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| 1 | Spatiotemporal pattern of urban forest leaf area index in response to rapid urbanization and urban greening显示文摘Rapid urbanization and urban greening have caused great changes to urban forests in China. Understanding spatiotemporal patterns of urban forest leaf area index(LAI) under rapid urbanization and urban greening is important for urban forest planning and management. We evaluated the potential for estimating urban forest LAI spatiotemporally by using Landsat TM imagery. We collected three scenes of Landsat TM(thematic mapper)images acquired in 1997, 2004 and 2010 and conducted a field survey to collect urban forest LAI. Finally, spatiotemporal maps of the urban forest LAI were created using a NDVI-based urban forest LAI predictive model.Our results show that normalized differential vegetation index(NDVI) could be used as a predictor for urban forest LAI similar to natural forests. Both rapid urbanization and urban greening contribute to the changing process of urban forest LAI. The urban forest has changed considerably from 1997 to 2010. Urban vegetated pixels decreased gradually from 1997 to 2010 due to intensive urbanization.Leaf area for the study area was 216.4, 145.2 and173.7 km^2 in the years 1997, 2004 and 2010, respectively.Urban forest LAI decreased sharply from 1997 to 2004 and increased slightly from 2004 to 2010 because of numerous greening policies. The urban forest LAI class distributions were skewed toward low values in 1997 and 2004. Moreover, the LAI presented a decreasing trend from suburban to downtown areas. We demonstrate the usefulness of TM remote-sensing in understanding spatiotemporal changing patterns of urban forest LAI under rapid urbanization and urban greening. | Zhibin Ren Yunxia Du Xingyuan He Ruiliang Pu Haifeng Zheng Haide Hu | 2018 | Journal of Forestry Research2018，29，3： | 4 |
| 2 | Tapering-induced enhancement of light extraction efficiency of nanowire deep ultraviolet LED by theoretical simulations显示文摘A nanowire(NW) structure provides an alternative scheme for deep ultraviolet light emitting diodes(DUV-LEDs)that promises high material quality and better light extraction efficiency(LEE). In this report, we investigate the influence of the tapering angle of closely packed Al Ga N NWs, which is found to exist naturally in molecular beam epitaxy(MBE) grown NW structures, on the LEE of NW DUV-LEDs. It is observed that, by having a small tapering angle, the vertical extraction is greatly enhanced for both transverse magnetic(TM) and transverse electric(TE) polarizations. Most notably, the vertical extraction of TM emission increased from 4.8% to 24.3%,which makes the LEE reasonably large to achieve high-performance DUV-LEDs. This is because the breaking of symmetry in the vertical direction changes the propagation of the light significantly to allow more coupling into radiation modes. Finally, we introduce errors to the NW positions to show the advantages of the tapered NW structures can be projected to random closely packed NW arrays. The results obtained in this paper can provide guidelines for designing efficient NW DUV-LEDs. | RONGHUI LIN SERGIO VALDES GALAN HAIDING SUN YANGRUI HU MOHD SHARIZAL ALIAS BILAL JANJUA TIEN KHEE NG BOON S.OOI XIAOHANG LI | 2018 | Photonics Research2018，6，5： | 3 |
| 3 | Boosted high-temperature electrical characteristics of AlGaN/GaN HEMTs with rationally designed compositionally graded AlGaN back barriers显示文摘Wide bandgap GaN-based HEMTs have shown great potential as key components in various power electronic systems but still face challenges in the pursuit of devices with stable operation capability especially in harsh environments.Here,we report a high-performance double heterojunction(DH)based AlGaN/GaN HEMT by incorporating a decreasing-Al-composition(DAC)graded AlGaN back barrier(BB)beneath the GaN channel.Thanks to the improved electron confinement enabled by graded BB,the DHHEMT exhibits significantly improved on-state drain current density and off-state breakdown voltage compared with a single heterojunction(SH)based HEMT.More intriguingly,with an additional Si Nx passivation layer,the surface states of the DH-HEMTs can be effectively suppressed,leading to an almost constant offstate leakage current and negligible gate contact degradation across the temperature range from 25℃to 150℃.These results highlight the superiority and reliability of the proposed graded AlGaN BB to boost device characteristics for applications under high temperatures and harsh conditions. | Haochen ZHANG Yue SUN Kunpeng HU Lei YANG Kun LIANG Zhanyong XING Hu WANG Mingshuo ZHANG Huabin YU Shi FANG Yang KANG Haiding SUN | 2023 | Science China(Information Sciences)2023，66，8： | 0 |
| 4 | Observation of polarity-switchable photoconductivity in lInitride/MoS_(x)core-shell nanowires显示文摘Ⅱ-Ⅴsemiconductor nanowires are indispensable building blocks for nanoscale electronic and optoelectronic devices.However,solely relying on their intrinsic physical and material properties sometimes limits device functionalities to meet the increasing demands in versatile and complex electronic world.By leveraging the distinctive nature of the one-dimensional geometry and large surface-to-volume ratio of the nanowires,new properties can be attained through monolithic integration of conventional nanowires with other easy-synthesized functional materials.Herein,we combine high-crystal-quality lInitridle nanowires with amorphous molybdenum sulfides(a-MoS)to construct II.nitride/a-MoS_(x) core-shell nanostructures.Upon light ilumination,such nanostructures exhibit striking spectrally distinctive photodetection characteristic in photoelectrochemical environment,demonstrating a negative photoresponsivity of-100.42 mA W^(-1)under 254 nm ilumination,and a positive photoresponsivity of 29.5 mA W^(-1)under 365 nm ilumination.Density functional theory calculations reveal that the successful surface modifcation of the nanowires via a-MoS_(x)decoration accelerates the reaction process at the electrolyte/nanowire interface,leading to the generation of opposite photocurrent signals under different photon ilumination.Most importantly,such polarity-switchable photoconductivity can be further tuned for multiple wavelength bands photodetection by simply adjusting the surrounding environment and/or tailoring the nanowire composition,showing great promise to build light-wavelength controllable sensing devices in the future. | Danhao Wang Wentiao Wu Shi Fang Yang Kang Xiaoning Wang Wei Hu Huabin Yu Haochen Zhang Xin Lu Yuanmin Luo Jr-Hau He Lan Fu Shibing Long Sheng Liu Haiding Sun | 2022 | Light(Science & Applications)2022，11，11： | 0 |
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