Chemical bath deposition of textured ZnO thin films in aqueous/ethanolic solution

ZnO thin films have been prepared by chemical bath deposition in aqueous/ethanolic solution. The film texture was successfully controlled by varying the volume ratio of water to ethanol. Films consisting of densely oriented nanorod arrays with the c-axis perpendicular to the substrate were fabricated in aqueous solution. The crystals became increasingly tilted as more ethanol was introduced to the solution, resulting in the cracked nanocolumns and the smoothed crystals. The crystal size was decreased with increasing ethanol content, and granular morphology was obtained in films deposited in ethanolic solution. A gradual evolution of the film texture is possibly due to the inhibited crystal growth in solution with higher ethanol content.     

Sputter deposition of NiTi thin film shape memory alloy using a heated target

In this paper we present a novel method for depositing NiTi thin film by DC sputtering. The film has transformation temperatures very close to that of the target. The new process involves heating the target and does not require compositional modification of the NiTi target. Results from X-ray diffraction, differential scanning calorimeter, four-point probe, Rutherford backscattering, and transmission electron microscopy are presented. These results indicate that compositional modification can be produced by varying the target temperature. Films produced from hot targets have compositions similar to the target while films produced from cold targets were Ti deficient. Films that were produced by gradual heating of the target have compositional gradation through the film thickness. The gradated films exhibit the two-way shape memory effect.     

Nanostructured nickel oxide films prepared by chemical vapor deposition and their electrochromic properties

The influence of the deposition conditions on the structural features and electrochromic properties of nickel oxide (NiO) films prepared by chemical vapor deposition has been investigated. NiO films have been prepared on fluorine doped tin oxide (FTO) coated glass substrates from nickel-acetylacetonate precursor and their electrochromic properties have been studied by cyclic voltammetry in a 0.1 M KOH solution at room temperature. Films exhibiting only the NiO phase were obtained at deposition temperatures higher than 450 degrees C in a wide range of reactor pressures (0.13 to 66.6 kPa). Particularly, NiO films prepared at 500-550 degrees C from 0.13 to 53.3 kPa are transparent in nature and exhibit a crystallite size varying from 10 to 60 nm. An appreciable anodic electrochromic change from transparent to black coloured resulted from a very porous surface morphology and film thickness of about 3.5 microm. The electrochromic change was maintained over 3000 switching cycles. Nanostructured 3.5 microm-thick NiO films showed a maximum difference in optical transmittance of about 40% in the near-infrared region. These results make the nanostructured NiO films comparables with those prepared by other deposition techniques.     

Chemical bath deposition of indium sulphide thin films: preparation and characterization

Indium sulphide (In₂S₃) thin films have been successfully deposited on different substrates under varying deposition conditions using chemical bath deposition technique. The deposition mechanism of In₂S₃ thin films from thioacetamide deposition bath has been proposed. Films have been characterized with respect to their crystalline structure, composition, optical and electrical properties by means of X-ray diffraction, TEM, EDAX, optical absorption, TRMC (time resolved microwave conductivity) and RBS. Films on glass substrates were amorphous and on FTO (flourine doped tin oxide coated) glass substrates were polycrystalline ( phase). The optical band gap of In₂S₃ thin film was estimated to be 2.75 eV. The as-deposited films were photoactive as evidenced by TRMC studies. The presence of oxygen in the film was detected by RBS analysis.     

Self-healing and self-organized gold nanoparticle films at a water/organic solvent interface

Gold nanoparticles (5 nm and 20 nm) have been synthesized and stabilized with mercaptoundecanol. These particles, although insoluble in water or common organic solvents, spread as a thin film at the liquid-liquid interface between a water phase and an organic phase. Films of these gold nanoparticles have been observed both by conventional transmission electron microscopy of deposited samples and by cryo-transmission electron microscopy of plunge-frozen samples. The film can be monolayered and extend over centimeter-sized areas. The particle films spontaneously re-assemble and self-organize at the interface when disrupted. This self-healing capacity of the film should make it possible to build a device for continuous production and deposition of the film.     

