Unusual phonon softening in delta-phase plutonium

The phonon density of states and adiabatic sound velocities were measured on fcc-stabilized 242Pu0.95Al0.05. The phonon frequencies and sound velocities decrease considerably (soften) with increasing temperature despite negligible thermal expansion. The frequency softening of the transverse branch along the [111] direction is anomalously large ( approximately 30%) and is very sensitive to alloy composition. The large magnitude of the phonon softening is not observed in any other fcc metals and may arise from an unusual temperature dependence of the electronic structure in this narrow 5f-band metal.     

Angle-resolved x-ray photoelectron spectroscopy study of GeO_x growth by plasma post-oxidation

The growth process of GeO_x films formed by plasma post-oxidation(PPO) at room temperature(RT) is investigated using angle-resolved x-ray photoelectron spectroscopy(AR-XPS). The experimental results show that the distributions of the Ge~(4+)states, a mixture of the Ge_(2+)and Ge~(3+)states, and the Ge~(1+)states are localized from the GeO_x surface to the GeO_x/Ge interface. Moreover, the Ge~(1+)states are predominant when the two outermost layers of Ge atoms are oxidized.These findings are helpful for establishing in-depth knowledge of the growth mechanism of the GeO_x layer and valuable for the optimization of Ge-based gate stacks for future complementary metal–oxide–semiconductor(MOS) field-effect transistor(CMOSFET) devices.     

自旋为1的双层平方晶格阻挫模型的相变

采用双时格林函数方法研究了自旋为1的双层平方晶格阻挫模型的相变行为.详细探讨了层间耦合相互作用J_c和单离子各向异性参数D对奈尔态(AF1)和共线态(AF2)之间相转换的影响.结果显示:只要参数J_c和D不同时为零,奈尔态和共线态在J₂=J₁/2(这里J₁和J₂分别描述的是系统自旋间最近邻和次近邻交换作用)时的相变温度相等,两个态共存.在低于相变点的温度范围内,AF1-AF2态之间可以发生相转换,其相变类型为一阶相变.当J₂≠J₁/2时,尽管AF1-AF2态有不同相变温度,但它们也可以共存.如果AF1(AF2)态的相变温度大,在低温,AF1(AF2)态更稳定;在高温,AF2(AF1)态更稳定;在中间温度范围内,AF1-AF2态之间也可以发生一阶相转换.     

基于Cu/SiO_x/Al结构的阻变存储器多值特性及机理的研究

采用氧化硅材料构建了Cu/SiOx/Al的三明治结构阻变存储器件.用半导体参数分析仪对其阻变特性进行测量,结果表明其具有明显的阻变特性,并且通过调节限制电流,得到了四个稳定的阻态,各相邻阻态的电阻比大于10,并且具有良好的数据保持能力.在不同温度条件下对各个阻态进行电学测试及拟合,明确了不同阻态的电子传输机理不尽相同:阻态1和阻态2为欧姆传导机制,阻态3为P-F(Pool-Frenkel)发射机制,阻态4为肖特基发射机制.根据电子传输机制,建立了铜细丝导电模型并对Cu/SiOx/Al阻变存储器件各个阻态的电致阻变机制进行解释.     

Ab initio study of structural, electronic and optical properties of MnHg(SCN)4 and FeHg(SCN)4

 The structural, electronic and optical properties of MnHg(SCN)₄ and FeHg(SCN)₄ were studied by means of quantum-mechanical calculations based on the density-functional theory and pseudopotential method. The lattice constants can be compared with the experimental values when the effects of temperature are considered. The peaks of partial density of states of S, C, N and Hg of FeHg(SCN)₄ have a tendency of shifting to the higher energy levels relative to those of MnHg(SCN)₄. The distributions of the 3d electronic states in the transition metal atoms show quite large difference and decide different optical properties. We found that absorptional peaks of FeHg(SCN)₄ lag behind those of MnHg(SCN)₄ and the peak in the infrared range has a higher absorptional intensity, which are in accord with the experimental results. By analyzing the distributions and transitions of the 3d electronic states, we explained the different absorption phenomena.     

