Improving SERS sensitivity of TiO2 by utilizing the heterogeneity of facet-potentials

Herein, the heterogeneity of the facet-potentials was used to improve the SERS activity of anatase TiO2 single crystals co-exposed with {0 0 1} and {1 0 1} facets. Using methylene blue (MB) as the model molecule, the influence of the exposed-facet-ratio on the SERS activity was explored. The molecules preferred to be adsorbed by defective {0 0 1} facets, but the SERS activity was not proportional to the enlarged {0 0 1} facets. The single crystal exposed with 20% {0 0 1} facets (S00120%) showed the highest SERS activity, and a high EF of 8 × 105 could be achieved. Based on the experimental analysis and density functional theory calculation, the SERS activity was proportionally correlated with the mobility of photo-induced electrons on defective {0 0 1} facets, which was promoted by the surface electric field pointing from exposed {1 0 1} facets to the junction edge, and then to {0 0 1} facets as a result of heterogeneous facet-potentials.