Structural and compositional studies of magnetron-sputtered Nd–Fe–B thin films on Si(100)

The structure and composition of the Nd–Fe–B thin films deposited on Si(100) have been investigated. Films have been prepared by direct-current magnetron sputtering in pure argon and xenon sputter media separately. Deposition has been carried out keeping the substrates at room temperature and 360°C. These films were subjected to the post-deposition annealing to a temperature of 60O°C in a vacuum of 5×10–7 Torr. The stoichiometry and structure of these films were analysed and correlated to the deposition and annealing conditions. Films deposited in xenon sputter medium showed better crystalline properties than those sputtered in pure argon. This difference was attributed to the presence of reflected high-energy neutral gas particles in the argon medium. Films deposited in xenon were found to be relatively rich in boron compared with argon-sputtered films. Post-deposition annealing resulted in the interdiffusion at the interface between the film and substrate. The use of a SiO2 film as a barrier layer between the silicon substrate and the Nd–Fe–B film has been explored. Thermally grown SiO2 was found to be an effective diffusion barrier. © 1998 Chapman & Hall     

Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films

The effects of residual water on the phase formation, composition, and microstructure evolution of magnetron sputter deposited crystalline alumina thin films have been investigated. To mimic different vacuum conditions, depositions have been carried out with varying partial pressures of H₂O. Films have been grown both with and without chromia nucleation layers. It is shown that films deposited onto chromia nucleation layers at relatively low temperatures (500 °C) consist of crystalline α-alumina if deposited at a low enough total pressure under ultra high vacuum (UHV) conditions. However, as water was introduced a gradual increase of the γ phase content in the film with increasing film thickness was observed. At the same time, the microstructure changed drastically from a dense columnar structure to a structure with small, equiaxed grains. Based on mass spectrometry measurements and previous ab initio calculations, we suggest that either bombardment of energetic negative (or later neutralized) species being accelerated over the target sheath voltage, adsorbed hydrogen on growth surfaces, or a combination of these effects, is responsible for the change in structure. For films containing the metastable γ phase under UHV conditions, no influence of residual water on the phase content was observed. The amounts of hydrogen incorporated into the films, as determined by elastic recoil detection analysis, were shown to be low. Overall, the results demonstrate that residual water present during film growth drastically affects film properties, also in cases where the hydrogen incorporation is found to be low.     

Structural analysis of porphyrin multilayer films on ITO assembled using copper(I)-catalyzed azide-alkyne cycloaddition by ATR IR

We report the use of grazing-angle attenuated total reflectance (GATR) IR and polarized UV-vis to determine the molecular structure of porphyrin based molecular multilayer films grown in a layer-by-layer (LbL) fashion using copper-catalyzed azide-alkyne cycloaddition (CuAAC). The molecular orientation and bonding motif present in multilayer films of this type could impact their photophysical and electrochemical properties as well as potential applications. Multilayer films of M(II) 5,10,15,20-tetra(4-ethynylphenyl)porphyrin (1 M = Zn, 2 M = Cu) and azido based linkers 3-5 were used to fabricate the films on ITO substrates. Electrochemically determined coverage of films containing 2 match the trends observed in the absorbance. GATR-IR spectral analysis of the films indicate that CuAAC reactivity is leading to 1,4-triazole linked multilayers with increasing porphyrin and linker IR characteristic peaks. Films grown using all azido-linkers (3-5) display an oscillating trend in azide IR intensity suggesting that the surface bound azido group reacts with 1 and that further layering can occur through additional reaction with linkers, regenerating the azide surface. Films containing linker 5 in particular show an overall increase in azide content suggesting that only two of the three available groups react during multilayer fabrication, causing an overall buildup of azide content in the film. Films of 1 with linker 3 and 5 showed an average porphyrin plane angle of 46.4° with respect to the substrate as determined by GATR FT-IR. Polarized UV-vis absorbance measurements correlate well with the growth angle calculated by IR. The orientation of the porphyrin plane within the multilayer structures suggests that the CuAAC-LbL process results in a film with a trans bonding motif.     

金刚石膜技术研究开发进展——专利文献分析

金刚石膜具有特别优异的性能,在高技术领域有着极为广泛的应用。本文采集1985年到2008年6月世界金刚石膜技术专利文献,并对其发展脉络和竞争格局进行定量和定性分析,揭示出国际上金刚石膜技术已处于较成熟阶段,工具级、热沉级金刚石膜产品已进入实用阶段,光学级和器件级金刚石膜技术尚未成熟;美国、日本技术实力占优势;德国、美国、日本市场被看好;不同应用领域竞争态势差异很大;通过引证分析得出了相关领域的核心的基础专利。     

Perpendicular magnetization in self-assembled films of citrate-capped gamma-Fe2O3 nanocrystals on Si(100) surfaces

gamma-Fe2O3 nanocrystals capped with citrate and octylamine have been chemically prepared. The octylamine-capped nanocrystals exhibit a tendency to form ordered lattices. Films of nanocrystals of varying thickness (454, 720, and 1400 microg/cm2 in the case of citrate-capped nanocrystals and 300 microg/cm2 in the case of octylamine-capped nanocrystals) have been prepared on Si(100) substrates by drop casting and have been characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. Magnetic measurements have been carried out on the films as well as on nanocrystal powders. The films of citrate-capped gamma-Fe2O3 nanocrystals exhibit enhanced perpendicular magnetization, with the anisotropy depending on the film thickness.     

