Room temperature synthesis of nanocrystalline anatase sols and preparation of uniform nanostructured TiO2 thin films: optical and structural properties

• Published in: Journal of physics. D, Applied physics Vol. 44; no. 5; p. 055402
• Main Authors: Hosseingholi, M, Pazouki, M, Hosseinnia, A, Aboutalebi, S H
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 09.02.2011; Institute of Physics
• Subjects: Anatase; Annealing; Chemical synthesis methods; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Dip coatings; Exact sciences and technology; Materials science; Methods of nanofabrication; Nanocrystals and nanoparticles; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures; Physics; Sols; Thin films; Titanium dioxide; Particle size; Anatase; Annealing temperature; High temperature; Nanostructures; Surface states; Thin films; Energy gap; Transparent thin film; Crystallites; Optical properties; Size effect; Dip coating; Absorption spectra; Optical films; Thermal annealing; Sol-gel process; Nanocrystal; Nanomaterial synthesis; Temperature dependence; Electronic properties; pH value; pH effect; Crystallinity; Heat treatments; Ultraviolet radiation; Surface cracks; Smooth surface
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/44/5/055402

Transparent TiO2 thin films were deposited on soda-lime glass substrates via the sol--gel method using a nanocrystalline TiO2 sol solution prepared at room temperature employing the dip-coating method. The effects of pH on crystallinity, particle size and stability of the synthesized TiO2 sols were investigated, systematically. TiO2 thin films were thickened by means of a sequential dip-coating process. The TiO2 films were transparent and exhibited proper adherence. The effects of thickness and annealing temperature on the structural and optical properties of the thin films were evaluated. The prepared powder was crystalline without any thermal treatment. The crystallite size of the particles (anatase) was in the range 4.2--12.1 nm depending on the initial pH value. Although only the anatase phase was observed at room temperature and 400 degree C, a further increase in annealing temperature up to 700 degree C resulted in the formation of the rutile phase. Even at high annealing temperatures, fairly smooth and homogeneous surfaces with no cracks and pores were observed. It was demonstrated that the films were transparent in the visible region with characteristic absorption in the UV region. Band gap of the as-deposited film was estimated to be 3.34 eV and was found to decrease with increasing annealing temperature.