Surface oxidation of vanadium dioxide films prepared by radio frequency magnetron sputtering

This paper reports that the thermochromic vanadium dioxide films were deposited on various transparent substrates by radio frequency magnetron sputtering, and then aged under circumstance for years. Samples were characterized with several different techniques such as x-ray diffraction, x-ray photoelectron spectroscopy, and Raman, when they were fresh from sputter chamber and aged after years, respectively, in order to determine their structure and composition. It finds that a small amount of sodium occurred on the surface of vanadium dioxide films, which was probably due to sodium ion diffusion from soda-lime glass when sputtering was performed at high substrate temperature. It also finds that aging for years significantly affected the nonstoichiometry of vanadium dioxide films, thus inducing much change in Raman modes.     

Preparation and properties of vanadium dioxide thermochromic thin films

Deposition of vanadium dioxide and the study of its electrical and optical properties at varying deposition conditions have been presented. The materials have been deposited by reactive r.f. magnetron sputtering technique in Ar, O₂ ambient followed by annealing post-treatment. Electrical conductivity measurements indicate that oxygen pressure plays an important role in obtaining VO₂ and atP _{O 2}=2.4% stoichiometric VO₂ can be obtained. The deposition rate of oxides decreases with increasing O₂ pressure and the rate of VO₂ was about 130Å/min. Optical studies show that VO₂ films exhibit thermochromism and it has the potential application for energy efficient solar energy utilization.     

二氧化钒薄膜的低温制备及其性能研究

针对VO₂薄膜在微测辐射热计上的应用，采用射频反应溅射法，在室温下制备氧化钒薄膜；研究了氧分压对薄膜沉积速率、电学性质及成分的影响.通过调节氧分压，先获得成分接近VO₂的非晶化薄膜，再在400℃空气中氧化退火，便可制得高电阻温度系数，低电阻率的VO₂薄膜，电阻温度系数约为-4%/℃，薄膜方块电阻为R_□为100—300kΩ；薄膜在室温下沉积，400℃下退火的制备方法与微机电加工(micro electromechanic 关键词： 二氧化钒 电阻温度系数 氧分压 射频反应溅射法     

掺钨VO_2薄膜的电致相变特性

采用直流磁控溅射与后退火工艺相结合的方法,在掺氟SnO_2(FTO)导电玻璃基底上制备了高质量的掺钨VO_2薄膜,对薄膜的结构、表面形貌和光电特性进行测试,分析了钨掺杂对其相变性能的影响.结果表明,室温下掺钨VO_2薄膜的阈值电压为4.2 V,观察到阈值电压下约有两个数量级的电流突变.随着温度升高,相变的阈值电压降低,且电流突变幅度减小.当施加8 V电压时,分别在不同温度下测试了掺钨VO_2薄膜的透过率.温度为20和50℃时,掺钨VO_2薄膜相变前后的红外透过率差量分别为23%和27%.与未掺杂的VO_2薄膜相比,掺钨VO_2薄膜具有相变温度低、阈值电压低和电阻率小的特点,在高速光电器件中有广阔的应用前景.     

Study of nanocrystalline V02 thin films prepared by magnetron sputtering and post-oxidation

Nanocrystalline VO2 thin films were deposited onto glass slides by direct current magnetron sputtering and postoxidation. These films undergo semiconductor-metal transition at 70 ℃, accompanied by a resistance drop of two magnitude orders. The crystal structures and surface morphologies of the VO2 films were characterized by x-ray diffraction （XRD） and atomic force microscope （AFM）, respectively. Results reveal that the average grain size of VO2 nanograins measured by XRD is smaller than those measured by AFM. In addition, Raman characterization indicates that stoichiometric VO2 and oxygen-rich VO2 phases coexist in the films, which is supported by x-ray photoelectron spectroscopy （XPS） results. Finally, the optical properties of the VO2 films in UV-visible range were also evaluated. The optical band gap corresponding to 2p-3d inter-band transition was deduced according to the transmission and reflection spectra. And the deduced value, Eopt2p-3d ： 1.81 eV, is in good agreement with that previously obtained by theoretical calculation.     

