Preparation of anatase TiO2 thin films by vacuum arc plasma evaporation

Anatase titanium dioxide (TiO₂) thin films with high photocatalytic activity have been prepared with deposition rates as high as 16 nm/min by a newly developed vacuum arc plasma evaporation (VAPE) method using sintered TiO₂ pellets as the source material. Highly transparent TiO₂ thin films prepared at substrate temperatures from room temperature to 400 °C exhibited photocatalytic activity, regardless whether oxygen (O₂) gas was introduced during the VAPE deposition. The highest photocatalytic activity and photo-induced hydrophilicity were obtained in anatase TiO₂ thin films prepared at 300 °C, which correlated to the best crystallinity of the films, as evidenced from X-ray diffraction. In addition, a transparent and conductive anatase TiO₂ thin film with a resistivity of 2.6 × 10^− 1 Ω cm was prepared at a substrate temperature of 400 °C without the introduction of O₂ gas.     

Photocatalytic activities of TiO2 thin films prepared on Galvanized Iron substrate by plasma-enhanced atomic layer deposition

Titanium dioxide (TiO₂) thin films were prepared on Galvanized Iron (GI) substrate by plasma-enhanced atomic layer deposition (PE-ALD) using tetrakis-dimethylamido titanium and O₂ plasma to investigate the photocatalytic activities. The PE-ALD TiO₂ thin films exhibited relatively high growth rate and the crystal structures of TiO₂ thin films depended on the growth temperatures. TiO₂ thin films deposited at 200 °C have amorphous phase, whereas those with anatase phase and bandgap energy about 3.2 eV were deposited at growth temperature of 250 °C and 300 °C. From contact angles measurement of water droplet, TiO₂ thin films with anatase phase and Activ™ glass exhibited superhydrophilic surfaces after UV light exposure. And from photo-induced degradation test of organic solution, anatase TiO₂ thin films and Activ™ glass decomposed organic solution under UV illumination. The anatase TiO₂ thin film on GI substrate showed higher photocatalytic efficiency than Activ™ glass after 5 h UV light exposure. Thus, we suggest that the anatase phase in TiO₂ thin film contributes to both superhydrophilicity and photocatalytic decomposition of 4-chlorophenol solution and anatase TiO₂ thin films are suitable for self-cleaning applications.     

Photocatalytic Property of TiO2 Films Deposited by Pulsed DC Magnetron Sputtering

TiO2 thin films were prepared by DC magnetron sputtering with the oxygen flow rate higher than the threshold. The film deposited for 5 h was of anatase phase with a preferred orientation along the <220> direction, but the films deposited for 2 and 3 h were amorphous. The transmittance and photocatalytic activity of the TiO2 films increased constantly with increasing film thickness. When the annealing temperature was lower than 700℃, only anatase grew in the TiO2 film. TiO2 phase changed from anatase to rutile when the annealing temperature was above 800℃. The photocatalytic activity decreased with increasing annealing temperature.     

Photocatalytic properties of Cr-doped TiO2 films prepared by oxygen cluster ion beam assisted deposition

We prepared Cr-doped titanium dioxide (TiO₂) films by oxygen (O₂) cluster ion beam assisted deposition method, and investigated photocatalytic properties of the films as well as crystallographic property, optical property and surface morphology. The films prepared at a substrate temperature below 200 °C were found to be amorphous from the X-ray diffraction measurement. For the substrate temperatures such as 300 °C and 400 °C, the films exhibited rutile and/or anatase structures. The film surface measured by the atomic force microscope (AFM) was smooth at an atomic level. Furthermore, the optical band gap decreased with increase of Cr-composition, and it was approximately 3.3 eV for the non-doped films, 3.2 eV for the 1% Cr-doped films and 3.1 eV for the 10% Cr-doped films, respectively. With regard to the photocatalytic properties of the Cr-doped TiO₂ films, we measured the change of contact angle as well as the photocatalytic degradation of methylene blue by the UV light irradiation. Compared with the non-doped films, the 1% Cr-doped films prepared at a substrate temperature of 400 °C showed high degradation efficiency. In addition, the contact angle of the 1% Cr-doped films with an initial value of 60° decreased to 10° by the UV light irradiation for 20 min, and the films exhibited the predominant properties of photocatalytic hydrophilicity even for the UV light irradiation with longer wavelengths.     