二氧化碳-甲烷混合气体水合物四相区实验研究

以水合物的形式封存CO₂和置换海底的天然气（CH₄）水合物需要对CO₂-CH₄混合水合物的四相平衡状态及数据有清楚的了解。本文通过实验和模型计算对不同组分的CO₂-CH₄混合水合物的较高四相区（Q2）相平衡进行了测定和表述。实验温度范围为273.16～297 15 K,压力范围分为0～10 MPa。四相区的温度压力范围分别是283.51到287.04 K和4.74到8.37 MPa,甲烷的摩尔组份为0～0.225。结果揭示了相平衡温度和压力随着甲烷组分而变化情况以及四相区的范围和临界点,同时还给出了CO₂-CH₄混合气体水合物在四相状态下的融化开始和融化结束点。实验结果与热力学模型计算得出的CO₂-CH₄混合气体水合物相平衡结果进行比较,两者很好吻合,四相平衡区域的存在范围得以明确。     

Unusual proton Zeeman spin relaxation in an organic solid: several crystal polymorphs or different glass structures?

Solid state proton Zeeman relaxation rate R_1z measurements in two isomers of an organic solid (1- and 2-ethylnaphthalene) are reported. The samples are liquids at room temperature and the temperature T and Larmor frequency ω dependence of R_1z depends strongly on how the sample is solidified. Methyl group (CH₃) rotation is responsible for the proton spin relaxation and the methyl groups serve as probes of the local environment. The R_1z measurements clearly distinguish between different solid states due to the differences in local structure at the several-molecule level. The experiments cannot be used to determine the states of these Van der Waals solids although interpreting the relaxation rate data suggests the states are unusual. We propose that these systems might exist in two (2-ethylnaphthalene) or more (1-ethylnaphthalene) polycrystalline polymorphs or that we are observing distinguishable glassy states, or, both. A phase transition is observed in 1-ethylnaphthalene. Variable temperature X-ray studies of organic systems that solidify well below room temperature are difficult, or at least not routine, and proton spin relaxation measurements serve as a convenient starting point for investigating such systems.     

钛酸锶钡材料在外加电场作用下的拉曼光谱研究

采用传统的固相反应烧结方法制 备Ba_xSr_1-xTiO₃（0.40≤ x ≤0.70）陶瓷,借助于Raman散射光谱,研究了陶瓷样品在不同原位电场作用下Raman振动模式的变化,观察到居里温度附近显著的电场诱导的四方–立方相之间的转变. 结果表明A₁（TO₃）和E（TO₄）两种振动模式与晶体的结构存在密切的联系,这两种模式源于O-Ti-O沿晶格中c轴的方向和ab面内的振动. A₁（TO₃）/E（TO₄）之间Raman峰的相对强度比,随外加场强的增加明显升高,顺电相逐渐转变为铁电相,晶格的畸变越来越明显,其宏观性能上表现为介电常数的降低,可调率的增加. 同时对居里温度附近电场诱导的结构相变对顺电相下介电非线性的贡献进行了探讨. 关键词： 钛酸锶钡 Raman散射光谱 结构相变     

