TiO2 Interface Research Articles

Interfacial band offset engineering with barium-doping towards enhanced performance of all inorganic CsPbI2Br perovskite solar cells.

This study investigates the incorporation of Ba2+ at a low concentration into CsPbI2Br, resulting in the formation of mixed CsPb1-xBaxI2Br perovskite films. Photovoltaic devices utilizing these Ba-doped CsPbI2Br (Ba-CsPbI2Br) perovskite films achieved a higher stabilized power conversion efficiency of 14.07% compared to 11.60% for pure CsPbI2Br films. First-principles density functional theory calculations indicate that the improved device performance can be attributed to the efficient transport of conduction electrons across the interface between Ba-CsPbI2Br and the TiO2 electron transporting layer (ETL). The Ba-CsPbI2Br/TiO2 interface exhibits a type-II staggered band alignment with a smaller conduction band offset (CBO) of 0.25 eV, in contrast to the CsPbI2Br/TiO2 interface with a CBO of 0.48 eV. The reduced CBO at the Ba-CsPbI2Br/TiO2 interface diminishes the barrier for conduction electrons to transfer from the Ba-CsPbI2Br layer to the TiO2 layer, facilitating efficient charge transport.

Realizing room temperature catalytic hydrogenation of sodium phenoxide by Ru/TiO2 for hydrogen storage.

Sodium phenoxide is a potentially promising hydrogen storage material due to its high hydrogen capacity and enhanced thermodynamic properties. Nevertheless, efficient catalysts are still lacking due to the high kinetic barrier for the reversible hydrogen uptake and release of sodium phenoxide. In the current work, a comparative study on the catalytic hydrogenation of sodium phenoxide was conducted. To our delight, a simple yet effective ruthenium-based catalyst was identified to respond aggressively to hydrogen in the solid-state hydrogenation of sodium phenoxide even at room temperature. The activity was enhanced by 6 fold with the as-synthesized 5.0% Ru/TiO2 catalyst as compared to that with commercial 5.0% Ru/Al2O3, respectively, under the same conditions.

Enhancing the photoconductivity and gas sensing performance of TiO2/SnO2 heterostructures tuned by the thickness of the SnO2 upper layer

In this report, polycrystalline TiO2/SnO2 heterostructures with variable SnO2 film thickness were deposited by DC sputtering. Scanning electron microscopy images show a cracked surface in all films. The latter gets more widespread as the SnO2 layer thickness increases with deposition time. Optical transmittance measurements were used to determine the thickness of the TiO2 and SnO2 polycrystalline films. Photocurrent measurements of pure SnO2 films using UVA irradiation revealed a good response for thinner SnO2 films, however, these decrease as film thickness increases. Besides, photocurrent response is enhanced for the TiO2/SnO2 heterostructures over pure SnO2 film. It is thought that a high photocurrent response can be produced due to the improved ability to separate the photoinduced electrons and holes, as well as due to suitable charge management at the TiO2 and SnO2 interface. Additionally, the large amount of active sites for the thinner SnO2 upper layer favors better room temperature gas response to ethanol than that obtained for single SnO2 films. These features make the TiO2/SnO2 heterostructure a promising candidate for room temperature gas sensors and photosensitivity applications.

Efficient Ti3C2Tx MXene/TiO2 Hybrid Photoanodes for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) remain a promising technology for clean energy conversion due to their low cost, simple manufacturing, and high scalability. However, to keep these devices competitive against other photovoltaics like organic (OSCs) and perovskite solar cells (PSCs), it is necessary to enhance their efficiency. These improvements can be achieved by optimizing the charge transport and non-radiative carrier recombination within the operating device. Here, we show the design, fabrication, and subsequent characterization of Ti3C2Tx MXene/TiO2 nanocomposite hybrid photoanodes, supported by computational modeling. Ti3C2Tx MXene/TiO2 hybrid photoanodes containing 0.050, 0.075, and 0.100 wt % two-dimensional (2D) Ti3C2Tx flakes were prepared and investigated. The power conversion efficiency (PCE) of the device is found to be enhanced by 20% when only 0.075 wt % Ti3C2Tx was added to TiO2 due to the increase of electron transport in the photoanode. The density functional theory (DFT) calculations of the MXene–TiO2 interface indicate that the anatase potential is lowered, thus increasing the energy difference between the conduction bands of the N719 dye and the nanocomposite and favoring the migration of electrons toward the output terminal. Moreover, DFT results suggest a better separation of the photocarriers at the nanocomposite–N719 interface, which is supported by the measurement of longer electron lifetimes in the photoanode. These features demonstrate that the introduction of Ti3C2Tx into the photoanode is relevant to promote the energy-to-current conversion of DSCCs. Future approaches shall focus on the implementation of different 2D MXene structures to further improve the performance of these class of materials for direct applications in photovoltaic devices and photochemistry.

