Search

N-Heteropolycyclic aromatic compounds are promising organic electron-transporting semiconductors for applications in field effect transistors. Here, we investigated the electronic properties of 1,3,8,10-tetraazaperopyrene derivatives adsorbed on Au(111) using a complementary experimental approach, namely scanning tunneling spectroscopy and two-photon photoemission combined with state-of-the-art density functional calculations. We find signatures of weak physisorption of the molecular layers, such as the absence of charge transfer, a nearly unperturbed surface state and an intact herringbone reconstruction underneath the molecular layer. Interestingly, molecular states in the energy region of the \emph{sp}- and \emph{d}-bands of the Au(111) substrate exhibit hole-like dispersive character. We ascribe this band character to hybridization with the delocalized states of the substrate. We suggest that such bands, which effectively leave the molecular frontier orbitals largely unperturbed, to be a promising lead for the design of organic-metal interfaces with a low charge injection barrier.

The SwissFEL Injector Test Facility operated at the Paul Scherrer Institute between 2010 and 2014, serving as a pilot plant and testbed for the development and realization of SwissFEL, the X-ray Free-Electron Laser facility under construction at the same institute. The test facility consisted of a laser-driven rf electron gun followed by an S-band booster linac, a magnetic bunch compression chicane and a diagnostic section including a transverse deflecting rf cavity. It delivered electron bunches of up to 200 pC charge and up to 250 MeV beam energy at a repetition rate of 10 Hz. The measurements performed at the test facility not only demonstrated the beam parameters required to drive the first stage of an FEL facility, but also led to significant advances in instrumentation technologies, beam characterization methods and the generation, transport and compression of ultra-low-emittance beams. We give a comprehensive overview of the commissioning experience of the principal subsystems and the beam physics measurements performed during the operation of the test facility, including the results of the test of an in-vacuum undulator prototype generating radiation in the vacuum ultraviolet and optical range., Comment: 60 pages, 70 figures; final version as published, except with table of contents and Fig. 68 in full resolution

Magnet power supplies in the PSI accelerator complex with their control and field-bus are old. Some components are more then 30 years old. To guarantee further maintenance and to meet the more demanding specifications for operation with the 2mA beam, they have to be replaced. The switched power supplies, developed for SLS, will be used. This implies a major redesign of part of the accelerator control system, which is now based on CAMAC, ROAD-C and other in house developed hardware including the machine protection system. The modified control for the new set-up will be based on VME and alternatively CAMAC, with dedicated processors for the functionality of the machine protection system., Comment: Poster WEAP041 presented at the 8th International Conference on Accelerator and Large Experimental Physics Control Systems

We have performed classical trajectory Monte Carlo (CTMC) studies of electron capture and ionization in multiply charged (Q=8) ion-Rydberg atom collisions at intermediate impact velocities. Impact parallel to the minor and to the major axis, respectively, of the initial Kepler electron ellipse has been investigated. The important role of the initial electron momentum distribution found for singly charged ion impact is strongly disminished for higher projectile charge, while the initial spatial distribution remains important for all values of Q studied., Comment: 3 pages, 5 figures

We calculate the resistivity and Giant Magnetoresistance (GMR) of a segmented nanowire consisting of two ferromagnetic segments separated by a thin paramagnetic spacer. The quantization of the electron motion due to the small nanowire cross-section is taken into account; s-d electron scattering gives rise to different mean free paths for spin-up and spin-down s-electrons. The calculated resistivity and GMR oscillate as a function of nanowire cross-section due to the difference in Fermi momenta of d-electrons with opposite spins. The GMR can reach values much higher than those which are obtained for "wires" of infinite cross-section (i.e., a multilayer). Similarly we have calculated the Tunneling Magnetoresistance (TMR) by replacing the paramagnetic spacer with an insulator spacer., Comment: 9 pages, 8 figures

We study lead nanodroplets containing 147 to 1415 atoms at temperatures ranging from the bulk melting point up to the beginning of the evaporation regime. Molecular dynamics simulation and an embedded atom potential are used. The structures, total energies, and mobility of atoms in the clusters are analyzed. We found that the liquid cluster of 147 atoms shows a pronounced tendency to form non-spherical shapes, and sometimes separates into two droplets. Bigger clusters disassemble by evaporation of monomers. We also explore shape oscillations of these nanodroplets using the nuclear liquid drop model.