电荷失配对SiC半超结垂直双扩散金属氧化物半导体场效应管击穿电压的影响

Si C半超结垂直双扩散金属氧化物半导体场效应管(VDMOSFET)相对于常规VDMOSFET在相同导通电阻下具有更大击穿电压.在N型外延层上进行离子注入形成半超结结构中的P柱是制造Si C半超结VDMOSFET的关键工艺.本文通过二维数值仿真研究了离子注入导致的电荷失配对4H-Si C超结和半超结VDMOSFET击穿电压的影响,在电荷失配程度为30%时出现半超结VDMOSFET的最大击穿电压.在本文的器件参数下,P柱浓度偏差导致击穿电压降低15%时,半超结VDMOSFET柱区浓度偏差范围相对于超结VDMOSFET可提高69.5%,这意味着半超结VDMOSFET对柱区离子注入的控制要求更低,工艺制造难度更低.     

Xylomexicanins E-H,new limonoids from Xylocarpus granatum

Four novel tetranortriterpenoids, xylomexicanins E–H (1–4), were isolated from the seeds of the Chinese mangrove, Xylocarpus granatum. Among them, xylomexicanin E (1) represents the first example of limonoid with azaspiro skeleton between B (pyrrolidine) and C rings, whose biosynthetic pathways were proposed. The structures were elucidated on the basis of one- and two-dimensional NMR (including ¹H, ¹³C NMR, DEPT, ¹H–¹H COSY, HSQC, HMBC, and NOESY) and confirmed by high-resolution mass spectrometry. Compound 2, the second example of a limonoid with a C-9–C-30 linkage, showed moderate activity against the A549 and RERF cell line with IC₅₀ value of 18.83 and 15.83 μM,     

A new taxane composed of two N-formyl rotamers from Taxus canadensis

A taxane with an amino-side chain on C-5 was identified for the first time from rooted cuttings of the Canadian yew, Taxus canadensis. The structure was characterized as 7β,9α,10β,13α-tetraacetoxy-5α-[3′-(N-formyl-N-methylamino)-3′-phenylpropanoyl]oxytaxa-4(20),12-diene (1) on the basis of 1D-, 2D-NMR data, and HR-FABMS analyses. The spectra revealed that in CDCl₃ solution 1 was composed of two rotamers (1a and 1b) in a ratio of approximately 2:1.     

Fabrication and characterization of 4H—SiC bipolar junction transistor with double base epilayer

In this paper we report on a novel structure of a 4H-SiC bipolar junction transistor with a double base epilayer that is continuously grown.The measured dc common-emitter current gain is 16.8 at IC = 28.6 mA(J C = 183.4 A/cm2),and it increases with the collector current density increasing.The specific on-state resistance(Rsp-on) is32.3mΩ·cm 2 and the open-base breakdown voltage reaches 410 V.The emitter N-type specific contact resistance and N + emitter layer sheet resistance are 1.7×10-3 Ω·cm2 and 150 /,respectively.     

Efficient iron(III)-catalyzed three-component coupling reaction of alkynes, CH2Cl2 and amines to propargylamines

An iron(III)-catalyzed three-component coupling reaction of alkynes, CH(2)Cl(2) and amines was developed for facile synthesis of propargylamines. Preliminary mechanism investigation using in situ FT-IR reveals that the crucial Fe-acetylide intermediate could be formed through C-H bond activation of alkynes thanks to cooperative effect of FeCl(3) and 1,1,3,3-tetramethylguanidine.     

Enantioseparation and absolute configuration determination of angular-type pyranocoumarins from peucedani radix using enzymatic hydrolysis and chiral HPLC-MS/MS analysis

