@article{PollingerSchmittSanderetal.2017,
  author    = {Pollinger, Florian and Schmitt, Stefan and Sander, Dirk and Tian, Zhen and Kirschner, J{\"u}rgen and Vrdoljak, Pavo and Stadler, Christoph and Maier, Florian and Marchetto, Helder and Schmidt, Thomas and Sch{\"o}ll, Achim and Umbach, Eberhard},
  title     = {Nanoscale patterning, macroscopic reconstruction, and enhanced surface stress by organic adsorption on vicinal surfaces},
  series = {New Journal of Physics},
  volume    = {19},
  journal   = {New Journal of Physics},
  doi       = {10.1088/1367-2630/aa55b8},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-171947},
  year      = {2017},
  abstract  = {Self-organization is a promising method within the framework of bottom-up architectures to generate nanostructures in an efficient way. The present work demonstrates that self- organization on the length scale of a few to several tens of nanometers can be achieved by a proper combination of a large (organic) molecule and a vicinal metal surface if the local bonding of the molecule on steps is significantly stronger than that on low-index surfaces. In this case thermal annealing may lead to large mass transport of the subjacent substrate atoms such that nanometer-wide and micrometer-long molecular stripes or other patterns are being formed on high-index planes. The formation of these patterns can be controlled by the initial surface orientation and adsorbate coverage. The patterns arrange self-organized in regular arrays by repulsive mechanical interactions over long distances accompanied by a significant enhancement of surface stress. We demonstrate this effect using the planar organic molecule PTCDA as adsorbate and Ag(10 8 7) and Ag(775)surfaces as substrate. The patterns are directly observed by STM, the formation of vicinal surfaces is monitored by highresolution electron diffraction, the microscopic surface morphology changes are followed by spectromicroscopy, and the macroscopic changes of surface stress are measured by a cantilever bending method. The in situ combination of these complementary techniques provides compelling evidence for elastic interaction and a significant stress contribution to long-range order and nanopattern formation.},
  language  = {en}
}
@article{ElsaesserSchieblMukhinetal.2017,
  author    = {Els{\"a}sser, S. and Schiebl, M. and Mukhin, A. A. and Balbashov, A. M. and Pimenov, A. and Geurts, J.},
  title     = {Impact of temperature-dependent local and global spin order in \(R\)MnO\(_3\) compounds for spin-phonon coupling and electromagnon activity},
  series = {New Journal of Physics},
  volume    = {19},
  journal   = {New Journal of Physics},
  doi       = {10.1088/1367-2630/aa55ed},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-171978},
  year      = {2017},
  abstract  = {The orthorhombic rare-earth manganite compounds \(R\)MnO\(_3\) show a global magnetic order for \(T\) < \(T\)\(_N\), and several representatives are multiferroic with a cycloidal spin ground state order for \(T\) < \(T\)\(_c\)\(_y\)\(_c\)\(_l\) < \(T\)\(_N\) \(\approx\) 40 K. We deduce from the temperature dependence of spin-phonon coupling in Raman spectroscopy for a series of \(R\)MnO\(_3\) compounds that their spin order locally persists up to about twice \(T\)\(_N\). Along the same line, our observation of the persistence of the electromagnon in GdMnO\(_3\) up to \(T\) \(\approx\) 100 K is attributed to a local cycloidal spin order for \(T\) > \(T\)\(_c\)\(_y\)\(_c\)\(_l\), in contrast to the hitherto assumed incommensurate sinusoidal phase in the intermediate temperature range. The development of the magnetization pattern can be described in terms of an order-disorder transition at \(T\)\(_c\)\(_y\)\(_c\)\(_l\) within a pseudospin model of localized spin cycloids with opposite chirality.},
  language  = {en}
}
@article{SanchezThierschmannMolenkamp2017,
  author    = {S{\´a}nchez, Rafael and Thierschmann, Holger and Molenkamp, Laurens W.},
  title     = {Single-electron thermal devices coupled to a mesoscopic gate},
  series = {New Journal of Physics},
  volume    = {19},
