Raman Scattering from a Molecule–Semiconductor Interface Tuned by an Electric Field: Density Functional Theory Approach

Abstract

Spectroscopic chemical characterization of atomic-scale interfaces is a challenging scientific problem. In the search for new spectroscopic capabilities, we investigate nonresonant Raman interactions that occur at the interface between organic adsorbates and inorganic surfaces. Our system is a trans-1,2-bis(4-pyridyl)ethylene molecule adsorbed to a semiconductor PbSe surface. We employ first-principles density functional methods to investigate the vibrational dynamics and Raman spectra of this absorbate–surface motif, and use an external electric bias to tune the degree of the interfacial chemical coupling. As a result, changes in the Raman spectra reveal a continuous transition between the weak and the strong coupling regimes. The strong coupling is associated with the vibration-induced charge transfer, which appears to be a damping mechanism that caps the chemical enhancement (CE) of the Raman spectra. This effect reduces the potential of CE to be used as merely an enhancing mechanism, but shows the potential of Raman scattering to probe changes in the interfacial electronic structure.