Conversion of CO2 to Methanol and Ethanol on Pt/CeOx/TiO2(110): Enabling Role of Water in C–C Bond Formation

The surface chemistry of alcohol synthesis from CO2 hydrogenation has been investigated using kinetic testing, ambient pressure X-ray photoelectron spectroscopy (AP-XPS), and DFT calculations over a multicomponent system, where Pt and ceria nanoparticles coexisted on a titania template, Pt/CeOx/TiO2(110). Due to its high ability to bind and activate CO2, not seen for typical Cu–ZnO catalysts, the Pt–CeOx–TiO2 interface is excellent for the hydrogenation of CO2 to methanol, with some ethanol also being produced (21% selectivity). The results of AP-XPS and DFT calculations indicate that the active state involves a mixture of Ti4+/Ti3+, Ce3+, and Pt0/Pt+. A fast pathway for the formation of CH3O species is only plausible when Ce3+ and Pt are present. The addition of water to the reaction feed facilitates the first hydrogenation of CO2 and substantially enhances the surface coverage of C-containing species (CH3O, HCOO, CO3, CHx), facilitating the formation of C–C bonds and the production of ethanol (38% selectivity).

The properties of perovskite solar cells with novel MAPbBr3/CsPbBr3 double absorber

Perovskite solar cells (PSCs) based on CsPbBr3 have garnered considerable attention due to their high stability and all-inorganic components. Although thermal annealing is a conventional and effective method to improve the quality of CsPbBr3 films, property improvement strategies are still scarce, especially for the vapor deposition process. In this work, a MAPbBr3 layer is introduced at the TiO2 and CsPbBr3 interface to construct a double-absorber heterojunction structure. It is found that the cubic phase of CsPbBr3 is formed directly on the MAPbBr3 underlayer due to the epitaxial growth. Furthermore, the heterojunction formed at the MAPbBr3/CsPbBr3 interface contributes to the superior extraction of the light-generated carriers. A power conversion efficiency (PCE) of 6.53% is obtained for the PSC with a double-absorber design. Despite the thickness of the epitaxial layer being shrunken after annealing at 150 °C for 30 min, a PCE of 5.90% is achieved, indicating the high thermal stability of the double-absorber device. Our work provides a new insight into quality engineering for the perovskite deposited by the vapor deposition process.

Boosting CO hydrogenation towards C2+ hydrocarbons over interfacial TiO2−x/Ni catalysts

Considerable attention has been drawn to tune the geometric and electronic structure of interfacial catalysts via modulating strong metal-support interactions (SMSI). Herein, we report the construction of a series of TiO2−x/Ni catalysts, where disordered TiO2−x overlayers immobilized onto the surface of Ni nanoparticles (~20 nm) are successfully engineered with SMSI effect. The optimal TiO2−x/Ni catalyst shows a CO conversion of ~19.8% in Fischer–Tropsch synthesis (FTS) process under atmospheric pressure at 220 °C. More importantly, ~64.6% of the product is C2+ paraffins, which is in sharp contrast to the result of the conventional Ni catalyst with the main product being methane. A combination study of advanced electron microscopy, multiple in-situ spectroscopic characterizations, and density functional theory calculations indicates the presence of Niδ−/TiO2−x interfacial sites, which could bind carbon atom strongly, inhibit methane formation and facilitate the C-C chain propagation, lead to the production of C2+ hydrocarbon on Ni surface.

Elucidating the Synergic Effect in Nanoscale MoS2 /TiO2 Heterointerface for Na-Ion Storage.