Study of nanocrystalline VO2 thin films prepared by magnetron sputtering and post-oxidation

Nanocrystalline VO2 thin films were deposited onto glass slides by direct current magnetron sputtering and postoxidation. These films undergo semiconductor-metal transition at 70°C, accompanied by a resistance drop of two magnitude orders. The crystal structures and surface morphologies of the VO2 films were characterized by x-ray diffraction (XRD) and atomic force microscope (AFM), respectively. Results reveal that the average grain size of VO2 nanograins measured by XRD is smaller than those measured by AFM. In addition, Raman characterization indicates that stoichiometric VO2 and oxygen-rich VO2 phases coexist in the films, which is supported by x-ray photoelectron spectroscopy (XPS) results. Finally, the optical properties of the VO2 films in UV-visible range were also evaluated. The optical band gap corresponding to 2p-3d inter-band transition was deduced according to the transmission and reflection spectra. And the deduced value, E opt2p-3d = 1.81 eV, is in good agreement with that previously obtained by theoretical calculation.     

Probing thermal properties of vanadium dioxide thin films by time-domain thermoreflectance without metal film

Vanadium dioxide(VO_2) is a strongly correlated material, and it has become known due to its sharp metal–insulator transition(MIT) near room temperature. Understanding the thermal properties and their change across MIT of VO_2 thin film is important for the applications of this material in various devices. Here, the changes in thermal conductivity of epitaxial and polycrystalline VO_2 thin film across MIT are probed by the time-domain thermoreflectance(TDTR) method.The measurements are performed in a direct way devoid of deposition of any metal thermoreflectance layer on the VO_2 film to attenuate the impact from extra thermal interfaces. It is demonstrated that the method is feasible for the VO_2 films with thickness values larger than 100 nm and beyond the phase transition region. The observed reasonable thermal conductivity change rates across MIT of VO_2 thin films with different crystal qualities are found to be correlated with the electrical conductivity change rate, which is different from the reported behavior of single crystal VO_2 nanowires. The recovery of the relationship between thermal conductivity and electrical conductivity in VO_2 film may be attributed to the increasing elastic electron scattering weight, caused by the defects in the film. This work demonstrates the possibility and limitation of investigating the thermal properties of VO_2 thin films by the TDTR method without depositing any metal thermoreflectance layer.     

氧化钒薄膜微观结构的研究

采用直流磁控反应溅射在Si(100)衬底上溅射得到(001)取向的V₂O₅薄膜.x射线衍射(XRD)、扫描电镜(SEM)和傅里叶变换红外光谱(FTIR)的结果表明，氧分压影响薄膜的成分和生长取向，在氧分压0.4Pa时溅射得到(001)取向的纳米V₂O₅薄膜，即沿c轴垂直衬底方向取向生长的薄膜.V₂O₅薄膜经过真空退火得到(001)取向的VO₂薄膜，晶体颗 关键词： 微观结构 氧化钒薄膜 择优取向 直流磁控溅射     

Structural, electrical, and optical properties of ZnInO alloy thin films

Indium zinc oxide (IZO) thin films with different percentages of In content (In/[In+Zn]) are synthesized on glass substrates by magnetron sputtering, and the structural, electrical and optical properties of IZO thin films deposited at different In₂O₃ target powers are investigated. IZO thin films grown at different In₂O₃ target sputtering powers show evident morphological variation and different grain sizes. As the In₂O₃ sputtering power rises, the grain size becomes larger and electrical mobility increases. The film grown with an In₂O₃ target power of 100 W displays the highest electrical mobility of 13.5 cm·V^-1·s^-1 and the lowest resistivity of 2.4 × 10^-3 Ω·cm. The average optical transmittance of the IZO thin film in the visible region reaches 80% and the band gap broadens with the increase of In₂O₃ target power, which is attributed to the increase in carrier concentration and is in accordance with Burstein-Moss shift theory.     

快速热处理制备相变氧化钒薄膜及其特性研究

采用直流对靶磁控溅射在Si<100>基底上沉积金属V薄膜, 然后分别在纯氧气环境和纯氮气环境下进行快速热处理制备具有 金属-半导体相变特性的氧化钒(VO_X)薄膜, 热处理条件分别为纯氧气环境下430℃/40 s, 450℃/40 s, 470℃/40 s, 450℃/30 s, 450℃/50 s, 纯氮气环境下500℃/15 s. 用X射线衍射仪、X射线光电子能谱、原子力显微镜 和扫描电子显微镜对薄膜的结晶结构、钒的价态和组分以及微观形貌进行分析. 利用四探针薄膜电阻测量方法和THz时域频谱技术分析薄膜的电学特性和光学特性. 结果表明: 金属V薄膜经过纯氧气环境450℃/40 s快速热处理 后形成了具有低相变特性的VO_X薄膜, 升温前后薄膜方块电阻变化幅度达到两个数量级, THz透射强度变化幅度较小. 为了提高薄膜的相变特性, 对制备的VO_X薄膜采用纯氮气环境500℃/15 s快速热处理, 薄膜的相变特性有了明显提升, 相变前后方块电阻变化达到3个数量级, THz透射强度变化达到56.33%.     

