一种可用于极化~3He实验的新型磁场系统

原子核自旋极化的~3He气体已被深入研究并广泛用于各种科学实验.在过去的极化~3He实验中,为了减小磁场梯度对纵向弛豫时间的影响,通常会建造大尺寸的亥姆霍兹线圈来提供所需均匀度的主磁场环境.本文通过计算得到了新的六正方形线圈系统,可以为极化~3He实验提供小型高均匀性的磁场装置.其中线圈系√统内部超过30%的区域磁场梯度满足(|▽B_x|~2+|▽B_y|~2)/B_0 10~(-4)cm~(-1),这一均匀区域比例超过了现在所有用于极化~3He实验的线圈装置.对于其他需要大均匀区域磁场环境的研究实验,新的六线圈系统也具有很好的应用价值.     

单晶六方SiC和多晶化学气相沉积SiC的常温辐照肿胀差异性

SiC具有耐辐射、低感生放射性、耐高温等特点,在先进核能系统中具有重要的应用.用1.5 MeV的Si离子在常温下注入单晶六方SiC和多晶化学气相沉积SiC,注量分别为1×10~(14)—2×10~(16)cm~(-2)和1×10~(15)—2×10~(16)cm~(-2),利用X射线衍射(XRD)仪和白光干涉仪测量材料的晶格常数和辐照肿胀随着注量增大的变化规律.结果显示:在1.5 MeV Si离子常温辐照下,注量达到2×10~(15)cm~(-2)时,单晶六方SiC完全非晶化;注量在1×10~(15)—5×10~(15)cm~(-2),单晶六方SiC的辐照肿胀明显高于多晶化学气相沉积SiC的辐照肿胀;注量达到1×10~(16)cm~(-2)时,单晶六方SiC和多晶化学气相沉积SiC的辐照肿胀达到饱和并趋于一致,肿胀结果表明常温辐照环境下多晶化学气相沉积SiC的非晶化阈值剂量大于单晶六方SiC.通过分析单晶六方SiC和多晶化学气相沉积SiC常温辐照肿胀差异的原因,研究了晶界对SiC材料非晶化肿胀规律的影响,并对XRD辐照肿胀测量方法的适用范围进行了讨论.     

75kG高均匀度Nb-Ti超导磁体

本文报道一个75kG Nb-Ti超导磁体.在直径2cm的球体内,磁场均匀度为7.52×10~(-5).当磁体通过超导开关闭环运行时,磁场的时间稳定度为2.33×10~(-5)hr~(-1)。并且通过我们发展的一种新方法,使磁体在闭环运行时,可以用微调线圈进行磁场的细微调节。     

Structure and luminescence of α-plane GaN on γ-plane sapphire substrate modified by Si implantation

We show the structural and optical properties of non-polar a-plane Ga N epitaxial films modified by Si ion implantation.Upon gradually raising Si fluences from 5×10~(13)cm~(-2)to 5×10~(15)cm~(-2),the n-type dopant concentration gradually increases from 4.6×10~(18)cm~(-2)to 4.5×10~(20)cm~(-2),while the generated vacancy density accordingly raises from3.7×10~(13)cm~(-2)to 3.8×10~(15)cm~(-2).Moreover,despite that the implantation enhances structural disorder,the epitaxial structure of the implanted region is still well preserved which is confirmed by Rutherford backscattering channeling spectrometry measurements.The monotonical uniaxial lattice expansion along the a direction (out-of-plane direction) is observed as a function of fluences till 1×10~(15)cm~(-2),which ceases at the overdose of 5×10~(15)cm~(-2)due to the partial amorphization in the surface region.Upon raising irradiation dose,a yellow emission in the as-grown sample is gradually quenched,probably due to the irradiation-induced generation of non-radiative recombination centers.     