钒掺杂W18O49纳米线的室温p型电导与NO2敏感性能

钨氧化物纳米线在高灵敏度低功耗气体传感器中极具应用潜力, 且通过掺杂改性可进一步显著改善其敏感性能. 本文以WCl₆为钨源, NH₄VO₃为掺杂剂, 采用溶剂热法合成了钒掺杂的W₁₈O₄₉纳米线. 利用扫描电镜、透射电镜、X射线衍射、X射线光电子能谱仪表征了纳米线的微结构, 并利用静态气敏性能测试系统评价了掺杂纳米线的NO₂敏感性能. 研究结果表明: 五价钒离子受主掺杂进入氧化钨晶格结构, 抑制了纳米线沿轴向的生长并导致了纳米线束的二次集聚; 室温下, 钒掺杂W₁₈O₄₉纳米线接触NO₂气体后表现出反常的p型响应特性; 随工作温度逐渐升高至约110 ℃时, 发生从p型到n型的电导特性转变; 该掺杂纳米线气敏元件对浓度低至80 ppb (1 ppb=10^-9) 的NO₂气体具有明显的室温敏感响应和良好的响应稳定性. 分析并探讨了钒掺杂W₁₈O₄₉纳米线的高室温敏感特性及其p-n电导转型机理, 认为钒掺杂W₁₈O₄₉纳米线在室温下的良好敏感响应及反常p型导电性与掺杂纳米线表面高密度非稳表面态诱导的低温气体强吸附有关. 关键词： 氧化钨 纳米线 气体传感器 室温灵敏度     

First-Principles Calculations of the AS,, Electronic Structures

The changes in the GaAs electronic structure due to the arsenic-antisite defect have been calculated by using LDF-LMTO-ASA method to a D_2d-symmetry-supercell ( Ga₁₅As₁₇□₃₂)c,o ntains 15 gallium atoms, 17 arsenic atoms and 32 empty spheres. The results show that the central AsGa atom is antibonding with its nearest neighbor arsenic atoms and therefore induces gap states in GaAs. The gap states are composed of A₁-like state and T₂-like state. The bonding properties of gap states have been analyzed in detail by using density of states (DOS) and combined coefficients of wavefunctions. Our results of E_A1 =E_v+0.70 eV and= E_T2+1.07eV are in good agreement with experiments as well as previous calculation results obtained by other self-consistent methods.     

Substitution Effects on MgB2 Superconductivity

With the help of supercell method, the first-principle calculations were performed for the study of doping crystal Mg_1-xAl_xB₂ and Mg(B_1-yC_y)₂. Analyzing the variations of the charge distribution and the partial densities of states, we found that the compounds with doping Al to MgB₂ compound and/or replacing boron by carbon exhibit new covalent bond effects and unexpected electronic properties, related to superconductivity. The study of the density of states indicates that superconductivity decreases with the increase of Al fraction and carbon concentration. There exists a transition of superconductor to non-superconductor with the change of Al doping fraction. The substitution of boron by carbon results in the decrease of the transition temperature since the decrease of the electron concentration and the lattice constant. The theoretical predictions agree with experimental observations.     

CaBa-铝酸盐玻璃中Cr4+谱线宽度随温度的变化

测量了15~300K温度范围内57.5%Al_1.5O-35%CaO-7.5%BaO玻璃中四价铬的发射光谱.这种材料中铬离子的能级处于Tanabe-Sugano图上弱场范围中,最低的激发态是³T₂,发射谱是一个宽带.按照单频近似理论拟合低温下的光谱,得到³T₂能级的零声子线位置E_zp=8400cm^-1,声子能量tω=320cm^-1,黄昆因子S=358.尽管单频近似能够较好地描述低温下的线形,发射光谱宽度随温度的变化却与单频近似理论的结果不符.讨论了这种差别的原因,认为可能的解释是与激发态耦合的声子能量大于与基态耦合的声子能量.     

Theoretical Study on the Low-Lying Electronic States of He2, He2+, and He2++

The equilibrium geometries, potential energy curves, spectroscopic dissociation energies of the ground and low-lying electronic states of He₂, He₂⁺ and He₂⁺⁺ are calculated using symmetry adapted cluster/symmetry adapted cluster-configuration interaction (SAC/SAC-CI) method with the basis sets CC-PV5Z. The corresponding dissociation limits for all states are derived based on atomic and molecular reaction statics. The analytical potential energy functions of these states are fitted with Murrell--Sorbie potential energy function from our calculation results. The spectroscopic constants B_e, α _e, ω _e, and ω _e χ _e of these states are calculated through the relationship between spectroscopic data and analytical energy function, which are in well agreement with the experimental data. In addition, the origin of the energy barrier in the ground state X¹Σ_g⁺ of He₂⁺⁺ energy curve are explained using the avoided crossing rules of valence bond model.     

