Surface Of TiO2 Thin Films Research Articles

Effect of sputtering power on optical properties of prepared TiO2 thin films by thermal oxidation of sputtered Ti layers

In this research, TiO2 thin films prepared via thermal oxidation of Ti layers were deposited by RF-magnetron sputtering method at three different sputtering powers. The effects of sputtering power on structure, surface and optical properties of TiO2 thin films grown on glass substrate were studied by X-ray diffraction (XRD), atomic force microscopic (AFM) and UV–visible spectrophotometer. The results reveal that, the structure of layers is changed from amorphous to crystalline at anatase phase by thermal oxidation of deposited Ti layers and rutile phase is formed when sputtering power is increased. The optical parameters: absorption coefficient, dielectric constants, extinction coefficient, refractive index, optical conductivity and dissipation factor are decreased with increase in sputtering power, but increase in optical band gap is observed. The roughness of thin films surface is affected by changes in sputtering power which is obtained by AFM images.

Nanosculpting of complex oxides by massive ionic transfer

Scanning probe microscopy (SPM)-based approaches have been extensively studied as methods to control the structure and properties of materials on the nanoscale. In many cases, the SPM probe is physically utilized to control structure and properties. In addition to physical modulation, it has been reported that voltage can be effectively used to modulate electrochemical phenomena on the sample surface. These studies suggest that electrochemical modulation of the structure and properties is possible by applying a voltage. Herein, in order to demonstrate voltage induced modulation of surface structure, we explored surface nanosculpting by creating electrochemically induced pits on the surface of TiO2 thin films through the application of voltage using the atomic force microscope tip. Using a unipolar negative voltage sweep, pits were successfully generated. Further, the electric potential distribution was simulated to unravel the relationship between the pit volume and the magnitude of the applied voltage. Finally, surface protrusion induced by positive voltage sweep was also observed to elucidate the complete process of electrochemically induced surface modulation. These results can offer fundamental information for understanding how surface structure can be modulated by electrochemical phenomena.

Irradiation-induced TiO2 nanorods for photoelectrochemical hydrogen production

In this work, well-ordered nanorods were fabricated on the surface of TiO2 thin films deposited on Ti sheets by an ion irradiation method using nitrogen ion irradiation with the energy of 65 keV to a fluence of 1 × 1017 ions/cm2. These TiO2 nanorods are about 120 nm in length and 20–40 nm in diameter. After post-irradiation annealing at 500 °C in O2, the nanorod array photoelectrode displays largely enhanced performance for photoelectrochemical (PEC) water splitting compared to that of the un-irradiated TiO2 thin films with a planar structure. The influences of the irradiated ion energy on the morphology and photocurrent density of the nanorods were investigated. The 65 keV N+ irradiated TiO2 thin films shows a higher photocurrent density than those of the 45 and 85 keV N+ irradiated TiO2 thin films. We also discussed the influence of annealing conditions on the PEC performance of TiO2 nanorods, and it was found that the nanorods annealed at 600 °C in vacuum produce a much higher photocurrent density of 0.6 mA/cm2 at 0.8 V (vs. a saturated calomel electrode), which is about 7 times higher than that of the nanorods annealed in oxygen. This work proposes that ion irradiation combination with thermal annealing in vacuum could be an effective approach for developing nanostructured materials for water splitting.

Electronic properties of nickel-doped TiO2 anatase

Atomistic details of electron transfer in semiconductor materials are characterized for TiO2 thin film surfaces doped with nickel. A periodic slab model of eight atomic layers exposes the (1 0 0) crystallographic surface and is covered with a monolayer of water. The density of states, absorption spectra, partial charge densities, molecular dynamics, and non-adiabatic couplings are compared between doped and undoped models. Our results show that Ni doping improves several electronic properties including lowering the band gap, increasing visible light absorption, and shortening the relaxation time of holes rather than electrons, which maximizes charge separation. The different mechanisms of electron and hole dynamics are discussed. The computed characteristics of a doped semiconductor material have practical potential for increasing efficiency of a photo-electrochemical cells.

