Optical properties of TiO₂ thin films prepared by chemical spray pyrolysis from aqueous solutions

Abstract

Titanium dioxide (TiO2) is known to have three different kinds of polymorphous crystalline forms: rutile, anatase, and brookite. The rutile phase is always formed at higher temperatures, while the anatase phase is formed at lower temperatures and transformed into rutile phase above 800 ºC. Various deposition techniques have been developed for depositing TiO2 thin films, including evaporation, sputtering, chemical vapour deposition and thermal oxidation of titanium. Among them, the Chemical Spray Pyrolysis (CSP) technique has many advantages, such as good conformal coverage, the possibility of epitaxial growth and the application to large area deposition. Also, this method is low cost and it is easy to control the deposition growth parameters. In the present work, TiO2 thin films have been deposited on p‐Si (001) and fused silica substrates by Chemical Spray Pyrolysis (CSP) method from aqueous solution containing titanium (IV) isopropoxide (Ti[OCH(CH3)2]4. As‐deposited thin films show anatase polycrystalline structure, and rutile phase formed for films annealed at 750ºC. SEM images have confirmed a smooth and crack‐free surface with low surface roughness. X‐ray photoelectron spectroscopy (XPS) combined with 4 keV Ar+ depth profiling has shown that crystallized films correspond to TiO2. Residual carbon coming from the organic precursor solution is only detected at the surface of the film. Thin films deposited on fused silica were highly transparent (more than 85%), with an indirect optical band gap of 3,43 and 3,33 eV for as‐deposited and annealed films, respectively, and refractive indexes in the range between 2.01–2.29. Spectroscopic Ellipsometry (SE) also has been used to extract optical parameters. SE data fitted to triple‐layer physical model revealed the same tendency to increase refractive index in annealed films. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A study of the physical properties and gas‐sensing performance of TiO2 nanofilms: Automated nebulizer spray pyrolysis method (ANSP)

“…In that order, separate analysis elements of core levels C 1s, O 1s, and Ti 2p 3/2, Ti 2p 1/2 indicated the binding energies at 286.14 eV, 530.90 eV and 458.43 eV, 465.24 eV, respectively. These calculations led to the conclusion that these titania anatase phase thin films have 7.65% of carbon, 45.16% of oxygen, 46.93% of Ti 4+ and the presence of this prime element and carbon is probably due to the use of organic precursors and the contamination caused by sample handling . The standard anatase titania (Ti 4+ ) phase was well fitted with the prepared film of TiO 2 .…”

Structural investigation and electronic band transitions of nanostructured TiO2 thin films

“…TiO 2 films can be deposited or grown on substrates such as Si, glass, sapphire, and quartz by using reactive sputtering, sol-gel spin coating, laser deposition, thermal evaporation, thermal oxidation of titanium, chemical vapor deposition and chemical spray pyrolysis techniques [7,[9][10][11][12]. The structural characteristics of TiO 2 films are affected by gas pressure and substrate temperature during the deposition process [13].…”

“…TiO2 has three different crystalline phase structures as rutile, anatase and brookite, which affect their optical and electrical characteristics [6,7]. The anatase and rutile structures are commonly used for technological applications.…”

“…The obtain the rutile structure at the low temperatures is very difficult. TiO 2 films have anatase phase below 800 °C while they have the rutile phase at higher temperatures [7,8]. With variations of the film deposition conditions and post-growth processes such as thermal annealing in different gas atmospheres (i.e.…”

Characterization of TiO₂ Thin Films Prepared by Vacuum Evaporation

“…There are three kinds of crystal types of typical TiO 2 : rutile, anatase and brookite. At present, there are a variety of methods for the preparation of TiO 2 films, such as sol-gel method [1][2],chemical vapor deposition [3], chemical spray pyrolysis [4] sputtering [5], pulsed laser deposition [6]. The structure, appearance and performance of different preparation techniques of thin films, such as the film thickness uniformity, and the glass substrate binding firmness, surface topography, has a different effect of crystal structure.…”