电子阻止本领S_e(E)的z振荡及其计算

本文应用Hartree-Fock-Slater势能代替Thomas-Fermi势能,得出电子阻止本领S_e(E)的归一化关系式;同时,结合有效原子序数概念,得出能量对S_e(E)影响的关系式,利用前一关系式,定量计算了S_e(E)随离子和靶原子的原子序数z变化的振荡关系,计算结果与实验值相当符合,利用后一关系式,定量计算了多种离子-靶体系的S_e(E),与文献[1]的关系式比较,本文结果更好地符合实验值,而且有更广的能量适用范围。     

球面换能器汇聚系统V(z)曲线的射线理论

作者根据几何声学原理,分析了反射式声学显微镜中球面换能器汇聚系统V(z)曲线的形成过程,求出了V(z)曲线的表达式,同时给出了实验结果。     

电子阻止本领Se(E)的z振荡及其计算

本文应用Hartree-Fock-Slater势能代替Thomas-Fermi势能,得出电子阻止本领S_e(E)的归一化关系式;同时,结合有效原子序数概念,得出能量对S_e(E)影响的关系式,利用前一关系式,定量计算了S_e(E)随离子和靶原子的原子序数z变化的振荡关系,计算结果与实验值相当符合,利用后一关系式,定量计算了多种离子-靶体系的S_e(E),与文献[1]的关系式比较,本文结果更好地符合实验值,而且有更广的能量适用范 关键词：     

X射线发射深度分布φ(ρz)计算与电子探针定量分析

本文利用Monte Carlo方法和修改了的原子散射总截面公式,计算了在合金中产生X射线的深度分布φ(ρz),并用于电子探针定量分析。对12种二元合金、一种三元合金和碳化硅中的碳作了计算,结果比ZAF方法和Shimizu方法好。尤其对碳的计算结果比ZAF方法更好,表明本文的计算方法用于轻元素定量分析是可行的。 关键词：     

用V(z)曲线分析压电陶瓷表面的声学特性

本文利用超声显微镜技术中的V(z)曲线,无损伤地测量了压电陶瓷表面上不同点声表面波(瑞利波)速度,定量地分析了陶瓷的一致性。同时又根据V(z)曲线中周期的起伏,定性地给出了表面颗粒均匀性及缺陷存在的可能性。文中给出了几种不同陶瓷材料的实验数据及分析结果,并简单地描述了V(z)曲线的理论与声表面波(瑞利波)速度的计算公式、测试方法。     

Structures and stabilities of CBHz (z ≤ 8) and CxB3-xHz (x = 1, 2, z ≤ 14): prediction of novel organo-boron radicals

Hydrogenated boron-carbon clusters, i.e. organo-borons, have received considerable attention both theoretically and experimentally. Herein, using a topology searching strategy, we systematically explore the structures and stabilities of small organo-borons with CBH_z (z ≤ 8) and C_xB_3-xH_z (x = 1, 2,z≤ 14) stoichiometry, with particular interests in the intrinsic stabilities of the organo-boron radicals. At the CCSD(T)/aug-cc-pVQZ//B3LYP/aug-cc-pVTZ and CCSD(T)/aug-cc-pVQZ//MP2/aug-cc-pVTZ levels, the stabilities of these global minimum organo-boron species were evaluated by considering dissociation pathways and the binding energy per atom. Aside from the five already studied radicals (CBH₂, CBH₄, C₂BH₂, C₂BH₄ and CB₂H₃), we predict six novel radicals, i.e. CBH₆, C₂BH₆, C₂BH₈, CB₂H, CB₂H₅ and CB₂H₇, which could be detected under suitable circumstances. However, observation of the highly hydrogenated CB₂H₉ radical is much less likely due to its minute stability towards H-extrusion. The computationally determined stable/meta-stable maximum hydrogenation numbers for CB, C₂B and CB₂ (6, 8 and 8, respectively) are in excellent agreement with a simple electron-counting model for C_xB_y chains. The newly predicted organo-boron radicals await future laboratory verification.     

