Hybrid chemical vapour and nanoceramic aerosol assisted deposition for multifunctional nanocomposite thin films

Hybrid atmospheric pressure chemical vapour and aerosol assisted deposition via the reaction of vanadium acetylacetonate and a suspension of preformed titanium dioxide or cerium dioxide nanoparticles, led to the production of vanadium dioxide nanocomposite thin films on glass substrates. The preformed nanoparticle oxides used for the aerosol were synthesised using a continuous hydrothermal flow synthesis route involving the rapid reaction of a metal salt solution with a flow of supercritical water in a flow reactor. Multifunctional nanocomposite thin films from the hybrid deposition process were characterised using scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The functional properties of the films were evaluated using variable temperature optical measurements to assess thermochromic behaviour and methylene blue photodecolourisation experiments to assess photocatalytic activity. The tests show that the films are multifunctional in that they are thermochromic (having a large change in infra-red reflectivity upon exceeding the thermochromic transition temperature) and have significant photocatalytic activity under irradiation with 254 nm light.     

Work function of vanadium dioxide thin films across the metal-insulator transition and the role of surface nonstoichiometry

Vanadium dioxide (VO(2)) undergoes a sharp metal-insulator transition (MIT) in the vicinity of room temperature and there is great interest in exploiting this effect in novel electronic and photonic devices. We have measured the work function of vanadium dioxide thin films across the phase transition using variable temperature Kelvin force microscopy (KFM). The work function is estimated to be ～5.15 eV in the insulating phase and increases by ～0.15 eV across the MIT. We further show that the work function change upon the phase transition is highly sensitive to near-surface stoichiometry studied by X-ray photoelectron spectroscopy. This change in work function is distinct from bulk resistance-versus temperature trends commonly used to evaluate synthesis protocols for such vanadium oxide films and optimize stoichiometry. The results are pertinent to understanding fundamental electronic properties of vanadium oxide as well as charge injection phenomena in solid-state devices incorporating complex oxides containing multivalence cations.     

晶粒尺寸对氧化钒薄膜电学与光学相变特性的影响

采用直流对靶磁控溅射方法制备氧化钒薄膜,通过改变热处理温度获得了具有不同晶粒尺寸的相变特性氧化钒薄膜,对氧化钒薄膜相变过程中电阻和红外光透射率随温度的突变性能进行研究.结果表明:经300℃和360℃热处理后,薄膜内二氧化钒原子分数达到40%,氧化钒薄膜具有绝缘体-金属相变特性,薄膜的晶粒尺寸分别为50nm和100nm;...     

Electron back-scattered diffraction of crystallized vanadium dioxide thin films on amorphous silicon dioxide

Crystalline films and isolated particles of vanadium dioxide (VO₂) were obtained through solid phase crystallization of amorphous vanadium oxide thin films sputtered on silicon dioxide. Electron back-scattered diffraction (EBSD) was used to study the crystals obtained in the thin films, to differentiate them from different vanadium oxide stoichiometries that may have formed during the annealing process, and to study their phase and orientation. EBSD showed that the crystallization process yielded crystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated particles, and did not show evidence of other vanadium oxide stoichiometries present. Indexing of the crystals for the orientation study was performed using EBSD patterns for the tetragonal phase of vanadium dioxide, since it was observed that EBSD patterns for the monoclinic and tetragonal phases of vanadium dioxide are not distinguishable by computer automated indexing. Using the EBSD patterns for the tetragonal phase of vanadium dioxide, orientation maps showed that all VO₂ crystals that were measurable (approximately the thickness of the film) had a preferred orientation with the c-axis of the tetragonal phase parallel to the plane of the specimen.     

