Ordered gallium arsenide (GaAs) nanowires are grown by molecular-beam epitaxy on GaAs (111)B substrates using Au-catalyzed vapor–liquid–solid growth defined by nanochannel alumina (NCA) templates. Field-emission scanning electron microscope images show highly ordered nanowires with a growth direction perpendicular to the substrate. The size (i.e., diameter) distribution of the wires is drastically narrowed by depositing the gold catalyst through an NCA template mask; this narrows the size distribution of the gold dots and arranges them in a well-ordered array, as defined by the NCA template. The nanowire diameter distribution full width at half maximum on the masked substrate is 5.1 nm, compared with 15.7 nm on an unmasked substrate.

GaAs nanowires were grown on GaAs (100) substrates by vapor–liquid–solid growth. About 8% of these nanowires grew in 〈110〉 directions with straight, Y-branched or L-shaped morphologies. The role of strain-induced reduction in surface free energy is discussed as a possible factor contributing to the evolution of 〈110〉 nanowires. Kinking and branching is attributed to growth instabilities resulting from equivalent surface free energies for 〈110〉 growth directions. Transmission electron microscopy verified that 〈110〉 nanowires are defect free.

No abstract

Growth of high-quality single-crystal AlGaAs nanowires was demonstrated using the vapor–liquid–solid (VLS) mechanism with molecular-beam epitaxy (MBE). Highly ordered AlGaAs nanowire arrays and GaAs∕AlGaAs multilayer nanowires were also prepared. Photoluminescence (PL) from homogeneous AlGaAs and GaAs∕AlGaAs multilayer nanowires was measured. The Al composition of the AlGaAs nanowires was found to be significantly lower than that for planar MBE films grown under the same conditions, as determined from PL and energy-dispersive x-ray spectroscopy measurements. This is explained in terms of the different growth mechanisms for VLS and normal MBE. Such AlGaAs nanowires are expected to have a wide range of applications in electronic and photonic devices.

No abstract

The development of low-cost multifunctional electrocatalysts with high activity for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is critical for the advancement of sophisticated energy conversion and storage devices. Herein, a trifunctional Ni(S 0.51 Se 0.49 ) 2 @NC catalyst is designed and fabricated using a dianionic regulation strategy. Synchrotron radiation X-ray absorption spectroscopy and density functional theory calculations reveal that simultaneous sulfidation and selenization can induce the electronic delocalization of Ni(S 0.51 Se 0.49 ) 2 active sites to enhance the adsorption of *OOH/*OH intermediate for ORR/OER and H* intermediate for HER. The OER and HER mechanisms are revealed by in situ Raman spectroscopy. The Ni(S 0.51 Se 0.49 ) 2 @NC exhibits trifunctional catalytic activity for the HER (111 mV at 10 mA cm −2 ), OER (320 mV at 10 mA cm −2 ), and ORR (half-wave potential of 0.83 V). The rechargeable zinc-air batteries (ZABs) exhibit an open-circuit voltage of 1.46 V, a specific capacity of 799.1 mAh g −1 , and excellent stability for 1000 cycles. The water electrolytic cell using Ni(S 0.51 Se 0.49 ) 2 @NC electrodes delivers a current density of 10 mA cm −2 at a cell voltage of 1.59 V, and it can be powered using the constructed ZABs. These findings contribute to developing low-cost and efficient non-noble metal multifunctional catalysts.

No abstract

No abstract