Optical and hydrophilic properties of nanostructure Cu loaded brookite TiO2 thin film

Copper loaded TiO₂ brookite thin films were deposited on glass substrates using the dip-coating method. The crystalline structure of the films was characterized by X-ray diffraction analysis. X-ray photoelectron spectroscopy was used to evaluate the properties of the film surfaces. The transmittance spectra of the films were obtained by the Shimadzu multi-purpose spectrophotometer. The water contact angle on the film surfaces during irradiation and storage in a dark place was measured by a contact angle analyzer. The results indicate that Cu loading did not affect the transmittance spectra, whereas it had a significant effect on the hydrophilicity of the TiO₂ film surface.     

VO2 thin films deposited on silicon substrates from V2O5 target: Limits in optical switching properties and modeling

Thermochromic VO₂ thin films presenting a phase change at T_c = 68 °C and having variable thickness were deposited on silicon substrates (Si-001) by radio-frequency sputtering. These thin films were obtained from optimized reduction of low cost V₂O₅ targets. Depending on deposition conditions, a non-thermochromic metastable VO₂ phase might also be obtained. The thermochromic thin films were characterized by X-ray diffraction, atomic force microscopy, ellipsometry techniques, Fourier transform infrared spectrometry and optical emissivity analyses. In the wavelength range 0.3 to 25 μm, the optical transmittance of the thermochromic films exhibited a large variation between 25 and 100 °C due to the phase transition at T_c: the contrast in transmittance (difference between the transmittance values to 25 °C and 100 °C) first increased with film thickness, then reached a maximum value. A model taking into account the optical properties of both types of VO₂ film fully justified such a maximum value. The n and k optical indexes were calculated from transmittance and reflectance spectra. A significant contrast in emissivity due to the phase transition was also observed between 25 and 100 °C.     

Structural,Optical and Photoluminescence Study of Nanocrystalline SnO2 Thin Films Deposited by Spray Pyrolysis

Undoped SnO₂ thin films prepared by spray pyrolysis method reveal polycrystalline nature with prominent peaks along (110), (101) and (211) planes. All the films are nanocrystalline with particle size lying in the range of 3·14–8·6 nm calculated by DS formula. Orientation along plane (200) decreases continuously as molar concentration of SnO₂ increases. Dislocation density along plane (110) also decreases as molar concentration increases except 0·4 M SnO₂ thin film. Scanning electron microscopy image of the films contain jelly structures along with agglomerated clusters of particles. SnO₂ synthesized successfully, which confirms by Fourier transform infra-red spectroscopy. The optical transmittance spectra of 0·2 M SnO₂ thin film shows transmittance about 50–60% transmission in visible and near infrared region with a sharp cut off in the ultraviolet region. The transmission decreases in visible and near infrared region as molar concentration increases. Broad UV emission at 398 nm is observed in photoluminescence spectra of the films along with a blue emission, when excited at 250 nm wavelength. Emission intensity randomly changed as SnO₂ molar concentration increases. When excited at 320 nm, one UV and two visible peaks appeared at 385, 460 and 485 nm, respectively.     

Preparation and optical properties of phase-change VO2 thin films

In this work, VO₂ thin films were prepared on three kinds of substrates by the sol-gel dipcoating method followed by heat treatment under vacuum. These thin films were analysed by x-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The infrared and ultraviolet-visible spectra of the VO₂ thin films were also recorded during heating and cooling between room temperature and 100°C. The experimental results show that VO₂ thin films thus prepared exhibit thermally induced reversible phase transition, and the largest changes in transmittance and reflectivity are approximately 58 and 25%, respectively, in the case of vacuum heat treatment at 400°C and silica glass substrates. The refractive index (n) decreases and the absorption coefficient (k) increases when heating these thin films from room temperature to 100°C, and vice versa for cooling. The reasons why the optical constants and infrared absorption spectra change so remarkably are discussed.     

Structural, morphological and optical properties of thermal annealed TiO thin films

Structural, morphological and optical properties of TiO thin films grown by single source thermal evaporation method were studied. The films were annealed from 300 to 520 °C in air after evaporation. Qualitative film analysis was performed with X-ray diffraction, atomic force microscopy and optical transmittance and reflectance spectra. A correlation was established between the optical properties, surface roughness and growth morphology of the evaporated TiO thin films. The X-ray diffraction spectra indicated the presence of the TiO₂ phase for the annealing temperature above 400 °C.     

