Phase Selectivity in Cr and N Co-Doped TiO2 Films by Modulated Sputter Growth and Post-Deposition Flash-Lamp-Annealing

Raúl Gago,David Esteban-Mendoza,Javier Palomares,Ignacio Jiménez,René Hübner,Frans Munnik,Slawomir Prucnal

doi:10.3390/coatings9070448

Abstract

In this paper, we report on the phase selectivity in Cr and N co-doped TiO2 (TiO2:Cr,N) sputtered films by means of interface engineering. In particular, monolithic TiO2:Cr,N films produced by continuous growth conditions result in the formation of a mixed-phase oxide with dominant rutile character. On the contrary, modulated growth by starting with a single-phase anatase TiO2:N buffer layer, can be used to imprint the anatase structure to a subsequent TiO2:Cr,N layer. The robustness of the process with respect to the growth conditions has also been investigated, especially regarding the maximum Cr content (<5 at.%) for single-phase anatase formation. Furthermore, post-deposition flash-lamp-annealing (FLA) in modulated coatings was used to improve the as-grown anatase TiO2:Cr,N phase, as well as to induce dopant activation (N substitutional sites) and diffusion. In this way, Cr can be distributed through the whole film thickness from an initial modulated architecture while preserving the structural phase. Hence, the combination of interface engineering and millisecond-range-FLA opens new opportunities for tailoring the structure of TiO2-based functional materials.

Highlights

IntroductionTitania or titanium dioxide (TiO2 ) is a functional wide band-gap semiconductor with tuneable electrical and optical properties by intrinsic (structure in single- or mixed-phase anatase/rutile and/or native defects) or extrinsic (doping) mechanisms [1]
Titania or titanium dioxide (TiO2 ) is a functional wide band-gap semiconductor with tuneable electrical and optical properties by intrinsic or extrinsic mechanisms [1]
One of the most interesting properties of TiO2 relies on its photoactivity, which has been exploited in many applications, such as photocatalysis, hydrogen production, pigments or solar cells [2,5]

Summary

Introduction

Titania or titanium dioxide (TiO2 ) is a functional wide band-gap semiconductor with tuneable electrical and optical properties by intrinsic (structure in single- or mixed-phase anatase/rutile and/or native defects) or extrinsic (doping) mechanisms [1]. One of the most interesting properties of TiO2 relies on its photoactivity, which has been exploited in many applications, such as photocatalysis, hydrogen production, pigments or solar cells [2,5]. Many efforts have been focused on band-gap narrowing for TiO2 to achieve a visible-light (VISL) response. Such a challenge is mainly realized via doping with foreign atoms at cation or anion sites [2]. In this respect, non-metal (anion) doping has been extensively studied, especially after the work by Asahi et al [7]

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