Theoretical and experimental study on the photoluminescence in BaTiO3 amorphous thin films prepared by the chemical route

A polymeric precursor method was used to synthesize BaTiO₃ amorphous thin film processed at low temperature. The luminescence spectra of BaTiO₃ amorphous thin films at room temperature revealed an intense single-emission band in the visible region. The visible emission band was found to be dependent of the thermal treatment history. Photoluminescence (PL) properties for different annealing temperatures were investigated. It was concluded that the intensity of PL is strongly dependent on both the heat treatment of the films and the presence of an inorganic disordered phase. Experimental optical absorption measurements showed the presence of a tail. These results are interpreted by the nature of these exponential optical edges and tails, associated with defects promoted by the disordered structure of the amorphous material. We discuss the nature of visible PL at room temperature in amorphous barium titanate in the light of the results of recent experimental and quantum mechanical theoretical studies. Our investigation of the electronic structure involved the use of first-principle molecular calculations to simulate the variation of the electronic structure in the barium titanate crystalline phase, which is known to have a direct band gap, and we also made an in-depth examination of amorphous barium titanate.     

Transparent nano composite PVA–TiO2 and PMMA–TiO2 thin films: Optical and dielectric properties

Transparent nano composite PVA–TiO₂ and PMMA–TiO₂ thin films were prepared by an easy and cost effective dip coating method. Al/PVA–TiO₂/Al and Al/PMMA–TiO₂/Al sandwich structures were prepared to study the dielectric behavior. The presence of metal–oxide (Ti–O) bond in the prepared films was confirmed by Fourier transform infrared spectroscopy. X-ray diffraction pattern indicated that the prepared films were predominantly amorphous in nature. Scanning electron micrographs showed cluster of TiO₂ nanoparticles distributed over the film surface and also there were no cracks and pin holes on the surface. The transmittance of the films was above 80% in the visible region and the optical band gap was estimated to be about 3.77 eV and 3.78 eV respectively for PVA–TiO₂ and PMMA–TiO₂ films by using Tauc's plot. The determined refractive index (n) values were between 1.6 and 2.3. High value of dielectric constant (?′ = 24.6 and ?′ = 26.8) was obtained for the prepared composite films. The conduction in the composite films was found to be due to electrons. The observed amorphous structure, good optical properties and dielectric behavior of the prepared nano composite thin films indicated that these films could be used in opto-electronic devices and in thin film transistors.     

Structural-optical study of high-dielectric-constant oxide films

High-k polycrystalline Pr₂O₃ and amorphous LaAlO₃ oxide thin films deposited on Si(0 0 1) are studied. The microstructure is investigated using X-ray diffraction and scanning electron microscopy. Optical properties are determined in the 0.75-6.5 eV photon energy range using spectroscopic ellipsometry. The polycrystalline Pr₂O₃ films have an optical gap of 3.86 eV and a dielectric constant of 16-26, which increases with film thickness. Similarly, very thin amorphous LaAlO₃ films have the optical gap of 5.8 eV, and a dielectric constant below 14 which also increases with film thickness. The lower dielectric constant compared to crystalline material is an intrinsic characteristic of amorphous films.     

Low temperature deposited Zr-B film applicable to extremely thin barrier for copper interconnect

We have prepared thin Zr-B films at low temperatures as a new material applicable to an extremely thin barrier against Cu diffusion in Si-ULSI metallization. The obtained Zr-B films mainly consist of the ZrB₂ phase with a nanocrystalline texture on SiO₂ and a fiber texture on Cu. The resistivity of the Zr-B films depends on the substrate of SiO₂ or Cu. The constituent ratio of B/Zr is almost 2, though the contaminants of oxygen, nitrogen, and carbon are incorporated in the film. The nanocrystalline structure of the Zr-B film on SiO₂ is stable due to annealing at temperatures up to 500 °C for 30 min. We applied the 3-nm thick Zr-B film to a diffusion barrier between Cu and SiO₂, and the stable barrier properties were confirmed. We can demonstrate that the thin Zr-B film is a promising candidate for thin film application to a metallization material in Si-ULSIs.     

