Photo-induced enhanced Raman spectroscopy (PIERS) has emerged as a highly sensitive surface-enhanced Raman spectroscopy (SERS) technique for the detection of ultra-low concentrations of organic molecules. The PIERS mechanism has been largely attributed to UV-induced formation of surface oxygen vacancies (V_o) in semiconductor materials, although alternative interpretations have been suggested. Very recently, PIERS has been proposed as a surface probe for photocatalytic materials, following V_o formation and healing kinetics. This work establishes comparison between PIERS and V_o-induced SERS approaches in defected noble-metal-free titanium dioxide (TiO_2-x) films to further confirm the role of V_o in PIERS. Upon application of three post-treatment methods (namely UV-induction, vacuum annealing and argon etching), correlation of V_o kinetics and distribution could be established. A proposed mechanism and further discussion on PIERS as a probe to explore photocatalytic materials are also presented.

This article is part of the theme issue ‘Exploring the length scales, timescales and chemistry of challenging materials (Part 2)’.