金属表面吸附有机分子的红外激光光声光谱研究

本文利用支线调谐的连续CO_2激光器,在9.2～10.8μm的波段范围内,采用光声光谱的方法作了金属银表面吸附有机分子的红外激光光声光谱工作,测量了覆盖在银表面上的四层花生酸分子(Arachidicacid)以及面密度分别为σ_1=1.4×10~(15)cm~(-2)和σ_2=5.5×10~(15)cm~(-2)的 2-醋酸纤维素分子(cellulose dia-cetate)的红外激光光声谱.观察到了覆盖在银表面上的四层花生酸分子在944cm~(-1)附近的光声谱峰值,与其固体样品的红外傅里叶谱比较,没有发现可观察到的移动;我们也观察到了σ_1=1.4×10~(15)cm~(-2)和σ_2=5.5×10~(15)cm~(-2)的2-醋酸纤维素样品分别在1054cm~(-1)和1059cm~(-1)处的峰值,与同样样品的固体红外透射谱比较,发现前者的峰值有约5cm~(-1)的红移,而后者在实验精度范围内没有明显的峰值的位移.     

NaK高位6~1∑~+态与H_2碰撞中转移能配置

脉冲激光激发NaK 2~1Σ~+←1~1Σ~+跃迁,单模Ti宝石激光器激发2~1Σ~+至高位态6~1Σ~+,研究了6~1Σ~+与H_2碰撞中的碰撞转移。3D→4P(1.7μm)和5S→4P(1.24μm)荧光发射说明了预解离和碰撞解离的产生。在不同的H_2密度下,通过以上能级的荧光测量得到了预解离率,碰撞解离及碰撞转移速率系数Γ_(3D)~P=(5.3±2.5)×10~8 s~(-1),Γ_(5S)~P=(3.1±1.5)×10~8 s~(-1),k_(3D)=(3.7±1.7)×10~(-11)cm~3·s~(-1),k_(5S)=(2.9±1.4)×10~(-11)cm~3·s~(-1),k_(4P→4S)=(1.1±0.5)×10~(-11)cm~3·s~(-1),k_(3D→4P)=(6.5±3.1)×10~(-12)cm~3·s~(-1),k_(5S→4P)=(4.1±1.9)×10~(-12)cm~3·s~(-1)在不同H_2密度下,记录时间分辨荧光,由Stern-Volmer公式得到6~1Σ~+→2~1Σ~+,2~1Σ~+→1~1Σ~+的自发辐射寿命分别为(28±10)ns和(15±4)ns。6~1Σ~+→2~1Σ~+6~1Σ~+→1~1Σ~+及2~1Σ~+→1~1Σ~+分子态间与H_2的碰撞转移速率系数分别为(1.8±0.6)×10~(-11)cm~3·s~(-1),(1.6±0.5)×10~(-10)cm~3·s~(-1)和(6.3±1.9)×10~(-11)cm~3·s~(-1)。转移到H_2的振动、转动和平动能各占总转移能的0.58,0.03和0.39。主要能量转移至振动和平动能,支持6~1Σ~+-H_2间的共线型碰撞机制。     

α-Al_2O_3单晶中Fe~(3+)离子的电子顺磁共振

本文对α-Al_2O_3单晶体中Fe~(3+)离子在室温下,X波段进行了电子顺磁共振研究,发现Fe~(3+)离子实际上占据四种磁性不等价晶位。在同一氧离子层间的两种晶位上的Fe~(3+)离子具有相同的自旋哈密顿参量,而不同氧离子层间的晶位上的Fe~(3+)离子具有不同的自旋哈密顿参量,两种自旋哈密顿参量为:(1)g=2.001,g=2.003,D=1679×10~(-4)cm~(-1),|α|=237×10~(-4)cm~(-1),α—F=317×10~(-4)cm~(-1);(2)g=2.001,g=2.006,D=1660×10~(-4)cm~(-1),|α|=243×10~(-4)cm~(-1),α—F=338×10~(-4)cm~(-1)。     

进一步寻找磁单极子的实验进展

本文介绍了进一步寻找磁单极子的实验进展。目前没有新的磁单极子候选者被观测到。慢磁单极子的实验流强上限:速度在(10~(-4)-10~(-2))c范围内的观测,低于3.0×10~(-12)cm~(-2)sr~(-1)s~(-1);在(10~(-3)-10~(-2))c范围的观测,低于4.1×10~(-13)cm~(-2)sr~(-1)s~(-1)。     

