Atomic layer deposition of thin films of titanium dioxide from titanium tetramethoxide and water

The atomic layer deposition of titanium oxide in the precursor systems Ti(OCH₃)₄-H₂O and Ti(OC₂H₅)₄-H₂O was compared. The growth rate of titanium oxide formed by the atomic layer deposition in the Ti(OCH₃)₄-H₂O system can be adequately estimated with due to regard for the number and size of ligands of a metal-containing precursor. The study in simulated body fluid solutions showed that polycrystallin TiO₂ coatings with anatase structure are prone to accelerated osseointegration and, consequently, promising for the development of new biomedical products.     

Atomic layer deposition of the titanium dioxide thin film from tetraethoxytitanium and water

Using the methods of Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction in the geometry of the grazing beam, and Fourier transform infrared spectroscopy, we studied the chemical composition and structure of thin films of titanium dioxide formed by atomic layer deposition from tetraethoxytitanium and water. It is shown that the films obtained are characterized by a high stoichiometry of composition and by amorphous or polycrystalline structure of the anatase modification, depending on the number of reaction cycles. Using a model of the process of atomic layer deposition that takes into account the size and number of ligands of the reacting molecules, we calculated the amount of titanium dioxide deposited in a single reaction cycle.     

Fe-doped and Mn-doped titanium dioxide thin films

Thin films of TiO₂ doped with Fe and Mn were deposited on F-doped SnO₂-coated glass by spin coating. Dopant concentrations of 3–7 wt% (metal basis) were used. The structural, chemical, and optical characteristics of the films were investigated. Laser Raman microspectroscopy and glancing angle X-ray diffraction data showed that the films consisted of the anatase polymorph of TiO₂. X-ray photoelectron spectroscopy data indicated the presence of Fe³⁺, Mn⁴⁺, and Mn³⁺ in the doped films, as predicted by calculated thermodynamic stability diagrams, and the occurrence of atomic disorder and associated structural distortion. Ultraviolet–visible spectrophotometry data showed that the optical indirect band gap of the films decreased significantly with increasing dopant levels, from 3.36 eV (undoped) to 2.95 eV (7 wt% Fe) and 2.90 eV (7 wt% Mn). These improvements are attributed to single (Fe) or multiple (Mn) shallow electron/hole trapping sites associated with the dopant ions.     

纳米二氧化钛粉体及薄膜制备的研究进展

本文对近几年有关纳米二氧化钛粉体及薄膜的制备研究进行综述。重点介绍及评述了以无机钛盐和有机钛盐为前驱体制备纳米二氧化钛粉体及利用自组装方法制备二氧钛薄膜的最新研究成果。对今后研究工作的趋势进行了探讨。     

Novel titanium compounds for metal-organic chemical vapor deposition of titanium dioxide films with an ultrahigh deposition rate

A new titanium diolate compound Ti(mpd)(mdop)(2) (1) containing a beta-ketoester and a dimeric derivative [Ti(mpd)(mdop)(mu-OMe)](2) [2; mpd = 2-methyl-2,4-pentanediolate, mdop = (CH(3))(3)CC(O)C(-)HCOOCH(3)] have been synthesized and characterized by FT-IR, (1)H NMR, (13)C NMR, mass spectroscopy, and elemental analysis. Complex 2 was further characterized by X-ray structural analysis. Both 1 and 2 are fairly stable in air and in solvents such as tetrahydrofuran and toluene. They are also thermally stable and do not leave any residue during flash evaporation at around 280 degrees C. The new titanium complexes were used as precursors for the deposition of TiO(2) thin films by liquid-source metal-organic chemical vapor deposition. Compared with commercial Ti precursors, such as Ti(mpd)(tmhd)(2) (tmhd = 2,2,6,6-tetramethylheptanedionate) and Ti(OPr(i)())(2)(tmhd)(2), the new titanium complexes demonstrated a much higher deposition rate of TiO(2) film growth (3-6 times) at 400-475 degrees C. The deposited TiO(2) film from complex 2 was found to be in a crystalline anatase phase with a smooth surface morphology and low carbon content. Crystal data for 2: 233(2) K, a = 12.570(4) A, b = 13.817(4) A, c = 11.157(3) A, beta = 101.059(5) degrees, monoclinic, space group P2(1)/c, Z = 2.     

Low temperature deposition of nanocrystalline titanium dioxide from titanium tetraisopropoxide

Effect of ozone and water vapor on the chemical deposition of TiO₂ from the gas phase in the system of titanium tetraisopropylate-oxygen was examined. Introduction of ozone in the reaction medium was shown to result in the precipitation of smooth TiO₂ layers at 240°C, and the addition of water vapor leads to the formation with higher rate of unconsolidated layers. Adding ozone to the reaction medium with low moisture content (up to 0.65 Pa) allows obtaining at temperatures 250–350°C with high rate of growth the TiO₂ layers with the anatase nanocrystals of high photocatalytic activity.     

