Xiangyu Li

Interlayer magnetostatic coupling and linear magnetoresistance in [Pd/Co]/MgO/Co junction sensor

We investigate interlayer magnetostatic coupling and linear magnetoresistance in [Pd/Co]/MgO/Co and [Pd/Co]/MgO/Co/MgO/[Co/Pd] tunnel junctions, where Co/Pd and Co ferromagnetic layers exhibit out-of-plane and in-plane magnetic anisotropy, respectively. Because of the magnetostatic interaction between Co moments and the stray field from Co/Pd stripe domains, the Co layer shows a significant enhancement of coercivity and exchange bias. Linear magnetoresistance is observed in both junctions in the field up to 15 kOe with the current perpendicular to the film plane, due to coherent rotation of the ferromagnets, making junctions with MgO barrier and orthogonal magnetization configuration a promising high magnetic field sensor.

Simulation of synaptic short-term plasticity using Ba(CF3SO3)2-doped polyethylene oxide electrolyte film.

The simulation of synaptic plasticity using new materials is critical in the study of brain-inspired computing. Devices composed of Ba(CF3SO3)2-doped polyethylene oxide (PEO) electrolyte film were fabricated and with pulse responses found to resemble the synaptic short-term plasticity (STP) of both short-term depression (STD) and short-term facilitation (STF) synapses. The values of the charge and discharge peaks of the pulse responses did not vary with input number when the pulse frequency was sufficiently low(~1u2009Hz). However, when the frequency was increased, the charge and discharge peaks decreased and increased, respectively, in gradual trends and approached stable values with respect to the input number. These stable values varied with the input frequency, which resulted in the depressed and potentiated weight modifications of the charge and discharge peaks, respectively. These electrical properties simulated the high and low band-pass filtering effects of STD and STF, respectively. The simulations were consistent with biological results and the corresponding biological parameters were successfully extracted. The study verified the feasibility of using organic electrolytes to mimic STP.

Thermo‐Driven Controllable Emulsion Separation by a Polymer‐Decorated Membrane with Switchable Wettability

A thermoresponsive Poly(N-isopropylacrylamide) (PNIPAAm)-modified nylon membrane was fabricated via hydrothermal route. Combining rough structure, proper pore size, and thermoresponsive wettability, the membrane can separate at least 16 types of stabilized oil-in-water and water-in-oil emulsions at different temperatures. Below the LCST (ca. 25u2009°C), the material exhibits hydrophilicity and underwater superoleophobicity, which can be used for the separation of various kinds of oil-in-water emulsions. Above the LCST (ca. 45u2009°C), the membrane shows the opposite property with high hydrophobicity and superoleophilicity, and it can then separate stabilized water-in-oil emulsions. The material exhibits excellent recyclability and high separation efficiency for various kinds of emulsions and the hydrothermal method is facile and low-cost. The membrane shows good potential in real situations such as on-demand oil-spill cleanup, industrial wastewater treatment, remote operation of oil/water emulsion separation units, and fuel purification.

Effect of heavy-ion on frequency selectivity of semiconducting polymer/electrolyte heterojunction

Heavy ion Nd3+ is introduced into the electrolyte layer to study frequency selectivity of a semiconducting polymer/electrolyte double-layer cell. This cell exhibits long-term depression under low-frequency stimulations and potentiation under high-frequency stimulations by positive triangular pulses, suggesting a conventional learning protocol, i.e., spike-rate-dependent plasticity. The frequency selectivity depends significantly on the input shape due to large ionic size and mass. The input threshold of the frequency selectivity is around the voltage inducing a negative differential resistance (VNDR) influenced by the loading rate. The typical value of VNDR is 0.3 V for a loading rate of 100 V s−1, but VNDR disappears when the loading rate exceeds 1000 V s−1. Besides, the frequency selectivity has not been observed under rectangular pulse input. Moreover, the possibility of bidirectional signal transfer has been tested simply by anti-connecting two individual cells. Our study suggests the possibility to realize signal pruning and synthetizing by changing ionic types.

A smart nano-V2O5/ODA-coated mesh for a co-responsive photo-induced wettability transition and ROS generation for in situ water purification

A co-responsive material is successfully fabricated by coating nano-vanadium pentoxide/octadecylamine (nano-V2O5/ODA) onto a copper mesh via a hydrothermal reaction. “Co-response” means that a material can realize a multi-performance transition under one environmental stimulus. Nano-V2O5 provides the material with a photo-induced wettability transition and reactive oxygen species (ROS) generation properties, while ODA produces a superhydrophobic material in its initial state. As a result, this material can achieve a reversible superhydrophobic/superhydrophilic transition under 254 nm ultraviolet (UV) light. By combining the wettability transition with ROS generation properties, a smart mesh can realize in situ photo-controlled water purification, i.e., the controllable and simultaneous removal of the oil and soluble contaminants. An extra V2O5-coated mesh is used as an auxiliary mesh to improve the oil removal and ROS generation efficiencies. Moreover, the mesh exhibits satisfactory reusability and physical/chemical stability, which is more promising for practical applications such as remote controlled water purification, timed discharge of sewage and microfluidic valves.

Influence of ionic size to the pulse responses of semiconducting polymer/electrolyte hetero-junctions

Pt/Poly[2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV)/polyethylene oxide (PEO) + Alkali ions/Ag devices were fabricated. Microstructure analysis indicated that Cs and K ions were doped initially into the semiconducting polymer after fabrication, which suggests resemblance to the resting state of bio-synapse. The pulse responses of Cs-doped device potentiated monotonically with increased frequency. K-doped device had a threshold frequency at about 60 Hz, and it responded in potentiation at frequency higher than this threshold. The special filtering effects should relate to the ionic states in nanoscale in both semiconducting polymer and electrolyte. Thus, these two types of device could be used in signal computing.