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Abstract: The effect of misorientation of 6H–SiC substrate on the structural quality of GaN epilayer grown by organometallic vapor phase epitaxy (MOVPE) has been investigated. The results reveal that the structural quality of GaN epilayer is significantly influenced by the misorientation of 6H–SiC substrate. Larger misorientation angle of 6H–SiC substrate results in better structural quality of GaN epilayer, such as narrower atomic step widths of GaN surface, less yellow luminescence band/edge emission (I y /I b ) ratio of PL, and lower dislocations density. It is also found that the I y /I b ratio of GaN epilayer is affected only by the misorientation angle of 6H–SiC substrate, but the screw dislocation density and edge dislocation density are influenced by both the misorientation angle and the misorientation direction of 6H–SiC substrate. GaN epilayer grown on 6H–SiC substrate with 2.3° misorientation angle towards direction has the best structural quality. [Copyright &y& Elsevier]

The preparation of a highly efficient and economical oxygen reduction reaction (ORR) catalyst is one of the greatest challenges for the application of proton exchange membrane fuel cells (PEMFCs). Herein, we integrated tube-terminated edges into the basal plane of Fe- and N-codoped carbon bubbles to obtain an excellent Fe-N x /C ORR electrocatalyst. The synthesis of the uniformly distributed Fe- and N-codoped tube-terminated edge-dominated carbon bubble (Fe-TTNCB) was based on a new self-sacrificing template strategy. The unique micro-meso/macromorphological design endowed the Fe-TTNCB catalysts with abundant surface-terminated features to facilitate the construction of edge-hosted Fe-Nx/C active sites, thus improving the mass transport properties and promoting the accessibility of oxygen to the active sites. Due to the synergistic effects among all of the above characteristics, the Fe-TTNCB catalysts had excellent ORR catalytic activity in 0.1 M KOH electrolyte with a half-wave potential of 0.905 V (E 1/2 , V vs. a reference hydrogen electrode (RHE)), which is 62 mV higher than that of commercial 20% Pt/C (0.843 V vs. RHE). Moreover, by integrating tube-terminated edges into the basal plane of Fe- and N-codoped carbon bubbles, the kinetic current density (J k) of the nonprecious metal Fe–N x /C electrocatalyst increased from 15.38 mA cm−2 (Fe- and N-codoped carbon bubble, Fe-NCB) and 32.25 mA cm−2 (Fe- and N-codoped hybrid carbon bubble, Fe-HNCB to 56.18 mA cm−2 (Fe-TTNCB) at 0.8 V, and E 1/2 was boosted from 0.87 V (Fe- and N-codoped carbon bubble, Fe-NCB) and 0.88 V (Fe-HNCB) to 0.905 V (Fe-TTNCB). Image 1 • Unique micro-meso/macromorphological Fe-N x /C catalysts were designed. • Tube-terminated edges boosted the catalytic activity when comparing the Fe-TTNCB and Fe-HNCB ORR activity. • The Fe-TTNCB catalytic activity had a half-wave potential of 0.905 V (E 1/2 , V vs. RHE). • The J k value increased from 15.38 mA cm−2 (Fe-NCB) and 32.25 mA cm−2 (Fe-HNCB) to 56.18 mA cm−2 (Fe-TTNCB) at 0.8 V. [ABSTRACT FROM AUTHOR]

Abstract: The influence of AlN buffer growth temperature on the quality and stress of 4.5μm GaN epilayer on 6H–SiC substrate by organometallic vapor phase epitaxy (MOVPE) has been investigated. The crystalline quality and the atomic surface morphology were improved, the density of the pits and the stress of the GaN epilayer were reduced by increasing the growth temperature of the AlN buffer in the range from 950°C to 1100°C. By employing the optimized 1100°C growth temperature of AlN buffer, very high quality of GaN epilayer was achieved. The X-ray full width of half maximums (FWHMs) of (002) and (102) reflection rocking curves of the GaN epilayer have been improved to 159arcsec and 194arcsec, respectively, and the surface RMS to only 0.31nm in the 5μm×5μm atomic force microscopy (AFM) scan. The stress of GaN epilayer was investigated by X-ray diffraction and Raman scattering as well. The degree of the tensile stress in GaN epilayer could be suppressed by increasing the growth temperature of AlN buffer. Finally, a high quality of crack-free 4.5μm thick GaN epilayer was obtained on 6H–SiC substrate using the optimized 1100°C AlN growth temperature. [Copyright &y& Elsevier]

• Cubic-phase FeF 3 nanocages were prepared by annealing (NH 4) 3 FeF 6 (3NH 4 F·FeF 3) double salt. • Non-equivalent Co-doping will lower the energy gap of FeF 3 and alleviate the localization degree of charge density around. • Co2+ dopants could modify the crystallization and morphology of FeF 3. • Sluggish diffusion kinetics and poor conductivity of FeF 3 has been improved by Co2+ dopants. • Li-storage capability and cyclability of FeF 3 was enhanced by Co2+ doping. [Display omitted] Theoretical calculation reveals that non-equivalent cobalt doping of 1% (in atomic ratio, at.) could lower the energy gap of cubic-phase FeF 3 from 4.27 eV to 0.27 eV, and fundamental change the charge density distribution around. Enlightened by these results, the electrochemical properties of iron fluoride cathode that limited by the intrinsic sluggish kinetics and poor electronic conductivity would be significantly improved by non-equivalent doping. Exemplified by porous FeF 3 nanocages prepared by pyrolysis of fast crystallized (NH 4) 3 FeF 6 (3NH 4 F·FeF 3) double salts, enhanced Li-storage capability and cyclability were demonstrated by non-equivalent cobalt doping due to defect-related modification of electron-/ion-conductivity and increase of active sites. [ABSTRACT FROM AUTHOR]

The in-situ fabrication of nanomaterials on conductive substrate is regarded as a viable way to prepare high-performance energy-storage materials, which not only can save the tedious production processes but also eliminate the binders and conductive agents. In this work, homogeneous vertically-aligned VO 2 nanobelt arrays growing directly on the vanadium foil are prepared via a facile hydrothermal method. Thanks to the unique nanoarrays structure in shortening ion diffusion path and providing ample space for infiltration of electrolyte, the nanobelt arrays demonstrate good electrochemical performance in alkali metal ion batteries. When employed as cathode for Li-ion batteries, a reversible specific capacity of 444.2 mAh g−1 at 50 mA g−1 and stable cyclic life over 900 cycles (lasting over 3120 h) with 83.9% capacity retention are successfully achieved. Furthermore, the VO 2 arrays also exhibit an acceptable Na+-storage property and maintain good structure integrity upon cycling. [ABSTRACT FROM AUTHOR]