Unravelling the Elusive Antiferromagnetic Order in Wurtzite and Zinc Blende CoO Polymorph Nanoparticles

Although cubic rock salt‐CoO has been extensively studied, the magnetic properties of the main nanoscale CoO polymorphs (hexagonal wurtzite and cubic zinc blende structures) are rather poorly understood. Here, a detailed magnetic and neutron diffraction study on zinc blende and wurtzite CoO nanoparticles is presented. The zinc blende‐CoO phase is antiferromagnetic with a 3rd type structure in a face‐centered cubic lattice and a Néel temperature of T_N (zinc‐blende) ≈225 K. Wurtzite‐CoO also presents an antiferromagnetic order, T_N (wurtzite) ≈109 K, although much more complex, with a 2nd type order along the c‐axis but an incommensurate order along the y‐axis. Importantly, the overall magnetic properties are overwhelmed by the uncompensated spins, which confer the system a ferromagnetic‐like behavior even at room temperature.     

Sb Incorporation in Wurtzite and Zinc Blende InAs1−xSbx Branches on InAs Template Nanowires

The physical properties of material largely depend on their crystal structure. Nanowire growth is an important method for attaining metastable crystal structures in III–V semiconductors, giving access to advantageous electronic and surface properties. Antimonides are an exception, as growing metastable wurtzite structure has proven to be challenging. As a result, the properties of these materials remain unknown. One promising means of accessing wurtzite antimonides is to use a wurtzite template to facilitate their growth. Here, a template technique using branched nanowire growth for realizing wurtzite antimonide material is demonstrated. On wurtzite InAs trunks, InAs_1?xSb_x branch nanowires at different Sb vapor phase compositions are grown. For comparison, branches on zinc blende nanowire trunks are also grown under identical conditions. Studying the crystal structure and the material composition of the grown branches at different x_v shows that the Sb incorporation is higher in zinc blende than in wurtzite. Branches grown on wurtzite trunks are usually correlated with stacking defects in the trunk, leading to the emergence of a zinc blende segment of higher Sb content growing parallel to the wurtzite structure within a branch. However, the average amount of Sb incorporated within the branch is determined by the vapor phase composition.     

Ag-O-N共掺杂闪锌矿ZnS光催化性质的第一性原理研究

采用第一性原理方法计算比较了Ag、O和N单掺杂、Ag-O和Ag-N二元掺杂以及Ag-O-N三元共掺杂闪锌矿ZnS的晶型结构、电荷分布、能带和态密度以及光学特性.N、O对晶格结构的影响大于Ag,结构优化和电荷分布结果显示晶格畸变随着掺杂组分的增多不断增大.形成能计算表明,N最易掺杂,组分越多,掺杂越难实现.Ag、O和N各组分掺杂ZnS后能带间隙均有所减小,Ag、N掺杂ZnS更有利于价带顶上移,部分能带越过费米能级,形成电子跃迁的过渡能级,有利于光催化反应.Ag-O-N三元掺杂ZnS后在可见光区的吸收峰最大,有利于提高ZnS对可见光的利用率.     

Fe-33Ni-4Co-1.2Nb超低膨胀合金研究

研究了一种雷达天线罩连接环用Fe-33Ni-4Co-1.2Nb低膨胀合金,该合金具有极低的膨胀系数(α20～100℃0.9×10-6/℃),同时,该合金也具有良好的机械力学性能和加工性能,试验表明,该合金较好地解决了天线罩与基体的连接问题,是制作天线罩连接环和其它需要低膨胀封接的良好材料。     

Sb掺杂闪锌矿GaAs电子结构和光学性质第一性原理研究

采用基于密度泛函理论(DFT)框架下广义梯度近似平面波超软赝势法,计算了不同浓度Sb掺杂闪锌矿GaAs体系GaAs1-xSbx(x=0,0.25,0.5,0.75,1)的电子结构和光学性质,包括能带、态密度、复介电函数和吸收系数。计算结果表明,Sb掺杂导致体系晶格常数线性增大,并使得体系导带和价带组成发生改变,禁带宽度呈二次多项式变化。随着掺杂浓度的增加,体系静态介电常数线性增大,吸收带边出现了明显的红移现象。分析了掺杂Sb诱发GaAs1-xSbx体系的电子和光学性质改变,为Sb掺杂闪锌矿GaAs在光电子学和微电子学方面的实际应用提供了一定的理论依据。     

Coherent Superposition of Electric- and Magnetic-Dipole Spin-Flip Transitions in Zinc Blende Semiconductors

