Inherent diode isolation in programmable metallization cell resistive memory elements

The feasibility of a storage element with inherent rectifying or isolation properties for use in passive memory arrays has been demonstrated using a programmable metallization cell structure with a doped (n-type) silicon electrode. The Cu/Cu–SiO₂/n-Si cell used in this study switches via the formation of a nanoscale Cu filament in the Cu–SiO₂ film which results in the creation of a Cu/n-Si Schottky contact with soft reverse breakdown characteristics. The reverse bias leakage current in the on-state diode is dependent on the programming current employed as this influences the area of the electrodeposit and hence the area of the Cu/n-Si junction. The programming current also controls the on-state resistance of the device, allowing multi-level cell (MLC) operation, in which discrete resistance levels are used to represent multiple logical bits in each physical cell. The Cu/Cu–SiO₂/n-Si elements with heavily doped silicon electrodes were readily erasable at voltage less than −5 V which allows them to be re-programmed. Lightly doped silicon electrode devices were not able to be erased due to their very high reverse breakdown voltage but exhibited extremely low leakage current levels potentially allowing them to be used in low energy one-time programmable arrays.     

Positron annihilation study of helium clustering in alpha irradiated copper

Abstract

Helium clustering in alpha irradiated copper has been investigated by positron annihilation spectroscopy. Pure copper samples have been homogeneously helium implanted using a cyclotron, yielding helium concentrations of 100 appm and 400 appm. Post-implantation positron lifetime and Doppler broadened annihilation lineshape measurements have been carried out on these Cu samples as a function of isochronal annealing temperature. An annealing stage observed in the isochronal annealing curve viz., a marked reduction in the resolved lifetime τ₂ and an increase of its intensity I ₂, is explained as due to the formation of helium bubble embryos. At higher annealing temperatures, τ₂ corresponding to helium bubbles increases and saturates while its intensity I ₂ decreases, indicating an increase in the size of the bubble with a concomitant decrease in the bubble concentration. This stage is interpreted to be the bubble growth stage. From an analysis of positron lifetime parameters in the growth stage, helium stom density, bubble size and bubble concentration have been deduced at various annealing temperatures. The bubble characteristics are found to be affected by the helium dose. The present results on direct helium implanted Cu are compared with those of our earlier study on n-irradiated Cu-B, where helium was introduced using ¹⁰B(n, α)⁷ Li reaction.     

Atomic diffusion in annealed Cu/SiO2/Si（100） system prepared by magnetron sputtering

Cu thin films are deposited on p-type Si (100) substrates by magnetron sputtering at room temperature. The inter-face reaction and atomic diffusion of Cu/SiO2/Si (100) systems are studied by x-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Some significant results can be obtained. The onset temperature of interdiffusion for Cu/SiO2/Si(100) is 350 C. With the annealing temperature increasing, the interdiffusion becomes more apparent. The calculated diffusion activation energy is about 0.91 eV. For the Cu/SiO2/Si (100) systems copper silicides are not formed below an annealing temperature of 350 C. The formation of the copper silicides phase is observed when the annealing temperature arrives at 450 C.     

EPR investigation of the spin-spin interactions in a Cu(II)-Gd(III)-Fe(III) heterospin system

The spin-spin interactions in a system that contains three different spin carriers, [{LCu}Gd(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O (1) [L²⁻, N,N-propylenedi(3-methoxysalicylideneiminato)], were investigated by electron paramagnetic resonance spectroscopy. Additional information was obtained by analyzing the discrete heterobinuclear system [LCu(OH₂)Gd(O₂NO)₃] (2), which contains the Cu(II)-Gd(III) pair also existing in the structure of 1, and the compounds [{LCu}Gd(H₂O)₃{Co(CN)₆}] _n ·3.5nH₂O and [{LCu}La(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O, which are isostructural with 1 and in which the paramagnetic low-spin Fe(III) and Gd(III) ions were replaced by diamagnetic low-spin Co(III) and La(III), respectively. The investigations were carried out in the temperature range of 293–4 K in both X- and Q-bands and also using a dual-mode X-band. The experimental spectra of the Cu(II)-Gd(III) pairs in 2 were interpreted as the sum of spectra of the ground spin state with total S = 4 and the excited state with S = 3 appearing due to the ferromagnetic exchange interaction between Cu(II) and Gd(III) ions. By fitting the experimental and simulated spectra, the zero-field splitting parameters of the Gd(III) ion are estimated and it is shown that no influence of the anisotropic interaction is detected. The magnetic properties of 1 are discussed from the perspective of the interaction of the Cu(II)-Gd(III) binuclear fragments with the Fe(III) ions.     