进一步寻找磁单极子的实验进展

本文介绍了进一步寻找磁单极子的实验进展。目前没有新的磁单极子候选者被观测到。慢磁单极子的实验流强上限:速度在(10~(-4)-10~(-2))c范围内的观测,低于3.0×10~(-12)cm~(-2)sr~(-1)s~(-1);在(10~(-3)-10~(-2))c范围的观测,低于4.1×10~(-13)cm~(-2)sr~(-1)s~(-1)。     

Improved Semipolar(11(2|-)2) GaN Quality Grown on m-Plane Sapphire Substrates by Metal Organic Chemical Vapor Deposition Using Self-Organized SiN_x Interlayer

The effect of a self-organized SiN_x interlayer on the defect density of(11(2|-)2) semipolar GaN grown on m-plane sapphire is studied by transmission electron microscopy,atomic force microscopy and high resolution x-ray diffraction.The SiN_x interlayer reduces the c-type dislocation density from 2.5 × 10~(10) cm~(-2) to 5 × 10~8 cm~(-2).The SiN_x interlayer produces regions that are free from basal plane stacking faults(BSFs) and dislocations.The overall BSF density is reduced from 2.1 × 10~5 cm~(-1) to 1.3 × 10~4 cm~(-1).The large dislocations and BSF reduction in semipolar(11(2|-)2) GaN with the SiN_x interlayer result from two primary mechanisms.The first mechanism is the direct dislocation blocking by the SiN_x interlayer,and the second mechanism is associated with the unique structure character of(11(2|-)2) semipolar GaN.     

H-ion Irradiation-induced Annealing in He-ion Implanted 4H-SiC

Radiation-induced defect annealing in He~+ ion-implanted 4 H-SiC via H~+ ion irradiation is investigated by Raman spectroscopy. There are 4 H-SiC wafers irradiated with 230 keV He~+ ions with fluences ranging from 5.0×10~(15) cm~(-2)to 2.0×10~(16) cm~(-2) at room temperature. The post-implantation samples are irradiated by 260 keV H~+ ions at a fluence of 5.0×10~(15) cm~(-2) at room temperature. The intensities of Raman lines decrease after He implantation,while they increase after H irradiation. The experimental results present that the magnitude of Raman line increment is related to the concentration of pre-existing defects formed by He implantation. A strong new peak located near 966 cm~(-1), which is assigned to 3 C-SiC LO(Γ) phonon, is found in the He-implanted sample with a fluence of 5.0×10~(15) cm~(-2) followed by H irradiation. However, for the He-implanted sample with a fluence of2.0×10~(16) cm~(-2) followed by H irradiation, no 3 C-SiC phonon vibrations are found. The detailed reason for H irradiation-induced phase transformation in the He-implanted 4 H-SiC is discussed.     

Spectra properties of Yb~(3+),Er~(3+):Sc_2SiO_5 crystal

The influence of Er3+ ions on the spectra of Yb~(3+),Er~(3+): Sc_2 SiO_5(SSO) single crystal, which was obtained by Czochralski(Cz) method, is discussed. The absorption coefficient at 980 nm was 13.36 cm~(-1) with a peak absorption cross-section of 1.46 × 10~(-20) cm2. The emission cross-sections at 1034 nm and 1062 nm were 5.5 × 10~(-21) cm~2 and4.9 × 10~(-21) cm~2, respectively. The fluorescence lifetime was estimated as 1.24 ms at 1061 nm. The mechanical properties of SSO single crystal were also presented.     

