Temperature effects on the switching kinetics of a Cu-Ta2O5-based atomic switch

Voltage-current (I-V) measurements in a wide temperature range from 88 to 573 K demonstrated the effects of temperature on the switching behavior of a Cu/Ta(2)O(5)/Pt resistive memory cell that is referred to as a gapless-type atomic switch. After the forming process, the cells were SET from the OFF state to the ON state at a positive bias to the Cu electrode and then RESET from the ON state to the OFF state at a negative bias. In a previous study (Tsuruoka et al 2010 Nanotechnology 21 425205), it was demonstrated that the SET process corresponds to the reformation of a metal filament between the electrodes by the inhomogeneous nucleation and subsequent growth of Cu whereas the RESET process can be attributed to the Joule-heating-assisted dissolution of the metal filament. In the work described here, we observed that the voltages at which the cells are SET and RESET (SET and RESET voltages) decreased in magnitude with an increase in temperature. From calculations of the nucleation rate of Cu nuclei based on the classical nucleation theory, it was found that the observed temperature variation of the SET voltage is primarily determined by supersaturation in the vicinity of the Pt electrode, which is controlled by the application of positive bias. The supersaturation required for spontaneous growth of a Cu nucleus decreases with increasing temperature, resulting in lower SET voltages at higher temperatures. The RESET voltage is determined by the thermal stability of the metal filament formed. Moreover, using the temperature variation in cell resistances of the ON state, the growth speed of the Cu nucleus after the nucleation was found to decease with increasing temperature. These results are consistent with our switching model.     

Operation kinetics of a DNA-based molecular switch

The influence of temperature variation, salt concentration, and pH on the operation kinetics of a simple DNA-based molecular switch is investigated. The device shows robust behavior over a wide range of temperatures, pH, and salt concentrations. In particular, the device operates well under physiological conditions. The experimental data can be qualitatively understood in terms of the influence temperature, salt concentration, and pH have on DNA strand interactions.     

Nonequilibrium quantum transport properties of a silver atomic switch

Combining nonequilibrium Green's function technique with density functional theory, electron transport, and structural properties of an Ag atomic switch through Ag2S have been investigated. We have found that an Ag atomic conductance channel in Ag2S is generated after structure optimization, resulting in large enhancement of the electron transmission coefficient at the Fermi level and metallic behavior of the Ag-Ag2S-Ag system. Such spontaneous metallization at the Ag-Ag2S interface may play an important role in fast switching of the Ag-Ag2S atomic switch.     

复配壳聚糖树脂对Cu2+的等温吸附及吸附动力学研究

以活性炭和壳聚糖为复配原料合成复配壳聚糖树脂,对树脂的结构进行扫描电镜和红外表征,并研究了复配壳聚糖树脂对Cu2+的等温吸附动力学特性。结果表明复配改性后的壳聚糖具有多孔结构,比表面积增大;交联反应发生在壳聚糖分子中的氨基和羟基上;复配壳聚糖树脂对Cu2+的吸附符合Langmuir和Freundlich等温吸附模型;其吸附动力学过程符合Lagergren二级动力学方程,吸附过程容易进行。     

A quantitative analysis of hydriding kinetics of magnesium in a Mg/Mg2Cu eutectic alloy

Comparing the hydriding kinetic equations of magnesium derived from a theoretical model with the experiemental data published by Kartyet al. [1], the kinetic mechanism of the hydriding reaction of magnesium in a Mg/Mg₂Cu eutectic alloy is analysed. As the eutectic structure of the alloy has the uniform interlamellar spacing of 1 Μm, one-dimensional growth of the hydride phase is assumed for the Mg₂Cu-catalysed magnesium. The concurrent hydriding reactions of the vapour-deposited pure magnesium as well as Mg₂Cu-catalysed magnesium are discussed. In both cases, the diffusion of hydrogen through the hydride phase is the rate-controlling step. Quantitative equations for the reaction and the effective particle size of pure magnesium are given, which can be used for reactor design.     

Solid-state kinetics and reaction mechanisms for the formation of Y2Cu2O5

The kinetics of Y₂Cu₂O₅ formation by the solid-state reaction between Y₂O₃ and CuO were followed by quantitative X-ray powder diffraction, the initial nucleation stages being probed by EPR spectroscopy. Analysis of fractional reaction versus time data showed a best fit to the mathematical model of Jander, with an activation energy of 58.2 kcal mol^–1. Preliminary comparative studies, employing different preparative routes; coprecipitation, accelerants and combustion synthesis are also reported.     

