TY - JOUR A1 - Gardiner, Lauren M. A1 - Kocyan, Alexander A1 - Motes, Martin A1 - Roberts, David L. A1 - Emerson, Brent C. T1 - Molecular phylogenetics of Vanda and related genera (Orchidaceae) JF - Botanical journal of the Linnean Society N2 - The genus Vanda and its affiliated taxa are a diverse group of horticulturally important species of orchids occurring mainly in South-East Asia, for which generic limits are poorly defined. Here, we present a molecular study using sequence data from three plastid DNA regions. It is shown that Vanda s.l. forms a clade containing approximately 73 species, including the previously accepted genera Ascocentrum, Euanthe, Christensonia, Neofinetia and Trudelia, and the species Aerides flabellata. Resolution of the phylogenetic relationships of species in Vanda s.l. is relatively poor, but existing morphological classifications for Vanda are incongruent with the results produced. Some novel species relationships are revealed, and a new morphological sectional classification is proposed based on support for these groupings and corresponding morphological characters shared by taxa and their geographical distributions. The putative occurrence of multiple pollination syndromes in this group of taxa, combined with complex biogeographical history of the South-East Asian region, is discussed in the context of these results.(c) 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173, 549-572. KW - Aeridinae KW - Ascocentrum KW - classification KW - Euanthe KW - matK KW - morphology KW - Neofinetia KW - psbA-trnH KW - trnL KW - trnL-F Y1 - 2013 U6 - https://doi.org/10.1111/boj.12102 SN - 0024-4074 SN - 1095-8339 VL - 173 IS - 4 SP - 549 EP - 572 PB - Wiley-Blackwell CY - Hoboken ER - TY - GEN A1 - Junginger, Mathias A1 - Kübel, Christian A1 - Schacher, Felix H. A1 - Müller, Axel H. E. A1 - Taubert, Andreas T1 - Crystal structure and chemical composition of biomimetic calcium phosphate nanofibers N2 - Calcium phosphate nanofibers with a diameter of only a few nanometers and a cotton-ball-like aggregate morphology have been reported several times in the literature. Although fiber formation seems reproducible in a variety of conditions, the crystal structure and chemical composition of the fibers have been elusive. Using scanning transmission electron microscopy, low dose electron (nano)diffraction, energy-dispersive X-ray spectroscopy, and energy-filtered transmission electron microscopy, we have assigned crystal structures and chemical compositions to the fibers. Moreover, we demonstrate that the mineralization process yields true polymer/calcium phosphate hybrid materials where the block copolymer template is closely associated with the calcium phosphate. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 244 KW - air-water-interface KW - polycationic monolayer KW - mineralization beneath KW - block-copolymers KW - aqueous-solution KW - morphology KW - orthophosphates KW - biomaterials KW - nucleation KW - clusters Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-95176 SP - 11301 EP - 11308 ER - TY - GEN A1 - Ott, Susan A1 - Höhle, Barbara T1 - Verb inflection in German-learning children with typical and atypical language acquisition BT - the impact of subsyllabic frequencies T2 - Journal of Child Language N2 - Previous research has shown that high phonotactic frequencies facilitate the production of regularly inflected verbs in English-learning children with specific language impairment (SLI) but not with typical development (TD). We asked whether this finding can be replicated for German, a language with a much more complex inflectional verb paradigm than English. Using an elicitation task, the production of inflected nonce verb forms (3 rd person singular with -t suffix) with either high- or low-frequency subsyllables was tested in sixteen German-learning children with SLI (ages 4;1–5 ;1), sixteen TD-children matched for chronological age (CA) and fourteen TD- children matched for verbal age (VA) (ages 3;0–3 ;11). The findings revealed that children with SLI, but not CA- or VA-children, showed differential performance between the two types of verbs, producing more inflectional errors when the verb forms resulted in low-frequency subsyllables than when they resulted in high-frequency subsyllables, replicating the results from English-learning children. T3 - Zweitveröffentlichungen der Universität Potsdam : Humanwissenschaftliche Reihe - 530 KW - english past tense KW - phonotactic probability KW - sentence repetition KW - nonword repetition KW - speaking children KW - impairment KW - morphology KW - infants KW - speech KW - words Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-416475 SN - 1866-8364 IS - 530 ER - TY - THES A1 - Pingel, Patrick T1 - Morphology, charge transport properties, and molecular doping of thiophene-based organic semiconducting thin films T1 - Morphologie, Ladungstransporteigenschaften und molekulares Dotieren thiophenbasierter organischer Halbleiterschichten N2 - Organic semiconductors combine the benefits of organic materials, i.e., low-cost production, mechanical flexibility, lightweight, and robustness, with the fundamental semiconductor properties light absorption, emission, and electrical conductivity. This class of material has several advantages over conventional inorganic semiconductors that have led, for instance, to the commercialization of organic light-emitting diodes which can nowadays be found in the displays of TVs and smartphones. Moreover, organic semiconductors will possibly lead to new electronic applications which rely on the unique mechanical and electrical properties of these materials. In order to push the development and the success of organic semiconductors forward, it is essential to understand the fundamental processes in these materials. This thesis concentrates on understanding how the charge transport in thiophene-based semiconductor layers depends on the layer morphology and how the charge transport properties can be intentionally modified by doping these layers with a strong electron acceptor. By means of optical spectroscopy, the layer morphologies of poly(3-hexylthiophene), P3HT, P3HT-fullerene bulk heterojunction blends, and oligomeric polyquaterthiophene, oligo-PQT-12, are studied as a function of temperature, molecular weight, and processing conditions. The analyses rely on the decomposition of the absorption contributions from the ordered and the disordered parts of the layers. The ordered-phase spectra are analyzed using Spano’s model. It is figured out that the fraction of aggregated chains and the interconnectivity of these domains is fundamental to a high charge carrier mobility. In P3HT layers, such structures can be grown with high-molecular weight, long P3HT chains. Low and medium molecular weight P3HT layers do also contain a significant amount of chain aggregates with high intragrain mobility; however, intergranular connectivity and, therefore, efficient macroscopic charge transport are absent. In P3HT-fullerene blend layers, a highly crystalline morphology that favors the hole transport and the solar cell efficiency can be induced by annealing procedures and the choice of a high-boiling point processing solvent. Based on scanning near-field and polarization optical microscopy, the morphology of oligo-PQT-12 layers is found to be highly crystalline which explains the rather high field-effect mobility in this material as compared to low molecular weight polythiophene fractions. On the other hand, crystalline dislocations and grain boundaries are identified which clearly limit the charge carrier mobility in oligo-PQT-12 layers. The charge transport properties of organic semiconductors can be widely tuned by molecular doping. Indeed, molecular doping is a key to highly efficient organic light-emitting diodes and solar cells. Despite this vital role, it is still not understood how mobile charge carriers are induced into the bulk semiconductor upon the doping process. This thesis contains a detailed study of the doping mechanism and the electrical properties of P3HT layers which have been p-doped by the strong molecular acceptor tetrafluorotetracyanoquinodimethane, F4TCNQ. The density of doping-induced mobile holes, their mobility, and the electrical conductivity are characterized in a broad range of acceptor concentrations. A long-standing debate on the nature of the charge transfer between P3HT and F4TCNQ is resolved by showing that almost every F4TCNQ acceptor undergoes a full-electron charge transfer with a P3HT site. However, only 5% of these charge transfer pairs can dissociate and induce a mobile hole into P3HT which contributes electrical conduction. Moreover, it is shown that the left-behind F4TCNQ ions broaden the density-of-states distribution for the