TY - JOUR A1 - Götz, T. A1 - Hoheisel, W. A1 - Träger, F. A1 - Vollmer, Michael T1 - Characterization of Large Supported Metal Clusters by Optical Spectroscopy JF - In: Zeitschrift für Physik / D Vol. 33 (1995) 2, pp 133-141 N2 - Small sodium and silver particles were generated on dielectric substrates like LiF, quartz and sapphire under ultrahigh vacuum conditions. The optical transmission spectra of the clusters were measured as a function of cluster size and shape, for low and high substrate temperatures as well as for s- and p- polarization of the incident light. Excitation of dipolar surface plasmon oscillations in the directions normal and parallel to the substrate surface could be identified. Furthermore, optical spectra for Na and Ag clusters were calculated with the classical Mie theory. The measured spectra vary strongly if the experimental conditions are changed and can be exploited, for example, to characterize the particles with regard to their size and shape. In particular, the axial ratio of the spheroidal clusters could be determined. Its value is considerably different for the two investigated metals and depends on the substrate material. Furthermore, the temperature of the substrate has a pronounced influence on the shape of the particles. At low temperature of T=100 K two-dimensional island growth is predominant. The particles extend only little in the direction perpendicular to the surface and coalesce readily at small coverage of metal atoms. In contrast, the clusters are truly three-dimensional at T=300 K. At this stage, sodium particles still exhibit a rather small axial ratio whereas silver clusters appear almost spherical. Thus, measurements of the optical spectra permit direct in situ monitoring of cluster growth during the nucleation of adsorbed atoms and of temperature induced shape variations. In addition to investigations of the shape of the particles, the quadrupolar surface plasmon mode was observed for Ag clusters. Y1 - 1995 U6 - https://doi.org/10.1007/BF01437432 ER - TY - JOUR A1 - Götz, T. A1 - Träger, F. A1 - Vollmer, Michael T1 - Desorption of metal atoms with laser light of different polarization JF - In: Applied physics / A 57 (1993) 1, pp 101-104 N2 - Laser-induced desorption of metal atoms from the surface of small metal particles has been investigated as a function of the shape of the particles and the polarization of the incident laser light. The particles were supported on LiF, quartz or sapphire substrates. In a first set of experiments, the shape of the particles was determined by recording optical transmission spectra with s- and p-polarized light incident under an angle of typically 40° with respect to the surface normal. The metal particles turn out to be oblate, the ratio of the axes perpendicular and parallel to the substrate surface being on the order of 0.5. This ratio decreases with increasing particle size. Also, the particles change shape if the temperature is raised. In further experiments, s- and p-polarized light has been used to stimulate desorption of atoms via surface plasmon excitation. It is found that the desorption rate markedly depends on the polarization of the light. This is explained by excitation of the collective electron oscillation along different axes of the non-spherical particles. Y1 - 1993 U6 - https://doi.org/10.1007/BF00331225 SP - 101 EP - 104 ER - TY - JOUR A1 - Götz, T. A1 - Hoheisel, W. A1 - Träger, F. A1 - Vollmer, Michael T1 - Interplay between collective and single electron excitations in large metal clusters JF - In: Zeitschrift für Physik / D 26 (1993), 267-269 Y1 - 1993 ER -