Oxygen vacancies (OVs) have been reported to significantly alter the photocatalytic properties of BiOCl nanosheets. However, their formation mechanism and their role in the enhancement of... Show moreOxygen vacancies (OVs) have been reported to significantly alter the photocatalytic properties of BiOCl nanosheets. However, their formation mechanism and their role in the enhancement of photoelectrochemical performance remain unclear. In this work, thermally induced oxygen vacancies are introduced in BiOCl nanosheets by annealing in He atmosphere at various temperatures and their formation mechanism is investigated by in-situ diffuse reflectance infrared (DRIFTS) measurements. The influence of OVs on band offset, carrier concentrations and photoelectrochemical performance are systematically studied. The results show that (1) the surface of BiOCl nanosheets is extremely sensitive to temperature and defects are formed at temperatures as low as 200 degrees C in inert atmosphere. (2) The formation of surface and bulk OVs in BiOCl is identified by a combination of XPS, in-situ DRIFTS, and EPR experiments. (3) The photocurrent of BiOCl is limited by the concentration of charge carriers and shallow defect states induced by bulk oxygen vacancies, while the modulation of these parameters can effectively increase light absorption and carrier concentration leading to an enhancement of photoelectrochemical performance of BiOCl. Show less
Mergers of neutron stars are known to be associated with short gamma-ray bursts(1-4). If the neutron-star equation of state is sufficiently stiff (that is, the pressure increases sharply as the... Show moreMergers of neutron stars are known to be associated with short gamma-ray bursts(1-4). If the neutron-star equation of state is sufficiently stiff (that is, the pressure increases sharply as the density increases), at least some such mergers will leave behind a supramassive or even a stable neutron star that spins rapidly with a strong magnetic field(5-8) (that is, a magnetar). Such a magnetar signature may have been observed in the form of the X-ray plateau that follows up to half of observed short gamma-ray bursts(9,10). However, it has been expected that some X-ray transients powered by binary neutron-star mergers may not be associated with a short gamma-ray burst(11,12). A fast X-ray transient (CDF-S XT1) was recently found to be associated with a faint host galaxy, the redshift of which is unknown(13). Its X-ray and host-galaxy properties allow several possible explanations including a short gamma-ray burst seen off-axis, a low-luminosity gamma-ray burst at high redshift, or a tidal disruption event involving an intermediate-mass black hole and a white dwarf(13). Here we report a second X-ray transient, CDF-S XT2, that is associated with a galaxy at redshift z = 0.738 (ref.(14)). The measured light curve is fully consistent with the X-ray transient being powered by a millisecond magnetar. More intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host galaxy with a moderate offset from the galaxy centre, as short gamma-ray bursts often do(15,16). The estimated event-rate density of similar X-ray transients, when corrected to the local value, is consistent with the event-rate density of binary neutron-star mergers that is robustly inferred from the detection of the gravitational-wave event GW170817. Show less
Southey, M.C.; Goldgar, D.E.; Winqvist, R.; Pylkas, K.; Couch, F.; Tischkowitz, M.; ... ; Tyrer, J. 2016
