Sijian Yuan

Magnetization dependence of training effect of exchange coupling in ferromagnet/FeMn bilayers

The exchange coupling and its training effect are studied as a function of the ferromagnetic layer magnetization by using various ferromagnet/FeMn bilayers with ferromagnetic materials Ni, Ni81Fe19, Ni50Fe50, Co, and Fe. The exchange coupling energy Jex increases with increasing MFM as Jex∝MFM. The training effect of the exchange field is related to both the ferromagnet magnetization and the magnetization reversal mechanism. For ferromagnet/FeMn bilayers with similar magnetization reversal mechanisms, the relative change of the exchange field decreases with increasing magnetization in an exponential manner.

Dependence of exchange coupling in Cu/FeMn/permalloy on the Cu buffer layer thickness

A wedged-Cu(0–30 nm)/Fe50Mn50(10.0 nm)/permalloy (25.0 nm) sample was prepared by a magnetron sputtering system. The exchange field HE at room temperature increases approximately linearly with the Cu layer thickness dCu up to 30.0 nm. The blocking temperature and the room temperature coercivity increase at small dCu and saturate with further increasing dCu: Additionally, HE changes linearly with temperature at low temperatures. These phenomena are related to the changes in the microstructure of the FeMn layer, due to the variation of Cu layer thickness. This work will be helpful to technological application of spin valve magneto-resistance devices. r 2002 Published by Elsevier Science B.V.

Positive isotropic resonance field shift of exchange coupled wedged-permalloy/FeMn bilayers

Exchange-coupled wedged-permalloy/uniform-FeMn bilayers are studied by ferromagnetic resonance and magnetometry measurements with applied field parallel to the film plane. An additional weak resonance peak was observed besides an intense resonance, indicating the existence of interfacial diffusion. For all samples, the exchange field measured by the ferromagnetic resonance is close to that by magnetometry measurements. For the wedged-Py/FeMn bilayers, the in-plane isotropic resonance field shift is positive and inversely proportional to the ferromagnetic layer thickness. It is originated from either specific geometry of Py layer thickness or interfacial diffusion.

Reversible air-induced optical and electrical modulation of methylammonium lead bromide (MAPbBr3) single crystals

The photoluminescence (PL) variations of organic-inorganic hybrid lead halide perovskites in different atmospheres are well documented, while the fundamental mechanism still lacks comprehensive understandings. This study reports the reversible optical and electrical properties of methylammonium lead bromide (MAPbBr3 or CH3NH3PbBr3) single crystals caused by air infiltration. With the change in the surrounding atmosphere from air to vacuum, the PL intensity of perovskite single crystals decreases, while the conductivity increases. By means of first-principles computational studies, the shallow trap states are considered as key elements in PL and conductivity changes. These results have important implications for the characterization and application of organic-inorganic hybrid lead halide perovskites in vacuum.

Temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystal

In this paper, the temperature-dependent electronic properties of inorganic-organic hybrid halide perovskite (CH3NH3PbBr3) single crystals are investigated. The dynamic current-time measurement results at different temperatures directly demonstrate that the electrical properties of the perovskite single crystal are dependent on the work temperature. We find that the Poole-Frankel conduction mechanism fits the current-voltage curves at small bias voltage (0–1 V) under darkness, which is mainly attributed to the surface defect states. The capability of carriers de-trapping from defects varies with different work temperatures, resulting in an increased current as the temperature increases under both darkness and illumination. In addition, the different transient photocurrent responses of incident light at two wavelengths (470 nm, 550 nm) further confirm the existence of defect states on the single crystal surface.

