Effect of Copassivation of Cl and Cu on CdTe Grain Boundaries

Using a first-principles method, we investigate the structural and electronic properties of grain boundaries (GBs) in polycrystalline CdTe and the effects of copassivation of elements with far distinct electronegativities. Of the two types of GBs studied in this Letter, we find that the Cd core is less harmful to the carrier transport, but is difficult to passivate with impurities such as Cl and Cu, whereas the Te core creates a high defect density below the conduction band minimum, but all these levels can be removed by copassivation of Cl and Cu. Our analysis indicates that for most polycrystalline systems copassivation or multipassivation is required to passivate the GBs.

Thermodynamic properties of Cu-3(CO3)(2)(OH)(2) and the spin-1/2 distorted diamond Heisenberg chain

The thermodynamic properties of the spin-1/2 diamond quantum Heisenberg chain model have been investigated by means of the transfer matrix renormalization group (TMRG) method. Considering different crystal structures, by changing the interactions among different spins and the external magnetic fields, we first investigate the magnetic susceptibility, magnetization, and specific heat of the distorted diamond chain as a model of ferrimagnetic spin systems. The susceptibility and the specific heat show different features for different ferromagnetic (F) and antiferromagnetic (AF) interactions and different magnetic fields. A 1/3 magnetization plateau is observed at low temperature in a magnetization curve. Then, we discuss the theoretical mechanism of the double-peak structure of the magnetic susceptibility and the three-peak structure of the specific heat of the compound Cu-3(CO3)(2)(OH)(2), on which an elegant measurement was performed by Kikuchi [Phys. Rev. Lett. 94, 227201 (2005)]. Our computed results are consistent with the main characteristics of the experimental data. Meanwhile, we find that the double-peak structure of susceptibility can be found in several different kinds of spin interactions in the diamond chain. Moreover, a three-peak behavior is observed in the TMRG results of magnetic susceptibility. In addition, we perform calculations relevant for some experiments and explain the characteristics of these materials. (c) 2007 American Institute of Physics.

Structural, morphological, and magnetic characteristics of Cu-implanted nonpolar GaN films

Diluted magnetic nonpolar GaN:Cu films have been fabricated by implanting Cu ions into unintentionally doped nonpolar a-plane(1 1 (2) over bar 0) GaN films and a subsequent thermal annealing process. The structural, morphological and magnetic characteristics of the samples have been investigated by means of high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and superconducting quantum interference device (SQUID). The sample shows a clear ferromagnetism behavior at room temperature. It is significantly shown that with a Cu concentration as low as 0.75% the sample exhibits a saturation magnetization about 0.65 mu(B)/Cu atom. Moreover, the possible origin of the ferromagnetism for the sample was also discussed briefly. (C) 2009 Elsevier B. V. All rights reserved.

The impact of implantation dose on the characteristics of diluted-magnetic nonpolar GaN:Cu films

Diluted-magnetic nonpolar GaN:Cu films have been fabricated by implanting Cu ions into p-type nonpolar a-plane (1120) GaN films with a subsequent thermal annealing process. The impact of the implantation dose on the structural. morphological and magnetic characteristics of the samples have been investigated by means of high-resolution X-ray diffraction (HRXRD). atomic force microscopy (AFM), and superconducting quantum interference device (SQUID). The XRD and AFM analyses show that the structural and morphological characteristics of samples deteriorated with the increase of implantation dose. According to the SQUID analysis. obvious room-temperature ferromagnetic properties of samples were detected. Moreover, the saturation magnetization per Cu atom decreased as the implantation dose increased. (C) 2009 Elsevier B.V. All rights reserved.

