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.     

Optical characterization of BaSm2Ti4O12 thin films by spectroscopic ellipsometry

We performed spectroscopic ellipsometric measurement to characterize BaSm₂Ti₄O₁₂ (BST) thin films grown on Pt/Ti/SiO₂/c-Si substrate by rf magnetron sputtering. The six BST films were prepared at various deposition temperatures and thermal annealing times. The resulting refractive indices and extinction coefficients of the BST films show only slight change by the deposition temperature but a significant change after thermal annealing, implying the importance of the post annealing process. The increase of the refractive index can be understood by the higher density of the BST films caused by the crystallization after annealing process.     

Microstructure, electrical and optical characteristics of Mg(Zr0.05Ti0.95)O3 thin films grown on Si substrate by sol-gel method

Optical properties and microstructures of Mg(Zr_0.05Ti_0.95)O₃ thin films prepared by sol-gel method on n-type Si(100) substrates at different annealing temperatures have been investigated. The surface structural and morphological characteristics analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscope (AFM) were found to be sensitive to the deposition conditions, such as annealing temperature (600-800 °C). The optical transmittance spectra of the Mg(Zr_0.05Ti_0.95)O₃ thin films were measured by using UV-visible recording spectro-photometer. The diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure. All films exhibited Mg(Zr_0.05Ti_0.95)O₃ peaks orientation perpendicular to the substrate surface and the grain size with the increase in the annealing temperature. The dependence of the microstructure and dielectric characteristics on annealing temperature was also investigated.     

Preparation of inorganic solid state thin film for electrochromic application

All oxide solid state ITO (indium tin oxide)/Li_yWO_3−x/Li_1−zMn₂O₄/ITO stacked structure was deposited on a silica glass substrate by pulsed laser deposition for its electrochromic application. The Li doped amorphous tungsten trioxide Li_yWO_3−x thin film prepared at room temperature and in oxygen pressure of 7 Pa got the color of blue due to the mixture valence state of tungsten. We found that the amorphous Li_1−zMn₂O₄ thin film was suitable for the electrochromic application in spite of the low ion conductivity along in-plane direction. The ITO electrode thin film deposited at room temperature showed the relatively high transmittance and the usable conductivity. The transmittance at a wavelength of 750 nm for the ITO/Li_yWO_3−x/Li_1−zMn₂O₄/ITO stacked film changed from 50% to 80% by the applied voltage, while the transmittance at around 450 nm did not change. The blue-colored electrochromic property could be observed for the all oxide solid state film.     

The effect of stress on the dielectric constants of Bi4Ti3O12 films

Both experiment and theory have shown that the stress has a notable impact on the polarization of Nd-doped Bi₄Ti₃O₁₂ films. In this paper, thermodynamic theory is used to study the effect of stress on the dielectric constants of Bi₄Ti₃O₁₂ films at room temperature with a two-dimensional model. Results indicate that the change of the dielectric constant for a-phase induced by the lattice distortion is far greater than that for c-phase. Considering the domain reorientation, the external tensile stress may lead to an obvious decrease in the effective dielectric constant of Bi₄Ti₃O₁₂ films.     

负极活性材料Li4Ti5O12的研究进展

介绍了负极材料Li₄Ti₅O₁₂的物理特性和电化学性能,详细介绍并评述了Li₄Ti₅O₁₂ 在锂离子电池和不对称型超级电容器中的应用情况,总结了Li₄Ti₅O₁₂的不同合成方法及材料的电化学改性研究进展.     

Effect of composition and deposition parameters on optical properties of Ge25Sb15−xBixS60 thin films

The optical constants of the Ge₂₅Sb_15−xBi_xS₆₀ (0?x?15) chalcogenide films, either as-deposited or after being annealed at various temperatures have been computed in the spectral wavelength range 400-2400 nm from the transmittance and reflectance measurements of normally-incident light. With the increase in bismuth content, the optical energy gap (which is indirect) decreases, while the refractive index increases. The effects of film thickness, substrate type, deposition rate and γ-radiation on optical properties have been studied. The effect of thermal annealing on the growth characteristics and stability of the films has been studied using X-ray diffraction and scanning electron microscopy. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model.     

