Nanostructured Titanium Dioxide Thin Films Research Articles

Nanostructured TiO2 thin films sputtered at room temperature as electron transport layer for flexible perovskite solar cell applications: Impact of varying RF power

This work examines the adoption of radio frequency (RF) sputtering at power ranging from 100 to 300 W to deposit nanostructured titanium dioxide (TiO2) thin films on indium tin oxide (ITO)-coated polyethylene terephthalate (PET) flexible substrate (ITO/PET) at room temperature. At higher RF power, X-ray diffraction (XRD) results exhibited evolution from amorphous into crystalline anatase with preferred (101) orientation and the films revealed spherical-like nanostructures with increasing grain size from 15.71 to 21.57 nm. Films transparency decreased from 79% to 70%. Estimated energy gap decreased from 3.57 to 3.36 eV, while refractive index increased from 2.19 to 2.25, denoting a red shift in the films. The thin film deposited at 300 W exhibited high conductivity and mobility of 19.65 × 10−5 Ω−1 cm−1 and 0.30 cm2/Vs, respectively. The film demonstrated its capability as an electron transport layer for flexible perovskite solar cells.

Synthesis and study the concentration effect on the photocatalytic activity of titania nanoparticles as anti-bactria using reactive magnetron sputtering technique

In this work, the dc reactive magnetron sputtering technique was used to prepare and deposit nanostructured titanium dioxide (TiO2) thin films on glass substrates. Titanium dioxide thin films of mixed phase (anatase+rutile) and single phase (anatase) were prepared using different gas mixing ratios, and for both of the two phases, they were diagnosed via x-ray diffraction (XRD). It was found that the contents of rutile in mixed phase dependent on the deposition time increased from the ratio of 40 to 46% and 50% as the deposition time increased from 3 h to 3.30 and 4 h. The photocatalytic activity of the mixed and single phase TiO2 was measured by kill the bacteria Escherichia coli (E.Coli) under exposure to UV-radiation. It was proven that the photocatalytic activity in the mixed phase (TiO2) gave better results weight fraction is 40% as an antibacterial activity. Based on the obtained results anti-bacterial activity of dioxide titanium nanoparticles was dependent on the concentration and phase of TiO2 and weight fraction of mixed-phase.

Horizontal vs Vertical Evolution of the Compositional and Morphological Profiles in Nanostructured Titania Thin-Films for Photocatalytic Application

Horizontal vs Vertical Evolution of the Compositional and Morphological Profiles in Nanostructured Titania Thin-Films for Photocatalytic Application

Study of Effect of the Chrome Additive on the Structural, Morphology and Optical Properties of Nanostructured Titanium dioxide Thin Film

Undoped Titanium dioxide (TiO2) and Cr-doped TiO2 films were prepared by Spray Pyrolysis Technique (SPT). XRD styles showed that TiO2 films were grown along dominant orientation of (111). Crystallite size increases from 8.95 nm to 9.70 nm as vanadium concentration increase, whereas the strain(%) parameter increased from 3.87 to 3.57. the AFM imaging shows that the Undoped TiO2 and TiO2: Cr thin films was discontinuous surface with spherically grains decreased from (65.95-44.23 nm) with increase doping from 0% to 3%, and root-mean square (rms) roughness of surface is about (9.70-2.41) nm. Spectrometric analysis of deposited films showed high transmittance in spectral range from 300 to 900 nm, whereas the corresponding value of bandgaps was ranged from 3.48 to- 3.38 eV by Cr doping. Results show that doping of TiO2 with Cr enhances the optical properties. the absorption coefficient (α), extinction coefficient (k) and refractive index (n) are increased when Cr additive is increasing.

Enhanced performance of planar perovskite solar cells using dip-coated TiO2 as electron transporting layer

Nanostructured titanium dioxide thin films (TiO2) have been deposited on indium tin oxide (ITO) substrate, using dip-coating process from partial hydrolysis and condensation of tetrabutylorthotitanate, and using butanol and acetic acid respectively as solvent and catalyst. The effect of film thickness on the microstructural, morphological and optical properties was investigated, as well as their applicability as electron transporting layer for planar perovskite solar cells (PSCs). In all cases, well-crystallized anatase TiO2 films with a relatively smooth and homogeneous surface were obtained, while the optical band-gap of the films showed a small increase from 3.25 eV to 3.4 eV by increasing the film thickness from 50 nm to 90 nm. On the other hand, the refractive index (n) tends towards a value of 2 above 400 nm, while the extinction coefficients (k) goes down to zero. In addition, these TiO2 films deposited on ITO/glass substrates were used as electron transporting layer in planar PSCs. Thus, the important role in electron transport obtained for TiO2, allowed to improve the performance of the device and indicated the potential of the dip-coated TiO2 as an electron transporting layer for planar PSCs.

