Probing Bright and Dark Surface-Plasmon Modes in Individual and Coupled Noble Metal Nanoparticles Using an Electron Beam

• Published in: Nano letters Vol. 9; no. 1; pp. 399 - 404
• Main Authors: Chu, Ming-Wen, Myroshnychenko, Viktor, Chen, Cheng Hsuan, Deng, Jing-Pei, Mou, Chung-Yuan, García de Abajo, F. Javier
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14.01.2009
• Subjects: Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Computer Simulation; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electrons; Exact sciences and technology; Light; Materials science; Metals - chemistry; Models, Chemical; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals; Nanostructures - chemistry; Nanostructures - ultrastructure; Nanotechnology - methods; Nanotubes; Particle Size; Physics; Scattering, Radiation; Structure of solids and liquids; crystallography; Surface and interface electron states; Surface Plasmon Resonance - methods; Gold; Symmetry property; Surface plasmons; Nanoparticles; Electron beams; Spatial distribution; EEL spectroscopy; Illumination; Energy losses; Dimers; Nanosphere; Scanning transmission electron microscopy; Nanorod; Nanostructured materials; Spatial resolution
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl803270x

The rich structure of bright and dark surface-plasmon modes localized in individual and coupled gold nanoparticles is unveiled by electron-energy-loss spectroscopy performed in a scanning transmission electron microscope. Spatially resolved maps of surface-plasmon modes in the ∼1.5−2.5 eV range (wavelengths ∼500−800 nm), collected for individual nanorods, coupled nanorod dimers, and touching nanosphere dimers, are in excellent agreement with theory. Surface-plasmon maps constructed from the spatially and spectrally resolved energy-loss signals are shown to mimic rather well the near fields calculated for external illumination in the case of bright surface-plasmon modes (i.e., those coupling to external light). Dark surface-plasmon modes that cannot be excited by optical means are also found, and our electron probing technique provides further insight into their corresponding spatial distribution and symmetry, which are not accessible to any other existing techniques. Our results initiate the study of a whole set of new dark surface-plasmon modes that should become a source of new applications in sensing and microscopy but have escaped experimental scrutiny so far.