共查询到20条相似文献,搜索用时 171 毫秒
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将石墨和六方氮化硼(h-BN)混合粉球磨120h形成的非晶B-C-N粉在4.5GPa,1600K等温退火45min. XRD,TEM和Raman散射测量结果表明,高压合成的产物由晶格常数为a1=0.2551nm,c1=0.6716nm的六方Ⅰ相和a2=1.2360nm,c2=0.8570nm的六方Ⅱ相组成,其中六方Ⅱ相为B-C-N 新相. 在室温该新相在1279,1368,1398cm-1出现三个特征Raman峰. 变温Raman测量结果表明,在测量温度T=93K时,样品中的主要相为六方Ⅰ相,随着温度的升高,六方Ⅰ相逐渐向六方Ⅱ相转变,当T>473K时,六方Ⅰ相完全转变成六方Ⅱ相. 当温度从673K降到93K过程中,样品又从六方Ⅱ相逐渐变回到六方Ⅰ相. 对这一相变的机理进行了讨论.
关键词:
B-C-N
机械球磨
高温高压
相转变 相似文献
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基于安德森紧束缚模型,本文研究了无序双层六角氮化硼量子薄膜的电子性质. 数值计算结果表明在双层都无序掺杂的情况下,六角氮化硼量子薄膜的电子是局域的, 其表现为绝缘体性质;而对于单层掺杂(无论是氮原子还是硼原子)的双层六角氮化硼量子薄膜, 在能谱的带尾出现了持续的迁移率边.这就说明在单层掺杂的双层六角氮化硼量子薄膜中产生了 金属绝缘体转变.这一结果证实了有序-无序分区掺杂的理论模型,为理解及调控双层六角氮化硼量子薄膜 的电子性质提供了有益的理论指导. 相似文献
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采用电子束蒸发方法在大面积玻璃基底和钽基底上沉积六硼化镧薄膜阴极。分别对玻璃基底上沉积的六硼化镧薄膜的生长取向、附着力与不同蒸发角度(0°, 30°,45°和60°)的关系进行了研究;对钽基底上沉积的六硼化镧薄膜阴极的逸出功进行了研究。结果表明:在基底温度为250 ℃时,制备的六硼化镧薄膜具有(100)晶面择优生长的特点;蒸发角度为45°时,六硼化镧薄膜(100)晶面的晶格常数与靶材相差最小,晶粒较小;根据优化的工艺制备的六硼化镧薄膜阴极的逸出功为2.56 eV。 相似文献
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石墨烯-六方氮化硼面内异质结构因可调控石墨烯的能带结构而受到广泛关注. 本文介绍了在超高真空体系内, 利用两步生长法在两类对石墨烯分别有强和弱电子掺杂的基底, 即Rh(111)和Ir(111)上制备石墨烯-六方氮化硼单原子层异质结构. 通过扫描隧道显微镜及扫描隧道谱对这两种材料的形貌和电子结构进行研究发现: 石墨烯和六方氮化硼倾向于拼接生长形成单层的异质结构, 而非形成各自分立的畴区; 在拼接边界处, 石墨烯和六方氮化硼原子结构连续无缺陷; 拼接边界多为锯齿形型, 该实验结果与密度泛函理论计算结果相符合; 拼接界面处的石墨烯和六方氮化硼分别具有各自本征的电子结构, 六方氮化硼对石墨烯未产生电子掺杂效应. 相似文献
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Radioactive isotope(RI) beams are used to investigate the characteristics of unstable nuclei. Fragment separators, which have large angular and energy acceptances, were required to obtain high RI beam intensity. Careful design is required due to the large high order aberrations induced by the large aperture magnets, which are used to collect rare isotopes obtained from a high energy primary heavy-ion beam hitting a target [1]. In our design study, a high energy 12C primary beam was used to produce neutron rich medium mass heavy ions such as 9Li. Mirror symmetric optics provides smaller high order aberration and thus a design study of a mirror symmetric in-flight projectile fragment separator was performed to obtain large angular and energy acceptances. We investigated the optimal material and thickness of the target for the production of a 9Li beam. Based on the simulation, a beryllium target was selected to give a large yield with a smaller energy spread of the secondary beam. We also investigated the optimal thickness of the aluminum energy degrader. The selections of the target material and thickness were investigated by using the code LISE++.After optimization of the material and the thickness of the target, we performed a design study of the optics of the in-flight separator for a high resolution with high acceptance. The designed optics of the in-flight separator consists of the four normal conducting quadrupole triplets, three sextupoles and two normal conducting dipoles. The horizontal and vertical angular acceptances of the designed separator are 40 mrad and 70 mrad, respectively. The separator has a mass resolution of 640 when the object size is taken to be 1 mm. The correction of the second order aberration in the designed optics was performed by three sextupole magnets. The path length of the designed separator is 20.183 m. The optics design and the high order aberrations were investigated by using the code ORBIT. 相似文献
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The magnet design for the HLS storage ring upgrade project 总被引:1,自引:0,他引:1
In order to improve the performance of the Hefei Light Source (HLS), in particular to get higher brilliance synchrotron radiation and increase the number of straight section insertion devices, an upgrade project called HLSII will be launched soon. The storage ring lattice, which has a double bend achromatic structure with four periods, comprises eight dipoles, 32 quadrupoles and 32 combined function sextupoles. The design and analysis of the magnets are shown in this paper, along with the optimization of the multipurpose combined function magnet, which consists of three magnets: skew quadrupole, horizontal dipole and vertical dipole, with the main sextupole magnet. This type of magnet is the first one that has been designed and used in China. The mechanical design and fabrication procedures for the magnets are also presented. 相似文献
