LOSURDO ET AL. VOL. 8 ’ NO. 3 ’ 3031–3041 ’ 2014 www.acsnano.org 3031 February 27, 2014 C 2014 American Chemical Society Demonstrating the Capability of the High-Performance Plasmonic GalliumÀGraphene Couple Maria Losurdo, †,‡, * Congwen Yi, † Alexandra Suvorova, § Sergey Rubanov, ^ Tong-Ho Kim, † Maria M. Giangregorio, ‡ Wenyuan Jiao, † Iris Bergmair, ) Giovanni Bruno, ‡ and April S. Brown † † Electrical and Computer Engineering Department, Duke University, Durham, North Carolina 27705, United States, ‡ Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, via Orabona 4, 70126 Bari, Italy, § Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Crawley, Western Australia 6009, Australia, ^ Electron Microscope Unit, Bio21 Institute, University of Melbourne, Melbourne, Victoria 3010, Australia, and ) Profactor GmbH, Im Stadtgut A2, 4407 Steyr-Gleink, Austria M etal nanoparticle (NP)/graphene platforms are useful not only as a structure for exploring the funda- mental properties of graphene, including grapheneÀmetal interfaces, 1 and grapheneÀ light interactions, 2 but also for creating functional structures. GrapheneÀmetal cou- ples promise to solve a number of current challenges. GrapheneÀmetal NP nanocom- posites are a novel class of materials with substantial promise to enhance device per- formance across numerous applications such as plasmonically enhanced photonics, 3 plasmonically enhanced graphene-based photodetectors, 4 plasmonic photocatalysis, 5 sensors, 6 memories, 7 and solar cells. 8 In ad- dition, metals on graphene can be used to control the Fermi energy across the system, enabling effective graphene doping. 9 Graphene/NP platforms are also of inter- est for surface-enhanced Raman spectros- copy (SERS) substrates for (bio)molecule detection. 10À15 SERS phenomena have been primarily studied using gold NPs de- posited on graphene/SiO 2 /Si substrates, 16 where, in addition to the electromagnetic * Address correspondence to maria.losurdo@cnr.it. Received for review January 24, 2014 and accepted February 27, 2014. Published online 10.1021/nn500472r ABSTRACT Metal nanoparticle (NP)Àgraphene multifunctional platforms are of great interest for exploring strong lightÀgraphene interactions enhanced by plasmons and for improving performance of numerous applications, such as sensing and catalysis. These platforms can also be used to carry out fundamental studies on charge transfer, and the findings can lead to new strategies for doping graphene. There have been a large number of studies on noble metal AuÀgraphene and AgÀgraphene platforms that have shown their potential for a number of applications. These studies have also highlighted some drawbacks that must be overcome to realize high performance. Here we demonstrate the promise of plasmonic gallium (Ga) nanoparticle (NP)Àgraphene hybrids as a means of modulating the graphene Fermi level, creating tunable localized surface plasmon resonances and, consequently, creating high-performance surface-enhanced Raman scattering (SERS) platforms. Four prominent peculiarities of Ga, differentiating it from the commonly used noble (gold and silver) metals are (1) the ability to create tunable (from the UV to the visible) plasmonic platforms, (2) its chemical stability leading to long-lifetime plasmonic platforms, (3) its ability to n-type dope graphene, and (4) its weak chemical interaction with graphene, which preserves the integrity of the graphene lattice. As a result of these factors, a Ga NP-enhanced graphene Raman intensity effect has been observed. To further elucidate the roles of the electromagnetic enhancement (or plasmonic) mechanism in relation to electron transfer, we compare graphene-on-Ga NP and Ga NP-on- graphene SERS platforms using the cationic dye rhodamine B, a drug model biomolecule, as the analyte. KEYWORDS: graphene . Ga nanoparticles . plasmon resonance . surface-enhanced Raman scattering . electron transfer ARTICLE