On the effects of electric fields in aerosol assisted chemical vapour deposition reactions of vanadyl acetylacetonate solutions in ethanol

Thin films of thermochromic vanadium dioxide have been deposited on glass substrates at 530 degrees C from the aerosol assisted chemical vapour deposition of vanadyl acetylacetonate solutions in ethanol under the influence of electric fields. Electric fields were generated by applying a potential difference between the top plate and the substrate of the reactor. The deposited films were analysed and characterised using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and variable temperature UV/Visible spectroscopy. The application of an electric field led to significant changes in the deposited films microstructure and functional properties. It was found that an increase in electric field strength caused a decrease in crystallite size and in an increase in the change in transmission in the near infrared when compared to films grown without the use of an electric field.     

磁控溅射沉积二氧化钒薄膜及其电致相变特性研究

采用反应射频磁控溅射技术在熔融石英玻璃衬底上制备了组分单一的二氧化钒薄膜。在制备好的二氧化钒薄膜上使用半导体工艺制备了金属叉指电极,通过半导体测试仪测试其电致相变特性。结果表明,当电极上所加电压达到一定阈值时电流发生突变,即薄膜发生半导体-金属相变。     

Vanadium dioxide thin films prepared by chemical vapour deposition from vanadium(III) acetylacetonate

Vanadium dioxide thin films were prepared by an atmospheric-pressure chemical vapour deposition method. The raw material was vanadium(III) acetylacetonate. Polycrystalline thin films were obtained at a reaction temperature of 500°C. Slow post-deposition cooling of the deposits on a substrate of fused quartz or sapphire single crystal yields vanadium dioxide films which are not mixed with other phases, i.e. V₃O₇ or V₄O₉. Optical and electrical switching behaviours strongly depend on film thickness. At a film thickness of about 300 nm the transition temperature showed a minimum value of 44 °C.     

Thermal lithography of thin films of vanadium dioxide

A technique is proposed for making microareas with sharply different optical and electrical properties in thin films of vanadium dioxide. The technique is based on vacuum annealing of thin films, which results in a yield of oxygen from vanadium dioxide with the formation of an oxygen vacancy in it.     

Atmospheric pressure chemical vapour deposition of thermochromic tungsten doped vanadium dioxide thin films for use in architectural glazing

Atmospheric pressure chemical vapour deposition of VCl₄, WCl₆ and water at 550 °C lead to the production of high quality tungsten doped vanadium dioxide thin films. Careful control of the gas phase precursors allowed for tungsten doping up to 8 at.%. The transition temperature of the thermochromic switch was tunable in the range 55 °C to − 23 °C. The films were analysed using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Their optical properties were examined using variable-temperature transmission and reflectance spectroscopy. It was found that incorporation of tungsten into the films led to an improvement in the colour from yellow/brown to green/blue depending on the level of tungsten incorporation. The films were optimized for optical transmission, thermochromic switching temperature, magnitude of the switching behaviour and colour to produce films that are suitable for use as an energy saving environmental glass product.     

Electron and Atomic Force Microscopy studies of photocatalytic titanium dioxide thin films deposited by DC magnetron sputtering

Titanium dioxide thin films were deposited on glass substrates and on fluorine doped tin oxides at room temperature by DC magnetron sputtering at different working gas pressures and were evaluated using photocatalytic degradation of an organic compound. The structural properties of the films were studied by electron microscopy techniques and Atomic Force Microscopy. Numerous structural defects were detected for samples deposited at 16 mTorr and it was associated with the highest photo-degradation rate. Also small band gap shift in titanium dioxide films was detected for different gas pressures. These behaviors are related with structural details derived from the synthesis conditions and the influence of structural defects on the photocatalytic activity is discussed.     

Electrical and optical switching properties of ion implanted VO2 thin films

The metal-insulator transition in vanadium dioxide thin films implanted with O⁺ ions was studied. Ion implantation lowered the metal-insulator transition temperature of the VO₂ films by 12 °C compared to the unimplanted ones, as measured both optically and electrically. The lowering of the transition temperature was accomplished without significantly reducing the mid-wave infrared optical transmission in the insulating state for wavelengths > 4.3 μm. Raman spectroscopy was used to examine changes to the crystalline structure of the implanted films. The Raman spectra indicate that ion implantation effects are not annealed out for temperatures up to 120 °C.     