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中国散裂中子源(CSNS)快循环同步加速器(RCS)把能量为80 MeV的束流储存并加速到1.6 GeV然后引出到靶站。为了减少RCS中的束流损失,有必要对RCS做色品校正,并减小动量偏移对束流光学的影响。尝试了多种色品校正方案并对不同色品校正方案做了比较。用三维跟踪程序SIMPSONS研究了色品校正六极铁与空间电荷效应对束流的影响。色品校正六极铁可以有效减小色品引起的频散,但是由于六极铁为非线性元件,导致不同振幅的粒子间有一定频散。模拟发现同时存在空间电荷效应和色品校正六极铁时,会有少量的束流损失。 相似文献
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本文将电偏转三级象差的工作推广,使适合于入射处就有电场的情况,导出一个能在任意平面上求三级偏转象差的公式,对分离式电偏转系统及叠合式偏转系统(Deflection Yoke)均适用。并经过数学处理,使公式简洁,换算方便,还将象差系数积分公式中的轴上场E0(z)的一、二级微商全部消除,以提高计算精度。为了和我们的前一工作相对应,符号的命名和计算格式也与文献[1]相同,最后还描述了顶点在屏上的圆锥形细束在偏转后产生的光栅畸变、场曲、象散、彗差等图形与这套系数的对应关系。这种关系也完全适合于磁偏转三级象差的情况。
关键词: 相似文献
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近来磁六极透镜作为球差校正器引起了人们的注意。本文研究了磁圆形透镜和磁六极透镜的场分布叠加形成的复合系统的象差。我们在复数域中定义了内积,采用了复数的表象和微分算符,全面讨论了这种复合系统的高斯光学性质及二、三、四级象差,得出了各级象差所有的象差系数的公式。
关键词: 相似文献
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A high energy heavy ion microbeam irradiation system is constructed at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS). A quadrupole focusing system, in combination with a series of slits, has been designed here. The IMP microbeam system is described in detail. The intrinsic and parasitic aberrations associated with the magnets are simulated. The ion beam optics of this microbeam system is investigated systematically. Then the optimized initial beam parameters are given for high spatial resolution and high hitting rates. 相似文献
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本文的主要目的在以近似方法讨论高级象差特性。首先由对称性讨论了二级象差的独立象差数,近似讨论了象差的几何意义,再由坐标变换的观点导出了光栏移动时象差变化的规律。由Fermat原理和同一光线可看作是各不同点发出的观点导出了物体移动时象差变化的规律。由于运用Fermat原理,所得的结果实际上是略去初级象差影响后的近似结果,因此表示式相当简单。然后我们把象差产生的原因分为二类。其一称作是本徵的,是入射光束无象差时必然产生的象差,用象差看作球差的观点导出了它们的表示式,结果表明,高级球差和本徵轴外球差是象差产生的原因,并导出了各种象差同时产生的状况。象差的另一类称作是衍生的,它们是由入射光线原有象差引起的初级象差差异,由初级象差理论即可得出它们的表示式。这一些高级象差的规律和近似表示可作为评断象差产生原因的半定量依据。最后,用Fermat原理讨论了高级色差问题,并说明Fermat原理之所以可在高级象差理论中应用的理由及不致误差过大的应用范围。 相似文献
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DAI Zhi-Yong XIE Yu-Tong LI Hong ZHANG Wen-Wei LIU Yun-Long PAN Hai-Feng ZHANG Lin-Wen DENG Jian-Jun 《中国物理C(英文版)》2009,33(9)
DRAGON-Ⅰ designed and manufactured by CAEP is a linear induction accelerator which can produce a 20 MeV-3 kA-60 us electron beam. The high performance required for the machine is determined by the beam quality and thus is greatly dependent on the accelerator alignment. In order to reduce the chromatic effect of the beam, the stretched wire technique has been developed to measure magnetic axes of the cells precisely, and the dipole steering magnets have been equipped into each cell to correct its magnetic axis misalignment. Finally, the laser tracker has been used to examine the installation error of the accelerator. In this paper, different alignment techniques and the primary results are presented and discussed. 相似文献
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We investigated the transverse beam dynamics in a thermal wave model by using a functional method. It can describe the beam optical elements separately with a kernel for a component. The method can be applied to general quadrupole magnets beyond a thin lens approximation as well as drift spaces. We found that the model can successfully describe the PARMILA simulation result through an FODO lattice structure for the Gaussian input beam without space charge effects. 相似文献
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A high energy heavy ion microbeam irradiation system is constructed at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS). A quadrupole focusing system, in combination with a series of slits, has been designed here. The IMP microbeam system is described in detail. The 相似文献