Titanium Dioxide Thin Films Research Articles

Patterning of plasmonic Au nanoparticles on the surfaces of TiOx thin films by solid state thermal dewetting

It is essential to study the thermal dewetting behavior of as-deposited nano-films for large scale and high-throughput fabrication. We report here on the nucleation of Au nanostructures onto titanium dioxide (TiOx) thin films surfaces, which occurred in consecutive steps. First, TiOx thin films were grown on quartz substrates reactively by e-beam evaporator and then thermally annealed at different temperatures, starting from 300°C to 900°C. Subsequently, a nano-film of Au was deposited on the top of these TiOx surfaces. The stacked Au / TiOx samples were post-annealed using muffle furnace at a temperature of 600°C for 1 h, to study the thermal dewetting properties and the controlled growth of the different TiOx morphologies on the formation of Au nanoparticles (NP) and their plasmonic response. Such dual-structures were characterized accordingly to probe their topological, morphological, structural, and optical properties, by means of x-ray photoelectron spectroscopy, scanning electron microscope, atomic force microscopy, and ultra-violet–visible–near infrared characterization techniques. The thermal dewetting properties were found to improve at high temperatures (>500 ° C), where the Au NP size distribution was found to follow a Gaussian pattern centered around 30 nm. The average surface roughness also increased significantly with respect to the TiOx dewetting temperature, which is mainly attributed to the porosity of the films. Finally, the absorption peak for Au nanostructures has shown a localized surface plasmon resonance close to 520 nm, along with a broad shoulder peak with a strong tail thereby reflecting the wide distribution of the formed Au NP sizes.

Experimental comparison between photoconductive and graphene-based photogating detection in a UV-A region.

Photoconductive detectors that use intrinsic absorbent materials include a wide range of detectors. In this paper, a photoconductive detector is fabricated using a titanium dioxide (T i O 2) thin film. The mechanism of the photodetector is changed to the photogating mechanism by transferring monolayer graphene onto the T i O 2 thin film, which shows a great responsivity with a slight change in the fabrication process. Since the maximum responsivity can be obtained by applying and adjusting the gate voltage, the gate voltage is set in all experiments, and the effect of the gate voltage is investigated in both detectors. It is observed that by increasing the gate voltage, the responsivity of the photogating detector increases to 40A/W at a gate voltage of 15V. However, in the photoconductive detector, the increase in the gate voltage does not have a particular effect on the detector responsivity. In the photogating detector, the increase in the responsivity due to the increase in the gate voltage is attributed to applying the gate voltage to the graphene layer and not the absorber layer. The efficiency of both detectors is confirmed up to a frequency of 5kHz.

Investigation of PP monofilament structural changes with various conditions used for deposition of TiO2 atomic layers by ALD technique

Atomic layer deposition (ALD) technology makes it possible to obtain biocompatible and homogeneous ultrathin oxide layers, which creates opportunities to modify the surface properties of PP surgical meshes, for example, through TiO2 deposition. The aim of this study was to investigate the changes occurring in the structural and physical properties of polypropylene (PP) monofilaments used for surgical mesh production after deposition of a thin film of titanium oxide by the ALD method under various conditions. The titanium oxide was deposited from TiCl4 and water in the temperature range 100 °C–160 °C. The surface morphologies and chemical compositions of the deposited layers were studied with scanning electron microscopy (SEM) with energy-dispersive X-ray chemical microanalysis (EDS). Structural investigations of the PP monofilaments were carried out with wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy. The thermal properties of the PP monofilament were characterized with differential scanning calorimetry (DSC). Additionally, the effects of structural changes were evaluated with tensile strength tests. The results made indicated the critical thermal conditions required for TiO2 deposition on PP substrates with the ALD method.

