Refractive Index Of TiO2 Films Research Articles

Solution route to large area all-TiO2 one-dimensional photonic crystals with high reflectivity and different structural colors

In this paper, wafer-scale dense and meosoporous TiO2 films are fabricated via spin-coating and thermal treatment. A photo-curable resin, acrylated polytitanoxane tetramer (Ti-resin), is synthesized as the precursor of TiO2 to deposit dense films. The refractive index of TiO2 films at 500 nm is tuned from 2.17 (dense) to 1.49 (porous) by changing film porosity via adding different amount of polystyrene (PS) to the precursor solvent. A reactive compatibilizer containing one mercapto group and three benzyl rings is synthesized to reduce phase separation and prevent film crack of porous films during the calcinations. The deposition protocol is optimized to prevent infiltration of dense TiO2 layers into porous TiO2 layers. Film thicknesses of both dense and porous TiO2 films can be linearly tuned by changing deposition number. All-TiO2 1D photonic crystals with different structural colors are successfully fabricated on quartz and silicon wafers with reflectivity of at least 90%, covering the spectrum from 400 to 800 nm.

Efficient Power Generation for Smart Homes Based Titanium Dioxide (TiO<sub>2</sub>)

Smart home uses a combination of the renewable energy power resources, the use of power generation from solar cells based on titanium dioxide (TiO2) which acts as the only type which produces an efficient solar cell power to obtain the electricity to recharge the standby storage device from the sunlight. The thin film of Titanium dioxide is synthesized by the sol-gel spin coating techniques at 2000 rpm on the glass. The films have a constant thickness of ~240nm. The annealing process consists of 150°C, 250°C and 350°C. The study of the absorbance and the wavelength values are important. At this condition, for the solar cell, the wavelength is around ~280nm to ~330nm. As the temperature of annealing increases the higher absorbance would be produced. The refractive index of TiO2 film is estimated at different annealing temperatures and it increases with the increasing of the annealing temperature. The application is suitable to smart home design. The dynamic output voltage obtained from the solar cells is interfaced with other circuitry such as inverters and interface charging circuit in order to inject the generated power into the standby storage device. The calculated result of this application is efficient to reduce the electrical bill by almost 30% of its original value.

Effect of TiO2 Antireflection Layer with Various Conductivities and Refractive Indices on Performance of Amorphous Silicon/Amorphous Silicon Germanium Tandem Solar Cells

TiO2 films were prepared by RF magnetron sputtering with process variations of substrate temperature and oxygen dilution ratio to investigate the effect of the optoelectronic properties of TiO2 films on antireflection characteristics in solar cells. With an increase in substrate temperature from RT to 350 °C, the conductivity and refractive index of TiO2 films increased. However, the absorption coefficient also increased. In the case of oxygen-diluted sputtering (0.5–1%), the conductivity and refractive index decreased with the increase in oxygen dilution. On the other hand, the absorption coefficient decreased simultaneously. To evaluate these optoelectronic property variations of TiO2 films in terms of the antireflection effect in solar cells, amorphous silicon (a-Si:H)/amorphous silicon germanium (a-SiGe:H) tandem solar cells with various optoelectronic properties and thicknesses (20–40 nm) of TiO2 films were fabricated. The TiO2 film deposited at 350 °C and 0.5% oxygen dilution showed a high conductivity (∼10-3 Ω-1 cm-1) and refractive index (∼2.56 at 550 nm). The fabricated tandem cell with the TiO2 antireflection layer showed an efficiency of 11.22%, whereas the reference cell without TiO2 exhibited an efficiency of 10.97%.

Influence of annealing temperature on Raman and photoluminescence spectra of electron beam evaporated TiO2 thin films

Titanium dioxide (TiO2) thin films were deposited on fused quartz substrates by electron beam evaporation method at room temperature. The films were annealed at different temperatures in ambient air. The surface morphology/roughness at different annealing temperatures were analyzed by atomic force microscopy (AFM). The crystallinity of the film has improved with the increase of annealing temperature. The effect of annealing temperature on optical, photoluminescence and Raman spectra of TiO2 films were investigated. The refractive index of TiO2 films were studied by envelope method and reflectance spectra and it is observed that the refractive index of the films was high. The photoluminescence intensity corresponding to green emission was enhanced with increase of annealing temperature. The peaks in Raman spectra depicts that the TiO2 film is of anatase phase after annealing at 300°C and higher. The films show high refractive index, good optical quality and photoluminescence characteristics suggest that possible usage in opto-electronic and optical coating applications.