Interface engineering in electrode materials is an attractive strategy for enhancing charge storage, enabling fast kinetics, and improving cycling stability for energy storage systems. Nevertheless, the performance improvement is usually ambiguously ascribed to the "synergetic effect", the fundamental understanding toward the effect of the interface at molecular level in composite materials remains elusive. In this work, a well-defined nanoscale MoS2 /TiO2 interface is rationally designed by immobilizing TiO2 nanocrystals on MoS2 nanosheets. The role of heterostructure interface between TiO2 and MoS2 by operando synchrotron X-ray diffraction (sXRD), solid-state nuclear magnetic resonance, and density functional theory calculations is investigated. It is found that the existence of a hetero-interfacial electric field can promote charge transfer kinetics. Based on operando sXRD, it is revealed that the heterostructure follows a solid-solution reaction mechanism with small volume changes during cycling. As such, the electrode demonstrates ultrafast Na+ ions storage of 300 mAh g-1 at 10 A g-1 and excellent reversible capacity of 540 mAh g-1 at 0.2 A g-1 . This work provides significant insights into understanding of heterostructure interface at molecular level, which suggests new strategies for creating unconventional nanocomposite electrode materials for energy storage systems.

24.20%-Efficiency MA-Free Perovskite Solar Cells Enabled by Siloxane Derivative Interface Engineering.

Suppressing defects at the interface between the TiO2 electron transport layer (ETL) and perovskite film is critical for high efficiency and stable perovskite solar cells (PSCs). Herein, a siloxane derivative diethylphosphatoethylsilicic acid (PSiOH) is developed to modify the interface of TiO2 ETL/FA0.83 Cs0.17 PbI3 perovskite. Comprehensive characteristics reveal that silicon hydroxyl (SiOH) in PSiOH can reduce surface defects, improve the electrical propertiesand optimize the energy band structure of TiO2 by forming a SiOTi bond, while the phosphate bond (PO) in PSiOH can passivate Pb-related defects on the perovskite bottom surface. Consequently, PSiOH-modified PSCs yield a remarkable power conversation efficiency of 24.20% and improved air, thermal, or illumination stabilities. This study provides insight into passivation defects at the buried interface for efficient and stable PSCs.

Time-dependent measurement of plasmon-induced charge separation on a gold nanoparticle/TiO2 interface by electrostatic force microscopy

Plasmon-induced charge separation (PICS) is an efficient way to use the hot carriers generated by localized surface plasmon resonance. Although the ultrafast dynamics of hot carrier generation and annihilation itself are well understood, the slow dynamics of PICS are not, despite their importance for the use of hot carriers in chemical reactions. In this work, we directly observed the slow dynamics of PICS on an Au nanoparticle (NP)/TiO2 interface by using electrostatic force microscopy with time-resolved measurements obtained by sideband signal of frequency shift. The change in contact potential difference induced by PICS had a bias voltage dependence, indicating that the number of holes in the Au NPs ([{mathrm{h}}_{mathrm{AuNP}}^{+}]) accumulated by laser irradiation depended on bias voltage. The decay constant for the annihilation of the separated charge on the Au NPs at the Au NP/TiO2 interface was directly determined to be ca. 150 ms, and the annihilation process was discussed in a simple model based on the transient Schottky barrier.

Kinetic Coupling of Redox and Acid Chemistry in Methanol Partial Oxidation on Vanadium Oxide Catalysts

Kinetic, isotopic, and spectroscopic studies establish the active site requirements for three kinetically coupled catalytic cycles catalyzed by redox, Brønsted, and Lewis acid–base sites, which occur during methanol and oxygen reactions on titania-supported vanadium oxide catalysts. The initial activation of methanol during its oxidative dehydrogenation to formaldehyde restricts the overall turnovers─this reaction proceeds via CH3OH dissociative adsorption followed by a kinetically relevant C–H bond scission of the CH3O intermediate on V–O redox site pairs found at the interface of VOx and TiO2. The Gibbs free energy change of these two steps (ΔGads and ΔG⧧, respectively) both decrease as V–O–V coordination decreases and V–O–Ti coordination increases, leading to higher turnovers per surface vanadium as VOx dispersion increases, except the extreme case of isolated VO4. Coupled kinetically with the oxidative dehydrogenation cycle is the Brønsted acid-catalyzed cycle that forms dimethoxymethane─this cycle proceeds via methanol- and formaldehyde-derived CH3OCH2OH adsorption to Brønsted sites at the VOx–TiO2 interface, followed by its kinetically relevant C–O bond scission. Its turnovers also increase with VOx dispersion following the same trend as the oxidative dehydrogenation cycle but at a much faster rate, so the reaction can readily approach chemical equilibrium. Alongside the other two catalytic cycles is the Tishchenko reaction that forms methyl formate from two formaldehyde molecules, produced by the methanol oxidative dehydrogenation cycle, on exposed Ti4+–O2– Lewis acid–base pairs uncovered by VOx─this cycle proceeds via kinetically relevant intermolecular C–O bond formation followed by a rapid 1,3-hydride shift. The interplay of coexisting redox, Brønsted, and Lewis sites, each with its unique catalytic roles, leads to different rates and yields of the three products. The active site structure and mechanistic knowledge established here allow us to optimize the product ratios required for downstream synthesis of larger oxygenates.

