Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 28 WEDNESDAY AFTERNOON
RIVA-TF-WeA-P.4 NITROGEN-DOPED TiO 2 THIN FILMS DEPOSITED ONTO
ITO/GLASS SUBSTRATES. Diana Mardare. Al.I.Cuza University, Faculty of Physics, Carol I
Blvd., No.11, Iasi 700506, ROMANIA. Luca Dumitru. Al.I.Cuza University, Faculty of Physics,
Carol I Blvd., No.11, Iasi 700506, ROMANIA
Titanium dioxide films are extensively used in optical thin film device applications owing to their
appropriate optical properties, high thermal and chemical stability in hostile environments. These
films present good durability, a high transmittance in the visible spectral range, and a high refractive
index, so that they are suitable for applications, such as: antireflection coatings, multilayer optical
coatings (used as optical filters), optical waveguides, etc. Also, TiO 2 has focussed a considerable attention
in the past decades as a material with a strong oxidation power, being considered one of the
best photocatalytic material which can be used in order to solve some of the world environmental
problems.
Titanium oxide crystallizes in three different forms: anatase (tetragonal), rutile (tetragonal) and
brookite (orthorhombic) and may also exist in an amorphous state. Rutile is a denser phase than anatase
and brookite, being also the most thermodynamically stable. By changing the deposition parameters,
by performing a heat treatment, or by doping with different impurities, the ratio of the
mentioned phases changes, leading to changes in optical and electrical properties of titanium oxide
thin films [1-3]. The three phases are characterized by different optical properties and determine different
transmittances, optical constants and optical band gaps of the thin films. The catalytic properties
are connected with the large band gap value of the anatase phase (3.2 eV) associated with a low
recombination rate of the charge carriers generated in the surface area by the incident photons.
Undoped and nitrogen-doped titanium oxide films were prepared by reactive magnetron sputtering
onto ITO/glass substrates. Film structure and surface morphology were investigated by X-ray diffraction
and atomic force microscopy. X-ray diffraction (XRD) studies revealed an amorphous structure
of the as-deposited thin films. The surface roughness was derived from AFM imaging. By heat
treatment the amorphous films became polycrystalline. The heat-treated-nitrogen-doped films have a
pure anatase structure, while the undoped ones contain only the rutile phase.
The contact angle of the deionized water with film surface was monitored during both photoactivation
and recovery regimes. The results are discussed in terms of the effects of surface roughness and
of rutile-anatase TiO 2 phase transformation induced by heat treatment and by nitrogen doping, as reflected
in optical transmittance results.
[1] D. Mardare, M. Tasca, M. Delibas and G. I. Rusu, Appl Surf Sci 156 (2000) 200.
[2] A. R. Bally, E. N. Korobeinikova, P. E. Schmid, F. Lévy and F. Bussy, J Phys D: Appl Phys 31
(1998) 1149.
[3] D. Mardare and P. Hones, Mater Sci Eng B 68 (1999) 42.
119