X射线晶体衍射实验

X射线及其通过晶体时衍射现象的发现是二十世纪物理学的伟大研究成果之一。作为近代物理实验的重要组成部分,X射线晶体衍射实验除了验证X射线和晶体的基本性质外,对于晶体(特别是固体)材料的研究、控制和改进生产工艺过程,具有非常重要的应用价值。自从X射线被发现,和X射线的一系列的实验出现以后,人类对物质结构的认识发生了质的飞跃,它不但推进了物理学的发展,而且也使化学、地质学、天文学、医学、工艺学等等许多科学领域得到新的重大的发展。近年来特别对生物化学的发展也起了重要的作用。作为这样一个重要的近代物理实验,了解它的发生、发展背景和它在现代科学发展过程中的作用。对于更好的学习和做好X射线晶体衍射实验,和进一步创造性工作是有意义的。     

Electronic structure,Dirac points and Fermi arc surface states in three-dimensional Dirac semimetal Na_3Bi from angle-resolved photoemission spectroscopy

The three-dimensional(3D) Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A_3Bi(A = Na, K, Rb). Here we report comprehensive high-resolution angle-resolved photoemission(ARPES) measurements on the two cleaved surfaces,(001) and(100), of Na_3Bi. On the(001) surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the k_x–k_y plane and by varying the photon energy to get access to different out-of-plane k_zs. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the(100) surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the(100) plane. We directly observe two isolated 3D Dirac nodes on the(100) surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ~150 me V before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na_3Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the3 D Dirac cones, on the possible formation of surface reconstruction of the(001) surface, and on the issue of basic Brillouin zone selection for the(100) surface.     

Comparison of TiO2 and ZrO2 Films Deposited by Electron-Beam Evaporation and by Sol-Gel Process

TiO2 and ZrO2 films are deposited by electron-beam （EB） evaporation and by sol-gel process. The film properties are characterized by visible and Fourier-transform infrared spectrometry, x-ray diffraction analysis, surface roughness measure, absorption and laser-induced damage threshold （LIDT） test. It is found that the sol-gel films have lower refractive index, packing density and roughness than EB deposited films due to their amorphous structure and high OH group concentration in the film. The high LIDT of sol-gel films is mainly due to their amorphous and porous structure, and low absorption. LIDT of EB deposited film is considerably affected by defects in the film, and LIDT of sol-gel deposited film is mainly effected by residual organic impurities and solvent trapped in the film.     

个体风险模型的Poisson复合模型近似

本文首先简要介绍了停止损失序在风险期望值相等时的一些推论 ,然后借助停止损失序详尽地讨论了仅取有限个值的随机变量的格点化 ,并以此作为出发点在多重衰减模型的框架下 ,给出了以 Poisson复合模型近似个体风险模型的一般步骤 ,同时导出了评价这一近似优劣程度的一个数量指标的解析表达式。     

双峰分布的超细颗粒动态光散射信号模拟及精度分析

为获取双峰分布超细颗粒的动态光散射模拟信号,通过建立动态光散射随机过程的AR模型,利用修正的Levison Durbin递推算法确定模型参数和阶数的方法模拟光散射信号.分别对10 nm与90 nm,200 nm与1 000 nm双峰分布颗粒的动态光散射信号进行模拟,得到的模拟信号光强自相关函数与理论值吻合,用双指数法对颗粒粒径反演,相对误差小于3.55%.通过分析模型阶数、采样时间、采样频率、模拟数据长度等参数对模拟精度的影响,得出双峰分布颗粒光散射信号的模拟精度与各参数的关系:在低于阈值阶数时,模型阶数选择对精度影响大,模型阶数越高,信号模拟的精度越高,高于阈值阶数时,模型阶数选择对精度影响不大,可选阈值阶数模型模拟信号.选定一定的采样时间,采样频率越高,模拟数据长度越长,模拟精度越高.     