Au thin films deposited on SnO2:In and glass: Substrate effects on the optical and electrical properties

We report on a detailed study on the optical and electrical properties of Au films made by sputter deposition onto glass substrates with and without transparent and electrically conducting layers of SnO₂:In. The Au films had thicknesses up to 10.7 nm and hence spanned the range for thin film growth from discrete islands, via large scale coalescence and formation of a meandering conducting network, to the formation of a more or less “holey” film. Scanning electron microscopy and atomic force microscopy demonstrated that the SnO₂:In films were considerably rougher than the glass itself, and this roughness influenced the Au film formation so that large scale coalescence set in at a somewhat larger thickness for films on SnO₂:In than on glass. Measurements of spectral optical transmittance and reflectance and of electrical resistance gave a fully consistent picture that could be reconciled with impeded Au film formation on the SnO₂:In layer; this led to pronounced “plateaus” in the near infrared optical spectra for Au films on SnO₂:In and a concomitant change from such two-layer films having a lower resistance than the single gold film at thicknesses below large scale coalescence to the opposite behavior for larger film thicknesses. Our work highlights the importance of the substrate roughness for transparent conductors comprising coinage metal films backed by wide band gap transparent conducting oxides.     

Characterization of high quality tantalum pentoxide film synthesized by oxygen plasma enhanced pulsed laser deposition

Tantalum pentoxide films were deposited on BK7 glass substrates using oxygen plasma enhanced pulsed laser deposition (OPE-PLD). X-ray diffraction, atomic force microscopy, ultraviolet–visible–near infrared scanning spectrophotometry, and spectroscopic ellipsometry were used to characterize the crystallinity, microscopic morphology and optical properties of films. Results show that the film roughness increased with the increase of oxygen pressure, and decreased with the application of OPE. Meanwhile the use of oxygen plasma in a 2 Pa O₂ pressure resulted in the transmittance of the thin film of 91.8% at its peak position (the transmittance of bare substrate). Moreover, the root-mean-square roughness as low as 0.736 nm, and refractive index of 2.18 at 633 nm wavelength, close to the refractive index of bulk Ta₂O₅ (~ 2.20 at 633 nm wavelength), were obtained.     

The solution growth route and characterization of electrochromic tungsten oxide thin films

Electrochromic tungsten oxide thin films were prepared by using an aqueous solution of Na₂WO₄·2H₂O and dimethyl sulfate. Various techniques were used for the characterization of the films such as X-ray diffraction, cyclic voltammetry, SEM analysis and VIS-spectroscopy. The thin film durability was tested in an aqueous solution of LiClO₄ (0.1 mol/dm³) for about 7000 cycles followed by cyclic voltammetry. No significant changes in the cyclic voltammograms were found, thus proving the high durability of the films.The optical transmittance spectra of coloured and bleached states showed significant change in the transmittance, which makes these films favorable for electrochromic devices.     

Effect of heat-treatment on the structural and optical properties of Cu2S thin films deposited by CBD method

Semiconducting Cu₂S thin films were successfully deposited on glass substrate under three different conditions such as as-deposited, post heat-treated and pre heated precursor solution by chemical bath deposition technique. Structural and optical properties of the films were characterized by X-ray diffraction (XRD), scanning electron microscope, energy dispersive X-ray (EDX) analysis and UV–Visible spectrophotometer. The XRD spectra showed the amorphous nature of thin films with hexagonal structure. The d value and micro strain increased and the average crystallite size decreased from 1.9 to 1.4 and 1.3 nm respectively when the as-deposited film was subjected to post heat-treatment and the precursor solution temperature was elevated. The presence of more nucleation centers and fast reaction rate decreased the average crystallite size in films grown with pre heated precursor solution. The noticed blue shift in energy gap and the shift of XRD peak position towards the lower 2θ side by heat-treatment could be considered as a sign of the quantum confined effect due to the formation of the nano-sized Cu₂S crystals on the surface. The transmittance of heat-treated Cu₂S films in the visible region matched the phototropic vision of human eye (~600 nm) which makes them suitable for solar control coatings on architectural windows and automobiles in the regions with warm climates. Low transmittance behaviour of pre heated Cu₂S films could be used for anti dazzling coatings for car windscreens and driving mirrors to reduce the dazzling effects of light at night. EDX spectra showed the chemical purity of the films. The observed broad absorption and blue shift in band gap of the heat-treated films were due to quantum confinement effect. Fourier transform infrared studies were also carried out and the results are presented.     

