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Acetone is flammable and harmful to human health and environment. It is urgent and significant to develop high sensitivity and efficiency sensors for acetone gas detecting. Herein, a novel nanoscale hollow–shell structure of CeO2 with high stability, sensitivity and selectivity for acetone gas detecting was designed. The as-developed nanoscale hollow–shell CeO2 sensor presents 270% sensing response, and the corresponding response and recovery are 6 s and 11 s when detecting 100 ppm acetone gas at 260 ℃. Remarkably, this sensor exhibits excellent stability in continual detection of 100 ppm acetone gas in 60 days. Furthermore, the developed nanoscale hollow–shell CeO2 sensor presents an outstanding selectivity to acetone gas among ethanol, methanol, xylene, ammonia, formaldehyde and ethylene glycol gases. DFT further reveals that there are 0.66 electrons of acetone molecule transferred to CeO2, which will decease CeO2 band gap from 2.74 eV to 1.91 eV, and consequently the conductivity enhanced after absorbing acetone gas. This developed CeO2 nanoscale hollow–shell sensor can be used as matrix sensor material for VOCs detection.

The Al-doped Mg2Si thin films were fabricated on sapphire substrates by magnetron sputtering technique, and the influences of different Al doping contents on the Raman scattering and room-temperature (RT) photoluminescence (PL) of Mg2Si thin films were investigated. The crystal structure, morphology, composition, Raman scattering and PL property of the thin film were examined using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy, respectively. XRD results indicate that the intensity of diffraction peaks of Al-doped Mg2Si thin films are higher than that of undoped Mg2Si thin film, and decrease with increasing Al doping content. The FESEM image shows a few cavities in the surface of the film. The EDS results show that the thin films have the Al content of 0, (1.17 ± 0.1) at.%, (1.53 ± 0.1) at.%, (1.86 ± 0.08) at.% and (2.76 ± 0.11) at.%, respectively. The results of Raman scattering measurement reveal that all samples have the characteristic peak of Mg2Si. And Al dopant-induced Raman peak centered at 441 cm−1 was detected. Room-temperature photoluminescence of the Mg2Si:Al film was observed for the first time. Two visible light luminescence peaks center about 580 nm (2.14 eV) and 630 nm (1.97 eV), respectively, which originate from the different energy levels transition at the interface between crystalline Mg2Si and MgO surface layer. With decreasing excitation power, the position of the maximum of PL has no obvious change and the intensity drops significantly.

Gallium nitride (GaN) is a promising material for high-frequency and high-power electronics owing to its high thermal stability, wide bandgap, and high breakdown voltage. Monocrystalline GaN films are usually produced by metal organic chemical vapor phase deposition using Si, SiC, or Al2O3 as the substrate. However, the difference in lattice constants and thermal expansion coefficients causes many defects in GaN epilayers. In particular, the formation of twins will strongly influence the electronic properties of GaN-based devices. In this study, the solidification process of GaN was simulated by molecular dynamics at a cooling rate of 1012 K/s, and the twin structures in GaN were discussed. The results of this simulation showed two types of twins, including coherent twin and rotating twin, which were analyzed by visualization technology. The formation of twins was related to the coexistence of zinc blende and wurtzite phases. Furthermore, the types of twins were closely associated to the stacking ways of zinc blende and wurtzite structures. In general, it is essential to study the microstructure and the structural evolution of twin GaN, in order to give references to experiments about the growth and characteristics of twins.

