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Nucleation and Growth of Magnetron-Sputtered Ag Nanoparticles as Witnessed by Time-Resolved Small Angle X-Ray Scattering
No full textKinetic aspects of the synthesis of Ag nanoparticles (NPs) by magnetron sputtering are studied by in situ and time-resolved small angle X-ray scat-tering (SAXS). Part of the NPs are found to become confined within a capture zone at 1–10 mm from the surface of the target and circumscribed by the plasma ring. Three regimes of the NP growth are identified: 1) early growth at which the average NP diameter rapidly increases to 90 nm; 2) cycling instabilities at which the SAXS signal periodically fluctuates either due to expelling of large NPs from the capture zone or due to the axial rotation of the NP cloud; and 3) steady-state synthesis at which stable synthesis of the NPs is achieved. The NP confinement within the capture zone is driven by the balance of forces, the electrostatic force being dominant. On reaching the critical size, large NPs acquire an excessive charge and become expelled from the capture zone via the electrostatic interactions. As a result, signifi-cant NP deposits are formed on the inner walls of the aggregation chamber as well as in the central area of the targe
Crystal-structure of active layers of small molecule organic photovoltaics before and after solvent vapor annealing
No full textIt is demonstrated by a detailed structural analysis that the crystallinity and the efficiency of small molecule based organic photovoltaics can be tuned by solvent vapor annealing (SVA). Blends made of the small molecule donor 2,2′-[(3,3′″,3″″,4′-tetraoctyl[2,2′:5′,2″:5″,2′″:5′″,2″″-quinquethiophene]-5,5″″-diyl)bis[(Z)-methylidyne(3-ethyl-4-oxo-5,2-thiazolidinediylidene)]]bis-propanedinitrile (DRCN5T) and the acceptor [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) were annealed using solvent vapors with either a high solubility for the donor (tetrahydrofuran), the acceptor (carbon disulfide) or both (chloroform). The samples were analyzed by grazing-incidence wide-angle X-ray scattering (GIWAXS), electron diffraction, X-ray pole figures, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). A phase separation of DRCN5T and PC71BM is induced by SVA leading to a crystallization of DRCN5T and the formation of a DRCN5T enriched layer. The DRCN5T crystallites possess the two dimensional oblique crystal system with the lattice parameters a = 19.2 Å, c = 27.1 Å, and β = 111.1° for the chloroform case. No major differences in the crystal structure for the other solvent vapors were observed. However, the solvent choice strongly influences the size of the DRCN5T enriched layer. Missing periodicity in the [010]-direction leads to the extinction of all Bragg reflections with k ≠ 0. The annealed samples are randomly orientated with respect to the normal of the substrate (fiber texture)
Exploration of iron ligand modes in dimeric iron (II) complexes by nuclear resonance scattering
No full textThe vibronic properties of two dimeric iron (II) high-spin complexes [5CpFeX]2 (5Cp = Pentaisopropyl-cyclopentadienyl, X = OH-(1), Br-(2)) have been studied using nuclear inelastic scattering (NIS). In order to assign the experimentally observed bands to the particular modes, theoretical calculations using density functional theory (DFT) have been performed based on the structural data obtained by X-ray crystallography. The calculated partial density of vibrational states (pDOS) reproduces the experimental data. Thus, we were able to assign almost each of the experimentally observed NIS bands to their corresponding molecular vibrational modes
Direct 2D spatial-coherence determination using the Fourier-analysis method: Multi-parameter characterization of the P04 beamline at PETRA III
No full textWe present a systematic 2D spatial-coherence analysis of the soft-X-ray beamline P04 at PETRA III for various beamline configurations. The influence of two different beam-defining apertures on the spatial coherence properties of the beam is discussed and optimal conditions for coherence-based experiments are found. A significant degradation of the spatial coherence in the vertical direction has been measured and sources of this degradation are identified and discussed. The Fourier-analysis method, which gives fast and simple access to the 2D spatial coherence function of the X-ray beam, is used for the experiment. Here, we exploit the charge scattering of a disordered nanodot sample allowing the use of arbitrary X-ray photon energies with this method
Microstructural and Phase Analysis of an Additively Manufactured Intermetallic TiAl Alloy using Metallographic Techniques and High-Energy X-Rays
