We report on the successful ‘‘soft landing’’ of size selected silver dimers and trimers in solid krypton matrices. Silver cluster cations, produced by sputtering, were mass selected in a quadrupole mass filter and then codeposited with krypton on a cooled sapphire or CaF2 window in the presence of low energy electrons. Neutralized cluster samples were interrogated in situ by excitation and fluorescence spectroscopy. Deposition of slow (≤20 eV) silver dimer cations gave rise to strong excitation bands (centered at λ=275 and 390 nm) from Ag2 plus the characteristic triplet signal of the atom. The spectra imply that fewer than 25% of the dimers were fragmented during the neutralization and deposition steps. In similar experiments with Ag3 we were able to assign trimer absorption bands at 331, 364, 402, 421, 458, and 514 nm and identify characteristic emission features at 381, 560, and 626 nm.
Local field distributions in random metal-dielectric films near a percolation threshold are experimentally studied using scanning near-field optical microscopy ͑SNOM͒. The surface-plasmon oscillations in such percolation films are localized in small nanometer-scale areas, ''hot spots,'' where the local fields are much larger than the field of an incident electromagnetic wave. The spatial positions of the hot spots vary with the wavelength and polarization of the incident beam. Local near-field spectroscopy of the hot spots is performed using our SNOM. It is shown that the resonance quality-factor of hot spots increases from the visible to the infrared. Giant local optical activity associated with chiral plasmon modes has been obtained. The hot spot's large local fields may result in local, frequency and spatially selective photomodification of percolation films.
This term is negligible in the more commonly observed dilute case such as described by Swift and Connick30 in which the paramagnetic shift reagent is present in much lower concentration than the diamagnetic substrate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.