Increased O 2p State Density Enabling Significant Photoinduced Charge Transfer for Surface-Enhanced Raman Scattering of Amorphous Zn(OH)<sub>2</sub>
Anran Li, Jian Yu, Jie Lin, Mo Chen, Xiaotian Wang, Lin Guo
Abstract
Enriching the electronic density of states (DOS) of semiconductors is the key to promoting charge transfer (CT) and achieving a large surface-enhanced Raman scattering (SERS) enhancement. Metal hydroxide semiconductors are anticipated to exhibit DOS that are higher than those of metal oxide because of their abundant O atoms; however, their SERS activity has not been verified. Here, combining density functional theory and experiments, we report a SERS sensitivity of amorphous Zn(OH)2 [a-Zn(OH)2] that is much higher than that of amorphous ZnO (a-ZnO), ascribed to the abundant O atoms and hence enriched O 2p state density near the Fermi level in a-Zn(OH)2, which gives rise to higher CT probabilities. Moreover, we find a-Zn(OH)2 exhibits significant advantages in energy-level matching over a-ZnO for efficient photoinduced CT via strong vibronic coupling, ascribed to the upshifted valence band maximum and the narrower band gap of a-Zn(OH)2. Via the synthesis of a-Zn(OH)2 nanocages, an ultrahigh enhancement factor of 1.29 × 106 is obtained in semiconductor-based SERS.