Effects of vanadium doping on structure and electrical properties of SrBi4Ti4O15 thin films

The effects of vanadium(V) doping into SrBi₄Ti₄O₁₅ (SBTi) thin films on the structure, ferroelectric, leakage current, dielectric, and fatigue properties have been studied. X-ray diffraction result showed that the crystal structure of the SBTi thin films with and without vanadium is the same. Enhanced ferroelectricity was observed in the V-doped SrBi₄Ti₄O₁₅ (SrBi_4−x/3Ti_4−xV_xO₁₅, SBTiV-x (x = 0.03, 0.06, and 0.09)) thin films compared to the pure SrBi₄Ti₄O₁₅ thin film. The values of remnant polarization (2P_r) and coercive field (2E_c) of the SBTiV-0.09 thin film capacitor were 40.9 μC/cm² and 105.6 kV/cm at an applied electric field of 187.5 kV/cm, respectively. The 2P_r value is over five times larger than that of the pure SBTi thin film capacitor. At 100 kHz, the values of dielectric constant and dielectric loss were 449 and 0.04, and 214 and 0.06 for the SBTiV-0.09 and the pure SBTi thin film capacitors, respectively. The leakage current density of the SBTiV-0.09 thin film capacitor measured at 100 kV/cm was 6.8 × 10⁻⁹ A/cm², which is more than two and a half orders of magnitude lower than that of the pure SBTi thin film capacitor. Furthermore, the SBTiV-0.09 thin film exhibited good fatigue endurance up to 10¹⁰ switching cycles. The improved electrical properties may be related to the reduction of internal defects such as bismuth and oxygen vacancies with changes in the grain size by doping of vanadium into SBTi.     

Effect of cobalt doping and annealing on properties of titania thin films prepared by sol-gel process

Undoped and cobalt doped titania (TiO₂) thin films have been prepared on Si(1 0 0) monocrystal and quartz substrate using the sol-gel deposition method and annealed in air at 450, 550, 650, 750, 850, 950 and 1050 °C. Several experimental techniques (AFM, XRD, Raman spectroscopy, XRR, EDX, XPS, XAS, UV-VIS spectroscopy) have been used to characterize these films. Further more the degree of light induced hydrophilicity was estimated by measuring the contact angle of a water droplet on the film. Increase of the annealing temperature and in smaller degree also cobalt doping predispose titania crystallite growth. The rutile phase was detected at lower temperatures in the cobalt doped films than in the undoped titania films. Cobalt in the cobalt doped TiO₂ was seen to be in Co²⁺ oxidation state, mainly in CoTiO₃ phase when films were annealed at temperatures higher than 650 °C. Cobalt compounds segregated into the sub-surface region and to the surface of the titania, where they formed islands. Cobalt doping red-shifted the fundamental absorption edge further into the visible range, however it did not enhance the light induced hydrophilicity of the thin film surface as compared to the undoped titania thin films.     

Wet-chemical dip-coating preparation of highly oriented copper-aluminum oxide thin film and its opto-electrical characterization

Transparent p-type semiconducting copper aluminum oxide thin film has been synthesized by a wet-chemical route. CuCl and AlCl₃, dissolved in HCl, are taken as starting materials. pH value of the solution is controlled by adding a measured amount of NaOH into it. Films are deposited by dip-coating technique on glass and Si substrates followed by annealing in air at 500 °C for 3 h. XRD pattern confirms the crystalline CuAlO₂ phase formation in the film and also indicates a strong (0 0 6) orientation. UV-vis spectrophotometric measurements show high transparency of the film in the visible region with a direct allowed bandgap of 3.94 eV. Electrical measurements depict the thermally activated conduction within the films. Thermoelectric measurements confirm the p-type nature of the films. Compositional analysis shows the presence of excess (nonstoichiometric) oxygen within the material, which is incorporated during the air-annealing of the film. According to defect equilibrium, this excess oxygen is predicted to cause the p-type conductivity of the film. This type of cost-effective solution-based technique is very useful for volume production of this kind of technologically important material for transparent electronic and other diverse applications.     