Reaction kinetics in the superconducting YBa2Cu3O7-x and SmBa2Cu3O7x

The compounds under investigation were prepared with nominal composition MBa₂ Cu₃ O_7-x, M being Y or Sm, through solid state reaction starting from Y₂O₃, Sm₂O₃, BaCO₃ and CuO powders. Reactions were investigated by thermo-gravimetric and differential thermal analysis in the temperature range 900–980°C. Reaction kinetics of MBa₂Cu₃O_7-x solid state synthesis were evaluated according to the mathematical relationships theoretically derived for phenomenological models. In the Y-based system the phase boundary model provides a reaction kinetics suitable to describe the process, while a three dimensional diffusion model fits the data in the Sm-based system. The influence of the mixing method on the reaction kinetics was evaluated. Microstructural features of superconducting samples were analyzed.     

Utilization of Si atomic steps for Cu nanowire fabrication

Techniques for controlling atomic step position at low-temperature and selective growth of Cu nanowires along the atomic step edges have been studied. By immersing the Si(111) substrates with well-defined step/terrace surfaces in the Cu-contained water with the dissolved oxygen content of less than 1 ppb, selective growth of Cu nanowires along the step edges was successfully achieved. Total reflection X-ray fluorescence spectroscopy (TXRF) revealed that the fabricated nanowires were composed of mono-atomic Cu rows. For step position control, the characteristics of step-flow pinning effect of SiO₂ films were investigated. Fine SiO₂ line patterns drawn by anodic oxidation using AFM probes enable us to obtain the step-free Si areas predetermined by the patterns.     

Magneto-Memristive Switching in a 2D Layer Antiferromagnet

Memristive devices whose resistance can be hysteretically switched by electric field or current are intensely pursued both for fundamental interest as well as potential applications in neuromorphic computing and phase-change memory. When the underlying material exhibits additional charge or spin order, the resistive states can be directly coupled, further allowing electrical control of the collective phases. The observation of abrupt, memristive switching of tunneling current in nanoscale junctions of ultrathin CrI₃, a natural layer antiferromagnet, is reported here. The coupling to spin order enables both tuning of the resistance hysteresis by magnetic field and electric-field switching of magnetization even in multilayer samples.     

Evaluation of interaction between histidine binding Cu2+ ion and histidine by atomic force microscopy

This paper presents a direct interaction force measurement between histidine molecules using AFM force-distance curve measurement. AFM force-distance curves between the histidine-modified cantilever and substrate in the different conditions with or without intercalating Cu2+ ion were measured and interpreted via Gaussian curve fitting analyses. The adhesion force between histidine molecules was shown to be 110 pN under the presence of Cu2+. The result was compareable to the measured adhesion force about 0 pN, which was measured by the removal of Cu2+ ion with the addition of EDTA. The result indicated the direct histidine-histidie interaction was difficult without the role of the bridigible ionic component. From the results, the possibility of direct measurement on chemical affinities between biomolecules was suggested by using AFM force-distance curve analyses. Especially, the current approach showed the possible affinity measurement techniques that elucidate the role of bridge ions.     

Switching transient analysis of a metal/ferroelectric/semiconductor switch diode with high speed response to infrared light

A thin PbTiO(3)-n-p(+) silicon switch diode has been developed, in which the switching voltage (the turned-on voltage) changes in proportion to the infrared light power. The diode has a rapid response time of 0.65 mus compared with other conventional infrared sensors. It is attributed to the rapid switching device structure and the smaller pyroelectric layer thickness, 50 nm. In this paper, we have analyzed the rapid switching transient response by using heat conduction and switching theory successfully. The experimental results are in agreement with the theoretical analysis.     

Spin-Polarized Current Switching of Co/Cu/Py Elongated Pac-Man Spin-Valve

We investigated spin-polarized current switching of elongated Pac-man (EPM) elements in a Pac-man shaped spin valve (Co/Cu/Py). The aspect ratio, pulse duration, and effect of antiferromagnetic (AFM) layer were simulated to obtain coherent switching. Pulse duration was varied on the picosecond (ps) scale and showed that ultra-fast switching could be achieved. A critical aspect ratio of 4.2 was found, where a minimum current density was observed. For antiparallel to parallel (AP-P) switching, a vortex formed during the switching process for aspect ratios less than 7. Aspect ratios of 7 or higher did not form a vortex and showed similar current densities to parallel to antiparallel (P-AP) switching as a result. It was found that the AFM layer prevented the formation of a vortex at the critical aspect ratio of 4.2 and effectively changed the switching mechanism. This allowed coherent switching with current densities for AP-P and P-AP to be only 7% from each other at the aspect ratio of 4.2.      