Li2O–ZnO–Co3O4–TiO2 composite thin-film electrocatalyst for efficient water oxidation catalysis

Thin films of different Li₂O–ZnO–Co₃O₄–TiO₂ (LZCT) compositions were prepared and employed as electrocatalysts (i.e., anodes) to perform water oxidation reaction (WOR). The electrocatalytic activities of these thin films were compared with those exhibited by the sodium salt of cobalt phosphate (Na₂CoP₂O₇) (CP) thin-film electrocatalyst, which is a well-known water oxidation catalyst (WOC). These results suggest that the 10Li₂O–10ZnO–40Co₃O₄–40TiO₂ composition exhibits a better catalytic activity in terms of higher faradaic efficiency (>98%), lower over potentials (<400?mV), higher reaction stability (up to 30 continuous cyclic voltammetry (CV) cycles), and the rate of O₂ and H₂ gas evolution in terms of current density (about 1?mA/cm²) in comparison with those exhibited by CP thin-film electrocatalyst. Furthermore, these LZCT thin films exhibited very high specific surface area values and due to the unique microstructure of ZnCo₂O₄ phase evolved out of these LZCT compositions at a calcination temperature of 550°C for 30?min it has been found to be responsible for the higher specific surface area values measured for these thin-film compositions.     

Overview about the optical properties and mechanical stress of different dielectric thin films produced by reactive-low-voltage-ion-plating

Thin films of Ta₂O₅, Nb₂O₅, and HfO₂ were deposited by reactive-low-voltage-ion-plating (RLVIP) on unheated glass and silicon substrates. The film thickness was about 200 nm. Optical properties as well as mechanical film stress of these layers were investigated in dependence of various deposition parameters, i.e. arc current and oxygen partial pressure. For an arc current in the range between 40 and 50 A and an oxygen partial pressure of at least 11 · 10^− 4 mbar good results were obtained. The refractive index and film thickness were calculated from spectrophotometric transmission data using the Swanepoel theory. For example at 550 nm wavelength the refractive index for thin RLVIP-Nb₂O₅-films was found to be n₅₅₀ = 2.40. The optical absorption was obtained by photo-thermal deflection spectrometry. For the investigated materials absorption coefficients in the range of k = 5 · 10^− 4 at 515 nm wavelength were measured. The mechanical film stress was determined by measuring the difference in bending of silicon substrates before and after the deposition process. For dense films, i.e. no water vapour sorption on atmosphere, the mechanical film stress was always compressive with values of some hundred MPa. In case of films deposited with higher arc currents (I_arc > 60A) and lower oxygen pressure (< 15 · 10^− 4 mbar) the influence of a post deposition heat treatment at 350 °C for 4 h on air was also investigated. For these films the properties could clearly be improved by such treatment. However, by using lower arc currents and higher oxygen partial pressure during the ion plating process, immediately dense and environmental stable films with good optical as well as mechanical properties could be achieved without post deposition heat treatment. All the results obtained will be presented in graphs and diagrams.     

Delayed onset of photochromism in molybdenum oxide films caused by photoinduced defect formation

We report the photochromic properties of amorphous MoO₃ films deposited by dc sputtering with different O₂ flow rates. The kinetics of film coloration under UV light irradiation is determined using optical transmission spectroscopy. Changes in the absorbance and refractive index were derived from the analysis of transmittance spectra. The absorbance spectra exhibited a growing broad peak centered around 830 nm, which was induced by the UV irradiation. In the early stages of irradiation, the absorbance of the films did not change but their refractive indices did change. This induction time was correlated with the O₂ partial pressure during the film deposition, which was controlled by the O₂ flow rate. The origins of this observation are discussed.     

Anisotropic grain growth of Bi4Ti3O12 in molten salt fluxes

Bismuth titanate (Bi₄Ti₃O₁₂) platelets were obtained by the molten salt synthesis method in NaCl-KCl and Na₂SO₄-K₂SO₄ fluxes, using an amorphous Bi₄Ti₃O₁₂ precursor and a mechanically mixed Bi₂O₃-TiO₂ mixture as the starting materials. It was found that the synthesizing temperature, salt species and starting materials could significantly affect the crystallization habit and morphology of Bi₄Ti₃O₁₂ platelets. Under the same processing conditions (i.e. in Na₂SO₄-K₂SO₄ flux at 1000 °C), the Bi₄Ti₃O₁₂ platelets synthesized from the Bi₂O₃-TiO₂ mixture generally showed a smaller particle size than those synthesized using the amorphous Bi₄Ti₃O₁₂ precursor. The Bi₄Ti₃O₁₂ platelets prepared in the chloride flux were faceted along either (0 0 1) or (1 1 2) planes, while those prepared in the sulfate flux were solely (0 0 1) faceted. The former system also had smaller particle size than the latter. Furthermore, the salt content and the addition of plate-like Bi₄Ti₃O₁₂ seeds in the amorphous Bi₄Ti₃O₁₂ precursor showed a strong influence on the particle size of the synthesized Bi₄Ti₃O₁₂ platelets. The particle size of Bi₄Ti₃O₁₂ platelets prepared in the sulfate flux decreased as the mole ratio of the sulfate salts to Bi₄Ti₃O₁₂ was increased from 7.9 to 23.7. And the addition of 10 wt.% plate-like Bi₄Ti₃O₁₂ seeds into the amorphous Bi₄Ti₃O₁₂ precursor led to a significant increase in the particle size of the resulting Bi₄Ti₃O₁₂ platelets.     