Strong room-temperature ferromagnetism in Cu-implanted nonpolar GaN films

This work was supported by the Natural Science Foundation of China (Grant No. 60876068) and The Project sponsored by SRF for ROCS (Grant No. 08Y1010000), SEM

Synthesis and photoluminescence of ZnS : Cu nanoparticles

The room-temperature photoluminescence (PL) of copper doped zinc sulfide (ZnS:Cu) nanoparticles were investigated. These ZnS:Cu nanoparticles were synthesized by a facile wet chemical method, with the copper concentration varying from 0 to 2 mol%. By Gaussian fitting, the PL spectrum of the undoped ZnS nanoparticles was deconvoluted into two blue luminescence peaks (centered at 411 nm and 455 nm, respectively), which both can be attributed to the recombination of the defect sates of ZnS. But for the doped samples, a third peak at about 500 nm was also identified. This green luminescence originates from the recombination between the shallow donor level (sulfur vacancy) and the t(2) level of Cu2+. With the increase of the CU2+ concentration, the green emission peak is systematically shifted to longer wavelength. In addition, it was found that the overall photoluminescence intensity is decreased at the Cu2+ concentration of 2%. The concentration quenching of the luminescence may be caused by the formation of CuS compound. (c) 2005 Elsevier B.V. All rights reserved.

Interlayer segregation of Cu atoms in Ta/NiFe/Cu/NiFe/FeMn/Ta spin-valve multilayers and its influence on magnetic properties

Experimental results show that the exchange coupling field (H-ex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. In order to find out the reason, the composition and chemical states at the surface of Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/Cu(4 nm), and Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) were studied using x-ray photoelectron spectroscopy. The results show that no elements from lower layers float out or segregate to the surface in the first and second samples. However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) multilayers, i.e., Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which causes the exchange coupling field (H-ex) of Ta/NiFe/Cu/NiFe/FeMn/Ta to be weaker than that of Ta/NiFe/FeMn/Ta. (C) 2002 American Institute of Physics.

Interlayer segregation of Cu atoms in metal multilayers

The experimental results show that the exchange coupling field H.. of NiFe/FeMn for TalNiFe/FeMn/Ta multilayers is higher than that for the spin valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. The composition and chemical states at the surface of Ta(12nm)/NiFe(7nm), Th(12nm)/NiFe(7nm)/Cu(4nm) and Ta(12nm)/NiFe(7nm)/Cu(3 nm)/NiFe(5 mn) were studied by using x-ray photoelectron spectroscopy. The results show that no element from the underlayers Boats out or segregates to the surface for Th(12 nm)/NiFe(7nm), Ta(12 nm)/NiFe(7nm)/Cu(4 mn). However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7nm)/Cu(3nm)/NiFe(5nm) multilayers, i.e. to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which will cause the exchange coupling field H.. of Ta/NiFe/FeMn/Ta multilayers to be higher than that of Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers.

Synthesis Gas Generation by Chemical-Looping Reforming Using Ce-Based Oxygen Carriers Modified with Fe, Cu, and Mn Oxides

Chemical-looping reforming (CLR) is a technology that can be used for partial oxidation and steam reforming of hydrocarbon fuels. It involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from combustion air to the fuel. Composite oxygen carriers of cerium oxide added with Fe, Cu, and Mn oxides were prepared by co-precipitation and investigated in a thermogravimetric analyzer and a fixed-bed reactor using methane as fuel and air as oxidizing gas. It was revealed that the addition of transition-metal oxides into cerium oxide can improve the reactivity of the Ce-based oxygen carrier. The three kinds of mixed oxides showed high CO and H-2 selectivity at above 800 degrees C. As for the Ce-Fe-O oxygen carrier, methane was converted to synthesis gas at a H-2/CO molar ratio close to 2:1 at a temperature of 800-900 degrees C; however, the methane thermolysis reaction was found on Ce-Cu-O and Ce-Mn-O oxygen carriers at 850-900 degrees C. Among the three kinds of oxygen carriers, Ce-Fe-O presented the best performance for methane CLR. On Ce-Fe-O oxygen carriers, the CO and H-2 selectivity decreased as the Fe content increased in the carrier particles. An optimal range of the Ce/Fe molar ratio is Ce/Fe > 1 for Ce-Fe-O oxygen carriers. Scanning electron microscopy (SEM) analysis revealed that the microstructure of the Ce-Fe-O oxides was not dramatically changed before and after 20 cyclic reactions. A small amount of Fe3C was found in the reacted Ce-Fe-O oxides by X-ray diffraction (XRD) analysis.