Effect of Zn impurity in K0.8Fe(2-δ-x)Zn(x)Se2

A series of K(0.8)Fe(2-δ-x)Zn(x)Se(2) single-crystal samples with nominal compositions 0?≤?x?≤?0.05 were grown and their physical properties were measured in order to study the effect of Zn impurity. It is found that the Zn impurity (x?≤?0.02) does not affect the superconducting transition temperature T(c) significantly. Meanwhile the hump in resistivity which corresponds to the transition from the insulating to metallic phase quickly shifts towards low temperatures. The results imply that there should be a phase separation in this system and Zn impurity causes the enhancement of the insulating phase. The negligible effect of Zn impurity on T(c) suggests an s-wave pairing in the superconducting phase. Meanwhile there is a possibility that the Zn impurity may selectively enter into the insulting phase.     

Suppression of Tc by Zn impurity in the electron-type LaFe0.925−y Co0.075ZnyAsO system

The effect of non-magnetic Zn impurity on superconductivity in electron-type pnictide superconductor LaFe_0.925−yCo_0.075Zn_yAsO is studied systematically. The optimally doped LaFe_0.925Co_0.075AsO without Zn impurity exhibits superconductivity at T_c^mid of 13.2 K, where T_c^mid is defiend as the mid-point in the resistive transition. In the presence of Zn impurity, the superconducting transition temperature, T_c^mid, is severely suppressed. The result is consistent with the theoretic prediction on the effect of non-magnetic impurity in the scenario of s_± pairing, but it is in sharp contrast to the previous report on the effect of Zn impurity in the F-doped systems. The possible interpretation of the different effects of Zn impurity on superconductivity in different systems is discussed.     

Impurity states and interlayer tunneling in high temperature superconductors

We argue that the scanning tunneling microscope (STM) images of resonant states generated by doping Zn or Ni impurities into Cu-O planes of BSCCO are the result of quantum interference of the impurity signal coming from several distinct paths. The impurity image seen on the surface is greatly affected by interlayer tunneling matrix elements. We find that the optimal tunneling path between the STM tip and the metal (Cu, Zn, or Ni) d(x(2)-y(2)) orbitals in the Cu-O plane involves intermediate excited states. This tunneling path leads to the fourfold nonlocal filter of the impurity state in Cu-O plane that explains the experimental impurity spectra. Applications of the tunneling filter to the Cu vacancy defects and "direct" tunneling into Cu-O planes are also discussed.     

Zn杂质扩散诱导AlGaInP/GaInP量子阱混杂

杂质扩散诱导量子阱混杂技术可用于制作腔面非吸收窗口,提高大功率半导体激光器的输出功率.以Zn2As2为扩散源,采用闭管扩散方式,在550℃下对650 nm半导体激光器的外延片进行了一系列Zn杂质扩散诱导量子阱混杂的实验.实验发现,随着扩散时间从20～120 min,样品光致发光(PL)谱蓝移偏移增加,峰值波长蓝移53 nm;当扩散时间超过60 min后,样品的PL谱中不仅出现了常见的蓝移峰,同时还出现了红移峰,峰值波长红移32 nm.分析表明PL谱蓝移来自Zn扩散引起的AlGaInP/GaInP间的量子阱混杂;红移来自Zn杂质扩散对样品中Ga0.51In0.49P缓冲层的影响.还研究了扩散温度(550℃)和扩散时间对样品晶体品质的影响,并在理论上计算了AlGaInP/GaInP量子阱混杂巾的Al-Ga的互扩散系数.     

New evidence for the Soret effect in pulsed laser experiments

The impurity profile evolution occurring in laser irradiated metals is shown to be governed by ordinary and thermal diffusion in two new cases. Soret coefficients are found in a dilute impurity case (Zn implanted Al) and in a more complex situation (NiAu mixing in a Ni matrix).     

