Alternative Nb2O5-TiO2 thin films for electrochromic devices

Thin films of mixed oxides of Nb₂O₅-TiO₂ with molar ratio Nb/Ti = 3, have been prepared by sol-gel sonocatalytic method. The precursor sols consist of a mixture of niobium salt NbCl₅, titanium alkoxide Ti(OPr ⁱ )₄, isopropanol and acetic acid. After addition of all components the mixture was sonicated. The films were deposited by dip-coating technique on ITO-Asahi Glass and then submitted to a final heat treatment at 560°C during 3 h in atmosphere of oxygen. The electrochromic properties of the films were investigated using in situ spectroelectrochemical method. The films exhibit a blue-gray coloration under lithium ions insertion with a reversible variation of the transmittance in the visible and near infrared range between 90% and 20%. The xerogels of Nb₂O₅-TiO₂ also were characterized by X-ray diffraction, thermal analysis (DTA/TGA) and IR measurements. The morphology of the films was observed by scanning electron microscopy (SEM) and the topography by atomic force microscopy (AFM). These films appear suitable for architectural applications, where a minimum performance in depth color is required.     

Photoluminescence from RF sputtered SiCBN thin films

Silicon carbon boron nitride (SiCBN) thin films were synthesized by reactive co-sputtering of silicon carbide (SiC) and boron nitride (BN) targets. As-deposited samples show distinct photoluminescence (PL) peaks at 465, 483 and 497 nm. The films were annealed in dry oxygen ambient at different temperatures to investigate the effect of annealing on film properties. Subsequent measurements on the annealed samples show diminished PL peak intensities. X-ray diffraction analysis shows that the as-deposited films are amorphous in nature and there is no change in the microstructure even after high temperature annealing. Surface characterization of the films by X-ray photoelectron spectroscopy reveals change in chemical composition at different annealing temperatures. Carbon concentrations in the films are sensitive to annealing temperatures and could cause the change in photoluminescence properties.     

Characterization of laser-ablated V2O5 thin films

Vanadium pentoxide thin films have been prepared by the pulsed laser deposition technique. The influence of substrate temperature on the growth of V₂O₅ films was studied. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements have been carried out in order to understand the growth mechanism. The crystallization in V₂O₅ thin films starts at deposition temperatures as low as 473 K and the grain size increased with deposition temperature. The films exhibited predominantly (0 0 1) orientation, representing the orthorhombic layered structure. The infrared (IR) and Raman measurements supported the above data.     

Optical absorption spectra of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

The optical absorption spectra of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ thin films have been studied. For higher photon energies, the absorption is found to be due to a direct forbidden electronic transition process from the oxygen 2p band to the vanadium 3d band in a similar way to that observed in crystalline V₂O₅. The exponential behaviour of absorption edge for lower photon energies is attributed to the electronic transitions between the tailed-off d-d states corresponding to V⁴⁺ ions. For co-evaporated V₂O₅/B₂O₃ films the optical energy gap is observed to increase with the increase in V₂O₅ content of the composite films.     

Infrared absorption spectra of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

The Fourier transform infrared spectra of different compositions of evaporated V₂O₅/B₂O₃ thin films have been investigated. Most of the absorption bands corresponding to V₂O₅ and B₂O₃ films coincide with those reported by other authors. The short-range order in amorphous V₂O₅ films is found to be conserved. The absorption spectra indicate a boroxol ring structure for B₂O₃ films. In co-evaporated V₂O₅/B₂O₃ films the boron is observed to substitute in the V₂O₅ network such that the coordination number of vanadium ion remains unchanged. The presence of a number of bands corresponding to -OH groups indicates the hygroscopic character of the films.     

Electron spin resonance studies of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

Electron spin resonance studies of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ amorphous thin films have been made. For lower molar contents of B₂O₃, the co-evaporated V₂O₅/B₂O₃ films show poorly resolved hyperfine structure, whereas for higher content of B₂O₃ the hyperfine spectra are well resolved. This behaviour of films is attributed to the increase in the lifetime of a particular V⁴⁺ ion due to Anderson localization of charge, as the degree of disorder increases with increase in the molar content of B₂O₃. The unpaired electron at a given time is localized on a single ⁵¹V nucleus. The low intensity of ESR signal for higher concentration of V₂O₅ in the co-evaporated V₂O₅/B₂O₃ films has been related to the less effective concentration of V⁴⁺ ions due to antiferromagnetic coupling of the V⁴⁺ ions.     