Kinetic rules of precipitation of thin films of titanium dioxide from the gas phase containing titanium tetraisopropylate

Precipitation of titanium dioxide layers from the gas phase in the reaction system containing titanium tetraisopropylate and oxygen at the total pressure 1 kPa is studied. It is shown that in the range of 300–500°C the precipitation proceeds in the kinetic regime and is accompanied by the formation of layers of monotonous thickness containing nanocrystalline phases of anatase and rutile. In the temperature range 300–350°C the activation energy value was 92.7 kJ mol^?1, and at higher temperatures (up to 500°C) it decreased to 17.5 kJ mol^?1. The increase in the precipitation temperature caused the increase in relative amount of rutile in the precipitated layers.     

Photocatalytic lithography based on thin films of amorphous hydrated titanium dioxide

The mechanism of photoactivation of amorphous hydrated titanium dioxide thin films containing palladium ions toward the reaction of electroless deposition of nickel was studied. It was shown that the photocatalytic reduction of palladium ions during UV irradiation results in the formation of intermediate Pd(I) states that subsequently disproportionate, yielding a Pd nanophase. The palladium nanoparticle-catalyzed electroless deposition of nickel on exposed areas of the titanium dioxide photolayer makes it possible to fabricate metal patterns having a 5-μm resolution, with the fast and irreversible capture of photoelectrons at the latent image formation step preventing the image from blurring, including the process on conducting substrates.     

Evolution of water vapor from indium-tin-oxide thin films fabricated by various deposition processes

Tin-doped In₂O₃ (indium-tin-oxide) transparent conducting films are widely used as electrodes of liquid crystal displays and low-E windows. In the present study, a systematic TDS study was undertaken for ITO films fabricated by various deposition processes; such as PVD, dip coating and spray deposition. Water vapor was the main gas evolved from the films; gas evolution from the silicon substrate was negligible. The evolution proceeded via two steps at approximately 373 and 473-623 K. The amount of the evolved water was in the order: (dip-coated film)>(PVD films)> (spray-deposited film). This order was identical to that of the film's resistivities. This revised version was published online in August 2006 with corrections to the Cover Date.     

Atomic-layer deposition of cadmium chalcogenides on silicon

The results of studies of the synthesis of ultrafine layers of cadmium selenide and telluride by atomic-layer deposition on the silicon surface of different orientations were summarized. The main tendencies of the chemisorption of the components and conditions of layer growth during the formation of nanostructures of these compounds were determined.     

Plasma deposition of thin films from a fluorine-containing cyclosiloxane

Thin films have been deposited from radio-frequency glow discharges fed with vapors of a silicon- and fluorine-containing organic compound, namely 2,4,6-tris[(3,3,3-trifluoropropyl) (methyl)] cyclotrisiloxane, in mixture with argon. 2,4,6-tris[(3,3,3-trifluoropropyl)(methyl)]cyclotrisiloxane A triode reactor has been utilized to deposit films by independently changing substrate temperature and bias-induced ion-bombardment. Laser interferometry, electron spectroscopy for chemical analysis and Fourier-transform infrared spectroscopy have been used to monitor film growth rate and composition. Results unambiguously show an activating effect of the ion-bombardment, which confirm the validity of the ion-assisted deposition model utilized for the plasma deposition of both teflon- and silicone-like films. In our experiments, low substrate temperature and bias conditions results in films with a “monomer-like” stoichiometry, while drastic conditions give origin to materials with a completely different composition and a markedly increased hardness. © 1994 John Wiley & Sons, Inc.     

Photoelectrochemical deposition of thin tellurium films

Effect of polychromatic light on the electrochemical deposition of tellurium(IV) ions on a glass carbon electrode from acid solutions of 0.45 M Na₂SO₄ + 0.05 M H₂SO₄ with pH 2.2 was studied. It is shown that electrochemical reduction of tellurium(IV) is possible in two stages in the potentiodynamic mode at potentials in the range from 0 to ?1000 mV. Elementary tellurium is formed in the first stage (E = ?320 ± 20 mV) and is reduced to telluride ions in the second (E = ?700 ± 50 mV). It is demonstrated that, under potentiodynamic deposition conditions, visible light affects the generation of Te^2? ions at potentials more positive than the electrochemical potential. The chronoamperometric method revealed differences in the behavior of transient currents in the dark and under illumination. The elemental composition and the film surface morphology were studied by electron-probe analysis.     

The influence of various deposition techniques on the photoelectrochemical properties of the titanium dioxide thin film

Thin sol–gel TiO₂ layers deposited on the conductive ITO glass by means of three various deposition techniques (dip-coating, inkjet printing and spray-coating) were used as photoanode in the three-compartment electrochemical cell. The thin TiO₂ films were treated at 450 °C and after calcination all samples possessed the crystallographic form of anatase. The relationship between surface structure and photo-induced conductivity of the nanostructured layers was investigated. It was found that the used deposition method significantly influenced the structural properties of prepared layers; mainly, the formation of defects and their quantity in the prepared films. The surface properties of the calcined layers were determined by XRD, Raman spectroscopy, SEM, AFM, UV–Vis analyses and by the optical microscopy. The photo-induced properties of nanoparticulate TiO₂/ITO photoanode were studied by electrochemical measurements combined with UV irradiation.     