doping-induced mobile holes, which is due to the longrange Coulomb attraction in the low-permittivity organic semiconductors. N2 - Organische Halbleiter kombinieren die molekulare Vielfalt und Anpassbarkeit, die mechanische Flexibilität und die preisgünstige Herstellung und Verarbeitung von Kunststoffen mit fundamentalen Halbleitereigenschaften wie Lichtabsorption und -emission und elektrischer Leitfähigkeit. Unlängst finden organische Leuchtdioden Anwendung in den Displays von TV-Geräten und Smartphones. Für die weitere Entwicklung und den Erfolg organischer Halbleiter ist das Verständnis derer physikalischer Grundlagen unabdingbar. Ein für viele Bauteile fundamentaler Prozess ist der Transport von Ladungsträgern in der organischen Schicht. Die Ladungstransporteigenschaften werden maßgeblich durch die Struktur dieser Schicht bestimmt, z.B. durch den Grad der molekularen Ordnung, die molekulare Verbindung von kristallinen Domänen und durch Defekte der molekularen Packung. Mittels optischer Spektroskopie werden in dieser Arbeit die temperatur-, molekulargewichts- und lösemittelabhängigen Struktureigenschaften poly- und oligothiophenbasierter Schichten untersucht. Dabei basiert die Analyse der Absorptionsspektren auf der Zerlegung in die spezifischen Anteile geordneten und ungeordneten Materials. Es wird gezeigt, dass sich hohe Ladungsträgerbeweglichkeiten dann erreichen lassen, wenn der Anteil der geordneten Bereiche und deren molekulare Verbindung in den Schichten möglichst hoch und die energetische Unordnung in diesen Bereichen möglichst klein ist. Der Ladungstransport in organischen Halbleitern kann außerdem gezielt beeinflusst werden, indem die Ladungsträgerdichte und die elektrische Leitfähigkeit durch molekulares Dotieren, d.h. durch das Einbringen von Elektronenakzeptoren oder -donatoren, eingestellt werden. Obwohl der Einsatz dotierter Schichten essentiell für effiziente Leuchtdioden und Solarzellen ist, ist der Mechanismus, der zur Erzeugung freier Ladungsträger im organischen Halbleiter führt, derzeit unverstanden. In dieser Arbeit wird der Ladungstransfer zwischen dem prototypischen Elektronendonator P3HT und dem Akzeptor F4TCNQ untersucht. Es wird gezeigt, dass, entgegen verbreiteter Vorstellungen, fast alle F4TCNQ-Akzeptoren einen ganzzahligen Ladungstransfer mit P3HT eingehen, aber nur 5% dieser Paare dissoziieren und einen beweglichen Ladungsträger erzeugen, der zur elektrischen Leitfähigkeit beiträgt. Weiterhin wird gezeigt, dass die zurückgelassenen F4TCNQ-Akzeptorionen Fallenzustände für die beweglichen Ladungsträger darstellen und so die Ladungsträgerbeweglichkeit in P3HT bei schwacher Dotierung absinkt. Die elektrischen Kenngrößen Ladungsträgerkonzentration, Beweglichkeit und Leitfähigkeit von F4TCNQ-dotierten P3HT-Schichten werden in dieser Arbeit erstmals in weiten Bereichen verschiedener Akzeptorkonzentrationen untersucht. KW - Polythiophen KW - organische Elektronik KW - molekulares Dotieren KW - organischer Halbleiter KW - Morphologie KW - polythiohene KW - organic electronics KW - molecular doping KW - organic semiconductor KW - morphology Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-69805 ER - TY - JOUR A1 - Sauter, Tilman A1 - Kratz, Karl A1 - Lendlein, Andreas T1 - Pore-size distribution controls shape-memory properties on the macro- and microscale of polymeric foams JF - Macromolecular chemistry and physics N2 - Open porous foams with identical foam density but different pore-size distributions (bimodal or monomodal) are prepared from a shape-memory polyetherurethane (PEU) by thermally induced phase separation. The shape-memory effect of the two PEU foams is explored by cyclic thermomechanical compression tests and microstructural analysis. The obtained results reveal that the PEU foam with a bimodal pore-size distribution exhibits an increased shape-recovery under stress-free conditions, both on the macro- (foam level) as well as the microscale (pore level). While bimodal pore-size distributions induce microscale bending during compression, buckling occurs in foams with monomodal pore-size distributions, leading to both a reduced and delayed shape recovery. KW - microstructure KW - morphology KW - polymer foams KW - pore-size distribution KW - shape-memory polymers Y1 - 2013 U6 - https://doi.org/10.1002/macp.201300062 SN - 1022-1352 VL - 214 IS - 11 SP - 1184 EP - 1188 PB - Wiley-VCH CY - Weinheim ER -