Abstract
Graphene is a two-dimensional (2D) material consisting of a single sheet of sp2 hybridized carbon atoms laced in a hexagonal lattice, with potentially wide usage as a Raman enhancement substrate, also termed graphene-enhanced Raman scattering (GERS), making it ideal for sensing applications. GERS improves upon traditional surface-enhanced Raman scattering (SERS), combining its single-molecule sensitivity and spectral fingerprinting of molecules, and graphene’s simple processing and superior uniformity. This enables fast and highly sensitive detection of a wide variety of analytes. Accordingly, GERS has been investigated for a wide variety of sensing applications, including chemical- and bio-sensing. As a derivative of GERS, the use of two-dimensional materials other than graphene for Raman enhancement has emerged, which possess remarkably interesting properties and potential wider applications in combination with GERS. In this review, we first introduce various types of 2D materials, including graphene, MoS2, doped graphene, their properties, and synthesis. Then, we describe the principles of GERS and comprehensively explain how the GERS enhancement factors are influenced by molecular and 2D material properties. In the last section, we discuss the application of GERS in chemical- and bio-sensing, and the prospects of such a novel sensing method.
Highlights
Graphene is made of sp2-hybridized carbon atoms arranged in two intersecting triangular lattices that combine to form a honeycomb pattern (Figure 1a)
Compared to its bulk counterpart, gNraanopmhaitteeri,altsh2e01b9,a9n, 5d16structure of graphene is unique: It exhibits Dirac cones at the K points in2 otfh2e0 Brillouin zone (Figure 1b). This causes the low-energy electron excitations to behave as massless Dirac fermions, which exhibit unconventional phenomena, including the anomalous integer quantum Hall.dTKhliesincatuusnensetlhineglo[3w].-energy electron excitations to behave as massless Dirac fermions, which exhibit unconventional phenomena, including the anomalous integer quantum Hall effect [2] and Klein tunneling [3]
The D band is a second order Raman mode consisting of an absorption of a photon by an electron at the K point, inelastic scattering by a phonon to the K’ point, and elastic scattering by a defect back to the K point followed by recombination with a hole and photon emission
Summary
The experimental isolation of graphene, a single layer of carbon atoms, opened the door to the world of two-dimensional (2D) materials by demonstrating the experimental existence and physical stability of atomically thin layers [1]. Compared to its bulk counterpart, gNraanopmhaitteeri,altsh2e01b9,a9n, 5d16structure of graphene is unique: It exhibits Dirac cones at the K points in otfh2e0 Brillouin zone (Figure 1b). Lv et al doped graphene with Si, which was shown to enhance the Raman signal of adsorbed dye molecules [19]. Raman spectroscopy is a useful tool used to characterize graphene and TMDs, as it can indicate the layer number and defect density in a non-destructive manner. The D band is a second order Raman mode consisting of an absorption of a photon by an electron at the K point, inelastic scattering by a phonon to the K’ point, and elastic scattering by a defect back to the K point followed by recombination with a hole and photon emission. Horizontal arrows and values indicate the HOMO-LUMO gaps in electronvolt (eV), and the energy, HOMO-EF, in eV [18]
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