Electrical conduction through MIM structures of evaporated V2O5 and V2O5/B2O3 amorphous thin films

The electrical conduction through vacuum-evaporated thin films of V₂O₅ and V₂O₅/B₂O₃ in MIM structures has been investigated. The high-field behaviour of both types of film is in accordance with the Poole-Frenkel type of mechanism. The increase in B₂O₃ content in co-evaporated V₂O₅/B₂03 films results in a decrease in the conductivity of the composite films. This is attributed to the expansion of the resultant film structure due to the network-forming effect of B₂O₃. The covaporated thin films of V₂O₅/B₂O₃ with a molar content of B₂O₃ larger than 40% are observed to be unstable because of their hygroscopic nature.     

X-ray photoelectron spectroscopic studies of evaporated V2O2and co-evaporated V2O5/B2O3 films

X-ray photoelectron spectra of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ thin films have been investigated. The photoelectron spectrum of a simple V₂O₅ film shows the splitting of the V 2p level in accordance with the spins. The values of binding energies corresponding to V 2p and O1s are comparable with those reported previously. For co-evaporated V₂O₅/B₂O₃ films a chemical shift in the O 1s level has been observed which has been attributed to the changed chemical environment of oxygen as a result of the presence of boron and vanadium atoms. The values of binding energies for V 2p_3/2 and O 1s corresponding to simple evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ show the presence of V₂O₄ species in the films.     

Optical absorption in co-evaporated V2O5-TeO2 thin films

The electron diffraction pattern shows that co-evaporated V₂O₅-TeO₂ thin film samples are amorphous at room temperature and become polycrystalline at temperatures higher than about 513 K. This behaviour is similar to that of amorphous V₂O₅ thin films. The optical absorption edge of amorphous thin films of V₂O₅-TeO₂ is studied in the wavelength range 200 to 900 nm and the FTIR spectra are studied in the wave number range 400 to 4000 cm^–1. The FTIR spectra of amorphous V₂O₅ thin film are found to be similar to those of amorphous V₂O₅-TeO₂ thin films. This suggests that the coordination number of the vanadium ion in V₂O₅-TeO₂ is the same as that in crystalline V₂O₅, and thus the optical absorption edge of amorphous V₂O₅-TeO₂ thin films can be described by direct forbidden transitions.     

Studies on the RF sputtered amorphous SiGe thin films

In this study, rf sputtered hydrogenated amorphous silicon-germanium thin films deposited at room temperature have been investigated by spectroscopic ellipsometry and Rutherford backscattering. Technological parameters were determined for good layer quality of amorphous material. The layer thicknesses were first evaluated from the Rutherford backscattering and spectroscopic ellipsometry measurements, then measured directly by step-profiler, and compared to each other. The inherence of technological parameters and composition of the layers is discussed. The text was submitted by the authors in English.     

Ta additive effect on RF magnetron sputtered CoCr films

Magnetic properties for sputtered CoCrTa films (18 at.% Cr and 2.0-3.0 at.% Ta), which were deposited under various background pressures P_i, and argon sputtering pressures, P _Ar, have been examined. The perpendicular anisotropy field H_k for CoCrTa films maintains high values of 5-6 kOe in a wide range of P_i and P_Ar , as compared with that for CoCr films. In order to optimize Ta composition, magnetic properties and crystalline microstructures for Ta additive content (0-4.0 at.%) have been investigated. H_k and perpendicular coercivity H_c⊥ increase with increasing Ta concentration above 2.0 at.% Ta. C-axis orientation is improved by adding Ta to CoCr films. However, above 3.0 at.% Ta, H_c⊥ steeply decreases and domain wall motion is observed, owing to the increase in crystalline grain size. The appropriate Ta composition is 2.0-3.0 at.%     