Formation of copper islands on a native SiO2 surface at elevated temperatures

A combination of in situ X-ray photoelectron spectroscopy analysis and ex situ scanning electron- and atomic force microscopy has been used to study the formation of copper islands upon Cu deposition at elevated temperatures as a basis for the guided growth of copper islands. Two different temperature regions have been found: (I) up to 250 °C only close packed islands are formed due to low diffusion length of copper atoms on the surface. The SiO₂ film acts as a barrier protecting the silicon substrate from diffusion of Cu atoms from oxide surface. (II) The deposition at temperatures above 300 °C leads to the formation of separate islands which are (primarily at higher temperatures) crystalline. At these temperatures, copper atoms diffuse through the SiO₂ layer. However, they are not entirely dissolved in the bulk but a fraction of them forms a Cu rich layer in the vicinity of SiO₂/Si interface. The high copper concentration in this layer lowers the concentration gradient between the surface and the substrate and, consequently, inhibits the diffusion of Cu atoms into the substrate. Hence, the Cu islands remain on the surface even at temperatures as high as 450 °C.     

Investigation of the chemical state of copper in Cu/SiO2 composite films by x-ray photoelectron spectroscopy

The concentration and chemical state of copper in the subsurface region of Cu/SiO₂ composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO₂) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO₂ matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material.     

Magnetic properties of DNA-templated Co/Cu naonoparticle chains

<正>According to ultraviolet(UV)-vis absorption spectra recorded in the DNA metallization process,DNA-templated Co/Cu binary nanoparticle chains are fabricated by incubating genome DNA of paralichthys olivaceus muscle in CoCl_2 and CuCl_2 mixture solution for 20 hours and reducing the complex for 2 hours.Transmission electron microscopy observation indicates that Co and Cu nanoparticles with 20 nm in diameter were randomly dispersed on the DNA template. The superconducting quantum interference device(SQUID) measurements display that the magnetic interaction between cobalt particles is greatly decreased by the copper particle.With increasing copper content,the coercivity of the systems enhance from 9 Oe to 100 Oe(1 Oe=79.5775 A/m).     

Surface modification of HMS material with silica sol leading to a remarkable enhanced catalytic performance of Cu/SiO2

Cu/SiO₂ catalysts with different bimodal pore structures adjusted by the ratio of HMS and silica sol were prepared via modified impregnation method. Structure evolutions of the catalyst were systematically characterized by N₂-physisorption, X-ray diffraction, H₂ temperature-programmed reduction, N₂O titration and X-ray photoelectron spectroscopy. The results show that the composite silica supported copper catalysts showed remarkably enhanced catalytic performance in the selective hydrogenation of dimethyl oxalate to ethylene glycol compared to the individual silica supported ones obtained by the same method. The dimethyl oxalate conversion and the ethylene glycol selectivity can reach 100% and 98% at 473 K with 2.5 MPa H₂ pressure and 1.5 h⁻¹ liquid hour space velocity of dimethyl oxalate over the optimized Cu/SiO₂ catalyst. The remarkably enhanced catalytic performance of Cu/SiO₂ catalysts might be attributed to the homogeneous dispersion and uniformity of the active copper species and to the larger copper surface areas attained on the HMS supports with large pore diameters and surface areas.     

Analysis of the excitation functions of (α, xnyp) reactions on natural copper

Excitation functions of the reactions⁶³Cu[(α, n), (α, 2n)+(α, pn)] and⁶⁵Cu[(α, n), (α, 2n), (α, 3n), (α, 4n)+(α, p3n)] were investigated up to 50 MeV using stacked foil activation technique and Ge(Li) gamma ray spectroscopy method. Since natural copper used as the target has two odd-mass stable isotopes of abundance,⁶³Cu(69.17%) and⁶⁵Cu(30.83%), their activation in some cases, gives the same residual nucleus through different reaction channels but with very different threshold energies. In such cases, the individual reaction cross sections are separated with the ratio of theoretical cross sections. The experimental results were compared with the predictions of preequilibrium hybrid model of Blann. A general agreement was found in all reactions using initial exciton numbern ₀=4(4p0h) and also preequilibrium fraction depends on the incident particle energy.     

