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We attain N-polar and Al-polar AlN thin films on Si(111) substrates by plasma-assisted molecular beam epitaxy. The polarity of AlN epilayers has been validated by wet chemical etching using tetramethylammonium hydroxide and by the direct cross-sectional observation of atomic stacking under high-angle annular dark-field scanning transmission electron microscopy. For the 290 nm-thick as-grown N-polar AlN epilayer, x-ray diffraction (XRD) (002) and (102) ω rocking curve peak full width half maximums (FWHMs) are 475 and 1177 arcsec, and the surface mean square roughness (RMS) is 0.30 nm. We flipped the polarity using the metal-flux-modulation-epitaxy (MME) strategy. The MME strategy promotes anti-phase boundaries (APBs) on the { 2 2 ¯ 01 } crystalline planes instead of commonly observed lateral planar APBs in AlN epilayers. Merging of the tilted APBs at ∼50 nm leads to a complete Al-polar surface. For the 180 nm-thick Al-polar AlN epilayer, XRD (002) and (102) peak FWHMs are 1505 and 2380 arcsec, and the surface RMS is 1.41 nm. Strain analysis by XRD and Raman spectroscopy indicates a uniform tensile strain of 0.160% across the N-polar AlN epilayer surface and a strain distribution of 0.113%–1.16% through the epilayer. In contrast, the Al-polar AlN epilayer exhibits a much broader tensile strain distribution of 0.482%–2.406% along the growth direction, potentially due to the interaction of polarity inversion and strain relaxation. [ABSTRACT FROM AUTHOR]

Photocatalytic selective oxidation of aromatic alcohols to aldehydes under mild conditions is of great significance for green and sustainable development, and design of photocatalysts with high efficiency is an interesting topic. Herein, we present a new conjugated microporous polymer photocatalyst named NiFe-CMP, composed of Ni-porphyrin and Fe-bipyridyl units, for efficient photocatalytic oxidation of aromatic alcohols. The porous structure of NiFe-CMP provides numerous absorption sites and exposes catalytically active centres, enhancing the reaction kinetics. Experimental and theoretical analyses indicate that the incorporation of Fe and Ni dual-metal sites not only enhances the dissociation of excitons into free charge carriers by regulating the electronic structures, but also reduces the reaction energy barrier for the formation of *O2 intermediates, thus promoting the massive production of ˙O2− active species. Impressively, NiFe-CMP manifests excellent catalytic performance, achieving a 96.2% conversion rate for the oxidation of benzyl alcohol to benzaldehyde under 4 hours of visible light radiation, over approximately 17 times higher than that of the pristine CMP. Besides, NiFe-CMP exhibits high recyclability and displays an excellent adaptability towards various aromatic alcohols. This work further advances the rational design of efficient photocatalysts for selective aromatic alcohol oxidation. [ABSTRACT FROM AUTHOR]

[Objective] The purpose of this paper is to explore the influence of different size soil samples on resistivity. [Method]Taking the laterite in Yunnan area as the research object, the remolded laterite with different water content, dry density and geometric size was prepared. The relationship between the resistivity characteristics under different geometric sizes was studied, and a reasonable, reliable and suitable resistivity model for laterite with different geometric sizes was constructed. [Result] The results showed that under the same conditions, the resistivity decreases with the increase of water content, increases with the increase of porosity, and decreases with the increase of volumetric water content. The change of geometric size changes the pore structure and saturation distribution of the soil, causing the change of resistivity, showing the increase of geometric size and the increase of resistivity. Based on the change relationship of resistivity characteristics, a resistivity volumetric water content model suitable for different geometric sizes is constructed, and the model has high fitting accuracy. [Conclusion] This experiment provides a way and reference for the non-destructive, rapid and economical estimation of water content in laterite areas with size and volume differentiation by high-density electrical method. [ABSTRACT FROM AUTHOR]

Carrier diffusion properties, including the diffusion length, diffusion coefficient, and carrier lifetime are important for photonic devices. In nitride semiconductors, there are many microscopic structures, which have a strong influence on carrier diffusion. In this paper, a method based on the photo-assisted Kelvin-probe force microscope and the confocal time-resolved photoluminescence spectrum at the same position is developed to map simultaneously the topography and the nanoscale vertical carrier diffusion on the semiconductor surface. On the surface without any dislocations, the hole diffusion length and diffusion coefficient are 161 ± 8 nm and 1.6 ± 0.2 cm2/s, respectively. Near the termination of the dislocation loops on the surface, it can be clearly seen that the diffusion length and diffusion coefficient gradually drop to about 13 ± 5 nm and 0.02 ± 0.01 cm2/s with a spatial resolution of about 100 nm. [ABSTRACT FROM AUTHOR]