First-principles studies of Raman spectra of electrified Si/water interfaces

We investigate the Raman spectra of liquid water in contact with a semiconductor surface using first principles molecular dynamics simulations. We focus on a hydrogenated silicon/water interface and compute the Raman spectra from time correlation functions of the polarizability. We establish a relationship between specific peaks in the Raman spectra and structural properties of the water network at the interface and we identify the influence and vibrational signatures of the electric field on the structure of the interfacial fluid. We find that in the case of negative bias, the applied field leads to a reduction of the number of hydrogen bonds (HBs) formed between the surface and the topmost water layer, and to an enhancement of the HB interactions between water molecules. Instead, for positive bias, the applied field leads to an enhancement of both the HB interactions between water and the surface and between water molecules, leading to a semi-ordered network at the interface. Our work provides valuable insights into electrified semiconductor/water interfaces at the molecular level, and into the identification of specific structural features through Raman spectroscopy.