  journal   = {New Journal of Physics},
  doi       = {10.1088/1367-2630/aa8b94},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172982},
  year      = {2017},
  abstract  = {We theoretically investigate the propagation of heat currents in a three-terminal quantum dot engine. Electron-electron interactions introduce state-dependent processes which can be resolved by energy-dependent tunneling rates. We identify the relevant transitions which define the operation of the system as a thermal transistor or a thermal diode. In the former case, thermal-induced charge fluctuations in the gate dot modify the thermal currents in the conductor with suppressed heat injection, resulting in huge amplification factors and the possible gating with arbitrarily low energy cost. In the latter case, enhanced correlations of the state-selective tunneling transitions redistribute heat flows giving high rectification coefficients and the unexpected cooling of one conductor terminal by heating the other one. We propose quantum dot arrays as a possible way to achieve the extreme tunneling asymmetries required for the different operations.},
  language  = {en}
}
@phdthesis{Then2017,
  author    = {Then, Patrick},
  title     = {Waveguide-based single molecule detection in flow},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-140548},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {In this work fluorescence-based single molecule detection at low concetration is investigated, with an emphasis on the usage of active transport and waveguides. Active transport allows to overcome the limits of diffusion-based systems in terms of the lowest detectable threshold of concentration. The effect of flow in single molecule experiments is investigated and a theoretical model is derived for laminar flow. Waveguides on the other hand promise compact detection schemes and show great potential for their possible integration into lab-on-a-chip applications. Their properties in single molecule experiments are analyzed with help of a method based on the reciprocity theorem of electromagnetic theory.},
  subject      = {Optik},
  language  = {en}
}
@article{SkryabinKartashovEgorovetal.2017,
  author    = {Skryabin, D.V. and Kartashov, Y.V. and Egorov, O.A. and Sich, M. and Chana, J.K. and Tapia Rodriguez, L.E. and Walker, P.M. and Clarke, E. and Royall, B. and Skolnick, M.S. and Krizhanovskii, D.N.},
  title     = {Backward Cherenkov radiation emitted by polariton solitons in a microcavity wire},
  series = {Nature Communications},
  volume    = {8},
  journal   = {Nature Communications},
  doi       = {10.1038/s41467-017-01751-6},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173046},
  year      = {2017},
  abstract  = {Exciton-polaritons in semiconductor microcavities form a highly nonlinear platform to study a variety of effects interfacing optical, condensed matter, quantum and statistical physics. We show that the complex polariton patterns generated by picosecond pulses in microcavity wire waveguides can be understood as the Cherenkov radiation emitted by bright polariton solitons, which is enabled by the unique microcavity polariton dispersion, which has momentum intervals with positive and negative group velocities. Unlike in optical fibres and semiconductor waveguides, we observe that the microcavity wire Cherenkov radiation is predominantly emitted with negative group velocity and therefore propagates backwards relative to the propagation direction of the emitting soliton. We have developed a theory of the microcavity wire polariton solitons and of their Cherenkov radiation and conducted a series of experiments, where we have measured polariton-soliton pulse compression, pulse breaking and emission of the backward Cherenkov radiation.},
  language  = {en}
}
@article{RudnoRudzińskiSyperekAndrezejewskietal.2017,
  author    = {Rudno-Rudziński, W. and Syperek, M. and Andrezejewski, J. and Maryński, A. and Misiewicz, J. and Somers, A. and H{\"o}fling, S. and Reithmaier, J. P. and Sęk, G.},
  title     = {Carrier delocalization in InAs/InGaAlAs/InP quantum-dash-based tunnel injection system for 1.55 μm emission},