Fractional-unit-cell-doped spinel/perovskite oxide interfaces with switchable carrier conduction

The two-dimensional hole gas (2DHG) at the polar LaAlO3/SrTiO3 interface remains elusive. Different from isostructural perovskite-type interfaces, the spinel/perovskite heterointerface of γ-Al2O3/SrTiO3 (GAO/STO) enables us to control interfacial states with sub-unit-cell precision. Herein, we present the epitaxial growth of fractionally doped GAO/STO heterointerfaces, where GAO is precisely doped on the scale of 1/4-unit-cell (0.2 nm) by ferromagnetic Fe3O4 and nonmagnetic ZnO atomic layers. Notably, the conduction of the engineered interfaces depends critically on the position of the dopant, where a coexistence of electron and hole conduction is measured at even sublayer-doped GAO/STO interfaces. First-principles density functional theory calculations indicate that electron conductivity is from the interfacial TiO2 layers of the STO substrate, while the hole conductivity is from the Zn-doped GAO film. The presence of hole conduction can be explained from the alternating structural feature of a doped layer without oxygen vacancies. This work sheds additional insight on the emergence of 2DHG at oxide interfaces and provides opportunities for atomically engineered oxide interfaces with non-isostructural layers.

The Effect of Deposition Conditions on Heterointerface‐Driven Band Alignment and Resistive Switching Properties

AbstractTitanium nitride and hafnium oxide stack have been widely used in various resistive memory elements since the materials are complementary‐metal‐oxide‐semiconductor compatible. The understanding of the interface properties between the electrode and the oxide is important in designing the memory behavior. To bridge this understanding, HfOx grown using plasma enhanced atomic layer deposition (PEALD) and thermal atomic layer deposition (TALD) are compared, in terms of band alignment and electrical performances in the HfOx/PEALD TiN stacks. X‐ray photoelectron spectroscopy reveals a thicker interfacial TiO2 layer in the PEALD HfOx/TiN stack whose interface resembles more to the PEALD HfOx/TiO2 interface (conduction band offset ΔEC = 1.63 eV), whereas the TALD HfOx stack interface resembles more to the TALD HfOx/TiN interface (ΔEC = 2.22 eV). The increase in the forming voltage and the early onset of reverse filament formation (RFF) in the I–V measurements for the PEALD HfOx stack confirms the presence of the thicker interfacial layer; the early onset of RFF is likely related to a smaller ΔEC. The findings show the importance of understanding the intricate details of the material stack, where ΔEC difference and the presence of a thicker TiO2 interfacial layer due to different deposition procedures affect the device performance.

Metal cations doping enhances selective adsorption of Cr3+ at oxide interfaces

Selective adsorbents for the sorted recovery of ppm-level mixed cation solutions have been identified as a promising strategy. However, the current design of adsorbents is still abided by the modification or enhancement for the common adsorption sites. The focus on other adsorption interfaces with innovative designs is rarely. In this paper, we report an adsorbent for shell-core type Fe3O4@TiO2 grown on the edge of montmorillonite. The selective adsorption of Cr3+ was accomplish by constructing an Fe3O4 (311)-TiO2 (101) interface through long-range bonds of Fe3+-O-Ti4+, which was in accordance with the Freundlich model. An adsorption amount of Cr3+ was obtained as 194.36 mg/g in the presence of (Cu2+, Sn4+)-Fe3+-O-Ti4+, which was much higher than that of the strongest interference Ni2+ (47.68 mg/g) on the same site, by virtue of promoting electron transport on the Fe3O4 surface through ion doping. Simultaneously, the more active TiO2 surface structure was enabled by polycrystalline surface distortion, which was triggered by the built-in electric field. The increased electron cloud density within Fe3O4 provided electrons, accelerated the enrichment of interfacial holes and endowed sufficient selective sites for restraining Cr3+. This work may provide some insight into the application of interfacial adsorbents for classified collection.