Systematic theoretical investigation of structure and electronic properties of pure copper and lithium doped copper clusters

The pure copper and lithium-doped copper clusters are studied using the unbiased CALYPSO structure searching method and density function theory to understand the evolution of various structure and electronic properties. Theoretical results show the growth behaviours of doped clusters are organised as follows: Li capped Cu_n clusters or Li substituted Cu_n+1 clusters as well as Cu capped Cu_n-1Li clusters. Moreover, the lowest energy structures of Cu_nLi favour planar structures for n ≤ 3 and three-dimensional structures for n = 4–12. In addition, the calculated averaged binding energies, fragmentation energies and second-order difference of energies exhibit obvious odd–even alternations as cluster size increasing. At last, the highest occupied-lowest unoccupied molecular orbital gaps, molecular orbital energy, magnetic property, natural population analysis, natural electron configurations, electrostatic potential, electron density difference, Infrared and Raman spectra and density of states are also, respectively, operative for characterising and rationalising the electronic properties of doped clusters.     

Crystal chemistry of the Tl2−xBa2Ca n Cu n+1O2n+6 (n=0, 1, 2) high-T c superconductors

We report on a comparative crystal chemical study of the Tl_2–xBa₂Ca _n Cu _n+1O_2n+6(n=0, 1, 2) high-T _c superconductors. Superconducting properties were determined by DC-conductivity and-susceptibility measurements. An X-ray diffraction analysis reveals the nonstoichiometry of the compounds as a link between structural and superconducting behavior. A comparison of the different structures gives evidence that T1 deficiency in the TlO double layers increases with increasingn; this deficiency causes apparent Cu valences larger than 2+in the superconducting phases thus maintaining the charge balance. By extracting appropriate chemical formulas and performing a bond strength calculation we obtained the mixed-valent oxidation state of copper for the superconducting tetragonal phases as being 2.17+(n=0), 2.25+(n=1) and 2.31+(n=2) respectively; for the non-superconducting orthorhombic phase Tl_2–xBa₂CuO_6–y a Cu valence of about 2+is suggested.     

Effect of heavy atom disorder on the intensities of powder XRD lines of YBa2Cu3O7-y

Abstract

It is shown that heavy atom disorder resulting from Y ? Ba, Ba ? Cu and Y ? Cu interchanges due to local stoichiometric constraints can cause significant changes in the intensities of X-ray powder diffraction lines of YBa₂Cu₃O_7-y . A comparison of the theoretically predicted intensities with published patterns for specimens prepared by the conventional dry route reveals that Ba ? Cu interchanges involving copper atoms in the CuO₂ planes can occur quite frequently and may be mistaken for (00l) texture.     

Influence of impurities on the low-temperature deformation of nanocrystalline copper

The influence of ZrO₂ particles on the low-temperature deformation of nanocrystalline copper produced by strong plastic deformation is investigated using equichannel angular pressing. A comparison is made between the deformation characteristics in tension and compression in the temperature range 4.2–400 K, measured for copper and the composite Cu:0.3 vol. % ZrO₂. It is shown that within 4.2–200 K the yield point σ _sm of the composite is higher than that for copper, attaining 680 MPa at 4.2 K, then the yield points are close in value up to room temperature, and diverge again as the temperature is raised. Possible causes of the dissimilar influence of an impurity on the strength and plasticity characteristics of nanocrystalline copper in various temperature intervals are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1639–1641 (September 1998)     

Cu/SiO2/Si(111)体系中Cu和Si的扩散及界面反应

室温下利用磁控溅射在p型Si(111)衬底上沉积了Cu薄膜. 利用X射线衍射和卢瑟福背散射分别对未退火以及在不同温度点退火后样品的结构进行了表征. 在此基础上，研究了Cu/SiO₂/Si(111)体系的扩散和界面反应. 实验结果表明：当退火温度高于450℃时出现明显的扩散现象，并且随着温度的升高，体系扩散现象会更加显著. 当退火温度低于450℃时没有铜硅化合物生成，当温度达到500℃时才有铜硅化合物生成. 关键词： 薄膜 扩散 界面反应 硅化物     

Density functional study of AunCu (n=1-7) clusters

The possible stable geometrical configurations and the relative stabilities of the lowest-lying isomers of copper-doped gold clusters,Au n Cu (n=1-7),are investigated using the density functional theory.Several low-lying isomers are determined.The results indicate that the ground-state Au n Cu clusters have planar structures for n=1-7.The stability trend of the Au n Cu clusters (n=1-7),shows that odd-numbered Au n Cu clusters are more stable than the neighbouring even-numbered ones,thereby indicating the Au 5 Cu clusters are magic cluster with high chemical stability.     

