A simple method for preparation of transparent hydrophobic silica-based coatings on different substrates

A facile, inexpensive, and general approach is explored for the fabrication of transparent silica/organic silicon hybrid sol, which could form transparent hydrophobic coatings on different substrates conveniently. The sol was prepared by using hexamethyldisilazane (HMDS) as a surface-modifying agent and the source of base catalyst required for the hydrolysis of tetraethoxysilane (TEOS). The resulting silica-based coatings on glass slide have shown an optical transmission over the visible range up to 89% (in reference to 100% transmission defined by a plain glass substrate) and high thermal stability. The water contact angle of the film reached 152^○. Hydrophobic coatings with excellent optical transmittance were also successfully formed on writing paper and aluminum foils. The transparent hydrophobic silica-based hybrid sol will have potential applications in creating outdoor building glass, protecting paper files from moisture and preventing metals from corrosion.     

Doped thin metal oxide films for catalytic gas sensors

TiO₂ and Pt doped TiO₂ thin films were grown by pulsed laser deposition on 〈0 0 1〉 SiO₂ substrates. The doped films were compared with undoped ones deposited in similar experimental conditions. An UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser was used for the irradiation of the TiO₂ or Pt doped TiO₂ targets. The substrate temperatures were fixed during the growth of the thin films at values within the 300-500 °C range. The films’ surface morphology was investigated by atomic force microscopy and their crystalline quality by X-ray diffractometry. The corresponding transmission spectra were recorded with the aid of a double beam spectrophotometer in the spectral range of 400-1100 nm. No contaminants or Pt segregation were detected in the synthesized anatase phase TiO₂ thin films composition. Titania crystallites growth inhibition was observed with the increase of the dopant concentration. The average optical transmittance in the visible-infrared spectral range of the films is higher than 85%, which makes them suitable for sensor applications.     

A new method for the determination of the thickness and the refractive index of thin dielectric films evaporated on metal substrates

A new ellipsometrical method for the accurate determination of the thickness and the refractive index and hence the dispersion for thin transparent films evaporated on metal substrates is put forward. Results for zinc sulphide thin films evaporated in vacuum, 10⁻⁵ mm Hg, on antimony are reported.     

Temperature coefficient of resistance of thin metal films on ceramic surfaces

The temperature coefficients (TCR) of vacuum-deposited thin-metal-film resistors were measured in vacuum, air, argon, and silicone oil, and different characteristics were obtained. The resistors were made by evaporating a nickel-chrome alloy (Nichrome 80 to 20) in vacuum onto ceramic substrates to produce a 500-ohms-persquare film. Measurements were made of films which were uncoated and of films which were coated with a protection layer of silicone monoxide in thicknesses from 5000 to 10000 å. When measured under vacuum, the resistors displayed a TCR which was lower than that obtained in air, argon, or silicone oil. In an argon environment, the resistors had lower TCR characteristics than they had in air or silicone oil. Even when the resistor films were protected by a 10000-å-thick layer of silicone monoxide, their TCR behavior differed in different gas environments. Most of the TCR's measured in the temperature range from ?55Ω to +150Ω C were between 5 and 50 parts per million per degree centigrade.     

Growth of thin, crystalline oxide, nitride and oxynitride films on metal and metal alloy surfaces

This paper reviews the current knowledge of the properties of ultrathin, well-ordered oxide, nitride and oxynitride films grown on metal and metal alloy surfaces. Different modes of preparation are discussed and the vibrational and structural properties are summarized. The focus will be put onto Al-oxides grown on surfaces of the intermetallic alloys NiAl, Ni₃Al and FeAl. The properties of Ga₂O₃ grown on surfaces of the intermetallic alloy CoGa are also described. In these cases Al- and Ga-atoms, respectively, segregate from the substrate and react with adsorbed oxygen. The grown Al- and Ga-oxide films, respectively, order at elevated temperatures. Systems are also discussed where Al-oxide is grown by oxidation of Al-atoms which are evaporated on surfaces of the transition metals Re and Ru. The growth of transition metal oxides CoO (1 1 1)/Co (0 0 0 1), CoO (1 0 0)/Co (1 1 2 0), NiO (1 0 0)/Ni (1 0 0), NiO/Ni (1 1 1) and Cr₂O₃/Cr (1 1 0) are also presented. Thin films of Al- and Ga-nitride, respectively, can be grown on the base of the intermetallic alloy NiAl and CoGa by low-temperature adsorption of ammonia. These nitride films order at elevated temperatures. Al- and Ga-oxynitride, respectively, can be grown on surfaces of NiAl and CoGa substrates by adsorption on nitric oxide. An ordering of these ultrathin oxynitride layers is observed at elevated temperatures.     

