@conference{
author = "Grce, Ana and Pjević, Dejan and Milosavljević, Momir and Grieseler, Rolf and Schaaf, Peter",
year = "2018",
abstract = "Titanium-dioxide nanostructures and thin films are interesting for application in environmental protection, for water and air purification from toxic compounds, and photocatalytic degradation of water, where separation of H2 is important for the development of new energy sources. Furthermore, they are interesting for fabrication of solar cells, various sensor applications, transparent conducting oxides (TCO), etc [1-3]. Stoichiometric TiO2 phase has a wide optoelectronic band gap of ~3.2 eV, which makes it a dielectric at lower temperatures and a semiconductor at higher temperatures. It has a high absorption coefficient in the range of UV radiation, but low in the visible light region, and this makes significant constrains for its usage as a photocatalyst. For reducing energy gap, better absorption in visible light region and more efficient application it is necessary to add doping material species, which can be metal or non-metal ions.When used as a photocatalyst in form of a powder, TiO2 nanoparticles are embedded in photosensitizing dyes which absorb visible light, or they are partly covered with nanoparticles of some transition metal to enhance injection of charge carriers. Recent developments involve the use of physical vapor deposition (vacuum evaporation or ion sputtering) to synthesize TiO2 thin film structures, and ion implantation for their doping. The advantage of using physical vapor deposition is that the Ti:O ratio can be varied, and the films can be deposited on any supporting or large area substrates. On the other hand, ion implantation is a proven technique for introducing dopant atomic species into the crystal lattice of semiconductor materials. In these experiments TiO2 thin films were synthesized by physical vapor deposition (PVD) method, using three different procedures: (i) reactive d.c. ion sputtering of pure Ti target, using Ar ions and introducing O2 in the deposition chamber; (ii) r.f. sputtering of TiO2 target, using Ar + O2 gas mixture; and (iii) reactive e-beam evaporation of pure Ti in the presence of introduced O2 . In case of reactive d.c. ion sputtering additional experiments involved a controlled introduction of nitrogen in the interaction chamber, which yielded doping of the deposited TiO2 thin films, in reducing their band gap and enhancing absorption of visible light. The films were deposited to a thickness of a few hundred nm on silicon wafers and glass slide substrates. Structural and compositional characterization of samples included X-ray diffraction analysis (XRD), transmission electron microscopy (TEM, HRTEM), Rutherford backscattering spectrometry (RBS), and X-ray photoelectron spectroscopy (XPS). Optical characterizations were done by measuringthe transmission and diffuse reflection UV/VIS spectra. Photocatalytic activity was measured by determining the photodegradation rate of organic solutions Structural characterization revealed that as-deposited samples grow in form of a mixture of very fine nanocrystalline grains of rutile and anatase TiO2 phases and TiO. Hence, in order to homogenize the TiO2 stoichiometry andinduce the growth of larger grains it was necessary to anneal the samples in air, at temperatures of 400 and 600 o C [4]. This procedure was performed on all samples after deposition. Bright-field cross-sectional images taken from two different TiO2 films deposited on Si wafers are shown in Fig. 1. Sharp contrast regions within the films indicate their polycrystalline structure. The results of investigations showed that it is possible to tailor the structure and properties of the obtained TiO2 thin films by adjusting the processing parameters.",
publisher = "Belgrade : Serbian Chemical Society",
journal = "ENVIROCHEM 2018 : 8th Symposium Chemistry and Environmental Protection : program and the book of abstracts",
title = "Nanostructured titanium-dioxide thin films for environmental applications",
pages = "205-206",
url = "https://hdl.handle.net/21.15107/rcub_vinar_12689"
}
