Effect of alloy formation processes in the Co-Cu system on the magnetic and magnetoresistance properties of multilayer Co/Cu films with ultrathin Co layers prepared by DC magnetron sputtering

This paper reports on a study of multilayer Co/Cu films with an effective thickness of the Co layer of ～3.5 Å, which were prepared by magnetron sputtering. The samples prepared have been found to have a metastable multiphase structure. An analysis of the data obtained by structural and, primarily, by magnetic methods has revealed that the main phases are the Co/Cu supersaturated solid solution (alloy) with a Co concentration of about 30 at %, the superparamagnetic phase, and the paramagnetic phase, which is accounted for by the presence of small (a few atoms at most) Co clusters embedded in the Cu matrix. A clearly pronounced maximum in the temperature dependences of the low-field magnetoresistance has been found, which is associated with the temperature of the magnetic phase transition of the supersaturated Co-Cu alloy.     

Tuning the Quantum Properties of ZnO Devices by Modulating Bulk Length and Doping

The quantum transport properties of ZnO devices with five different bulk configurations are investigated with numerical methods. The calculation results reveal that the transport property at a higher energy range can be tuned by changing the length of central scattering. By substituting some Zn atoms with Cu atoms, it is found that the doped Cu atoms have an obvious effect on the quantum properties at the entire energy range investigated, and could result in different transmission. The properties of ZnO devices are also influenced by the doping positions of Cu atoms. The tuning mechanism relies on the shifting of carrier distributions in the scattering center of the device.     

Growth of CuO chains on Ag(110) surfaces

The (AgO) chains grown along the 〈001〉 direction on Ag(110) disappeared by the reaction with Cu atoms at room temperature, and new one-dimensional chains grew in the 〈110〉 direction. The STM images at different bias potentials suggest the growth of (CuO) chains in the 〈110〉 direction on the Ag(110) surface. The (CuO) chains on the Ag(110) surface disappeared by heating to 470 K, but they reappeared by exposing to O₂ at room temperature.     

Direct observation of the quantum tunneling of single hydrogen atoms with a scanning tunneling microscope

Single hydrogen atoms were imaged on the Cu(001) surface by scanning tunneling microscopy (STM). The vibrations of individual H and D atoms against the surface were excited and detected by inelastic electron tunneling spectroscopy (STM-IETS). Variable temperature measurements of H atom diffusion showed a transition from thermally activated diffusion to quantum tunneling at 60 K. Regimes of phonon-assisted and electron-limited quantum tunneling were observed. The thermal diffusion rate of D atoms varied over 7 orders of magnitude between 80 and 50 K with no transition to quantum tunneling down to a thermal hopping rate of 4x10(-7) s(-1).     

快速凝固Co-Cu包晶合金的电学性能

研究了Co-Cu包晶合金快速凝固过程中的相选择和组织形成特征, 探索了冷却速率、组织结构和晶体位向与合金电阻率之间的相关规律.实验发现, 快速凝固可使Co在(Cu)中的固溶度扩展至20%.Cu含量大于80%时, L+αCo→(Cu)包晶转变被抑制, (Cu)可从过冷熔体中直接形核析出.Cu含量在40%—70%范围时, Co-Cu合金的液相分离受到抑制, 凝固组织沿条带厚度方向分为两个晶区.细晶区中αCo和(Cu)相竞争形核并生长, αCo枝晶形态细密，细小的（Cu）等轴晶均匀分布于αCo的基体之中.粗晶区αCo相为领先相, 富Cu相分布于αCo枝晶的晶界处.随着冷速的增大, 合金组织显著细化, 晶界增多,对自由电子的散射作用增强, 合金电阻率显著增大.当晶界散射系数r＝0996—0999时, 可采用M-S模型综合分析快速凝固Co-Cu合金的电阻率. 关键词： 电阻率 快速凝固 相结构 晶体生长     

多壳层铜纳米线结构和电子特性的第一性原理研究

基于密度泛函理论框架下的第一性原理计算,系统地研究了多壳层Cu纳米线的稳定结构和电子特性.得到不同线径多壳层Cu纳米线的平衡态晶格常数相差不大,都表现出金属特性,且其单原子平均结合能和量子电导随着纳米线直径的增加而增加.纳米线中内壳层Cu原子表现出体相结构Cu原子相似的电子特性,而表面壳层由于配位数的减少,其3d态能量范围变窄且整体向费米能级发生移动.电荷密度分析表明,相对于体相Cu晶体中原子间的相互作用,纳米线表面壳层Cu原子与其最近邻原子间的相互作用明显增强.     

