Structural and electrical analysis of In–Sb–Te‐based PCM cells

Two In–Sb–Te compounds with low Te content (12 at.% and 17 at.%), deposited by metalorganic chemical vapour deposition, were implemented into prototype phase‐change memory devices of size 50 × 50 nm² and 93 × 93 nm². These chalcogenides yielded devices with higher threshold voltage than those based on Ge–Sb–Te alloys. The endurance and programming window were markedly improved (from 10³ to 10⁶ cycles and from 1 to 2 orders of magnitude, respectively) when employing the Te‐richer alloy. Moreover, in situ structural and electrical analysis on TiN/In–Sb–Te/dielectric stacks provided additional insight on the thermal stability of the two ternary phases In₃SbTe₂ and InSb_0.8Te_0.2, which were found to coexist in these compounds. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bioinspired Nanozymes with pH‐Independent and Metal Ions‐Controllable Activity: Field‐Programmable Logic Conversion of Sole Logic Gate System

In nature, different environmental factors make organisms to be programmed into different forms. However, it is difficult and significant to realize the field‐programmable logic conversion of sole logic system for molecular logic gates. Here, the concept of pH‐programmable “logic conversion” on the single logic gate based on the peculiar enzyme‐mimicking activity is presented. Inspired by natural enzymes with high pH‐stability and metal ions‐stimulated activity, pH‐independent and metal ions‐controllable catalase mimics (Co₃O₄ nanozymes) are designed by protein‐directed method. Although pH cannot directly change the activity of nanozymes, pH can change the existence state of metal ions and then the electron transfer rate on nanozymes. So, versatile roles of metal ions for catalase‐like and electrocatalytic activities are discovered on the premise of pH‐independency. For the proof‐of‐concept, OR/INHIBIT‐ and INHIBIT/AND‐switchable logic gates are facilely constructed using pH as the environmental stimulus and metal ions as inputs. Hence, the transformation of logic gate functions is realized without the change of logic gate elements and input molecules. This contribution may not only broaden the species and application area of nanozymes, but also open novel avenues for the molecular logic conversion and the metal ions sensor.     

Quantum‐Memory‐Assisted Entropic Uncertainty Relations

Uncertainty relations take a crucial and fundamental part in the frame of quantum theory, and are bringing on many marvelous applications in the emerging field of quantum information sciences. Especially, as entropy is imposed into the uncertainty principle, entropy‐based uncertainty relations lead to a number of applications including quantum key distribution, entanglement witness, quantum steering, quantum metrology, and quantum teleportation. Herein, the history of the development of the uncertainty relations is discussed, especially focusing on the recent progress with regard to quantum‐memory‐assisted entropic uncertainty relations and dynamical characteristics of the measured uncertainty in some explicit physical systems. The aims are to help deepen the understanding of entropic uncertainty relations and prompt further explorations for versatile applications of the relations on achieving practical quantum tasks.     

Fluorination of Al2O3 blocking layer for improving the performance of metal‐oxide‐nitride‐oxide‐silicon flash memory

The characteristics of Al₂O₃ film grown by atomic‐layer deposition as blocking layer with and without fluorine plasma treatment were investigated based on a capacitor structure of Al/Al₂O₃/TaON/SiO₂/Si. The physical structure was studied by transmission electron microscopy, and the chemical composition of the blocking layer was analyzed by X‐ray photoelectron spectroscopy and secondary ion mass spectroscopy. Moreover, the surface roughness of the blocking layer was investigated by atomic force microscopy. Compared with a capacitor with Al₂O₃ blocking layer, the one with fluorinated Al₂O₃ displayed higher programming/erasing speeds, better endurance property and better charge retention characteristic because the fluorination could reduce excess oxygen and traps in the blocking layer, thus forming a larger barrier height at the interface between the charge‐trapping layer and the blocking layer. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interface‐engineered resistive memory using plasma‐modified electrode on polyimide substrate

In this study, we report a low power Ni/GeO_x /TiO_y /TaN resistive random access memory (RRAM) using plasma‐modified electrode. The low sub‐mA switching current, highly uniform switching cycles (only 4% variation for the set) and good high‐temperature current distribution at 125 °C are simultaneously achieved in this RRAM device. Such good performance can be ascribed to interface plasma treatment on TaN electrode where the resulting Ta–N ionic bond increases the oxidation resistance and reduces the oxygen vacancy concentration near TaN interface that is favorable to lower switching power and improve high‐temperature current distribution.

     

A low‐cost X‐ray‐transparent experimental cell for synchrotron‐based X‐ray microtomography studies under geological reservoir conditions

A new modular X‐ray‐transparent experimental cell enables tomographic investigations of fluid rock interaction under natural reservoir conditions (confining pressure up to 20 MPa, pore fluid pressure up to 15 MPa, temperature ranging from 296 to 473 K). The portable cell can be used at synchrotron radiation sources that deliver a minimum X‐ray flux density of 10⁹ photons mm^?2 s^?1 in the energy range 30–100 keV to acquire tomographic datasets in less than 60 s. It has been successfully used in three experiments at the bending‐magnet beamline 2BM at the Advanced Photon Source. The cell can be easily machined and assembled from off‐the‐shelf components at relatively low costs, and its modular design allows it to be adapted to a wide range of experiments and lower‐energy X‐ray sources.     

