Engineering large-scaled electrochromic semiconductor films as reproductive SERS substrates for operando investigation at the solid/liquid interfaces

Although surface-enhanced Raman spectroscopy (SERS) has been applied for gathering fingerprint information, even in single molecule analysis, the decayed Raman signals in aqueous solutions largely obstruct the on-site insight reaction process. In this study, large-scaled semiconductor films with multi-walled (TiO₂/WO₃/TiO₂) nanopore distribution are fabricated by combining electrochemical anodization and sputtering technique, and then employed as the SERS substrates for detection of molecules at the solid/liquid interfaces. Given the remarkably improved electrochromic property of the multi-walled film, such SERS substrates were endowed with tunable oxygen vacancy (V_O) density and distribution via simply applying electrochemical bias voltage, which enabled one to achieve an enhanced charge transfer efficiency and thus a remarkably increased Raman signal even in solution. The V_O-rich SERS substrate is highly repeatable, thus providing a reliable platform for in-situ monitoring of the target molecules or intermediates at the solid/liquid interfaces.