In-situ growth of oriented PbTiO3 thin films by low temperature metalorganic chemical vapor deposition

Oriented PbTiO₃ thin films were successfully grown on (200)-oriented Pt/SiO₂/Si by metalorganic chemical vapor deposition at low temperature range from 350°C to 400°C, using -diketonate complex of Pb(tmhd)₂ and titanium isopropoxide as source precursors. Dependences of orientation and formation of crystalline PbTiO₃ phase on Pb/Ti ratio and substrate temperature was investigated. Crystalline phases and preferred orientations were determined by X-ray diffraction technique, and surface morphology was identified with scanning electron microscopy. As the deposition temperature was raised from 350°C to 400°C at two fixed Pb/Ti ratios of 3.3 and 5.0, structures of PbTiO3w₃ films transformed from amorphous to polycrystalline and preferred orientation changed from random to [100] parallel to the surface. Similar results were also observed in the films deposited at 400°C with the increase of Pb/Ti ratio from 1.1 to 5.0. As the Pb/Ti ratio increased, the dielectric constant and current density increased due to crystallization of the PbTiO₃ films. It is found that the control of excess Pb precursor amount through Pb/Ti ratio change is the key process parameter for the formation of crystalline PbTiO₃ phase in the low temperature MOCVD process.     

Preparation, characterization and photocatalytic activity of in situ Fe-doped TiO2 thin films

Fe-doped TiO₂ thin films were prepared in situ on stainless steel substrates by liquid phase deposition, followed by calcination at various temperatures. It was found that some Fe³⁺ ions were in situ doped into the TiO₂ thin films. At 400 °C, the film became photoactive due to the formation of anatase phase. At 500 °C, the film showed the highest photocatalytic activity due to an optimal Fe³⁺ ion concentration in the film. At 900 °C, the photocatalytic activity of the films decreased significantly due to the further increase of Fe³⁺ ion concentration, the formation of rutile phase and the sintering and growth of TiO₂ crystallites.     

Fabrication of TiO2 nanotubes by atomic layer deposition and their photocatalytic and photoelectrochemical applications

The formation of TiO(2) nanotubes was conducted by atomic layer deposition (ALD) with tris-(8-hydroxyquinoline) gallium (GaQ(3)) nanowires as a template at different substrate temperatures, 50, 100, and 200?°C. TiO(2) nanotubes were formed only at 50 and 100?°C. Although a higher growth rate at 50?°C was observed, nanotubes with better uniformity, conformality, and less residual chloride were obtained at 100?°C because of a different formation mechanism. A photocatalysis test of TiO(2) nanotubes prepared by different cycle numbers at 100?°C was conducted. It showed that TiO(2) nanotubes prepared by 400 cycles of ALD and treated at 700?°C for 1 h to form anatase phase had the best photocatalytic performance. Compared with P-25, the nanotubes showed higher photocatalytic degradation of rhodamine B and water splitting efficiency.     

Structural and electrical properties of RuO2 thin films prepared by rf-magnetron sputtering and annealing at different temperatures

Conductive ruthenium oxide (RuO₂) thin films have been deposited at different substrate temperatures on various substrates by radio-frequency (rf) magnetron sputtering and were later annealed at different temperatures. The thickness of the films ranges from 50 to 700 nm. Films deposited at higher temperatures show larger grain size (about 140 nm) with (200) preferred orientation. Films deposited at lower substrate temperature have smaller grains (about 55 nm) with (110) preferred orientation. The electrical resistivity decreases slightly with increasing film thickness but is more influenced by the deposition and annealing temperature. Maximum resistivity is 861 μΩ cm, observed for films deposited at room temperature on glass substrates. Minimum resistivity is 40 μΩ cm observed for a thin film (50 nm) deposited at 540°C on a quartz substrate. Micro-Raman investigations indicate that strain-free well-crystallized thin films are deposited on oxidized Si substrates.     

