Nanostructured ZnO network films deposited on Al2O3 substrates by chemical bath deposition

Nanostructured ZnO network films have been fabricated on Al₂O₃ substrates by the combination of chemical bath deposition and thermal decomposition process. Layered basic zinc nitrate (LBZN) network films were deposited on the Al₂O₃ substrates with LBZN crystal seeds in methanol solution of zinc nitrate hexahydrate and hexamethylenetetramine. The LBZN precursor films were then transformed into nanostructured ZnO films by heating at 260 °C in air. During the thermal decomposition process abnormal exothermic heat effect was observed at 200-210 °C and CH₃ groups were found in the as-deposited films. We propose that methanol molecules are integrated in the LBZN films forming LBZN-CH₃OH complex and that the heat effect comes from the exothermic release of the methanol.     

Optical and structural characteristics of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films synthesized from yttrium acetylacetonate

Yttrium oxide thin films are deposited on silicon substrates using the ultrasonic spray pyrolysis technique from the thermal decomposition of a β-diketonate, yttrium acetylacetonate (Y(acac)₃). The decomposition of Y(acac)₃ was studied by thermogravimetry, differential scanning calorimetry, mass spectrometry, and infrared spectroscopy. It was found that a β-diketone ligand is lost during the initial steps of decomposition of the Y(acac)₃. The rest of the complex is then dissociated or degraded partially until Y₂O₃ is obtained in the final step with the presence of carbon related residues. Then the Y(acac)₃ was used to synthesize Y₂O₃ thin films using the spray pyrolysis technique. The films were deposited on silicon substrates at temperatures in the range of 400–550 °C. The films were characterized by ellipsometry, infrared spectroscopy, atomic force microscopy, and X-ray diffraction. The films presented a low surface roughness with an index of refraction close to 1.8. The crystalline structure of the films depended on the substrate temperature; films deposited at 400 °C were mainly amorphous, but higher deposition temperatures (450–550 °C), resulted in polycrystalline with a cubic crystalline phase.     

Preparation and properties of Bi2S3 films

Bi₂S₃ semiconducting films were prepared by spray pyrolysis of solutions containing bismuth(III) salts and thiourea. The deposition of the films was found to occur via the formation of thiourea complexes, followed by their thermal decomposition. Some physical properties of the films were studied     

Structural characterization and photocatalytic activity of ultrathin TiO2 films fabricated by Langmuir-Blodgett technique with octadecylamine

TiO₂ thin films with nanometer-scale thicknesses were prepared by the hydrolysis of titanium potassium oxalate using octadecylamine (ODA) Langmuir-Blodgett (LB) films as templates. After optimizing conditions in immersion process, the amount of TiO₂ generated in the ODA LB film was found to be precisely controlled by the number of deposited ODA layers. Morphological measurements showed that uniform TiO₂ film with surface roughness of less than 1.3 nm could be prepared from the monolayer LB films through subsequent heat-treatment process, while generation of cracks became less noticeable on the 5-layer film after heat-treatment at lower holding temperature with slow heating rate. In addition, photocatalytic activities of the TiO₂ films were examined from the decomposition of cadmium stearate (CdSt) LB films and stearic acid (SA) cast films for different time intervals of irradiation with UV light. Atomic force microscopy measurements showed that an almost flat surface of the CdSt LB film changes to a moth-eaten appearance as a result of decomposition under UV light irradiation. Furthermore, the post-heat-treatment at higher temperatures resulted in decreased photocatalytic activity of the TiO₂ film for the decomposition of SA cast film.     

Characterization of evaporated tellurium oxide films

The evaporation of tellurium dioxide was carried out by resistive heating and electron-beam evaporation, and the resulting films were subsequently characterized using X-ray diffraction, infrared absorption spectroscopy and electron diffraction techniques. The infrared results of these films showed a marked deviation from the initial stoichiometry, indicating decomposition of the compound. From X-ray and electron diffraction data, it was found that the films had Te₂O₅ stoichiometry. Electron-beam evaporated films showed single crystal growth on a sodium chloride substrate, while those films obtained by resistive heating were wholly amorphous. Furthermore, when fabricated into capacitors, these films showed high capacitance and high dielectric strength (4.6×10⁶V cm^–1) suitable for passive devices.     

