Fig. 3From: High-Performance All-Optical Terahertz Modulator Based on Graphene/TiO2/Si Trilayer HeterojunctionsAbsorption spectra and UPS spectra. a The absorption spectra of Si and TiO2/Si. b UPS spectra of Si, TiO2, graphene, and Au. c Enlarged parts of b showing the secondary electron onset. d Enlarged parts of b showing the valence band maximumBack to article page