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尿素能够显著破坏甲壳素/壳聚糖分子氢键结构和疏水相互作用,增加其临界胶束浓度,促进多糖大分子的溶解,并能减少其在溶液中的自聚集现象.碱-尿素水溶液可以作为一种新型的甲壳素/壳聚糖绿色溶剂,有望用于对刺激性要求较为苛刻的食品、生物医学等领域.壳聚糖衍生物特别是其与过渡金属离子的配合物具有良好的尿素吸附功能,可用于尿毒症患者血液中小分子毒物的吸附,对机体刺激性小且不吸附血清蛋白等生物大分子.有望成为血液灌流治疗法中清除尿素等小分子毒性物质的良好吸附剂.壳聚糖还可以作为包膜材料,制备壳聚糖包膜尿素,与普通的包膜尿素相比性能更为优越. 相似文献
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主要研究因变量存在缺失且协变量部分包含测量误差情形下,如何对变系数部分线性模型同时进行参数估计和变量选择.我们利用插补方法来处理缺失数据,并结合修正的profile最小二乘估计和SCAD惩罚对参数进行估计和变量选择.并且证明所得的估计具有渐近正态性和Oracle性质.通过数值模拟进一步研究所得估计的有限样本性质. 相似文献
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Characterization of Al2O3 /GaN/AlGaN/GaN metalinsulator-semiconductor high electron mobility transistors with different gate recess depths 下载免费PDF全文
In this paper,in order to solve the interface-trap issue and enhance the transconductance induced by high-k dielectric in metal-insulator-semiconductor (MIS) high electron mobility transistors (HEMTs),we demonstrate better performances of recessed-gate Al 2 O 3 MIS-HEMTs which are fabricated by Fluorine-based Si 3 N 4 etching and chlorinebased AlGaN etching with three etching times (15 s,17 s and 19 s).The gate leakage current of MIS-HEMT is about three orders of magnitude lower than that of AlGaN/GaN HEMT.Through the recessed-gate etching,the transconductance increases effectively.When the recessed-gate depth is 1.02 nm,the best interface performance with τ it =(0.20-1.59) μs and D it =(0.55-1.08)×10 12 cm 2 ·eV 1 can be obtained.After chlorine-based etching,the interface trap density reduces considerably without generating any new type of trap.The accumulated chlorine ions and the N vacancies in the AlGaN surface caused by the plasma etching can degrade the breakdown and the high frequency performances of devices.By comparing the characteristics of recessed-gate MIS-HEMTs with different etching times,it is found that a low power chlorine-based plasma etching for a short time (15 s in this paper) can enhance the performances of MIS-HEMTs effectively. 相似文献
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An enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMTs) was fabricated with 15-nm AlGaN barrier layer. E-mode operation was achieved by using fluorine plasma treatment and post-gate rapid thermal annealing. The thin barrier depletion-HEMTs with a threshold voltage typically around --1.7 V, which is higher than that of the 22-nm barrier depletion-mode HEMTs (--3.5 V). Therefore, the thin barrier is emerging as an excellent candidate to realize the enhancement-mode operation. With 0.6-μ m gate length, the devices treated by fluorine plasma for 150-W RF power at 150 s exhibited a threshold voltage of 1.3 V. The maximum drain current and maximum transconductance are 300 mA/mm, and 177 mS/mm, respectively. Compared with the 22-nm barrier E-mode devices, VT of the thin barrier HEMTs is much more stable under the gate step-stress. 相似文献
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In this paper, we have discussed the effect of electrical stress on GaN light emitting diode (LED). With the lapse of time, the LED with an applied large current stress can reduce its current more than without such a stress under a large forward-voltage drop. Its scanning electron microscopy (SEM) image shows that there exist several pits on the surface of the p-metal. With an electrical stress applied, the number of pits greatly increases. We also find that the degradation of GaN LED is related to the oxidized Ni/Au ohmic contact to p-GaN. The electrical activation of H-passivated Mg acceptors is described in detail. Annealing is performed in ambient air for 10 min and the differential resistances at a forward-voltage drop of 5 V are taken to evaluate the activation of the Mg acceptors. These results suggest some mechanisms of degradation responsible for these phenomena, which are described in the paper. 相似文献