Observation of strong optical absorption at the surface of small particles

[摘要] Experiments are presented in which strong optical absorption at the surface of small metal particles is been observed. This was accomplished by the following method. Na clusters with rough surfaces were prepared on a transparent substrate. They provide the possibility of localized electronic excitations in the surface region in addition to the well-known plasmon-polaritons in the bulk. The particles were irradiated with pulsed laser light and their temperature rise was derived from measurements of the kinetic energy distribution of thermally desorbed Na dimers. From the temperature increase, the heat generated in the particles during decay of both surface and bulk excitations was calculated and taken as a measure of the total absorption cross-section. Separation of the bulk and surface contributions was achieved by repeating the experiments after removal of the surface roughness by annealing. We find that the surface contributes as much as 32% to the total optical absorption at lambda = 532 nm for Na clusters of a mean radius R of 21 mm. (C) 1997 Elsevier Science B.V.

[发布日期] 1997-11-06

[关键词] alkali metals;clusters;laser induced thermal desorption;surface structure;morphology, roughness, and topography;visible/ultraviolet absorption spectroscopy