Regensburg 2004 – scientific programme

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DS: Dünne Schichten

DS 12: Schichteigenschaften II

DS 12.6: Talk

Wednesday, March 10, 2004, 16:30–16:45, HS 31

Preparation and characterization of nanocrystalline anatase TiO₂ films — •A. Orendorz, B. Huber, J. Wüsten, H. Gnaser, and C. Ziegler — Department of Physics, University of Kaiserslautern, D-67663 Kaiserslautern, Germany

Using TiO₂ particles with nominal sizes of 6 nm, 12 nm, or 20 nm, nanocrystalline anatase TiO₂ films with a typical thickness of some µm were deposited on various substrates. Structural investigations of the films by means of TEM and XRD revealed that, as in the primary TiO₂ particles, only the anatase phase of TiO₂ occurs in the films and that no preferential orientation of the nanoparticles exists. The average particle sizes in the films determined from the XRD data agree within about 10 % with the above-quoted size values of the primary particles. Depth profiles by SIMS showed a homogeneous distribution of Ti and O throughout the films and a low concentration of impurity species (atomic concentrations < 10⁻⁴). The electrical conductivity σ of the nanocrystalline films was determined as a function of the sample temperature T and of the oxygen partial pressure p(O₂) under UHV conditions. Over a wide range of p(O₂) and for 200 ^∘C ≤ T ≤ 500 ^∘C a dependence σ ∝ p(O₂)⁻ⁿ was observed. Furthermore, it was noted that the exponent n exhibits a pronounced dependence on the particle size and on T, but also on the type of substrate. The values derived for n (∼ 0.5 ≤ n ≤ 1.3) are distinctly larger than those reported for TiO₂ bulk specimens; hence, in the nanocrystalline films σ decreases more rapidly with increasing p(O₂). In first measurements obtained by UPS and by IPE, the electronic structure of the nanocrystalline films was probed in the region of the band gap.