Resistive Switching Properties and Failure Behaviors of(Pt,Cu)/Amorphous ZrO_2/Pt Sandwich Structures

The effect of Pt and Cu electrodes on the resistive switching properties and failure behaviors of amorphous ZrO_2 ?lms were investigated. Compared with Cu/ZrO_2/Pt structures, the Pt/ZrO_2/Pt structures exhibit better resistive switching properties such as the higher resistance ratio of OFF/ON states, the longer switching cycles and narrow distribution of OFF state resistance(Roff). The switching mechanism in the Pt/ZrO_2/Pt structure can be attributed to the formation and rupture of oxygen vacancy ?laments; while in the Cu/Zr O2/Pt structure, there exist both oxygen vacancy ?laments and Cu ?laments. The formation of Cu?laments is related to the redox reaction of Cu electrode under the applied voltage. The inhomogeneous dispersive injection of Cu ions results in the dispersive Roff and signi?cant decrease of operate voltage.Schematic diagrams of the formation of conductive ?laments and the failure mechanism in the Cu/ZrO_2/Pt structures are also proposed.     

Charge-trapping characteristics of Al2O3/Cu/Al2O3 nanolaminate structures prepared through atomic layer deposition

The nanolaminate Al2O3/Cu/Al2O3 structures were constructed on p-type Si (001) substrates using atomic layer deposition (ALD) process with the aim to fabricating nonvolatile charge-trap memories. Low temperature Cu thin layers were deposited through plasma-enhanced atomic layre depositon of Cu aminoalkoxide (Cu(dmamb)2) combined with hydrogen plasma and Al2O3 layers were prepared by thermal atomic layer deposition of trimethylaluminum (TMA) combined with H2O. Nonvolatile features were confirmed using capacitance-voltage (C-V) measurements. The copper film functions as a charge-trapping layer and the Al2O3 thin layers were employed as tunneling and control oxide layers. Line shapes and binding energies of Cu metal and the thin layer of 6 nm Cu in nanolaminate structures were observed in the X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (TEM) image. The V(FB) shift width of the Al2O3 (28 nm)/Cu (6 nm)/Al2O3 (4.2 nm)/Si laminate structure is found to be 4.75 V in voltage sweeping between -10 and +10 V, leading to the trap density of 1.68 x 10(18) cm(-3).     

Biocompatibility and Cu ions release kinetics of copper-bearing titanium alloys

To reduce the risk of implant-associated infections,we previously designed and developed a series of medical copper (Cu)-bearing titanium alloys that release Cu ions and hence play an antibacterial role.However,both excessive and deficient Cu levels adversely affect human health;therefore,the aim of the present study was to comprehensively evaluate the short-and long-term biosafety of Cu-bearing titanium alloys (Ti6Al4V-Cu and Ti-Cu) both in vitro and in vivo.Moreover,the predominant kinetic mechanism of Cu ions release and its effect on biosafety were also investigated.The results indicate that the biocompat-ibility of the Cu-bearing titanium alloys meets the requirements of ISO standards and the Cu ion release kinetics display a good correlation over the entire time period in the normal zero-order model with an almost constant release rate.The release rate maintained at a parts per billion level safe for humans;consequently,we can conclude that our Cu-bearing titanium alloys have satisfactory biocompatibility.     

Grain growth kinetics in a supercooled liquid region of Zr65Cu27.5Al7.5 and Zr65Cu35 metallic glasses

The grain growth kinetics of a Zr₂Cu crystalline phase in a supercooled liquid region of Zr₆₅Cu_27.5Al_7.5 and Zr₆₅Cu₃₅ metallic glasses was examined at different temperatures. Since no significant changes in the constitution and strain in Zr₂Cu phase were seen for the annealed samples, the grain size calculated from a half value width of the X-ray diffraction peak by Scherrer's formula was used. The grain growth is controlled by a single kinetics with a thermal activation process of Arrhenius type, which is described by

Ageing of mass-selected Cu/Au and Au/Cu core/shell clusters probed with atomic resolution

Bimetallic clusters can display new characteristics that cannot be obtained by varying either the size of pure metallic systems or the composition of bulk bimetals. We have demonstrated that both copper (Cu)-rich core/gold (Au)-rich shell and Au-rich/Cu-rich shell clusters can be prepared using the radio frequency (RF) magnetron-sputtering gas phase cluster beam synthesis method with subsequent mass selection. Here we present an aberration-corrected scanning transmission electron microscopy (STEM) study of the ageing of the deposited clusters. We find that the Au-rich core/Cu-rich shell structure is unstable against both storage in vacuum and exposure to air, losing the Cu-rich shell. However, the Cu-rich core/Au-rich shell structure is found to be much more stable, even when exposed to air.