VOx/TiOx/Ti多层薄膜的制备工艺与内耗研究

用磁控反应溅射法在玻璃和镅片衬底上制备Vox/TiOx/Ti多层薄膜.用X射线衍射(XRD)、QJ31单臂电桥、薄膜内耗仪等测试了薄膜的晶体结构、电阻、内耗.分别进行了薄膜的制备工艺与内耗研究.测试分析结果表明:试样的晶体结构、电阻-温度曲线、杨氏模量的突变均表明多层薄膜在66℃左右发生相变.样品的电阻温度系数为-4.35%/℃.并且真空退火有利于二氧化钒相生成.     

双靶磁控溅射制备掺W氧化钒薄膜的研究

用双靶磁控溅射制备了掺钨氧化钒薄膜。Ｘ射线电子谱（ＸＰＳ）对所沉积的薄膜进行了分析,发现掺Ｗ氧化钒薄膜的相结构比较复杂。通过特征峰标定了这些相。用面积灵敏度因子方法得到Ｗ掺杂量的结果。原子力显微镜给出了薄膜的表面形貌。其表面形貌特征随沉积条件的不同有一定的变化。     

Nano-polycrystalline vanadium oxide thin films prepared by pulsed laser deposition

Nano-polycrystalline vanadium oxide thin films have been successfully produced by pulsed laser deposition on Si(100) substrates using a pure vanadium target in an oxygen atmosphere. The vanadium oxide thin film is amorphous when deposited at relatively low substrate temperature (500 degrees C) and enhancing substrate temperature (600-800 degrees C) appears to be efficient in crystallizing VOx thin films. Nano-polycrystalline V3O7 thin film has been achieved when deposited at oxygen pressure of 8 Pa and substrate temperature of 600 degrees C. Nano-polycrystalline VO2 thin films with a preferred (011) orientation have been obtained when deposited at oxygen pressure of 0.8 Pa and substrate temperatures of 600-800 degrees C. The vanadium oxide thin films deposited at high oxygen pressure (8 Pa) reveal a mix-valence of V5+ and V4+, while the VOx thin films deposited at low oxygen pressure (0.8 Pa) display a valence of V4+. The nano-polycrystalline vanadium oxide thin films prepared by pulsed laser deposition have smooth surface with high qualities of mean crystallite size ranging from 30 to 230 nm and Ra ranging from 1.5 to 22.2 nm. Relative low substrate temperature and oxygen pressure are benifit to aquire nano-polycrystalline VOx thin films with small grain size and low surface roughness.     

氧化钒薄膜作为锂离子微电池阴极膜的磁控溅射技术的制备

研究了用磁控溅射系统来制备氧化钒薄膜,通过优化工艺条件制备出可用作锂离子微电池阴极膜的非晶态五氧化二钒（α-V2O5）薄膜。并使用X射线衍射（XRD）与X射线光电子谱（XPS）来表征薄膜的晶向及化学组分。结果表明通过调节氧气以及氩气的流量、基片的温度和溅射功率,可以制备出高纯度的α-V2O5薄膜。而且,半电池体系V2O5/LiPF6/Li被构造用于表征在锂电池中作为阴极膜的五氧化二钒（α-V2O5）的电学性质。在此电池系统经过10个循环放电后,薄膜放电电容趋于稳定值。     

Structural, electrical and optical properties of thermochromic VO2 thin films obtained by reactive electron beam evaporation

We present the structural and physical characterization of vanadium dioxide (VO₂) thin films prepared by reactive electron beam evaporation from a vanadium target under oxygen atmosphere. We correlate the experimental parameters (substrate temperature, oxygen flow) with the films structural properties under a radiofrequency incident power fixed to 50 W. Most of the obtained layers exhibit monocrystalline structures matching that of the monoclinic VO₂ phase. The temperature dependence of the electrical resistivity and optical transmission for the obtained films show that they present thermoelectric and thermochromic properties, with a phase transition temperature around 68 °C. The results show that for specific experimental conditions the VO₂ layers exhibit sharp changes in electrical and optical properties across the phase transition.     