No full textDue to the unique combination of low density and their excellent properties-profile at elevated temperatures, intermetallic γ-titanium aluminide based alloys are a promising structural material for applications in aviation and the automotive industry. Additive manufacturing of a TiAl alloy of nominal composition Ti-48Al-2Cr-2Nb (in at. %), using electron beam melting, resulted in a banded and anisotropic microstructure. In this work, the present microstructure was examined by means of visible light and scanning electron microscopy with regard to morphology and phase distribution. Furthermore, a three-dimensional representation of the microstructure was generated based on differently oriented metallographic specimens. Phase analysis was performed using high-energy X-ray diffraction in order to quantitatively determine present phase fractions and to relate them to findings from microstructural analysis
Search for a charged Higgs boson decaying into top and bottom quarks in events with electrons or muons in proton-proton collisions at s√= 13 TeV
No full textA search is presented for a charged Higgs boson heavier than the top quark, produced in association with a top quark, or with a top and a bottom quark, and decaying into a top-bottom quark-antiquark pair. The search is performed using proton-proton collision data collected by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. Events are selected by the presence of a single isolated charged lepton (electron or muon) or an opposite-sign dilepton (electron or muon) pair, categorized according to the jet multiplicity and the number of jets identified as originating from b quarks. Multivariate analysis techniques are used to enhance the discrimination between signal and background in each category. The data are compatible with the standard model, and 95% confidence level upper limits of 9.6–0.01 pb are set on the charged Higgs boson production cross section times branching fraction to a top-bottom quark-antiquark pair, for charged Higgs boson mass hypotheses ranging from 200 GeV to 3 TeV. The upper limits are interpreted in different minimal supersymmetric extensions of the standard model
Evidence for WW production from double-parton interactions in proton-proton collisions at 13 TeV
No full textA search for WW production from double-parton scattering processes using same-charge electron-muon and dimuon events is reported, based on proton-proton collision data collected at a center-of-mass energy of 13 TeV. The analyzed data set corresponds to an integrated luminosity of 77.4 fb, collected using the CMS detector at the LHC in 2016 and 2017. Multivariate classifiers are used to discriminate between the signal and the dominant background processes. A maximum likelihood fit is performed to extract the signal cross section. This leads to the first evidence for WW production via double-parton scattering, with a significance of 3.9 standard deviations. The measured inclusive cross section is 1.41 0.28 (stat) 0.28 (syst) pb
Status of the WHIZARD generator for linear collider
No full textThis summarizes the talk given at the LCWS 2019 conference in Sendai, Japan, on the progress of the WHIZARD event generator in terms of new physics features and technical improvements relevant for the physics programme of future lepton and especially linear colliders. It takes as a reference the version 2.8.2 released in October 2019, and also takes into account the development until version 2.8.3 to be released in February 2020
Development of a test DAQ system for the CMS Phase-2 outer tracker upgrade
No full textThe CMS detector at the LHC is foreseen to experience a major upgrade in order to cope with increased radiation flux due to the high-luminosity operation phase of the accelerator. The CMS tracker will be replaced completely, introducing a new module concept in the outer part of the subsystem, which will exploit the strong magnetic field inside the CMS detector to select high transverse momentum particles locally and send the corresponding information to the triggering system thus enhancing the efficiency of the latter.In order to allow for module prototyping and production testing, an intermediate DAQ system, referred to as μDTC, was developed in the scope of this thesis. The system allows for prototype configuration, control, monitoring and read-out, and provides all the necessary infrastructure for the module qualification. This thesis describes the upgrade project with a focus on the existing module prototypes and the structure of the FPGA firmware developed for the μDTC. A sequence of test beam measurement campaigns was carried out using the aforementioned DAQ system, and the results obtained from two of them are described in detail in the text
