@phdthesis{64, abstract = {{Dieses Dissertation beschäftigt sich mit der Untersuchung von Clustern, mittels extrem kurzer Laserpulse. "Extrem kurz" bedeutet in diesem Zusammenhang 140 bis 1600 Femtosekunden. In dieser Zeit kann sich das Licht nur etwa einen zehntel bis einen halben Millimeter ausdehnen. Die Fokussierung dieser Strahlung erzeugt elektrische Felder, die denen im Innern eines Atoms entsprechen. Bei der Wechselwirkung von Clustern mit solchen L.aserpulsen sind interessante Effekte zu beobachten: Es entstehen in Bereichen niedriger Laserintensität mehrfach geladene Pt- und Pb-Cluster. Deren kleinste auftretende Größe kann mit den Voraussagen des Tröpfchenmodells verglichen werden. Direkt in dem Fokus der Laserstrahlung, dort wo die Materie den obigen extremen Feldern ausgesetzt wird, ist die Stärke der Anregung so groß, daß die Cluster vollständig in hochgeladene Atome zerfallen. Es zelgt sich eine interessante Abhängigkeit der erreichbaren Aufladung der Atome (L.adungszustand) von der Länge des Laserpulses. Ein einfaches Modell aus Epansion und optischer Respons des Clusters kann diesen Effekt qualitativ erklären. Vergleichsmessungen an Kohlenstoff zeigen nicht dieses Verhalten. Zwingend notwendig scheint die Möglichkeit der kollektiven Anregung der Valenzelektronen von Metallclustern zu sein.}}, author = {{Köller, Lars}}, isbn = {{3-932136-63-2}}, keywords = {{Femtosekunden Laserpulse, Metall Cluster, Wechselwirkung, kollektive Anregung, Plasmonen, Resonanz, hochgeladene Atome}}, pages = {{130}}, publisher = {{Verlag Hans Jacobs}}, title = {{{Wechselwirkung von Metall-Clustern mit intensiven fs-Laserpulsen}}}, year = {{2000}}, } @article{737, abstract = {{The multiply charging process of platinum cluster ions under intense field conditions show a strong dependence on the width of the femtosecond laser pulse. Increasing the pulse width from 140 to 600 fs while keeping the energy per pulse constant leads to an increase in the highest observed charge state z∗ of the ejected atoms from z∗=13 to z∗=20. This increased charging efficiency is explained by the evolution of the plasmon energy of the metal cluster upon the change in electron density during the Coulomb explosion process. Thus the time dependence of the charging of a cluster in an intense light field has been observed in real time.}}, author = {{Köller, Lars and Schumacher, M. and Köhn, J. and Teuber, S. and Tiggesbäumker, J. and Meiwes-Broer, Karl-Heinz}}, issn = {{1079-7114}}, journal = {{Physical Review Letters}}, number = {{19}}, pages = {{3783--3786}}, publisher = {{American Physical Society (APS)}}, title = {{{Plasmon-Enhanced Multi-Ionization of Small Metal Clusters in Strong Femtosecond Laser Fields}}}, doi = {{https://doi.org/10.1103/PhysRevLett.82.3783}}, volume = {{82}}, year = {{1999}}, } @article{739, abstract = {{Carbon and metal clusters are excited by strong femtosecond laser pulses with up to 1016 W/cm2, yielding ionized clusters and highly charged atomic ions. For small carbon clusters and fullerenes the abundance of charged species correlates with the laser power, while for metal clusters the ionization efficiency is additionally strongly affected by the chosen laser pulse width which may result in an enhanced up–charging of the metal particle. In the case of platinum atomic charge states up to z=20 are detected at a pulse duration of about 600 fs. This observation is in accordance with a model based on a multi–plasmon excitation process. }}, author = {{Schumacher, M. and Teuber, S. and Köller, Lars and Köhn, J. and Tiggesbäumker, T. and Meiwes-Broer, Karl-Heinz}}, issn = {{1434-6060}}, journal = {{The European physical journal : D, Atomic, molecular, optical and plasma physics}}, number = {{1}}, pages = {{411--414}}, publisher = {{Springer}}, title = {{{Clusters in Strong Laser Fields: Comparison Between Carbon, Platinum, and Lead Clusters}}}, doi = {{https://doi.org/10.1007/s100530050468}}, volume = {{9}}, year = {{1999}}, } @article{734, abstract = {{We report on investigations of platinum clusters with about five to 400 atoms that are deposited from a cluster beam on to crystalline graphite surfaces. Scanning tunneling spectroscopy in an UHV environment at liquid helium temperatures reveals the existence of distinct peaks in the conductivity of the cluster-on-surface system. For negative voltages, the peak separations scale with the inverse particle height, which hints at a quantum size effect in these metallic “quantum dots”.}}, author = {{Bettac, A. and Köller, Lars and Rank, V. and Meiwes-Broer, Karl-Heinz}}, issn = {{0039-6028}}, journal = {{Surface Science : a journal devoted to the physics and chemistry of interfaces}}, keywords = {{Clusters, Conductivity, Platinum, Quantum size effect, Scanning tunneling, spectroscopy}}, pages = {{475--479}}, publisher = {{Elsevier}}, title = {{{Scanning Tunneling Spectroscopy on Deposited Platnium Clusters}}}, doi = {{10.1016/S0039-6028(98)00028-4}}, volume = {{402-404}}, year = {{1998}}, } @article{740, abstract = {{A pinhole grid spectrometer is used to measure the light emission from the plasma of the pulsed arc cluster ion source (PACIS). Spectra of various metals and carbon have been measured between 20 and 100 nm. In the case of carbon the average electron temperature is estimated to about 0.69 eV. Higher temperatures up to 0.79 eV are measured when inserting seeding gas which flushes the discharge volume with approx. one atmosphere of helium. An operation under this source conditions leads to the generation of an intense charged cluster beam. The application of the source as a bright light source in the VUV region is discussed.}}, author = {{Seeger, K. and Köller, Lars and Tiggesbäumker, J. and Meiwes-Broer, Karl-Heinz}}, issn = {{1434-6060 }}, journal = {{The European physical journal : D, Atomic, molecular, optical and plasma physics }}, number = {{2}}, pages = {{179--182}}, publisher = {{Springer}}, title = {{{VUV-Spectroscopy of the Plasma Light Emission Generated by the Pulsed Arc Cluster Ion Source (PACIS)}}}, doi = {{10.1007/s100530050162}}, volume = {{3}}, year = {{1998}}, } @article{743, abstract = {{We report measurements of the photodestruction cross sections of small sputtered negatively charged silver clusters (AgN−, 5 ≤ N ≤ 19). Resonance-like peaks are observed in the optical spectra which can be attributed to collective electron excitations. In contrast to neutral and positively charged clusters, the resonance energies are far above the electron emission threshold. With decreasing cluster size the resonance positions distinctly shift towards lower energies. This red-shift is explained by an extension of a semi-empirical model by Liebsch which we previously used to interpret the blue-shift in AgN+ [J. Tiggesbäumker, L. Köller, K.H. Meiwes-Broer and A. Liebsch, Phys. Rev. A 48 (1993) R1749], now including the polarizabilities of small metal clusters.