Hydrazinium Salt as Additive To Improve Film Morphology and Carrier Lifetime for High-Efficiency Planar-Heterojunction Perovskite Solar Cells via One-Step Method

One-step solution process is the simplest method to fabricate organic-inorganic metal halide perovskite thin films, which however does not work well when employed in the planar-heterojunction (PHJ) solar cells due to the generally poor film morphology. Here we show that hydrazinium chloride can be used as an additive in the precursor solution to produce perovskite films featuring higher coverage and better crystallinity. The light absorption ability and charge carrier lifetime are both significantly improved accordingly. Under the optimal additive ratio, the average power conversion efficiency (PCE) of the inverted PHJ perovskite solar cells greatly increases by as much as 70%, and the champion device shows a satisfying PCE of 12.66%. These results suggest that N2H5Cl is a promising additive for fabricating high-efficiency perovskite solar cells via one-step method, which could be of interest in the future commercial solar cell industry.

Tunable flexible artificial synapses: a new path toward a wearable electronic system

The flexible electronics has been deemed to be a promising approach to the wearable electronic systems. However, the mismatching between the existing flexible deices and the conventional computing paradigm results an impasse in this field. In this work, a new way to access to this goal is proposed by combining flexible devices and the neuromorphic architecture together. To achieve that, a high-performance flexible artificial synapse is created based on a carefully designed and optimized memristive transistor. The device exhibits high-performance which has near-linear non-volatile resistance change under 10,000 identical pulse signals within the 515% dynamic range, and has the energy consumption as low as 45 fJ per pulse. It also displays multiple synaptic plasticity features, which demonstrates its potential for real-time online learning. Besides, the adaptability by virtue of its three-terminal structure specifically contributes its improved uniformity, repeatability, and reduced power consumption. This work offers a very viable solution for the future wearable computing.Artificial synapses: memristive transistors with mechanical and synaptic flexibilityMechanically flexible artificial synapses based on memristive transistors demonstrate different kinds of synaptic plasticity. The synapse is a fundamental component in neuromorphic computing (a brain-inspired computing approach that aims to provide more efficient computing compared to conventional approaches). Yiqiang Zhan, Lirong Zheng, and Fernando Seoane with collaborators in Sweden and China now report an artificial synapse based on a memristive transistor that is mechanically flexible. Key to the design of their synapse is a three-terminal structure, which enables gate tuning. The ability to adjust the voltage on the gate terminal enables variations in the device to be compensated thereby improving performance uniformity and repeatability. The researchers also show that gate tuning can reduce the total energy consumption per spiking event to 45 fJ and demonstrate a variety of synaptic plastic features important for replicating neuromorphic behavior.

A wide-range operating synaptic device based on organic ferroelectricity with low energy consumption

In this work, a wide-range operating synaptic device based on organic ferroelectricity has been demonstrated. The device possesses a simple two-terminal structure by using a ferroelectric phase-separated polymer blend as the active layer and gold/indium tin oxide (ITO) as the top/bottom electrodes, and exhibits a distinctive history-dependent resistive switching behavior at room temperature. And the device with low energy consumption (∼50 fJ μm−2 per synaptic event) can provide a reliable synaptic function of potentiation, depression and the complex memory behavior simulation of differential responses to diverse stimulations. In addition, using simulations, the accuracy of 32 × 32 pixel image recognition is improved from 76.21% to 85.06% in the classical model Cifar-10 with 1024 levels of the device, which is an important step towards the higher performance goal in image recognition based on memristive neuromorphic networks.

Aerosol jet printed silver nanowire transparent electrode for flexible electronic application

Aerosol jet printing technology enables fine feature deposition of electronic materials onto low-temperature, non-planar substrates without masks. In this work, silver nanowires (AgNWs) are proposed to be printed into transparent flexible electrodes using a Maskless Mesoscale Material Deposition Aerosol Jet® printing system on a glass substrate. The influence of the most significant process parameters, including printing cycles, printing speed, and nozzle size, on the performance of AgNW electrodes was systematically studied. The morphologies of printed patterns were characterized by scanning electron microscopy, and the transmittance was evaluated using an ultraviolet-visible spectrophotometer. Under optimum conditions, high transparent AgNW electrodes with a sheet resistance of 57.68 Ω/sq and a linewidth of 50.9 μm were obtained, which is an important step towards a higher performance goal for flexible electronic applications.