Superconductivity of (Sn1−z Pbz)1−x InxTe alloys

The temperature dependences of the electrical resistivity of (Sn_1?z Pb_z)_1?x In_xTe alloys with different concentrations of lead (z=0–0.60) and indium (x=0.03–0.20) were studied at temperatures T=0.4–4.2 K in magnetic fields from zero to H=15 kOe. A resistivity drop of no less than three-four orders of magnitude was observed in this range of alloy compositions. Application of a magnetic field above a critical level resulted in a recovery of the sample resistivity to the original value. The observed resistivity drop is identified with a superconducting transition. The critical parameters of the superconducting transition (T _c and H _c2) were determined at the drop to one half the normal resistivity level. Experimental dependences of the critical supercon-ducting-transition temperature T _c and of the second critical magnetic field H _c2 on the contents of lead (z) and indium (x) were measured. The data obtained confirm a strong localization of the In impurity states and are evidence of the extrinsic nature of superconductivity in the class of materials under study. It was established that as the Pb content in (Sn_1?z Pb_z)_1?x In_xTe increases, T _c and H _c2 decrease as the Fermi level E _F (fixed in the In impurity resonance band) leaves the Δ extremum and the superconductivity breaks down when E _F leaves the LΣ saddle point in the valence-band energy spectrum.     

Synthesis and characterization of (Bi2O3)1−x−y−z(Gd2O3)x (Sm2O3)y(Eu2O3)z quaternary solid solutions for solid oxide fuel cell

Sm₂O₃, Gd₂O₃, Eu₂O₃ triple-doped Bi₂O₃ based quaternary solid solutions were synthesized as a candidate electrolyte material using the solid-state reaction technique. The structural, thermal and electrical conductivity features of the ceramic samples were examined and compared by using X-ray powder diffraction (XRD), thermal gravimetry/differantial thermal analysis (TG/DTA) and the four-point probe technique (4PPT). The result of XRD measurements indicated that the (Bi₂O₃)_{(1−x−y−z)}(Gd₂O₃)_x(Sm₂O₃)_y(Eu₂O₃)_z (x = 10/y = 10/z = 5, 15, 20 mol % and x = 10/y = 5, 10, 15, 20/z = 10 mol %) samples have a stable face-centered cubic δ-phase and mixed phase crystallographic structure. The phase stability was also checked by the DTA evaluations results. The temperature dependent electrical conductivity measurements showed that the highest electrical conductivity was observed for the sample of the (Bi₂O₃)_0.75(Gd₂O₃)_0.10(Sm₂O₃)_0.05(Eu₂O₃)_0.10 system which has a stable and δ-phase was found as 6.67 × 10⁻³ (Ω cm)⁻¹ at 650 °C. This sample can be used as an electrolyte material in the solid oxide fuel cells (SOFCs) which is possible to operate at intermediate temperature ranges. The activation energy was also calculated at a low temperature range (350–650 °C) and high temperature range (above 650 °C). The values for the samples vary from 0.63 eV to 1.08 eV at low temperature and at high temperature they vary from 0.43 eV to 0.75 eV.     

Sr_(1-y)Eu_ySi_2O_(2-z)N_(2+2z/3)的发光性质及其在白光LED上的应用

采用高温固相法合成出系列黄绿色Sr1-yEuySi2O2-zN2+2z/3荧光材料,进行了光学性质表征并探索了其在LED上的应用。在Eu2+掺杂浓度为0～0.200范围内,所合成的化合物为系列色坐标可调的黄绿光-黄光连续固溶体,在250～500nm具有高的激发效率,激发和发射光谱位置及其发射强度随Eu2+浓度改变产生规律性变化;利用光谱理论系统研究了Eu2+的最低5d吸收能级、5d轨道重心移动、晶体场分裂和Stokes位移对激发和发射光谱位置、半峰全宽和荧光寿命的影响及其相互关系。该类荧光材料在77～425K具有良好的温度特性,425K时的发射强度为77K的58%左右。首次将它们和近紫外LED(～400nm)、蓝光LED(～460nm)封装成高亮度黄绿光和黄光LED以及白光LED,发光效率高达19lm/W,这些封装的LED的发光性能也随着Eu2+浓度,以及粉胶比例变化而呈规律性变化。     

Sm(Co,Cu,Fe,Zr)z反磁化过程的微磁学分析

通过微磁学有限元方法研究了微结构对各向异性的Sm(Co,Cu,Fe,Zr)z磁性能的影响， 并 对不同温度下的退磁曲线进行了计算.计算结果表明，矫顽力随着2∶17相晶粒尺寸的增大 而增大，随1∶5晶界相厚度的增大而减小；通过减小晶界相厚度或增大晶粒尺寸可以有效提 高 磁能积.反磁化的物理机制主要为形核机制，主要表现为首先在晶界相形成反磁化核，随 着 磁场的增大反磁化核不断长大，最后导致整个磁体的磁化反转；而当温度升高时，晶界相逐 渐变成非磁性相，使得反磁化核难以形成，因此出现了反常的矫顽力温度依赖关系. 关键词： 微磁学 有限元 微结构 磁性能     

