Enhanced magnetic anisotropy of nickel nanosheet prepared in Na-4 mica

Nanosheets of nickel with thickness equal to 0.6 nm have been grown within the interlayer spaces of Na-4 mica. The sheets are made up of percolative clusters of nanodisks. Magnetization characteristics indicate a superparamagnetic behavior with a blocking temperature of 428 K. The magnetic anisotropy constant as extracted from the coercivity data has been found to be higher than that of bulk nickel by two orders of magnitude. This is ascribed to a large aspect ratio of the nickel nanophase. The Bloch exponent is also found to be considerably different from that of bulk nickel because of a size effect. The Bloch equation is still found to be valid for the two dimensional structures.     

Electronic and optical properties of V doped AlN nanosheet: DFT calculations

Electronic and optical properties of pure and V-doped AlN nanosheet have been investigated using density functional theory, and the dielectric tensor is calculated using the random phase approximation (RPA). The results of structural calculations show that the V atoms tend to replace instead of aluminum atoms with the lowest formation energy. In addition, study of the electronic properties shows that pure AlN nanosheet is a p-type semiconductor that by increasing one V atom, it possesses the metallic properties and magnetic moment becomes Zero. Moreover, by replacing two V atoms, the half-metallic behavior with 100% spin polarization can be found, and each supercell gains a net magnetic moment of 3.99 µ_B. Optical properties like the dielectric function, the energy loss function, the absorption coefficients, the refractive index are calculated for both parallel and perpendicular electric field polarizations, and the results show that the optical spectra are anisotropic.     

各种强度均匀磁场下氢原子定态问题统一求解

以简明的方式统一处理了塞曼效应，反常塞曼效应，帕邢－巴克效应以及中间强度均匀磁场下氢原子谱线的分分裂，移动和强度计算等问题。     

表面吸附氧原子的GaAs电子结构及光学性质的研究

在密度泛函理论的基础上,利用第一性原理计算了表面吸附氧原子的GaAs的电子结构及光学性质。结果表明,表面氧原子的吸附导致表面能带向深部移动,禁带中出现由As 4p轨道和Ga 4p轨道构成的杂质能级,以及由As 4s轨道和Ga 4s轨道分裂形成的表面态能级;氧原子的吸附还导致表面d态和sp态电子的重新分布;氧原子的存在改善了晶格周期的缺陷性,改变电子跃迁的过程,影响晶体的光学性质。     

过渡金属锇在高压下的力学特性

基于密度泛函理论平面波赝势法的第一性原理计算,研究了过渡金属锇在高压下的状态方程、弹性常数和其它力学性质。 计算结果表明：过渡金属锇具有很高的体积模量B0（423.9 GPa）和弹性常数C11（771.3 GPa）与C33（852.0 GPa）,与金刚石的（B0=452.8 GPa,C11=C33=1 082.9 GPa）比较,具有超低压缩特性;表征材料抵抗剪切变形能力的弹性常数C44（269.8 GPa）和切变模量（276.8 GPa）只有金刚石的（C44=586.9 GPa,G=537.5 GPa）一半,而所成的又是纯金属键,因此锇不具有超硬性。最后,定性分析了它的高体积模量和低硬度的微观电子机制,这对于设计与合成新的超硬性材料具有启发意义。     

First-principles perspectives on detection properties of sulphur mustard gas using novel electroresistive ϵ-Arsenene nanosheet device

ABSTRACT

The feasibility of using ?-Arsenene (?-As) nanosheet device to detect the target vapour, 2-chloroethyl chloromethyl sulphide (one of sulphur mustard gas molecule) is investigated in the research by applying density functional theory method. The firm nature of ?-As nanosheet is verified using formation energy, and the electronic features are estimated for the pristine and target vapour adsorbed ?-As sheets. In addition, the adsorption attributes are computed to resolve the most preferred site of target vapour adsorption. Moreover, the transmission and current–voltage characteristics are explored to validate the modification in the resistivity and conductivity of ?-As device upon adsorption of the target vapour. Furthermore, the selectivity of ?-As sheets towards humidity, CO and CO₂ are also studied and ?-As sheets are highly selective to sulphur mustard gas molecules. The properties examined emphasise the employment of ?-As nanosheet molecular device to act as a chemo-sensor towards the target vapour, 2-chloroethyl chloromethyl sulphide.     

