Optical Near-Field Mapping of Plasmonic Nanoprisms

• Published in: Nano letters 2008-10, Vol.8 (10), p.3357-3363
• Main Authors: Rang, Matthias, Jones, Andrew C, Zhou, Fei, Li, Zhi-Yuan, Wiley, Benjamin J, Xia, Younan, Raschke, Markus B
• Format: Article
• Language: English
• Subjects: Applied sciences; Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Crystallization; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronics; Equipment Design; Exact sciences and technology; General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Light; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Microscopy - methods; Microscopy, Atomic Force; Molecular electronics, nanoelectronics; Nanoparticles - chemistry; Nanostructures - chemistry; Nanotechnology - methods; Optics and Photonics; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; Silver - chemistry; Spectrum Analysis, Raman - methods; Surface and interface electron states; Surface Plasmon Resonance - instrumentation; Surface Plasmon Resonance - methods; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl801808b

The optical local-field enhancement on nanometer length scales provides the basis for plasmonic metal nanostructures to serve as molecular sensors and as nanophotonic devices. However, particle morphology and the associated surface plasmon resonance alone do not uniquely reflect the important details of the local field distribution. Here, we use interferometric homodyne tip-scattering near-field microscopy for plasmonic near-field imaging of crystalline triangular silver nanoprisms. Strong spatial field variation on lengths scales as short as 20 nm are observed sensitively depending on structural details and environment. The poles of the dipole and quadrupole plasmon modes, as identified by phase-sensitive probing and calculations performed in the discrete dipole approximation (DDA), reflect the particle symmetry. Together with the observation that the largest enhancement is not necessarily found to be associated with the tips of the nanoprisms, our results provide critical information for the selection of particle geometries as building blocks for plasmonic device applications.