Fast electrochromic response of porous-structured cobalt oxide (Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) thin films by novel nebulizer spray pyrolysis technique

Electrochromic effect of cobalt oxide thin films was studied as a function of substrate temperature (573–673 K). Tricobalt tetraoxide (Co₃O₄) thin films were deposited on glass and fluorine-doped tin oxide (FTO) substrates by nebulized spray technique using cobalt nitrate as precursor material. The XRD patterns indicated (311) plane was dominant for all the films irrespective of the deposition temperature. Williamson-Hall (W-H) analysis was made to understand the strain variation in the prepared Co₃O₄ films under different deposition temperature by employing uniform deformation model (UDM). Scanning electron microscopy images revealed porous morphology for the film prepared at 623 K. The optical parameters such as refractive index (n), extinction coefficient (k), and band gap were derived from UV-visible spectra of Co₃O₄ films. The electrochromic performance of the deposited Co₃O₄ films was analyzed through cyclic voltammetry, chronocoulometry, chronoamperometry, and iono-optical studies.     

Effects of the substrate temperature on the properties of CuIn5S8 thin films

Structural, optical and electrical properties of CuIn₅S₈ thin films grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The CuIn₅S₈ thin films were carried out at substrate temperatures in the temperature range 100-300 °C. The effects of heated substrate on their physico-chemical properties were investigated using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), optical transmission and hot probe method. X-ray diffraction revealed that the films are strong preferred orientation along the (3 1 1) plane upon substrate temperature 200 °C and amorphous for the substrate temperatures below 200 °C. No secondary phases are observed for all the films. The composition is greatly affected by heated substrate. From the optical transmission and reflection, an important absorption coefficient exceeds 10⁵ cm⁻¹ at 800 nm was found. As increasing the substrate temperature, the optical energy band gap decreases from 1.70 eV for the unheated films to 1.25 eV for the deposited films at 300 °C. It was found that CuIn₅S₈ thin film is an n-type semiconductor at 250° C.     

Optical properties of molybdenum oxide thin films deposited by?chemical vapor transport of MoO3(OH)2

MoO₃ thin films are useful for optical devices due to their electrochromic properties. In this study, deposition of MoO₂ thin films was successfully accomplished by chemical vapor transport (CVT) of volatile MoO₃(OH)₂. Subsequently, a MoO₃ thin film was obtained by annealing of the deposited MoO₂ at 400°C in an O₂ atmosphere. As annealing commenced, the optical transmittance of the films increased and their absorbance peaks were broadened and red-shifted due to reduced oxygen vacancy. Thus, the molybdenum oxide thin films can successfully be deposited using the CVT technique.     

Highly uniform electrochromic tungsten oxide thin films deposited by e-beam evaporation for energy saving systems

In the last few decades, there has been a surge of interest in using tungsten oxide thin films as an active layer of electrochromic device. These devices have several practical applications such as smart window of buildings and automobile glazing for energy saving. The main objective of this work was to construct highly homogeneous and uniform e-beam evaporated amorphous WO_3-x based films into electrochromic devices, which were fully characterized for switching speed, coloration efficiencies and cycling voltammetry responses. Fabricated devices contain indium doped transparent oxide coated glass as the transparent conductive electrode, ～200?nm thickness of WO_3-x as the cathodically coloring material and a lithium perchlorate based conducting gel electrolyte. X-ray diffraction patterns indicate that all as-deposited films are amorphous. Experimental results showed that both solid and liquid electrolyte electrochromic devices are initially very transparent that exhibit perfect optical modulation and coloration efficiency (up to 68.7?cm²/C and 52.6?cm²/C at 630?nm, respectively) due to easier intercalation of the Li⁺ within their structure. One of the more significant findings to emerge from this study is that e-beam coated electrochromic devices based on tungsten oxide thin films showed superior performance among to other coating methods. Therefore, excellent reversibility of color change behavior is attractive for pertinent use in electrochromic energy storage devices.     

