DOI: 10.1002/chem.201002027 Surface-Enhanced Raman Scattering of Single- and Few-Layer Graphene by the Deposition of Gold Nanoparticles Jisook Lee, [a] Sangdeok Shim, [b] Bongsoo Kim, [c] and Hyeon Suk Shin* [a] Introduction Raman spectroscopy has been utilized as a powerful tool for the characterization of graphene, as it can identify the number of layers, the electronic structure, the edge struc- ture, the type of doping and any defects in the graphene. [1] A Si substrate with a metal oxide layer of a specific thick- ness has been employed to enhance the Raman signal, which is called interference-enhanced Raman scattering (IERS). [2] In particular, its enhancement of nearly 30 times of the Raman signal of graphene on a Si wafer with a 300 nm-thick SiO 2 layer makes Raman spectroscopy very useful in graphene research. [2b] It has also been reported that inserting a Ag layer between the layers of metal oxide (Al 2 O 3 ) and Si further enhances the Raman signal. This is ascribed to a combination of IERS and surface-enhanced Raman scattering (SERS). [3] As Ag does not make contact with the graphene in this case, the enhancement factor of SERS due to the Ag layer only ranged from 5 to 20. [3] The increased enhancement factor to 60 has been recently re- ported in the system that gold disc was deposited on me- chanically exfoliated single-layer graphene. [4a] In addition to that, some SERS studies have been tried in reduced gra- phene oxide samples with gold nanoparticles [4b,c] and gold rods [4d] and CVD-grown graphene samples with a thermally deposited gold film and a close-packed gold nanosphere layer, [4e] in which enhancement factors were still low. So far, however, any characteristic change depending on the number of graphene layer in SERS has not been reported. The deposition of Au film on graphene was recently re- ported. [5] The morphology of the Au film, including the grain size and the spacing between the grains when it is de- posited on graphene is strongly affected by the layer number of graphene, forming grains of a larger size and spacing in few-layer graphene compared to those in single- layer graphene. While the difference in the morphology of the Au film could be readily distinguished by scanning elec- tron microscopy (SEM), making possible distinction of gra- phene samples that have a distribution of different layer numbers, the exact layer number could not be determined. It was also reported from the Raman spectra that the nature of the graphene was not altered after the deposition of Au. [5] The present study reports the SERS of graphene onto which metal nanoparticles are deposited by thermal evapo- ration. It was found that the enhancement factor of SERS varied strongly depending on the density of the evaporated Au nanoparticles and the excitation wavelength. Moreover, the SERS intensity was higher for single-layer graphene than for few-layer graphene. The D band in a SERS spec- Abstract: Surface-enhanced Raman scattering (SERS) of graphene on a SiO 2 ACHTUNGTRENNUNG(300 nm)/Si substrate was investi- gated by depositing Au nanoparticles using thermal evaporation. This provid- ed a maximum enhancement of 120 times for single-layer graphene at 633 nm excitation. SERS spectra and scan images of single-layer and few- layer graphene were acquired. Single- layer graphene provides much larger SERS enhancement compared to few- layer graphene, while in single-layer graphene the enhancement of the G band was larger than that of the 2D band. Furthermore, the D bands were identified in the SERS spectra; these bands were not observed in a normal Raman spectrum without Au deposi- tion. Appearance of the D band is as- cribed to the considerable SERS en- hancement and not to an Au deposi- tion-induced defect. Lastly, SERS en- hancement of graphene on a transpar- ent glass substrate was compared with that on the SiO 2 ACHTUNGTRENNUNG(300 nm)/Si substrate to exclude enhancement by multiple reflections between the Si substrate and deposited Au nanoparticles. The contribution of multiple reflections to total enhancement on the SiO 2 - ACHTUNGTRENNUNG(300 nm)/Si substrate was 1.6 times out of average SERS enhancement factor, 71 times. Keywords: gold · graphene · Ram- an spectroscopy · surface chemistry [a] J. Lee, Prof. H. S. Shin Interdisciplinary School of Green Energy Ulsan National Institute of Science and Technology (UNIST) Banyeonri 100, Ulsan 689-805 (South Korea) Fax: (+ 82) 52-217-2909 E-mail : shin@unist.ac.kr [b] Dr. S. Shim Central R&D Institute, Samsung Electro-Mechanics 314 Maetan-dong, Suwon 443-743 (South Korea) [c] Prof. B. Kim Department of Chemistry Korea Advanced Institute of Science and Technology (KAIST) Daejeon 305-701 (South Korea) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201002027. Chem. Eur. J. 2011, 17, 2381 – 2387  2011 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 2381 FULL PAPER