Fluorine doped vanadium dioxide thin films for smart windows

Thermochromic fluorine doped thin films of vanadium dioxide were deposited from the aerosol assisted chemical vapour deposition reaction of vanadyl acetylacetonate, ethanol and trifluoroacetic acid on glass substrates. The films were characterised with scanning electron microscopy, variable temperature Raman spectroscopy and variable temperature UV/Vis spectroscopy. The incorporation of fluorine in the films led to an increase in the visible transmittance of the films whilst retaining the thermochromic properties. This approach shows promise for improving the aesthetic properties of vanadium dioxide thin films.     

On the effects of electric fields in aerosol assisted chemical vapour deposition reactions of vanadyl acetylacetonate solutions in ethanol

Thin films of thermochromic vanadium dioxide have been deposited on glass substrates at 530 degrees C from the aerosol assisted chemical vapour deposition of vanadyl acetylacetonate solutions in ethanol under the influence of electric fields. Electric fields were generated by applying a potential difference between the top plate and the substrate of the reactor. The deposited films were analysed and characterised using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and variable temperature UV/Visible spectroscopy. The application of an electric field led to significant changes in the deposited films microstructure and functional properties. It was found that an increase in electric field strength caused a decrease in crystallite size and in an increase in the change in transmission in the near infrared when compared to films grown without the use of an electric field.     

Atmospheric pressure chemical vapour deposition of thermochromic tungsten doped vanadium dioxide thin films for use in architectural glazing

Atmospheric pressure chemical vapour deposition of VCl₄, WCl₆ and water at 550 °C lead to the production of high quality tungsten doped vanadium dioxide thin films. Careful control of the gas phase precursors allowed for tungsten doping up to 8 at.%. The transition temperature of the thermochromic switch was tunable in the range 55 °C to − 23 °C. The films were analysed using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Their optical properties were examined using variable-temperature transmission and reflectance spectroscopy. It was found that incorporation of tungsten into the films led to an improvement in the colour from yellow/brown to green/blue depending on the level of tungsten incorporation. The films were optimized for optical transmission, thermochromic switching temperature, magnitude of the switching behaviour and colour to produce films that are suitable for use as an energy saving environmental glass product.     

Structural, electrical and optical properties of thermochromic VO2 thin films obtained by reactive electron beam evaporation

We present the structural and physical characterization of vanadium dioxide (VO₂) thin films prepared by reactive electron beam evaporation from a vanadium target under oxygen atmosphere. We correlate the experimental parameters (substrate temperature, oxygen flow) with the films structural properties under a radiofrequency incident power fixed to 50 W. Most of the obtained layers exhibit monocrystalline structures matching that of the monoclinic VO₂ phase. The temperature dependence of the electrical resistivity and optical transmission for the obtained films show that they present thermoelectric and thermochromic properties, with a phase transition temperature around 68 °C. The results show that for specific experimental conditions the VO₂ layers exhibit sharp changes in electrical and optical properties across the phase transition.     

Photocatalytic activity studies of TiO2 thin films prepared by r.f. magnetron reactive sputtering

A series of transparent titanium dioxide thin films have been obtained on microscope glass slides by means of r.f. magnetron reactive sputtering using Ar and O₂ mixed gases. The photocatalytic activity of the TiO₂ thin films was evaluated by the degradation of rhodamine B dye wastewater. The influences of substrate temperatures and total sputtering pressures on the photocatalytic activity of the TiO₂ films were investigated. It was observed that substrate temperature had little influences on the photocatalytic activity, but the photocatalytic activity of the TiO₂ thin films was improved by decreasing the total sputtering pressure.     

Titanium dioxide thin films, their structure and its effect on their photoactivity and photocatalytic properties

Atomic Layer Deposition has been used to deposit titanium dioxide thin films on soda-lime glass substrates. A series of films with thicknesses from 2.6 to 260 nm has been created and the film structure has been studied with X-ray diffraction. It has been observed that at a reaction temperature of 350 °C, titanium dioxide thin films initially grow as anatase but after a certain thickness, growth continues as rutile. The photoactivity and photocatalytic activity of the films have been found to reach their maximum at a film thickness of 15 nm. At this thickness, the film structure shows a small fraction of rutile crystallites in a largely anatase matrix indicating that both crystal phases are necessary for the maximum activity.     

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.     

Electron and Atomic Force Microscopy studies of photocatalytic titanium dioxide thin films deposited by DC magnetron sputtering

Titanium dioxide thin films were deposited on glass substrates and on fluorine doped tin oxides at room temperature by DC magnetron sputtering at different working gas pressures and were evaluated using photocatalytic degradation of an organic compound. The structural properties of the films were studied by electron microscopy techniques and Atomic Force Microscopy. Numerous structural defects were detected for samples deposited at 16 mTorr and it was associated with the highest photo-degradation rate. Also small band gap shift in titanium dioxide films was detected for different gas pressures. These behaviors are related with structural details derived from the synthesis conditions and the influence of structural defects on the photocatalytic activity is discussed.     

