Electronic and magnetic structures of V-doped zinc blende Zn1-xVxNyO1-y and Zn1-xVxPyO1-y

Electronic and magnetic structures of zinc blende ZnO doped with V impurities are studied by first-principles calculations based on the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA).Calculations for the substitution of O by N or P are performed and the magnetic moment is found to be sensitive to the N or P content.Furthermore,the system exhibits a half-metallic band structure accompanied by the broadening of vanadium bands.The mechanism responsible for ferromagnetism is also discussed and the stability of the ferromagnetic state compared with that of the paramagnetic state is systematically investigated by calculating the total energy difference between them by using supercell method.     

Crystal structures of stage-n iodine-intercalated compounds IBi2nSr2nCanCu2nOx

The crystal structure of stage-3 iodine-intercalated superconducting IBi₆Sr₆Ca₃Cu₆O_x has been determined by transmission electron microscopy to belong to the space group Pma2 with lattice parameters a=5.4Å, B=5.4Å and C=49.4Å. Ioidine atoms intercalated between every three Bi---O bilayers expand the distance between the Bi---O layers by 3.6Å and alter the atomic stacking across Bi---O layers from the staggered configuration characteristic of host superconducting Bi₂Sr₂CaCu₂O_x to an aligned configuration characteristic of stage-1 iodine-intercalated superconducting IBi₂Sr₂CaCu₂O_x. Higher-stage intercalation has also been observed as stacking faults which predominantly contain both stage-2 and stage-3 phases. The space groups and c-axis dimensions of the higher-stage phases have been deduced to be Pma2 with c=3.6+15.3n Å when stage number n is odd, and Bbmb with c=2(3.6+15.3n) Å when n is even.     

Spacer layer thickness fluctuation scattering in a modulation-doped AlxGa1-xAs/GaAs/AlxGa1-xAs quantum well

We theoretically study the influence of spacer layer thickness fluctuation（SLTF） on the mobility of a twodimensional electron gas（2DEG） in the modulation-doped Al x Ga 1 x As/GaAs/Al x Ga 1 x As quantum well.The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained.The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer.     

Different temperature dependence of carrier transport properties between AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures

The temperature dependence of carrier transport properties of AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures has been investigated.It is shown that the Hall mobility in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures is higher than that in Al0.25Ga0.75N/GaN heterostructures at temperatures above 500 K,even the mobility in the former is much lower than that in the latter at 300 K.More importantly,the electron sheet density in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures decreases slightly,whereas the electron sheet density in Al0.25Ga0.75N/GaN heterostructures gradually increases with increasing temperature above 500 K.It is believed that an electron depletion layer is formed due to the negative polarization charges at the InyGa1-yN/GaN heterointerface induced by the compressive strain in the InyGa1-yN channel,which e-ectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.     

Ba1-xB2-y-zO4SixAlyGaz晶体和频可调谐深紫外飞秒激光器

介绍了一种基于新型非线性晶体Ba_1-xB_2-y-zO₄Si_xAl_yGa_z 的可调谐深紫外飞秒激光光源. 从理论上分析了基频光和倍频光在通过非线性晶体时所造成的空间走离和群速度失配, 为了补偿空间走离以及波长调谐过程中晶体折射造成的光束偏离现象, 将两块相同的倍频晶体成镜像放置来产生二次谐波. 并调节延迟线的长度来补偿基频光和倍频光之间的群速度失配, 从而提高和频转换效率. 然后通过和频方式进行三倍频和四倍频来突破晶体相位匹配条件的限制, 产生了波长低于200 nm的深紫外飞秒激光. 利用钛宝石激光器提供基频光光源, 最终在250–300 nm, 192.5–210 nm 范围内获得了高重频、可调谐超短脉冲紫外和深紫外激光. 并在基频光波长为800 nm时, 得到的二倍频、三倍频和四倍频的功率分别为1.28 W, 194 mW和5.8 mW, 相对于前一级的转换效率依次为46.14%, 15.16%和3%. 采用互相关法测量得到266.7 nm紫外激光的脉冲宽度约为640.4 fs.     