Theoretical analysis of the growth mode for thin metallic films on oxide substrates

We show how the growth mode of a thin metallic film on an insulating substrate can be predicted theoretically by combining thermodynamic considerations with ab initio calculations for ordered metal/insulator interfaces at low coverage. Our approach is illustrated by calculations for Ag film deposited on an MgO substrate. Ab initio calculations predict high mobility of adsorbed Ag atoms on MgO, even at low temperatures, which greatly aids their aggregation.     

Quantum size effects in metal thin films grown on quasicrystalline substrates

We have investigated by scanning tunneling microscopy the growth of Bi and Ag thin films on the fivefold surface of Al63Cu24Fe13 and Al72Pd19.5Mn8.5 quasicrystal, respectively. For both systems, we observe the formation of islands with magic height, corresponding to the stacking of a specific number of atomic layers. We interpret this unusual growth morphology in terms of quantum size effects, arising from the confinement of the electron within the film. The magic island heights are thus a direct manifestation of the electronic structure of the quasicrystalline substrates.     

Development of porous metal oxide thin films by co-evaporation

This paper focuses on the development of mixed metal oxide thin films and physical characterization of the films. The films were produced by co-evaporation of titanium oxide and tungsten oxide powders. This allowed the development of titanium oxide-tungsten oxide films as analyzed using XPS. Examination in the SEM and AFM showed that the films were nanoporous with the pore size and pore orientation varying as a function of the deposition angle. UV-vis spectra of the films show an increase of transmittance with increasing deposition angle which is attributed to the structure and porosity of the films. Raman analysis indicated that the as-deposited films have broad and weak Raman characteristics, attributed to the nanocrystal nature of the films and the presence of defects, and the peak broadening deceases after annealing the film, as expected.     

Quantitative analysis of multi-element oxide thin films by angle-resolved XPS: Application to ultra-thin oxide films on MgAl substrates

An original procedure has been developed for the quantitative analysis and microstructural interpretation of angle-resolved X-ray photoelectron spectra (AR-XPS) of very thin (<6 nm), multi-element oxide films as grown on metallic binary alloy substrates by, e.g., thermal or plasma oxidation. To this end, first an approach has been given to retrieve the different metallic, oxidic and oxygen primary zero-loss (PZL) intensities from the measured AR-XPS spectra of the bare and oxidized alloy. The principal equations for the determination of the oxide-film thickness, composition and constitution from the resolved PZL intensities have been presented. On this basis, various corresponding calculation routes have been distinguished. The procedure has been applied to the case of very thin (<6 nm), mixed (Mg, Al)-oxide films on bare Mg-based MgAl substrates as grown by dry, thermal oxidation at room temperature. The results obtained on the thickness, composition, defect structure and constitution of the oxide-film have been discussed as function of the bulk Al alloying content and the applied partial pressure of oxygen.     

Synthesis and microstructure of metal oxide thin films containing metal nanoparticles by liquid phase deposition (LPD) method

Au nanoparticles dispersed SiO₂-TiO₂ composite films have been prepared by a novel wet process, Liquid Phase Deposition (LPD) method. The composite films were characterized by XRD, XPS, TEM, ICP, SEM and UV-VIS absorption spectroscopy. The results showed that the SiO₂-TiO₂ composite films containing Au^III and Au^I ionic species were co-deposited from a mixed solution of ammonium silicofluoride, ammonium hexafluorotitanate, boric acid and tetrachloroauric acid. The heat treatment induced the reduction of Au ions and formation of Au nanoparticles in the film. TEM observation revealed that the Au nanoparticles with 5-10 nm in diameter were found to be dispersed uniformly in the SiO₂-TiO₂ matrix. The optical absorption band due to the surface plasmon resonance of dispersed Au particles were observed at the wavelength of 550 nm and shifted toward longer wavelength with increasing heat treatment temperature. Received 28 November 2000     