The properties of transparent semiconductor Zn1 − xTixO thin films prepared by the sol-gel method

Transparent semiconductor thin films of Zn_1 − xTi_xO (0 ≦ x ≦ 0.12) were deposited on alkali-free glass substrates by the sol-gel method. The effects of Ti addition on the crystallization, microstructure, optical properties and resistivity of ZnO thin films were investigated. The as-coated films were preheated at 300 °C, and then annealed at 500 °C in air ambiance. X-ray diffraction results showed all polycrystalline Zn_1 − xTi_xO thin films with preferred orientation along the (002) plane. Ti incorporated within the ZnO thin films not only decreased surface roughness but also increased optical transmittance and electrical resistivity. In the present study, the Zn_0.88Ti_0.12O film exhibited the best properties, namely an average transmittance of 91.0% (an increase of ~ 12% over the pure ZnO film) and an RMS roughness value of 1.04 nm.     

Delayed onset of photochromism in molybdenum oxide films caused by photoinduced defect formation

Abstract

We report the photochromic properties of amorphous MoO₃ films deposited by dc sputtering with different O₂ flow rates. The kinetics of film coloration under UV light irradiation is determined using optical transmission spectroscopy. Changes in the absorbance and refractive index were derived from the analysis of transmittance spectra. The absorbance spectra exhibited a growing broad peak centered around 830 nm, which was induced by the UV irradiation. In the early stages of irradiation, the absorbance of the films did not change but their refractive indices did change. This induction time was correlated with the O₂ partial pressure during the film deposition, which was controlled by the O₂ flow rate. The origins of this observation are discussed.     

Novel Li4Ti5O12/Sn nano-composites as anode material for lithium ion batteries

Li₄Ti₅O₁₂/Sn nano-composites have been prepared as anode material for lithium ion batteries by high-energy mechanical milling method. Structure of the samples has been characterized by X-ray diffraction (XRD), which reveals the formation of phase-pure materials. Scanning electron microscope (SEM) and transmission electron microscope (TEM) suggests that the primary particles are around 100 nm size. The local environment of the metal cations is confirmed by Fourier transform infrared (FT-IR) and the X-ray photoelectron spectroscopy (XPS) confirms that titanium is present in Ti⁴⁺ state. The electrochemical properties have been evaluated by galvanostatic charge/discharge studies. Li₄Ti₅O₁₂/Sn-10% composite delivers stable and enhanced discharge capacity of 200 mAh g⁻¹ indicates that the electrochemical performance of Li₄Ti₅O₁₂/Sn nano-composites is associated with the size and distribution of the Sn particles in the Li₄Ti₅O₁₂ matrix. The smaller the size and more homogeneous dispersion of Sn particles in the Li₄Ti₅O₁₂ matrix exhibits better cycling performance of Li₄Ti₅O₁₂/Sn composites as compared to bare Li₄Ti₅O₁₂ and Sn particles. Further, Li₄Ti₅O₁₂ provides a facile microstructure to fairly accommodate the volume expansion during the alloying and dealloying of Sn with lithium.     

低维纳米立方相Li_4Mn_5O_(12)的制备及锂吸附性能

以MnSO4·H2O和(NH4)2S2O8为原料通过控制水热反应条件合成了纯的四方相β-MnO2纳米氧化物,进一步通过低温固相法制备了立方相Li4Mn5O12,经酸浸脱锂后得到对Li+具有特殊选择性的MnO2离子筛.用XRD、HRTEM、SAED、吸附等温线、吸附动力学及共存金属离子的分配系数等手段对产物的晶相结构和Li+选择性吸附性能进行了研究.HRTEM和SAED图像表明氧化物MnO2、前驱体Li4Mn5O12和离子筛MnO2均为低维纳米棒.离子筛的最大吸附量达到6.6mmol/g,且当Li+初始浓度仅为5.0mmol/L时,离子筛的吸附量即可达到约5.0mmol/g,这对于在海水或锂离子浓度极低的盐湖卤水提锂具有重要的实用意义.     