Comparative study of (Ba,Sr)TiO3 films prepared by electron cyclotron resonance plasma sputtering and metal-organic decomposition

(Ba,Sr)TiO₃ films were prepared on Pt/Ti/SiO₂/Si substrates by mirror-confinement-type electron cyclotron resonance (ECR) plasma sputtering as well as by metal-organic decomposition (MOD). The films prepared by ECR plasma sputtering were crystallized at lower temperatures with better crystallinity and a denser structure than those by MOD. As for dielectric constant, films prepared by ECR plasma sputtering exhibited a relatively high value over 500 at a low annealing temperature of 873 K, whereas films by MOD exhibited approximately 350. This is attributed to the better crystallinity and the denser structure of the films by ECR plasma sputtering. The leakage current density of the films was found to be similar in both processes.     

Deposition of Conductive Films on Semiconductor Substrates via Molybdenum Hexacarbonyl Decomposition in Glow Discharge

The properties of films deposited via molybdenum hexacarbonyl decomposition in glow discharge are found to depend strongly on the nature of the substrate and the sign of bias. Molybdenum films are obtained on SiO₂/Si at any bias and on Si, GaAs, InP, and InAs substrates at positive bias. At negative bias, molybdenum silicide films are produced on Si. The films deposited at positive bias have the highest electrical conductivity. X-ray diffraction, Auger electron spectroscopy, and sheet resistance data are used to elucidate the mechanism of film deposition via molybdenum hexacarbonyl decomposition in glow discharge.     

Metastable phases in vapour-deposited Al-Zr thin films

Transmission electron microscopy and diffraction techniques were employed to characterize the metastable phases formed in vapour-deposited Al-Zr thin films both in the as-deposited and annealed conditions. The as-deposited films contained only the supersaturated solid solutions in alloys containing 3, 6 and 9.4 wt.%Zr. During decomposition, three metastable phases were found to form, with the stoichiometries of Al₆Zr (orthorhombic), Al₁₁Zr₂ (cubic) and AlZr (cubic). Further, a vacancy-ordered τ₅ phase based on AlZr was also detected. Details of the microstructure and the transformation behaviour on annealing are discussed.     

Simple way for preparation of ZnO films by surfactant mediated spray pyrolysis

Nanocrystalline porous ZnO films are deposited onto alumina foil substrates by polyvinyl alcohol (PVA) modified spray pyrolysis. Water and ethanol–water mixture were used for preparation of the sols. The effect of polyvinyl alcohol on the morphological and photocatalytical properties of ZnO films was studied. It was found that the polyvinyl alcohol plays important role in formation of porous films structure with ganglia like morphology. Relatively compact granular morphology was observed for the ZnO samples, grown without organic surfactant. The X-ray diffraction patterns revealed the formation of phase-pure ZnO thin films. The FTIR spectra and DTA-TG analyses of the precursor mixtures: Zn(CH₃COOH)₂·2H₂O and Zn(NO₃)₂·6H₂0 with PVA revealed that ZnO is formed before the final decomposition of the polymer at 350 °C.     

Formation and transformation of ZnTiO3 prepared by sputtering process

Zinc titanate (ZnTiO₃) films were prepared using RF magnetron sputtering at substrate temperatures ranging from 30 to 400 °C. Subsequent annealing of the as-deposited films was performed at temperatures ranging from 600 to 900 °C. It was found that all as-deposited films were amorphous, as confirmed by XRD. This was further confirmed by the onset of crystallization that took place at annealing temperatures 600 °C. The phase transformation for the as-deposited films and annealed films were investigated in this study. The results revealed that pure ZnTiO₃ (hexagonal phase) can exist, and was obtained at temperatures between 700 and 800 °C. However, it was found that decomposition from hexagonal ZnTiO₃ to cubic Zn₂TiO₄ and rutile TiO₂ took place with a further increase in temperature to 900 °C.     