Ag-Au合金/SiO$lt;sub$gt;2$lt;/sub$gt;复合薄膜的制备与表征

以AgNO₃,HAuCl₄和正硅酸乙酯为主要原料,利用溶胶-凝胶法和旋涂技术,通过热处理和紫外光辐射还原得到了不同n_Ag/n_Au（1∶0,2∶1,1∶2,0∶1）的Ag-Au合金/SiO₂复合薄膜.从扫描电子显微镜和X射线衍射谱的结果可以看出得到的薄膜均匀性好,复合薄膜中合金颗粒的尺寸为10 nm左右.利用紫外-可见分光光谱仪研究了复合薄膜的光吸收性能,结果表明,随着n_Ag/n_Au的降低,吸收峰的位置也由最初的Ag纳米粒子的等离子共振吸收峰430 nm附近,逐渐红移到Au纳米粒子的等离子共振吸收峰605和880 nm附近.从光吸收谱可以看出,n_Ag∶n_Au＝2∶1和1∶2的两个样品分别在515,730 nm附近和550,730 nm附近出现表面等离子共振吸收峰.这表明Au-Ag合金固溶体的形成. 关键词： 2')" href="#">Ag-Au合金/SiO₂ 紫外辐射 光吸收性能     

XAFS investigations of copper(II) complexes with tetradentate Schiff base ligands

X‐ray absorption fine structure spectra have been investigated at the K‐edge of copper in copper(II) salen/salophen complexes: [Cu(salen)] (1), [Cu(salen)CuCl₂].H₂O (2), [Cu(salophen)] (3) and [Cu(salophen) CuCl₂].H₂O (4), where salen^2? = N,N′‐ethylenebis (salicylidenaminato); salophen^2? = o‐phenylenediaminebis(salicylidenaminato). Complexes 1 and 3 are supposed to have one type of copper centers (called (Cu1)) and complexes 2 and 4 two types of copper centers (called (Cu1) and (Cu2)) having different coordination environments and geometries. A theoretical model has been generated using the available crystallographic data of complex 1 and it has been used for analysis of the extended X‐ray absorption fine structure (EXAFS) data of the four complexes to obtain the structural parameters for (Cu1) center. For this center, the obtained Cu–Cu distance (3.2 Å) verifies the binuclear nature of all the complexes. For determining the coordination geometry around (Cu2) center in 2 and 4, a theoretical model has been generated using the crystal structure of a Cu(II) complex, [Cu(C₁₆H₁₂N₂O₂Cl₂)]. This theoretical model has been fitted to the EXAFS data of 2 and 4 to obtain the structural parameters for (Cu2) center. The present analysis shows that (Cu1) center has square pyramidal geometry involving 2N and 3O donor atoms, whereas (Cu2) center has distorted tetrahedral geometry with 2O and 2Cl donor atoms. The values of the chemical shifts and presence of typical Cu(II) X‐ray absorption near‐edge spectroscopy features suggest that copper is in the +2 oxidation state in all these complexes. The intensity of ls → 3d pre‐edge feature has been used to investigate the geometry and binuclear nature of the complexes. Copyright © 2012 John Wiley & Sons, Ltd.     

Alpha particle induced reactions on copper and tantalum

Alpha particle induced reactions in the target elements copper and tantalum were studied. The excitation functions of⁶³Cu(α, n) +⁶⁵Cu(α, 3n),⁶⁵Cu(α, 2n),¹⁸¹Ta(α, 2n) and¹⁸¹Ta(α, 4n) were measured up to 75 MeV.Eight new energy point cross-sections were measured for the first time. The experimental results were compared with the predictions of updated hybrid model (ALICE/85/300) as well as with index model using the initial exciton numbern ₀=4 (4poh) and level density parameter,a=A/8. A general agreement was found for all the reactions with both the models.     

Spin-valve magnetoresistive structures based on Co/Tb multilayer films

The effect of the layer thickness on the magnetic properties of {Co/Tb}_n, {Co/Tb}_n/Co, and {Co/Tb}_n/Co/Cu/Co multilayer films is studied. The dependence of the hysteresis and magnetoresistive properties of {Co(1 nm)/Tb(1 nm)}_n/Co(5 nm)/Cu(L _Cu)/Co(5 nm) structures on the thickness of the {Co/Tb}_n layer and copper spacing are obtained. The feasibility of spin-valve structures based on {Co/Tb}_n multilayer films with in-plane anisotropy is demonstrated.     

Ion-beam sputtering of quartz samples: Material properties observed in the mass spectra of secondary ions

Matrix effects are analyzed in the secondary ion mass spectra of quartz samples and SiO₂ and SiO _x films. The spectral relations between Si⁺, O⁺, and Si _n O _m ⁺ ions and the corresponding atomic fragments of the matrix are discussed. Previously revealed correlations between the mass spectrum and the structural features of SiO₂ and SiO _x are analyzed via the kinetic models of ion mixing.