Spin resonance (SR) studies offer an important and unique opportunity for investigating coherent superposition of electric-and magnetic-dipole spin-flip transitions in semiconductors. We will focus on far-infrared studies of conduction-electron spin-flip transitions in narrow-gap semiconductors, where this effect is most clearly evident. Although the SR transition is normally electric-dipole-forbidden, it is well known that there exist mechanisms (e.g., nonparabolicity and inversion asymmetry) that relax these selection rules. In comparing the relative importance of these mechanisms, it will be shown that the combination of spin–orbit coupling and inversion asymmetry (as developed by E. I. Rashba and V. I. Sheka) is the dominant process allowing electric-dipole-induced spin-flip transitions. In this review, special attention will be given to the interference of the electric- and magnetic-dipole matrix elements, which provide a unique opportunity for determining the inversion-asymmetry parameter (including its sign) in zinc blende narrow-gap semiconductors. This effect can also serve as a basis for observing spin-based electromagnetically induced transparency—a phenomenon of considerable contemporary interest from both fundamental and applied viewpoints.     

Phase Composition and Distribution of Ni-, Co-, Fe-, Mn-, and Cr-Based Inclusions in Carbonado Polycrystals

The phase composition and distribution of inclusions of the Ni, Co, Fe, Mn, and Cr metal catalysts in carbonado polycrystals 8 mm in diameter were studied. The polycrystals (>90 wt % diamond) were found to contain inclusions of solid solutions of carbon in Ni and Co and the carbides Fe₃C, Mn₅C₂, and Cr₃C₂. The concentration of inclusions was shown to increase with distance from the catalyst insert. The results are interpreted in terms of the model for the growth of polycrystalline diamond via corrugation of graphite layers, their dissolution in the catalyst melt owing to structural matching with its fcc lattice, and stabilization of the diamond structure at high supersaturations in the p–T stability region of diamond.     

Electronic Structure and Magnetic Properties of Doped GaAs (Zinc Blende) with Double Impurities and Defects

Using ab-initio calculations based on Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA) method in connection with the local density approximation (LDA), we study theoretically the electronic and magnetic properties of a system based on GaAs material. These properties have been studied, with different point defects in GaAs, which are Gallium interstitials (Ga_i), Gallium antisites (Ga_As), Gallium vacancies (V_Ga), Arsenic interstitials (As_i) and Arsenic antisites (As_Ga), Arsenic vacancies (V_As), and in-doped or codoped system Ga_1?x Co _x As and Ga_1?y?z Co _y Fe _z As, respectively. This work presents detailed information about total and local density of states at different concentrations of these defects and doped elements; the stability of the ferromagnetic state compared with the spin-glass state has been discussed. The result of electronic properties shows that codoped GaAs material with Fe and Co become ferromagnetic, also doped GaAs with Co or Fe with a defect (hole in Ga) is stable in the ferromagnetic state. The Curie temperature is estimated from the total energy difference between the Disorder Local Moment (DLM) and the (FM) state by using a mapping on the Heisenberg model in mean field approximation.     

Young's modulus of Fe-, Co-, Pd- and Pt-based amorphous wires produced by the in-rotating-water spinning method

This paper presents the Young's modulus of Fe_100?x?y Si _x B _y , Fe_100?x?y P _x C _y , Co_100?x?y Si _x B _y , Pd_77.5Cu₆Si_16.5, Pd₄₈Ni₃₂P₂₀ and Pt₆₀Ni₁₅P₂₅ amorphous wires determined from the Young's modulus sound velocity measurement. With increasing metalloid content, the Young's modulus increases from 1.58×10¹¹ to 1.87×10¹¹ N m^?2 for Fe-Si-B, from 1.40×10¹¹ to 1.52×10¹¹ N m^?2 for Fe-P-C and from 1.73×10¹¹ to 1.75×10¹¹ N m^?2 for Co-Si-B systems. The increase in Young's modulus with the amount of metalloid elements is the largest for B, followed by Si, C and then P. The Young's modulus of Fe- and Co-Si-B amorphous wires increases significantly with the replacement of iron or cobalt by IV–VII group transition metals. It was recognized that there existed a strong correlation between Young's modulus (E) and tensile fracture strength (σ _f); the ratio of σ _f to E is approximated to be 0.02 for all the amorphous wires investigated. These results imply that the Young's modulus is dominated mainly by the structural and compositional short-range orderings due to the strong interaction between metal and metalloid atoms which hinders the internal displacements. The existence of a constant ratio for σ _f/E was interpreted to originate from a common mechanism for plastic flow of the amorphous wires. Further, it was noted that the Young's modulus of the Fe- and Co-based amorphous wires with diameters of ? 100 to 120 Μm was slightly lower than that of the amorphous ribbons with thicknesses of ? 20 to 25 Μm. This difference was attributed to the difference in structural ordering due to the differences in the solidification processes.     