}}, author = {{Tiggesbäumker, Josef and Köller, Lars and Meiwes-Broer, Karl-Heinz}}, issn = {{0009-2614 }}, journal = {{Chemical Physics Letters}}, number = {{3-4}}, pages = {{428--432}}, publisher = {{Elsevier}}, title = {{{Bound-Free Collective Electron Excitations in Negatively Charged Silver Clusters}}}, doi = {{https://doi.org/10.1016/0009-2614(96)00950-5}}, volume = {{260}}, year = {{1996}}, } @article{747, abstract = {{We report measurements of the photodestruction cross sections of small sputtered negatively charged silver clusters (AgN−, 5 ≤ N ≤ 19). Resonance-like peaks are observed in the optical spectra which can be attributed to collective electron excitations. In contrast to neutral and positively charged clusters, the resonance energies are far above the electron emission threshold. With decreasing cluster size the resonance positions distinctly shift towards lower energies. This red-shift is explained by an extension of a semi-empirical model by Liebsch which we previously used to interpret the blue-shift in AgN+ [J. Tiggesbäumker, L. Köller, K.H. Meiwes-Broer and A. Liebsch, Phys. Rev. A 48 (1993) R1749], now including the polarizabilities of small metal clusters.}}, author = {{Tiggesbäumker, Josef and Köller, Lars and Meiwes-Broer, Karl-Heinz}}, issn = {{0009-2614 }}, journal = {{Chemical Physics Letters}}, number = {{3-4}}, pages = {{428--432}}, publisher = {{Elsevier}}, title = {{{Bound-Free Collective Electron Excitation in Negatively Charged Metal Clusters}}}, doi = {{https://doi.org/10.1016/0009-2614(96)00950-5}}, volume = {{260}}, year = {{1996}}, } @article{748, abstract = {{The use of sum rules appears to be a powerful tool for obtaining experimental data on static properties of charged metal clusters which are currently not available. For this purpose the optical spectra of the clusters must be known. The measured absorption profiles of sputtered, i.e. hot, and which have been measured in our group give information about the desired properties. The extracted static polarizabilities show a distinct shell structure which reflects the overall lectronic shape of the cluster. A comparison is made with AgN and positive alkali metal clusters. The polarizabilities of closed-shell and are in reasonable agreement with SIC-LDA corrected RPA polarizabilities.}}, author = {{Tiggesbäumker, Josef and Köller, Lars and Meiwes-Broer, Karl-Heinz}}, issn = {{0218-625X }}, journal = {{Surface Review and Letters}}, number = {{1}}, pages = {{509--513}}, publisher = {{World Scientific Publ. }}, title = {{{Static Polarizabilities of Charged Silver Metal Clusters Extracted from the Optical Spectra}}}, doi = {{https://doi.org/10.1142/S0218625X96000929}}, volume = {{3}}, year = {{1996}}, } @article{735, author = {{Köller, Lars and Seeger, K. and Tiggesbäumker, J. and Meiwes-Broer, Karl-Heinz}}, journal = {{-}}, location = {{Werder bei Potsdam}}, title = {{{XUV-Emission aus der Bogenentladungs-Clusterquelle}}}, year = {{1995}}, } @techreport{738, author = {{Köller, Lars and Meiwes-Broer, Karl-Heinz and Lüder, Ch. and Velegrakis, M.}}, title = {{{Time of flight spectroscopy of intense cluster ion beams produced by a Pulsed Arc Cluster Ion Source (PACIS)}}}, year = {{1995}}, } @article{741, author = {{Seeger, K. and Köller, Lars and Tiggesbäumker, J. and Meiwes-Broer, K.-H.}}, journal = {{-}}, location = {{ Richmond, USA}}, title = {{{XUV-emission of the pulsed arc cluster ion source (PACIS)}}}, year = {{1995}}, } @article{746, abstract = {{Photodepletion spectroscopy is used to measure the optical activity of sputtered Ag ionic clusters with up to 70 atoms. With decreasing cluster size the giant resonance caused by collective excitation of the valence electrons shifts to higher frequencies. This blue shift is qualitatively explained in terms of a reduced s-d screening interaction in the surface region of the particles.