dioxide

We demonstrate thermally controlled plasmon resonance modulation of single gold nanoparticles on vanadium dioxide thin films by performing dark-field spectroscopy measurements at different temperatures. The plasmon resonance of the nanoparticles exhibits a significant blueshift in the visible range when the vanadium dioxide film undergoes its insulator-to-metal phase transition around 67 °C. More importantly, the resonance shift shows a clear hysteresis, mirroring the behavior of the vanadium dioxide film. At a fixed wavelength, the scattering intensity of Au particles also shows a hysteretic behavior decorated with an overshoot before (after) the insulator-metal (metal-insulator) phase transition of the vanadium dioxide film, suggesting that the nanoparticle is probing local variations in the phase transition.     

Thermal oxidation-grown vanadium dioxide thin films on FTO (Fluorine-doped tin oxide) substrates

By deposition of metallic vanadium on FTO substrate in Argon atmosphere at room temperature, the sample was then annealed in furnace for 2 h at the temperature of 410 °C in air ambient. (1 1 0) -orientated vanadium dioxide films were prepared on the FTO surface. A maximum transmittance of ∼40% happened at 900–1250 nm region at room temperature. The change of optical transmittance at this region was ∼25% between semiconducting and metallic states. In particular, vanadium dioxide thin films on FTO exhibit semiconductor–metal phase transition at ∼51 °C, the width of the hysteresis loop is ∼8 °C.     

Fabrication of low phase transition temperature vanadium oxide films by direct current reactive magnetron sputtering and oxidation post-anneal method

Vanadium oxide thin films were deposited on ordinary glass substrates by direct current (DC) magnetron sputtering from a vanadium metal target and subsequent oxidation annealing. The deposition and annealing parameters were given in detail. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). The phase transitions of films were observed by measuring their electrical and optical property variations at different temperature. The results indicated that the films fabricated had a semiconductor–metal phase transition temperature of about 30 °C.     

磁控溅射制备W掺杂VO2/FTO复合薄膜及其性能分析

为了获得相变温度低且热致变色性能优越的光学材料, 室温下在F:SnO₂ (FTO)导电玻璃基板表面沉积钨钒金属膜, 再经空气气氛下的热氧化处理, 制备了W掺杂VO₂/FTO复合薄膜, 利用X射线光电子能谱、X射线衍射和扫描电镜对薄膜的结构和表面形貌进行了分析. 结果表明: 高温热氧化处理过程中没有生成W, F, V混合氧化物, W以替换V原子的方式掺杂. 与采用相同工艺和条件制备的纯VO₂/FTO复合薄膜相比, W掺杂VO₂薄膜没有改变晶面取向, 仍具有(110)晶面择优取向, 相变温度下降到35 ℃左右, 热滞回线收窄到4 ℃, 高低温下的近红外光透过率变化量提高到28%. 薄膜的结晶程度明显提高, 表面变得平滑致密, 具有很好的一致性, 对光电薄膜器件的设计开发和工业化生产具有重要意义. 关键词： W掺杂 2')" href="#">VO₂ FTO导电玻璃 磁控溅射     

Effect of vacuum heat treatment on the metal-semiconductor phase transition in thin vanadium dioxide films

The effect of vacuum heat treatment of thin vanadium dioxide films on the parameters of the metal-semiconductor phase transition is studied. The results of heat treatment are compared with those obtained upon irradiation of the synthesized films by medium-energy electrons. The elemental composition of the films that is found by the Rutherford backscattering (RBS) method suggests that an observed change in the hysteresis loop of the films is associated with the reduction of the vanadium dioxide upon heating in a vacuum.     

Electrical conduction and bipolar switching properties in transparent vanadium oxide resistive random access memory (RRAM) devices

In this study, the electrical conduction and bipolar switching properties in transparent vanadium oxide thin films are investigated and discussed. (110)-oriented vanadium oxide thin films were well deposited onto transparent ITO substrates for the possible development of applications in the structure of system-on-panel devices. For the as-deposited vanadium oxide thin films, they were prepared for 1 h by a rf magnetron sputtering method of rf power 130 W, chamber pressure 10 mTorr, substrate temperature 550 °C, and different oxygen concentrations. In addition, the Al/V₂O₅/ITO device presents reliable and bipolar switching behavior. The on/off ratio and switching cycling of two stable states are found and discussed. We suggest that the current–voltage characteristics are governed by ohmic contact and Poole?Frankel emission transport model mechanisms in low- and high-voltage regions, respectively.     

Relaxation oscillations in circuits containing sandwich switches based on vanadium dioxide

Electrical switching with an S-shaped I–V characteristic is studied in metal/oxide/metal structures based on vanadium oxide thin films fabricated by electrochemical oxidation. This switching effect is associated with the metal–insulator phase transition in VO₂, and the channels consisting of vanadium dioxide are formed in the initial anodic films during the process of electroforming. An expression for the relaxation oscillation frequency, as a function of the external circuit RC factor and I–V curve parameters, is obtained. It is shown that the experimental data on the frequency–capacitance dependence match well this theoretical relation. Applied aspects of the obtained results, particularly concerning oscillatory neural networks and frequency-output sensors, are discussed.     

The characteristics of Au:VO2 nanocomposite thin film for photo-electricity applications

Au nanoparticles have been fabricated on normal glass substrates using nanosphere lithography (NSL) method. Vanadium dioxide has been deposited on Au/glass by reactive radio frequency (rf) magnetron sputtering. The structure and composition were determined by X-ray diffraction and X-ray photoelectron spectroscope. Electrical and optical properties of bare VO₂ and Au:VO₂ nanocomposite thin films were measured. Typical hysteresis behavior and sharp phase transition were observed. Nanopartical Au could effectively reduce the transition temperature to 40 °C. The transmittance spectrum for both Au:VO₂ nanocomposite thin film shows high transmittance under transition temperature and low transmittance above transition temperature. The characteristics present the Au:VO₂ nanocomposite thin film can be used for applications, such as “smart window” or “laser protector”.