  series = {AIP Advances},
  volume    = {7},
  journal   = {AIP Advances},
  number    = {1},
  doi       = {10.1063/1.4975634},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-181787},
  year      = {2017},
  abstract  = {We have investigated optical properties of hybrid two-dimensional-zero-dimensional (2D-0D) tunnel structures containing strongly elongated InAs/InP(001) quantum dots (called quantum dashes), emitting at 1.55 μm. These quantum dashes (QDashes) are separated by a 2.3 nm-width barrier from an InGaAs quantum well (QW), lattice matched to InP. We have tailored quantum-mechanical coupling between the states confined in QDashes and a QW by changing the QW thickness. By combining modulation spectroscopy and photoluminescence excitation, we have determined the energies of all relevant optical transitions in the system and proven the carrier transfer from the QW to the QDashes, which is the fundamental requirement for the tunnel injection scheme. A transformation between 0D and mixed-type 2D-0D character of an electron and a hole confinement in the ground state of the hybrid system have been probed by time-resolved photoluminescence that revealed considerable changes in PL decay time with the QW width changes. The experimental discoveries have been explained by band structure calculations in the framework of the eight-band k·p model showing that they are driven by delocalization of the lowest energy hole state. The hole delocalization process from the 0D QDash confinement is unfavorable for optical devices based on such tunnel injection structures.},
  language  = {en}
}
@article{RyczkoMisiewiczHoflingetal.2017,
  author    = {Ryczko, K. and Misiewicz, J. and Hofling, S. and Kamp, M. and Sęk, G.},
  title     = {Optimizing the active region of interband cascade lasers for passive mode-locking},
  series = {AIP Advances},
  volume    = {7},
  journal   = {AIP Advances},
  number    = {1},
  doi       = {10.1063/1.4973937},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-181790},
  year      = {2017},
  abstract  = {The work proposes possible designs of active regions for a mode-locked interband cascade laser emitting in the mid infrared. For that purpose we investigated the electronic structure properties of respectively modified GaSb-based type II W-shaped quantum wells, including the effect of external bias in order to simultaneously fulfil the requirements for both the absorber as well as the gain sections of a device. The results show that introducing multiple InAs layers in type II InAs/GaInSb quantum wells or introducing a tensely-strained GaAsSb layer into "W-shaped" type II QWs offers significant difference in optical transitions' oscillator strengths (characteristic lifetimes) of the two oppositely polarized parts of such a laser, being promising for utilization in mode-locked devices.},
  language  = {en}
}
@article{ThierschmannArnoldMittermuelleretal.2015,
  author    = {Thierschmann, H and Arnold, F and Mitterm{\"u}ller, M and Maier, L and Heyn, C and Hansen, W and Buhmann, H and Molenkamp, L W},
  title     = {Thermal gating of charge currents with Coulomb coupled quantum dots},
  series = {New Journal of Physics},
  volume    = {17},
  journal   = {New Journal of Physics},
  number    = {113003},
  doi       = {10.1088/1367-2630/17/11/113003},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-145196},
  year      = {2015},
  abstract  = {We have observed thermal gating, i.e. electrostatic gating induced by hot electrons. The effect occurs in a device consisting of two capacitively coupled quantum dots. The double dot system is coupled to a hot electron reservoir on one side (QD1), while the conductance of the second dot (QD2) is monitored. When a bias across QD2 is applied we observe a current which is strongly dependent on the temperature of the heat reservoir. This current can be either enhanced or suppressed, depending on the relative energetic alignment of the QD levels. Thus, the system can be used to control a charge current by hot electrons.},
  language  = {en}
}