Epitaxial growth of ferromagnetic CrO2 films in air

Epitaxial growth of CrO₂ films under atmospheric pressure has been investigated. Single crystal films of CrO₂ were obtained by the thermal decomposition of gaseous CrO₃ onto the substrates of rutile single crystals in air. The optimum temperature of the substrate for the pure CrO₂ epitaxial films was found to be 390°C. At the substrate temperature of 380°C, the obtained film included Cr₂O₅ as impurities, and Cr₂O₃ appeared at 400°C. Magnetic domain patterns of these films were observed by longitudinal Kerr effect. The growth patterns of domain were obtained with applied field.     

Diffusional processes in thin films of Au/CeO2 on NiCr superalloy

Gold films deposited onto CeO₂ intermediate layers on Inconel substrates by means of thermal decomposition of organometallic solutions lose their coating identity, i.e. reflectivity, as a result of heating at temperatures between 500 and 850 °C in air. The main cause is the out-diffusion of chromium from the Inconel substrate through the CeO₂ intermediate layer to the gold film surface and the subsequent oxidation of the chromium. The predominant diffusion mechanism was found to be through grain boundaries in the gold film, with an activation energy of 1.00±0.05 eV. This relatively low value of the activation energy was attributed to in situ grain growth in the gold films that take place during the diffusion. In this temperature regime it could be assumed that the CeO₂ intermediate layer is a semidiffusion barrier, since no concentration of gold could be observed in the Inconel substrate. However, at temperatures higher than 750 °C, slight decomposition of the CeO₂ was detected.     

Influence of gas pressure on low-temperature preparation and film properties of nanocrystalline 3C-SiC thin films by HW-CVD using SiH4/CH4/H2 system

We investigated an influence of gas pressure on low-temperature preparation of nanocrystalline cubic silicon carbide (nc-3C-SiC) films by hot-wire chemical vapour deposition (HW-CVD) using SiH₄/CH₄/H₂ system. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra revealed that the films prepared below 1.5 Torr were Si-nanocrystallite-embedded hydrogenated amorphous SiC. On the other hand, nc-3C-SiC films were successfully prepared at gas pressure above 2 Torr. The high gas pressure plays two important roles in low-temperature preparation of nc-3C-SiC films: (1) leading to sufficient decomposition of CH₄ molecules through a gas phase reaction and an increase in the incorporation of carbon atoms into film and (2) promoting a creation of H radicals on the heated filament, allowing the sufficient coverage of growing film surface and a selective etching of amorphous network structure and/or crystalline-Si phase. It was found that total gas pressure is a key parameter for low-temperature preparation of nc-3C-SiC films.     

Kinetics of SiC chemical vapor deposition from methylsilane

The kinetics of heterogeneous decomposition of methylsilane in a pumped hot-wall reactor were studied just below the critical partial pressure for homogeneous decomposition. The activation energies of the process derived from gas-phase conversion measurements and from deposition rates of SiC were found to be equal (about 230 kJ/mol). The nature of the diluent (H₂, He, or Ar) has only a weak effect on the reaction order in methylsilane (m ≃= 1 ), as well as on the composition and structure of amorphous Si_0.53C_0.47 films.     

Reactive DC magnetron deposition of copper nitride films for write-once optical recording

Copper nitride (Cu_xN) films were prepared on glass slides by reactive direct current (DC) magnetron sputtering under different nitrogen flow rates and substrate temperature, respectively. X-ray diffraction and reflectance spectra were employed to characterize the films. The Cu_xN films can completely decompose through heat treatment at temperature as low as 160 °C. The reflectance spectra of the as-deposited films are quite different from that of the decomposed films in a wide wavelength range from UV to infrared. Its relatively low decomposition temperature and large reflectance change before and after decomposition makes it a potential write-once optical recording medium.     

Structural,optical and photoconducting properties of sprayed CdSe films

CdSe films were grown by the pyrolytic decomposition of a mixture of aqueous solutions of selenourea (NH₂CSeNH₂) and CdCl₂·5H₂O. The effect of changes in the selenium-to-cadmium ion ratio on the photoconductivity was examined. The as-grown films had low resistance and showed poor photoconductivity gain. When the films were annealed in air the resistance as well as the gain increased appreciably. These changes have been attributed to chemisorption of oxygen. The samples with one part CdCl₂·5H₂O and one part NH₂CSeNH₂ were found to be the most photosensitive, the ratio of dark resistance to light resistance being of the order of 10⁵. The spectral response of the resistance of these films shows a dip in the region of 690 nm, which is in close agreement with the band gap determined from optical absorption measurements.     

