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

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

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

Catalytic Oxygenation of Hydrocarbons by Mono-mu-oxo Dicopper(II) Species Resulting from O-O Cleavage of Tetranuclear Cu-I/Cu-II Peroxo Complexes

One of the challenges of catalysis is the transformation of inert C−H bonds to useful products. Copper-containing monooxygenases play an important role in this regard. Here we show that low-temperature oxygenation of dinuclear copper(I) complexes leads to unusual tetranuclear, mixed-valent $μ_4$-peroxo [Cu$^I$/Cu$^{II}$]$_2$ complexes. These Cu$_4$O$_2$ intermediates promote irreversible and thermally activated O−O bond homolysis, generating Cu$_2$O complexes that catalyze strongly exergonic H-atom abstraction from hydrocarbons, coupled to O-transfer. The Cu$_2$O species can also be produced with N$_2$O, demonstrating their capability for small-molecule activation. The binding and cleavage of O$_2$ leading to the primary Cu$_4$O$_2$ intermediate and the Cu$_2$O complexes, respectively, is elucidated with a range of solution spectroscopic methods and mass spectrometry. The unique reactivities of these species establish an unprecedented, 100 % atom-economic scenario for the catalytic, copper-mediated monooxygenation of organic substrates, employing both O-atoms of O$_2$

Jet delivery system for Raman scattering on bio-inorganic compounds

We present a micro-jet sample delivery system for Raman measurements. Compared to cuvette measurements, the observed Raman signal is enhanced by more than one order of magnitude and does not contain signal distortions from the liquid-glass interface. Furthermore, the signal stability of repeated measurements is enhanced due to reduced sample damage effects by constantly replenishing the sample. This allows the study of sensitive samples that can only be produced in low concentrations. Our setup consists of a controlled sample environment that can be either under vacuum or an exchange gas, which allows the study of samples that are unstable in air. Finally, by matching the effective source point of the Raman instrument with the diameter of the jet, controlled experiments using laser beams of different wavelengths are possible. We see future applications of our setup for resonance Raman and time-resolved Raman measurements of bioinorganic samples

Photoinduced metastable dd-exciton-driven metal-insulator transitions in quasi-one-dimensional transition metal oxides

10.1038/s42005-020-00451-wCommunications Physics3120

The TRIXS end station for femtosecond timeresolved resonant inelastic x ray scattering experiments at the soft x ray free electron laser FLASH

We present the experimental end station TRIXS dedicated to time resolved soft x ray resonant inelastic x ray scattering RIXS experiments on solid samples at the free electron laser FLASH. Using monochromatized ultrashort femtosecond XUV soft x ray photon pulses in combination with a synchronized optical laser in a pump probe scheme, the TRIXS setup allows measuring sub picosecond time resolved highresolution RIXS spectra in the energy range from 35 eV to 210 eV, thus spanning the M edge M1 and M2,3 absorption resonances of 3d transition metals and N4,5 edges of rare earth elements. A Kirkpatrick Baez refocusing mirror system at the first branch of the plane grating monochromator beamline PG1 provides a focus of 6 6 lm2 FWHM at the sample. The RIXS spectrometer reaches an energy resolution of 35 160 meV over the entire spectral range. The optical laser system based on a chirped pulse optical parametric amplifier provides approximately 100 fs FWHM long photon pulses at the fundamental wavelength of 800 nm and a fluence of 120 mJ cm2 at a sample for optical pump XUV probe measurements. Furthermore, optical frequency conversion enables experiments at 400 nm or 267 nm with a fluence of 80 and 30 mJ cm2, respectively. Some of the first pump probe RIXS spectra measured with this setup are shown. The measured time resolution for time resolved RIXS measurements has been characterized as 287 fs FWHM for the used energy resolutio

Functional Printing of Conductive Silver-Nanowire Photopolymer Composites

We investigated the fabrication and functional behaviour of conductive silver-nanowire-polymer composites for prospective use in printing applications. Silver-nanowires with an aspect ratio of up to 1000 were synthesized using the polyol route and embedded in a UV-curable and printable polymer matrix. Sheet resistances in the composites down to 13 Ω/sq at an optical transmission of about 90% were accomplished. The silver-nanowire composite morphology and network structure was investigated by electron microscopy, atomic force microscopy, profilometry, ellipsometry as well as surface sensitive X-ray scattering. By implementing different printing applications, we demonstrate that our silver nanowires can be used in different polymer composites. On the one hand, we used a tough composite for a 2D-printed film as top contact on a solar cell. On the other hand, a flexible composite was applied for a 3D-printed flexible capacitor

The TRIXS end-station for femtosecond time-resolved resonant inelastic X-ray free-electron laser FLASH

We present the experimental end-station TRIXS dedicated to time-resolved soft x-ray resonant inelastic x-ray scattering (RIXS) experiments on solid samples at the free-electron laser FLASH. Using monochromatized ultrashort femtosecond XUV/soft x-ray photon pulses in combination with a synchronized optical laser in a pump-probe scheme, the TRIXS setup allows measuring sub-picosecond time-resolved high-resolution RIXS spectra in the energy range from 35 eV to 210 eV, thus spanning the M-edge (M$_1$ and M$_{2,3}$) absorption resonances of 3d transition metals and N$_{4,5}$-edges of rare earth elements. A Kirkpatrick–Baez refocusing mirror system at the first branch of the plane grating monochromator beamline (PG1) provides a focus of (6 × 6) $μm^2$ (FWHM) at the sample. The RIXS spectrometer reaches an energy resolution of 35–160 meV over the entire spectral range. The optical laser system based on a chirped pulse optical parametric amplifier provides approximately 100 fs (FWHM) long photon pulses at the fundamental wavelength of 800 nm and a fluence of 120 mJ/cm$^2$ at a sample for optical pump-XUV probe measurements. Furthermore, optical frequency conversion enables experiments at 400 nm or 267 nm with a fluence of 80 and 30 mJ/cm$^2$, respectively. Some of the first (pump-probe) RIXS spectra measured with this setup are shown. The measured time resolution for time-resolved RIXS measurements has been characterized as 287 fs (FWHM) for the used energy resolution

Transferring the entatic-state principle to copper photochemistry

The entatic state denotes a distorted coordination geometry of a complex from its typical arrangement that generates an improvement to its function. The entatic-state principle has been observed to apply to copper electron-transfer proteins and it results in a lowering of the reorganization energy of the electron-transfer process. It is thus crucial for a multitude of biochemical processes, but its importance to photoactive complexes is unexplored. Here we study a copper complex—with a specifically designed constraining ligand geometry—that exhibits metal-to-ligand charge-transfer state lifetimes that are very short. The guanidine–quinoline ligand used here acts on the bis(chelated) copper(I) centre, allowing only small structural changes after photoexcitation that result in very fast structural dynamics. The data were collected using a multimethod approach that featured time-resolved ultraviolet–visible, infrared and X-ray absorption and optical emission spectroscopy. Through supporting density functional calculations, we deliver a detailed picture of the structural dynamics in the picosecond-to-nanosecond time range