@phdthesis{Fuchs2015,
  author    = {Fuchs, Franziska},
  title     = {Optical spectroscopy on silicon vacancy defects in silicon carbide},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-124071},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2015},
  abstract  = {This work sheds light on different aspects of the silicon vacancy in SiC: (1) Defect creation via irradiation is shown both with electrons and neutrons. Optical properties have been determined: the excitation of the vacancy is most efficient at excitation wavelengths between 720nm and 800nm. The PL decay yields a characteristic excited state lifetime of (6.3±0.6)ns. (2) Defect engineering, meaning the controlled creation of vacancies in SiC with varying neutron fluence. The defect density could be engineered over eight orders of magnitude. On the one hand, in the sample with highest emitter density, the huge PL signal could even be enhanced by factor of five via annealing mechanisms. On the other hand, in the low defect density samples, single defects with photostable room temperature NIR emission were doubtlessly proven. Their lifetime of around 7ns confirmed the value of the transient measurement. (3) Also electrical excitation of the defects has been demonstrated in a SiC LED structure. (4) The investigations revealed for the first time that silicon vacancies can even exist SiC nanocrystals down to sizes of about 60 nm. The defects in the nanocrystals show stable PL emission in the NIR and even magnetic resonance in the 600nm fraction. In conclusion, this work ascertains on the one hand basic properties of the silicon vacancy in silicon carbide. On the other hand, proof-of-principle measurements test the potential for various defect-based applications of the vacancy in SiC, and confirm the feasibility of e.g. electrically driven single photon sources or nanosensing applications in the near future.},
  subject      = {Siliciumcarbid},
  language  = {en}
}
@article{OPUS4-14339,
  title     = {Measurement of transverse energy-energy correlations in multi-jet events in pp collisions at \(\sqrt {s}\)=7 TeV using the ATLAS detector and determination of the strong coupling constant αs(m\(_{Z}\))},
  series = {Physics Letters B},
  volume    = {750},
  journal   = {Physics Letters B},
  organization    = {ATLAS Collaboration},
  doi       = {10.1016/j.physletb.2015.09.050},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-143398},
  pages     = {427-447},
  year      = {2015},
  abstract  = {High transverse momentum jets produced in pp collisions at a centre of mass energy of 7 TeV are used to measure the transverse energy-energy correlation function and its associated azimuthal asymmetry. The data were recorded with the ATLAS detector at the LHC in the year 2011 and correspond to an integrated luminosity of 158 pb\(^{-1}\). The selection criteria demand the average transverse momentum of the two leading jets in an event to be larger than 250 GeV. The data at detector level are well described by Monte Carlo event generators. They are unfolded to the particle level and compared with theoretical calculations at next-to-leading-order accuracy. The agreement between data and theory is good and provides a precision test of perturbative Quantum Chromodynamics at large momentum transfers. From this comparison, the strong coupling constant given at the Z   boson mass is determined to be αs(m\(_{Z}\))=0.1173±0.0010 (exp.) \(^{+0.0065}_{-0.0026}\) (theo.).},
  language  = {en}
}
@article{OPUS4-14337,
  title     = {Measurement of the branching ratio Γ(Λ\(^0_b\)→ψ(2S)Λ\(^0\))/Γ(Λ\(^0_b\)→J/ψΛ\(^0\)) with the ATLAS detector},
  series = {Physics Letters B},
  volume    = {751},
  journal   = {Physics Letters B},
  organization    = {ATLAS Collaboration},
  doi       = {10.1016/j.physletb.2015.10.009},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-143375},
  pages     = {63-80},
  year      = {2015},