Sm-Co-Ti三元系相关系及某些单相化合物的结构与磁性

通过X射线衍射和磁性测量研究了Sm-Co-Ti三元体系富Co区固相线下的相关系,并探索了Co基3:29型化合物存在的可能性,进而研究了某些单相化合物的结构和磁性.实验表明,该体系中存在三个三元化合物SmCo_7-xTi_x,Sm₂Co_17-xTi_x和SmCo_12-xTi_x,其固溶区分别为0.32≤x≤0.54,0≤x≤1.13和1.45≤x≤1.95.按Sm_9.31Co_90-xTi_x(3≤x≤15)成分配料,Sm按其质量的15%,20%,25%三个比例过量加入,在1303—1403K温度范围内退火,均未发现3∶29相.在制备出的SmCo_12-xTi_x,和Sm₂Co_17-xTi_x两个系列化合物中,随着Ti含量的增加,它们的居里温度和饱和磁化强度都单调降低.Sm₂Co_17-xTi_x化合物在居里温度以下表现为单轴各向异性,而SmCo_12-xTi_x化合物表现为面各向异性.SmCo_12-xTi_x和Sm₂Co_17-xTi_x化合物1.5K下的磁晶各向异性场随Ti含量的变化都呈现一个极大值,这可能与Ti原子的择优占位有关关键词：稀土过渡族化合物X射线衍射相图磁晶各向异性     

GaAs相变和热力学性质的密度泛函理论研究

利用平面波赝势密度泛函方法,对GaAs从闪锌矿结构到CsCl 结构的相变进行了理论研究.通过Birch-Murnaghan状态方程拟合闪锌矿结构GaAs的能量和体积,得到了GaAs的热力学性质.我们发现对 GaAs来说,闪锌矿结构通常比CsCl结构稳定,由闪锌矿结构到CsCl结构的相变压力在37.019 GPa左右.计算所得到的晶格常数、体弹模量及体弹模量对压强的一阶导数与实验值以及其他作者的计算值相符合.     

The structural and optical properties of gallium arsenic nanoparticles

Spherical gallium arsenic nanoparticles prepared by thermal evaporation method have been fabricated successfully. The structural and optical properties of GaAs nanoparticles are studied in detail. It is found that while the growth pressure rises from 0.4 to 5 Torr, the average size of GaAs nanoparticles increases from 6 to 12 nm and standard deviation keeps almost the same (2 nm) except for 0.5 Torr. By using transmission electron microscopy and Raman spectra, a critical preparation condition has been found which characterize the amorphous to crystal transition of GaAs nanoparticles.     

Exploration the p-type doping mechanism of GaAs nanowires from first-principles study

Using first-principle calculations, we present a systematic investigation upon the influence of p-type doping on the structural and electronic properties of H-passivated GaAs nanowires with wurtzite structure. The GaAs nanowire models of different doping types, different doping elements, different doping positions and different doping concentrations are established. The calculated formation energies show that Zn element becomes more competitive or even slightly favored in realizing p-type doping compared to Be element. For an individual Zn incorporation model, Zn atom tends to substitute the subsurface Ga atom. As increasing Zn doping concentration, the p-type doping process becomes more and more difficult. Besides, both interstitial and substitutional doping lead to the distortion of atomic structure near impurity atoms and cause the ionicity of GaAs nanowires enhanced. The p-type doped GaAs nanowires models are all direct band gap semiconductors. After substitutional doping, the total density of state curves shift toward higher energy sides and the Fermi level entering valence bands. Our calculations provide a significant reference for the preparation of p-type doping GaAs nanowire, which has a promising potential application in the field of photocathodes.     

GaAs光电阴极激活时Cs的吸附效率研究

从NEA GaAs光电阴极的激活光电流曲线发现,当系统真空度不很高时,在首次Cs激活阶段,表面掺杂浓度较低的阴极材料,其光电流产生需要的时间也较长.同时,随着系统真空度的提高,这种时间上的差异又变得不再明显.该现象表明,Cs原子在阴极表面的吸附效率同表面层掺杂浓度以及系统真空度之间有直接的联系.为定量分析这种关系,本文根据实验数据建立了Cs在阴极表面吸附效率的数学模型,利用该模型仿真的结果同实验现象非常符合.该研究对进一步开展变掺杂阴极结构设计和制备工艺研究具有重要的价值和意义.关键词：GaAs光电阴极吸附效率真空度表面掺杂浓度     

GaAs光电阴极激活后的表面势垒评估研究

根据阴极制备过程中单独Cs激活和Cs-O交替激活两个阶段产生的光电流的峰值比,结合对电子穿过表面单势垒和双势垒后能量分布的理论曲线,提出了一种评估NEA GaAs光阴极表面势垒参数的新方法.利用该方法研究的结果完全符合双偶极层模型理论,并且和对实测阴极电子能量分布曲线拟合的结果非常一致.该方法简单、有效,在不增加测试手段的前提下,丰富了对NEA GaAs光电阴极激活效果及表面特征评价的方法和途径.关键词：GaAs光电阴极表面势垒能量分布