Theoretical prediction of structural, electronic and optical properties of quaternary alloy Zn1-xBexSySe1-y

Within density functional theory based on the full potential-linearized augmented plane wave method, we carry out the first-principles calculation of the structural, electronic, and optical properties of the zinc blende quaternary alloy Zn_1-xBe_xS_ySe_1-y. The Perdew-Burke-Ernzerhof generalized gradient approximation based on the optimization of total energy and the Engel-Vosko generalized gradient approximation based on the optimization of the corresponding potential are used. Our investigation on the effect of the composition on lattice constants, bulk modulus, band gap, optical dielectric constant, and refractive index shows a non-linear dependence. The energy gap E_g(x, y) has been determined over the entire compositions x and y. In addition, the energy band gap of the technologically important quaternary alloy Zn_1-xBe_xS_ySe_1-y in conditions of being lattice matched to ZnS substrate has been investigated. It is noteworthy that the present work is the first theoretical study of the quaternary alloy of interest.     

Resonances in the KSKSKL system produced in collisions of negative pions with a carbon target at a momentum of 40 GeV

The experimental spectrum of the K _S K _S K _L system from the reaction π ⁻C → K _S K _S K _L + Y at amomentum of 40 GeV was obtained experimentally with the aim of studying resonance states featuring open strangeness and occurring in the high-mass region. The experiment was performed at the 6-m spectrometer installed at the Institute for High Energy Physics (IHEP, Protvino). The spectrum displays, along with well-known resonances [K ₁(1640), K ₂(1770), K ₂(1820), K ₂(1980)], which fit in the quark-antiquark classification, the exotic resonances K ₂(2280) and K ₄(2500). The K ₂(2280) resonance exhibits the properties of a hybrid and has an exotic decay mode producing a triplet of known resonance states related to each other by quark-gluon mixing. The mechanism of the formation of the observed hybrid K ₂(2280) is dominated by the exchange of a natural spin-parity in the t channel of the reaction. The mode of decay into f ₀(980)K _L and the mode of decay into f ₂(1270)K _L are observed for the K ₂(1770) and the K ₂(1980) resonance, respectively. __________ Translated from Yadernaya Fizika, Vol. 66, No. 5, 2003, pp. 860–867. Original Russian Text Copyright ? 2003 by Tikhomirov, Erofeev, Erofeeva, Luzin.     

Luminescence from Si-Si1−xGex/Si1−yCy-Si structures

Near band edge photoluminescence has been obtained from Si_1−yC_y quantum well (QW) and neighboring Si_1−xGe_x/Si_1−yC_y double QW (DQW) structures. Enhanced no-phonon recombination is observed from the DQW structures and it is attributed to a breaking of the k-selection rule in the presence of the heterointerface. The luminescence persists for measurement temperatures up to 30–50 K and the intensity exhibits a quenching behavior with an activation energy equal to 8–20 meV. In electroluminescence only recombination in the Si_1−xGe_x layer has been observed from neighboring Si_1−xGe_x and Si_1−yC_y DQW structures.     

Structures and electronic properties of SimN8-m（0 〈 m 〈 8） clusters： a density functional theory study

The geometries, electronic structures and related properties of SimN8-m（0 〈 m 〈 8） clusters are studied using density functional theory （DFT） with hybrid functional B3LYP. The calculated results reveal several trends. For any stoichiometric clusters, the lowest energy isomers with an alteration of N and Si atoms are favourable in energy if the numbers of Si and N atoms are large enough to form ... Si N-Si-N... alternative chains. The bond lengths of single Si-N bonds are very close to the corresponding values of the bulk and other SiN clusters. The geometries for N-rich and Si4N4 clusters are planar structures, but three-dimensional structures are favourable in energy for Si-rich clusters. With the increase of m, the isotropic polarizability and average polarizability increase, the total binding energies generally decrease, the HOMO-LUMO gap and vertical ionization potential oscillate with increasing number of valence electrons, and their values with even valence electrons are larger than those with odd valence electrons. The atomic charges, IR and Raman properties are also reported.     

