CaSTL Seminar by Xing Chen and Pengchong Liu

XING CHEN

Title: Atomistic description of nanoplasmonics: from near field to surface-enhanced Raman scattering

Abstract: An atomistic electrodynamics model, where the NPs in terms of a macroscopic homogenous dielectric constant is replaced by an atomic representation with dielectric properties depending on the local chemical environment, successfully describes the plasmonics behavior in quantum size region. By using this model, we explored the near field fluctuation and  the origin of the SERS varying with time evolution.

PENGCHONG LIU
Title: Single Molecule Imaging Using Atomistic Near-Field Tip-Enhanced Raman Spectroscopy
Abstract: Advances in tip-enhanced Raman spectroscopy (TERS) have demonstrated ultrahigh spatial resolution so that the vibrational modes of individual molecules can be visualized. The spatial resolution of TERS is determined by the confinement of the plasmon-induced field in the junction, however, the conditions necessary for achieving the high spatial confinement required for imaging individual molecules is not fully understood. Here, we present a systematic theoretical study of TERS imaging of single molecules, using an hybrid atomistic electrodynamics quantum mechanical method. This approach provides a consistent treatment of the molecule and the plasmonic near- field under conditions where they cannot be treated separately. In our simulations we demonstrate that TERS is capable of uniquely resolving intricate molecule vibrations with atomic resolution, although we find that TERS images are extremely sensitive to 1 the near-field in the junction. To achieve the atomic resolution, it requires the near- field to be confined within a few Ångstroms in diameter and the near-field focal plane to be in the molecule plane. Furthermore, we demonstrate that the traditional surface selection rules of TERS are altered due to the significant field-confinement which leads to significant field-gradient effects in the Raman scattering. This work provides insights into single molecule imaging based on TERS and the Raman scattering of molecules in nanojunctions with atomic dimensions.