High contrast optical switching in vanadium dioxide thin films

Thermochromic vanadium dioxide thin films prepared by radio-frequency sputtering exhibit controllable transmittance at 1550 nm with a dynamic range exceeding 10³. Efficient optical control with a laser beam at 532 nm is demonstrated with intensities as low as 3 W/cm². Optical switch-on times as short as 100 μs are reported.     

Effect of nonstoichiometry on Raman scattering of VO2 films

We report on Raman scattering of VO2 films prepared by radio frequency magnetron sputtering under different conditions. Our investigations revealed that the dominated Raman peaks shift towards high frequency for both V-rich and O-rich VO2 films, compared with the stoichiometry VO2 films. The experimental evidence is presented and the cause for nonstoichiometry dependence of Raman spectra of VO2 films is discussed.     

Structural and optical properties of sputtered gadolinium nitride films

Rare-earth (RE) materials have high magnetic moments and form a wide range of magnetic structures. There has been speculation in the literature that rare-earth nitrides may form half-metallic ferromagnetics. This is surprising because, based on a simple ionic model, trivalent rare-earth nitrides would be expected to be insulators with a similar electronic structure to the divalent rare-earth chalcogenides. However if it is the case that they are half-metallic or narrow gap insulators, then they have potential applications in spin-filtering devices. In the present investigation, We have deposited GdN films on glass substrate at room temperature by Ar/N₂ mixed gas plasma-radio frequency (rf) sputtering method. The structure and the complex optical properties as well as the energy gap of GdN thin films as a function of N₂ partial pressure are determined.     

Structural and transport properties of Li-intercalated vanadium pentoxide nanocrystalline films

The X-ray diffraction (XRD), transmission electron microscopy, density, electrical and thermoelectric power (TEP) properties of nanocrystalline Li _x V₂O₅ ? nH₂O xerogel films (0 ≤ x ≤ 22 mol.%) were investigated. The films were produced by the sol–gel technique (colloidal route), which was used to enable high-purity, uniform preparation. The relative intensity of the (002) XRD line increased with increasing Li content. The particle size was found to be about 6.0 nm. Electrical conductivity and thermoelectric power were measured parallel to the substrate surface in the temperature range 300–480 K for the as-prepared films. The electrical conductivity showed that all the samples were semiconductors and that conductivity increased with increasing Li content. The conductivity of the present system was primarily determined by hopping carrier mobility, which was found to vary from 6.81 × 10^?6 to 0.33 × 10^?6 cm² V^?1 s^?1 at 380 K. The carrier density was evaluated to be 8.73 × 10¹⁹–1.118 × 10²¹ cm^?3. The conduction was confirmed to obey non-adiabatic small polaron hopping. The thermoelectric power, or Seebeck effect, increased with increasing Li content. The results obtained indicate an n-type semiconducting behavior within the temperature range investigated.     

Structural and optical properties of nano-structured tungsten-doped ZnO thin films grown by pulsed laser deposition

Novel highly c-oriented tungsten-doped zinc oxide (WZO) thin films with 1 wt% were grown by pulsed laser deposition (PLD) technique on corning 1737F glass substrate. The effects of laser energy on the structural, morphological as well as optical transmission properties of the films were studied. The films were highly transparent with average transmittance exceeding 87% in the wavelength region lying between 400 and 2500 nm. X-ray diffraction analysis (XRD) results indicated that the WZO films had c-axis preferred orientation with wurtzite structure. Film thickness and the full width at half maximum (FWHM) of the (0 0 2) peaks of the films were found to be dependent on laser fluence. The composition determined through Rutherford backscattering spectroscopy (RBS) appeared to be independent of the laser fluence. By assuming a direct band gap transition, the band gap values of 3.36, 3.34 and 3.31 eV were obtained for corresponding laser fluence of 1, 1.7 and 2.7 J cm⁻², respectively. Compared with the reported undoped ZnO band gap value of 3.37 eV, it is conjectured that the observed low band gap values obtained in this study may be attributable to tungsten incorporation in the films as well as the increase in laser fluence. The high transparency makes the films useful as optical windows while the high band gap values support the idea that the films could be good candidates for optoelectronic applications.     