Methanol Adsorption on TiO2 Film Studied by Sum Frequency Generation Vibrational Spectroscopy

A broadband infrared surface sum frequency generation vibrational spectroscopy (SFG-VS) and an in situ UV excitation setup devoted to studying surface photocatalysis have been constructed. With a home-made compact high vacuum cell, organic contaminants on TiO2 thin film surface prepared by RF magnetron sputtering were in situ removed under 266 nm irradiation in 10 kPa O2 atmosphere. We obtained the methanol spectrum in the CH3 stretching vibration region on TiO2 surface with changing the methanol pressure at room temperature. Features of both molecular and dissociative methanol, methoxy, adsorbed on this surface were resolved. The CH3 symmetric stretching vibration frequency and Fermi resonance of molecular methanol is red-shifted by about 6–8 cm−1 from low to high coverage. Moreover, the recombination of dissociative methanol and H on surfaces in vacuum was also observed. Our results suggest two equilibria exist: between molecular methanol in the gas phase and that on surfaces, and between molecular methanol and dissociative methanol on surfaces.

Study the target effect on the structural, surface and optical properties of TiO2 thin film fabricated by RF sputtering method

The effect of target (Ti metal target and TiO2 target) on Titanium Dioxide (TiO2) thin films grown on ITO coated glass substrate by RF magnetron sputtering has been investigated. A comparative study of both the films was done in respect of crystalline structure, surface morphology and optical properties by using X-ray diffractometer (XRD), Atomic Force Microscopy (AFM) studies and ellipsometric measurements. The XRD results confirmed the crystalline structure and indicated that the deposited films have the intensities of anatase phase. The surface morphology and roughness values indicated that the film using Ti metal target has a smoother surface and densely packed with grains as compared to films obtained using TiO2 target. A high transmission in the visible region, and direct band gap of 3.67eV and 3.75eV for films derived by using Ti metal and TiO2 target respectively and indirect bandgap of 3.39eV for the films derived from both the targets (Ti metal and TiO2 target) were observed by the ellipsometric measurements.

Slurry components of TiO2 thin film in chemical mechanical polishing

A chemical mechanical polishing (CMP) process was selected to smooth TiO2 thin film surface and improve the removal rate. Meanwhile, the optimal process conditions were used in TiO2 thin film CMP. The effects of silica sols concentration, slurry pH, chelating agent and active agent concentration on surface roughness and material removal rate were investigated. Our experimental results indicated that we got lower surface roughness (1.26 Å, the scanned area was 10 × 10 μm2) and higher polishing rate (65.6 nm/min), the optimal parameters were: silica sols concentration 8.0%, pH value 9.0, active agent concentration 50 mL/L, chelating agent concentration 10 mL/L, respectively.

Biocompatibility and Surface Properties of TiO₂ Thin Films Deposited by DC Magnetron Sputtering.

We present the study of the biocompatibility and surface properties of titanium dioxide (TiO2) thin films deposited by direct current magnetron sputtering. These films are deposited on a quartz substrate at room temperature and annealed with different temperatures (100, 300, 500, 800 and 1100 °C). The biocompatibility of the TiO2 thin films is analyzed using primary cultures of dorsal root ganglion (DRG) of Wistar rats, whose neurons are incubated on the TiO2 thin films and on a control substrate during 18 to 24 h. These neurons are activated by electrical stimuli and its ionic currents and action potential activity recorded. Through X-ray diffraction (XRD), the surface of TiO2 thin films showed a good quality, homogeneity and roughness. The XRD results showed the anatase to rutile phase transition in TiO2 thin films at temperatures between 500 and 1100 °C. This phase had a grain size from 15 to 38 nm, which allowed a suitable structural and crystal phase stability of the TiO2 thin films for low and high temperature. The biocompatibility experiments of these films indicated that they were appropriated for culture of living neurons which displayed normal electrical behavior.