Tailoring the structural and optical properties of fabricated TiO2 thin films by O2 duty cycle in reactive gas-timing magnetron sputtering

Titanium dioxide (TiO2) thin films were deposited on silicon (100) and glass substrates via conventional reactive sputtering and reactive gas-timing (RGT) sputtering techniques. The duty cycle of supplied O2 gas determined its effect on the properties of the TiO2 films through spectroscopic ellipsometry (SE). With the best triple-layer model for SE fitting, the films' structure and optical properties were analyzed and compared. The high-resolution transmission electron microscope (HR-TEM) showed good agreement with the structure of the SE model, while the grazing-incidence X-ray diffraction (GIXRD) confirmed the crystallinity of the films. The results showed that the duty cycle was a crucial factor in the deposition rate and crystalline phase of the TiO2 films. The optical reflectance (%R) spectra were measured by a UV-VIS-NIR spectrophotometer, representing anti-reflection properties at a specific wavelength related to the duty cycle. Moreover, the omnidirectional optical transmittance (Omni-T) profiles were also determined. The results showed that the transmittances (%T) of TiO2 film near those specific wavelengths were enhanced over the bare glass substrate at a wide angle. In addition, photoelectron spectroscopy (PES) was used to confirm the chemical states and atomic compositions.

Spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films

We experimentally demonstrate spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films. The width of the compositional gradient interface (CGI) between films is varied from 1.4 to 2.0 nm via sputtering. Spin-torque ferromagnetic resonance is observed in the ferromagnetic ${\mathrm{Ni}}_{95}{\mathrm{Cu}}_{5}$ alloy fabricated on a Ti/W bilayer with the CGI. The positive spin torque increases with decreasing CGI width, but a negative spin torque is superimposed owing to the negative spin Hall effect in bulk tungsten. A structural undulation in the CGI eliminates this variation in positive spin torque. The CGI width dependence of the spin torque is associated with the generation of spin and/or orbital angular momentum flow at the CGI. Spin-torque generation using a CGI expands the range of material choice for magnetic nonvolatile memory applications.

NV microscopy of thermally controlled stresses caused by thin Cr2O3 films.

Many modern applications, including quantum computing and quantum sensing, use substrate-film interfaces. Particularly, thin films of chromium or titanium and their oxides are commonly used to bind various structures, such as resonators, masks, or microwave antennas, to a diamond surface. Due to different thermal expansions of involved materials, such films and structures could produce significant stresses, which need to be measured or predicted. In this paper, we demonstrate imaging of stresses in the top layer of diamond with deposited structures of Cr2O3 at temperatures 19°C and 37°C by using stress-sensitive optically detected magnetic resonances (ODMR) in NV centers. We also calculated stresses in the diamond-film interface by using finite-element analysis and correlated them to measured ODMR frequency shifts. As predicted by the simulation, the measured high-contrast frequency-shift patterns are only due to thermal stresses, whose spin-stress coupling constant along the NV axis is 21±1 MHz/GPa, that is in agreement with constants previously obtained from single NV centers in diamond cantilever. We demonstrate that NV microscopy is a convenient platform for optically detecting and quantifying spatial distributions of stresses in diamond-based photonic devices with micrometer precision and propose thin films as a means for local application of temperature-controlled stresses. Our results also show that thin-film structures produce significant stresses in diamond substrates, which should be accounted for in NV-based applications.

Solid‐State NMR Spectroscopic Investigation of TiO2 Grown on Silica Nanoparticles by Solution Atomic Layer Deposition

AbstractAtomic layer deposition in solution (sALD) is just emerging as a technology for the preparation of thin films. Unlike ALD from the gas phase, it allows for mild reaction conditions in a solvent phase and at room temperature, thus decreasing the energy requirements of the process and widening the range of accessible precursor molecules. In this work, the deposition of thin films of titania on silica is investigated using titanium(IV) isopropoxide (TTIP) and water as precursors, which are alternatingly brought into contact with the support in a home‐built plug flow reactor. The mechanism of covalent grafting of the precursor to the surface, subsequent hydrolysis, and reaction to a layer of titania are investigated in detail using magic angle spinning (MAS) solid‐state nuclear magnetic resonance (NMR) spectroscopy. TTIP preferentially reacts with Q2 groups of condensed silica. 2D solid‐state NMR spectra allow to clearly show the successful grafting of this compound to the support by the appearance of a characteristic signal at −107 ppm, which is tentatively attributed to silicon nuclei in a SiOTi bond, and to reveal the presence of titanol groups on the emerging TiO2 film.