Fabrication of textured SnO2:F thin films by spray pyrolysis

Transparent conductive SnO₂:F thin films with textured surfaces were fabricated on soda-lime-silica glass substrates by spray pyrolysis. Structure, morphology, optical and electrical properties of the films were investigated. Results show that the film structure, morphology, haze, transmittance and sheet resistance are dependent on the substrate temperature and film thickness. An optimal 810 nm-thick SnO₂:F film with textured surface deposited at 520 °C exhibits polycrystalline rutile tetragonal structure with a (2 0 0) orientation. The sheet resistance, average transmittance in visible region, and haze of this film were 8 Ω/□, 80.04% and 11.07%, respectively, which are suitable for the electrode used in the hydrogenated amorphous silicon solar cells.     

Annealing effect on the structural and optical properties of a Cd1−xZnxS thin film for photovoltaic applications

Herein is a report of a study on a Cd_1−xZn_xS thin film grown on an ITO substrate using a chemical bath deposition technique. The as-deposited films were annealed in air at 400 °C for 30 min. The composition, surface morphology and structural properties of the as-deposited and annealed Cd_1−xZn_xS thin films were studied using EDX, SEM and X-ray diffraction techniques. The annealed films have been observed to possess a crystalline nature with a hexagonal structure. The optical absorption spectra were recorded within the range of 350-800 nm. The band gap of the as-deposited thin films varied from 2.46 to 2.62 eV, whereas in the annealed film these varied from 2.42 to 2.59 eV. The decreased band gap of the films after annealing was due to the improved crystalline nature of the material.     

Structural, optical and electrical properties of ZnO/Zn2GeO4 porous-like thin film and wires

Zinc oxide/zinc germanium oxide (ZnO/Zn₂GeO₄) porous-like thin film and wires has been fabricated by simple thermal evaporation method at temperature about 1120 °C for 2.5 h. The structural and optical properties of the porous-like-thin film and wires have been investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. Metal semiconductor metal (MSM) photodetector structure was used to evaluate the electrical characteristics by using current-voltage (I-V) measurements. Room temperature photoluminescence spectrum of the sample shows one prominent ultraviolet peak at 378 nm and a shoulder at 370 nm. In addition, broad visible blue emission peak at wavelength 480 nm and green emission peak at 500 nm are also observed. Strong photoelectric properties of the MSM in the UV demonstrated that the porous-like-thin film and wires contribute to its photosensitivity and therefore making ZnO/Zn₂GeO₄ wires potential photodetector in the shorter wavelength applications.     

Structure, electrochromic and optical properties of WO3 film prepared by dip coating-pyrolysis

The tungsten oxide (WO₃) film was grown by dip coating-pyrolysis method with the PEG-400 as the structure-directing agent. Microstructure of the WO₃ film was characterized by TG-DSC, XRD and SEM techniques. It was found that the film annealed at 350 °C for 2 h comprised cubic WO₃ and orthorhombic WO₃. The measurements of the cyclic voltammetry (CV) and UV-vis spectrum suggested that the WO₃ film had a good electrochromic reversibility performance. The film possessed excellent modulation to the visible light and the maximal average transmittance modulation reached 70.06%.     

退火气压对Bi3.25La0.75Ti3O12铁电薄膜的微观结构和铁电性能的影响

采用sol-gel法在Pt/TiO₂/SiO₂/p-Si(100)衬底上制备了Bi_3.25La_0.75Ti₃O₁₂(BLT)铁电薄膜,研究了在750 ℃时不同退火气压(p_{O2:10^-4—3 atm)对薄膜微观结构和电学性能的影响.XRD和拉曼光谱结果表明在10^-4和3 atm氧气压下退火 关键词： 3.25}La_0.75Ti₃O₁₂')" href="#">Bi_3.25La_0.75Ti₃O₁₂ 铁电性能 sol-gel法 正交化度     