天然杂质对黄铁矿的电子结构及催化活性的影响

采用密度泛函理论和平面波赝势方法对含天然杂质黄铁矿的电子结构和光学性质进行了计算,并讨论了二十种天然杂质:钴、镍、砷、硒、碲、铜、金、银、钼、锌、铊、锡、钌、钯、铂、汞、镉、铋、铅和锑,对黄铁矿催化活性的影响.结果表明在过渡金属杂质中,杂质能级主要由它们的d轨道产生,而在主族金属及非金属杂质中,杂质能级主要由它们的s或p轨道产生.含铜、钼、砷、金、银或镍的黄铁矿对氧的还原的电催化能力增强.除锌、钼、钌、砷、锑、硒和碲外,其余杂质能增强黄铁矿表面俘获电子的能力,使光生电子和空穴复合的概率减小.光学性质计算表 关键词： 天然黄铁矿 杂质 电子结构 光学性质     

Spin- and charge density perturbations and short-range order in Fe–Cu and Fe–Zn BCC alloys: A Mössbauer study

A model used to describe the ⁵⁷Fe Mössbauer spectra for the binary BCC iron alloys rich in iron has been extended to account for the alloy crystallographic ordering. The ordering is accounted for by introducing single order parameter. Extension of the model is described in detail. The model has been tested applying it to the Fe–Cu alloys obtained by the arc melting and to the Fe–Zn alloys prepared by the solid state reaction. Random alloys are obtained up to ∼2 at% of Cu, and up to ∼8 at% of Zn. For higher impurity (minor alloy component) concentration it has been found that Cu atoms try to avoid Fe atoms in the iron matrix as nearest neighbors, while the opposite happens to the Zn atoms, albeit at much lesser scale, i.e., Zn–Zn interactions are much weaker than Fe–Zn interactions at the nearest neighbor distance. Perturbations to the iron magnetic hyperfine field (spin density) and electron (charge) density on the iron nucleus have been obtained for both series of alloys versus impurity concentration.     

Local density of states around a magnetic impurity in high- T(c) superconductors based on the t-J model

The local density of states (LDOS) around a magnetic impurity in high- T(c) superconductors is studied using the two-dimensional t-J model with a realistic band structure. The order parameters are determined in a self-consistent way within the Gutzwiller approximation and the Bogoliubov-de Gennes theory. In sharp contrast with the nonmagnetic impurity case, the LDOS near the magnetic impurity shows two resonance peaks reflecting the presence of spin-dependent resonance states. It is also shown that these resonance states are approximately localized around the impurity. The present results have an immediate connection with the scanning tunneling spectroscopy observation of Bi2Sr2Ca(Cu1-xNi[Zn](x))(2)O(8+delta).     

双次曝光积分效应实现杂质浓度分布均匀化

 激光诱导扩散中,当入射激光光强为高斯分布甚至均匀分布时，微小扩散区的温度分布不均匀。由于扩散系数是温度的函数，必将导致扩散后杂质浓度分布的均匀性较差，无法制作出高性能的p-n结。提出采用多次激光诱导扩散的积分效应来实现杂质浓度分布的均匀化整形。对于InP衬底的CO_{2激光诱导Zn扩散,利用温度闭环测控系统测得的基片表面热斑温度场分布，分析计算了两次激光诱导扩散重叠区域的浓度分布积分效应。在此基础上模拟计算出，用双次曝光积分效应做杂质浓度分布的均匀化整形时，基片上两次激光照射位置的最佳间隔为20 μm。这为改进激光诱导扩散工艺，用多次曝光实现面均匀的杂质浓度分布奠定了理论基础。}     

Quasiparticle lifetimes due to A1 impurities in Zn

We have calculated the quasiparticle lifetimes due to Al impurities in Zn. For the Zn electronic structure we use the wave functions, Fermi velocities and surface elements calculated by Tomlinson and Swihart who based their work on the accurate pseudopotential fit to the de Haas-van Alphen data obtained by Stark and Falicov. The impurity pseudopotential form factor is obtained from the procedure developed by Shaw.     

Zinc impurities in d-wave superconductors

We study the two-dimensional Hubbard model with nonmagnetic Zn impurities modeled by binary diagonal disorder using quantum Monte Carlo within the dynamical cluster approximation. With increasing Zn content we find a strong suppression of d-wave superconductivity and an enhancement of antiferromagnetic spin correlations. T(c) vanishes linearly with Zn impurity concentration. The spin susceptibility changes from pseudogap to Curie-Weiss-like behavior indicating the existence of free magnetic moments in the Zn doped system. We interpret these results within the resonating-valence-bond picture.     

