Nitrogen incorporation during PVD deposition of TiO2:N thin films

DARINA MANOVA; LINA FRANCO ARIAS; AXEL HOFELE; IVO ALANI; ARIEL KLEIMAN; IGLIKA ASENOVA; ULRICH DECKER; ADRIANA MÁRQUEZ; STEPHAN MÄNDL

Buenos Aires

Conferencia; 13th International Conference on Plasma Based Ion Implantation & Deposition (PBII&D 2015); 2015

Titanium dioxide with its allotropic modifications ? rutile and anatase ? is known for its photoactivity upon illumination with UV light. Either a superhydrophilic surface, e.g. for anti-fogging purposes, or a catalytically active surface for removal of volatile organic compounds (VOCs) can be obtained by tailoring the phase composition and the grain size using several different methods. However, materials and surfaces more sensitive to visible light are desired as the absolute irradiation intensity is increasing for longer wavelengths. However, a too strong reduction of the bandgap will adversely affect the photoactivity: the photocatalysis is limited earlier than the hydrophilicity as the electrochemical redox pairings with sufficiently activated electron-hole pairs are no longer accessible.Using PVD methods as vacuum arc deposition or plasma based ion implantation and deposition, versatile bandgap engineering is possible with both methods yielding nearly identical results. However, the very strong affinity of oxygen towards titanium necessitates a reduced total pressure to accommodate any nitrogen at all. In these preliminary investigations, the nitrogen content and the optical properties have been investigated as a function of different processing conditions. While an increasing nitrogen content in the deposited film for increasing nitrogen addition in the gas phase is found, additional plasma excitation does not increase the nitrogen content. In contrast, substrate heating towards a moderate 200 °C without inducing major phase transitions leads to a strong increase of the nitrogen content. The absolute quantification of the nitrogen content is difficult as XPS depth profiling is known to influence the oxidation state of titanium while SIMS is suffering from matrix effects with the nitrogen containing species showing different ionization levels depending on the film chemistry. Nevertheless, comparisons for calibration with TiN thin films, TiO2 implanted with nitrogen using a conventional ion implanter and SRIM simulations show that about 5 ? 7.5 at.% nitrogen can be incorporated in the PVD thin films before they losetheir transparency. Besides a small shift towards lower band gaps, strong absorption centers are found within the band gap with increasing nitrogen content. Again, substrate heating does ameliorate the effects of nitrogen incorporation as dynamic annealing occurs during the deposition. Detailed investigations on the photoactivity and the crystalline structure are in progress.