B. von Issendorff

Atomically precise (catalytic) particles synthesized by a novel cluster deposition instrument

We report a new high vacuum instrument which is dedicated to the preparation of well-defined clusters supported on model and technologically relevant supports for catalytic and materials investigations. The instrument is based on deposition of size selected metallic cluster ions that are produced by a high flux magnetron cluster source. The throughput of the apparatus is maximized by collecting and focusing ions utilizing a conical octupole ion guide and a linear ion guide. The size selection is achieved by a quadrupole mass filter. The new design of the sample holder provides for the preparation of multiple samples on supports of various sizes and shapes in one session. After cluster deposition onto the support of interest, samples will be taken out of the chamber for a variety of testing and characterization.

Spectroscopic observation of a metastable electronically excited He4

Abstract In the size distribution of ionized helium clusters produced by electron impact ionization of very large neutral clusters ( N > 10 5 atoms), He 4 + is the most abundant small cluster ion. This observation has recently received considerable attention, since in theoretical calculations no specially stable structure for the tetramer ion could be found. Measurements of the photoabsorption cross section and of the fragment kinetic energy release now indicate that this ‘magic’ He 4 + is in a metastable electronically excited state.

X-ray spectroscopy on size-selected clusters in an ion trap: from the molecular limit to bulk properties

An experiment was designed to perform x-ray and VUV spectroscopy on size-selected clusters in the gas phase. Using a radio frequency ion trap and a quadrupole mass filter combined with an intense magnetron sputter source made it possible to record x-ray absorption spectra of mass-selected clusters in ion yield mode. These measurements clearly reveal the development from richly structured atomic spectra to bulk-like line shapes in transition metal clusters.

Pb 4f photoelectron spectroscopy on mass-selected anionic lead clusters at FLASH

4f core level photoelectron spectroscopy has been performed on negatively charged lead clusters, in the size range of 10?90 atoms. We deploy 4.7?nm radiation from the free-electron laser FLASH, yielding sufficiently high photon flux to investigate mass-selected systems in a beam. A new photoelectron detection system based on a hemispherical spectrometer and a time-resolving delayline detector makes it possible to assign electron signals to each micro-pulse of FLASH. The resulting 4f binding energies show good agreement with the metallic sphere model, giving evidence for a fast screening of the 4f core holes. By comparing the present work with previous 5d and valence region data, the paper presents a comprehensive overview of the energetics of lead clusters, from atoms to bulk. Special care is taken to discuss the differences of the valence- and core-level anion cluster photoionizations. Whereas in the valence case the escaping photoelectron interacts with a neutral system near its ground state, core-level ionization leads to transiently highly excited neutral clusters. Thus, the photoelectron signal might carry information on the relaxation dynamics.

Communication: Highest occupied molecular orbital–lowest unoccupied molecular orbital gaps of doped silicon clusters from core level spectroscopy

A method to determine band gaps of size-selected and isolated nanoparticles by combination of valence band and core-level photoionization spectroscopy is presented. This approach is widely applicable and provides a convenient alternative to current standard techniques for the determination of band gaps by optical or photoelectron spectroscopy. A first application to vanadium doped silicon clusters confirms a striking size-dependence of their highest occupied-lowest unoccupied molecular orbital gaps.

Gas-phase calorimetry of protonated water clusters

Protonated water clusters with 60 to 79 molecules have been studied by nanocalorimetry. The technique is based on multi-collision excitations of the accelerated clusters with helium. The caloric curves indicate transitions that resemble those of water clusters charged by an excess electron, but the transition temperatures of the protonated clusters are higher.