团簇增强的纳秒激光电离产生Xez+(z≤20)高价离子

利用功率密度为1011—1012W·cm-2的1064nm纳秒激光电离氙原子团簇，在飞行时间质谱中观察到电离态高达+20的高价离子.不同脉冲束位置实验表明，仅当激光作用于分子束的中段时，才能观察到高价离子，且高价离子的强度随束源压力的增加而迅速增强.实验结果表明束中大尺寸团簇的存在与高价离子的形成密切相关.讨论了高价离子产生的可能机理. 关键词： 氙 纳秒激光 高价离子 飞行时间质谱     

Method of envelope functions and intervalley Γ-X z interaction of states in (001) III–V semiconductor heterostructures

The kp method is used to analyze the problem of intervalley Γ-X _z interaction of conduction-band states in the (001) lattice-matched III–V semiconductor heterostructures. A convenient basis for expansion of the wave function is systematically selected and a multiband system of equations is derived for the envelope functions which is then reduced to a system of three equations for three valleys Γ₁, X ₁, and X ₃) by using a unitary transformation. Intervalley Γ-X _z mixing is described by short-range potentials localized at heterojunctions. The expressions for the parameters determining the Γ-X _z mixing strength explicitly contain the chemical-composition profile of the structure since mixing is naturally stronger for abrupt heterojunctions than for structures with a continuously varying chemical composition. It is shown that direct Γ_{1?X 1} interaction of comparable strength to the Γ₁?X ₃ interaction exists. This must be taken into account when interpreting tunnel and optical experiments since the X ₁ valley is substantially lower in energy than the X ₃ valley.     

Density functional study of ternary AuxAgyCuz and AuxAgyCuz+ clusters (x + y+z = 5, 6)

ABSTRACT

We report a theoretical investigation of neutral Au_xAg_yCu_z and cationic Au_xAg_yCu_z⁺ ternary clusters, for x?+?y+z?=?5 and 6. Our study is performed within density functional theory at the TPSSTPSS/SDD level. The geometries, chemical order, binding energy, mixing energy, second difference in the energy, adiabatic ionisation potential of these clusters are evaluated as a function of the whole concentration range. The most probable dissociation channels and the corresponding dissociation energies for the most stable clusters are also determined and discussed.     

Elastic and thermal properties of Zr z Nb1 − z C x N y solid solutions

The temperature and concentration dependences of the elastic moduli and the thermal linear expansion coefficient of Zr _z Nb_{1 ? z} C _x N _y solid solutions containing from 3 to 8 at % of structural vacancies in a nonmetallic sublattice have been found. The temperature dependences of the Debye temperature Θ_D(T) have been calculated using the elastic data and the data on the heat capacity. It has been shown, using carbide NbC_0.97 as an example, that the Θ_D(T) dependences found from the elastic properties and the heat capacity coincide in the temperature range ～220–300 K. By analogy with the niobium carbide, the heat capacity C _p (300) of Zr _z Nb_{1 ? z} C _x N _y solid solutions of various compositions is calculated based on the values of Θ_D(300) determined from the elastic properties.     

Spin-reorientation transition at isoelectronic substitution in double-layer manganites (La1−z Prz)1.2Sr1.8Mn2O7

The transport, magnetic, and thermal properties of single crystal double-layer manganites of the Ruddlesden-Popper series (La_1?z Pr_z)_1.2Sr_1.8Mn₂O₇ (z=0.1 or 0.4) were studied. The compounds exhibit the colossal negative magnetoresistance effect in the region of a transition into a ferromagnetic state. Upon the isoelectronic substitution of Pr³⁺ for La³⁺, the Curie temperature decreases, while the easy magnetization axis rotates from the ab plane to the c axis. The observed effect is related to a change in the occupancy of $d{x^2-y^2} $ and $d{3z^2-r^2} $ orbitals as a result of stretching of the MnO₆ octahedra.     

Investigation of very neutron deficient Ru and Rh nuclei with the help of (40Ca;yp+zαγ) reactions