Simulations of the effects of density and temperature profile on SMBI penetration depth based on the HL-2A tokamak configuration

Using the trans-neut module of the BOUT++ code, we study how the fueling penetration depth of supersonic molecular beam injection(SMBI) is affected by plasma density and temperature profiles. The plasma densities and temperatures in L-mode are initialized to be a set of linear profiles with different core plasma densities and temperatures. The plasma profiles are relaxed to a set of steady states with different core plasma densities or temperatures. For a fixed gradient, the steady profiles are characterized by the core plasma density and temperature. The SMBI is investigated based on the final steady profiles with different core plasma densities or temperatures. The simulated results suggest that the SMB injection will be blocked by dense core plasma and high-temperature plasma. Once the core plasma density is set to be N_(i0)= 1.4N_0(N_0= 1 × 10~(19)m~(-3)) it produces a deeper penetration depth. When N_(i0) is increased from 1.4N_0 to 3.9N_0 at intervals of 0.8N_0, keeping a constant core temperature of T_(e0)= 725 eV at the radial position of ψ = 0.65, the penetration depth gradually decreases. Meanwhile, when the density is fixed at N_(i0)= 1.4N_0 and the core plasma temperature T_(e0) is set to 365 eV,the penetration depth increases. The penetration depth decreases as T_(e0) is increased from 365 eV to 2759 eV. Sufficiently large N_(i0) or T_(e0) causes most of the injected molecules to stay in the scrape-off-layer(SOL) region, lowering the fueling efficiency.     

BP+基态和激发态的势能曲线和光谱性质的研究

本文利用量子化学中的多参考组态相互作用方法(MRCI), 在aug-cc-pVQZ级别计算了在环境科学中具有重要作用的离子BP⁺. 得到了对应三个离解极限B⁺(¹S_g)+P(⁴S_u), B⁺(¹S_g)+P(²D_u)以及B⁺(¹S_g)+P(²P_u)的6个Λ-S态势能曲线. 在计算中还考虑了Davidson修正(+Q)和标量相对论效应, 用以提高计算精度. 通过分析Λ-S态的电子结构, 确认了电子态的多组态特性. 计算中首次纳入了旋轨耦合效应, 获得了由BP⁺离子的6个Λ-S态分裂出的10个Ω 态的势能曲线. 计算得到的势能曲线表明相同对称性的Ω 态的势能曲线存在着明显的避免交叉. 在得到的Λ-S态和Ω 态的势能曲线的基础上, 运用LEVEL8.0程序通过求解核径向的Schrödinger 方程, 得到了相应的Λ-S态和Ω 态的光谱常数T_e, R_e, ω_e, ω_eχ_e, B_e和D_e, 其中基态X⁴∑^-的光谱常数与已有的理论值符合的非常好, 文中其他电子态的光谱常数均为首次报道. 关键词： 多参考组态相互作用方法(MRCI) 势能曲线 光谱常数 旋轨耦合效应     

三自旋体系长寿命核自旋单重态的制备

长寿命核自旋单重态的寿命（T_S）可以长于常规的纵向弛豫时间（T₁）,基于这个独特的优势,长寿命核自旋单重态具有较好的应用价值.本文对已有脉冲序列进行了改进,给出了适用于任意三自旋弱耦合体系长寿命核自旋单重态制备的参数计算方法,发现在同一个三自旋体系内核自旋单重态具有多种不同比例系数组合的形式,并以丙烯酸为例制备出了两种长寿命核自旋单重态,实验上观察到不同的核自旋单重态的寿命存在差异,另外我们还探究了温度对丙烯酸核自旋单重态寿命的影响.     

