Polycrystalline TiO2 Thin Films Research Articles

Wetting Properties of Transparent Anatase/Rutile Mixed Phase Glancing Angle Magnetron Sputtered Nano-TiO2 Films.

Transparent polycrystalline TiO2 thin films have been deposited on unheated glass substrates using RF reactive magnetron sputtering. Depositions were carried out at different glancing angles and with different total gas mixture pressures. The variation of these parameters affected the crystal phase composition and the surface morphology. Depending on the glancing angle and the pressure, rutile, mixed anatase/ rutile and pure anatase were deposited at low substrate temperature. Both hydrophilic and hydrophobic TiO2 were obtained, exhibiting fast photoconversion to superhydrophilic upon UV irradiation. The effect of the materials physicochemical properties on the wettability and rate of the UV induced superhydrophilicity is evaluated.

Influence of deposition temperature on the structural and dispersion parameters of TiO2 thin films

Polycrystalline TiO2 thin films were deposited onto quartz substrates using RF magnetron sputtering technique at different substrate temperatures (573 K, 623 K, 673 K, and 773 K). X-ray diffraction (XRD) measurements revealed the isolation of anatase phase with (101) preferred crystal orientation for the film deposited at 773 K. Moreover, the topographical features of this film clarified the smoothness of the deposited films, with root mean square roughness (RMS) of 0.5 nm. The optical properties of the as-prepared thin films at different deposition temperatures was enlightened through structural correlation. Most of the films were transparent with transmittance intensity extending from 50 to 90% within the visible range. Due to the smoothness of the deposited films, the transmittance and reflectance spectra exhibited an oscillatory behavior. Additionally, from single effective oscillator model, the dispersion parameters were estimated. For the deposited films, the single oscillator energy (Eo), dispersion energy (Ed), lattice dielectric constant (eL), and infinite permittivity (e∞) extended in the range (3.42 ~ 3.99), (9.83 ~ 24.12), (4.39 ~ 7.75), and (3.88 ~ 7.04), respectively.

Effect of laser irradiation on the structural, morphological and electrical properties of polycrystalline TiO2 thin films

Abstract TiO 2 thin film is deposited on glass substrate by sol-gel dip coating technique. After deposition, films were irradiated by continuous wave (CW) diode laser at an angle of 45°. XRD shows both the anatase and brookite phases of TiO 2 . Nano particles of regular and control sizes are appeared in SEM micrographs. Therefore, shape and size of nano particles can be control by using Laser irradiation. The average sheet resistivity of TiO 2 thin film irradiated by 0, 2, 4 and 6 min are 6.72 × 10 5 , 5.32 × 10 5 , 3.44 × 10 5 and 4.95 × 10 5 (ohm-m) respectively, according to four point probe.

Reduced Heterogeneity of Electron Transfer into Polycrystalline TiO2 Films: Site Specific Kinetics Revealed by Single-Particle Spectroscopy

The presenting surface of TiO2 is one of the key factors that influence the photoinduced charge injection process from covalently bound chromophores. However, the dependence of electron transfer (ET) on TiO2 surface properties (structure, defects, and facets) remains poorly understood due to the difficulties of deconvoluting the signal from a multitude of surface binding sites in highly heterogeneous ET systems. In an effort to correlate TiO2 surface features with ET, we compare the photoinduced ET dynamics from single quantum dots (QDs) to polycrystalline TiO2 thin films (pc-TiO2) grown by atomic layer deposition (ALD) with that of porous TiO2 nanoparticle films (np-TiO2) by utilizing single-particle fluorescence spectroscopy. Unlike the broad distribution of ET rates (deduced from fluorescence lifetimes) on np-TiO2, QDs on pc-TiO2 exhibit two narrowly distributed ET rates that we attribute to reduced site heterogeneity. Variable temperature pc-TiO2 annealing studies suggest that the double-peaked distri...

Polycrystalline TiO<SUB>2</SUB> Thin Films with Different Thicknesses Deposited on Unheated Substrates Using RF Magnetron Sputtering

Different film thicknesses of polycrystalline TiO2 thin films deposited on various unheated substrates using radio frequency (RF) magnetron sputtering is investigated. The crystalline structure, optical properties, and surface morphology and roughness were measured using an X-ray diffractometer (XRD), a field-emission scanning electron microscope (FESEM), an atomic force microscope (AFM), and a UV-Vis spectrophotometer. Polycrystalline phases were formed on unheated substrates due to the plasma particle bombardment. Crystalline structures more easily formed on the glass substrate and only nanocrystalline structures formed on the ITO glass substrate due to the surface roughness of substrates. The absorption edge and optical band gap depended on the crystalline particle size and phase structure. The XRD results indicate that 500-nm-thick film on a glass substrate had the strongest intensities of mixed anatase and rutile phases.

Random Circuit Breaker Network Model for Unipolar Resistance Switching

The random circuit breaker network model is proposed for unipolar resistance switching behavior. This model describes reversible dynamic processes involving two quasi-metastable states. The formation and rupture of conducting channels (see figure) in the polycrystalline TiO2 thin films may be analyzed by the self organized avalanche process in the random circuit breaker network model. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2089/2008/adma200702024_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Synthesis and characterization of TiO2 thin films on organic self-assembled monolayers: Part I. Film formation from aqueous solutions

Self-assembled monolayers (SAMs) bearing sulfonate (-SO3H) surface functional groups, on single-crystal Si wafers, were used as substrates for the deposition of TiO2 thin films from aqueous solutions. Polycrystalline TiO2 thin films over 50 nm thick formed in 2 h by hydrolysis of TiCl4 in aqueous HCI solutions at 80 °C. The films were pore-free, showed excellent adherence and uniformity, and consisted of anatase crystallites 2–4 nm in diameter. Annealing at temperatures up to 600 °C caused coarsening of the anatase grains, but no loss of adherence or structural integrity.

RF relaxation oscillations in polycrystalline TiO2 thin films

Negative resistance oscillations were studied in polycrystalline TiO2 thin films in the TiTiO2Cr device structure. Stable oscillations were readily produced in the 1–3 MHz frequency range and showed lifetimes of more than 8 × 1011 cycles. A simple equivalent circuit model for current controlled negative resistance (CCNR) devices was used to interpret the bias voltage and temperature dependence of amplitude and frequency of negative resistance oscillations. Bias voltage dependence was found not to involve changes in the device parameters. Temperature variations produced changes in the device threshold and minimum (holding) voltages and the “on” and “off” state resistances. The “on” state and “off” state resistances showed thermal activation energies of 0.006 and 0.052 eV respectively. I-V characteristics for these devices are shown to be in agreement with the theory of filamentary double injection space charge limited currents.