Optical properties of small inorganic and organic metal particles

Mise au point. Donnees sur le phenomene de diffusion Raman augmentee en surface (SERS) et sur sa relation avec les effets de «rugosite» et de resonance electromagnetique; sur l'augmentation classique; sur l'interaction polariton plasmon de surface-adsorbat comparee a l'interaction electron du metal-adsorbat; sur la relation entre l'effet de resonance electromagnetique et SERS; et enfin sur les interactions entre les electrons du metal et l'adsorbat dans la SERS

Surface-enhanced Raman scattering: “Classical” and “Chemical” origins

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.

Deposition of mass selected silver clusters in rare gas matrices

Optical absorption spectra are reported for Li, Na, and Ag in various stages of aggregation ranging from atom to microcrystal. The samples were prepared by the simultaneous condensation of rare gas and metal vapor onto a liquid helium temperature substrate. The dependence of the strength of the individual absorption lines on metal concentration and on selective light induced diffusion allowed the tentative assignment of spectral features to one, two, three, and four atom clusters. Comparison of the observed transition energies with an empirical, extended Huckel calculation seems to indicate that the trimers are triangular and the four atom clusters have tetrahedral shape. For metal concentrations higher than 10% the sharp molecular lines abruptly disappear and a single broad plasmon absorption, characteristic of microcrystals, appears. The shape of this absorption band can be explained using a continuum theory of dielectric response if microcrystal size, shape, and mutual interaction are properly taken in...

Optical absorption of matrix isolated Li, Na, and Ag clusters and microcrystals

Results of experiments on lithium doped rare gas solids (Ar, Kr, and Xe) prepared by laser ablation of solid lithium are presented, including near UV–visible absorption spectra, and photobleaching and annealing studies of the matrices, as well as visible emission spectra of the laser ablated Li plume. The UV–visible absorption spectra of Li/Ar and Li/Kr matrices generated by cocondensing the rare gas and laser ablated Li atoms at 12 K are dominated by a ‘‘blue‐shifted triplet’’ absorption not observed in previously published studies. Control experiments on Li/Ar and Li/Kr matrices generated using a Knudsen oven as the Li atom source showed exclusively an ‘‘unshifted triplet’’ absorption, in agreement with previous studies. The new absorption features are attributed to Li atoms trapped in novel sites in the Ar and Kr solids; sites not accessible to Li atoms generated by the conventional Knudsen effusion technique. Spectra of Li/Xe samples prepared by the laser ablation method showed exclusively the unshift...

H. Abe

Papers

The Isolation/Aggregation of Metal Atoms in Solid Noble Gases