Effect of acid nature in the starting solution on surface and photocatalytic properties of TiO2 thin films

TiO2 thin films were successfully prepared by dip-coating method. The prepared sols were obtained through the hydrolysis of tetraethyl-orthotitanate Ti(OC2H5) 4under controlled pH by two different acids HNO3 and HCl. The effect aging time of the starting solution on the photocatalytic degradation of methylene blue (MB) was studied. The degradation of MB dissolved in water and optical properties are followed by spectroscopy. Structure and microstructure of films have been determined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Further investigation of the surface electrical change distribution and chemistry is investigated by advanced scanning kelvin probe measurements. Rietveld analysis reveals the formation of single pure nanocrystalline anatase phase, i.e. 16nm. SEM and AFM analyses reveal smooth surfaces with a positive surface skewness but with very high surface kurtosis of the HNO3–TiO2 film (1.9) compared to the HCl–TiO2 film (0.065). This was confirmed by the peakedness of its surface, which could influence surface wettability and enhances its photocatalytic degradation properties. Optical measurements show a higher transparency for HNO3/TiO2 compared to HCl/TiO2, 80 and 40%, respectively with an energy bandgap around 3.25–3.30eV. The results show a stable photocatalytic activity of 80% for thin films prepared by HNO3 independently of time of the aging solution, while the films prepared by HCl show a much lower photocatalytic activity of 40%, which increases by increasing the aging time. The unique nanostructure and surface texture as well as its surface potential are the main factors for obtaining the above promising photocatalytic results.

Characterization of Cr(v)-induced genotoxicity using CdTe nanocrystals as fluorescent probes

CdTe nanocrystals capped by cysteamine were synthesized to study Cr(V)-induced genotoxicity. On the surface of TiO2 thin films, the stepwise process of DNA breakage induced by Cr(V)-GSH complexes was vividly observed by using CdTe-DNA self-assembled fluorescent probes; in acetate buffer solution, an analytical method was developed to detect Cr(V)-induced genotoxicity with CdTe fluorescent probes.

Adsorption Equilibrium and Kinetics ofGardenia BlueonTiO2Photoelectrode for Dye-Sensitized Solar Cells

Nanostructured porous TiO2paste was deposited on the FTO conductive glass using squeeze printing technique in order to obtain a TiO2thin film with a thickness of 10 μm and an area of 4 cm2.Gardenia blue (GB)extracted fromGardeniajasminodeElliswas employed as the natural dye for a dye-sensitized solar cell (DSSC). Adsorption studies indicated that the maximum adsorption capacity of GB on the surface of TiO2thin film was approximately 417 mgGB/g TiO2photoelectrode. The commercial and natural dyes, N-719 andGB, respectively, were employed to measure the adsorption kinetic data, which were analyzed by pseudo-first-order and pseudo-second-order models. The energy conversion efficiency of the TiO2electrode with successive adsorptions ofGBdye was about 0.2%.

Enhanced visible light absorption by TiO2 film patterned with Ag nanoparticles arrays

Well patterned Ag nanoparticle (NP) arrays were fabricated on TiO2 thin film (TF). Scanning electron microscopy shows Ag NPs distribution on the TiO2 TF surface. The overall Raman scattering intensity increased for the Ag/TiO2 TF system. The enhanced Raman scattering of Ag/TiO2 TF was due to the formation of strong electromagnetic field around the Ag NPs under photon excitation. Optical absorption measurement shows three times enhancement in visible light absorption for the Ag NPs containing samples as compared to bare TiO2 TF. The photoluminescence emission intensity from the Ag NPs/TiO2 TF sample reduced due to the formation of Ag–O complex on the TiO2 surface.

Homoleptic “Star” Ru(II) Polypyridyl Complexes: Shielded Chromophores to Study Charge-Transfer at the Sensitizer-TiO2 Interface

Three homoleptic star-shaped ruthenium polypyridyl complexes, termed Star YZ1, Star YZ2, and Star YZ3, where the Ru(II) center is coordinated to three bipyridine ligands each carrying two oligo(phenylene ethynylene) (OPE) rigid linker units terminating with isophthalic ester (Ipa) groups for binding to metal-oxide surfaces were synthesized. In Star YZ3, each OPE linker was substituted with two n-butoxy (n-BuO) solubilizing groups. Star complex YZ4, which is homoleptic but lacks the octahedral symmetry, was synthesized as a reference compound. The Star complexes were synthesized using two approaches: in the first, Ru(4,4'-(Br)2-2,2'-bpy)3 was reacted in a Sonogashira cross coupling reaction with the ethynyl-OPE-Ipa linkers; in the second, the 2,2'-bpy-OPE-Ipa ligands were reacted with Ru(DMSO)4(PF6)2. The photophysical behavior of the Star complexes were studied in fluid solution and anchored to the surface of mesoporous nanocrystalline TiO2 thin films (Star/TiO2). To a first approximation the excited state behavior in CH3CN was unchanged when the compounds were anchored to a TiO2 thin film, indicating that the highly symmetrical (octahedral) and rigid molecular structure of the ligands shielded the chromophoric core from the TiO2 semiconductor. Inefficient excited state injection, φ(inj) < 0.05, was observed to occur on a nanosecond time scale with slow recombination. In addition, the presence of n-BuO groups on the linker unit gave a large increase in the extinction coefficient of YZ3, which allows for enhanced harvesting of sunlight. The results indicate that molecular design on the nanometer length scale can be utilized to control excited state relaxation pathways at semiconductor surfaces.