Enhanced effect of vacuum-deposited SiO2 overlayer on photo-induced hydrophilicity of TiO2 film

Photo-induced hydrophilicity of SiO₂/TiO₂ multilayer film prepared by using the vacuum deposition method was investigated by means of water contact angle measurement. Using black light irradiation of the films centering at a wavelength of 365 nm, an extreme photo-induced hydrophilicity was achieved when the TiO₂ film was covered by SiO₂ overlayer ranging from 10 to 20 nm in thickness. These multilayer films exhibited much more extreme hydrophilicity than the TiO₂ film without SiO₂ overlayer. The surface analyses revealed that the enhanced photo-induced hydrophilic surface of the multilayer films exhibited an improved photo-catalytic activity towards decomposition of organic substances on their surfaces. It was found that significant growth of the SiOH group occurred in the uppermost surface of the SiO₂ overlayer of the multilayer films through the depth profile measurement of TOF-SIMS. This result suggests that the photo-generated reactive species such as hole created in the TiO₂ film may transmit the SiO₂ layer to reach the surface. The enhanced photo-induced hydrophilicity of the films can be explained by a synergetic effect of the improved photo-catalytic activity of the multilayer film and the stable hydrophilicity of SiO₂ itself.     

In situ preparation of Calcium hydroxide films

The in situ preparation of Calcium hydroxide films in an ultra high vacuum (UHV) is constrained by the decomposition of species at the surface and the absence of OH bulk diffusion. Therefore, it is not possible to prepare such films simply by water exposure to a Calcium layer.We present four different approaches for the preparation of Ca(OH)₂ films in an UHV. Two of these methods are found to be ineffective for the preparation, the other two are shown to produce Calcium hydroxide films. Both of the two effective procedures make use of H₂ gas exposure. Metastable Induced Electron Spectroscopy, Ultraviolet Photoelectron Spectroscopy, and X-ray Photoelectron Spectroscopy are employed to verify quality and purity of the films.     

Processing of chemical solution-deposited BaTiO<Subscript>3</Subscript>-based thin films on Ni foils

BaTiO₃ films on base metal foils are of interest for capacitor applications, but the processing requires reducing atmospheres that influence the film defect chemistry and density. In this study, powders dried from barium titanate solutions and barium titanate films were studied by X-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis, infrared spectroscopy, and spectroscopic ellipsometry at various points in the processing. It was found that atmospheres designed to minimize Ni oxidation delay decomposition of organics, leading to retained carbonate phases. Thus, crystallization of the barium titanate occurs via decomposition of a barium carbonate phase. Retained organics that are present during high temperature processing can cause porosity in the films. On annealing at 1000 °C, there is slightly increase in the refractive index of the film due to further crystallization and densification. The final refractive index is comparable to that of 95% dense barium titanate ceramics. Re-oxidation did not change the refractive index of the film over the wavelength range from 350 to 650 nm.     

Broad band optical characterization of sol-gel TiO2 thin film microstructure evolution with temperature

Titanium dioxide (TiO₂) thin films have been produced by spin coating a titanium isopropoxide sol on silicon wafer substrates. The structural evolution of the thin films in terms of decomposition, crystallization and densification has been monitored as a function of annealing temperature from 100 to 700 °C using optical characterization and other techniques. The effect of annealing temperature on the refractive index and extinction coefficient of these TiO₂ thin films was studied in the range of 0.62 to 4.96 eV photon energy (250-2000 nm wavelength) using spectroscopic ellipsometry. Thermal gravimetric analysis and atomic force microscopy support the ellipsometry data and provide information about structural transformations in the titania thin films with respect to different annealing temperatures. These data help construct a coherent picture of the decomposition of the sol-gel precursors and the creation of dense layers of TiO₂. It was observed that the refractive index increased from 2.02 to 2.45 at 2.48 eV (500 nm) in sol-gel spin coated titania films for annealing temperatures from 100 °C to 700 °C.