RF sputtered ZnO-ITO films for high temperature CO sensors

In this work is reported the development of ceramic sensors based on ZnO-doped ITO thin films for engine diagnostics able to withstand the harsh environments associated with exhausts. ZnO-ITO films were deposited by RF-sputtering and have been employed in the development of thin films-based carbon monoxide resistive sensors operating at high temperature (500 °C). ZnO-ITO films, with different Zn/In ratio and thickness around 3 µm., have been deposited by changing the power on the targets. The effects of both the working temperature and the ZnO loading on the sensors performances were investigated. Undoped ITO film has shown negligible response to CO, whereas ZnO-ITO films were found to be sensitive at the required working temperatures. The reported results show how the ZnO-ITO devices under study can be promising sensors for CO monitoring in real exhausts of car engines.     

In-plane magnetic anisotropy in RF sputtered Fe---N thin films

We have fabricated Fe(N) thin films with varied N₂ partial pressure and studied the microstructure, morphology, magnetic properties and resistivity by using X-ray diffraction, atomic force microscopy, transmission electron microscopy, vibrating-sample magnetometer and angle-resolved M-H hysteresis Loop tracer and standard four-point probe method. In the presence of low N₂ partial pressure, Fe(N) films showed a basic bcc -Fe structure with a preferred (110) texture. A variation of in-plane magnetic anisotropy of the Fe(N) films was observed with the changing of N component. The evolution of in-plane anisotropy in the films was attributed to the directional order mechanism. Nitrogen atoms play an important role in refining the -Fe grains and inducing uniaxial anisotropy.     

Two methods of obtaining sol–gel Nb2O5 thin films for electrochromic devices

Nb2O5 coatings prepared by the sol–gel route using the dip coating technique with sols prepared from alkoxide or chloroalkoxide (two different methods: sonocatalytic and conventional) precursors are a promising alternative for WO3 electrochromic coatings. The crystalline films (TT phase) sintered at 560 and 600°C are transparent and present a deep blue colour under Li+ ion insertion. Electrochemical stability is excellent as these systems are fully reversible and stable and no change in colour, amount of charge exchanged and corrosion effect could be observed after 2000 voltammetry cycles between 2 and –1.8 V versus Ag. The electrochemical and optical properties of these coatings have been determined as a function of sintering temperature. The superficial structure was visualized by atomic force microscopy (AFM) and scanning electron microscopy (SEM) and the Li+ diffusion coefficient was determined for both kinds of coatings. © 1998 Chapman & Hall     

RF susceptibility of magnetron sputtered YBa[]Cu[]O[]−x films

We measured the complex susceptibility of two different quality magnetron sputtered YBa₂Cu₃O_7−x films in RF range. Temperature and static magnetic field dependence of complex magnetic susceptibility is a useful indicator of appearance of phase coherence in the film including fluctuation region above T_c. The characteristics showed a low frequency type behaviour at loss peak and diamagnetic drop at near transition temperature and normal state non-zero susceptibility. One of our samples displayed an enhanced diamagnetism in the normal state close to T_c, which was probably attributed to the combination of the normal skin effect and excess conductivity due to superconductive fluctuations. The low temperature susceptibility was also frequency dependent and qualitatively agreed with the vortex-glass scaling model.     

A.c. conduction through MIM sandwich samples of evaporated thin films of V2O5 and V2O5/B2O3

The a.c. electrical properties of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ films have been investigated. The conductivity in both types of film follows the theory of Elliott for single polaron hopping. The behaviour of capacitance, tangent of loss angle and dielectric loss agrees with the model proposed by Goswami and Goswami. The co-evaporated films of V₂O₅/B₂O₃ show better dielectric properties than simple V₂O₅ with increasing content of B₂O₃. Because of their hygroscopic character, the films with B₂O₃ content larger than 40% are observed to be unstable in the atmosphere.     

氧分压对反应磁控溅射ZrO2薄膜光学透射率的影响

从氧空位、表面粗糙度及晶界三方面,讨论了氧分压对射频反应磁控溅射ZrO2薄膜光学透射率的影响.结果表明,随氧分压增大,氧空位的减少使单斜相逐渐占优,缺氧状况的改善使薄膜透射率逐渐升高;高氧分压下,出现颗粒聚集现象,表面粗糙度大幅增加及晶粒的聚集长大,使薄膜透射率下降.