Optical and Morphological Characteristics of Nanostructured Titanium Dioxide Thin Films Prepared by DC Reactive Magnetron Sputtering Technique

In this work, the optical characteristics of nanostructured titanium dioxide thin films prepared by DC reactive magnetron sputtering technique. These characteristics were controlled by controlling the spatial distribution of plasma column generated between discharge electrodes throughout varying the inter-electrode distance from 2 to 5cm, discharge current from 10 to 50 mA and working pressure from 0.04 to 0.1 mbar. The absorption spectra, x-ray diffraction patterns and atomic force microscopy of the prepared films were recorded at different inter-electrode distances and compared to the published results. This is good attempt to optimize the optical characteristics of nanostructured titanium dioxide thin films for optical and spectral applications.

Impact of Catalytic Additive on Spray Deposited and Nanoporous Titania Thin Films Observed via in Situ X-ray Scattering: Implications for Enhanced Photovoltaics

With the aim of obtaining nanostructured titania thin films for the potential use in hybrid or dye sensitized solar cells, the amphiphilic diblock copolymer polystyrene-b-poly(ethylene oxide) is employed as a structure directing template in combination with sol–gel chemistry. For easy upscaling, spraying is used as a deposition technique. In situ grazing incidence small-angle X-ray scattering (GISAXS) measurements are performed during spraying and show that most titania structures are already formed within the solution prior to deposition. However, structural rearrangement is enabled during the deposition period when small amounts of hydrochloric acid (HCl) are used as a catalytic additive to the spray solution. This behavior is ascribed to an altering of the reaction dynamics and phase separation in the presence of HCl, which significantly improves the templating effect of the employed diblock copolymer. With HCl as an additive the final nanoscale morphologies exhibit smaller pore sizes and strongly enhanced order as compared to thin films sprayed from solutions that do not contain HCl as quantified with atomic force microscopy, scanning electron microscopy, and GISAXS.

Wet Imprinting of Channel-Type Superstructures in Nanostructured Titania Thin Films at Low Temperatures for Hybrid Solar Cells.

Hierarchically structured titania films, exhibiting interconnected foam-like nanostructures and large-scale channel-type superstructures, were achieved in an energy-saving way at low temperatures by a polymer template-assisted sol-gel synthesis in combination with a wet-imprinting process. The surface morphology was probed with scanning electron microscopy and atomic force microscopy, whereas the inner morphology was characterized with grazing incidence small-angle X-ray scattering measurements. Compared to the initial hybrid films, the titania films showed reduced structure sizes caused by removal of the polymer template. UV/Vis measurements showed an additional light-scattering effect at various angles of light incidence in the hierarchically structured titania films, which resulted in higher light absorption in the wet-imprinted active layer. To give proof of viability, the titania films were evaluated as photoanodes for dye-free hybrid solar cells. The dye-free layout allowed for low-cost fabrication, avoided problems related to dye bleaching, and was a more environmentally friendly alternative to using dyes. Under different angles of light incidence, the enhancement in the short-circuit current density was in good agreement with the improvement in light absorption in the superstructured active layer, demonstrating a positive impact of the superstructures on the photovoltaic performance of hybrid solar cells.

Preparation of nanostructured titania thin films by sol–gel technology

This study is concerned with the preparation of hydrolytically active heteroligand complex [Ti(OC4H9)3.61(O2C5H7)0.39] from titanium butoxide and acetylacetone and with the gel formation kinetics in a solution of this complex upon hydrolysis and polycondensation. Single-layer and double-layer thin films of a solution of this precursor were coated on polished silicon substrates using the dip-coating method. The crystallization of nanostructured titania films during the heat treatment of these xerogel coatings was studied using various protocols; the anatase–rutile phase transition temperature was found to depend on the film thickness. The effects of the precursor solution viscosity on the film thickness and crystallite size were determined.