硅基二氧化钒相变薄膜电学特性研究

本文以原子层沉积超薄氧化铝(Al₂ O₃)为过渡层, 采用射频反应磁控溅射法在硅半导体基片上制备了颗粒致密并具有(011)择优取向的二氧化钒(VO₂)薄膜. 该薄膜具有显著的绝缘体–金属相变特性, 相变电阻变化超过3 个数量级, 热滞回线宽度约为6℃. 基于VO₂薄膜构建了平面二端器件并测试了不同温度下I-V曲线, 观测到超过2个数量级的电流跃迁幅度, 显示了优越的电致相变特性. 室温下电致相变阈值电压为8.6 V, 电致相变弛豫电压宽度约0.1 V. 随着温度升高到60℃, 其电致相变所需要的阈值电压减小到2.7 V. 本实验制备的VO₂薄膜在光电存储、开关、太赫兹调控器件中具有广泛的应用价值.     

Angle-dependent THz tomography – characterization of thin ceramic oxide films for fuel cell applications

A time-resolved THz tomography system for the incidence-angle-dependent three-dimensional characterization of layered structures is presented. The capabilities of the developed system are demonstrated on multi-layer ceramic samples used for solid oxide fuel cells (SOFC). Appropriate methods for determining unknown refractive indices are discussed. It is shown how the angle of incidence of a THz imaging system has a significant influence on measured signals. This fact can be exploited especially in Brewster-angle configurations to enhance the capabilities of any THz tomography system. Data evaluation algorithms are presented. Received: 8 June 2000 / Revised version: 13 September 2000 / Published online: 10 January 2001     

High refractive index and transparent heavy metal oxide glassy thin films

Heavy metal oxide thin films of the ternary system Nb₂O₅–GeO₂–PbO have been prepared by pulsed laser deposition in an O₂ environment from either glassy or crystalline bulk samples. The range of ([Pb]+[Nb]) content in which the films are optically homogeneous and transparent is much broader (0.5–1.0) than that of the bulk samples considered in the present work (0.55–0.62). The imaginary part of the refractive index is very low in all cases (k<10^-3), whereas the real part increases linearly with the ([Pb]+[Nb]) content up to values as high as 2.35. The optical energy gap has been found to be strongly dependent on [Pb], whereas it is almost independent of [Nb]. This dependence is discussed in terms of the role of Pb and Nb as network modifiers or formers. Received: 5 August 2002 / Accepted: 8 August 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +34-91/564-5557, E-mail: j.gonzalo@io.cfmac.csic.es     

Interface effects for metal oxide thin films deposited on another metal oxide I. SnO deposited on SiO2

The growing mode of SnO overlayers deposited on SiO₂ has been studied by ISS and XPS. This study has shown that SnO spreads on the surface of SiO₂. The oxidation state of tin under different experimental conditions of preparation has been characterized by XPS and ELS and a procedure has been found to produce pure SnO. For comparison, SnO has been evaporated on highly oriented pyrolytic graphite (HOPG). In this case, independent of the deposited amount of SnO, XPS and ELS did not show any significant difference in the photoemission and loss features of this material as a function of coverage (i.e. there are no size effects). On the contrary, at low coverages of SnO deposited on SiO₂ XPS showed a shift of 1 eV in the BE of the Sn 3d_5/2 peak another of 1.7 eV in the values of the Auger parameter with respect to the values found for the bulk material. These shifts, very common on deposited metal particles, have been previously reported by us for TiO₂/SiO₂, and are tentatively attributed to t of the interaction of small deposits of SnO with the surface of SiO₂. The characterization by ELS and valence band photoemission of SnO completes the set of results reported in this paper.     

