UV/Ozone-Oxidized Large-Scale Graphene Platform with Large Chemical Enhancement in Surface-Enhanced Raman Scattering

Abstract

We fabricated a highly oxidized large-scale graphene platform using chemical vapor deposition (CVD) and UV/ozone-based oxidation methods. This platform offers a large-scale surface-enhanced Raman scattering (SERS) substrate with large chemical enhancement in SERS and reproducible SERS signals over a centimeter-scale graphene surface. After UV-induced ozone generation, ozone molecules were reacted with graphene to produce oxygen-containing groups on graphene and induced the p-type doping of the graphene. These modifications introduced the structural disorder and defects on the graphene surface and resulted in a large chemical mechanism-based signal enhancement from Raman dye molecules [rhodamine B (RhB), rhodamine 6G (R6G), and crystal violet (CV) in this case] on graphene. Importantly, the enhancement factors were increased from ∼10(3) before ozone treatment to ∼10(4), which is the largest chemical enhancement factor ever on graphene, after 5 min ozone treatment due to both high oxidation and p-doping effects on graphene surface. Over a centimeter-scale area of this UV/ozone-oxidized graphene substrate, strong SERS signals were repeatedly and reproducibly detected. In a UV/ozone-based micropattern, UV/ozone-treated areas were highly Raman-active while nontreated areas displayed very weak Raman signals.

Theory of Raman enhancement by two-dimensional materials: Applications for graphene-enhanced Raman spectroscopy

“…However, as it was experimentally observed originally in 2010 by Ling et al [1], the Raman intensity of phthalocyanine, rhodamine 6G, protoporphyrin IX, and crystal violet molecules all have very different enhancement factors. Furthermore, it has been shown that enhancement factors are strongly dependent on which molecule is being probed, on the laser excitation energy used, on the two-dimensional (2D) material used for the enhancement surface [8][9][10] and even on the Fermi energy of the system, as controlled by a gate voltage [6,11,12]. The dependence of the enhancement on all these parameters cannot be explained either in terms of multiple reflections, nor by the quenching of the luminescence, nor even by a combination of both.…”

Oxidation of graphene in ozone under ultraviolet light

“…Recently, various studies have dealt with the oxidation of graphene by ozone and O ions. [5][6][7][8][9][10][11][12][13][14] In an ozone generator, C atoms are removed from the graphene lattice and vacancies are formed. The morphology of exposed singlelayer and multilayer graphene samples reflects a highly disordered nature, which varies with the thickness.…”

“…5 After ozone generation by ultraviolet light, ozone molecules react with graphene to produce O-containing groups and induce p-type doping. 8 Theoretically, it has been predicted that O atoms lined up on pristine graphene form a stable unzipped structure, in which an epoxy group breaks the lower sp 2 bond. 9,14 In addition, the fact that the energy gap can be tuned in a wide range from 0 to 4 eV demonstrates that functionalization of graphene by oxidation has serious effects on the electronic states.…”

“…12 The second, which is more common and simple, is the application of ozone as generated by ultraviolet light in atmosphere. 5,8,11 In this case, O 2 molecules absorb 185 nm photons, which have sufficient energy to break the molecular bond to form two Oð 3 3 , involved in the oxidization process. By determining the optimized structures of graphene oxidized by these species, we find that Oð 3 PÞ can bond effectively to the C atoms of the graphene, see Fig.…”

Tuning the underwater oleophobicity of graphene oxide coatings via UV irradiation

“…UV irradiation has been proved to be capable of either reducing or oxidizing graphene-based materials, depending on the reducing or oxidative nature of the surrounding environment. [12][13][14][15][16][17][18] We demonstrate that by simply controlling the UV etching time for dispersed GO flakes in water, the resulting GO coatings can be converted into underwater superoleophobic coatings. In addition, this method is very promising for large-scale production.…”