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Fabricating van der Waals Heterostructures with Precise Rotational Alignment
Published on: July 5, 2019
Raman Enhancement of Molecules Sandwiched between van der Waals Materials
Xielin Wang1,2, Nguyen Tuan Hung3, Shengxi Huang2,4,5
1Applied Physics Graduate Program, Smalley-Curl Institute, Rice University, Houston, Texas77005, United States.
Abstract:
Raman enhancement has been widely observed for molecules adsorbed on van der Waals (vdW) materials including graphene, MoS2, hexagonal boron nitride, and transition-metal dichalcogenides. This enhancement is often dominated by a chemical mechanism. However, how the Raman response evolves when a molecule is sandwiched between two vdW layers remains unclear. Here, using copper phthalocyanine (CuPc) as a probe, we compare three sandwich structures: graphene/CuPc/TiS2, graphene/CuPc/TiSe2, and graphene/CuPc/graphene, spanning asymmetric to near-symmetric dual-interface geometries. We find that adding a second interface in contact with the molecule can suppress, moderate, or enhance the Raman response of CuPc depending on the contacting material pair and vibrational symmetry. The graphene/CuPc/graphene sandwich shows stronger enhancement than single-interface CuPc/graphene, with an excitation wavelength dependence. These results show that the dual-interface Raman response is influenced by interface-dependent charge-transfer effects and increased nonradiative damping. This work provides an experimental framework for understanding Raman enhancement in molecule-sandwiched structures.
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