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Multi-functional photodetector is very important in spectral information acquisition but is difficult to implement. In this work, a self-driven multifunctional ultraviolet photodetector based on (Al,Ga)N nanowire/hydrogel interface is proposed and demonstrated successfully. It is found that the conventional photodetector has two functional interfaces with the full contact between nanowires and liquid-electrolyte, which is very difficult to modulate the competition carrier transport process. Thanks to the design of local contact between (Al,Ga)N nanowires and quasi-solid hydrogel, only one functional interface operates in the photodetector, achieving the slow/fast response speed over 20 times difference at 0 V bias (1080/1217 ms under 310 nm illumination and 46/45 ms under 365 nm illumination). Such unique behavior of switchable response speed is mainly attributed to the balance of dynamic carrier transport across the (Al,Ga)N/GaN and nanowire/hydrogel local contact interfaces. Moreover, the local contact interface proves excellent reusability and the photocurrent density remains at 94.7% after preserving for 2 months. Particularly, taking advantage of the slow/fast response characteristic, the proposed self-driven ultraviolet photodetector is demonstrated to have the ability to distinguish light wavelengths and can be integrated with hydrogel into an array detection system for the image display. [Display omitted] • A novel photodetector with (Al,Ga)N nanowire/hydrogel interface is realized. • The self-driven photodetector shows a special switchable response speed. • The use of hydrogel breaks the limitation of traditional liquid-electrolyte and cell. • The response speed is fast for PEC-type devices with nanostructure. • Self-driven photodetector array can distinguish light wavelengths and display images. [ABSTRACT FROM AUTHOR]

In this study, quasi-static tests were conducted on six steel-concrete-steel composite wall (SCSCW) specimens with novel dumbbell-shaped connectors (DSCs) to investigate their seismic performance. The research parameters included the connector arrangement scheme and the axial load. The failure mode, load-displacement curve, and strain data were analyzed in detail. All the specimens exhibited flexural failure, and the experimental phenomena included the local buckling of external steel plates and compressive failure of internal concrete. The local buckling located between the foundation and first row of connectors, had a limited effect on the bearing capacity of the specimens. The connectors effectively controlled the buckling range of the external steel plates. With increasing axial load, the deformation capacity of the specimens decreased significantly. Under the same displacement, the greater the axial load, the greater the secant stiffness, and the higher the accumulated energy dissipation value. When the load reached its peak value, the yield range of the bottom front steel plates of specimen with large axial load was less than that of the specimen with small axial load. The theoretical formula accurately calculated the flexural bearing capacity of SCSCWs, and the maximum error and the average ratio which was defined as experimental value to calculated value were 9% and 1.02, respectively. The horizontal load-displacement relationship of the specimens was calculated using the OpenSees software, and the maximum error of the bearing capacity was 4%. The parametric analysis showed that increasing the steel plate thickness can effectively improve the bearing capacity of SCSCWs. [Display omitted] • Quasi-static tests were conducted to study the seismic behavior of specimens. • Novel dumbbell-shaped connectors were used in steel-concrete-steel composite walls. • Theoretical formula for the sectional bearing capacity of specimens. • Finite element analysis was performed by OpenSees software. [ABSTRACT FROM AUTHOR]

Prior research shows mixed results on the relationship between well-being and economic growth, and the relationship between well-being and population size, yet consistent associations between well-being and green space. This paper aims to analyse the relationship between city residents' well-being and three established indicators: economic growth (as measured by GDP per capita), population size, and green space. A Big Data approach based on the lexica used on social media was proposed to develop well-being indicators. Using the 2016 data of Weibo (i.e. the Chinese version of Twitter), this study finds that the relationship between residents' well-being and GDP per capita and the relationship between residents' well-being and population size both form inverted U-shaped curves. Specifically, for poor cities, levels of well-being increase as GDP per capita increases. But after peaking at around the median GDP per capita point, levels of well-being drop as the city's economy continues to increase. Similarly, levels of well-being increase with population size for small cities, but decrease for those cities whose population sizes rank in the top quarter. In contrast, there is a positive relationship between well-being and the percentage of green space for all cities. Implications and future directions are discussed. [ABSTRACT FROM AUTHOR]