Influence of calcination ambient and film thickness on the optical and structural properties of sol-gel TiO2 thin films

Influence of both calcination ambient and film thickness on the optical and structural properties of sol-gel derived TiO₂ thin films have been studied. X-ray diffraction results show that prepared films are in an anatase form of TiO₂. Films calcined in argon or in low vacuum (∼2 × 10⁻¹ mbar) are found to be smaller in crystallite size, more transparent at low wavelength region of ∼300-450 nm, denser, have higher refractive index and band gap energy compared to air-calcined films. Scanning electron microscopic study reveals that surfaces of TiO₂ films calcined in argon or in low vacuum are formed by densely packed nano-sized particulates. Presence of voids and signs of agglomeration can be seen clearly in the surface microstructure of air-calcined films. In the thickness range ∼200-300 nm, band gap energy and crystallite size of TiO₂ films remain practically unaffected with film thickness but refractive index of thinner film is found to be marginally higher than that of thicker film. In this work, it has been shown that apart from temperature and soaking time, partial pressure of oxygen of the ambient is also an important parameter by which crystallite size, microstructure and optical properties of the TiO₂ films may be tailored during calcination period.     

Structural phototransformations in thin selenium films

Light-induced changes in thin amorphous selenium films deposited by pulsed laser evaporation were investigated. Films under 300 nm thick were found to undergo a photocoagulation process in which smooth continuous areas became mottled and discontinuous after exposure for about 10 min to white light at 10 mW cm^-2. Thicker films, if exposed for 10 h or more, formed micron-scale crystallites by a mechanism previously described by Dresner and Stringfellow. The likely mechanism for the photocoagulation process involves the light-induced relaxation of a metastable void-filled short-chain selenium film into a denser equilibrated film which does not readily wet glass or silicon. Both photocoagulation and photocrystallization processes were used to produce patterns on selenium-coated substrates; the effect of varying film thickness and exposure time on the pattern contrast ratio was studied.     

Preparation of MgF2-SiO2 thin films with a low refractive index by a solgel process

Porous MgF(2)-SiO(2) thin films consisting of MgF(2) particles connected by an amorphous SiO(2) binder are prepared by a solgel process. The films have a low refractive index of 1.26, sufficient strength to withstand wiping by a cloth, and a high environmental resistance. The refractive index of the film can be controlled by changing the processing conditions. Films can be uniformly formed on curved substrates and at relatively low temperatures, such as 100 degrees C. The low refractive index of the film, which cannot be achieved by conventional dry processes, is effective in improving the performance of antireflective coatings.     

Crystalline structure of germanium films on silicon substrates: I. Investigation of the perfection of germanium heteroepitaxial films on silicon by X-ray diffraction methods

The purpose of this paper is to describe an investigation of the structural perfection of heteroepitaxial Ge films on silicon by different X-ray diffraction methods. Quantitative information about the degree of structural perfection of the films has been obtained by X-ray intensity jumps measured near the K-edge absorption of germanium and by rocking curves. Structural damage in the films and substrates has been studied by X-ray topographical methods. The possibility of obtaining independent film and substrate topograms has been shown. Elastic strains arising during the film growth lead to film and substrate fragmentation. Films and substrates have the same configuration and sizes of fragments. A new X-ray method for the heteroepitaxial films thickness measurement has been proposed.     

Structural, Optical and Electrical Properties of Evaporated CdSe Films

CdSe films are of great interest for use in thin film photoelectric devices. A simple chemical precipitation method is adopted for the first time to synthesise CdSe powder. Films on glass obtained at different substrate temperatures TS such as 300, 373, 423 and 473 K have been characterised by X-ray diffraction, optical absorption and Hall measurements.     