Zn$lt;sub$gt;1-$lt;i$gt;x$lt;/i$gt;$lt;/sub$gt;Mg$lt;sub$gt;$lt;i$gt;x$lt;/i$gt;$lt;/sub$gt;O薄膜的光致发光特性研究

采用脉冲激光沉积方法在单晶Si（100）衬底上制备出c轴取向的Zn_1-xMg_xO单晶薄膜,通过荧光光谱仪研究了薄膜的光致发光特性.实验结果表明,Mg含量增加,Zn_1-xMg_xO单晶薄膜的紫外发光峰蓝移,发光峰强度减弱,缺陷发光强度增强.同时发现,由于Mg的掺杂,引入了一些束缚能较大的局域束缚态.对于氧气氛下制备的样品,实验发现紫外峰和绿光带发光峰同时增强,但是R值减小,紫外峰红移.对绿光发光机理研究发现,绿光发光带主要与锌空位、氧间隙（O_i）或锌位氧（O_Zn）等缺陷有关,它是由多个缺陷发光峰组成,各缺陷发光峰强度相对变化导致了绿光发光带的整体移动. 关键词： 1-xMg_xO薄膜')" href="#">Zn_1-xMg_xO薄膜 光致发光 脉冲激光沉积     

Noise behavior of amorphous GexSi1−xOy for microbolometer applications

High resistivity sputtered a-Ge_xSi_1−xO_y compound was investigated for application to microbolometer fabrication for thermal imaging. Noise behavior of the fabricated bolometers was measured, showing no evidence of random telegraph switching (RTS) noise. 1/f noise was measured at several measuring currents, resulting in a 1/f noise factor of 2.9 × 10⁻¹¹ that can be used for further design and modeling.     

Negative luminescence from In1−xAlxSb and CdxHg1−xTe diodes

Indium aluminium antimonide (In_1−xAl_xSb) and cadmium mercury telluride (Cd_xHg_1−xTe) heterostructure diodes, which comprise a near intrinsic active region bounded by more highly doped contact regions, exhibit positive or negative luminescence at medium to long infrared wavelengths when forward or reverse biased respectively at room temperature. In reverse bias, the carrier densities in the near intrinsic region are reduced below their equilibrium values by the effects of exclusion and extraction. In consequence, the radiative recombination is reduced and the devices emit less infrared radiation than the thermal equilibrium value. The observed intensity of the negative luminescence is in general agreement with expected values.     

过渡族元素掺杂BaTiO3-Tb1-xDyxFe2-y层状复合材料中的磁电效应

用溶胶-凝胶法制备1.0%mol Mn,Cr,Co掺杂 BaTiO₃(BTO)粉体,在1350℃下烧结成多晶陶瓷样品.X射线衍射和差示扫描量热分析表明,室温下掺杂BaTiO₃具有四方钙钛矿结构;居里点和相变潜热随Cr,Mn,Co掺杂逐渐降低.将掺杂BaTiO₃与Tb_1-xDy_xFe_2-y(TDF)胶合制成双层磁电复合材料,并研究了Cr:BTO-TDF,Mn∶BTO-TDF,Co:BTO-TDF层状复合材料中的磁电效应.实验表明,在340×80 A·m^-1偏置磁场下, Cr:BTO-TDF的横向磁电电压系数达到最大值586 mV·cm^-1·(80 A·m^-1)^-1.在400×80 A·m^-1偏置磁场下,Mn∶BTO-TDF和Co:BTO-TDF的横向磁电电压系数的最大值分别为480 mV·cm^-1·(80 A·m^-1)^-1和445mV·cm^-1·(80 A·m^-1)^-1.研究表明掺杂BaTiO₃-TDF层状复合材料中具有较强的磁电耦合.作为无铅压电材料,掺杂BaTiO₃制备的磁电效应器件颇具应用前景. 关键词： 磁电效应 双层复合材料 3')" href="#">掺杂BaTiO₃ 1-xDy_xFe_2-y')" href="#">Tb_1-xDy_xFe_2-y     

Blue cathodoluminescence from thulium implanted AlxGa1−xN and InxAl1−xN

Room temperature cathodoluminescence (RTCL) was obtained from Tm implanted Al_xGa_1−xN with different AlN contents (in the range 0≤x≤0.2) and from implanted In_xAl_1−xN with different InN contents (x=0.13 and 0.19) close to the lattice match with GaN. The Tm³⁺ emission spectrum depends critically on the host material. The blue emission from Al_xGa_1−xN:Tm peaks in intensity for an AlN content of x0.11. The emission is enhanced by up to a factor of 50 times with an increase of annealing temperature from 1000 to 1300 C. The blue emission from In_0.13Al_0.87N:Tm, annealed at 1200 C, is more than ten times stronger than that from Al_xGa_1−xN:Tm, x≤0.2. However, the intensity decreases significantly as the InN fraction increases from 0.13 to 0.19.     