  abstract  = {An observation of the View the Λ\(^0_b\)→ψ(2S)Λ\(^0\) decay and a comparison of its branching fraction with that of the Λ\(^0_b\)→J/ψΛ\(^0\) decay has been made with the ATLAS detector in proton-proton collisions at \(\sqrt {s}\)=8 TeV at the LHC using an integrated luminosity of 20.6 fb\(^{-1}\). The J/ψJ/ψ and ψ(2S) mesons are reconstructed in their decays to a muon pair, while the Λ\(^0\)→pπ\(^-\) decay is exploited for the Λ\(^0\) baryon reconstruction. The Λ\(^0_b\) baryons are reconstructed with transverse momentum p\(_T\)>10 GeV pT>10 GeV and pseudorapidity |η|<2.1. The measured branching ratio of the Λ\(^0_b\)→ψ(2S)Λ\(^0\) and Λ\(^0_b\)→J/ψΛ\(^0\) decays is Γ(Λ\(^0_b\)→ψ(2S)Λ\(^0\))/Γ(Λ\(^0_b\)→J/ψΛ\(^0\))=0.501±0.033(stat)±0.019(syst), lower than the expectation from the covariant quark model.},
  language  = {en}
}
@article{OPUS4-14423,
  title     = {Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detector},
  series = {Physics Letters B},
  volume    = {749},
  journal   = {Physics Letters B},
  organization    = {ATLAS Collaboration},
  doi       = {10.1016/j.physletb.2015.07.079},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-144231},
  pages     = {519-541},
  year      = {2015},
  abstract  = {A search for the associated production of the Higgs boson with a top quark pair is performed in multilepton final states using 20.3 fb\(^{-1}\) of proton-proton collision data recorded by the ATLAS experiment at \(\sqrt {s}\)=8 TeV at the Large Hadron Collider. Five final states, targeting the decays H→WW\(^{*}\), ττ, and ZZ\(^{*}\), are examined for the presence of the Standard Model (SM) Higgs boson: two same-charge light leptons (e or μ) without a hadronically decaying τ lepton; three light leptons; two same-charge light leptons with a hadronically decaying τ lepton; four light leptons; and one light lepton and two hadronically decaying τ leptons. No significant excess of events is observed above the background expectation. The best fit for the t\(\overline{t}\)H production cross section, assuming a Higgs boson mass of 125 GeV, is 2.1\(^{+1.4}_{-1.2}\) times the SM expectation, and the observed (expected) upper limit at the 95\% confidence level is 4.7 (2.4) times the SM rate. The p-value for compatibility with the background-only hypothesis is 1.8σ; the expectation in the presence of a Standard Model signal is 0.9σ.},
  language  = {en}
}
@article{OPUS4-14424,
  title     = {Measurement of exclusive γγ→ℓ\(^{+}\)ℓ\(^{-}\) production in proton-proton collisions at \(\sqrt {s}\)=7 TeV with the ATLAS detector},
  series = {Physics Letters B},
  volume    = {749},
  journal   = {Physics Letters B},
  organization    = {ATLAS Collaboration},
  doi       = {10.1016/j.physletb.2015.07.069},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-144247},
  pages     = {242-261},
  year      = {2015},
  abstract  = {This Letter reports a measurement of the exclusive γγ→ℓ\(^{+}\)ℓ\(^{-}\) (ℓ=e, μℓ=e, μ) cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of 4.6 fb\(^{-1}\). For the electron or muon pairs satisfying exclusive selection criteria, a fit to the dilepton acoplanarity distribution is used to extract the fiducial cross-sections. The cross-section in the electron channel is determined to be \(^{excl.}_{γγ→e^{+}e^{-}}\)=0.428 ± 0.035 (stat.) ± 0.018 (syst.) pb for a phase-space region with invariant mass of the electron pairs greater than 24 GeV, in which both electrons have transverse momentum p\(_{T}\)>12 GeV and pseudorapidity |η|<2.4. For muon pairs with invariant mass greater than 20 GeV, muon transverse momentum p\(_{T}\)>10 GeV and pseudorapidity |η|<2.4, the cross-section is determined to be \(^{excl.}_{γγ→μ^{+}μ^{-}}\) =0.628 ± 0.032 (stat.) ± 0.021 (syst.) pb. When proton absorptive effects due to the finite size of the proton are taken into account in the theory calculation, the measured cross-sections are found to be consistent with the theory prediction.},
  language  = {en}
}
@article{OPUS4-14422,
  title     = {Measurement of colour flow with the jet pull angle in t\(\overline{t}\) events using the ATLAS detector at \(\sqrt {s}\)=8 TeV},
  series = {Physics Letters B},
  volume    = {750},
  journal   = {Physics Letters B},
  organization    = {ATLAS Collaboration},
