Ultrafast rotational motions of supported nanoclusters probed by electron diffraction

In crystals, microscopic energy flow is governed by electronic and vibrational excitations. In nanoscale materials, however, translations and rotations of entire nanoparticles represent additional fundamental excitations. The observation of such motions is elusive as most ultrafast techniques are insensitive to motions of the phonons’ frame of reference. Here, we study heterostructures of size-selected Au nanoclusters with partial (111) orientation on few-layer graphite with femtosecond electron diffraction. We demonstrate that ultrafast, constrained rotations of nanoclusters, so-called librations, in photo-induced non-equilibrium conditions can be observed separately from vibrational structural dynamics. Molecular dynamics and electron diffraction simulations provide quantitative understanding on librations-induced deviations from the conventional temperature dependence of diffraction patterns. We find that nanocluster librations with a period of ∼20 picoseconds are triggered quasi-impulsively by graphene flexural motions. These ultrafast structural dynamics modulate the Au/C interface and hence are expected to play a key role in energy- and mass-transport at the nanoscale

A 13.56 MHz inductive power transfer system operating with corroded coils

This paper describes experiments which investigate the effects resulting from corrosion of air-core coils for high frequency inductive power transfer (HF-IPT). A group of coils were treated by exposing them to corrosive conditions for thirty days. Afterwards, the coils were measured with an impedance analyser and the coil with the lowest Q-factor was selected for further experiments. The treated coil was tested at the transmit side of a HF-IPT system, where the system DC-to-DC efficiency was measured and compared against an equivalent system using an untreated transmit coil. The total losses measured increased when the system was operating with the treated coil across a broad loading range, and thermal images were used to establish the additional losses on the treated coil. Analysis of the treated coil identified widespread damage to the surface of the coil. However, it was specific aggressive corrosion only found locally which was able to significantly reduce the Q-factor of the treated coil by 20%

Printed recyclable and self-poled polymer piezoelectric generators through single-walled carbon nanotube templating

With an increasing global energy demand, along with a rising uptake of portable electronic devices, it is of great importance to investigate the viability of alternative energy harvesting technologies. Flexible piezoelectric generators (PEGs) are able to convert mechanical energy to electricity, making them an ideal candidate to decrease reliance on conventional energy sources and to power flexible, portable and implantable electronics. In this study, we show a low-energy production pathway for transparent PEGs based on poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) via shear-induced alignment of its dipoles through extrusion printing, complemented by spatial dipolar templating onto single-walled carbon nanotubes (SWCNTs) at low concentrations (<0.05 wt%). The resulting composite PEGs show up to a 500% enhancement in the piezoelectric charge coefficient d33 relative to extrusion printed pristine PVDF-TrFE, with similar enhancements in energy harvesting, exhibiting a power density of up to 20 μW cm−3 at 0.02 wt% SWCNTs. The extrusion printed composite PEGs show recyclability using only a green solvent (acetone) and are found to exhibit piezoelectric energy harvesting with a power density of up to 71 μW cm−3 upon reprinting, overcoming two of the most significant hurdles towards commercial production of flexible PEGs

Interfacial piezoelectric polarization locking in printable Ti₃C₂Tx MXene-fluoropolymer composites

AbstractPiezoelectric fluoropolymers convert mechanical energy to electricity and are ideal for sustainably providing power to electronic devices. To convert mechanical energy, a net polarization must be induced in the fluoropolymer, which is currently achieved via an energy-intensive electrical poling process. Eliminating this process will enable the low-energy production of efficient energy harvesters. Here, by combining molecular dynamics simulations, piezoresponse force microscopy, and electrodynamic measurements, we reveal a hitherto unseen polarization locking phenomena of poly(vinylidene fluoride&ndash;co&ndash;trifluoroethylene) (PVDF-TrFE) perpendicular to the basal plane of two-dimensional (2D) Ti3C2Tx MXene nanosheets. This polarization locking, driven by strong electrostatic interactions enabled exceptional energy harvesting performance, with a measured piezoelectric charge coefficient, d33, of &minus;52.0 picocoulombs per newton, significantly higher than electrically poled PVDF-TrFE (approximately &minus;38 picocoulombs per newton). This study provides a new fundamental and low-energy input mechanism of poling fluoropolymers, which enables new levels of performance in electromechanical technologies.</jats:p