Structural and thermoelectric properties of HfNiSn half-Heusler thin films

The bulk thermoelectric properties of half-Heusler alloys have recently been extensively studied due to their potential as thermoelectric materials. However, only a few publications have been addressed on thin film systems. The present study investigated the structural and thermoelectric properties of HfNiSn half-Heusler alloy thin films grown at different substrate temperatures: 25 °C, 200 °C, and 400 °C. The crystalline phase and structural variation of the films were determined by X-ray diffraction and scanning electron microscopy. Polycrystalline thin films were obtained for utilizing lower substrate temperatures. The HfNiSn thin films exhibited preferred (111) orientation when substrate temperature was higher than 400 °C. The in-plane Seebeck coefficient and resistivity of HfNiSn thin films with preferred orientation were much lower than those of films without orientation. This implies the thermoelectric properties of HfNiSn alloy may exhibit anisotropic characteristics. The best Seebeck coefficient and power factor of HfNiSn thin films obtained in this work are −68 μV/K and 1.3 μW/K²cm, respectively, measured at room temperature. The effects of partial substitution of Sn by Sb on thermoelectric properties of HfNiSn thin films were also studied with a “pseudo-combinatorial” approach.     

Effect of thermal annealing on the microstructure and morphology of erbium films

The effects of thermal annealing on the microstructure and morphology of erbium films were investigated by X-ray diffraction and scanning electron microscopy. All the erbium films were fabricated by electron-beam vapor deposition. The columnar grain sizes of as-received erbium films increased with the substrate temperatures and were enlarged by the coalescence and migration of grains during the high temperature annealing. The intrinsic stresses of erbium films, fabricated at a low substrate temperature (200 °C), were relaxed accompanied with the appearance of cracks on the films surface. The films deposited at 200 °C had (002) preferred orientation, and the film deposited at 450 °C had mixed (100) and (101) texture. The peak positions and the full width at half maximum of (100), (002), and (101) diffraction lines of erbium shift towards higher angles and sharply decrease during the annealing process, indicating that the stress inside the film was relaxed.     

Preparation of immobilized nano-columnar TiO2 grains by chemical vapor deposition

Nano-columnar TiO2 grains are prepared and immobilized by chemical vapor deposition using TiCl4, H2 and O2 at low temperature. The structure of TiO2 is analyzed by X-ray diffraction (XRD), the morphology is observed by scanning electron microscopy (SEM) and the adhesion is estimated by measuring the critical load in scratch test. Results show that the structure of TiO2 films depend on the deposition temperature changing from amorphous, anatase, rutile, and both anatase and rutile phases as prepared at temperatures of 200, 300, 400 and 500 degrees C, respectively. The nano-columnar TiO2 grains are formed in both rutile and anatase phases, while it could be only rutile phase by increasing TiCl4 flow rate. The morphologies of TiO2 changes from smooth to nano-columnar grains as the deposition temperature increased from 200 to 400 degrees C. Excellent adhesion strength of crystalline TiO2 was obtained and it could be improved by increasing the TiCl4 flow rate in range of 0.3-0.6 sccm, where the critical load of TiO2 increases from 17 to 21 N.     

Low-temperature atomic layer deposition of ZnO thin films: Control of crystallinity and orientation

Low-temperature atomic layer deposition (ALD) processes are intensely looked for to extend the usability of the technique to applications where sensitive substrates such as polymers or biological materials need to be coated by high-quality thin films. A preferred film orientation, on the other hand, is often required to enhance the desired film properties. Here we demonstrate that smooth, crystalline ZnO thin films can be deposited from diethylzinc and water by ALD even at room temperature. The depositions were carried out on Si(100) substrates in the temperature range from 23 to 140 °C. Highly c-axis-oriented films were realized at temperatures below ~ 80 °C. The film crystallinity could be further enhanced by post-deposition annealing under O₂ or N₂ atmosphere at 400-600 °C while keeping the original film orientation intact.     

Phase determination of filtered vacuum arc deposited TiO2 thin films by optical modeling