  doi       = {10.1016/j.physletb.2015.09.051},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-144229},
  pages     = {475-493},
  year      = {2015},
  abstract  = {The distribution and orientation of energy inside jets is predicted to be an experimental handle on colour connections between the hard-scatter quarks and gluons initiating the jets. This Letter presents a measurement of the distribution of one such variable, the jet pull angle. The pull angle is measured for jets produced in t\(\overline{t}\) events with one W boson decaying leptonically and the other decaying to jets using 20.3 fb\(^{-1}\) of data recorded with the ATLAS detector at a centre-of-mass energy of \(\sqrt {s}\)=8 TeV at the LHC. The jet pull angle distribution is corrected for detector resolution and acceptance effects and is compared to various models.},
  language  = {en}
}
@article{OPUS4-13827,
  title     = {Search for the \(X_b\) and other hidden-beauty states in the \(π^+π^-ϒ\)(1S) channel at ATLAS},
  series = {Physics Letters B},
  volume    = {740},
  journal   = {Physics Letters B},
  organization    = {ATLAS Collaboration},
  doi       = {10.1016/j.physletb.2014.11.055},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-138273},
  pages     = {199-217},
  year      = {2014},
  abstract  = {This Letter presents a search for a hidden-beauty counterpart of the X(3872) in the mass ranges of 10.05-10.31 GeV and 10.40-11.00 GeV, in the channel X\(_b\)→π\(^+\)π\(^-\)ϒ(1S)(→μ\(^+\)μ\(^-\)), using 16.2 fb\(^{-1}\) of s=8 TeV \(pp\) collision data collected by the ATLAS detector at the LHC. No evidence for new narrow states is found, and upper limits are set on the product of the X\(_b\) cross section and branching fraction, relative to those of the ϒ(2S), at the 95\% confidence level using the CLSCLS approach. These limits range from 0.8\% to 4.0\%, depending on mass. For masses above 10.1 GeV, the expected upper limits from this analysis are the most restrictive to date. Searches for production of the ϒ(1\(^3\)D\(_J\)), ϒ(10860), and ϒ(11020) states also reveal no significant signals.},
  language  = {en}
}
@article{ScholzSauerWiessneretal.2013,
  author    = {Scholz, M. and Sauer, C. and Wiessner, M. and Nguyen, N. and Scholl, A. and Reinert, F.},
  title     = {Structure formation in organic thin films observed in real time by energy dispersive near-edge x-ray absorption fine-structure spectroscopy},
  series = {New Journal of Physics},
  volume    = {15},
  journal   = {New Journal of Physics},
  number    = {083052},
  doi       = {10.1088/1367-2630/15/8/083052},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-129749},
  year      = {2013},
  abstract  = {We study the structure formation of 1,4,5,8-naphthalenetetracarboxylicacid- dianhydride (NTCDA) multilayer films on Ag(111) surfaces by energy dispersive near-edge x-ray absorption fine-structure spectroscopy (NEXAFS) and photoelectron spectroscopy. The time resolution of seconds of the method allows us to identify several sub-processes, which occur during the post-growth three-dimensional structural ordering, as well as their characteristic time scales. After deposition at low temperature the NTCDA molecules are preferentially flat lying and the films exhibit no long-range order. Upon annealing the molecules flip into an upright orientation followed by an aggregation in a transient phase which exists for several minutes. Finally, threedimensional islands are established with bulk-crystalline structure involving substantial mass transport on the surface and morphological roughening. By applying the Kolmogorov-Johnson-Mehl-Avrami model the activation energies of the temperature-driven sub-processes can be derived from the time evolution of the NEXAFS signal.},
  language  = {en}
}
@phdthesis{Foertig2013,
  author    = {F{\"o}rtig, Alexander},
  title     = {Recombination Dynamics in Organic Solar Cells},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-83895},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2013},