Characteristics of TiO2 Surfaces Etched by Capacitively Coupled Radio Frequency N2 and He Plasmas

We have investigated characteristics of anatase TiO2 thin film surfaces etched by a capacitively coupled radio frequency N2 plasma from the viewpoint of both an experiment and a simulation. The result obtained with use of the N2 plasma is compared with that obtained with use of the He plasma. The experimental O/Ti ratio at the surface etched by the N2 plasma increases as a function of etching time. The increase in the experimental O/Ti ratio is independent of a change in gas pressure. The above-mentioned experimental results agree with the simulation result that the Ti atoms at the surface are preferentially removed by N2+ ions. The experimental O/Ti ratio at the surface etched by the He plasma also increases, which does not agree with the simulation result that the O atoms are preferentially removed by He+ ions. The O-1s XPS spectra of the surface etched by the He plasma show the peak associated with oxygen and water adsorbed by the surface. In the case where the component of the adsorbed oxygen and water in each spectrum is subtracted, the experimental O/Ti ratio at the surface etched by the He plasma shows a decrease. This is consistent with the simulation result. The adsorption of oxygen and water seems to be caused by ambient air. Morphology of the surface etched by the N2 plasma is almost similar to that of the as-grown surface regardless of the changes both in etching time and in gas pressure. In contrast, morphology of the surface etched by the He plasma changes as the etching time increases. This result is independent of the gas pressure.

Synthesis of highly active thin film based on TiO2 nanomaterial for self-cleaning application

Highly active self-cleaning surfaces were prepared from hydrothermally treated TiO2 nanomaterials for different times (0, 12, 24 and 36h) under acidic condition. TiO2 thin films were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM). TiO2 thin film (hydrothermal 24h) exhibited hybrid morphology from accumulated plates, clusters, rods and spheres. The photo self-cleaning activity in term of quantitative determination of the active oxidative species (OH) produced on the thin film surfaces was evaluated using fluorescent probe method. The results show that, the highly active thin film is the hydrothermally treated for 24h at 200°C. The structural, morphology and photoactivity properties of nano-TiO2 thin films make it promising surfaces for self-cleaning application. Mineralization of commercial textile dye (Remazol Red RB-133, RR) from highly active TiO2 thin film surface was applied. Moreover, the durability of this nano-TiO2 thin film (hydrothermal 24h) was studied.

Effect of Dry Etching of TiO2 Thin Films Using Inductively Coupled Plasma

In this study, the effect of the dry etching of titanium dioxide (TiO2) thin films was investigated with addition of O2 to BCl3/Ar plasma. The maximum etch rate of TiO2 thin films and the selectivity of TiO2 to SiO2 were 100 nm/min and 1.07 in O2/BCl3/Ar (= 3:4:16 sccm) plasma, respectively. In addition, the etch rate and selectivity were measured as functions of the etching parameters, such as the gas mixing ratio, RF power, DC-bias voltage, and process pressure. The chemical state on the etched surface of TiO2 thin films were investigated by the x-ray photoelectron spectroscopy. To determine the re-deposition and reorganization of residues on the surface, the surface morphology and roughness of TiO2 thin films were examined by the atomic force microscopy.