Complete Perovskite Solar Cells with Gold Electrodes Studied in the Visible and Near-Infrared Ranges

Complete solar cells with the triple-cation perovskite (FA0.76MA0.19Cs0.05Pb(I0.81Br0.19)3) sandwiched between spiro-OMeTAD (2,2′,7,7′-tetrakis-(N,N-di-4methoxyphenylamino)-9,9′-spirobifluorene) and mesoporous titania layers were examined using femtosecond transient absorption (TA) and steady-state absorption in the visible and near-infrared (NIR) regions. We demonstrate in this paper that the transmission spectroscopic measurements through a gold layer are possible and open the way to investigate the solar cells in working conditions (with applied voltage and/or additional illumination). We show that a gold electrode does not exhibit a significant TA signal itself but causes a difference in the perovskite response at around 800 nm and in the NIR range. The irradiation with a femtosecond laser, 1 Sun stationary illumination, or applied voltage causes significant changes in the TA spectra and kinetics at the TiO2 interface, most probably due to ion segregation or ion rearrangement process. The transmission signal in the NIR range is shown to be dominated by spectral modulation due to light interference; however, the process of hole injection at spiro-OMeTAD interfaces can be extracted. Finally, application of an appropriate forward bias enables the suppression of electron and hole injection to contact materials and results in increased lifetime of charge population in the perovskite.

Effects of electronic structure and magnetic performance at the surface/interface of r-GO and TiO2 in r-GO/TiO2 composite thin films: X-ray absorption near-edge structure and x-ray photoelectron spectroscopy

Titanium dioxide (TiO2) and reduced graphene oxide (r-GO) were synthesized separately by the radio frequency reactive magnetron sputtering technique on a Si-substrate (TiO2/Si) and the improved Hummers method, respectively. For deposition of r-GO onto TiO2, an aqueous solution of r-GO was deposited on the TiO2/Si thin film by the spin coating process to fabricate the (r-GO/TiO2)/Si composite thin-film. The (r-GO/TiO2)/Si composite thin-film is characterized using different spectroscopic techniques to study the effects at the interface of TiO2 and r-GO in the surface defects, vacancy, incorporation of the different oxygenated moiety, microstructural, surface morphological, electronic, and magnetic performance. Our motivation is to contribute and understand mainly the tuning of the electronic structure and magnetic performance of the (r-GO/TiO2)/Si composite structure for the development of future promising optoelectronic and spintronic applications. We found that the magnetic performance is improved due to the change in the electronic properties of r-GO deposited on TiO2 thin films. Thus, the role of the interfacial defects in the (r-GO/TiO2)/Si thin film and the mechanism of the tuning of the electronic structure and magnetic performance are elucidated comprehensively.

The promoted photocatalytic mechanism of N-doped graphene/TiO2 composites: From experiment to theory

Degradation of unsymmetrical dimethylhydrazine (UDMH) by graphene-based semiconductor composites is an effective photocatalytic method. To make full use of the solar energy, the composites were doped by non-metal atoms. One critical issue for the composites is understanding the electronic property relating to light absorption and carrier transfer. In this study, the NG (N-doped graphene)/TiO2 composites were fabricated, characterized and deeply investigated based on the density functional theory (DFT) calculation. Particularly, the resultant new energy levels in the band structure could decrease the bandgap of semiconductor, promote charge-transfer at the interface of graphene and TiO2, improve the light absorption, and finally enhance the photocatalytic activities. An excellent agreement of electron properties is found between our theoretical calculations and the characterization analysis of UV–vis DRS and RAMAN spectra. A possible photocatalytic mechanism based on the band structure and ESR result was developed. Thus, the NG/TiO2 composite could be a promising photocatalyst for UDMH degradation under the visible light.

