Bifacial Raman Enhancement on Monolayer Two-Dimensional Materials

Abstract

Understanding the charge interaction between molecules and two-dimensional (2D) materials is essential for the design of functional devices. Here, we report the bifacial Raman enhancement of molecules on monolayer graphene and hexagonal boron nitride (h-BN). Taking advantage of the atomically thick layered structure, we show that both surfaces of 2D materials can interact with molecules and simultaneously enhance their Raman scattering. Different enhancement features were observed for monolayer graphene and h-BN. The intensity decrease of particular Raman modes of copper phthalocyanine (CuPc) on both surfaces of h-BN suggests that z-dipoles exist and are partially canceled out between the two interfaces, while the twice Raman intensities of the characteristic Raman modes of CuPc on both surfaces of graphene compared to that on one surface evidenced the charge transfer process. These results provide an approach to modify 2D materials by bifacial adsorption of molecules, and the findings can inspire the design of functional 2D material-based devices.

A review on graphene based transition metal oxide composites and its application towards supercapacitor electrodes

“…To eliminate substrate effect, suspended graphene have been used. This suspended geometry allows exfoliating directly the impressive characteristics of graphene [27,28]. Combined study has shown over the past 50 years that electrons and holes at electron graphene point or (Dirac point) (Intersection point of the linear dispersion curve is called Dirac point) have zero efficient mass.…”

Double‐Sided Graphene‐Enhanced Raman Scattering and Fluorescence Quenching in Hybrid Biological Structures

“…Figure shows that single‐layer graphene can simultaneously induce autofluorescence quenching and Raman enhancement even in complex macromolecular systems like tissues, both effects (FLQ and GERS) being explained by charge transfer between molecules and graphene. [ 20,22,32 ] Broad autofluorescence emission occurs from naturally fluorescent tissue molecules and/or due to chemical changes of molecules during fixation and processing steps. There are mainly two approaches to minimize autofluorescence, employing chemicals and photobleaching; however, these treatments can modify tissue integrity irreversibly.…”

“…Van der Waals, π‐π stacking, and hydrophobic interactions are primarily considered responsible for the biomolecular interplay with graphene and thus for the GERS and FLQ effects. [ 20,32,40–42 ]…”

“…where a bifacial Raman enhancement was observed for copper phthalocyanine (CuPc) probe molecules at both interfaces of mechanically exfoliated single‐layer graphene. [ 32 ] Moreover, the graphene itself is affected by the presence of top and bottom molecules resulting in Raman enhancements (peaks 5, 6) and spectral changes that will be next correlated to doping, defect, and strain levels in the graphene films. [ 29 ]…”

“…The charge transfer paths involve the wave function overlap as well as electron‐photon and electron‐phonon coupling between graphene and molecules, while the charge shift direction is difficult to assess because of the presence of different molecules on both sides of graphene. [ 19,32 ] The combination of these factors for our biomolecule—monolayer graphene—kidney tissue hybrid structures is illustrated in Figure 3f. Knowing the hole doping concentration p ≈ −4.01 × 10 12 cm –2 in graphene on kidney tissues evaluated by Raman, we estimated an E F down shift of ≈−0.26 eV using , where n is the carrier concentration in cm –2 , ℏ = 6.58 × 10 –16 eVs is the reduced Planck's constant, and | v F | = 1.1 × 10 6 ms –1 is the Fermi velocity.…”