与HBr(Χ~1Σ~+v″=1,J″=12)碰撞的CO_2(00~00)转动态分布

利用受激拉曼泵浦激发HBr分子至Χ~1Σ~+(1,12)激发态,由相干反斯托克斯-拉曼散射(CARS)光谱确定分子的激发.通过测量CARS谱相对强度,得到了HBr分子Χ~1Σ~+态(1,12)能级的布居数密度为n_1=0.54×10~(13) cm~(-3).在一次碰撞条件下,测量碰撞前后CO_2(00~00,J)态的激光感应荧光强度比,得到CO_2转动态的双指数分布.由二分量指数拟合得到T_a=261 K的低能分布和T_b=978 K的高能分布.结果表明,碰撞后约有65%的分子处于低J态,属于弹性或近弹性的弱碰撞;约有35%的分子处于高J态,属于非弹性的强碰撞.在振动-转动平动(V-RT)能量转移过程中,CO_2(00~00,J)态的总出现速率系数为(1.3±0.3)×10~(-10) cm~3 molecule~(-1)s~(-1);低转动态的平均倒空速率系数为(2.9±0.8)×10~(-10) cm~3 molecule~(-1)s~(-1).总的出现速率系数比平均倒空速率系数小,但在量级上保持一致.对CO_2 J=60-74高转动态,随着J值的增加,质心平移温度和质心平移能的平均改变增加.对低转动态,在碰撞过程中,J态既可能出现也可能被倒空,平移能的改变不易确定.     

Crystal growth and spectral properties of Tb:Lu_2O_3

The crystal growth,x-ray diffraction pattern,absorption spectrum,emission spectrum,and fluorescence lifetime of a Tb:Lu_2O_3 single crystal were studied.Excited at 483 nm,the peak absorption cross-section was calculated to be 3.5×10~(-22)cm~2,and the full width at half maximum was found to be 2.85 nm.The Judd-Ofelt(J-O)intensity parameters ?_2,?_4,and ?_6 were computed to be 3.79×10~(-20)cm~2,1.30×10~(-20)cm~2,and 1.08×10~(-20)cm~2,with a spectroscopic quality factor ?_4/?_6 being 1.20.The emission cross-sections of green emission around 543 nm and yellow emission around 584 nm were calculated to be 9.43×10~(-22)cm~2 and 1.32×10~(-22)cm~2,respectively.The fluorescence lifetimeτexp of ~5D_4 was fitted to be 1.13 ms.The data suggest that the Tb:Lu_2O_3 crystal could be a potential candidate for green and yellow laser operation.     

一类阴离子自由基液态电极材料研究

将碱金属溶于含有芳香化合物的醚类溶剂,碱金属的一个电子转移给芳香化合物形成一个碱金属离子和一个阴离子自由基,同时溶于醚类溶剂得到一类具有高电子电导率和离子电导率的蓝黑色液体.当碱金属为钠、芳香化合物为联苯、醚类溶剂为乙二醇二甲醚时,其电子电导率和离子电导率分别为8.4×10~(-3)S.cm~(-1)和3.6×10~(-3)S.cm~(-1),电极电位为0.09 V vs.Na/Na~+,适合作为负极材料,具有原材料低廉、易于制备等优点.我们将该液体作为负极,分别以苯醌和蒽醌(AQ)溶液作为正极构建了一种新型二次电池,结果表明以AQ溶液作为正极的电池具有长循环寿命、低成本的优势.该阴离子自由基液态负极材料的提出为开发新型的储能电池提供了新思路.     

Observation of Shubnikov-de Haas Oscillations in Large-Scale Weyl Semimetal WTe_2 Films

Topological Weyl semimetal WTe_2 with large-scale film form has a promising prospect for new-generation spintronic devices.However,it remains a hard task to suppress the defect states in large-scale WTe_2 films due to the chemical nature.Here we significantly improve the crystalline quality and remove the Te vacancies in WTe_2 films by post annealing.We observe the distinct Shubnikov-de Haas quantum oscillations in WTe_2 films.The nontrivial Berry phase can be revealed by Landau fan diagram anal.ysis.The Hall mobility of WTe_2 films can reach 1245 cm~2 V~(-1)s~(-1) and 1423 cm~2 V~(-1)s~(-1) for holes and electrons with the carrier density of 5×10~(19) cm~(-3) and2×10~(19) cm~(-3),respectively.Our work provides a feasible route to obtain high-quality Weyl semimetal films for the future topological quantum device applications.     