Simple square pulses for implementing spike‐timing‐dependent plasticity in phase‐change memory

Phase‐change memory (PCM) is a promising candidate as an artificial synapse. A compact operation method to implement synaptic functions with low power consumption is critical for constructing large‐scale neuromorphic system. Here we propose a square spike strategy for implementing spike‐timing‐dependent plasticity (STDP) in PCM. Based on the heat accumulation effect in PCM, modulating the time intervals of pre‐ and post‐spikes results in different heat generation and dissipation conditions, which lead to various crystalline/ amorphous ratios in the phase change material layer in devices with diverse synaptic weights. Four forms of STDP learning rule are experimentally demonstrated. This study will further promote the development of PCM technology involved in neuromorphic systems. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Self‐formed Schottky barrier induced selector‐less RRAM for cross‐point memory applications

We propose a selector‐less Pr_0.7Ca_0.3MnO₃ (PCMO) based resistive‐switching RAM (RRAM) for high‐density cross‐point memory array applications. First, we investigate the inhomogeneous barrier with an effective barrier height (Φ_eff), i.e., self‐formed Schottky barrier. In addition, a scalable 4F² selector‐less cross‐point 1 kb RRAM array has been successfully fabricated, demonstrating set, reset, and read operation for high cell efficiency and high‐density memory applications. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High speed in spin‐torque‐based magnetic memory using magnetic nanocontacts

Magnetization switching by a spin‐polarized current in perpendicular anisotropy devices with magnetic nanocontact (NC) is investigated using a micromagnetic formalism. The critical switching current (i_cr) and switching time (τ₀) can be reduced when a soft layer is exchange coupled to the NC. The study reveals that devices with fewer NCs have smaller i_cr compared to those with a large number. Furthermore, τ₀ for nanoconstricted devices is almost constant with anisotropy field (H_k), in contrast to devices without NCs that show an exponential increase with H_k. This suggests that nanoconstricted devices could be used to improve thermal stability, while reducing i_cr and τ₀. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Particle‐in‐Cell Simulations for Ion Thrusters

The Particle‐in‐Cell (PIC) method was used to study two different ion thruster concepts: Hall Effect Thrusters (HETs) and High Efficiency Multistage Plasma Thrusters (HEMPs), in particular the plasma properties in the discharge chamber due to the different magnetic field configurations. Special attention was paid to the simulation of plasma particles fluxes on the thrusters inner surfaces. In both cases PIC proved itself as a powerful tool, delivering important insight into the basic physics of the different thruster concepts.The simulations demonstrated that the new HEMP thruster concept allows for a high thermal efficiency due to both minimal energy dissipation and high acceleration efficiency. In the HEMP thruster the plasma contact to the wall is limited only to very small areas of the magnetic field cusps, which results in much smaller ion flux to the thruster channel surface as compared to HET. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fully room‐temperature‐fabricated TiN/TaOx/Pt nonvolatile memory devices

The reliable resistive switching properties of TiN/TaO_x/Pt structures fabricated with a fully room‐temperature process are demonstrated in this letter. The devices exhibited a low operation voltage of 0.6 V as well as good endurance up to 10⁵ cycles. No data loss was reported upon continuous readout for more than 10⁴ s at 125 °C. Multilevel storage is feasible due to the dependence of the low resistance state (LRS) on the initial “SET” (switch from high to low RS) compliance current. The values of LRS showed no dependence on the size of the device, which correlated with the localized conductive filament mechanism. This nonvolatile multilevel memory effect and the fully room‐temperature fabrication process make the TiN/TaO_x/Pt memory devices promising for future nonvolatile memory application. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

XOR/XNOR directed logic circuit based on coupled‐resonator‐induced transparency

The coupled‐resonator‐induced transparency (CRIT) effect in parallel‐coupled double microring resonators (MRRs) has been widely studied, and various applications based on the CRIT have been demonstrated. As an application of the CRIT, we propose and demonstrate a directed logic circuit that can implement the XOR and XNOR operations. Two electrical signals applied to the two MRRs represent the two operands of the logical operations, and the operational results are represented by the output optical signal. As a proof‐of‐concept, the thermo‐optic modulating scheme is employed with an operational speed of 10 kbps.     

In vivo physiological saline‐infused hepatic vessel imaging using a two‐crystal‐interferometer‐based phase‐contrast X‐ray technique

Using a two‐crystal‐interferometer‐based phase‐contrast X‐ray imaging system, the portal vein, capillary vessel area and hepatic vein of live rats were revealed sequentially by injecting physiological saline via the portal vein. Vessels greater than 0.06 mm in diameter were clearly shown with low levels of X‐rays (552 µGy). This suggests that in vivo vessel imaging of small animals can be performed as conventional angiography without the side effects of the presently used iodine contrast agents.