Retaining a dissipation-free state while carrying large electrical currents is a challenge that needs to be solved to enable commercial applications of high-temperature superconductivity. Here, we show that the controlled combination of two effective pinning centres (randomly distributed nanoparticles and self-assembled columnar defects) is possible and effective. By simply changing the temperature or growth rate during pulsed-laser deposition of BaZrO(3)-doped YBa(2)Cu(3)O(7) films, we can vary the ratio of these defects, tuning the field and angular critical-current (Ic) performance to maximize Ic. We show that the defects' microstructure is governed by the growth kinetics and that the best results are obtained with a mixture of splayed columnar defects and random nanoparticles. The very high Ic arises from a complex vortex pinning landscape where columnar defects provide large pinning energy, while splay and nanoparticles inhibit flux creep. This knowledge is used to produce thick films with remarkable Ic(H) and nearly isotropic angle dependence.

Silicon crystals have an important role in the electronics industry, and silicon nanoparticles have applications in areas such as nanoelectromechanical systems, photonics and biotechnology. However, the elastic-plastic transition observed in silicon is not fully understood; in particular, it is not known if the plasticity of silicon is determined by dislocations or by transformations between phases. Here, based on compression experiments and molecular dynamics simulations, we show that the mechanical properties of bulk silicon and silicon nanoparticles are significantly different. We find that bulk silicon exists in a state of relative constraint, with its plasticity dominated by phase transformations, whereas silicon nanoparticles are less constrained and display dislocation-driven plasticity. This transition, which we call deconfinement, can also explain the absence of phase transformations in deformed silicon nanowedges. Furthermore, the phenomenon is in agreement with effects observed in shape-memory alloy nanopillars, and provides insight into the origin of incipient plasticity.

Semicrystalline poly(3-hexyl-2,5-thienylene vinylene) (P3HTV) with a low band gap of 1.65 eV has been synthesized by acyclic diene metathesis polymerization and incorporated into bulk heterojunction (BHJ) organic solar cells. The polymer was thermally characterized by differential scanning calorimetry and thermogravimetric analysis and was blended with the electron acceptor methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) to make a light-harvesting charge-transfer thin film. The properties of P3HTV/PCBM blends were studied as a function of PCBM composition by wide-angle X-ray scattering, atomic force microscopy, transmission electron microscopy, UV−vis absorption spectroscopy, and charge-transport and photovoltaic measurements. The PCBM solubility limit, that is, the phase separation point, was estimated to be 50 wt % PCBM. The phase behavior of the blend was directly correlated with electrical transport behavior in a field-effect transistor testbed. At the phase separation point, charge carrier transport switches from hole only to ambipolar (both electron and hole) due to the formation of an electron-transporting percolating network of PCBM domains. BHJ solar cells were constructed with P3HTV films blended with varying weight fractions of PCBM. In these cells, spun-cast films of P3HTV/PCBM mixtures were sandwiched between poly(3,4-ethylene dioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS)-coated ITO and Al electrodes. The best performance of polymer solar cells was observed at 50−60% PCBM, near the phase separation point at which power conversion efficiencies of 0.80−0.92% were measured under AM 1.5, 100 mW/cm2 illumination.