Thermal oxidation-grown vanadium dioxide thin films on FTO (Fluorine-doped tin oxide) substrates

By deposition of metallic vanadium on FTO substrate in Argon atmosphere at room temperature, the sample was then annealed in furnace for 2 h at the temperature of 410 °C in air ambient. (1 1 0) -orientated vanadium dioxide films were prepared on the FTO surface. A maximum transmittance of ∼40% happened at 900–1250 nm region at room temperature. The change of optical transmittance at this region was ∼25% between semiconducting and metallic states. In particular, vanadium dioxide thin films on FTO exhibit semiconductor–metal phase transition at ∼51 °C, the width of the hysteresis loop is ∼8 °C.     

Properties of Eu-doped zinc oxide thin films grown on glass substrates by radio-frequency magnetron sputtering

Eu-doped ZnO (EZO) thin films were prepared on glass substrates at various growth temperatures by radio-frequency magnetron sputtering. The properties of deposited thin films showed a significant dependence on the growth temperature. The preferential growth orientation of all the thin films was occurred along the ZnO (002) plane. The maximum crystallite size and the minimum average transmittance in the wavelength range of 450–1100 nm were observed for the EZO thin film deposited at 25 °C. A red shift of the optical band gap was observed in the growth temperature range of 25–300 °C. The highest figure of merit, an index for evaluating the performance of transparent conducting thin films, was obtained at 200 °C of growth temperature. These results indicated that the high-quality EZO film was obtained at a growth temperature of 200 °C.     

Luminescent materials based on thin metal oxide films doped with rare earth ions

Luminescent films of TiO₂: Sm were prepared by the sol-gel method using the spray pyrolysis technique. Various techniques (including IR absorption, Raman, AFM, XPS, photoluminescence) were used to characterize the samples. After a thermal treatment up to 750°C, intense Sm³⁺ luminescence with a well-resolved fine structure was observed under optical excitation within the fundamental absorption band of the TiO₂ host. After further thermal treatments up to 950°C, the luminescence was quenched, although no anataseto-rutile phase transformation was observed. This behavior is attributed to nanocrystallinity and segregation of Sm ions in the surface layer. The text was submitted by the authors in English.     

Influence of preparation conditions on the dispersion parameters of sprayed iron oxide thin films

Iron oxide thin films were prepared by spray pyrolysis technique (SPT) at various substrate temperatures (T_sub) and different deposition time. X-ray diffraction (XRD) analysis showed that, at T_sub ≥ 350 °C, a single phase of α-Fe₂O₃ film is formed which has the rhombohedral structure. Moreover, the crystallinity was improved by increasing T_sub. The effect of T_sub as well as deposition time on the optical dispersion of these films has been investigated. The optical transmittance and reflectance measurements were performed by using spectrophotometer in the wavelength range from 300 to 2500 nm. The refractive index was determined by using Murmann's exact equation. It was observed that, the refractive index increased with increasing in both the T_sub and film thickness. The optical dispersion parameters have been evaluated and analyzed by using Wemple-Didomenico equation. The obtained results showed that, the dielectric properties have weak dependencies of growth temperature and film thickness. At T_sub ≥ 350 °C, the average values of oscillator energy, E_o and dispersion energy, E_d were found to be 5.96 and 34.08 eV. While at different thickness, the average values of dispersion energies were found to be 3.93 and 17.08 eV. Also, the average values of oscillator strength S_o and single resonant frequency ω_o were estimated 10.78 × 10¹³ m⁻² and 5.99 × 10¹⁵ Hz, while at different thickness were evaluating 4.81 × 10¹³ m⁻² and 6.11 × 10¹⁵ Hz. Furthermore, the optical parameters such as wavelength of single oscillator λ_o, plasma frequency ω_p, and dielectric constant ? have been evaluated. The carrier concentration N_opt by using Drud's theory was obtained the range of 5.07 × 10²⁵ m⁻³ to 1.04 × 10²⁶ m⁻³.     

Stresses and deformation processes in thin films on substrates

The stresses that develop in thin films on substrates can be detrimental to the reliability of thin film electronic devices. In order to design these devices for improved mechanical reliability, an understanding of the origin of these stresses and the controlling deformation processes in thin films is needed. This review begins with a discussion of the basic techniques used for measuring stresses in thin films and for studying the mechanical properties of thin films. The proposed models for the origin of stresses in thin films are then reviewed. Finally, the effects of microstructure and substrate constraint on thin film deformation processes are discussed.