Two-Dimensional Heterostructure as a Platform for Surface-Enhanced Raman Scattering

Abstract

Raman enhancement on a flat nonmetallic surface has attracted increasing attention, ever since the discovery of graphene enhanced Raman scattering. Recently, diverse two-dimensional layered materials have been applied as a flat surface for the Raman enhancement, attributed to different mechanisms. Looking beyond these isolated materials, atomic layers can be reassembled to design a heterostructure stacked layer by layer with an arbitrary chosen sequence, which allows the flow of charge carriers between neighboring layers and offers novel functionalities. Here, we demonstrate the heterostructure as a novel Raman enhancement platform. The WSe (W) monolayer and graphene (G) were stacked together to form a heterostructure with an area of 10 mm × 10 mm. Heterostructures with different stacked structuress are used as platforms for the enhanced Raman scattering, including G/W, W/G, G/W/G/W, and W/G/G/W. On the surface of the heterostructure, the intensity of the Raman scattering is much stronger compared with isolated layers, using the copper phthalocyanine (CuPc) molecule as a probe. It is found that the Raman enhancement effect on heterostructures depends on stacked methods. Phonon modes of CuPc have the strongest enhancement on G/W. W/G and W/G/G/W have a stronger enhancement than that on the isolated WSe monolayer, while lower than the graphene monolayer. The G/W/G/W/substrate demonstrated a comparable Raman enhancement effect than the G/W/substrate. These differences are due to the different interlayer couplings in heterostructures related to electron transition probability rates, which are further proved by first-principle calculations and probe-pump measurements.

Extraordinary Sensitivity of Surface‐Enhanced Raman Spectroscopy of Molecules on MoS2 (WS2) Nanodomes/Graphene van der Waals Heterostructure Substrates

“…The CM effect is dictated by the interface electronic structures between the analyte and substrate and can be optimized by selecting a substrate with favorable band alignment with the highest‐occupied molecular orbital (HOMO) and the lowest‐unoccupied molecular orbital (LUMO) at the interface where the analyte (or probe molecule) bond to the substrate. Thus, tuning of the substrate electronic structure is important to an enhanced CM effect . This has prompted intensive research exploring graphene‐based SERS substrates considering the unique 2D atomically flat surface with delocalized π bonds, chemical inertness, biological compatibility, superior electronic and photonic properties, and the intrinsic Fermi energy at ≈4.5 eV that is compatible, as well as tunable, for CM enhancement with a large number of probe molecules .…”

Recent Advances in van der Waals Heterojunctions Based on Semiconducting Transition Metal Dichalcogenides

“…This phenomenon is similar to that of monolayer MoS 2 . [118] It is reported that electron-hole pairs can be separated at the interface between MX 2 and graphene under illumination due to the formation of a built-in electric field (as shown in Figure 13c,d).…”

A Review of Recent Applications of Ion Beam Techniques on Nanomaterial Surface Modification: Design of Nanostructures and Energy Harvesting

“…By using ion beams, the properties of 2D materials could be modified in atomic scales . Defects could be introduced in on‐demand way, which brings out intermediate state in the band structures of specific 2D materials, extending the broadband applications in laser technology and sensing . For vertically stacked 2D materials, the out‐of‐plane charge transport can be enhanced through controllable formation of ion implanted point defects, leading to fast photoresponsivity for optimized devices .…”

“…This result demonstrates that ion beam techniques also have promising prospects for modulating the performance of 2D materials‐based photodetectors. In addition, ion beam irradiation may also cause compressing effect along vertical dimension for few‐layer heterostructure materials, resulting in significant enhancement of layer‐to‐layer coupling …”