Nanostructured carbon substrate improves the photoelectrochemical water splitting activity of cluster-assembled TiO2 thin films

The supersonic cluster beam deposition (SCBD) of titanium oxide nanoparticles is a versatile and effective bottom-up approach for the fabrication of nanostructured titanium dioxide (ns-TiO2) thin films; here we report on its application to the production of photoelectrodes for photoelectrochemical water splitting. The use of a cluster-assembled carbon (ns-C) thin film deposited by SCBD as a substrate layer for the titania nanoparticles deposition is also investigated and demonstrated to originate C:TiO2 nanocomposite photoelectrodes with increased surface roughness and more than four-fold enhanced IPCE (ca. 4.5% under monochromatic illumination at 330 nm employing KOH 1 M as aqueous electrolyte solution and without any external bias) compared to pure TiO2 photoelectrodes deposited by the same technique and featuring the same TiO2 thickness (ca. 250 nm). Electrochemical impedance spectroscopy (EIS) has been used to correlate the increase of the IPCE to an optimized electrode structure, electrolyte accessibility and electric conductivity. These results are promising towards the practical use of nanoparticle-assembled materials and the improving of their properties.

Linker-free deposition and adhesion of Photosystem I onto nanostructured TiO2 for biohybrid photoelectrochemical cells.

Photosystem I (PSI) from oxygenic photosynthetic organisms is an attractive sensitizer for nano-biohybrid solar cells as it has a combined light-harvesting and reaction center in one protein complex and operates at a quantum yield close to one in biological systems. Using a linker-free deposition technique enabled by an electrospray system, PSI was coupled to 1-D nanostructured titanium dioxide thin films to fabricate an electrode for a photoelectrochemical cell. After deposition, the surfactant in the PSI aggregate was dissolved in the surfactant-free electrolyte, ensuring that partly hydrophobic PSI was not resuspended and stayed in contact with titanium dioxide. A maximum current density of 4.15 mA cm(-2) was measured after 10 min of electrospray deposition, and this is the highest current density reported so far for PSI-based photoelectrochemical cells. The high current is attributed to 1D nanostructure of titanium dioxide and orientation of the PSI onto the surface, which allows easy transfer of electrons.

A micro oxygen sensor based on a nano sol-gel TiO2 thin film.

An oxygen gas microsensor based on nanostructured sol-gel TiO2 thin films with a buried Pd layer was developed on a silicon substrate. The nanostructured titania thin films for O2 sensors were prepared by the sol-gel process and became anatase after heat treatment. A sandwich TiO2 square board with an area of 350 μm × 350 μm was defined by both wet etching and dry etching processes and the wet one was applied in the final process due to its advantages of easy control for the final structure. A pair of 150 nm Pt micro interdigitated electrodes with 50 nm Ti buffer layer was fabricated on the board by a lift-off process. The sensor chip was tested in a furnace with changing the O2 concentration from 1.0% to 20% by monitoring its electrical resistance. Results showed that after several testing cycles the sensor's output becomes stable, and its sensitivity is 0.054 with deviation 2.65 × 10−4 and hysteresis is 8.5%. Due to its simple fabrication process, the sensor has potential for application in environmental monitoring, where lower power consumption and small size are required.

Interaction of Bacterial Cells with Cluster-Assembled Nanostructured Titania Surfaces: An Atomic Force Microscopy Study

The nanoscale interaction of bacterial cells with solid surfaces is a key issue in biomedicine because it constitutes the first pathogenic event in the complex series of biofilm development on prosthetic devices. We report on an Atomic Force Microscopy study of the interaction of Escherichia coli and Pseudomonas aeruginosa bacterial cells with nanostructured titania thin films with controlled and reproducible nanometer-scale morphology, produced by assembling Ti clusters from the gas phase in a Supersonic Cluster Beam Deposition apparatus. The results demonstrate that bacterial adhesion and biofilm formation are significantly influenced by a pure physical stimulus, that is, the nanoscale variation of surface topography. The increase of nanoscale film roughness promotes bacterial adhesion with respect to flat substrates; remarkably, Pseudomonas aeruginosa cells lose their flagella on nanostructured TiO2 thin films upon adhesion, as opposed to same bacteria onto reference smooth glass substrates. Further, we have observed increased cell biovolume and other biofilm properties on nanostructured substrates in comparison with smooth glasses. These findings suggest that the design of innovative biomaterials with a suitable patterning of biomaterials surfaces can be an effective approach to control the adhesion of microorganisms to in vivo implant surfaces with active biological functionalities.

