Plasmonic field enhancement of individual nanoparticles by correlated scanning and photoemission electron microscopy

Abstract

We present results of a combined two-photon photoemission and scanning electron microscopy investigation to determine the electromagnetic enhancement factors of silver-coated spherical nanoparticles deposited on an atomically flat mica substrate. Femtosecond laser excitation of the nanoparticles produces intense photoemission, attributed to near-resonant excitation of localized surface plasmons. Enhancement factors are determined by comparing the respective two-photon photoemission yields measured for single nanoparticles and the surrounding flat surface. For p-polarized, 400 nm (∼3.1 eV) femtosecond radiation, a distribution of enhancement factors is found with a large percentage (67%) of the nanoparticles falling within a median range. A correlated scanning electron microscopy analysis demonstrated that the nanoparticles typifying the median of the distribution are characterized by spherical shapes and relatively smooth silver film morphologies. In contrast, the largest enhancement factors were produced by a small percentage (7%) of particles that displayed silver coating defects that altered the overall particle structure. Comparisons are made between the experimentally measured enhancement factors and previously reported calculations of the localized near-field enhancement for isolated silver nanoparticles.

Controlled synthesis of highly-branched plasmonic gold nanoparticles through peptoid engineering

“…15b ) reveal that individual coral-shaped particles support a plasmonic enhancement factor of as high as 10 5 , which is 2–3 orders of magnitudes stronger than those achieved from Pep- 5 -induced Au NPs (Supplementary Fig. 16 ) and other previously reported plasmonic NPs 41 , 42 . These data confirm that the unique plasmonic enhancement arises from the coral-shaped morphology.…”

Engineering metallic nanostructures for plasmonics and nanophotonics

“…In contrast, photoemission spectroscopy involves measuring the energy of emitted electrons following multiphoton absorption of intense laser radiation (Kubo et al, 2005, Kubo et al, 2007b, Kubo et al, 2007a, Hrelescu et al, 2011, Peppernick et al, 2011, Mikkelsen et al, 2009, Aeschlimann et al, 2010, Stockman et al, 2007, Cinchetti et al, 2005, Douillard et al, 2008, Aeschlimann et al, 2007, Berndt et al, 2009, Chelaru and Heringdorf, 2007, Heringdorf et al, 2007, Lin et al, 2009). The emitted electron energy is measured with an energy resolution better than 50 meV while the laser beam is scanned over the sample to generate a spatial profile.…”

Single nanoparticle plasmonics

“…This capability is harnessed in a common and commercially available approach called photoelectron emission microscopy (PEEM), which has been used to map, with a resolution down to 20 nm, the photoemission enhancement in a number of patterned surfaces, [103][104][105] slits, 106 and a small number of single particles including crescents. 107 Recent advances have coupled PEEM with 2-photon photoemission as well as sophisticated interferometric pump-probe approaches yielding improved contrast; 104,108 coupling with femtosecond excitation has also been achieved to probe ultrafast processes, 105,106,[109][110][111] while aberration correction improved the lateral resolution down to a few nanometres. 15,112 PEEM, however, can be a complex tool requiring sophisticated electron optics and special care to avoid distortions due to charging.…”