Characteristics of CeOx–VO2 composite thin films synthesized by sol–gel process

Pure vanadium dioxide (VO₂) and CeOx–VO₂ (1.5 < x < 2) composite thin films were grown on muscovite substrate by inorganic sol–gel process using vanadium pentaoxide and cerium(III) nitrate hexahydrate powder as precursor. The crystalline structure, morphology and phase transition properties of the thin films were systematically investigated by X-ray diffraction, Raman, X-ray photoelectron spectroscopy, FE-SEM and optical transmission measurements. High quality of the VO₂ and CeOx–VO₂ composite films were obtained, in which the relative fractions of +4 valence state vanadium were above 70 % though the concentrations of cerium reached 9.77 at %. However, much of cerium compounds were formed at the edge of grains and the addition of cerium resulted in more clearly defined grain boundaries as shown in SEM images. Meanwhile, the composite films exhibited excellent phase transition properties and the infrared transmittance decreased from about 70 to 10 % at λ = 4 μm bellow and above the metal–insulator phase transition temperature. The metal–insulator phase transition temperatures were quite similar with about 66 °C of the pure VO₂ and CeOx–VO₂ composite thin films. But hysteresis widths increased with more addition of cerium, due to the limiting effect of grain boundaries on the propagation of the phase transition. Particularly, the CeOx–VO₂ composite film with an addition of 7.82 at % Ce showed a largest hysteresis width with about 20.6 °C. In addition, the thermochromic performance of visible transmittance did not change obviously with more addition of cerium.     

Synthesis and characterisation of W-doped VO2 by Aerosol Assisted Chemical Vapour Deposition

W-doped vanadium dioxide thin films were deposited by Aerosol Assisted Chemical Vapour Deposition. Samples were characterised with several different techniques (i.e. X-ray Diffraction, Raman, Scanning Electron Microscopy-Energy Dispersive X-ray Analysis), to determine their composition and morphology. A study of their optical properties was also performed, to test the suitability of these materials as intelligent window coatings. Good changes in the transmittance and reflectance were observed above the transition temperature (decrease and increase respectively). A linear decrease in the transition temperature with increasing tungsten content was also seen, lowering it to room temperature.     

脉冲激光沉积法制备VO_2热致变色薄膜研究进展

基于半导体和金属间的相变特性,伴随着温度、电场、压力的变化,具有相关智能特性的VO_2薄膜材料具有较大的应用潜力.本文主要阐述脉冲激光沉积技术在制备金属氧化物方面的物理过程和技术特点,详细介绍脉冲激光沉积制备VO_2薄膜材料的工艺参数和国内外研究进展,并与几种常规制备方法进行对比,给出脉冲激光沉积掺杂对VO_2薄膜材料特性的影响,以及采用脉冲激光沉积制备VO_2纳米材料,讨论了脉冲激光沉积制备具有智能特性的VO_2薄膜材料存在的问题和发展方向.     

Impact of substrate temperature on the microstructure, electrical and optical properties of sputtered nanoparticle V2O5 thin films

Applying reactive direct current (DC) magnetron sputtering method, nanoparticle vanadium pentoxide thin films were deposited onto glass slides and KBr substrates at different substrate temperatures. The films were characterized by X-ray photoelectron spectroscopy and atomic force microscope. Infrared spectra were recorded with a Fourier transform infrared spectrophotometer. It was found that, excepting the compositions, the film growth and vanadium oxygen bonds were strongly affected by the substrate temperature. Electrical measurements indicated that the square resistances of films showed an exponential decrease from 46 MΩ/□ to 33 kΩ/□ with substrate temperature increasing from 433 K to 593 K, and that the square resistance-temperature curves of films exhibited typical semiconducting behavior. Optical investigations were carried out in the near infrared and ultraviolet-visible range. Transmittance varied from about 95 to 55% in near-infrared range when the substrate temperature was elevated. In ultraviolet-visible range, optical band gaps and refractive indexes of films were deduced according to the transmission and reflection spectra.