@article{GoetzHoheiselTraegeretal.1995, author = {G{\"o}tz, T. and Hoheisel, W. and Tr{\"a}ger, F. and Vollmer, Michael}, title = {Characterization of Large Supported Metal Clusters by Optical Spectroscopy}, series = {In: Zeitschrift f{\"u}r Physik / D Vol. 33 (1995) 2, pp 133-141}, journal = {In: Zeitschrift f{\"u}r Physik / D Vol. 33 (1995) 2, pp 133-141}, doi = {10.1007/BF01437432}, year = {1995}, abstract = {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.}, language = {en} } @inproceedings{Vollmer1994, author = {Vollmer, Michael}, title = {Ablation of Metal Particles with Laser Light: Shape and Polarization Effects}, series = {In: Laser ablation: mechanisms and applications - II : second international conference, Knoxville, TN April 1993 / eds.: John C. Miller ...- New York : American Inst. of Physics, 1994. - (AIP conference proceedings / American Institute of Physics. - Melville, NY, 1970- ; 288) (Laser ablation: mechanisms and applications. - New York : American Institute of Physics ; 2). - S. 32 ff}, booktitle = {In: Laser ablation: mechanisms and applications - II : second international conference, Knoxville, TN April 1993 / eds.: John C. Miller ...- New York : American Inst. of Physics, 1994. - (AIP conference proceedings / American Institute of Physics. - Melville, NY, 1970- ; 288) (Laser ablation: mechanisms and applications. - New York : American Institute of Physics ; 2). - S. 32 ff}, pages = {32 -- 37}, year = {1994}, language = {en} } @article{HoevelFritzHilgeretal.1993, author = {H{\"o}vel, H. and Fritz, S. and Hilger, A. and Kreibig, U. and Vollmer, Michael}, title = {Width of cluster plasmon resonances: Bulk dielectric functions and chemical interface damping}, series = {In: Phys. Rev. B 48 (1993) 24, 18178-18188}, journal = {In: Phys. Rev. B 48 (1993) 24, 18178-18188}, doi = {10.1103/PhysRevB.48.18178}, year = {1993}, abstract = {The damping of collective electron resonances in clusters which develop into plasmon polaritons at larger sizes is investigated for free, supported, and embedded neutral metal clusters. Embedding of free 2 nm Ag clusters of 2-nm diameter into a SiO2 matrix leads to an increase of the width of the resonances by more than a factor of 3. The optical spectra are compared with the Mie theory using size-effect-modified dielectric functions of the solid state. The results corroborate the assumption that the widths of the resonances strongly depend on chemical interface effects. The results are briefly discussed with regard to limited-mean-free-path and quantum-size-effect theories and a recent approach by Persson. It is demonstrated that the widths of the spectra of supported and embedded clusters have to be interpreted with care since true intrinsic size effects of the clusters appear to be less effective than previously believed and can be obscured by the chemical interface damping. © 1993 The American Physical Society}, language = {en} } @article{GoetzTraegerVollmer1993, author = {G{\"o}tz, T. and Tr{\"a}ger, F. and Vollmer, Michael}, title = {Desorption of metal atoms with laser light of different polarization}, series = {In: Applied physics / A 57 (1993) 1, pp 101-104}, journal = {In: Applied physics / A 57 (1993) 1, pp 101-104}, doi = {10.1007/BF00331225}, pages = {101 -- 104}, year = {1993}, abstract = {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.}, language = {en} } @article{HoheiselVollmerTraeger1993, author = {Hoheisel, W. and Vollmer, Michael and Tr{\"a}ger, F.}, title = {Desorption of metal atoms with laser light: Mechanistic studies}, series = {In: Physical Review / B 48 1993) 23, 17463-17476}, journal = {In: Physical Review / B 48 1993) 23, 17463-17476}, doi = {10.1103/PhysRevB.48.17463}, year = {1993}, abstract = {Results on laser-induced desorption of metal atoms from small metal particles are presented. Experiments have been performed on sodium, potassium, and silver particles supported on a LiF(100) single-crystal surface under ultrahigh vacuum conditions. Measurements include the determination of the desorption rate as a function of laser wavelength, laser intensity, average particle size, and substrate temperature, the determination of the kinetic energy of the desorbed atoms, the investigation of the optical spectra of the supported metal particles, and