Influence of a partially oxidized calcium cathode on the performance of polymeric light emitting diodes

We investigated the influence of the presence of oxygen during the deposition of the calcium cathode on the structure and on the performance of polymeric light emitting diodes (pLEDs). The oxygen background pressure during deposition of the calcium cathode of polymeric LEDs was varied. Subsequently, the oxygen depth distribution was measured and correlated with the performance of the pLEDs. The devices have been fabricated in a recently built ultraclean setup. The polymer layers of the pLEDs have been spincoated in a dry nitrogen atmosphere and transported directly into an ultrahigh vacuum chamber where the metal electrodes have been deposited by evaporation. We used indium–tin–oxide as anode, OC1C10 PPV as electroluminescent polymer, calcium as cathode, and aluminum as protecting layer. We achieved reproducibility of about 15% in current and brightness for devices fabricated in an oxygen atmosphere o

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Measurement of event-shape observables in Z→ℓ+ℓ− events in pp collisions at √ s=7 TeV with the ATLAS detector at the LHC

Event-shape observables measured using charged particles in inclusive $Z$-boson events are presented, using the electron and muon decay modes of the $Z$ bosons. The measurements are based on an integrated luminosity of $1.1 {\rm fb}^{-1}$ of proton--proton collisions recorded by the ATLAS detector at the LHC at a centre-of-mass energy $\sqrt{s}=7$ TeV. Charged-particle distributions, excluding the lepton--antilepton pair from the $Z$-boson decay, are measured in different ranges of transverse momentum of the $Z$ boson. Distributions include multiplicity, scalar sum of transverse momenta, beam thrust, transverse thrust, spherocity, and $\mathcal{F}$-parameter, which are in particular sensitive to properties of the underlying event at small values of the $Z$-boson transverse momentum. The Sherpa event generator shows larger deviations from the measured observables than Pythia8 and Herwig7. Typically, all three Monte Carlo generators provide predictions that are in better agreement with the data at high $Z$-boson transverse momenta than at low $Z$-boson transverse momenta and for the observables that are less sensitive to the number of charged particles in the event.Comment: 36 pages plus author list + cover page (54 pages total), 14 figures, 4 tables, submitted to EPJC, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2014-0

Mass distribution in the Galactic Center based on interferometric astrometry of multiple stellar orbits

Galaxie

Ion beam analysis at cryogenic temperatures for polymer light emitting diodes

A review. The application of ion beam anal. on polymer light emitting diodes became possible by the development of a set-up which allows measurements at cryogenic temps. (10-30 K). The set-up is equipped with a sample holder which combines compatibility with a load-lock, necessary for introduction of samples under controlled conditions, and a good thermal contact. A no. of examples are reviewed in which interface stability and oxidn. effects in poly-LEDs are studied with Rutherford backscattering spectrometry and elastic recoil detectio

Ion beam analysis at cryogenic temperatures for polymer light emitting diodes

A review. The application of ion beam anal. on polymer light emitting diodes became possible by the development of a set-up which allows measurements at cryogenic temps. (10-30 K). The set-up is equipped with a sample holder which combines compatibility with a load-lock, necessary for introduction of samples under controlled conditions, and a good thermal contact. A no. of examples are reviewed in which interface stability and oxidn. effects in poly-LEDs are studied with Rutherford backscattering spectrometry and elastic recoil detectio

The XMM-Newton survey of the Small Magellanic Cloud: XMMUJ010633.1-731543 and XMMUJ010743.1-715953, two new Be/X-ray binary systems

In the course of the XMM-Newton survey of the Small Magellanic Cloud (SMC), two new bright X-ray sources were discovered exhibiting the spectral characteristics of high-mass X-ray binaries - but revealing only weak evidence for pulsations in just one of the objects (at 153 s in XMMUJ010743.1-715953). The accurate X-ray source locations permit the identification of these X-ray sources with Be stars, thereby strongly suggesting that these systems are new Be/X-ray binaries. From blue spectra the proposed classification for XMMUJ010633.1-731543 is B0.5-1Ve and for XMMUJ010743.1-715953 it is B2IV-Ve. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS

Degradation effects in polymer light emitting devices due to heat treatment

The characteristics of polymer light emitting diodes (PLEDs) (ITO/PPV/Ca) depend strongly on the conditions during preparation and operation. We studied the effects of heat treatment (during and after preparation) of PLEDs with OC1C10-PPV as active layer. PLEDs showed a reduction of both the current and the light output to 40 % after annealing for only 30 min at 65 °C. Effects on I-V characteristics were studied by measuring single carrier devices (hole- and electron-dominated devices). The current reduction after heat treatment can be ascribed to degradation of the ITO/PPV and the Ca/PPV interfaces

Degradation effects in poly para-phenylene vinylene derivatives due to controlled oxygen exposure

The influence of oxygen exposure on three chem. different poly(p-phenylenevinylene) (PPV) derivs. used in polymeric light emitting devices (PLEDs) has been investigated. During device prepn., PPV layers have been exposed to oxygen either in the dark or during the irradn. with visible light, before the cathode was applied. Device efficiency was studied by elec. and optical characterization and correlated to oxygen depth profiles measured with Elastic Recoil Detection Anal. (ERDA). Treatment with oxygen during light exposure leads to a decrease in current, light output and efficiency. It was found that two different PPV derivs. show the same current and light output redn. with different oxygen uptake. This behavior is explained in terms of a different chem. structure and the no. of structural defects (tolane-bisbenzyl moieties (TBBs)) incorporated. For two PPV derivs. treated with oxygen in the dark a redn. in current and light output was found, while the efficiency was unchanged. Another PPV deriv., however, shows a shift in the on-set voltage of the light output accompanied by an increased oxygen level at the PPV/Ca interface. It is concluded that after exposure in the dark, oxygen is incorporated in the PPV by Van der Waals interaction. During evapn. of the cathodes, oxygen will diffuse to the cathode and will be gettered by the calcium, which results in the formation of an electron injection barrie