  abstract  = {Neben herk{\"o}mmlichen, konventionellen anorganischen Solarzellen — haupts{\"a}chlich auf Silizium basierend — ist die Organische Photovoltaik (OPV) auf dem besten Wege in naher Zukunft eine kosteng{\"u}nstige, umweltfreundliche, komplement{\"a}re Technolgie darzustellen. Die Produktionskosten, die Lebenszeit der Solarzellen sowie deren Wirkungsgrad m{\"u}ssen dabei weiter optimiert werden, um einen Markteintritt der OPV zu erm{\"o}glichen. Die vorliegende Arbeit befasst sich mit der Effizienz organischer Solarzellen und deren Limitierung durch die Rekombination von Ladungstr{\"a}gern. Um funktionsf{\"a}hige Zellen zu untersuchen, werden zeitaufgel{\"o}ste Experimente wie die Messung der transienten Photospannung (TPV), des transienten Photostroms (TPC), die Ladungsextraktion (CE) sowie die time delayed collection field (TDCF) Methode angewandt. Untersucht werden sowohl fl{\"u}ssig prozessierte als auch aufgedampfte Proben, unterschiedliche Materialzusammensetzungen und verschiedene Probengeometrien. Das Standardmaterialsystem der OPV, P3HT:PC61BM, wird bei verschiedenen emperaturen und Beleuchtungsst{\"a}rken auf die Lebenszeit und Dichte der photogenerierten Ladungstr{\"a}ger {\"u}berpr{\"u}ft. F{\"u}r den Fall spannungsunabh{\"a}ngiger Generation von Ladungstr{\"a}gern zeigt sich die Anwendbarkeit der Shockley-Gleichung auf organische Solarzellen. Des Weiteren wird ein konsistentes Modell erl{\"a}utert, welches den Idealtit{\"a}tsfaktor direkt mit der Rekombination von freien mit gefangenen, exponentiell verteilten Ladungstr{\"a}gern verkn{\"u}pft. Ein Ansatz, bekannt unter der Bezeichung j=V Rekonstruktion, erm{\"o}glicht es, den leistungslimitierenden Verlustmechanismus in unbehandelten und thermisch geheizten P3HT:PC61BM Solarzellen zu identifizieren. Dieses Verf ahren, welches TPV, CE und TDCF Messungen beinhaltet, wird auf Proben basierend auf dem neuartigen, low-band gap Polymer PTB7 in Verbindung mit dem Fulleren PC71BM ausgeweitet. W{\"a}hrend in der Zelle hergestellt aus reinem Chlorbenzol betr{\"a}chtliche geminale wie nichtgeminale Verluste zu beobachten sind, erleichtert die Zugabe eines L{\"o}sungsmittelzusatzes die Polaronenpaartrennung, was zu einer starken Reduktion geminaler Verluste f{\"u}hrt. In einer Kooperation mit dem IMEC Institut in Leuven, werden abschließend die beiden bedeutensten Probenarchitekturen organischer Solarzellen, die planare und die Misch{\"u}bergang Struktur, jeweils basierend auf CuPC und C60, bez{\"u}glich nichtgeminaler Rekombination und Ladungstr{\"a}gerverteilung miteinander verglichen. Neben den beiden experimentellen Techniken um TPV und CE werden makroskopische Simulationen herangezogen, um den Ursprung unterschiedlichen Voc vs. Lichtintensit{\"a}t-Verhaltens zu erkl{\"a}ren.},
  subject      = {Organische Solarzelle},
  language  = {en}
}
@phdthesis{Galmbacher2007,
  author    = {Galmbacher, Matthias},
  title     = {Lernen mit dynamisch-ikonischen Repr{\"a}sentationen aufgezeigt an Inhalten zur Mechanik},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-29271},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2007},
  abstract  = {Im Physikunterricht wurde lange Zeit die Bedeutung quantitativer Zusammenh{\"a}nge f{\"u}r das Physiklernen {\"u}berbewertet, qualitative Zusammenh{\"a}nge spielten dagegen eine eher untergeordnete Rolle. Dies f{\"u}hrte dazu, dass das Wissen der Sch{\"u}ler zumeist ober­fl{\"a}ch­lich blieb und nicht auf neue Situationen angewendet werden konnte. TIMSS und Pisa offenbarten diese Schwierigkeiten. In den Abschlussberichten wurde kritisiert, dass die Sch{\"u}ler kaum in der Lage seien, Lernstoff zu transferieren oder pro­blem­l{\"o}send zu denken. Um physikalische Abl{\"a}ufe deuten und entsprechende Probleme l{\"o}sen zu k{\"o}nnen, ist qua­litativ-konzeptuelles Wissen n{\"o}tig. Dieses kann, wie Forschungs­ergebnisse belegen, am besten durch die konstruktivistisch motivierte Gestaltung von Lern­situationen sowie durch die Inte­gration externer Repr{\"a}sentationen von Versuchs­aussagen in den Schul­unter­richt er­reicht werden. Eine konkrete Umsetzung dieser Bedingungen stellt der Ein­satz rechner­gest{\"u}tzter Experimente dar, der heutzutage ohne allzu