the study of the influence of adsorbate molecules on the desorption rate. Furthermore, theoretical extinction and absorption spectra of the metal particles have been calculated with the classical electrodynamical Mie theory as a function of average particle size and excitation wavelength. Also, the radial electric field at the particle surface was computed. The results of the experiments and theoretical calculations are combined to give a consistent picture of the mechanism of metal-atom desorption by electronic excitation with laser light. A realistic surface potential from which the atoms escape and nonlocal optical effects are taken into account. The latter introduce additional absorption channels by the formation of electron-hole pairs in the surface layer of the particle which relax into antibonding states before desorption occurs. Finally, the mechanism is discussed in the light of similar phenomena observed for thin metal films. Possibilities for future work are outlined. © 1993 The American Physical Society}, language = {en} } @article{GoetzHoheiselTraegeretal.1993, author = {G{\"o}tz, T. and Hoheisel, W. and Tr{\"a}ger, F. and Vollmer, Michael}, title = {Interplay between collective and single electron excitations in large metal clusters}, series = {In: Zeitschrift f{\"u}r Physik / D 26 (1993), 267-269}, journal = {In: Zeitschrift f{\"u}r Physik / D 26 (1993), 267-269}, year = {1993}, language = {en} } @incollection{VollmerKreibig1992, author = {Vollmer, Michael and Kreibig, U.}, title = {Collective excitations of large metal clusters}, series = {In: Nuclear physics concepts in the study of atomic cluster physics : proceedings of the 88th W.-E.-Heraeus-Seminar, held at Bad Honnef, FRG, 26 - 29 November 1991 / R. Schmidt ... (ed.). - Berlin [u.a.] : Springer, 1992. - (Lecture notes in physics ; Vol. 404). - ISBN 3-540-55625-7 ; 0-387-55625-7. - S. 266-276}, booktitle = {In: Nuclear physics concepts in the study of atomic cluster physics : proceedings of the 88th W.-E.-Heraeus-Seminar, held at Bad Honnef, FRG, 26 - 29 November 1991 / R. Schmidt ... (ed.). - Berlin [u.a.] : Springer, 1992. - (Lecture notes in physics ; Vol. 404). - ISBN 3-540-55625-7 ; 0-387-55625-7. - S. 266-276}, doi = {10.1007/3-540-55625-7_30}, pages = {266 -- 276}, year = {1992}, abstract = {Studies of the evolution of the optical properties of metal clusters as a function of size have gained considerable attention in the last few years. One theoretical approach starts from large metal clusters, which can be described by classical electrodynamics, provided the dielectric functions of the clusters are known. the resulting resonant features in the absorption spectra are commonly called surface plasmons and are collective excitations of the electron system.The present paper discusses the electrodynamic (Mie) theory for large clusters of different metals, also considering the range of validity of this approach towards smaller cluster sizes. More details can be found in an extended review on this topic which is to be published soon [1].}, language = {en} } @inproceedings{MoellmannPinnoVollmer2009, author = {M{\"o}llmann, Klaus-Peter and Pinno, Frank and Vollmer, Michael}, title = {Microscopic and high-speed thermal imaging: a powerful tool in physics R\&D}, series = {In: InfraMation proceedings Vol.10 (2009), 303-317}, booktitle = {In: InfraMation proceedings Vol.10 (2009), 303-317}, pages = {303 -- 317}, year = {2009}, language = {en} } @inproceedings{VollmerMoellmannPinno2008, author = {Vollmer, Michael and M{\"o}llmann, Klaus-Peter and Pinno, Frank}, title = {Cheese cubes, light bulbs, soft drinks: An unusual approach to study convection, radiation and size dependent heating and cooling}, series = {In: InfraMation proceedings Vol. 9 (2008), p. 477-492}, booktitle = {In: InfraMation proceedings Vol. 9 (2008), p. 477-492}, pages = {477 -- 492}, year = {2008}, language = {en} } @inproceedings{MoellmannPinnoVollmer2008, author = {M{\"o}llmann, Klaus-Peter and Pinno, Frank and Vollmer, Michael}, title = {Night sky radiant cooling - influence on outdoor thermal imaging analysis}, series = {In: InfraMation proceedings Vol. 9 (2008), 279-295}, booktitle = {In: InfraMation proceedings Vol. 9 (2008), 279-295}, pages = {279 -- 295}, year = {2008}, language = {en} }