Biopolymer‐Templated Deposition of Ordered and Polymorph Titanium Dioxide Thin Films for Improved Surface‐Enhanced Raman Scattering Sensitivity
Qing Chen, Marie Betker, Constantin Harder, Calvin J. Brett, Matthias Schwartzkopf, Nils Ulrich, María Eugenia Toimil‐Molares, C. Trautmann, Daniel Söderberg, Christian L. Weindl, Volker Körstgens, Peter Müller‐Buschbaum, Mingming Ma, Stephan V. Roth
Abstract
Abstract Titanium dioxide (TiO 2 ) is an excellent candidate material for semiconductor metal oxide‐based substrates for surface‐enhanced Raman scattering (SERS). Biotemplated fabrication of TiO 2 thin films with a 3D network is a promising route for effectively transferring the morphology and ordering of the template into the TiO 2 layer. The control over the crystallinity of TiO 2 remains a challenge due to the low thermal stability of biopolymers. Here is reported a novel strategy of the cellulose nanofibril (CNF)‐directed assembly of TiO 2 /CNF thin films with tailored morphology and crystallinity as SERS substrates. Polymorphous TiO 2 /CNF thin films with well‐defined morphology are obtained by combining atomic layer deposition and thermal annealing. A high enhancement factor of 1.79 × 10 6 in terms of semiconductor metal oxide nanomaterial (SMON)‐based SERS substrates is obtained from the annealed TiO 2 /CNF thin films with a TiO 2 layer thickness of 10 nm fabricated on indium tin oxide (ITO), when probed by 4‐mercaptobenzoic acid molecules. Common SERS probes down to 10 n m can be detected on these TiO 2 /CNF substrates, indicating superior sensitivity of TiO 2 /CNF thin films among SMON SERS substrates. This improvement in SERS sensitivity is realized through a cooperative modulation of the template morphology of the CNF network and the crystalline state of TiO 2 .