YH,YD,YT分子基态的结构与势能函数

在Y的有效核势近似下, 对H分别选6-311++G(3df,2pd), AUG-cc-PVTZ, AUG-cc-PVQZ基组, 应用密度泛函理论的B3LYP方法, 优化计算了YH(D,T)分子基态的能量, 平衡结构, 和谐振频率.根据原子分子反应静力学原理, 导出了YH(D,T)分子基态的合理离解极限. 通过优化计算结果和已有的实验和理论数据对比, 得出LANL2TZ/AUG-cc-PVQZ混合基组为对体系进行计算的最优基组. 基于此, 在B3LYP/LANL2TZ/AUG-cc-PVQZ水平对YH(D,T)分子基态的势能面进行了单点能扫描. 并采用最小二乘法拟合得到了相应的Murrell-Sorbie势能函数. 计算出了这些分子的力常数(f₂, f₃, f₄)和光谱常数(B_e, α_e, ω_e, ω_eχ_e, D_e).结果与已有的实验数据符合得很好.     

氧化钨纳米线气敏传感器的制备及其室温NO_2敏感特性

纳米结构的氧化钨有高比表面积和气体吸附能力,在气体传感器领域得到了广泛研究.本文采用磁控溅射金属钨薄膜和两步热氧化工艺在二氧化硅衬底上生长出氧化钨纳米线.通过改变第二步氧化温度,研究退火温度对氧化钨纳米线气敏特性的影响.采用扫描电子显微镜、X射线衍射仪、X射线光电子能谱分析仪和透射射电子显微镜表征材料的微观特性和晶体结构,利用静态配气法测试气敏性能.研究结果表明,经过退火处理后氧化钨纳米线密度略微降低,300℃比400℃退火后的氧化钨结晶性差,对应的表面态含量多,有利于室温气体敏感性.测试NO_2的气敏性能,经过对比得出300℃退火温度下制备的氧化钨纳米线在室温下表现出较很好的气敏响应,对6 ppm(1 ppm=10~(-6))NO_2达到2.5,对检测极限0.5 ppm NO_2响应达1.37.氧化钨纳米线在室温下表现出反常的P型响应,是因为氧化钨纳米线表面被氧气吸附形成反型层,空穴取代电子成为主要载流子所致.     

锂离子电池正极材料Li2FeSiO4的电子结构与输运特性

采用基于密度泛函理论第一性原理方法, 研究了对称性为Pmn2₁的正交结构聚阴离子型硅酸盐Li₂FeSiO₄及其相关脱锂相LiFeSiO₄的电子结构, 并进一步采用玻尔兹曼理论对其输运性质进行计算. 电荷密度分析表明, 由于强Si–O共价键的存在使Li₂FeSiO₄晶体结构在嵌脱锂过程中始终保持稳定, 体积变化率只有2.7%. 能带结构与态密度计算结果表明, 费米能级附近的电子结构主要受Fe-d轨道中电子的影响, Li₂FeSiO₄ 的带隙宽度明显小于LiFeSiO₄, 说明前者的电子输运能力优于后者. 输运性质计算表明, 电导率在300–800 K时对温度的变化并不敏感, 同时也证明了Li₂FeSiO₄晶体的电导率大于LiFeSiO₄晶体, 与能带和态密度分析结论一致.     

High field phenomena in thin plasma nitrided SiO2 films

The effects of high field tunnel electron injection on the electrical properties of Al - thin plasma nitrided SiO₂ films - Si (p-type) structures are studied. Under high field injection, it has been observed that electron trapping, positive charge generation near the Si-SiO₂ interface (slow states) and fast state generation at the Si-SiO₂ interface have taken place. After high temperature N₂ annealing, the nitridation induced electron trap density is considerably decreased. Furthermore, under high field injection the generation rate of both the slow states and the interface states and consequently, the degradation rate of the nitrided oxide films have been also decreased after annealing.