Understanding the Behavior of New Plasmonic Probes with Sub-Nanometric Resolution in Field Enhanced Scanning Optical Microscopy

EDUARDO. M. PERASSI; ALBERTO F. SCARPETTINI; MARTIN E. MASIP; ANDREA V. BRAGAS; EDUARDO A. CORONADO

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Año: 2011 vol. 115 p. 10455 - 10461

1932-7447

Recently, using field enhanced scanning opticalmicroscopy (FESOM), a new kind of plasmonic nanostructuredprobes has been introduced capable to achieve subnanometricvertical resolution on atomically flat samples. These plasmonicprobes consisting in silica (SiO2) microspheres decorated with5 nm diameter spherical Ag nanoparticles (NPs) exhibit amultiple peaked experimental extinction spectra in colloidaldispersion. The subnanometric resolution achieved in FESOMis observed when they are attached to a metal tip and illuminatedat 632 nm. On the contrary, these probes lack of resolution inFESOMmeasurements upon 532 nm laser light illumination. Inthis work, the complex extinction properties of these probes aswell as their near field optical properties are compared andanalyzed by means of rigorous electrodynamic simulations. The calculations show that the far and near field optical behavior canonly be explained in a consistent way in terms of the plasmonic response of small Ag NPs clusters on the silica surface. Using thesecluster configurations, the near field simulations of the optical response are also found to be in excellent agreement with theexperimental FESOMapproach curves, demonstrating in this way the subnanometric resolution achieved at 632 nm and the almostnull response at 532 nm.