Electron back-scattered diffraction of crystallized vanadium dioxide thin films on amorphous silicon dioxide

Crystalline films and isolated particles of vanadium dioxide (VO₂) were obtained through solid phase crystallization of amorphous vanadium oxide thin films sputtered on silicon dioxide. Electron back-scattered diffraction (EBSD) was used to study the crystals obtained in the thin films, to differentiate them from different vanadium oxide stoichiometries that may have formed during the annealing process, and to study their phase and orientation. EBSD showed that the crystallization process yielded crystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated particles, and did not show evidence of other vanadium oxide stoichiometries present. Indexing of the crystals for the orientation study was performed using EBSD patterns for the tetragonal phase of vanadium dioxide, since it was observed that EBSD patterns for the monoclinic and tetragonal phases of vanadium dioxide are not distinguishable by computer automated indexing. Using the EBSD patterns for the tetragonal phase of vanadium dioxide, orientation maps showed that all VO₂ crystals that were measurable (approximately the thickness of the film) had a preferred orientation with the c-axis of the tetragonal phase parallel to the plane of the specimen.     

Vanadium dioxide thin films prepared by chemical vapour deposition from vanadium(III) acetylacetonate

Vanadium dioxide thin films were prepared by an atmospheric-pressure chemical vapour deposition method. The raw material was vanadium(III) acetylacetonate. Polycrystalline thin films were obtained at a reaction temperature of 500°C. Slow post-deposition cooling of the deposits on a substrate of fused quartz or sapphire single crystal yields vanadium dioxide films which are not mixed with other phases, i.e. V₃O₇ or V₄O₉. Optical and electrical switching behaviours strongly depend on film thickness. At a film thickness of about 300 nm the transition temperature showed a minimum value of 44 °C.     

Surface properties of doped and undoped TiO2 thin films deposited by magnetron sputtering

In this work, transparent titanium dioxide (TiO₂) thin films were deposited onto microscope glass slides by means of the d.c. reactive magnetron sputtering method. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible spectroscopy (UV) and contact angle analysis using the Owens-Wendt method for the surface energy calculation. The photocatalytic activity of the films was tested by measuring the photodegradation of Rhodamine-B (RhB) dye under radiation of UV light. Iron-doped TiO₂ films were also prepared in order to study the Fe-doping effect on TiO₂ photocatalytic activity. The influences of different iron concentrations on the contact angle of the series of Fe-doped TiO₂ thin films, were investigated. The influences of total sputtering pressures on TiO₂ photocatalytic activity were also investigated. It was observed that the photocatalytic activity of the TiO₂ thin films was slightly improved by increasing the total sputtering pressure. Moreover, it was also observed that in general, iron-doping was detrimental for photocatalytic activity, nevertheless the films with low iron concentrations showed better photocatalytic activity than those with high iron concentrations. It was found that iron-doping has changed the wettability appetency of TiO₂ coated surfaces.     

Chemical vapour deposition of nitrogen-doped titanium dioxide thin films

Nitrogen-doped titanium dioxide is often considered as a promising nanomaterial for photocatalytic applications. Here we report the first results of a study of APCVD of N-doped TiO2 thin films prepared with the use of ammonia as a source of nitrogen and titanium tetraisopropoxide (TTIP) as a source of Ti and O atoms. The obtained films were analyzed with X-ray diffraction, infrared spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, UV-Vis spectroscopy, and ellipsometry. It was found that the film growth rate in the TTIP-NH3-Ar reaction system varied insignificantly with substrate temperature in the range of 450,..., 750 degrees C and did not exceed 4.4 nm/min. Yellow and orange layers with nitrogen content of about 7.6% were formed at the deposition temperature higher than 600 degrees C. The results of the structure analysis of the deposited films showed that addition of ammonia led to stabilization of the amorphous phase in the films. The effect of ammonia on optical and photocatalytic properties was also considered.     

磁控溅射沉积二氧化钒薄膜及其电致相变特性研究

采用反应射频磁控溅射技术在熔融石英玻璃衬底上制备了组分单一的二氧化钒薄膜。在制备好的二氧化钒薄膜上使用半导体工艺制备了金属叉指电极,通过半导体测试仪测试其电致相变特性。结果表明,当电极上所加电压达到一定阈值时电流发生突变,即薄膜发生半导体-金属相变。     

Microstructure and optical properties of photoactive TiO2:N thin films

In this work, we have chosen oxidation of TiN thin films as a feasible method for preparation of nitrogen-doped titanium dioxide thin films, TiO₂:N, for photocatalytic applications. DC reactive magnetron sputtering with the plasma emission control was used for deposition of stoichiometric TiN thin films. The microstructure and chemical composition of films before and after oxidation were investigated by means of RBS, X-ray diffraction (XRD) in grazing incidence diffraction (GID) configuration, AFM and XPS techniques. The electrical conductivity was measured by the van der Pauw method as a function of the oxidation temperature. The optical transmittance and reflectance spectra of the films were measured over the visible and UV ranges of the light spectrum. GID diffraction patterns of as-sputtered TiN thin films and those after oxidation indicate that TiO₂ rutile is formed at around 300 °C. Nitrogen is still present as indicated by XPS studies even when XRD detects the rutile only. Optical absorption of thin films oxidized at 450 °C is shifted towards the visible range of the light spectrum.     