Thin films of TiO₂ were produced using filtered vacuum arc deposition. Arc currents were 275, 300, 325 A, and the oxygen pressure during deposition was 0.93 Pa. The substrates were glass microscope slides, at temperatures of 25 °C (RT), 200 °C, and 400 °C. Film thickness was in the range 100 to 250 nm, depending on the deposition conditions. Film structure and chemical composition were determined using XRD and XPS analyses, respectively. As-deposited films were amorphous, except to two samples that were found to be crystalline (deposited with 300 A, 325 A at 400 °C), and the crystalline phase was close to that of anatase. All of the films were partially crystallized by annealing in air at 450 °C for 1 h. The O:Ti atomic concentration ratio was in the range 1.6:1-2:1, independent of deposition conditions. The optical parameters, refractive index and the extinction coefficient of the films were determined using variable angle spectroscopic ellipsometry. In addition, the optical transmission of the films were determined in the UV-VIS and IR regions. The average optical transmission in the VIS spectrum was 70-85%, affected by the interference in the film with 90% maxima and 60% minima. The refractive index at λ = 550 nm was in the range 2.4 to 2.7, depending on the deposition conditions and annealing. Using the semi-empirical model of Wemple and DiDomenico for the dielectric function below the interband absorption edge of ionic and covalent solids, the dispersion energy parameters of TiO₂ (E_o, E_d) were calculated. The underlying structural order of the amorphous films was inferred by comparing the dispersion energy parameters of the amorphous films with those of crystalline TiO₂. As expected, the refractive index of the amorphous films depended on the underlying phase of the film. The optical analyses indicated that the underlying phase of the amorphous films deposited on RT substrates was close to anatase, whereas the underlying phase of the amorphous films deposited on 400 °C substrates and annealed at 450 °C for 1 h consisted of both anatase and rutile. Thus, although the XRD analyses could not indicate the underlying phase of the amorphous films, it could be determined by the optical analyses.     

TiO2 anatase thin films deposited by spray pyrolysis of an aerosol of titanium diisopropoxide

Titanium dioxide thin films were deposited on crystalline silicon (100) and fused quartz substrates by spray pyrolysis (SP) of an aerosol, generated ultrasonically, of titanium diisopropoxide. The evolution of the crystallization, studied by X-ray diffraction (XRD), atomic force (AFM) and scanning electron microscopy (SEM), reflection and transmission spectroscopies, shows that the deposition process is nearly close to the classical chemical vapor deposition (CVD) technique, producing films with smooth surface and good crystalline properties. At deposition temperatures below 400 °C, the films grow in amorphous phase with a flat surface (roughness∼0.5 nm); while for equal or higher values to this temperature, the films develop a crystalline phase corresponding to the TiO₂ anatase phase and the surface roughness is increased. After annealing at 750 °C, the samples deposited on Si show a transition to the rutile phase oriented in (111) direction, while for those films deposited on fused quartz no phase transition is observed.     

Structural and electrical characterization of TiO2 films grown by spray pyrolysis

The sol-gel spray pyrolysis method was used to grow TiO₂ thin films onto silicon wafers at substrate temperatures between 315 and 500 °C using pulsed spray solution feed followed by annealing in the temperature interval from 500 to 800 °C in air. According to FTIR, XRD, and Raman, the anatase/rutile phase transformation temperature was found to depend on the film deposition temperature. Film thickness and refractive index were determined by Ellipsometry, giving the refractive indexes of 2.1-2.3 and 2.2-2.6 for anatase and rutile, respectively. According to AFM, film roughness increases with annealing temperature from 700 to 800 °C from 0.60 to 1.10 nm and from 0.35 to 0.70 nm for the films deposited at 375 and 435 °C, respectively. The effective dielectric constant values were in the range of 36 to 46 for anatase and 53 to 70 for rutile at 10 kHz. The conductivity activation energy for TiO₂ films with anatase and rutile structure was found to be 100 and 60 meV, respectively.     

Preparation of anatase TiO2 thin films for dye-sensitized solar cells by DC reactive magnetron sputtering technique

Anatase titanium dioxide (TiO₂) thin films are prepared by DC reactive magnetron sputtering using Ti target as the source material. In this work argon and oxygen are used as sputtering and reactive gas respectively. DC power is used at 100 W per 1 h. The distance between the target and substrate is fixed at 4 cm. The glass substrate temperature value varies from room temperature to 400 °C. The crystalline structure of the films is determined by X-ray diffraction analysis. All the films deposited at temperatures lower than 300 °C were amorphous, whereas films obtained at higher temperature grew in crystalline anatase phase. Phase transition from amorphous to anatase is observed at 400 °C annealing temperature. Transmittances of the TiO₂ thin films were measured using UV-visible NIR spectrophotometer. The direct and indirect optical band gap for room temperature and substrate temperature at 400 °C is found to be 3.50, 3.41 eV and 3.50, 3.54 eV respectively. The transmittance of TiO₂ thin films is noted higher than 75%. A comparison among all the films obtained at room temperature showed a transmittance value higher for films obtained at substrate temperature of 400 °C. The morphology of the films and the identification of the surface chemical stoichiometry of the deposited film at 400 °C were studied respectively, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The surface roughness and the grain size are measured using AFM.     

