Fabrication of quantum-sized Cd S-coated Ti O2 nanotube array with efficient photoelectrochemical performance using modified successive ionic layer absorption and reaction(SILAR) method

Quantum-sized CdS-coated TiO2 nanotube array （Q-CdS-TiO2 NTA） was fabricated by the modified successive ionic layer absorption and reaction method. Scanning electron microscope and transmission electron microscope images showed the regular structure of TiO2 NTA, where quantum-sized CdS （diameter 〈10nm） deposited on both the inside and outside of TiO2 nanotube wall. Fabrication conditions including immersing cycles, calcination temperature and drying process were well optimized, and the Q-CdS-TiO2 NTA and its photoelectrochemical （PEC） properties were characterized by X-ray fluorescence spectrometer, UV-Vis diffuse reflectance spectra and photovoltage. Distinct increases in visible light absorption and photocurrent were observed as the immersing cycle was increased from 5 to 20 times. The additional drying process accelerated the CdS crystal growth rate, and thus, the fabrication time could be shortened accordingly. Calcination temperature influenced the PEC property of Q-CdS-TiO2 NTA deeply, and the optimized calcination temperature was found as 500 ℃. As the Q-CdS-TiO2 NTA was fabricated under such condition, the visible photocurrent density increased to 2.8 mA/cm and the photovoltage between 350 and 480 nm was enhanced by 2.33 times than that without calcination. This study is expected to optimize Q-CdS-TiO2 NTA fabrication conditions for the purpose of improving its PEC performance.

A first-principles study of the size-dependent electronic properties of SiC nanotubes

We investigate the structural and electronic properties of SiC nanotubes(NTs) with hexagonal cross sections by a first-principles calculation using plane-wave ultra-soft pseudo-potential technology based on the density-functional theory.Our results reveal that surface-layer C and Si atoms relax significantly upon decreasing the tube-wall thickness because of surface-size and quantum-size effects.We also find that all relaxed SiC NTs stay stably on the nanoscale because of an admixture of sp2 and sp3 hybridization between C and Si atoms and a strong covalent,and that the band gap tends to decrease with increasing tube-wall thickness.Our calculations further indicate that both C and Si atoms on the inner and outer surface of SiC NTs contribute to defect states at the top of the valence band and at the bottom of the conduction band.These results provide reference information for a thorough understanding of the properties of SiC nanostructures and also enable more precise monitoring and control of the growth of SiC nanostructures.