TiO2薄膜的结构和光催化活性研究

薄膜型的TiO2光催化剂克服了悬浮型的许多缺点,具有广阔的应用前景.阐述TiO2的结构及其影响因素;评述了晶型、晶粒尺寸、结晶度和晶格缺陷、表面积和表面预处理、表面羟基、温度、薄膜厚度、基体、光源及光强等因素对TiO2薄膜光催化活性的影响;探讨了提高TiO2薄膜光催化活性的措施,包括掺杂、贵金属沉积、半导体复合、表面光敏化等.指出需进一步研究的问题:加强影响因素的综合研究,探索最佳的工艺条件和反应条件;进一步提高TiO2薄膜的光催化效率;将光源种类从紫外光扩展到可见光;将TiO2薄膜的光催化性能同其它性能结合起来研究.     

Growth of vanadium oxide films on InP under mild conditions and thermal oxidation of the resultant structures

Techniques have been developed for producing vanadium oxide films (10 nm to 1 μm thick) on indium phosphide using vanadium(V) oxide gels and sols through immersion and deposition from aerosol. Using scanning tunneling microscopy and X-ray diffraction, we have studied the influence of annealing temperature and time on the morphology and composition of the films and the influence of the films on the thermal oxidation of InP.     

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.     

Effects of structure of anodic TiO(2) nanotube arrays on photocatalytic activity for the degradation of 2,3-dichlorophenol in aqueous solution

In this study titanium dioxide nanotube (TNT) arrays were prepared by an anodic oxidation process with post-calcination. The morphology and structure of the TNT films were studied by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of the TNT films was evaluated in terms of the degradation of 2,3-dichlorophenol in aqueous solution under UV light irradiation. The effects of the nanotube structure including tube length and tube wall thickness, and crystallinity on the photocatalytic activity were investigated in detail. The results showed that the large specific surface area, high pore volume, thin tube wall, and optimal tube length would be important factors to achieve the good performance of TNT films. Moreover, the TNT films calcined at 500 degrees C for 1h with the higher degree of crystallinity exhibited the higher photocatalytic activity than other TNT films calcined at 300 and 800 degrees C. Consequently, these results indicate that the optimization of TiO(2) nanotube structures is critical to achieve the high performance of photocatalytic reaction.     

Work function of vanadium dioxide thin films across the metal-insulator transition and the role of surface nonstoichiometry

Vanadium dioxide (VO(2)) undergoes a sharp metal-insulator transition (MIT) in the vicinity of room temperature and there is great interest in exploiting this effect in novel electronic and photonic devices. We have measured the work function of vanadium dioxide thin films across the phase transition using variable temperature Kelvin force microscopy (KFM). The work function is estimated to be ～5.15 eV in the insulating phase and increases by ～0.15 eV across the MIT. We further show that the work function change upon the phase transition is highly sensitive to near-surface stoichiometry studied by X-ray photoelectron spectroscopy. This change in work function is distinct from bulk resistance-versus temperature trends commonly used to evaluate synthesis protocols for such vanadium oxide films and optimize stoichiometry. The results are pertinent to understanding fundamental electronic properties of vanadium oxide as well as charge injection phenomena in solid-state devices incorporating complex oxides containing multivalence cations.     

Characteristics of CeOx–VO2 composite thin films synthesized by sol–gel process

Pure vanadium dioxide (VO₂) and CeOx–VO₂ (1.5 < x < 2) composite thin films were grown on muscovite substrate by inorganic sol–gel process using vanadium pentaoxide and cerium(III) nitrate hexahydrate powder as precursor. The crystalline structure, morphology and phase transition properties of the thin films were systematically investigated by X-ray diffraction, Raman, X-ray photoelectron spectroscopy, FE-SEM and optical transmission measurements. High quality of the VO₂ and CeOx–VO₂ composite films were obtained, in which the relative fractions of +4 valence state vanadium were above 70 % though the concentrations of cerium reached 9.77 at %. However, much of cerium compounds were formed at the edge of grains and the addition of cerium resulted in more clearly defined grain boundaries as shown in SEM images. Meanwhile, the composite films exhibited excellent phase transition properties and the infrared transmittance decreased from about 70 to 10 % at λ = 4 μm bellow and above the metal–insulator phase transition temperature. The metal–insulator phase transition temperatures were quite similar with about 66 °C of the pure VO₂ and CeOx–VO₂ composite thin films. But hysteresis widths increased with more addition of cerium, due to the limiting effect of grain boundaries on the propagation of the phase transition. Particularly, the CeOx–VO₂ composite film with an addition of 7.82 at % Ce showed a largest hysteresis width with about 20.6 °C. In addition, the thermochromic performance of visible transmittance did not change obviously with more addition of cerium.