To understand the photoluminescence mechanisms and optimize the design of Mg 2 Si-based light-emitting devices, Mg 2 Si films were fabricated on silicon (111) and glass substrates by magnetron sputtering technique, and the influences of different substrates on the photoelectric properties of Mg 2 Si films were investigated systematically. The crystal structure, cross-sectional morphology, composition ratios and temperature-dependent photoluminescence (PL) of the Mg 2 Si films were examined using X-ray diffraction (XRD), Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and PL measurement system, respectively. XRD results indicate that the Mg 2 Si film on Si (111) displays polycrystalline structure, whereas Mg 2 Si film on glass substrate is of like-monocrystalline structure.SEM results show that Mg 2 Si film on glass substrate is very compact with a typical dense columnar structure, and the film on Si substrate represents slight delamination phenomenon. EDS results suggest that the stoichiometry of Mg and Si is approximately 2:1. Photoluminescence (PL) of Mg 2 Si films was observed for the first time. The PL emission wavelengths of Mg 2 Si are almost independence on temperature in the range of 77–300 K. The PL intensity decreases gradually with increasing temperature. The PL intensity of Mg 2 Si films on glass substrate is much larger than that of Mg 2 Si film on Si (111) substrate. The activation energy of 18 meV is determined from the quenching of major luminescence peak(1342 nm) as a function of temperature in the Mg 2 Si film grown on Si (111) substrate, which is much smaller than that deduced in the sample grown on glass substrate (about 25meV). The small activation energy can be attributed to the additional nonradiative centers originated from relatively poor crystal quality.The physical mechanism responsible for the measured ∼1342 nm and other three longer wavelengths emissions may be respectively result from strong Mg i donor level to valence band transitions and other defect-related radiative recombination occurred in the Mg 2 Si films.

Lithium-sulfur (Li–S) batteries have attracted extensive attention in the past decades owing to their high theoretical energy density, low-cost and eco-friendliness. However, poorly cycling stability and rapidly decay caused by shuttle effects at high-sulfur loading condition restrain their practical applications. Focusing on these issues, N-doped hollow porous carbon nanotubes (N-HPCNT) as a self-supporting sulfur cathode is developed. The inherent conductivity and abundant pores of 3D continuous framework not only allow a high-sulfur content (67 wt%) and block the polysulfides via physical confinement, but also trap the polysulfides by the nitrogen heteroatoms (4.60 wt%) via strong chemisorption. Benefiting from the above-mentioned merits, the self-supporting S/N-HPCNT cathode with 3 mg cm−2 sulfur delivers high reversible capacity, super rate capability (1152 and 852.8 mAh g−1 at 0.2 and 3 C, respectively) and long cycling stability (717.9 mAh g−1 after 500 cycles at 1 C). Even under a higher sulfur loading (8 mg cm−2), it still exhibits a stable areal capacity of 7.72 mAh cm−2 (corresponding to 965.1 mAh g−1) after 60 cycles. This work provides a pathway for developing high performance Li–S batteries.

Magnesium films of various thicknesses were first deposited on silicon (1 1 1) substrates by magnetron sputtering method and then annealed in annealing furnace filled with argon gas. The effects of the magnesium film thickness and the annealing temperature on the formation of Mg2Si films were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The Mg2Si thin films thus obtained were found to be polycrystalline and the Mg2Si (2 2 0) orientation is preferred regardless of the magnesium film thickness and annealing temperature. XRD results indicate that high quality magnesium silicide films are produced if the magnesium/silicon samples are annealed at 400 °C for 5 h. Otherwise, the synthesized films annealed at annealing temperatures lower than 350 °C or higher than 450 °C contain magnesium crystallites or magnesium oxide. SEM images have revealed that microstructure grains in the polycrystalline films are about 1–5 μm in dimensions, and the texture of the Mg2Si films becomes denser and more homogeneous as the thickness of the magnesium film increases.

Fe films were deposited on both heated and not-heated Si (100) substrates using direct current magnetron sputtering, and were subsequently annealed by pulsed laser with various laser energy densities. Direct formation of single-phase α-FeSi 2 was confirmed using X-ray diffraction and the surface morphology of films was characterized by scanning electron microscopy. The results show that the crystallinity of the films deposited at room temperature is improved with increasing laser energy densities, while the crystallinity of the films deposited on heated substrates is improved with increasing substrate temperatures. For the samples deposited at the room temperature, the optimal laser energy density for the formation of α-FeSi 2 is 0.95 J cm − 2 .

KeyWords Plus: YAG-TB PHOSPHOR; LUMINESCENT PROPERTIES; COMBUSTION PROCESS; SPRAY-PYROLYSIS; CE PHOSPHOR; PHOTOLUMINESCENCE; PARTICLES; MORPHOLOGY; POWDERS 通讯作者地址: Zeng, RJ (通讯作者), Xiamen Univ, Coll Mat Sci, Sinning S Rd 22, Xiamen 361005, Peoples R China 地址: 1. Xiamen Univ, Coll Mat Sci, Xiamen 361005, Peoples R China 电子邮件地址: rjzjqz@xmu.edu.cn