Type of presentation: Poster

MS-1-P-3503 Imaging and microanalysis of plasmonic Ga nanoparticles

Suvorova A. A.¹, Losurdo M.², Brown A. S.³, Rubanov S.⁴, Bruno G.²

¹Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth, Australia, ²Institute of Inorganic Methodologies and Plasmas at National Council of Research (CNR), Bari, Italy, ³Electrical and Computer Engineering Department, Duke University, Durham, North Carolina 27705, United States, ⁴Electron Microscope Unit, Bio21 Institute, University of Melbourne, Melbourne, Victoria 3010, Australia

alexandra.suvorova@uwa.edu.au

Plasmonic nanoparticles (NPs) are of considerable interest due to plasmon tunability and potential applications as biosensors, photonic, optoelectronic and photovoltaic devices. These applications rely on the fabrication of metallic NPs on technologically important substrates and on the possibility to control the surface plasmon resonance (SPR) properties. The ability to create tunable (from the UV to the visible) plasmonic nanosystems using Ga NPs is differentiating gallium from the commonly used noble (gold and silver) metals. In our previous work, we have demonstrated the efficiency of Ga NP-based platforms in localized surface plasmon resonances (LSPR) tunable over the UV to the near IR spectral range^1-3.

Here we describe a range of imaging and microanalysis electron microscopy techniques that are highly suitable for the study of the Ga-based plasmonic nanosystems. Ga nanoparticles were deposited onto sapphire, silicon, glass and graphene substrates in a Veeco GEN II molecular beam epitaxial system under ultrahigh vacuum conditions at room temperature with a constant Ga flux. TEM cross-sectional samples were prepared by the FEI Nova dual beam focused ion beam (FIB) system. A range of microanalytical electron microscopy techniques can be used to characterise the NPs at the nanoscale level. Scanning electron microscopy (SEM) imaging has been applied to study morphology and growth dependent modifications of the Ga NPs. Transmission electron microscopy (TEM) and associated analytical tools have been used to determine the structural and compositional properties of the nanostructures at a subnanometer scale. High resolution imaging revealed crystalline core/ amorphous shell structure for Ga NPs grown on sapphire and amorphous Ga structure for Ga NPs grown on other substrates. Energy-filtered imaging showed compositional uniformity of the Ga core and the presence of oxide layer on the NPs surface. Low-loss imaging confirms the presence of Ga, with particle contrast being maximised close to the Ga plasmon energy (13.8eV). The Ga plasmon signal is significantly higher for the crystalline core of the Ga NPs. In summary, a range of electron microscopy techniques can be used to identify and characterise Ga NPs at the nanoscale level. Such information is important for understanding structural and optical properties of Ga-based nanosystems.

¹Wu, P. C.; Kim, T. H.; Brown, A. S.; Losurdo, M.; Bruno, G.; Everitt, H. O. Appl.Phys. Lett. 2007, 90, 103119.

²Yi, C.; Kim, T. H.; Jiao, W.; Yang, Y.; Lazarides, A.; Hingerl, K.;Bruno, G.; Brown, A. S.; Losurdo, M. N. Small 2012, 8, 2721–2730.

³M Losurdo, C Yi, A Suvorova, S Rubanov, T-Ho Kim, M M. Giangregorio, W Jiao, I Bergmair, G Bruno, A. S. Brown ACS Nano 2014 in press

Fig. 1: SEM image of Ga NPs grown on sapphire.	Fig. 2: TEM image showing the Ga NPs in cross-section.
Fig. 3: EFTEM imaging: zero-loss image of Ga NPs.	Fig. 4: Low loss imaging of Ga NPs showing core/shell structure