Phase Variation of Ultrathin WO3 Electron‐Transport Layer Prepared by Scalable Langmuir–Blodgett Technique to Boost Efficiency of Dye Sensitized Solar Cells

In third‐generation solar cells, dye sensitized (DSCs) and perovskite (PSCs) both, the role of electron‐transport layers (ETLs) is to block hole transfer at fluorine‐doped tin oxide/mesoporous TiO2 interface, while efficiently transporting the electron at this interface. Conventional solution‐processed dense anatase TiO2 ETL is limited by its low electron mobility. WO3, despite having higher electron mobility and chemical stability, has seldom been used as ETL in DSCs/PSCs, owing to poor crystalline structure and interfacial charge transfer in ETLs prepared using existing methods. Herein this paper, ultrathin and uniform WO3 films of different crystalline structures, such as tetragonal (t‐), orthorhombic (o−), hexagonal (h−), and monoclinic (m−), prepared by scalable Langmuir–Blodgett method, are reported. The efficiency (η) of DSCs fabricated with ETL having high‐symmetry phases of WO3 (h‐WO3, o‐WO3, t‐WO3) is found to exceed the efficiency of devices having ETL of low‐symmetry WO3 phase (m‐WO3). Further, highest η ≈ 9.53%, tantamount to an improvement of 13%, is found in DSCs fabricated with ETL having a mixed phase of o‐ and t‐WO3 and surpassed η of devices based on TiO2 ETLs (8.4%). Herein, the role of structure/phase of WO3 ETLs toward enhancing device performance and outperforming the conventional TiO2 ETLs‐based DSCs is highlighted.

In-situ exfoliation and assembly of 2D/2D g-C3N4/TiO2(B) hierarchical microflower: Enhanced photo-oxidation of benzyl alcohol under visible light

This study demonstrates the successfully fabrication of 2D/2D g-C3N4/TiO2(B) hierarchical microflowers via a hydrothermal in-situ exfoliation and assembled method. The structural and optical properties of g-C3N4/TiO2(B) are characterized by X-ray diffraction, transmission electron microscopy, as well as spectroscopic techniques. The recombination of g-C3N4 with TiO2(B) significantly improves the photocatalytic performance in the photo-oxidation of benzyl alcohol to benzaldehyde using visible light (λ > 420 nm). Trapping experiments and electron spin resonance spectroscopy indicate the active radicals of ⋅O2−, ⋅OH and h+ are responsible for the enhanced activity. The heterojunction interface between g-C3N4 sheets and TiO2(110) facets boosts separation efficiency of photogenerated charges, thus resulting into the high catalytic performance of g-C3N4/TiO2(B) composites. Density functional theory (DFT) calculations reveal that the charge transfer between the TiO2(B) and g-C3N4 interface and the consequent formation of a built-in electric field at the interface, which are responsible for the high catalytic performance of g-C3N4/TiO2(B) composites. The study firstly reports a simple in-situ hydrothermal growth protocol to efficiently construct 2D/2D g-C3N4/TiO2(B) heterojunction composites and offer guidelines for design of a new synthetic strategy to prepare efficient photocatalysts.

Evaluation of Coating Ability of TiO2 Nanoparticles onto Aluminum Alloy Sheet by Physicochemical Analysis

TiO2 nanoparticle films were successively coated onto aluminum (Al) alloy sheet using a coating technique at 150C for 5 h. This was a chemical sintering method, integrated with Al/TiO2/Al sandwich coupling and used weak acid as a binder. To evaluate the coating ability of the TiO2 nanoparticles on the aluminum alloy sheet, the physicochemical characteristics of the film samples were analyzed by means of SEM-EDS, FT-IR and XRD. The TiO2 films prepared by the coating technique at 150C for 5 h were compared with TiO2 films prepared by the doctor-blade technique at 500C for 10 min using two different organics as binders. The results of the physicochemical analysis indicated that the coating technique at 150C for 5 h provided superior coating ability of TiO2 nanoparticles onto aluminum alloy sheet than the doctor-blade technique. This may have been because of reduction of the thermal gradient at the TiO2 interface, which affected the relaxation of internal and external stresses on the TiO2 film on the aluminum alloy substrate. In this work, the TiO2 film prepared by chemical sintering method, integrated with Al/TiO2/Al sandwich coupling at 150C for 5 h using weak acid mixed with 5 wt.% ammonia as a binder proved to produce the optimum TiO2 film; however, film thickness control using the coating technique at 150C for 5 h still needs to be developed.