Presentation Information
[9a-A22-2]TERS Analysis of Raman-Forbidden Low-Frequency Phonons in MoS2
〇(D)Zhen Zong1, Takayuki Umakoshi1, Prabhat Verma1 (1.Osaka Univ.)
Keywords:
tip-enhanced Raman spectroscopy,low-frequency Raman modes,forbidden Raman modes
Raman spectroscopy, including tip-enhanced Raman spectroscopy (TERS), is widely used to study material properties through vibrational responses. However, conventional Raman scattering detects only modes allowed by Raman selection rules, leaving many informative phonons Raman-forbidden. This limitation is especially important in 2D van der Waals materials, where optoelectronic properties of the material strongly depend on interlayer interactions, which show up as low-frequency vibrations in Raman scattering, many of which are symmetry-forbidden. Such modes can be activated by relaxing the selection rules, which can be achieved through external perturbations, such as strong gradient incident illumination or mechanical pressure. Plasmonic nanostructures provide strong near-field gradients, while their contact with the sample introduces local strain or deformation, both of which help relax Raman selection rules. This work provides a nanoscale spectroscopic approach for investigating Raman-forbidden low-frequency phonons in 2D materials. Strong near-field gradients generated by Ag nanoparticles activate otherwise inaccessible modes, while LF-TERS enables their nanoscale detection and imaging. This capability reveals hidden structural information and offers a sensitive tool for evaluating local variations relevant to 2D device performance. More details will be discussed in the presentation.