Influence of growth parameters on the microstructures of erbium films deposited on Si(111) substrates

Erbium films were grown on single crystal Si(111) substrates by electron beam vapor deposition. The microstructures of the erbium films were systematically investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Results indicate that the surface morphologies and microstructures of the erbium films with Si as substrates are susceptible to the substrate temperatures when the deposition rates are fixed. The pure erbium films with columnar grains were obtained at temperatures below 200 °C, but in the films grown at temperatures higher than 350 °C, some pinholes that are composed of erbium silicides were found. The pinholes have triangular shapes which is in accordance with the geometry of the underlying Si(111) substrate. The films grown at a substrate temperature equal or greater than 450 °C have cracks which would be formed due to the different shrinkage degree of erbium and silicon when the substrate temperature was cooled down to room temperature. The films grown at 200 °C show the (002) preferred orientation, which is consistent to the prediction by the theory of surface energy minimization. The deposition rate and deposition time are considered as factors to affect the reaction of the erbium film and the silicon substrate.     

Growth and characterization of Bi2Se3 thin films by pulsed laser deposition using alloy target

Bi₂Se₃ thin films were deposited on the (100) oriented Si substrates by pulsed laser deposition technique at different substrate temperatures (room temperature −400 °C). The effects of the substrate temperature on the structural and electrical properties of the Bi₂Se₃ films were studied. The film prepared at room temperature showed a very poor polycrystalline structure with the mainly orthorhombic phase. The crystallinity of the films was improved by heating the substrate during the deposition and the crystal phase of the film changed to the rhombohedral phase as the substrate temperature was higher than 200 °C. The stoichiometry of the films and the chemical state of Bi and Se elements in the films were studied by fitting the Se 3d and the Bi 4d5/2 peaks of the X-ray photoelectron spectra. The hexagonal structure was seen clearly for the film prepared at the substrate temperature of 400 °C. The surface roughness of the film increased as the substrate temperature was increased. The electrical resistivity of the film decreased from 1 × 10⁻³ to 3 × 10⁻⁴ Ω cm as the substrate temperature was increased from room temperature to 400 °C.     

Oriented growth of thin films of samarium oxide by MOCVD

Thin films of Sm₂O₃ have been grown on Si(100) and fused quartz by low-pressure chemical vapour deposition using an adducted β-diketonate precursor. The films on quartz are cubic, with no preferred orientation at lower growth temperatures (∼ 550°C), while they grow with a strong (111) orientation as the temperature is raised (to 625°C). On Si(100), highly oriented films of cubic Sm₂O₃ at 625°C, and a mixture of monoclinic and cubic polymorphs of Sm₂O₃ at higher temperatures, are formed. Films grown on either substrate are very smooth and fine-grained. Infrared spectroscopic study reveals that films grown above 600° C are free of carbon.     

Preparation of cobalt oxide films by plasma-enhanced metalorganic chemical vapour deposition

Co oxide films were prepared on glass substrates at 150–400°C by plasma-enhanced metalorganic chemical vapour deposition using cobalt (II) acetylacetonate as a source material. NaCl-type CoO films were formed at low O₂ flow rate of 7cm³ min^–1 and at a substrate temperature of 150–400°C. The CoO films possessed (100) orientation, independent of substrate temperature. Deposition rates of the CoO films were 40–47 nm min^–1. The CoO film deposited at 400 °C was composed of closely packed columnar grains and average diameter size at film surface was 60 nm. At high O₂ flow rate of 20–50 cm³ min^–1, high crystalline spinel-type Co₃O₄ films were formed at a substrate temperature of 150–400°C. The Co₃O₄ film deposited at 400°C possessed (100) preferred orientation and the film deposited at 150°C possessed (111) preferred orientation. Deposition rates of the Co₃O₄ films were 20–41 nm min^–1. Both Co₃O₄ films with (100) and (111) orientation had columnar structure. The shape and average size of the columnar grains at the film surface were different; a square shape and 35 nm for (100)-oriented Co₃O₄ film and a hexagonal shape and 60 nm for (111)-oriented film, respectively.