Conductance-strain behavior in silver-nanowire composites: network properties of a tunable strain sensor

Highly flexible and conductive nano-composite materials are promising candidates for stretchable and flexible electronics. We report on the strain–resistance relation of a silver-nanowire photopolymer composite during repetitive stretching. Resistance measurements reveal a gradual change of the hysteretic resistance curves towards a linear and non-hysteretic behavior. Furthermore, a decrease in resistance and an increase in electrical sensitivity to strain over the first five stretching cycles can be observed. Sensitivity gauge factors between 10 and 500 at 23% strain were found depending on the nanowire concentration and stretching cycle. We model the electrical behavior of the investigated silver nanowire composites upon repetitive stretching considering the strain induced changes in the local force distribution within the polymer matrix and the tunnel resistance between the nanowires by using a Monte Carlo method

Electrical and network properties of flexible silver-nanowire composite electrodes under mechanical strain

Flexible and conductive silver-nanowire photopolymer composites are fabricated and studied under mechanical strain. The initial resistances of the unstretched flexible composites are between 0.27 Ω mm−1 and 1.2 Ω mm−1 for silver-nanowire concentrations between 120 μg cm−2 and 40 μg cm−2. Stretching of the samples leads to an increased resistance by a factor of between 72 for 120 μg cm−2 and 343 for 40 μg cm−2 at elongations of 23%. In order to correlate network morphology and electrical properties, micrographs are recorded during stretching. The Fiber Image Network Evaluation (FINE) algorithm determines morphological silver-nanowire network properties under stretching. For unstretched and stretched samples, an isotropic nanowire network is found with only small changes in fiber orientation. Monte-Carlo simulations on 2D percolation networks of 1D conductive wires and the corresponding network resistance due to tunneling of electrons at nanowire junctions confirm that the elastic polymer matrix under strain exhibits forces in agreement with Hooke's law. By variation of a critical force distribution the resistance curves are accurately reproduced. This results in a model that is dominated by quantum-mechanical tunneling at nanowire junctions explaining the electrical behavior and the sensitivity of nanowire-composites with different filler concentrations under mechanical strain

Phonon spectra of pure and acceptor doped BaZrO3 investigated with visible and UV Raman spectroscopy

We report results from visible and UV Raman spectroscopy studies of the phonon spectra of a polycrystalline sample of the prototypical perovskite type oxide BaZrO3 and a 500 nm thick film of its Y-doped, proton conducting, counterpart BaZr0.8Y0.2O2.9. Analysis of the Raman spectra measured using different excitation energies (between 3.44 eV and 5.17 eV) reveals the activation of strong resonance Raman effects involving all lattice vibrational modes. Specifically, two characteristic energies were identified for BaZrO3, one around 5 eV and one at higher energy, respectively, and one for BaZr0.8Y0.2O2.9, above 5 eV. Apart from the large difference in spectral intensity between the non-resonant and resonant conditions, the spectra are overall similar to each other, suggesting that the vibrational spectra of the perovskites are stable when investigated using an UV laser as excitation source. These results encourage further use of UV Raman spectroscopy as a novel approach for the study of lattice vibrational dynamics and local structure in proton conducting perovskites, and open up for, e.g., time-resolved experiments on thin films targeted at understanding the role of lattice vibrations in proton transport in these kinds of materials

Optically Induced Avoided Crossing in Graphene

Degenerate states in condensed matter are frequently the cause of unwanted fluctuations, which prevent the formation of ordered phases and reduce their functionalities. Removing these degeneracies has been a common theme in materials design, pursued for example by strain engineering at interfaces. Here, we explore a non-equilibrium approach to lift degeneracies in solids. We show that coherent driving of the crystal lattice in bi- and multilayer graphene, boosts the coupling between two doubly-degenerate modes of E1u and E2g symmetry, which are virtually uncoupled at equilibrium. New vibronic states result from anharmonic driving of the E1u mode to large amplitdues, boosting its coupling to the E2g mode. The vibrational structure of the driven state is probed with time-resolved Raman scattering, which reveals laser-field dependent mode splitting and enhanced lifetimes. We expect this phenomenon to be generally observable in many materials systems, affecting the non-equilibrium emergent phases in matter.Comment: 13 pages, 4 figure

Historische Pragmatik

›Historische Pragmatik‹ bezeichnet ein eigenständiges Teilgebiet der Pragmatik, das sich seit den 1990er Jahren stark entwickelt und ausdifferenziert hat. Es befasst sich im Wesentlichen mit pragmatischen Fragestellungen an historischem Sprachmaterial. Fragen der Sprachverwendung werden zusammengebracht mit Fragen der historischen Linguistik zu früheren Sprachformen, zur Entwicklung von Sprache und Sprachen und somit ganz generell zu den Fragen des Sprachwandels. Die historische Pragmatik setzt in den meisten Fällen ein Verständnis von Pragmatik voraus, bei dem es ganz wesentlich auch um den sozialen Kontext der Sprachverwendung geht. Dieses Verständnis von Pragmatik wird oft unter dem Begriff ›Soziopragmatik‹ subsumiert und orientiert sich nicht unwesentlich an Arbeiten in der Soziologie und Anthropologie

Photoluminescence of Fully Inorganic Colloidal Gold Nanocluster and Their Manipulation Using Surface Charge Effects

International audienceFully inorganic, colloidal gold nanoclusters (NCs) constitute a new class of nanomaterials that are clearly distinguishable from their commonly studied metal–organic ligand-capped counterparts. As their synthesis by chemical methods is challenging, details about their optical properties remain widely unknown. In this work, laser fragmentation in liquids is performed to produce fully inorganic and size-controlled colloidal gold NCs with monomodal particle size distributions and an fcc-like structure. Results reveal that these NCs exhibit highly pronounced photoluminescence with quantum yields of 2%. The emission behavior of small (2–2.5 nm) and ultrasmall (<1 nm) NCs is significantly different and dominated by either core- or surface-based emission states. It is further verified that emission intensities are a function of the surface charge density, which is easily controllable by the pH of the surrounding medium. This experimentally observed correlation between surface charge and photoluminescence emission intensity is confirmed by density functional theoretical simulations, demonstrating that fully inorganic NCs provide an appropriate material to bridge the gap between experimental and computational studies of NCs. The presented study deepens the understanding of electronic structures in fully inorganic colloidal gold NCs and how to systematically tune their optical properties via surface charge density and particle size