Phase Formation and Selectivity on Cr (co-)Doped TiOU+2082 through Interface Engineering and Post-Deposition Flash Lamp Annealing

Many applications of TiO₂ partially rely on its good performance as solvent for numerous impurities [1]. In particular, metal (cation) dopants have been used to functionalize or enhance TiO₂ as catalyst [2], diluted magnetic semiconductor [3] or transparent conductor [4]. One of the most interesting properties of TiO₂ relies on its photoactivity, exploited in many applications from catalysis, hydrogen production, pigments or solar cells [2]. However, TiO₂ is mostly active in the ultraviolet (UV) region of the solar spectrum (band-gap > 3 eV) and there is a great interest in band-gap narrowing of TiO₂ to achieve visible-light (VISL) response [2]. Metal doping do so and increases VISL absorption significantly but, unfortunately, introduces structural distortions in the host matrix that result in carrier recombination centers [5]. Apart from the structural quality, another relevant consideration on the production of doped TiO₂ relies on the particular oxide matrix phase (anatase/rutile) [6]. For example, anatase has superior photoactivity than rutile although phase mixtures with high anatase content may present even higher photoactivity [7]. Therefore, special attention should also be devoted to the phase selectivity. Moreover, (heavily) doped TiO₂ may display a completely different electronic structure that the pristine oxide material.
The aim of this study is to promote customized phase formation in Cr (co-)doped TiO₂ films produced by magnetron co-sputtering. Special attention is paid to the structural arrangements around host and dopant sites from the X-ray absorption near-edge structure. We report the conditions driving to single- or mixed-phase formation with the novelty of exploring film architectures based on interface engineering and/or post-deposition flash-lamp annealing (FLA) [8]. The latter is a non-contact rapid thermal processing extensively used in Microelectronics but yet to be explored in the present context. Hence, FLA can be attractive for many industrial applications dealing with the synthesis of band-gap engineered TiO₂-based materials.
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