Highlights • Nanocolumn selective-area growth was achieved by nanosphere lithography and etching. • The shadow effect and Ti growth suppression contribute to selective-area growth. • InGaN sections selective-area grown could be beneficial to uniform In distribution. Abstract In this paper, the selective-area growth (SAG) of GaN-based nanocolumns (NCs) on silicon (Si) has been investigated experimentally. A low-cost and facile method has been proposed and implemented to fabricate the SAG NCs, which contains the processes of nanosphere lithography (NSL) and plasma-assisted molecular beam epitaxy (MBE). SAG NCs grown by this method indicates a higher ability to modulate the NC distributions than those grown by the conventional patterned method. According to photoluminescence results, InGaN/GaN NCs grown on Si nanopillars produced by NSL and etching show the more uniform indium (In) distribution than those grown on the openings of patterned Si substrate. Furthermore, according to the kinetic processes during MBE growth, it is proposed that the SAG of NCs results from the combination of the shadow effect of Si nano-pillars and the growth suppression of titanium (Ti) film. [ABSTRACT FROM AUTHOR]

Highlights • Deep-UV emission at 260 nm has been obtained from AlGaN-based MQW structures. • High AlGaN and AlGaN/AlN MQW structures has been grown by PA-MBE. • Larger Al flux ratio and higher growth temperature contribute to increasing Al content of AlGaN. • The emission wavelength was tuned by controlling the thickness of AlGaN quantum well. Abstract Deep ultraviolet (UV) emission at 260 nm has been obtained from high Al content AlGaN/AlN multi-quantum well (MQW) structures by plasma-assisted molecular beam epitaxy (PA-MBE) on AlN template on sapphire substrates. The effect of III/V ratio and growth temperature on structural and optical properties of AlGaN was studied. It was observed that Al content in AlGaN material increased with increasing Al flux ratio or growth temperature. By altering growth conditions, AlGaN with high Al content of 47–80% was obtained. Further studies indicate that AlGaN layers have excellent surface morphology and optical properties grown in slightly metal-rich condition. As for AlGaN/AlN MQW, the emission wavelength was tuned by controlling the thickness of AlGaN quantum well, and deep ultraviolet emission below up to 260 nm was obtained from AlGaN (2.4 nm)/AlN(6.9 nm) MQW at room temperature. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • An opposite photocatalytic oxidation behaviors of BiOCl and TiO 2 was observed. • BiOCl tends to decomposite perhalocarboxylate by hole transfer. • TiO 2 preferred to oxidize organic pollutants mediated by hydroxyl radical. • Different photocatalytic behaviors are attributed to the surface site of reactant adsorption and hole trapping. Abstract Although all the semiconductor-based photocatalysis is initiated by photoinduced conduction band electron and valence band hole, the reaction pathway and activity of the electron and hole would be largely dependent on the type of the photocatalyst. It is essential to distinguish and understand the photocatalyst-dependence of a specific reaction. In the present study, we compared the photocatalytic behaviors of BiOCl and TiO 2 for the degradation of different pollutants including perfluorooctanoic acid (PFOA), chloroacetic acids and benzoic acid. We found that the decompositions of perhalocarboxylate acids (PHCAs) such as PFOA and trichloroacetic acid (TCA) were much rapider over BiOCl than on the TiO 2 (commercial P25). The surface-area- normalized rate constants for the oxidation of TCA have five orders of magnitude of difference between these two systems. By contrast, the degradation rates of OH-sensitive organic pollutants such as dichloroacetic acid, monochloroacetic acid and benzoic acid were much higher on the TiO 2. Moreover, much more meta-substituted hydroxylated intermediate was observed during the photocatalytic oxidation of benzoic acid on BiOCl. In addition, PFOA and TCA were degraded efficiently in the BiOCl system even in the presence of other labile organic compounds (such as acetic acid). All the experimental results definitely indicate that BiOCl photocatalyst prefers to directly oxidize the PHCAs and benzoic acid by the hole transfer, while TiO 2 tends to oxidize the solvent water molecule to OH radical. The mechanism underlying on the different activity of BiOCl and TiO 2 are further discussed. [ABSTRACT FROM AUTHOR]