Impurities and quantum interference in the chains of YBa2Cu3O6+x

Motivated by recent experiments, we study the electronic structure near impurities in the chains of YBa2Cu3O6+x. Using a model of proximity induced chain superconductivity, we show that a resonance state in the chain density of states is induced only by a magnetic impurity. The spatial form of the resonance reflects the particle-hole nature of chain superconductivity and therefore distinguishes it from other broken symmetry phases. Because of quantum interference effects between impurities, the chains can undergo a quantum phase transition into a polarized state.     

Dependence of the Distribution of Atomic Chain Lengths on a Vicinal Surface on External Parameters

The growth of one-dimensional atomic chains along the vicinal surface has been studied by the kinetic Monte Carlo method. It has been shown that their growth is determined exclusively by kinetic parameters such as the temperature, flux of deposited atoms, and degree of coating rather than by the binding energy and quantum effects. Conditions under which chains with “magic lengths” appear have been determined.     

A reversible reaction forming (---Cu---O---) strings and (Cu)6-clusters on Ag(110) shown by STM

An artificial new surface of (---Cu---O---) chains grown on Ag(110) surface was prepared by reacting a surface with Cu atoms, where the (---Cu---O---) chains grow in the [1 0] direction and are self-assembled on the Ag(110) surface in a (2 x 2)-p2mg structure. When the Cu---O/Ag(110) surface was heated in vacuum, the (---Cu---O---) chain decomposed to uniform cluster dots arranged along the [1 0] direction, where the cluster dots were composed of six Cu atoms. When the Ag(110) surface with the Cu---cluster dots was exposed to O₂, the (---Cu---O---) lines were redrawn along the [1 0] direction by reacting a s in the [1 0] direction with O₂. This is a reversible chemical reaction in one dimensional regime proved in atomic resolution.     

Exploiting quantum parallelism to simulate quantum random many-body systems

We present an algorithm that exploits quantum parallelism to simulate randomness in a quantum system. In our scheme, all possible realizations of the random parameters are encoded quantum mechanically in a superposition state of an auxiliary system. We show how our algorithm allows for the efficient simulation of dynamics of quantum random spin chains with known numerical methods. We propose an experimental realization based on atoms in optical lattices in which disorder could be simulated in parallel and in a controlled way through the interaction with another atomic species.     

Landau-Zener sweeps and sudden quenches in coupled Bose-Hubbard chains

We simulate numerically the dynamics of strongly correlated bosons in a two-leg ladder subject to a time-dependent energy bias between the two chains. When all atoms are initially in the leg with higher energy, we find a drastic reduction of the interchain particle transfer for slow linear sweeps, in quantitative agreement with recent experiments. This effect is preceded by a rapid broadening of the quasimomentum distribution of atoms, signaling the presence of a bath of low-energy excitations in the chains. We further investigate the scenario of quantum quenches to fixed values of the energy bias. We find that for a large enough density the momentum distribution relaxes to that of an equilibrium thermal state with the same energy.     

Two-site Kondo effect in atomic chains

Linear CoCu(n)Co clusters on Cu(111) fabricated by atomic manipulation represent a two-site Kondo system with tunable interaction. Scanning tunneling spectroscopy reveals oscillations of the Kondo temperature T(K) with the number n of Cu atoms for n≥3. Density functional calculations show that the Ruderman-Kittel-Kasuya-Yosida interaction mediated by the Cu chains causes the oscillations. Calculations find ferromagnetic and antiferromagnetic interaction for n=1 and 2, respectively. Both interactions lead to a decrease of T(K) as experimentally observed.     