Bi-functional photocatalytic heterostructures combining titania thin films with carbon quantum dots (C-QDs/TiO2) for effective elimination of water pollutants

In this study, carbon quantum dots (C-QDs), prepared via hydrothermal-microwave procedures, were successfully combined with nanostructured titania (TiO2). The photocatalytic oxidation/reduction activity of the C-QDs/TiO2 composite films was evaluated in the decomposition of organic-inorganic contaminants from aqueous solutions under UV illumination. Physicochemical characterizations were applied to investigate the crystal structure of the carbon quantum dots and the composites. It was found that the prepared C-QDs/TiO2 composites had great contribution to the photocatalytic reduction of hexavalent chromium (Cr+6) species and 4-Nitrophenol (PNP) as well as to the photocatalytic oxidation of methylene blue (MB) and Rhodamine B (RhB) dyes. The mechanism of the photocatalytic reaction was studied with trapping experiments, revealing that the electron (e−) radical species were powerfully supported for the photocatalytic reduction of Cr+6 and PNP and the holes (h+) are the main active species for the photocatalytic oxidation reactions.

Microstructure-induced functionality in titanium dioxide thin films

Microstructure-induced functionality in titanium dioxide thin films

Indium and hafnium chloride modified titanium oxide thin films

Titanium oxide (TiO2) thin films were prepared by the sol-gel spin-coating technique. The influences of indium (In), hafnium (Hf), and In&Hf doping on electrochemical and structural properties were investigated. The structural properties of undoped and doped TiO2 were investigated using thermogravimetric/differential thermal (TG/DTA), X-ray Powder Diffraction (XRD), and atomic force microscopy (AFM). The optical properties were investigated using ultraviolet–visible (UV–Vis) spectroscopy, and band gap energies were calculated using the Tauc method from transmission measurement. The results showed that TiO2 had better electrochemical properties, and the band gap increased with In&Hf doping.

Bidimensional SnSe2-Mesoporous Ordered Titania Heterostructures for Photocatalytically Activated Anti-Fingerprint Optically Transparent Layers.

The design of functional coatings for touchscreens and haptic interfaces is of paramount importance for smartphones, tablets, and computers. Among the functional properties, the ability to suppress or eliminate fingerprints from specific surfaces is one of the most critical. We produced photoactivated anti-fingerprint coatings by embedding 2D-SnSe2 nanoflakes in ordered mesoporous titania thin films. The SnSe2 nanostructures were produced by solvent-assisted sonication employing 1-Methyl-2-pyrrolidinone. The combination of SnSe2 and nanocrystalline anatase titania enables the formation of photoactivated heterostructures with an enhanced ability to remove fingerprints from their surface. These results were achieved through careful design of the heterostructure and controlled processing of the films by liquid phase deposition. The self-assembly process is unaffected by the addition of SnSe2, and the titania mesoporous films keep their three-dimensional pore organization. The coating layers show high optical transparency and a homogeneous distribution of SnSe2 within the matrix. An evaluation of photocatalytic activity was performed by observing the degradation of stearic acid and Rhodamine B layers deposited on the photoactive films as a function of radiation exposure time. FTIR and UV-Vis spectroscopies were used for the photodegradation tests. Additionally, infrared imaging was employed to assess the anti-fingerprinting property. The photodegradation process, following pseudo-first-order kinetics, shows a tremendous improvement over bare mesoporous titania films. Furthermore, exposure of the films to sunlight and UV light completely removes the fingerprints, opening the route to several self-cleaning applications.

Titanium Dioxide Thin Films Produced on FTO Substrate Using the Sol-Gel Process: The Effect of the Dispersant on Optical, Surface and Electrochemical Features.

In this study, TiO2 thin films formed by dip-coating on an FTO substrate were obtained and characterized using surface, optical and electrochemical techniques. The impact of the dispersant (polyethylene glycol-PEG) on the surface (morphology, wettability, surface energy), optical (band gap and Urbach energy) and electrochemical (charge-transfer resistance, flat band potential) properties were investigated. When PEG was added to the sol-gel solution, the optical gap energy of the resultant films was reduced from 3.25 to 3.12 eV, and the Urbach energy increased from 646 to 709 meV. The dispersant addition in the sol-gel process influences surface features, as evidenced by lower contact-angle values and higher surface energy achieved for a compact film with a homogenous nanoparticle structure and larger crystallinity size. Electrochemical measurements (cycle voltammetry, electrochemical impedance spectroscopy and the Mott-Schottky technique) revealed improved catalytic properties of the TiO2 film, due to a higher insertion/extraction rate of protons into the TiO2 nanostructure, as well as a decrease in charge-transfer resistance from 418 k to 23.4 k and a decrease in flat band potential from 0.055 eV to -0.019 eV. The obtained TiO2 films are a promising alternative for technological applications, due to their advantageous surface, optical and electrochemical features.

