Nanoplasmonic electron acceleration in silver clusters studied by angular-resolved electron spectroscopy

The nanoplasmonic field enhancement effects in the energetic electron emission from few-nm-sized silver clusters exposed to intense femtosecond dual pulses are investigated by high-resolution double differential electron spectroscopy. For moderate laser intensities of 10 14Wcm -2, the delaydependent and angular-resolved electron spectra show laser-aligned emission of electrons up to keV kinetic energies, exceeding the ponderomotive potential by two orders of magnitude. The importance of the nanoplasmonic field enhancement due to resonant Mie-plasmon excitation observed for optimal pulse delays is investigated by a direct comparison with molecular dynamics results. The excellent agreement of the key signatures in the delay-dependent and angular-resolved spectra with simulation results allows for a quantitative analysis of the laser and plasmonic contributions to the acceleration process. The extracted field enhancement at resonance verifies the dominance of surfaceplasmon-assisted re-scattering

METASTABLE DECAY AND COLLISIONS OF SPUTTERED METAL AND SILICON CLUSTER IONS

Les agrégats ioniques, positifs ou négatifs, sont obtenus par bombardement d'une surface par des ions de gaz rares. Une corrélation grossière entre le sputtering yield Y et le nombre maximum d'atomes n dans l'agrégat produit est mise en évidence. La largeur en énergie cinétique des ions formés décroît avec n, tout en restant en général plus importante que celle des agrégats neutres ionisés. La dissociation unimoléculaire qui est dominante conduit à des anomalies en intensité dans les spectres de masse des agrégats. Les taux de dissociation dépendent fortement du temps et mettent en évidence des différences entre les énergies de liaison des agrégats. La distribution en masse des fragments produits par collision d'agrégats sur une cible de gaz rare est très liée aux taux de dissociation.Cluster ions and anions are produced by rare gas ion bombardment of surfaces. A rough correlation between sputtering yield Y and maximum number of atoms in the cluster n is found. Kinetic energy spreads decrease with n, generally being larger than those of ionized neutrals. Strong unimolecular decay leads to intensity anomalies in cluster mass spectra. Decay rate constants are strongly time dependent and reveal differences in cluster binding energies. Fragment patterns resulting from keV cluster collisions in a rare gas target turn out to be strongly related to the decay rates

Adsorbate-induced one-dimensional long-range modulation of an epitaxial insulator film

Using low-energy electron diffraction and scanning tunneling micrsocopy, we found that epitaxial NaCl films grown on Ge(100) with thicknesses up to (at least) 15 monolayers can be modulated with a period of six lattice constants and an amplitude directed mainly normal to their surface. The (6*1) periodicity on the NaCl films is induced by a preadsorbed Na layer at very low coverages (?0.06), that form chain structures with a sixfold periodicity in one dimension. At 10 monolayers thickness of NaCl a modulation amplitude of 0.28 Å was obtained. © 2002 American Institute of Physics

Verfahren zur Erzeugung metallischer Materialstrukturen im nm- und sub-nm-Bereich Abschlussbericht

Metallic nanoparticles on solid surfaces are interesting for future applications as they exhibit a variety of new physical and chemical properties. These are mainly due to the confinement of the electronic wave functions to the small cluster volumes. The potential use ranges from miniaturized electronic components and sensors to applications in the chemical catalysis. Within this project several physical methods have been developed and/or applied for the generation and analysis of metallic nanostructures. Small aggregates with up to about 100 atoms were deposited from cluster sources as beams onto prepared surfaces in vacuum. Additionally we investigated the texturing of the surface with an STM in air and the subsequent deposition of atoms and clusters which yielded larger aggregates at the preformed pinning sites. Another way is the thermal processing of magnetic adsorbate layers which induces the growth of ordered ferromagnetic nanostructures. The prototype of a low-temperature STM with temperatures down to 5 Kelvin has been tested and used for the structural and electronic analysis. With the new setup we could show for the first time that small platinum clusters deposited from a beam onto graphite exhibit a quantization in their electrical conductance. Although this property was observed at low temperatures it might be important for future applications. The STM is now commercially available. (orig.)Available from TIB Hannover: F98B1480+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Erzeugung, Charakterisierung und Abscheidung ionisierter Cluster Teilprojekt: Deposition massenseparierter Cluster und Schichtanalyse. Abschlussbericht

SIGLEAvailable from TIB Hannover: F93B717+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Formation of coherent rotational wavepackets in small molecule-helium clusters using impulsive alignment

We show that rotational line spectra of molecular clusters with near zero permanent dipole moments can be observed using impulsive alignment. Aligned rotational wavepackets were generated by non-resonant interaction with intense femtosecond laser pump pulses and then probed using Coulomb explosion by a second, timedelayed femtosecond laser pulse. By means of a Fourier transform a rich spectrum of rotational eigenstates was derived. For the smallest cluster, C2H2–He, we were able to establish essentially all rotational eigenstates up to the dissociation threshold on the basis of theoretical level predictions. The C2H2–He complex is found to exhibit distinct features of large amplitude motion and very early onset of free internal rotor energy level structure