großen technischen Aufwand rea­lisiert werden kann. Diese Experimente erleichtern es dem Lernenden, durch den direk­ten Umgang mit realen Abl{\"a}ufen, physikalische Konzepte zu erschließen und somit qua­litative Zusammenh{\"a}nge zu verstehen. W{\"a}hrend man lange Zeit von einer grunds{\"a}tzlichen Lernwirksamkeit animierter Lern­um­gebungen ausging, zeigen dagegen neuere Untersuchungen eher Gegenteiliges auf. Sch{\"u}ler m{\"u}ssen offensichtlich erst lernen, wie mit multicodierten Re­pr{\"a}­sentationen zu arbeiten ist. Die vorliegende Arbeit will einen Beitrag dazu leisten, he­raus­zufinden, wie lernwirksam sogenannte dynamisch-ikonische Repr{\"a}sentationen (DIR) sind, die physikalische Gr{\"o}ßen vor dem Hintergrund konkreter Versuchsabl{\"a}ufe visuali­sieren. Dazu bearbeiteten im Rahmen einer DFG-Studie insgesamt 110 Sch{\"u}ler jeweils 16 Projekte, in denen mechanische Konzepte (Ort, Geschwindigkeit, Beschleu­nigung und Kraft) aufgegriffen wurden. Es zeigte sich, dass die Probanden mit den ein­ge­setzten DIR nicht erfolgreicher lernen konnten als ver­gleich­bare Sch{\"u}ler, die die gleichen Lerninhalte ohne die Unter­st{\"u}tzung der DIR erarbeiteten. Im Gegen­teil: Sch{\"u}ler mit einem geringen visuellen Vorstellungsverm{\"o}gen schnitten aufgrund der Darbietung einer zus{\"a}tzlichen Codierung schlechter ab als ihre Mit­sch{\"u}ler. Andererseits belegen Untersuchungen von Blaschke, dass solche Repr{\"a}sen­ta­tionen in der Erarbeitungsphase einer neu entwickelten Unter­richts­kon­zep­tion auch und gerade von schw{\"a}cheren Sch{\"u}lern konstruktiv zum Wissens­erwerb genutzt werden konnten. Es scheint also, dass die Lerner zun{\"a}chst Hilfe beim Umgang mit neuartigen Re­pr{\"a}­sen­ta­tions­formen ben{\"o}tigen, bevor sie diese f{\"u}r den weiteren Aufbau ad{\"a}qua­ter physi­ka­lischer Modelle nutzen k{\"o}nnen. Eine experimentelle Unter­suchung mit Sch{\"u}­lern der 10. Jahrgangsstufe best{\"a}tigte diese Vermutung. Hier lernten 24 Probanden in zwei Gruppen die mechanischen Konzepte zu Ort, Geschwin­dig­keit und Beschleunigung kennen, bevor sie im Unter­richt behandelt wurden. W{\"a}hrend die Teil­nehmer der ersten Gruppe nur die Simulationen von Bewegungsabl{\"a}ufen und die zuge­h{\"o}rigen Liniendiagramme sahen, wurden f{\"u}r die zweite Gruppe unterst{\"u}tzend DIR eingesetzt, die den Zusammenhang von Bewe­gungs­ablauf und Linien­diagramm veranschaulichen sollten. In beiden Gruppen war es den Probanden m{\"o}glich, Fragen zu stellen und Hilfe von einem Tutor zu erhalten. Die Ergebnis­se zeigten auf, dass es den Sch{\"u}lern durch diese Maßnahme erm{\"o}glicht wurde, die DIR erfolgreich zum Wissens­er­werb einzusetzen und sig­nifikant besser abzuschneiden als die Teilnehmer in der Kon­troll­­gruppe. In einer weiteren Untersuchung wurde abschließend der Frage nachgegangen, ob DIR unter Anleitung eines Tutors eventuell bereits in der Unterstufe sinnvoll eingesetzt werden k{\"o}nnen. Ausgangspunkt dieser {\"U}berlegung war die Tatsache, dass mit der Einf{\"u}hrung des neuen bayerischen G8-Lehrplans wesentliche Inhalte, die Bestand­teil der vorherigen Untersuchungen waren, aus dem Physik­unterricht der 11. Jgst. in die 7. Jahrgangsstufe verlegt wurden. So bot es sich an, mit den Inhalten auch die DIR in der Unterstufe ein­zusetzen. Die Un­tersuchungen einer quasiexperimentellen Feldstudie in zwei siebten Klassen belegten, dass die betrachte­ten Repr{\"a}sentationen beim Aufbau entsprechender Kon­zepte keinesfalls hinderlich, sondern sogar f{\"o}rder­lich sein d{\"u}rften. Denn die Sch{\"u}ler­gruppe, die mit Hilfe der DIR lernte, schnitt im direkten hypothesenpr{\"u}fenden Vergleich mit der Kontrollklasse deutlich besser ab. Ein Kurztest, der die Nachhaltigkeit des Gelernten nach etwa einem Jahr {\"u}berpr{\"u}fen sollte, zeigte zudem auf, dass die Sch{\"u}ler der DIR-Gruppe die Konzepte, die unter Zuhilfenahme der DIR erarbeitet wurden, im Vergleich zu Sch{\"u}lern der Kontrollklasse und zu Sch{\"u}lern aus 11. Klassen insgesamt {\"u}berraschend gut verstanden und behalten hatten.},
  subject      = {Multimedia},
  language  = {de}
}