Crystalline Structure, Morphology, and Adherence of Thick TiO2 Films Grown on 304 and 316L Stainless Steels by Atomic Layer Deposition

Titanium dioxide (TiO2) thin films are widely used in transparent optoelectronic devices due to their excellent properties, as well as in photocatalysis, cosmetics, and many other biomedical applications. In this work, TiO2 thin films were deposited onto AISI 304 and AISI 316L stainless steel substrates by atomic layer deposition, followed by comparative evaluation of the mixture of anatase and rutile phase by X-ray diffraction, Raman maps, morphology by SEM-FEG-AFM, and adhesion of the films on the two substrates, aiming to evaluate the scratch resistance. Raman spectroscopy mapping and X-ray diffraction with Rietveld refinement showed that the films were composed of anatase and rutile phases, in different percentages. Scratch testing using a diamond tip on the TiO2 film was employed to evaluate the film adherence and to determine the friction coefficient, with the results showing satisfactory adherence of the films on both substrates.

Improvement of the Surface Properties of Polyether Ether Ketone via Arc Evaporation for Biomedical Applications.

Polyether ether ketone is a bioinert polymer, that is of high interest in research and medicine as an alternative material for the replacement of bone implants made of metal. The biggest deficit of this polymer is its hydrophobic surface, which is rather unfavorable for cell adhesion and thus leads to slow osseointegration. In order to address this drawback, 3D-printed and polymer extruded polyether ether ketone disc samples that were surface-modified with titanium thin films of four different thicknesses via arc evaporation were investigated and compared with non-modified disc samples. Depending on the modification time, the thickness of the coatings ranged from 40 nm to 450 nm. The 3D-printing process does not affect the surface or bulk properties of polyether ether ketone. It turned out that the chemical composition of the coatings obtained did not depend on the type of substrate. Titanium coatings contain titanium oxide and have an amorphous structure. Microdroplets formed on the sample surfaces during treatment with an arc evaporator contain a rutile phase in their composition. Surface modification of the samples via arc evaporation resulted in an increase in the arithmetic mean roughness from 20 nm to 40 nm for the extruded samples and from 40 nm to 100 nm for the 3D-printed samples, with the mean height difference increasing from 100 nm to 250 nm and from 140 nm to 450 nm. Despite the fact that the hardness and reduced elastic modulus of the unmodified 3D-printed samples (0.33 GPa and 5.80 GPa) are higher than those of the unmodified extruded samples (0.22 GPa and 3.40 GPa), the surface properties of the samples after modification are approximately the same. The water contact angles of the polyether ether ketone sample surfaces decrease from 70° to 10° for the extruded samples and from 80° to 6° for the 3D-printed samples as the thickness of the titanium coating increases, making this type of coating promising for biomedical applications.

Lateral proximity effect in direct laser thermochemical recording on thin titanium films

Lateral proximity effect in direct laser thermochemical recording on thin titanium films

Characterization and photocatalytic activity of different molar ratios of TiO2 thin films prepared by Sol-Gel process

Photocatalytic application has been of large interest due to its new technology for organic pollution. Among the photocatalyst, titanium dioxide thin film is known as a photocatalyst for the elimination of organic pollutants. In this research, the structural and optical properties of TiO2 thin films prepared on glass substrates were studied, using a sol-gel (spin coating) technique. TiO2 thin films were deposited with molar ratio y between [TTIP] and [AcAc] concentration, which varied from 0.5 to 2. Photocatalytic properties of TiO2 thin films are studied by using sunlight and photodegradation of methylene blue as a water pollutant evaluated until the photocatalytic process enhances with the molar ratio. Absorbance spectra were measured using a spectrophotometer. Test results showed that the photocatalytic sunlight /TiO2 thin film is a promising method for treating wastewater. The quantity of acetylacetone in the precursor solution had no significant effect on the optical and structural properties of the TiO2 thin films. Films consisted of the anatase phase, with a band gap in the range of 3.38–3.51 eV and thickness in the range of 534–618 nm. However, the molar ratio effect on photocatalytic preperties, the best photodegradation rate reaches to 94% in y = 0.66 at t = 180 min.