Materials for solar-transmitting heat-reflecting coatings

A coating for solar energy applications which combines heat reflection with transparency to solar radiation may be of four different types: a metallic film which is sufficiently thin to be transparent; a metal-based multilayer coating; a wide band gap heavily doped semiconductor such as SnO₂ or In₂O₃; a conducting microgrid. We prepared such coatings on glass by evaporating thin films of silver, copper, gold, aluminium, cobalt, iron, chromium and nickel of various thicknesses and by spraying SnO₂ films. The spectral variations in the transmittance, and the front side and back side reflectances were measured in the wavelength range 0.4–15 μm. The properties of a three-layer coating of the dielectric/metal/dielectric type were calculated with a multilayer program using known bulk optical constants. The effect of these films when coated onto a domestic window was demonstrated with a heat transfer calculation using an equivalent thermal net. When a large transmittance over a broad range of the solar spectrum is required, gold is an equally good, or a slightly better, choice than silver as the metal in a three-layer coating. In general, an SnO₂ film exhibits a higher solar transmittance as well as a higher emittance than a coating containing metals. This implies that the oxide is to be preferred as a coating on a window when the maximum passive solar heating is sought. However, a metal-based coating could be better when a very low U_L value is the most important requirement.     

Electrical and optical properties of reactive sputtered TiO x thin films for uncooled IR detector applications

Nanostructured titanium oxide (nano-TiO _x ) thin films for uncooled IR detectors were fabricated by dc reactive magnetron sputtering and post-deposition annealed in oxygen atmosphere. The crystalline structure and surface morphology were characterized by glancing incidence X-ray diffraction (GIXRD) and field emission scanning microscopy. The results of GIXRD measurements indicate that TiO _x thin film deposited at room temperature is amorphous. A mixture of anatase and rutile nanocrystalline structure phase were present in oxygen annealed TiO _x thin film. A weak absorption peak around 438 cm^?1 corresponding to Ti–O stretching vibration is observed by Fourier transform infrared spectroscopy with annealed TiO _x thin film. The X-ray photoelectron spectra reveals Ti³⁺ and Ti⁴⁺ ions are coexisting in TiO _x films. The optical spectra of the films indicate that the optical absorption edge of the nano-TiO _x film exhibits a red shift compared to the as-deposited film. Furthermore, compared to bulk TiO _x , a blue shift was observed in both of the deposited and annealed films due to quantum size effect. The dependence of resistivity on temperature reveals both the absolute value of temperature coefficient of resistivity (TCR) and activation energy of TiO _x thin film increase significantly after annealing in oxygen.     

Preparation of Cr(N,O) thin films by RF reactive unbalanced magnetron sputtering

Chromium oxynitride thin films were deposited by radio-frequency (RF) reactive unbalanced magnetron sputtering at various O₂ flow rates onto Si(100) and glassy carbon substrates. The compositions of the thin films were analyzed by Rutherford backscattering spectroscopy. The thin films were found to contain up to 44 at.% oxygen. In Fourier-transform infrared spectra, a peak attributed to the Cr-N bond of CrN was observed, but no peak attributable to the Cr-O bond of Cr₂O₃ was found. The textures of the thin films were observed by transmission electron microscopy, which revealed that samples had a columnar structure. The hardness of the thin films was measured by nanoindentation. The hardness increased from 20 GPa to a maximum value of 31 GPa with increasing oxygen content.     

Influence of gamma irradiation on the refractive index of Fe-doped barium titanate thin films

Polycrystalline Fe-doped barium titanate (Fe-doped BaTiO₃) thin films were grown by thermal decomposition of the precursors deposited from a sol-gel system onto quartz substrates. The changes in the transmittance spectra induced by gamma irradiation on the Fe-doped BaTiO₃ thin films were quantified. The values for the optical energy band gap were in the range of 3.42-3.95 eV depending on the annealing time. The refractive index of the film, as measured in the 350-750 nm wavelength range was in the 2.17-1.88 range for the as prepared film, and this increased to 2.34-1.95 after gamma irradiation at 15 kGy. The extinction coefficient of the film was in the order of 10⁻² and increased after gamma irradiation. We obtained tuneable complex refractive index of the films by exposure to various gamma rays doses.     

Comparative study of physical properties of vapor chopped and nonchopped Al2O3 thin films

Aluminium oxide being environmentally stable and having high transmittance is an interesting material for optoelectronics devices. Aluminium oxide thin films have been successfully deposited by hot water oxidation of vacuum evaporated aluminium thin films. The surface morphology, surface roughness, optical transmission, band gap, refractive index and intrinsic stress of Al₂O₃ thin films were studied. The cost effective vapor chopping technique was used. It was observed that, optical transmittance of vapor chopped Al₂O₃ thin film showed higher transmittance than the nonchopped film. The optical band gap of vapor chopped thin film was higher than the nonchopped Al₂O₃, whereas surface roughness and refractive index were lower due to vapor chopping.     

