Breakdown voltage enhancement in GaN channel and AlGaN channel HEMTs using large gate metal height

A large gate metal height technique is proposed to enhance breakdown voltage in GaN channel and AlGaN channel high-electron-mobility-transistors(HEMTs).For GaN channel HEMTs with gate-drain spacing LGD=2.5μm,the breakdown voltage VBR increases from 518 V to 582 V by increasing gate metal height h from 0.2μm to 0.4μm.For GaN channel HEMTs with LGD=7μm,VBR increases from 953 V to 1310 V by increasing h from 0.8μm to 1.6μm.The breakdown voltage enhancement results from the increase of the gate sidewall capacitance and depletion region extension.For Al0.4Ga0.6N channel HEMT with LGD=7μm,VBR increases from 1535 V to 1763 V by increasing h from 0.8μm to 1.6μm,resulting in a high average breakdown electric field of 2.51 MV/cm.Simulation and analysis indicate that the high gate metal height is an effective method to enhance breakdown voltage in GaN-based HEMTs,and this method can be utilized in all the lateral semiconductor devices.

Facile synthesis and antitumor activity of novel 2-trifluoromethylthieno[2,3-d]pyrimidine derivatives

A series of novel 2-trifluoromethylthieno[2,3-d]pyrimidine derivatives were synthesized by a facile three-step procedure that afforded advantages of mild reaction conditions, simple protocol and good yields. The structures of the final compounds were confirmed by 1R, NMR, El-MS, elemental analysis, and X-ray diffraction. Preliminary bioassay results showed that some of the analogs exhibit excellent antitumor activity against MCF-7 and HepG2, especially compounds 3a, 3b, 3e and 3h exhibited higher activity than the positive control gefitinib.

Personalized course generation and evolution based on genetic algorithms

Online learners are individuals,and their learning abilities,knowledge,and learning performance differ substantially and are ever changing.These individual characteristics pose considerable challenges to online learning courses.In this paper,we propose an online course generation and evolution approach based on genetic algorithms to provide personalized learning.The courses generated consider not only the difficulty level of a concept and the time spent by an individual learner on the concept,but also the changing learning performance of the individual learner during the learning process.We present a layered topological sort algorithm,which converges towards an optimal solution while considering multiple objectives.Our general approach makes use of the stochastic convergence of genetic algorithms.Experimental results show that the proposed algorithm is superior to the free browsing learning mode typically enabled by online learning environments because of the precise selection of learning content relevant to the individual learner,which results in good learning performance.

A nanosilica/exfoliated graphene composite film-modified electrode for sensitive detection of methyl parathion

Graphene nanosheets （GS） were easily prepared through liquid-phase exfoliation of graphite powder in N,N-dimethylformamide （DMF） with the assistance of sodium citrate. Then, GS was coated onto a glassy carbon electrode （GCE） surface by drop to fabricate a GS]GCE nanointerface. Subsequently, by using tetraethylorthosilicate sol as precursor, nanosilica was electrochemically deposited onto the GS]GCE surface to produce a nanocomposite film electrode （nanosilicaJGSJGCE）. Electrochemical behaviors of methyl parathion （MP） on the nanosilica/GS/GCE surface were investigated thoroughly. It was found that the nanosilicaJGS nanocomposites can improve the redox peak currents of MP significantly due to the synergetic effect. The oxidation peak current was linearly related to MP concentration in the range from 0.0005 μmol/L to 5.6 μmol/L. The detection limit was calculated to be 0.07 nmol/L （SJN = 3）. The developed method was used to determine MP in real samples. The recoveries were in the range from 95.4% to 104.2%, demonstrating satisfactory results.

Monodisperse Spherical Sandwiched Structured SiO_(2)@CsPbX_(3)@SiO_(2) Perovskite Composites for the Determination of Fe^(3+) Ion in Water Samples

The application of all-inorganic CsPbX_(3)(X=Cl^(-),Br^(-)and I^(-))perovskite nanocrystals(PNCs)is hindered by their poor stability under diff erent environments(moisture,UV light and high temperature).Herein,we demonstrate a novel in-situ growth and post-coating technique to prepare monodisperse spherical sandwiched structured SiO_(2)@CsPbX_(3)@SiO_(2)perovskite composites.In this strategy,the environmental stability of CsPbX_(3)PNCs is remarkably improved due to protecting evenly distribution in the surface of composites through the design of spherical sandwiched structure,and the negative eff ects of SiO_(2)coating on photoluminescence property of CsPbX_(3)PNCs could be reduced eff ectively.Furthermore,regular monodisperse spherical structure and uniform size of composites greatly benefit their application in relative fields.The experiment results indicate that the as-prepared product have outstanding abilities of water-,oxidation-and UV radiation resistance.Finally,the SiO_(2)@CsPbBr_(3)@SiO_(2)perovskite composites are successfully used for highly sensitive detection of Fe^(3+)in water sample.The results show limit of detection(LOD)is 3μM and good linearity is between 10 and 70μM(R^(2)=0.9963).Furthermore,the proposed perovskite composites have been successfully applied for the analysis of Fe^(3+)in real samples with satisfactory results.