Phase transformation of nanostructured titanium dioxide thin films grown by sol–gel method

Nanostructured TiO2 thin films were deposited on quartz glass at room temperature by sol–gel dip coating method. The effects of annealing temperature between 200∘C to 1100∘C were investigated on the structural, morphological, and optical properties of these films. The X-ray diffraction results showed that nanostructured TiO2 thin film annealed at between 200∘C to 600∘C was amorphous transformed into the anatase phase at 700∘C, and further into rutile phase at 1000∘C. The crystallite size of TiO2 thin films was increased with increasing annealing temperature. From atomic force microscopy images it was confirmed that the microstructure of annealed thin films changed from column to nubbly. Besides, surface roughness of the thin films increases from 1.82 to 5.20 nm, and at the same time, average grain size as well grows up from about 39 to 313 nm with increase of the annealing temperature. The transmittance of the thin films annealed at 1000 and 1100∘C was reduced significantly in the wavelength range of about 300–700 nm due to the change of crystallite phase. Refractive index and optical high dielectric constant of the n-TiO2 thin films were increased with increasing annealing temperature, and the film thickness and the optical band gap of nanostructured TiO2 thin films were decreased.

Photocatalytic Active Titania Thin Films through Oxidation of Metallic Ti in Aqueous H2O2 Solutions Containing Various Block Copolymers

Abstract Various nanostructured titania thin films were fabricated by direct oxidation of metallic Ti substrates in hydrogen peroxide solutions with the additives of nitric acid and block copolymers of P123 or F127. X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) were utilized to analyze the morphology and structure of the titania films. Photocatalytic properties of the thin films were evaluated by the degradation of rhodamine B in water under the illumination of a high-pressure mercury lamp. The film only with the block copolymer additive consists of rod-like titania; while flower-like titania aggregates are achieved when both block copolymers and nitric acid are added to the hydrogen peroxide solution. After a subsequent calcination at 450 °C, all the titania films are crystallized further to a mixture of anatase and rutile with a similar average grain size. An indirect bandgap of 2.65–2.85 eV is estimated for the present films, which is significantly lower that of the bulk titania. The titania film derived with the P123 additive shows higher photocatalytic activity than that with the F127 additive, either with or without the additive of nitric acid.

Quantitative Characterization of the Influence of the Nanoscale Morphology of Nanostructured Surfaces on Bacterial Adhesion and Biofilm Formation

Bacterial infection of implants and prosthetic devices is one of the most common causes of implant failure. The nanostructured surface of biocompatible materials strongly influences the adhesion and proliferation of mammalian cells on solid substrates. The observation of this phenomenon has led to an increased effort to develop new strategies to prevent bacterial adhesion and biofilm formation, primarily through nanoengineering the topology of the materials used in implantable devices. While several studies have demonstrated the influence of nanoscale surface morphology on prokaryotic cell attachment, none have provided a quantitative understanding of this phenomenon. Using supersonic cluster beam deposition, we produced nanostructured titania thin films with controlled and reproducible nanoscale morphology respectively. We characterized the surface morphology; composition and wettability by means of atomic force microscopy, X-ray photoemission spectroscopy and contact angle measurements. We studied how protein adsorption is influenced by the physico-chemical surface parameters. Lastly, we characterized Escherichia coli and Staphylococcus aureus adhesion on nanostructured titania surfaces. Our results show that the increase in surface pore aspect ratio and volume, related to the increase of surface roughness, improves protein adsorption, which in turn downplays bacterial adhesion and biofilm formation. As roughness increases up to about 20 nm, bacterial adhesion and biofilm formation are enhanced; the further increase of roughness causes a significant decrease of bacterial adhesion and inhibits biofilm formation. We interpret the observed trend in bacterial adhesion as the combined effect of passivation and flattening effects induced by morphology-dependent protein adsorption. Our findings demonstrate that bacterial adhesion and biofilm formation on nanostructured titanium oxide surfaces are significantly influenced by nanoscale morphological features. The quantitative information, provided by this study about the relation between surface nanoscale morphology and bacterial adhesion points towards the rational design of implant surfaces that control or inhibit bacterial adhesion and biofilm formation.