金属有机物化学气相沉积法生长Ga2（1-x）In2xO3薄膜的结构及光电性能研究

采用金属有机物化学气相沉积（MOCVD）法在蓝宝石（0001）衬底上制备出了Ga_2（1-x）In_2xO₃（x=01—09）薄膜,研究了薄膜的结构、电学和光学特性以及退火处理对薄膜性质的影响.测量结果表明：当In组分x=02时,样品为单斜β-Ga₂O₃结构;x=05的样品,薄膜呈现非晶结构,退火处理后薄膜结构得到明显的改善 关键词： 金属有机物化学气相沉积 2（1-x）In_2xO₃薄膜')" href="#">Ga_2（1-x）In_2xO₃薄膜 蓝宝石衬底 退火     

Functional and optical properties of Au:TiO2 nanocomposite films: The influence of thermal annealing

A set of nanocomposite thin films consisting of Au nanoclusters dispersed in a TiO₂ dielectric matrix was deposited by reactive magnetron sputtering, and subjected to thermal annealing in vacuum, at temperatures ranging from 200 to 800 °C. The obtained results show that the structure and the size of Au clusters, together with the matrix crystallinity, changed as a result of the annealing, and were shown to be able to change the optical properties of the films and keeping good mechanical properties, opening thus a wide number of possible applications. The crystallization of the gold nanoclusters induced by the annealing was followed by a systematic change in the overall coating behaviour, namely the appearance of surface plasmon resonance (SPR) behaviour. This effect enables to tailor the thin films reflectivity, absorbance and colour coordinates, contributing to the importance of this thin film system. The different attained optical characteristics (reflectance values ranging from interference to metallic-like behaviours and colour varying for interference rainbow-like to several tones of red-brownish), associated with a reasonable mechanical resistance of the coatings (good adhesion to different substrates and hardness values ranging from 5 to 7.5 GPa), induce the possibility to use this film system in a wide range of decorative applications.     

Effects of different deposition conditions on the properties of Cu2S thin films

Cu₂S thin films deposited on glass substrate by chemical bath deposition were studied at different deposition temperatures and times. The results of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), the Hall Effect measurement system and UV-Vis absorption spectroscopy indicate that both deposition temperature and time are important to obtain polycrystalline thin films. XRD showed that the polycrystalline Cu₂S thin films have monoclinic structure. Meanwhile, the structural variations were analyzed using SEM. EDX analysis results of the thin film showed that the atomic ratio of Cu/S was close to 2:1. It was found from the Hall Effect measurement that the resistivity varied from 4.59?×?10^?3 to 13.8?×?10^?3 (Ω?cm). The mobility values of the Cu₂S thin films having p-type conductivity varied from 15.16 to 134.6?cm²/V.s. The dark electrical resistivity measurements were studied at temperatures in the range 303–423?K. The electrical activation energies of Cu₂S thin films were calculated by using Arrhenius plots, from which two different activation energy values are estimated for each thin film. Using UV-Vis absorption spectroscopy (Ultraviolet/visible), the direct and indirect allowed optical band gap values were determined to lie between 2.16 and 2.37?eV and 1.79 and 1.99?eV, respectively. In addition, the values of the refractive index (n) and the extinction coefficient (k) were determined.     

Electrochromic materials from the visible to the infrared region: an example WO<Subscript>3</Subscript>

Herein, the example of the most typical electrochromic material, namely WO₃, is used to illustrate the potential of electrochromic materials for controlling infrared reflectance and hence, emissivity. Playing with various growth parameters, contrast in reflectance between the inserted H _xWO₃ and deinserted WO₃ states as high as 73% in mid-wavelength band (MW, 3–5 μm) was achieved for 320 nm WO₃ films. The latter electrochromic materials were radio frequency sputtered on Au substrate at ambient temperature in 6 Pa of chamber pressure. In comparison, for long wavelength band (LW, 8–12 μm), the contrast in reflectance did not exceed 30%. The origins of the various electrochromic behaviours are correlated to the film structure, morphology and composition, indicating better properties for porous, nonstoichiometric films. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.