One sentence summary:We describe a general liquid-phase method to exfoliate layered compounds to give monoand few-layer flakes in large quantities. TMDs consist of hexagonal layers of metal atoms, M, sandwiched between two layers of chalcogen atoms, X, with stoichiometry MX 2 . While the bonding within these tri-layer sheets is covalent, adjacent sheets stack via van der Waals interactions to form a 3D crystal. TMDs occur in more than 40 different types (2, 3) depending on the combination of chalcogen (S, Se or Te) and transition metal(3). Depending on the co-ordination and oxidation state of the metal atoms, TMDs can be metallic, semi-metallic or semiconducting(2, 3), e.g. WS 2 is a semiconductor while NbSe 2 is a metal(3). In addition, superconductivity(4) and charge density wave effects(5) have been observed in some TMDs. This versatility makes them potentially useful in many areas of electronics.However, like graphene(6), layered materials must be exfoliated to fulfil their full potential. For example, films of exfoliated Bi 2 Te 3 should display enhanced thermoelectric efficiency by suppression of thermal conductivity(7). Exfoliation of 2D topological insulators such as Bi 2 Te 3 and Bi 2 Se 3 would reduce residual bulk conductance, 4 highlighting surface effects. In addition, we can expect changes in electronic properties as the number of layers is reduced e.g. the indirect bandgap of bulk MoS 2 becomes direct in few-layer flakes(8). Although exfoliation can be achieved mechanically on a small scale(9, 10), liquid phase exfoliation methods are required for many applications(11).Critically, a simple liquid exfoliation method would allow the formation of novel hybrid and composite materials. While TMDs can be chemically exfoliated in liquids(12-14), this method is time consuming, extremely sensitive to the environment and incompatible with most solvents.We demonstrate exfoliation of bulk TMD crystals in common solvents to give mono-and few layer nano-sheets. This method is insensitive to air and water and can potentially be scaled up to give large quantities of exfoliated material. In addition, we show that this procedure allows the formation of hybrid films with enhanced properties.We initially sonicated commercial MoS 2 , WS 2 and BN (15, 16) powders in a number of solvents with varying surface tensions. The resultant dispersions were centrifuged and the supernatant decanted (Section S3). Optical absorption spectroscopy showed that the amount of material retained (characterised by / A l C α = , where A/l is the absorbance per length, α is the extinction coefficient and C is the concentration) was maximised for solvents with surface tension close to 40 mJ/m 2 (17, 18) ( Fig. 1A-C). Detailed analysis, within the framework of Hansen solubility parameter theory(19), shows successful solvents to be those with dispersive, polar and H-bonding components of the cohesive energy density within certain well-defined ranges (Section S4, Figs. S2-S3). This can be interpreted to mean that successful solvents are those w...

Reducing loss in microwave dielectrics is critical to improving performance in wireless communications systems. Grain boundaries in polycrystalline microwave dielectric ceramics have long been suspected of increasing dielectric loss. They are often cited as the main contributor to the observed difference in dielectric losses between single crystals and polycrystalline ceramics. The exact configuration of grain boundaries is problematic to quantify in practice and their influence on the dielectric loss difficult to distinguish from other defects such as porosity, oxygen vacancies, impurities, and dislocations. Here we measure the sensitivity of a single grain boundary in a magnesium oxide bi‐crystal to the polarization of an applied microwave field as a function of temperature.

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Here we use global and local magnetometry and Hall probe imaging to investigate the electromagnetic connectivity of the superconducting current path in the oxygendeficient fluorine-free Nd-based oxypnictides. High resolution transmission electron microscopy and scanning electron microscopy show strongly-layered crystallites, evidence for a ~ 5nm amorphous oxide around individual particles, and second phase neodymium oxide which may be responsible for the large paramagnetic background at high field and at high temperatures. From global magnetometry and electrical transport measurements it is clear that there is a small supercurrent flowing on macroscopic sample dimensions (mm), with a lower bound for the average (over this length scale) critical current density of the order of 10 3 A/cm 2 . From magnetometry of powder samples and local Hall probe imaging of a single large conglomerate particle ~120 microns it is clear that on smaller scales, there is better current connectivity with a critical current density of the order of 5 x 10 4 A/cm 2 . We find enhanced flux creep around the second peak anomaly in the magnetisation curve and an irreversibility line significantly below H c2 (T) as determined by ac calorimetry.

Spectromicroscopy of tissue surrounding failed CoCr metal-on-metal hip replacements detected corroded nanoscale debris in periprosthetic tissue in two chemical states, with concomitant mitochondrial damage. The majority of debris contained Cr(3+), with trace amounts of oxidised cobalt. A minority phase containing a core of metallic chromium and cobalt was also observed.