Optical permittivity,thermo-optical and electrical properties of nickel oxide nanostructures with heavy cupper doping

In this research, physical properties of nickel oxide nano-structured layers doped with various amount of Cu atoms (20–60 at.%) is studied using spray pyrolysis method on the glass substrate. The FESEM images show formations of nanostructures of about 20–60 nm and the XRD patterns show layers have a polycrystalline cubic structure nature with (111) as the preferred direction that its intensity reduces as the doping density increases. Analyzing transmittance UV. Vis spectra shows the variations of optical band gap of the samples are due to occurrence of doping atoms and quantum confined effects. Optical permittivity of different doped films have been compared using new numerical method and show the prominent effect of doping percent to real and imaginary parts of electrical permittivity. Also Hall effect results shows that Cu atoms substituted by Ni atoms sites play as acceptor atoms in the crystalline lattice. Finally, thermo-optical properties of the films have been studied using Nd–YAG laser illumination.     

Understanding the junction degradation mechanism in CdS/CdTe solar cells using a Cd-deficient CdTe layer

It is known that CdTe solar cells are often degraded under solar illumination. But the degradation mechanism is not fully proved because it does not appear consistently. The junction degradation in CdS/CdTe solar cells was investigated using a CdTe layer with Cd deficient composition, where Cd vacancy concentration is high. It was found that the Cu atoms easily filled the Cd vacancies in CdTe and transport to junction area from Cu back contact. PL measurement and spectral quantum efficiency measurement showed that the incorporation of Cu atoms in CdS forms a defect energy level at 1.55 eV below the conduction band in CdS. As a result, the junction built-in potential is decreased and light penetration into CdTe absorber is shielded. For reliable and stable CdTe cells, the formation of Cd vacancy in CdTe should be avoided by careful control of CdTe.     

利用Gupta势结合遗传算法研究ConCu55－n(n=0—55)混合团簇的结构演化及基态能量

采用半经验的Gupta多体势结合遗传算法对Co_nCu_55－n(n=0—55)混合团簇的基态结构和能量进行了研究,发现这些混合团簇的基态结构是在Co₅₅,Cu₅₅单质团簇(Mackay二十面体)的基础之上发生的畸变;从n=0(Cu₅₅)开始,Co原子从中心到表面,从棱到顶点依次、连续替换Cu原子;基态结构与键能较大键的数目及其平均键长有关;Co₁₃Cu₄₂具有最稳定的结构,13个Co原子全部位于团簇内部形成Mackay二十面体对整个团簇的稳定性有显著影响. 关键词： 团簇 结构和能量 Gupta势 遗传算法     

Substrate effects on the magnetic ground state of 3d transition metal chains

We investigate the electronic and magnetic properties of linear chains of 3d atoms, namely Cr and Mn, supported on a monolayer of copper nitride on Cu(1 0 0) using first principles LSDA calculations. Based on these results, we also calculate the intrachain magnetic coupling by means of an effective Heisenberg model. We obtain that, the sp occupation of the chains, the chemical environment and the lattice relaxation determine the magnetic properties of the investigated nanochains.     

Effect of transition metal (Fe, Cu, Ni, Rh)-doped small silver chains on optics of plasmon resonances

Doping can control and tune the optical properties of current nanoalloys. In this study, the optical generation of plasmon resonance mode in pure-Ag and transition metal (Fe, Cu, Ni, Rh) single-doped Ag chains is investigated using time-dependent density functional theory. Results show that the redshift of plasmon energy appears and intensity of longitudinal mode enhances with increasing the number of Ag atoms in pure silver chains. The Ag chains doped with transition metal (TM) atom create an additional peak with a local plasmon resonance mode which is related to charge redistribution in the chain around TM atom.     

Long-range quantum gates using dipolar crystals

We propose the use of dipolar spin chains to enable long-range quantum logic between distant qubits. In our approach, an effective interaction between remote qubits is achieved by adiabatically following the ground state of the dipolar chain across the paramagnet to crystal phase transition. We demonstrate that the proposed quantum gate is particularly robust against disorder and derive scaling relations, showing that high-fidelity qubit coupling is possible in the presence of realistic imperfections. Possible experimental implementations in systems ranging from ultracold Rydberg atoms to arrays of nitrogen vacancy defect centers in diamond are discussed.     

A charge density wave model for reconstructed monolayers of Co on Cu(100)

We have grown in ultra high vacuum Co on top of a clean unreconstructed Cu(100) surface. The system shows upon absorption of one third of a Co monolayer a c(2 × 2) structure as low energy electron diffraction measurements reveal. The electronic structure of the 1 × 1 Co-Cu(100) is calculated. We then interpret the c(2 × 2) reconstruction as being due to a ferromagnetic induced charge density wave.