Photo-induced surface charge separation in Cr-implanted TiO2 thin film

Surface charge separation efficiencies of uniformly Cr-distributed rutile grown by pulse laser deposition (PLD) using Cr/TiO 2 multi-targets and rutile with Cr concentration gradient produced by ion implantation with the appropriate post-annealing process were characterized by photo-induced transient charge separation (PITCS) measurement. Cr depth profiles were obtained by secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) was used to determine that both surface Cr concentrations were the same. PITCS can be measured without direct contacts and without an externally applied field, and demonstrate the inherent property of charge separation without disturbing spontaneously formed surface band bending. There was a large charge separation for implanted rutile with Cr gradient, even in the visible light region (∼520 nm), which was more remarkable than that of uniform rutile and epitaxial anatase films.