}}, author = {{Tiggesbäumker, Josef and Köller, Lars and Meiwes-Broer, Karl-Heinz and Liebsch, Ansgar}}, issn = {{2469-9934}}, journal = {{Physical Review A : covering atomic, molecular, and optiacal physics and quantum information}}, number = {{3}}, pages = {{R1749--R1752}}, publisher = {{Inst.}}, title = {{{Blue Shift of the Mie Plasma Frequency in Ag Clusters and Particles}}}, doi = {{https://doi.org/10.1103/PhysRevA.48.R1749}}, volume = {{48}}, year = {{1993}}, } @article{742, abstract = {{The collinear ion-beam depletion technique is used to measure absolute photofragmentation cross sections of small silver-cluster ions in the range from 2.3 to 5.7 eV. Giant resonances are found which can be interpreted in terms of a collective electron oscillation. The optical spectra of spherical Ag+9 and Ag+21 show a large blue-shift of the resonance energy relative to the respective experimental surface value. For non-spherical clusters, a splitting of the giant resonance is found, in qualitative accordance with jellium calculations.}}, author = {{Tiggesbäumker, J. and Köller, Lars and O. Lutz, H. and Meiwes-Broer, Karl-Heinz}}, issn = {{0009-2614 }}, journal = {{Chemical Physics Letters}}, number = {{1-2}}, pages = {{42--47}}, publisher = {{Elsevier}}, title = {{{Giant Resonances in Silver-Cluster Photofragmentation}}}, doi = {{https://doi.org/10.1016/0009-2614(92)86099-4}}, volume = {{190}}, year = {{1992}}, } @inbook{744, abstract = {{Silver cluster ions are produced by sputtering of solid silver by 25 keV Xe+ bombardment. After mass selection, collinear ion beam depletion technique is used to measure absolute photofragmentation cross-sections in the photon energy range from ħω = 2.3 to 5.7 eV. Giant resonances are found which can be interpreted in terms of a collective electron oscillation. The optical spectra of spherical Ag 9 + and Ag 21 + show a blue shift of the resonance energy, in contrast to an expected behaviour within the jellium model. For Ag 11 +, a splitting of the giant resonance is found.}}, author = {{Tiggesbäumker, J. and Köller, Lars and O. Lutz, H. and Meiwes-Broer, Karl-Heinz}}, booktitle = {{Physics and Chemistry of Finite Systems: From Clusters to Crystals}}, editor = {{Jena, P. and N. Khanna, S. and K. Rao, B.}}, isbn = {{978-94-017-2647-4}}, keywords = {{Oscillator Strength, Collective Excitation, Giant Dipole Resonance, Silver Cluster, Gigant Resonance}}, pages = {{1001--1006}}, publisher = {{Springer}}, title = {{{Collective Excitation in Silver Cluster Ions}}}, doi = {{https://doi.org/10.1007/978-94-017-2645-0_135}}, volume = {{374}}, year = {{1992}}, } @inbook{745, abstract = {{Positive and negative silver cluster ions are produced by sputtering of solid silver by 25 keV Xe+ bombaxdment. After mass selection, collinear ion beam depletion is used to measure absolute photofragmentation cross-sections in the photon energy range from ħω = 2.0 to 5.7 eV. Giant resonances are found which can be interpreted in terms of a collective electron oscillation. For spherical clusters (e.g., Ag19−, Ag21+) single resonances dominate the spectra, whereas deformation (e.g., Ag9−, Ag11+) induces a splitting into two components.}}, author = {{Tiggesbäumker, J. and Köller, Lars and O. Lutz, H. and Meiwes-Broer, Karl-Heinz}}, booktitle = {{Nuclear Concepts in Atomic Cluster Physics}}, editor = {{Schmidt, Rüdiger}}, isbn = {{978-3-540-55625-1}}, location = {{Bad Honnef}}, pages = {{245--253}}, publisher = {{Springer}}, title = {{{Collective Excitation in Silver Cluster Anions and Kations}}}, doi = {{https://doi.org/10.1007/3-540-55625-7_27}}, volume = {{404}}, year = {{1992}}, }