Angular-type pyranocoumarins from Peucedani Radix (Chinese name: Qian-hu) have exhibited potential for use on treatment of cancer and pulmonary hypertension. Due to the existence of C-3' and C-4' chiral centers, compounds belonging to this chemical type commonly exist in enantiomers and/or diastereoisomers, which may elicit distinct activities during their interactions with the human body. In the present study, a new method, which combines enzymatic hydrolysis with chiral LC-MS/MS analysis, has been developed to determine the absolute configurations of these angular-type pyranocoumarins. Pyranocoumarins isolated from Qian-hu, their enantiomers, or metabolites were individually incubated with rat liver microsomes. As the common end product from enzymatic hydrolysis of all tested pyranocoumarins, cis-khellactone was collected and its absolute configuration was determined by comparison with (+)-cis-khellactone and (-)-cis-khellactone using chiral LC-MS/MS. The absolute configurations of all tested parent pyranocoumarins were determined by combination of LC-MS/MS, NMR and polarimetric analysis. The results revealed that the metabolite cis-khellactone retained the same absolute configurations of the stereogenic carbons as the respective parent compound. This method was proven to be rapid and sensitive and also has advantages in discriminating single enantiomers and mixtures of optical isomers with different ratios.     

琼脂糖凝胶电泳法分离金属性和半导体性单壁碳纳米管

琼脂糖凝胶电泳(AGE)是实现金属性单壁碳纳米管(m-SWCNTs)和半导体性单壁碳纳米管(s-SWCNTs)低成本、规模化分离的有效技术之一。本研究利用琼脂糖凝胶电泳分离单壁碳纳米管。通过紫外-可见-近红外吸收光谱和拉曼光谱对色谱带进行分段表征,发现电泳中迁移的最快的部分m-SWCNTs含量最高。考察了琼脂糖的浓度对SWCNTs中m-SWCNTs分离的影响。结果表明:高的琼脂糖浓度有利于m-SWC-NTs的富集,可以通过扩大电荷密度带来的迁移速率的差异来使SWCNTs中的m-SWCNTs得到更有效的分离。     

Four new epoxy taxanes from needles of Taxus cuspidata (Taxaceae)

Four new epoxy taxoids were isolated from the needles of Taxus cuspidata. Their structures were established as 2a,9a-diacetoxy-5a-cinnamoyloxy-11,12-epoxy-10ss-hydroxytax-4(20)-en-13-one (1), 2a,10ss-diacetoxy-5a-cinnamoyloxy-11,12-epoxy-9a-hydroxytax-4(20)-en-13-one (2), 2a,9a-diacetoxy-11,12-epoxy-10ss,20-dihydroxytax-4-en-13-one (3) and 2a,10ss-diacetoxy-11,12-epoxy-9a,20-dihydroxytax-4-en-13-one (4) on the basis of spectral analysis including 1H-NMR, 13C-NMR, 1H-1H-COSY, HSQC, HMBC and HRFABMS. Compounds 3 and 4 are the first example of 11,12-epoxy taxoids with C-4 double bond found in T. cuspidata.     

Lateral depletion-mode 4H-SiC n-channel junction field-effect transistors operational at 400℃

This paper presents the development of lateral depletion-mode n-channel 4 H-SiC junction field-effect transistors(LJFETs)using double-mesa process toward high-temperature integrated circuit(IC)applications.At room temperature,the fabricated LJFETs show a drain-to-source saturation current of 23.03μA/μm,which corresponds to a current density of 7678 A/cm².The gate-to-source parasitic resistance of 17.56 kΩ·μm is reduced to contribute only 13.49%of the on-resistance of 130.15 kΩ·μm,which helps to improve the transconductance up to 8.61μS/μm.High temperature characteristics of LJFETs were performed from room temperature to 400℃.At temperatures up to 400℃in air,it is observed that the fabricated LJFETs still show normally-on operating characteristics.The drain-to-source saturation current,transconductance and intrinsic gain at 400℃are 7.47μA/μm,2.35μS/μm and 41.35,respectively.These results show significant improvement over state-of-the-art and make them attractive for high-temperature IC applications.     

Structure preserving quaternion full orthogonalization method with applications

This article proposes a structure-preserving quaternion full orthogonalization method (QFOM) for solving quaternion linear systems arising from color image restoration. The method is based on the quaternion Arnoldi procedure preserving the quaternion Hessenberg form. Combining with the preconditioning techniques, we further derive a variant of the QFOM for solving the linear systems, which can greatly improve the rate of convergence of QFOM. Numerical experiments on randomly generated data and color image restoration problems illustrate the effectiveness of the proposed algorithms in comparison with some existing methods.