The effect of Sn dopant on crystal structure and photocatalytic behavior of nanostructured titania thin films

In this study, preparation of Sn doped (0–30 mol % Sn) TiO2 dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of Sn content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission SEM (FE-SEM), and high resolution transmission electron microscopy (HR-TEM). Surface topography and surface chemical state of thin films were examined by atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). XRD patterns showed an increase in peak intensities of the rutile crystalline phase by increasing the Sn dopant. The prepared Sn-doped TiO2 photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue solution under UV irradiation. The result shows that doping an appropriate amount of Sn can effectively improve the photo-catalytic activity of TiO2 thin films, and the optimum dopant amount is found to be 15 mol%. The Sn4+ dopants substituted Ti4+ in the lattice of TiO2 and increased surface oxygen vacancies and the surface hydroxyl groups. TEM results showed small increase in planar spacing (was detected by HR-TEM caused by Sn dopants in titania based crystals).

Electrical Properties of Nanostructured Titanium Dioxide Thin Films Prepared by Sol-Gel Spin-Coating Method

This paper investigated the electrical properties of nanostructured Titanium Dioxide (TiO2) thin films prepared by the sol-gel method at different annealing temperatures. The precursor used was Titanium (IV) butoxide at concentration of 0.4 M. The TiO2 thin films were deposited on the glass and silicon substrates by using the spin coating technique. The influence of annealing temperatures on the electrical, structural, surface morphology and optical properties of the films were characterized by I-V measurement, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and UV-Vis Spectroscopy, respectively. It was found that the electrical properties of TiO2¬ thin films were changed due to the changes of annealing temperatures. As the annealing temperatures rises, the resistivity of the film found to be decreased. The result also shows that films which does not applied annealing temperature called as deposited were found to be amorphous while the films with annealing temperature T = 350oC and above became crystalline structure. The anatase phase can be obtained at annealing temperatures from T = 350oC up to T = 500oC.

Cathodoluminescence Evaluation of Oxygen Vacancy Population in Nanostructured Titania Thin Films for Photocatalytic Applications

Room-temperature results of cathodoluminescence (CL) spectroscopy investigations are presented for nanostructured titanium dioxide (anatase) thin films (500 nm thick) deposited via RF magnetron sputtering on high-purity silica substrates. The collected CL bands of the anatase thin films, as deposited and after different annealing cycles, showed a broad morphology consisting of three Voigtian bands located at 500, 550, and 610 nm that were partially overlapping. The overall CL emission increased with increasing temperature and time of the annealing cycle as a consequence of the increased crystallinity of the thin film. A clear trend was found for the oxygen-vacancy-related band (located at 610 nm), whose relative intensity decreased, as compared with the as-grown sample, after annealing in air; the higher the annealing temperature, the lower the relative intensity. We evaluated the photoactivity of the nanostructured thin film samples by measuring their photocatalytic activity in aqueous solution toward the degradation of phenol. A relationship between the decrease in oxygen vacancy concentration as a consequence of the annealing and the increase in the photoactivity was highlighted.

Hydrophilic and optical properties of nanostructured titania prepared by sol–gel dip coating

Nanostructured titania thin films were prepared under controlled atmospheric conditions by the sol–gel dip-coating technique on glass, fused silica and (1 0 0)-silicon substrates. Two different sol–gel routes were employed by using different precursor solutions, a highly acid solution and a polymer-like solution. The influence of sol composition and of the substrate type on the morphology, coating porosity, surface roughness, crystalline phases and grain size of the titania films were investigated in detail. In addition, the relationship between microstructural/morphological properties and the optical properties (energy gap, refractive index and extinction coefficient) and the hydrophilic performance of the coatings were evaluated. Our experimental results clearly indicate that the sol composition and substrate type remarkably influence the films' morphology and microstructure; moreover, they consequently modify the optical response and hydrophilic performances of the samples, showing that superhydrophilic titania coatings can be obtained opportunely by choosing the composition of the precursor sol–gel solution. Blue shift of the band gap energy and a band structure mutation from indirect to direct were also revealed. The hydrophilic properties and the change in the band gaps transition can be attributed to oxygen vacancies on the surface of the titania nanocrystallites that gives rise to Ti3+ sites and, consequently, to structural changes/defects of the anatase nanoarchitecture. These findings allow us to design and tailor the optical and hydrophilic properties of the titania coatings.