Sol-gel made titanium dioxide nanostructured thin films as gas-sensing materials for the detection of oxygen

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Plasma deposition of silicon nitride-like thin films from organosilicon precursors

Plasmas containing hexamethyldisilazane or hexamethylcyclotrisilazane and nitrogen or ammonia were used to deposit silicon nitride-like films at low substrate temperature (T<60°C). Optical properties (refractive index and absorption coefficient), chemical composition of the deposit and film growth rate were examined with respect to the deposition parameters (rf power, pressure and feed composition). As deposited films from ammonia containing mixtures were silicon nitride-like, contained carbon, and were nearly oxygen free. Furthermore, only Si−N, Si−H, and N−H bonds were identified in as-deposited films. The reactive Si−H bonds progressively transformed into Si−O bonds as the films were exposed to air. Films deposited from highly ammonia-diluted mixtures, high RF power and low pressure showed the highest stability with refractive indices as high as 1.8.     

Cathodic electrophoretic deposition of manganese dioxide films

Cathodic electrophoretic deposition (EPD) method has been developed for the deposition of manganese dioxide films. It was shown that phosphate ester (PE) is an effective charging additive, which provides stabilization of manganese dioxide nanoparticles in suspensions. The influence of PE concentration and deposition voltage on the deposition efficiency has been studied. EPD has been utilized for the fabrication of porous nanostructured films with thickness in the range of 0.5–20 μm for application in electrochemical supercapacitors (ES). Cyclic voltammetry and chronopotentiometry data for the films tested in the 0.1 M Na₂SO₄ solutions showed capacitive behavior in the voltage window of 1 V. The highest specific capacitance (SC) of 377 F g⁻¹ was obtained at a scan rate of 2 mV s⁻¹. The SC decreased with increasing film thickness and increasing scan rate in the range of 2–100 mV s⁻¹. The deposition mechanism, kinetics of deposition and charge storage properties of the films are discussed.     

Thick titanium dioxide films for semiconductor photocatalysis

Thick paste TiO₂ films are prepared and tested for photocatalytic and photoinduced superhydrophilic (PSH) activity. The films are effective photocatalysts for the destruction of stearic acid using near or far UV and all the sol–gel films tested exhibited a quantum yield for this process of typically 0.15%. These quantum yields are significantly greater (4–8-fold) than those for titania films produced by an APCVD technique, including the commercial self-cleaning glass product Activ™. The films are mechanically robust and optically clear and, as photocatalysts for stearic acid removal, are photochemically stable and reproducible. The kinetics of stearic acid photomineralisation are zero order with an activation energy of ca. 2.5 kJ mol⁻¹. All titania films tested, including those produced by APCVD, exhibit PSH. The light-induced fall, and dark recovery, in the water droplet contact angle made with titania paste films are similar in profile shape to those described by others for thin titania films produced by a traditional sol–gel route.     

Effect of the substrate nature on the formation of thin titanium dioxide films by molecular layering

Results of structural studies of titanium dioxide films synthesized on glass, silicon, and mica substrates by molecular layering are presented. An analysis of data furnished by electron and X-ray diffraction analyses and atomic-force microscopy of the samples in different growth stages revealed the effect of the substrate nature on the structure of the titanium oxide coatings synthesized.     

Pulsed laser ablation and deposition of thin films

Pulsed laser ablation is a simple, but versatile, experimental method that finds use as a means of patterning a very diverse range of materials, and in wide areas of thin film deposition and multi-layer research. Superficially, at least, the technique is conceptually simple also, but this apparent simplicity hides a wealth of fascinating, and still incompletely understood, chemical physics. This overview traces our current physico-chemical understanding of the evolution of material from target ablation through to the deposited film, addressing the initial laser-target interactions by which solid material enters the gas phase, the processing and propagation of material in the plume of ejected material, and the eventual accommodation of gas phase species onto the substrate that is to be coated. It is intended that this Review be of interest both to materials scientists interested in thin film growth, and to chemical physicists whose primary interest is with more fundamental aspects of the processes of pulsed laser ablation and deposition.     

Electrochemical deposition and characterization of SnS thin films

Thin films of SnS were cathodically deposited onto stainless steel substrates from bath containing 0.025 M SnSO₄, 0.25 M KSCN and 0.25 M Na₂SO₄. The mechanism of electrochemical co-deposition of tin and sulphur was investigated by cyclic voltammetry. Analysis of the chronoamperometric current–time transients suggested that, in the potential range −560 to −590 mV vs saturated calomel electrode, the electrodeposition of SnS involved progressive nucleation model. However, at a potential −600 mV, the electrodeposition involved instantaneous nucleation model. The deposits have been characterized by scanning electron microscopy, X-ray diffraction and optical measurements. SnS films were found to be polycrystalline with an optical energy gap of 1.38 eV.