Gas sensing properties of mixtures of copper and titanium oxides thin films

The subject of the current studies were mixtures of copper and titanium oxide thin films,with various elemental compositions, deposited by magnetron sputtering and annealed in the postprocess.The effect of elemental composition and annealing temperature on the morphology of thinfilms was determined using scanning electron microscope images. The crystal structure and chemicalcomposition of copper‒titanium oxide (CuTi)Ox mixtures were investigated by X-ray diffraction.Hydrogen gas sensing experiments were performed for hydrogen with concentrations ranging from 100to 1,000 ppm. The resistance of the prepared (CuTi)Ox mixtures increased during hydrogen exposure,demonstrating the applicability of these oxides in hydrogen sensing. In addition, better sensor responseswere obtained for the mixtures in comparison to single copper oxides or titanium oxides. Mixturesof copper oxides and titanium oxides may be promising materials for hydrogen sensor applications.Keywords: mixtures of copper and titanium oxides, hydrogen gas sensors, mixed copper and titaniumoxides, thin films, magnetron sputtering

Enhanced photocatalysis and photohydrophilicity in TiO2–W5O14 nanocomposite thin films grown by in-lay sputtering

Investigation on the photocatalytic and photoinduced hydrophilic properties of pure and nitrogen doped TiO2–W5O14 nanocomposite thin films grown by in-lay sputtering process is reported. For comparison, similar properties of reactively sputtered nanocrystalline titanium dioxide (TiO2) and nanowire tungsten oxide (W18O49) thin films are studied as well. Structurally, TiO2–W5O14 thin films are highly crystalline and strongly multiphased while TiO2 and W18O49 thin films are anatase, monoclinic, respectively. The band gap of nitrogen doped TiO2–W5O14 thin film is ∼2.82 eV while that of TiO2 and W18O49 thin films are ∼3.27 eV. Surface morphology of TiO2–W5O14 and TiO2 films show nanocrystalline particulates of sizes 15–70 nm, 20–50 nm, respectively while W18O49 films show randomly dispersed nanowires with average diameter of ∼50 nm and maximum length of ∼30 μm. Owing to bandgap shift in visible range, porous surface structures and crystallinity, the nitrogen doped TiO2–W5O14 nanocomposite thin films are found to exhibit better (i) photohydrophilicity with water contact angle of ∼7° in 2 h under UV-A irradiation and (ii) photocatalytic efficiency with methylene blue degradation rate of −1.12μmol/(l.d), −0.78 μmol/(l.d) under ultraviolet and visible light sources, respectively.

Structural Color Generation on Transparent and Flexible Substrates by Nanosecond Laser Induced Periodic Surface Structures

AbstractLaser patterning to fabricate micro/nanoscale structures attracts enormous attention as they find many functional applications owing to their controllable structure and unique properties. The present work proposes a unique solution‐based method to fabricate laser‐induced periodic surface structure (LIPSS) patterns on a thin film of Titanium (IV) butoxide and Ag organometallic (OM) solution‐coated glass substrates with near infra‐red (NIR) nanosecond (ns) laser. The formation of periodic patterns has been confirmed, the thin film solution concentration affects the LIPSS pattern thickness and a continuous pattern is achieved with the diluted solution. Parametric studies demonstrate that the LIPSS patterns could be achieved with optimal solution dilution, laser fluence, scan speed, and pulse duration. A high power and faster scan speed result in discontinued, and defective patterns. The photothermal process such as material reorganization followed by electromagnetic absorption that takes place during laser patterning is mainly responsible for the fabrication of controlled structures. LIPSS patterned surfaces exhibit iridescent surface coloration while illuminated with white light, and the color spectrum from red to blue is distinguished. LIPSS patterned substrates serve as mold and structures are transferrable to the poly dimethyl siloxane (PDMS) film and exhibit iridescent structural coloration like LIPSS patterned substrates.

Bendability of polycrystalline titania thin films fabricated on plastic substrates by the sol–gel transfer technique via firing at temperatures over 600 °C

Bendability of polycrystalline titania thin films fabricated on plastic substrates by the sol–gel transfer technique via firing at temperatures over 600 °C