Laser Induced Damage Threshold at 355 and 1064nm of Ta2O5 Films of Different Phases

Ta2O5 films axe deposited on fused silica substrates by conventional electron beam evaporation method. By annealing at different temperatures, Ta2 O5 films of amorphous, hexagonal and orthorhombic phases are obtained and confirmed by x-ray diffractometer （XRD） results. X-ray photoelectron spectroscopy （XPS） analysis shows that chemical composition of all the films is stoichiometry. It is found that the amorphous Ta2 O5 film achieves the highest laser induced damage threshold （LIDT） either at 355 or 1064nm, followed by hexagonal phase and finally orthorhombic phase. The damage morphologies at 355 and 1064nm are different as the former shows a uniform fused area while the latter is centred on one or more defect points, which is induced by different damage mechanisms. The decrease of the LIDT at 1064nm is attributed to the increasing structural defect, while at 355nm is due to the combination effect of the increasing structural defect and decreasing band gap energy.     

基于共掺杂调控C32多极矩的二阶非线性光学响应

基于密度泛函(DFT)理论,采用CAM-B3LYP方法,以C₃₂分子为多极矩构建骨架,设计了两类替位式共掺杂的富勒烯衍生物C₂₈B₂N₂和C₂₈B₂P₂,共16种同分异构体,并对它们的电子性质、线性极化率α和一阶超极化率β进行研究。结果表明,掺杂后分子的HOMO-LUMO能隙变小,C₂₈B₂P₂的α和β值均大于C28B2N2系列。其中偶极分子具有大的β值,八极分子则有较小的β值,筛选出具有优异的二阶非线性光学(NLO)响应特性的结构。含时密度泛函理论(TD-DFT)的结果表明,与C₃₂相比,掺杂后所有结构的吸收光谱的响应范围变宽,最大吸收强度减弱,且最大吸收波长的位置发生红移或蓝移。基于完全态求和(SOS)方法,分别用二能级或三能级公式解释了两类共掺杂结构中β值最大的来源,并且证明了与之有关的电子激发类型为π→π*激发。     

气态ClO2体积分数与爆炸压力的关系

采用20 L柱状爆炸罐研究了气态ClO2的爆炸特性,得出了气态ClO2分解爆炸的体积分数下限为9.5%,不存在上限。在实验条件下,气态ClO2的爆炸压力随体积分数的增加而增大,体积分数为90%时,最大爆炸超压达到0.64 MPa,且气态ClO2的爆炸压力与其体积分数梯度有关。最大爆炸超压出现的时间随气态ClO2体积分数的增加而缩短,体积分数为10%时,最大爆压在2 195 ms时出现,当体积分数达到70%时,最大爆压出现的时间在10 ms以内,体积分数继续增加,最大爆压出现的时间基本维持在8 ms。     

金属钯／铂卟啉室温Lin光探针在生物医学领域的应用研究

钯（Ⅱ）／铂（Ⅱ）卟啉络合物在室温下发射长寿命（ms)、长波长的Lin光，这些特点使其在生物分析方面成为有用的探针。本文综述了该探针在Lin光免疫标记、肿瘤诊断、DNA测定、生物传感器及其它方面的研究进展。引用文献43篇。     

低能氘分子团(d_3~ )与固体靶原子相互作用过程中的团簇效应研究

通过对三个氘原子组成的氘分子团与三个分立的氘原子在轰击固体靶原子时所激发的Ｘ射线产额的差别的研究，进而揭示氘分子团在以库仑激发方式与靶原子相互作用中所体现出的团簇优势。实验结果显示，在１０－１００ｋｅＶ／ｄ能区，每个分子团中的氘核所激发的Ｘ射线产额平均为相同能量的普通氘核所激发的Ｘ射线产额的２．５倍。而且该比值具有较很弱的能量相关性。基于原子库仑相互作用规律对实验现象做了初步解释和简要估算，提出了分子团与靶原子作用模型。