Surface plasmon mapping of dumbbell-shaped gold nanorods: the effect of silver coating.
ABSTRACT We report on the identification of surface plasmons in individual gold dumbbell-shaped nanoparticles (AuDBs), as well as AuDBs coated with silver. We use spatially resolved electron energy-loss spectroscopy in a scanning electron microscope, which allows us to map plasmon-energy and intensity spatial distributions. Two dominant plasmon resonances are experimentally resolved in both AuDBs and silver-coated AuDBs. The intensity of these features is peaked either at the tips or at the sides of the nanoparticles. We present boundary element method simulations in good agreement with the experiment, allowing us to elucidate the nature of such modes. While the lower-energy, tip-focused plasmon is of longitudinal character for all dumbbells under consideration, the second side-bound plasmon has a more involved symmetry, starting as a longitudinal quadrupole in homogeneous AuDBs and picking up transversal components when silver coating is added. The longitudinal dipolar mode energy is found to blue-shift upon coating with silver. We find that the substrate produces sizable shifts in the plasmons of silver-coated AuDBs. Our analysis portraits a complex plasmonic scenario in metal nanoparticles coated with silver, including a transition from the original homogeneous gold dumbbell plasmons to the modes of homogeneous silver rods. We believe that these findings can have potential application to plasmon engineering.
- SourceAvailable from: Marek Grzelczak[show abstract] [hide abstract]
ABSTRACT: Nanoplasmonics is a rapidly developing field of research and technology that is based on the ability of small metal particles to interact strongly with light of wavelength significantly larger than their size. The development of nanoplasmonics has been closely associated with the application of colloid science to the controlled growth of metal nanocrystals in solution and to directing the self-assembly of such nanocrystals into organized arrays with enhanced collective properties. Engineering the morphology and the assembly of metal nanoparticles is a key step toward the fabrication of devices with great potential in detection and diagnosis as well as in a wide variety of other fields. In this Feature Article, we provide an overview of the recent work in our laboratory, which in our view somehow reflects the evolution of the field itself and provides guidelines for future research.Langmuir 02/2013; · 4.19 Impact Factor
Surface Plasmon Mapping of Dumbbell-Shaped Gold Nanorods: The
effect of Silver Coating
F Attouchi 1, O Stéphan1, M Kociak1, B Rodríguez-González2,3, M. Fernanda Cardinal2,3,
V Myroshnychenko4, F.J García de Abajo4, L M. Liz-Marzán2.
1. Laboratoire de Physique des Solides, CNRS, UMR8502, Université Paris Sud XI, F91405 Orsay, France
2.Departamento de Química Física, Universidade de Vigo, 36310 Vigo, Spain
3.International Iberian Nanotechnology Laboratory, Braga 4715, Portugal.
4.IQFR-CSIC, Serrano 119, 28006 Madrid, Spain.
Keywords: STEM, EELS, nanoparticles, plasmons, core-shell, silver, gold.
During the last decade plasmonics has emerged as a growing research area that it is
expected to continue expanding during the coming years. Plasmonics of metallic nanoparticles
(NPs), commonly made of gold or silver, is focused on the optical properties of their surface
plasmons (SPs) as the origin of remarkable optical effects. Because the electromagnetic field of a
plasmon is confined to the vicinity of the sub-wavelength-sized nanoparticles, these modes are
called localized surface plasmon resonances (LSPRs).
We will present our recents investigations on localized surface plasmon resonances (LSPRs)
of gold dumbbells (AuDBs) and silver-coated gold dumbbells (AuDB@Ag) nanoparticles by using
spatially resolved electron energy-loss spectroscopy (EELS) performed in a scanning electron
microscope, which allows us to map plasmon energy and intensity spatial distributions .
Gold dumbbell-like nanoparticles (AuDB) and silver-coated AuDB@Ag were synthesized by
chemical seeded growth methods . Two dominant plasmon resonances are experimentally
resolved in both AuDBs and silver-coated AuDBs. For gold dumbbells three plasmon modes have
been found, one of which is actually dark as it can be hardly excited by light. In contrast, silver-
coated gold dumbbells show two dominant modes. We will present also the boundary element
method (BEM)  simulations in good agreement with the experimenst, allowing us to interpret the
nature of such modes.
While the lower-energy, tip-focused plasmon is of longitudinal character for all dumbbells
under consideration, the second side-bound plasmon has a more involved symmetry, starting as a
longitudinal quadrupole in homogeneous AuDBs and picking up transversal components when silver
coating is added. The longitudinal dipolar mode energy is found to blue-shift upon coating with
silver. We find that the substrate produces sizeable shifts in the plasmons of silver-coated AuDBs.
Our analysis portraits a complex plasmonic scenario in metal nanoparticles coated with silver,
including a transition from the original homogeneous gold dumbbell plasmons to the modes of
homogeneous silver rods ( Figure1). We have found that the energy-loss spectra of AuDB@Ag
particles are mainly governed by silver optical response that actually results in the screening of the
gold dumbbell plasmon modes. This suggests the possibility of keeping the interesting properties of
silver nanoparticles (especially the low dissipation) while using for the core of the nanoparticle a
metal (other than gold) easier to shape and control than silver. We believe that these findings can
have potential application to plasmon engineering .
 J Nelayah, M Kociak, O Stephan, F.J Garcia de Abajo, M Tence, L Henrard, D Taverna, I
Pastoriza-Santos, L. M Liz-Marzan and C Colliex,Nat. Phys 3 (2007), p.348-353.
 M. F Cardinal, B Rodríguez-González, R.A Alvarez-Puebla, J Pérez-Juste, L.M Liz-Marzán, J.
Phys. Chem. C 114 (2010), p.10417-10423.
 V Myroshnychenko, J Rodríguez-Fernández, I Pastoriza-Santos, A. M Funston, C Novo, P
Mulvaney, L. M Liz-Marzán, Abajo, F. J. G. de Chem. Soc. Rev. 37(2008), p.1792-1805.
 B Rodríguez-González, F Attouchi, M Fernanda Cardinal, Viktor Myroshnychenko, Odile
Stéphan,F.J García de Abajo,L.M Liz-Marzán and M Kociak, Langmuir( to be published).
 The authors gratefully acknowledge financial support from the European Union under the
Framework 6 program under a contract for an Integrated Infrastructure Initiative. Reference 026019
ESTEEM. LM acknowledges financial support from the Spanish MICINN (grant MAT2010-15374).
The CSIC team acknowledges support from the European Union (NMP4-2006-016881-SPANS,
NMP4-SL-2008-213669-ENSEMBLE, FP7-ICT-2009-4-248909-LIMA, and FP7-ICT-2009-4-248855-
N4E), the Spanish MICINN (MAT2010-14885 and Consolider NanoLight.es), and Ibercivis. V.M.
acknowledges the Spanish CSIC - JAE grant.
Figure 1. Examples of typical results obtained on the AuDb (1) and tha AuDb@Ag (2) nanoparticle: EELS
spectra (b) acquired at the two positions indicated by points on the HAADF image of the examined particle
(a)and the corresponding energy (c) and intensity (d) maps obtained for each mode.