A Molecular Dynamics Study on the (11-20) Domain Boundary Structures in Epitaxial Wurtzite GaN

1.IntroductionGaN[1]fasanimportantmaterialinthemanufac-ture0fsemic0nduct0rdevices,isattractingextensiveresearchinterestsb0thinscienceandinindustrv.Theepitaxial-fabricatedGaNfi1mc0ntainsaheavyden-sityofdefectstructures.Thegeneral0pini0ncon-sidersthatlatticedefectsintr0ducenon-radiativere-combinati0ncentresinIII-Vsemiconductor.There-combinationcentresreducetheefficiencvandlifetimeoftheph0t0electrondevicesmadefromthesemicon-ductor.Hence,itisquiteimp0rtantt0haveaclearunderstandingofthenature0f…     

Room-temperature ferromagnetism in Fe-doped, Fe- and Cu-codoped ZnO diluted magnetic semiconductor

Magnetic properties of Zn_0.975Fe_0.025O and Zn_0.97Fe_0.025Cu_0.005O crystallites fabricated by hydrothermal method are investigated. X-ray diffraction and Raman measurements indicate that the samples have pure ZnO wurtzite structure and Fe²⁺ ions have substituted Zn²⁺ sites. Magnetic measurements indicate that Fe doping can induce room-temperature ferromagnetism, while codoping with Cu might enhance the magnetic moment but reduce the Curie temperature in ZnO.     

Structures, varistor properties, and electrical stability of ZnO thin films

In this letter, we report the structures, varistor properties, and electrical stability of ZnO thin films deposited by the gas discharge activated reaction evaporation (GDARE) technique. The X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the thin films thus prepared have polycrystalline structures with the preferred orientation along the (002) plane whose surface consists of ZnO aggregates with sizes of 50-200 nm. The ZnO thin films deposited by GDARE and annealed at 250 °C for 2 h have strong nonlinear varistor-type I-V characteristics. The nonlinear coefficient (α) of a single-layered ZnO thin film sample was 33 and that of a triple-layered sample obtained by the many-time deposition was 62. The varistor voltages (V_1mA) of the two samples are found rather close each other. Under a DC bias of 0.75 V_1mA and a temperature of 150 °C these thin films exhibit good electrical stability with a degradation rate coefficient K_T of 0.05 mA/h^1/2.     

Structures and magnetic properties of ZnO nanoislands

Using first-principles calculations, we systematically study the atomic structures and electronic properties for two dimensional triangular ZnO nanoislands that are graphite-like with monolayer and bilayer thickness. We find that the monolayer ZnO nanoisland with oxygen-terminated zigzag-edges is magnetic at its ground state, and the magnetism comes from the oxygen-edge states. The other monolayer and bilayer ZnO nanoislands with different edge structures are all nonmagnetic at their ground states. It is further revealed that for different ZnO nanoislands, their magnetic properties are quite dependent on their sizes, with larger nanoislands having larger magnetic moments.     

氧化锌低维结构材料场发射性能研究进展

ZnO具有负的电子亲和势、丰富的结构和形貌可设计性以及良好的机械和化学稳定性等优点,是一种最有前途的阴极电子发射材料.结合作者实验室的工作,综述了近年来迅速发展的ZnO低维结构的场发射特性以及制备方法、形貌结构、排列及密度、表面吸附、掺杂和热处理等因素对其场发射性能的影响,介绍了四针状氧化锌晶须(T-ZnOw)作为场发射阴极材料的优势.     

Si对Fe-2.5B合金在锌液中腐蚀机制的影响

Si的加入改变了Fe-2.5B合金的微观组织,进而影响到这种合金在锌液中的耐腐蚀性能.当Si含量为2-8%wt时,Fe-2.5B-XSi是亚共晶组织,Si分布在α-Fe和Fe2B相中.配制一系列由单相α-Fe组成的合金,其Si含量与Fe-2.5B-XSi合金中的α-Fe相中的Si含量相同,在液锌中测试这两组试样的腐蚀速率,据此可以推断出Fe2B相的腐蚀速率.结果表明,随Si含量的增加,α-Fe相的腐蚀速率下降,其原因是随Si含量的增加,α-Fe与锌液反应生成的块状FeSi相增多,该相对锌的扩散起阻挡作用.随Si含量增加,Fe2B相的腐蚀速率上升,原因是随Si含量的增加,Fe2B相的点阵参数、晶胞体积增加,即硅削弱Fe2B中键的结合强度,降低了Fe2B的稳定性.两相的相互作用使Fe-2.5B合金随Si含量的增加,耐腐蚀性能增强.