Fig. 1: NIR light-induced irreversible accumulated SERS behavior of the 4MBA/Ag/Ag-doped TiO2 hybrid system.

Three mechanisms are proposed to explain this phenomenon: (1) NIR light induces a thermal effect on the substrate, which results in higher crystallinity to change polarizability; (2) NIR light induces CT between the substrate and 4MBA with the assistance of VO defects; (3) the electrostatic attraction causes the reorientation of 4MBA molecule on the surface of the Ag/Ag-doped TiO2 substrate. Here, the green arrows represent the transfer path of electrons between the Ag/Ag-doped TiO2 substrate and 4MBA molecules, and the red arrows display filling of VO defect by oxygen atoms.