A simulation study on p-doping level of polymer host material in P3HT:PCBM bulk heterojunction solar cells

In this study,we investigate the influence of doping on the charge transfer and device characteristics parameters in the bulk heterojunction solar cells based on poly(3-hexylthiophene)(P3HT) and a methanofuUerene derivative(PCBM).Organic semiconductors are also known to be not pure and they have defects and impurities,some of them are being charged and act as p-type or n-type dopants.Calculations of the solar cell characteristics parameters versus the p-doping level have been done at three different n-dopings(N_d) that consist of 5 × 10~(17) cm~(-3),10~(18) cm~(-3),and 5 × 10~(18) cm~(-3).We perform the analysis of the doping concentration through the drift-diffusion model,and calculate the current and voltage doping dependency.We find that at three different n-dopant levels,optimum p-type doping is about N_p = 6 × 10~(18) cm~(-3).Simulation results have shown that by increasing doping level,V_(oc) monotonically increases by doping.Cell efficiency reaches its maximum at somewhat higher doping as FF has its peak at N_p = 3 × 10~(18) cm~(-3).Moreover,this paper demonstrates that the optimum value for the p-doping is about N_p = 6 × 10~(18) cm~(-3) and optimum value for n-dopant is N_d = 10~(18) cm~(-3),respectively.The simulated results confirm that doping considerably affects the performance of organic solar cells.     

新疆大中小城市夏季对流层NO_2垂直柱浓度变化特征

利用地基多轴差分光谱仪(Mini MAX—DOAS),选择新疆乌鲁木齐、库尔勒、博乐市具有代表性的大中小城市,于2014年6—8月对其市区、工业区、农田区的对流层NO_2浓度进行观测。结果表明:(1)大中小城市夏季大气对流层NO_2垂直柱浓度的日变化有波峰和波谷的波动,其峰值在大中小城市中有所差异,表现为乌鲁木齐(7.590×10~(15)molec·cm~(-2))库尔勒(7.559×10~(15)molec·cm~(-2))博乐(3.578×10~(15)molec·cm~(-2));(2)大中小城市夏季大气对流层NO_2垂直柱浓度大小与城市地表条件差异有关,尤其与观测区的车流量有密切关系,表现为市区(4.643×10~(15)molec·cm~(-2))工业区(4.469×10~(15)molec·cm~(-2))农田区(2.425×10~(15)molec·cm~(-2));(3)不同天气条件下大中小城市大气对流层NO_2的垂直柱浓度特征为雨天(3.082×10~(15)molec·cm~(-2))时浓度最小,说明降水对NO_2的浓度具有重要的影响。     

俄歇复合、电子泄漏和空穴注入对深紫外发光二极管效率衰退的影响（英文）

研究了俄歇复合、电子泄漏和空穴注入对深紫外发光二极管(DUV LED)效率衰退的影响。结果表明,当俄歇复合系数从10~(-32) cm~6·s~(-1)增大到10~(-30) cm~6·s~(-1)时,俄歇复合对效率衰退的影响很小。当俄歇复合系数增大到10~(-29) cm~6·s~(-1)时,俄歇复合对效率衰退有显著的影响。然而,对于AlGaN材料而言,俄歇复合系数很难达到10~(-29) cm~6·s~(-1)。此外,本研究还发现,即使设置的俄歇复合系数等于10~(-32) cm~6·s~(-1),DUV LED的效率衰退依旧随着电子泄漏的增加而增大。因此,这进一步证明了电子泄漏是导致DUV LED效率衰退的主要因素。此外,本工作还证明了空穴注入效率的提高可以有效地抑制DUV LED的效率衰退问题,这主要是由于更多的电子与空穴在量子阱中复合产生了光子,降低了电子从有源区中泄漏的几率。     

光折变晶体钛酸钡锶电荷传输参数的测量

报道用两波耦合技术测量光折变晶体钛酸钡锶(Ba_(1-x)Sr_xTiO-3,BST)的电荷传输参数φμτ在激光波长λ=515nm和光功率密度I—1W/cm~2下测得光折变响应时间为0.5sec.考虑到BST晶体吸收系数的光强相关性,修改了光栅形成率的函数变量,得到BST晶体的暗电导σ_a和电荷传输参数φμτ的拟合值分别为1.0×10~(-11)(Ωcm)~(-1)和2.8×10~(-10)cm~2/V.