Use of Multilayer Oxide Films Prepared by RF-Magnetron Sputtering as Transparent IR-Reflector

A transparent-conducting indium tin oxide (ITO)/Titanium di-oxide (TiO2) multilayer optical filter has been developed using conducting and transparent ITO and transparent insulating TiO2 films grown by RF-magnetron sputtering. The objective is to cut off the infrared portion of the solar spectrum to avoid the heating effect. The electrical resistivity of ITO film is 1.2×10-4 Ω·cm, the sheet resistance is below 8 Ω/□ and the visible optical transmission is above 85%. The refractive index of this film is 1.9. On the other hand, TiO2 is highly resistive (resistivity is of the order of 1010 Ω·cm), and has 85% visible optical transmission and very low absorption in the visible and infrared regions. The refractive index of TiO2 film is 2.6 at a substrate temperature 250°C and 2.9 at 450°C. At 450°C, the rutile titanium dioxide structure was formed which was confirmed on the basis of diffraction rings. In the multilayered ITO/TiO2 structure ITO and TiO2 layers were alternately deposited. Thicknesses of the ITO and TiO2 layers were optimized to achieve the best result. The multilayer has the same sheet resistance as that of ITO film and about 92% visible transmission with the plasma resonant frequency at 840 nm. The X-ray diffraction (XRD) pattern of the ITO/TiO2 multilayer indicates a the random orientation of crystal growth.

Properties of TiO2 Thin Films on GaAs Prepared by Metalorganic Chemical Vapor Deposition

The deposition of polycrystalline TiO2 films on GaAs substrate is studied by metalorganic chemical vapor deposition (MOCVD) with Ti(i-OC3H7)4 and O2 as the precursors in a temperature range of 280–550°C. The structure, growth rate and grain size of TiO2 films depend on the deposition temperature. The film composition was measured by dispersive X-ray spectroscopy. From capacitance–voltage and current–voltage measurements of the Al/TiO2/GaAs/Au–Zn structure, the dielectric constant can reach 64 with the leakage current of 1×10-5 A/cm2 at 0.05 MV/cm at 350°C and the refractive index of TiO2 films can reach 2.2. At 300°C, the dielectric constant and leakage current density were 43 and 1×10-5 A/cm2 at 0.05 MV/cm and the refractive index of TiO2 films can reach 2.4.

Properties of TiO2 Thin Films on InP Substrate Prepared by Liquid Phase Deposition

The deposition of TiO2 films on InP substrate is studied by liquid phase deposition (LPD) with H2TiF6 and H3BO3 as the starting materials at the growth temperature of 75°C. The growth rate of TiO2 is about 42 Å/min. The surface morphology of the TiO2 films was mirror-like. The film stoichiometry was measured by energy dispersion spectroscopy (EDS). The refractive index of TiO2 films measured by ellipsometry reached 1.6. The structure of TiO2 is polycrystalline as determined by X-ray diffraction examination. From current–voltage measurement of the Al/TiO2/InP structure, the leakage current is 1×10-5 A/cm2 under the electric field intensity of 0.12 MV/cm.

Comparison of the characteristics of TiO2 films prepared by low-pressure and plasma-enhanced chemical vapor deposition

Thin films of titanium dioxide (TiO2) were deposited on silicon wafers at 450 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD), in the same reactor, using Ti(O-i-C3H7)4 and oxygen as the reactants. The crystal structure, surface morphology, composition, chemical binding state and refractive index of the TiO2 films, deposited with various r.f. powers, were characterized. Without plasma, LPCVD TiO2 films show polycrystalline anatase structure, with a rough, granular surface and a typical refractive index of 2.43. On the contrary, the PECVD TiO2 films are amorphous, with a smooth surface. By varying the r.f. power from 50 to 150 W, the refractive index of PECVD TiO2 film increases with increasing power and becomes higher than 2.8 at 125 and 150 W. Despite the very different crystal structure, surface morphology and optical properties, the composition and chemical binding states of LPCVD and PECVD TiO2 films are similar. The effect of plasma on the characteristics of CVD TiO2 films is discussed.

Development of New Modifiers for Titanium Alkoxide-Based Sol-Gel Process

The effects of several hydroxyketones such as acetol, actoin, γ-ketobutanol themselves and their combinations with monoethanolamine (MEA) or ethylenediamine (ED) on the stabilization of titanium tetraisopropoxide (TTIP) in isopropanol solution are examined. Acetoin itself and the imine derivatives of acetol and acetoin were found to show extraordinarily strong stabilizing effect for the alkoxide. The properties including the crystal modifications and refractive index of TiO2 films that were dip-coated using each stabilized solution are examined and discussed in comparison with those of the films obtained from the diethanolamine (DEA) systems. The effect of UV-light irradiation to the gel films on the crystallization of TiO2 is also examined and discussed.