LiNi1-x-yCoxMnyO2正极材料的制备与电化学性能

LiNi_1-x-yCo_xMn_yO₂正极材料作为最有商业化前途的锂离子电池正极材料，近年来成为研究者关注的焦点。但目前针对该材料合成工艺的研究还较少。对LiNi_0.8Co_0.15Mn_0.05O₂开展了不同的烧结工艺研究，并对制备出的正极材料进行了表征和性能测试。研究发现在0.1C (电池容量额定值)倍率下充放电比容量为200 mA·h·g-1左右，在1C倍率循环100次下，480 ℃@3 h + 780 ℃@5 h和500 ℃@5 h + 780 ℃@10 h两种烧结工艺下容量保持率分别为94%和86%，说明用这两种工艺制备的正极材料的综合性能最优。     

Vortex core physics in the cuprate superconductor Nd2−xCexCuOy

Flux-flow voltage steps and negative differential resistivity in the cuprate Nd_2−xCe_xCuO_y are explained in terms of subbands between the Fermi energy and the energy gap affecting the quasiparticle dynamics.     

固相反应法制备的CoxZn1-xO磁性能的研究

采用固相反应烧结法制备了Co掺杂ZnO的粉末和压片样品. XRD衍射表明样品中Co²⁺离子取代Zn²⁺离子进入了ZnO晶格中. 在室温下样品均表现为顺磁性, 利用密度泛函理论(DFT+U)方法计算得到的Co₂Zn₁₄O₁₆体系反铁磁基态更稳定, 并通过Co, O原子电子迁移变化, 表明了CoZnO体系中磁性机理更倾向于Co²⁺—O^2-—Co²⁺成键的间接交换作用模型. 改进了安德森模型中的直接交换积分J_pd公式. 提出两个可能的途径来实现具有本征铁磁性氧化物半导体.     

The effects of the intense laser field on bound states in GaxIn1-xNyAs1-yN/GaAs single quantum well

We have investigated the effects of the intense laser field and nitrogen concentration on bound state energy levels in Ga _x In_{1- x} N _y As_{1- y} N/GaAs quantum well. The results show that both intense laser field and N-incorporation into the GaInNAs have strong influences on carrier localization. We hope that our results can stimulate further investigations of the related physics, as well as device applications of group-III nitrides.     

First-principles investigation of BAs and BxGa1-xAs alloys

First-principles investigation of BAs and BxGa1-xAs alloys Using first-principles calculations in the generalized gradient approximation, the electronic properties of BAs and BxGa1-xAs alloys are studied. At the Brillouin-zone centre, the lowest conduction band is the three-degenerate p-like Г15c state rather than s-like Г1c state, and the conduction band minimum （CBM） is along the A line between the Г and X points-at approximately 11/14（1,0,0）2π/a. With boron content at 0%-18.75%, BxGa1-xAs alloys have a small （2.6 eV） and relatively composition-independent band-gap bowing parameter, the band-gap increases monotonically by -18meV/B% with increasing boron content. In addition, the formation enthalpies of mixing for BxGa1-xAs alloys with boron content at 6.25% and 12.5% are calculated, and the large formation enthalpies may explain the difficulty in alloying boron to GaAs.     

LixNayCoO2的制备和热电性质

用固相反应方法，成功地合成了具有交互生长结构的Li_xNa_yCoO₂单相多晶系列样品. 热电势测量表明，该系统的室温热电势比Na_xCoO₂体系约高出60μV/K. 基于空穴载流子具有O2p特征，提出Li_xNa_yCoO₂中额外的热电势来源于氧空穴的占位熵. 关键词： xNa_yCoO₂')" href="#">Li_xNa_yCoO₂ 热电势 热电材料