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In this work, we demonstrate multi-channel GaN varactors with enhanced quality-factor (Q-factor) and cutoff frequency (f0) and present a comprehensive investigation of their current conduction mechanisms. The varactors were based on 1x-, 2x-, and 3x-channel GaN-on-SiC epitaxy with excellent channel conductivity, showing great enhancement of ∼270% both in Q-factor and in f0, thanks to the reduced resistance and capacitance by multi-channels in AC conduction. The DC leakage current (I) in the three types of devices is dominated by Poole–Frenkel (PF) emission and trap-assisted tunneling, before the depletion of the topmost channel and after the depletion of the bottommost channel, respectively. The I in multi-channel devices is dominated by two-dimensional variable range hopping of electrons along the vertical direction between channels, when the topmost channel is depleted while the bottommost channel is not. The analysis is supported by excellent agreement between experimental results and theoretical models, along with activation energies (EA) quantitatively and statistically determined, presenting a promising technology with key understandings for future performance enhancement. [ABSTRACT FROM AUTHOR]

Ecosystem water use efficiency (WUE) and ecosystem photosynthetic efficiency (EPE) are key indicators in studies of the carbon–water cycle in terrestrial ecosystems. Analyses of WUE and EPE can enhance our understanding of the relationship between ecosystem light use efficiency and WUE. Although several studies of individual indexes (i.e., either WUE or EPE) have been conducted, analyses of variation in both WUE and EPE, as well as their relationships, have rarely been conducted. Here, we analyzed spatial and temporal variation in WUE and EPE in Central Asia. Specifically, time trend analysis was conducted to characterize temporal and spatial changes in WUE and EPE in Central Asia from 2001 to 2020 at different altitudes and latitudes. Pearson correlation analysis was used to characterize the effects of precipitation and temperature on WUE and EPE. WUE decreased and EPE increased in Central Asia over the 20-year study period; this might have been due to interannual variations in precipitation and temperature. WUE was highest in August, and EPE was highest in June and July. Substantial spatial heterogeneity in WUE and EPE was observed; WUE was highly variable in Central Asia as well as in western and southern Central Asia. Major changes in EPE were observed in northern, eastern, and southern Central Asia. We also found that both WUE and EPE decreased with the increase in altitude. WUE was positively correlated with temperature and negatively correlated with precipitation, whereas EPE was positively correlated with both temperature and precipitation. The increase in photosynthetic efficiency might be one of the main factors contributing to increases in ecosystem productivity in arid environments. The temporal and spatial variation in WUE and EPE observed in our study will aid ecosystem research, providing a reliable theoretical basis for ecosystem research in areas with scarce large-scale data, integrated water resources management, and ecosystem restoration efforts. Our findings also enhance our understanding of the terrestrial carbon–water cycle and have implications for predicting ecosystem responses to climate change. The results of this study provide insights that will aid studies of the terrestrial carbon–water cycle under the background of climate change. It is of great significance to further study the carbon water cycle in the future. [ABSTRACT FROM AUTHOR]

In this work, we focused on investigating the transport-limited trapping effects in GaN-on-Si buffer layers as well as impact of the thickness of buffer layers (TBuf) upon such effects. Vertical transport dynamics of charges within the buffer layers and their key energy levels are quantitatively and statistically investigated and analyzed. The results show that an increased TBuf diminishes both impurity conduction of the defect band formed by carbon doping as well as the injection of electrons from the substrate, greatly diminishing the current collapse and improving the stability of the device. Such enhancement is mainly attributed to the reduced vertical electric field within the thickened epitaxy, which provides an additional pathway to address the current collapse and yields more efficient power GaN-on-Si devices. [ABSTRACT FROM AUTHOR]

Heterostructure engineering plays a vital role in regulating the material interface, thus boosting the electron transportation pathway in advanced catalysis. Herein, a novel Bi 2 O 3 /BiO 2 heterojunction catalyst was synthesized via a molten alkali-assisted dealumination strategy and exhibited rich structural dynamics for an electrocatalytic CO 2 reduction reaction (ECO 2 RR). By coupling in situ X-ray diffraction and Raman spectroscopy measurements, we found that the as-synthesized Bi 2 O 3 /BiO 2 heterostructure can be transformed into a novel Bi/BiO 2 Mott-Schottky heterostructure, leading to enhanced adsorption performance for CO 2 and *OCHO intermediates. Consequently, high selectivity toward formate larger than 95% was rendered in a wide potential window along with an optimum partial current density of -111.42 mA cm -2 that benchmarked with the state-of-the-art Bi-based ECO 2 RR catalysts. This work reports the construction and fruitful structural dynamic insights of a novel heterojunction electrocatalyst for ECO 2 RR, which paves the way for the rational design of efficient heterojunction electrocatalysts for ECO 2 RR and beyond.

Developing efficient recycling technologies for large-scale spent batteries is the key to build a zero-waste city. Herein, a [Al 8.5 Fe 0.5 P 12 O 48 ]·[C 24 H 72 N 16 ]·[Li·4H 2 O]·[12H 2 O] (AlFePO-Li) zeolite, crystallizing in space group I 4̅3 m with a = 16.6778(3) Å, has been constructed via the hydrothermal treatment of spent LiFePO 4 battery. Benefiting from the three-dimensional 12-member-ring channels in its structure and chemical adsorption, excellent Pb 2+ removal capacity up to 723.8 mg g -1 has been achieved. Detailed adsorption mechanism study revealed that the cation exchange capacity is significantly contributed by ion exchange of the protonated organic amine cations in the zeolite channel and the protons from the framework dangling phosphate group. This work demonstrates a novel method of reutilizing spent LIBs to construct zeolite for heavy metal removal. It is of great importance to achieve sustainable development based on the "resource utilization" and "trash-to-treasure" strategy.

Search for simple and efficient recycling methods to utilize spent lithium-ion batteries is crucial for achieving sustainable resource development and reducing the hazardous materials released from the spent batteries. Herein, we have developed a new strategy to utilize the spent LiFePO 4 batteries by utilizing the cathode plate as raw material to synthesize mesoporous core-shell adsorbent Mm@SiO 2 (Mm denoted as the magnetic material) through a simple alkaline leaching process. The as-converted material exhibits excellent adsorption capacity when it has been used to remove heavy metal ions in heavy metal polluted water. The adsorption capacities for Cu 2+ , Cd 2+ , and Mn 2+ have been achieved up to 71.23, 80.31 and 68.73 mg g -1 , respectively. The detailed adsorption mechanism has been elucidated with comprehensive characterization techniques, including TEM, XPS, NEXAS, and EXAFS, the edge shared [Cu 2 O 8 ] bipyramids can be fit against the EXAFS data to represent the atomic-scale local structure after Mm@SiO 2 adsorbs Cu 2+ . The present work demonstrates a novel routine to reutilize the spent lithium batteries, which is of great importance to achieve sustainable development based on the "waste-to-treasure" and "waste-to-control-waste" strategy for simultaneously reducing the hazardous release from industrial solid waste and heavy metal polluted water., (Copyright © 2020. Published by Elsevier B.V.)