真空还原制备的VO2热致相变薄膜Raman光谱和红外光谱研究

报道了利用真空还原制备的VO2薄膜的红外透射光谱和Raman光谱,并进行370－900nm波段的光透射测试以及900nm波长的热滞回线特性测试,表明所制备VO2薄膜具有优良的热致相变光学特性,结晶状态不同的薄膜其Raman谱位置有明显改变,室温时的红外光谱表现出较好的红外振动特性。讨论了薄膜结晶状态对Raman位移的影响以及VO2薄膜的红外光谱。     

硫系Ge-As-S玻璃和薄膜的特性

用差热分析，X射线衍射分析和透射光谱分析等手段研究了硫系Ge-As-S玻璃和薄膜的性能，结果表明，Ce-As-S体系的成玻能力较强在空气中自然冷却就能成玻，其（Tg-Tc)/Tg值为0.127-0.289，经激光辐射后的Ge-As-S玻璃薄膜的透射光谱曲线向短波方向移动，且平移的大小随激光功率的增加而增加，薄膜的透射光谱线的平移表明激光辐射导致薄膜光致结构变化，利用电子束辐射极化，通过Maker条纹测试方法在Ge-As-S玻璃中观察到二次谐波。     

不同衬底上溅射TiO2薄膜的光学性能研究

在硅片和石英上利用射频溅射法沉积了TiO2薄膜,并分别在空气中进行了退火处理。利用椭偏光谱仪对硅片上薄膜进行了椭偏测试,利用紫外-可见分光光度计对石英上薄膜进行了透射光谱测试。利用解谱软件对椭偏谱和透射谱进行了建模解谱,获得了不同基片上薄膜在不同退火温度下的折射指数和消光系数,发现和TiO2块材的光学常数也有明显的区别。通过计算得到了系列薄膜的光学带隙,带隙值范围从3.35～3.88eV,可以为薄膜态TiO2体系的光学应用、设计和相关理论研究提供一定的依据。     

High performance humidity sensing properties of indium tin oxide (ITO) thin films by sol–gel spin coating method

The tin doped indium oxide (ITO) thin films prepared by sol–gel spin coating method with In(NO₃)3H₂O and SnCl₄·5H₂O as indium and tin sources respectively is presented. The as deposited samples were annealed at 500 °C for 2 h in order to improve the crystallinity. The structural, morphological and optical properties of the films were analysed by using X-ray diffraction, scanning electron microscope (SEM), UV–Vis transmission spectra and photoluminescence, spectra analysis. The SEM images ensure the uniform and smooth surface of the as prepared and annealed film. The optical transmittance of more than 85 % has been observed in the UV–Vis region with a band gap of 3.91 and 3.73 eV for the as prepared and annealed films of ITO respectively. The PL spectra reveal that the optical properties were significantly improved due to the annealing effect. The annealed film shows high sensitivity for humidity approximately two order changes in the resistance and the sensitivity increases for different relative humidity from 10 to 90 % due to the physisorption between the water molecules and the surface of the thin films.     

连续式离子层吸附与反应法沉积CuSCN薄膜及其微观结构、光学特性研究

采用乙二醇作溶剂,以连续式离子层吸附与反应法(SILAR)实现硫氰酸亚铜(CuSCN)薄膜在ITO、TiO2薄膜以及玻璃衬底上的沉积.通过X射线衍射、扫描电镜和紫外-可见光透过谱等手段表征薄膜结晶性、表面和断面微观形貌以及光学特性.结果表明,衬底以及溶剂性质均对SILAR法薄膜沉积过程存在重要影响.ITO衬底上获得的CuSCN薄膜更为致密,呈结晶态,而TiO2薄膜衬底上的CuSCN薄膜主要由颗粒组成,为非晶态.随沉积次数增加,薄膜表面粗糙度增大,光学透过率逐渐下降.在优化条件下(ITO衬底,20次沉积循环),所得CuSCN薄膜表面致密均匀,可见光透过率约60%.     

A comparison of the optical properties of glass and of evaporated amorphous thin films of BaO-TeO2

Two series of glass and thin film specimens of BaO-TeO₂ were prepared. The optical absorption edges and infrared absorption spectra were investigated. It was found that the fundamental absorption edge is a function of BaO content in both kinds of films and that the absorption is due to indirect electronic transitions. The values of optical gap for blown films were greater than those of thin evaporated films, but the widths of the band tails were greater for the evaporated thin films, which were expected to be more disordered than the thin blown glass films.