Local structure of Zn<Superscript>2+</Superscript> impurity centers in a LiF: U,Zn crystal

The local structure of Zn²⁺ impurity centers in a uranium-activated lithium fluoride crystal LiF: U,Zn is calculated in the framework of the shell model in the pair potential approximation.     

Direct evidence for As as a Zn-site impurity in ZnO

Arsenic has been reported in the literature as one of the few p-type dopants in the technologically promising II-VI semiconductor ZnO. However, there is an ongoing debate whether the p-type character is due to As simply replacing O atoms or to the formation of more complicated defect complexes, possibly involving As on Zn sites. We have determined the lattice location of implanted As in ZnO by means of conversion-electron emission channeling from radioactive (73)As. In contrast to what one might expect from its nature as a group V element, we find that As does not occupy substitutional O sites but in its large majority substitutional Zn sites. Arsenic in ZnO (and probably also in GaN) is thus an interesting example for an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system.     

超导材料的正常态下杂质锌引起的非均匀性

本文采用含有非磁性杂质的二维t-J模型来描述掺锌的高温氧化物超导材料,并利用非均匀双时格林函数理论对有限尺寸的材料进行了数值计算.在 Fermion-Spin 理论框架下,我们分别研究了非磁性杂质引起的电荷和自旋的不均匀性及对材料正常态特性的影响.我们发现:一方面非磁性杂质锌对其附近的自旋反铁磁关联有强烈的影响,能使周围的最近邻关联函数的绝对值比均匀情况增加很多;另一方面,空位子会受到其周围自旋的影响而出现相应的分布不均匀性,进而又影响自旋关联的不均匀性.并且,围绕杂质锌能够形成自旋激发和空位激发的局域态.     

The apparent Dingle temperature in Zn−Mn,Zn−Cr,and Zn−Fe

The apparent Dingle temperature of the 3rd zone needles in several alloys of Zn?Mn, Zn?Cr and Zn?Fe has been determined from the absolute amplitude of the de Haas-van Alphen effect over the temperature range 1.6 K to 4.2 K and the field range 0 to 9 kG. The results show clearly that potential scatteringnot spin scattering dominates in all three systems. In addition, a “cross-over” behaviour in the de Haas-van Alphen amplitudes results from the scattering of the magnetic moments of the impurity spin.     

Charge Transfer and F-Type Centers in Alkaline-Earth Fluorides Activated by Cd2+ or Zn2+ Ions

Optics and Spectroscopy - Photoluminescence spectra of impurity centers containing anion vacancy Cd+ $${{{v}}_{a}}$$ or Zn+ $${{{v}}_{a}}$$ in alkali-earth fluorides have been studied. A comparison...     

Evidence for native-defect donors in n-type ZnO

Recent theory has found that native defects such as the O vacancy V(O) and Zn interstitial Zn(I) have high formation energies in n-type ZnO and, thus, are not important donors, especially in comparison to impurities such as H. In contrast, we use both theory and experiment to show that, under N ambient, the complex Zn(I)-N(O) is a stronger candidate than H or any other known impurity for a 30 meV donor commonly found in bulk ZnO grown from the vapor phase. Since the Zn vacancy is also the dominant acceptor in such material, we must conclude that native defects are important donors and acceptors in ZnO.     

Experimental observation of localization-delocalization of Cooper pairs in Nd1.85Ce0.15CuO4

Localization—delocalization of cooper pairs on ⁶⁷Zn impurity centers in the copper sublattice in the high-temperature superconductor Nd_1.85Ce_0.15CuO₄ was observed by emission Mössbauer spectroscopy on ⁶⁷Cu (⁶⁷Zn).     

An interfacial complex in ZnO and its influence on charge transport

The segregation of native defects and Bi impurities to a high-angle grain boundary in ZnO is studied by first-principles calculations. It is found that the presence of Bi(Zn) increases the concentration of native defects of acceptor type in the grain boundary. This leads to the formation of a Bi(Zn)+V(Zn)+O(i) interfacial complex under O-rich conditions and exhibits a localized acceptor state. This state, which is different from that of the isolated impurity, gives the grain boundary p-type character and when embedded between n-type ZnO grains is consistent with the double Schottky barrier model for Bi-doped ZnO varistors.