Modeling of conducting bridge evolution in bipolar vanadium oxide-based resistive switching memory

We investigate the resistive switching characteristics of a Cu/VOx/W structure. The VOx film is deposited by radio- frequency magnetron sputtering on the Cu electrode as a dielectric layer. The prepared VOx sample structure shows reproducible bipolar resistive switching characteristics with ultra-low switching voltage and good cycling endurance. A modified physical model is proposed to elucidate the typical switching behavior of the vanadium oxide-based resistive switching memory with a sudden resistance transition, and the self-saturation of reset current as a function of compliance current is observed in the test, which is attributed to the conducting mechanism is discussed in detail. growth pattern of the conducting filaments. Additionally, the related     

Structural and optical properties of RF magnetron sputtered aluminum nitride films without external substrate heating

We report structural and optical properties of aluminum nitride (AlN) thin films prepared by RF magnetron sputtering. A ceramic AlN target was used to sputter deposit AlN films without external substrate heating in Ar-N₂ (1:1) ambient. The X-ray diffraction and high resolution transmission electron microscopy results revealed that the films were preferentially oriented along c-axis. Cross-sectional imaging revealed columnar growth perpendicular to the substrate. The secondary ion mass spectroscopy analysis confirmed that aluminum and nitrogen distribution was uniform within the thickness of the film. The optical band gap of 5.3 eV was evaluated by UV-vis spectroscopy. Photo-luminescence broad band was observed in the range of 420-600 nm with two maxima, centered at 433 nm and 466 nm wavelengths related to the energy states originated during the film growth. A structural property correlation has been carried out to explore the possible application of such important well oriented nano-structured two-dimensional semiconducting objects.     

基于二氧化钒宽、窄带可切换的双功能超材料吸收器研究

本文提出了一种宽、窄带可切换的双功能超材料吸收器.在超材料吸收器的结构中,引入了相变材料二氧化钒(VO2),仅利用单个可切换超表面就能实现不同的功能,其不同功能之间的相互转换通过VO2绝缘态和金属态之间的可逆相变特性实现.当VO2处于金属态时,设计的结构可以看作一个超材料宽带吸收器.仿真结果表明,在1.55THz至2....     

Al和Sb共掺对ZnO有序阵列薄膜的结构和光学性能的影响

采用水热合成法在预先生长的ZnO种子层的玻璃衬底上制备出Al和Sb共掺ZnO纳米棒有序阵列薄膜. 通过X射线衍射、扫描电镜、透射电镜和选区电子衍射分析表明:所制备的薄膜由垂直于ZnO种子层的纳米棒组成, 呈单晶六角纤锌矿ZnO结构, 且沿[001]方向择优生长, 纳米棒的平均直径和长度分别为27.8 nm和1.02 μm. Al和Sb共掺ZnO纳米棒有序阵列薄膜的拉曼散射分析表明:相对于未掺杂ZnO薄膜的拉曼振动峰(580 cm^-1), Al和Sb共掺ZnO阵列薄膜的E₁(LO)振动模式存在拉曼位移. 当Al和Sb的掺杂量为3.0at%,4.0at%,5.0at%,6.0at%时, Al和Sb共掺ZnO阵列薄膜的拉曼振动峰的位移量分别为3,10,14,12 cm^-1. E₁ (LO) 振动模式位移是由Al和Sb掺杂ZnO产生的缺陷引起的. 室温光致发光结果表明:掺杂Al和Sb后, ZnO薄膜在545 nm处的发光强度减小,在414 nm处的发光强度增加. 这是由于掺杂Al和Sb后, ZnO薄膜中Zn_i缺陷增加, O_i缺陷减少引起的. 关键词： Al和Sb共掺ZnO薄膜 纳米棒有序阵列 结构表征 拉曼散射     

The electrical, optical properties of AlSb polycrystalline thin films deposited by magnetron co-sputtering without annealing

In order to fabricate AlSb polycrystalline thin films without post annealing, this paper studies a technology of magnetron co-sputtering onto intentionally heated substrate. It compares the structural characteristics and electrical properties of AlSb films which are deposited at different substrate temperatures. It finds that the films prepared at a substrate temperature of 450 oC exhibit an enhanced grain growth with an average grain size of 21 nm and the lattice constant is 0.61562 nm that goes well with unstained lattice constant (0.61355 nm). The ln(σ_dark) ～1/T curves show that the conductivity activation energy is about 0.38 eV when the film is deposited at 450 oC without an annealing. The transmittance and reflectance spectra show that the film deposited at 450 oC has an optical band gap of 1.6 eV. These results indicate that we have prepared AlSb polycrystalline films which do not need a post annealing.