Film morphology modification in ion-assisted glancing angle deposition

Porous structured films grown with the glancing angle deposition technique have been widely studied for thin film optical device applications. We report the use of ion assistance to modify the structural and optical properties of porous silicon dioxide and titanium dioxide columnar thin films grown at deposition angles of 70° and 85°. Optical characterization studies show that tilted columnar structures will undergo an increase in tilt angle and film density with increasing ion dose. These two trends contrast with unassisted films where film density and column tilt angle are primarily controlled by the deposition angle. Thus, a regime of film structures simultaneously exhibiting high film density and large column tilt angle is enabled by incorporating an ion-assisted process. The phisweep substrate motion algorithm for minimizing columnar anisotropy used in conjunction with ion-assisted deposition provides additional control over film morphology and expands the utility of this modified fabrication process.     

Growth mechanism investigation of SnO2 thin films deposited by aerosol pyrolysis for biosensor applications: Importance of the thickness

Transparent conductive oxide films are suitable sensitive layers for gas sensors and biosensors, provided that their intrinsic properties are controlled, notably considering their thickness dependence. The present paper reports on a study of the variation of some physical properties of polycrystalline Sb doped SnO₂ films according to the film thickness. Films were deposited onto Si and glass substrates by aerosol pyrolysis. Their thickness was varied in a range of 20-280 nm. The electrical resistivity, the roughness, the optical constant, the microstructure and the texture were investigated. Correlated evolutions of the resistivity and the surface roughness are found in relation with the evolutions of both the microstructure and the texture. Two main successive growth steps were evidenced which are delimited by a critical film thickness. Below this thickness of approximately 100-120 nm, a strong dependence of physical properties with the thickness is evidenced whereas for thicker films no significant change is evidenced. A two-step growth model is proposed to explain this behaviour. This mechanism growth is to be considered in view of the integration of SnO₂ films as sensitive layers in biosensors. Notably, in the case of biosensors based on the label-free electrochemical detection of biomolecules, it is recommended to use films with thicknesses ranging above the critical thickness value of 100-120 nm in order to obtain optimized, reproducible and comparable responses of biosensors.     

A comparison of TiN films produced by reactive d.c. sputtering and ion-assisted deposition

The properties of TiN films produced by reactive d.c. sputtering have been compared with those formed by deposition during irradiation by 10 keV nitrogen ions. Films were deposited on aluminium, nickel, molybdenum, silicon and titanium substrates which were chosen because they have a range of mechanical properties. The composition of the films has been studied by Rutherford backscattering, nuclear reaction analysis and transmission electron microscopy and data concerning their hardness and adhesion are also presented. It was found that the films produced by ion-assisted deposition (IAD) were nearly stoichiometric TiN with a predominant (100) orientation while the reactively sputtered films were less crystalline and contained a significant amount of oxygen and carbon throughout the film. There was also considerable improvement in the adhesion of the IAD films but their hardness was only marginally improved.     

Electrical conduction and transmission electron microscopy studies of CdSe0.8Te0.2 thin films

Electrical resistance of CdSe_0.8Te_0.2 thin films were found to be dependent on various film parameters such as substrate temperature, film thickness, deposition rate and post-deposition heat treatment in different environments. A decrease in film resistivity was observed for thicker films and for those heat treated in vacuum. Films deposited at higher substrate temperatures and faster rates showed an increase in film resistivity. A spectrum of activation energies was observed in the films which fell within either of the activation energies observed in CdSe or CdTe films. Films heated in an oxygen environment showed an increase in film resistivity with a different activation energy. Transmission electron microscopy (TEM) of the films showed an improvement in crystallinity with increasing film thickness and substrate temperature, and a reduction in crystallinity with increasing deposition rate.     

Effects of substrate temperature on the microstructure and photocatalytic reactivity of TiO2 films

Transmission electronic microscopy is used to study the structure, morphology and orientation of thin TiO2 films prepared by reactive magnetron sputtering on glass slides at different substrate temperatures (100 to 400 °C). The TiO2 films are used to purify a dye in waste water. The microstructure and photocatalytic reactivity of TiO2 films have been shown to be functions of deposition temperature. In the temperature range examined, all film samples have a porous nanostructure and the dimension of particles grown with increasing deposition temperature. Films are amorphous at temperatures of 100 °C and only anatase phase forms at 200 °C and above. Films deposited between 200 to 300 °C show a preferred orientation, while films at 400 °C change into complete random orientation. Deposition at 250 °C yields high efficiency in photocatalytic degradation owing to the high degree of preferred orientation and nanocrystalline/nanoporous anatase phase. © 1998 Kluwer Academic Publishers