⁴⁰Ca beams from the Munich tandem and from the Munich heavy ion postaccelerator have been used to produce very neutron deficient Ru and Rh nuclei with⁵⁸Ni (⁴⁰Ca,yp+zαγ) reactions. The nuclei⁹²Ru,⁹⁴Ru and⁹⁵Rh have been studied with in-beam γ ray spectroscopy consisting of the measurement of excitation functions, γ γ coincidences, γ ray angular distributions and life times with the recoil distance method. The following new level energies, spin parity values and half-lives have been deduced:⁹²Ru: 865.3 keV 2⁺; 1,855.8 (4⁺); 2,672.7 (6⁺); 2,834.6 (8⁺) 100±14 ns; 3,640.3 (10⁺), 4,206.1 (12⁺)⁹⁴Ru: 2,624.7 (5^?) 530 _?200 ⁺⁵⁰⁰ ps; 3,991.7 (10⁺); 4,197.9 (9^?); 4,489.3 (11^?) 780±120 ps; 4,717.1 (12⁺) 35±3ps; 5,568.4 (13^?); 5.826.8 (14^?); 6,360.3 (14^?); 6,614.7 (13⁺); 7,158.3 (14⁺); 7,774.1 (15); 8,412.1 (16); 9,042.2 (17)⁹⁵Rh: 1,350.7 (13/2⁺); 2,067.2 (17/2⁺); 2,236.2 (17/2^?) 15±5ns; 2,449.0 (21/2⁺) 2.1±0.3 ns; 3,241.2 (21/2^?); 3,724.1 (25/2⁺); 3.908.9 (25/2^?); 4,307.2 (27/2⁺); 4,457.9; 4,716.9; 5,063.2; 6,797.3; 7,627.4 The residual activities have been studied with multi spectra analysis'. The decay scheme of⁹⁴Rh(25±2 s) has been established.     

基于z轴权重的麦粒图像三维重建

为得到清晰的麦粒重建切片,利用共轭射线弥补Radon空间数据缺失,在FDK(Feldkamp-Davis-Kress)重建算法的基础上,引入z轴权重函数来优化麦粒切片图像的重建结果。针对三维头模型,z-FDK算法重建结果的均方根误差比FDK算法的小3.6927,大大抑制了FDK算法中的z轴方向强度下降。实验结果表明,针对卵期、低龄幼虫期和高龄幼虫期的麦粒投影图像,z-FDK算法的平均梯度和对比度噪声比均大于FDK算法,重建麦粒茸毛端和胚部端两个区域的灰度值增大,伪影得到改善。     

Co~(2 )-Ti~(4 )和Cu~(2 )-Nb~(5 )离子取代BaFe_(12)O_(19)单晶体中Fe~(3 )离子的研究

本文对用Co~(2 )-Ti~(4 )和Cu~(2 )-Nb~(5 )离子取代BaFe_(12)O_(19)单晶体中Fe~(3 )离子进行了研究,以Bi_2O_3作为助熔剂生长出了BaFe_(12-2x)Co_x~(2 )Ti_x~(4 )O_(19)(x=0;0.04;0.09;0.13;0.27和0.68)以及BaFe_(12-x)[Nb_(1/3)~(5 )Cu_(2/3)~(2 )]_xO_(19)(x=0;0.28;0.44和0.60)这两系列的单晶体,测定了100—300K温度范围内样品的磁化强度σ与单轴各向异性常数K_1,我们发现,对CO~(2 )-Ti~(4 )取代的样品,当x≤0.09时,其σ与K_1随x的增加而缓慢增加;当x>0.09时,其σ与K_1随x的增加而迅速降低,至x=1.1时,K_1变为零,对Nb~(5 )-Cu~(2 )取代的样品,其σ值在整个成份范围内基本保持不变,且有缓慢增加趋势;而K_1值则随x增加而单调下降,提出了取代离子在M型六角铁氧体中可能的分布模型来解释我们的结果。     

金属玻璃(Fe_(1-x)Co_x)_(78)Si_(10)B_(12)的感生各向异性

本文研究了金属玻璃(Fe_(1-x)CO_x)_(78)Si_(10)B_(12)的磁化感生各向异性、应变感生各向异性随成分和温度的变化。磁化感生各向异性常数K_(um)为正值,x=0.7时为最大;不可逆的应变感生各向异性常数K_(usi)为正值,x=0.5时为最大;可逆的应变感生各向异性常数K_(usr)除了x>0.975区均为负值,在x=0.7时为最大;感生各向异性常数在温度变化时与M_s~α成正比,α在3.4和7.5之间随成分和退火工艺而变化。用短程有序模型解释了部分实验结果。     

Pb_(0.50)Sr_(0.75)Y_(0.70)Ca_(0.25)Cu_(1.70)O_y单晶的磁阻研究

对低掺杂区非超导的Pb_(6.56)Sr_(?)Y_(?)Ca_(?)Cu_(?)O_y单晶样品进行了电阻和磁阻的测量,发现在低温下电阻温度关系遵从变程跳跃传导的R=R_(?)exp[(T_(?)/T)~(?)]的变化规律,这说明该样品处于强局域化区域.在低温下的磁阻为负并有明显的各向异性,这表明这类体系的磁阻主要来自于轨道效应的贡献,并且可能受到自旋-轨道散射的影响.