Characterizations and electrochemical performance of pure and metal-doped Li4Ti5O12 for anode materials of lithium-ion batteries

Pure and metal (Cu, Al, Sn, and V)-doped Li₄Ti₅O₁₂ powders are prepared with solid-state reaction method. The effects of dopants on the physical and electrochemical properties are characterized by using TGA, XRD, and SEM. Compared with pure Li₄Ti₅O₁₂, metal-doped Li₄Ti₅O₁₂ powders show structural stability and enhanced lithium ion diffusivity brought by doped metal ions. Voltage characteristics and initial charge–discharge characteristics according to the C rates in pure and metal-doped Li₄Ti₅O₁₂ electrode materials are studied. Pure Li₄Ti₅O₁₂ powder shows a relatively good discharge capacity of 164 mAh/g at a rate 0.2C, and some of metal-doped Li₄Ti₅O₁₂ powders show higher discharge capacities. Metal-doped Li₄Ti₅O₁₂ powders are promising candidates as anode materials for lithium-ion batteries.     

Composition dependence of optical constants in ferroelectric Ba(Ti1 − x,Nix)O3 thin films by optical transmittance technique

Ba(Ti_1 − x,Ni_x)O₃ ferroelectric thin films with perovskite structure are prepared on fused quartz substrates by a sol-gel process. Optical transmittance measurements indicate that Ni-doping has an obvious effect on the energy band structure of BaTiO₃. It has been found that the refractive index n, extinction coefficient k, and band gap energy E_g of the films are functions of the film composition. The E_g of Ba(Ti_1 − x,Ni_x)O₃ decreases approximately linearly as the Ni content increases, which is attributed to the decline of conduction band energy level with increasing the Ni content. On the other hand, n and k both increase linearly with increasing the Ni content because of the increase of packing density. These results indicate that thin films might have potential applications in BaTiO₃-based thin-film optical devices.     

Optical and structural properties of TiO2 films as a function of Nb doping concentration

Ti_1?Cx Nb _x O₂ (x?=?0?C0.06) films were prepared on quartz substrates by sol?Cgel spin coating and characterized by a variety techniques. The effect of Nb doping on the structural and optical properties of Ti_1?Cx Nb _x O₂ films were mainly investigated by X-Ray diffraction (XRD), Raman spectroscopy, Field-emission scanning electron microscopy and UV?Cvis transmittance spectroscopy. XRD and Raman study showed that the Nb doping inhibited the grain growth. The grain size decreased from 39.4 to 23.4?nm as the doping concentration increased from 0 to 0.06 in atomic percent. The UV?Cvis transmittance spectroscopy analysis revealed that the films exhibited 55?C65% transmittance in the visible region and the band gap of films became wider with increasing Nb doping concentration.     

Transparent conducting Nb-doped anatase TiO2 (TNO) thin films sputtered from various oxide targets

Transparent conducting Nb-doped anatase TiO₂ (TNO) epitaxial films were sputtered from TiO₂-, Ti₂O₃-, and Ti-based targets at various oxygen partial pressures (Po₂). Using the TiO₂- and Ti₂O₃-based targets, highly conductive films showing a resistivity (ρ) of ~ 3 × 10^− 4 Ω cm could be formed without postdeposition treatment. In the case of the TNO films formed from the Ti-based target, reductive annealing had to be carried out at a temperature of 600 °C to achieve similar resistivity values. Thus, the use of oxide targets is preferable to obtain as-grown transparent conducting TNO films. In particular, the Ti₂O₃-based target is practically advantageous, because it offers a wide range of optimal Po₂ values at which ρ values of the order of 10^− 4 Ω cm are achievable.     

Transmittance enhancement of micro-grating structure sapphire with high-refractive index Y2O3 layer

The theoretical analysis of micro-grating structure sapphire (sapphire MGS) with Y₂O₃ layer using the finite-difference time-domain method is presented. The results show that the total transmittance and reflectance of Y₂O₃/sapphire MGS have a close relationship with the thickness of Y₂O₃ layer, where about 300 nm is the ideal thickness. According to the simulant results, 300 and 600 nm of thicknesses of Y₂O₃ layer deposited onto sapphire MGS substrate by reactive magnetron sputtering method are studied experimentally. The experimental results agree well with the calculated data and further have better optical properties because of the rough surface of Y₂O₃ layer. It illustrates that the 300-nm Y₂O₃/sapphire MGS exhibits the best increase in the total transmittance and diffuse transmittance due to the greater graded refractive index profile than sapphire MGS. The results of this paper have potential applications in solar cells and diffraction grating.