Influence of temperature, voltage and hydrogen on the reversible transition of electrical conductivity in sol–gel grown nanocrystalline TiO2 thin film

Undoped nanocrystalline p-type TiO2 thin film was deposited by sol–gel method on a thermally oxidized p-Si (2–5 Ω cm resistivity and $$ \left\langle {100} \right\rangle $$ orientation) substrate. The thin film was characterized by two-dimensional X-ray Diffraction (2D-XRD) and Field Emission Scanning Electron Microscopy (FESEM) to confirm the formation of stable nano crystalline anatase titania and to determine the grain size (~10 nm). Optical absorption spectroscopy was carried out to ascertain the band gap of the material. Two lateral Pd contacts were used as the metal electrodes to TiO2 thin film to study the electrical conductivity. A clear p- to n-type transition was observed at 240 °C and a bias voltage of 0.83 V and the effect was enhanced on exposure to H2 gas. The thin film showed fully n-type conductivity at 275 °C and 0.1 V. However, the reversal of the type of conductivity from n- to p-type was observed below 240 °C during lowering the temperature. The creation of oxygen vacancy and the diffusion of lattice oxygen to the surface of TiO2 thin film might be the most possible mechanism of such transitions. Presence of hydrogen enhanced the process.

Characteristics of TiO2Thin Film Surfaces Treated by Helium and Air Dielectric Barrier Discharge Plasmas

The characteristics of TiO2 thin film surfaces treated with He and air dielectric barrier discharge (DBD) plasmas at different gas pressures are investigated. There is a difference between the two DBD plasma characteristics: for He-DBD, which is an atmospheric pressure glow discharge (APGD), the breakdown voltage and discharge current hardly change with increasing gas pressure, whereas for air-DBD, which is basically a filamentary discharge, they increase with increasing gas pressure. There is also a difference between the characteristics of TiO2 surfaces treated with the two DBDs. The surface roughness for He-DBD is lower than the roughness of the as-grown surface, whereas that for air-DBD is higher. The surface hydrophilicity for He-DBD is more enhanced than the hydrophilicity of the as-grown surface regardless of UV irradiation. The hydrophilicity for air-DBD is dependent on UV irradiation. It is more enhanced with UV irradiation; it is not improved adequately without UV irradiation.

Characteristics of TiO2 Thin Film Surfaces Treated by Helium and Air Dielectric Barrier Discharge Plasmas

The characteristics of TiO2 thin film surfaces treated with He and air dielectric barrier discharge (DBD) plasmas at different gas pressures are investigated. There is a difference between the two DBD plasma characteristics: for He-DBD, which is an atmospheric pressure glow discharge (APGD), the breakdown voltage and discharge current hardly change with increasing gas pressure, whereas for air-DBD, which is basically a filamentary discharge, they increase with increasing gas pressure. There is also a difference between the characteristics of TiO2 surfaces treated with the two DBDs. The surface roughness for He-DBD is lower than the roughness of the as-grown surface, whereas that for air-DBD is higher. The surface hydrophilicity for He-DBD is more enhanced than the hydrophilicity of the as-grown surface regardless of UV irradiation. The hydrophilicity for air-DBD is dependent on UV irradiation. It is more enhanced with UV irradiation; it is not improved adequately without UV irradiation.

Anatase (100) thin film surface computational model for photoelectrochemical cell

AbstractUsing computational approaches, one is able to better understand electron transfer and specific atomistic behaviors in semiconductor materials; it is also more cost and time effective than experimental methods. If computed semiconductor characteristics show promise, experimentalists can synthesize and further examine the structure. Specifically, doping TiO2 thin film surfaces with platinum and ruthenium have shown great promise for efficient H2 production and is beneficial in comparison to other materials such as the pure silicon used for most of today's solar cells. In computational studies, TiO2 anatase thin film (100) surfaces are doped with platinum and ruthenium. The formulas used are Pt2Ti32O72H16 or Ru2Ti32O72H16 with the (100) crystallographic surface exposed and covered with a monolayer of water. Optimization is completed by density functional theory and Perdue Burke Ernzerhof, (PBE) in Vienna Ab‐initio simulation package (VASP) software. The density of states, absorption spectra, and partial charge densities are compared between slabs doped by the two elements as well as Ti32 O72H16 with no dopant as a standard for reference. The information can be used to show the mechanism of how doping the titanium dioxide nanocrystals facilitates photoinduced charge transfer at the surfaces, which is useful in understanding photoelectrochemical water splitting. © 2012 Wiley Periodicals, Inc.