Bioinspired interactive neuromorphic devices

The performance of conventional computer based on von Neumann architecture is limited due to the physical separation of memory and processor. By synergistically integrating various sensors with synaptic devices, recently emerging interactive neuromorphic devices can directly sense/store/process various stimuli information from external environments and implement functions of perception, learning, memory, and computation. In this review, we present the basic model of bioinspired interactive neuromorphic devices and discuss the performance metrics. Next, we summarize the recent progress and development of bioinspired interactive neuromorphic devices, which are classified into neuromorphic tactile systems, visual systems, auditory systems, and multisensory system. They are discussed in detail from the aspects of materials, device architectures, operating mechanisms, synaptic plasticity, and potential applications. Additionally, the bioinspired interactive neuromorphic devices that can fuse multiple/mixed sensing signals are proposed to address more realistic and sophisticated problems. Finally, we discuss the pros and cons regarding to the computing neurons and integrating sensory neurons and deliver the perspectives on interactive neuromorphic devices at the material, device, network, and system levels. It is believed the neuromorphic devices can provide promising solutions to next generation of interactive sensation/memory/computation toward the development of multimodal, low-power, and large-scale intelligent systems endowed with neuromorphic features.     

Multi-band circuit model of tunable THz absorber based on graphene sheet and ribbons

Terahertz (THz) absorbers due to the high potential of providing reliable applications in modern devices and technology are increasingly being investigated. Recently, a dual-band THz absorber based on a graphene sheet and ribbons has been proposed in which the results were obtained using Full-wave simulations and its authors have not provided any specific design method. In this work, we have proposed and investigated that tunable THz absorber by its circuit model. A developed transmission line method beside the analytical circuit model of graphene continues sheet and periodic arrays of graphene ribbons are used to obtain analytical expressions for the circuit model. Here, first of all, we have compared the results of the proposed method with the results of that paper and secondly, using impedance matching concept we have proposed multi-band tunable THz absorber with near-unity absorption by the same structure. Then, we have compared the results of our circuit method with the Full-wave simulations. In either case, our proposed method in addition to excellent performance in terms of runtime and memory sources, has an acceptable agreement with the results of the Full-wave simulations. The proposed method is general and can be applied to design and simulate the other sub-wavelength structures.     

PAPR reduction in CO-OFDM systems using IPTS and modified clipping and filtering

Aiming at the problem of the peak to average power ratio (PAPR) in coherent optical orthogonal frequency division multiplexing (CO-OFDM), a hybrid PAPR reduction technique of the CO-OFDM system by combining iterative partial transmit sequence (IPTS) scheme with modified clipping and filtering (MCF) is proposed. The simulation results show that at the complementary cumulative distribution function (CCDF) of 10^-4, the PAPR of proposed scheme is optimized by 1.86 dB and 2.13 dB compared with those of IPTS and CF schemes, respectively. Meanwhile, when the bit error rate (BER) is 10^-3, the optical signal to noise ratio (OSNR) are optimized by 1.57 dB and 0.66 dB compared with those of CF and IPTS-CF schemes, respectively.     

An optical modulation format generation scheme based on spectral filtering and frequency-to-time mapping

An optical modulation format generation scheme based on spectral filtering and frequency-to-time mapping is experimentally demonstrated. Many modulation formats with continuously adjustable duty radio and bit rate can be formed by changing the dispersion of dispersion element and the bandwidth of shaped spectrum in this scheme. In the experiment, non-return-to-zero (NRZ) signal with bit rate of 29.41 Gbit/s and 1/2 duty ratio return-to-zero (RZ) signal with bit rate of 13.51 Gbit/s are obtained. The maximum bit rate of modulation format signal is also analyzed.     

Optimization of the annealing process and nanoscale piezoelectric properties of (002) AlN thin films

In this paper, the effects of different annealing processes on the texture, surface morphology, and piezoelectric properties of aluminum nitride (AlN) thin films and the performance of AlN-based surface acoustic wave (SAW) devices were systematically investigated. Based on the crystallinity and the morphology results, it is evident that in-situ annealing method is superior to ex-situ annealing. For the AlN thin films, the crystallization and piezoelectricity were both enhanced and then receded as the annealing temperature increased from 300 to 600?°C. We demonstrated that good (002) orientation, excellent grain distribution and high relative piezoelectric coefficient of the AlN thin films were achieved via in-situ annealing at 500?°C. Meanwhile, the AlN thin films exhibited excellent polarization properties and polarization maintaining characteristics. Additionally, the uniform interdigital transducer (IDT) with 8 μm period (finger width?=?2 μm) were designed and the IDT/AlN/SiO₂/Si SAW devices with the center frequency f ₀ of 495 MHz and insert loss of ?24.1 dB were fabricated.     

Cooperative Catalysis toward Oxygen Reduction Reaction under Dual Coordination Environments on Intrinsic AMnO3-Type Perovskites via Regulating Stacking Configurations of Coordination Units

It remains challenging for pure-phase catalysts to achieve high performance during the electrochemical oxygen reduction reaction to overcome the sluggish kinetics without the assistance of extrinsic conditions. Herein, a series of pristine perovskites, i.e., AMnO₃ (A = Ca, Sr, and Ba), are proposed with various octahedron stacking configurations to demonstrate the cooperative catalysis over SrMnO₃ jointly explored by experiments and first-principles calculations. Comparing with the unitary stacking of coordination units in CaMnO₃ or BaMnO₃, the intrinsic SrMnO₃ with a mixture of corner-sharing and face-sharing octahedron stacking configurations demonstrates superior activity (E_half-wave = 0.81 V), and charge–discharge stability over 400 h without the voltage gap (≈0.8 V) increasing in zinc–air batteries. The theoretical study reveals that, on the SrMnO₃(110) surface, the active sites switch from coordinatively unsaturated atop Mn (*OO, *OOH) to Mn–Mn bridge (*O, *OH). Therefore, the intrinsic dual coordination environments of Mn–O_corner and Mn–O_face enable cooperative modulation of the interaction strength of the oxygen intermediates with the surface, inducing the decrease of the *OH desorption energy (rate-limiting step) unrestricted by scaling relationships with the overpotential of ≈0.28 V. This finding provides insights into catalyst design through screening intrinsic structures with multiple coordination unit stacking configurations.     

Unrevealing Temporal Mechanoluminescence Behaviors at High Frequency via Piezoelectric Actuation

Mechanoluminescence (ML) materials present widespread applications. Empirically, modulation for a given ML material is achieved by application of programmed mechanical actuation with different amplitude, repetition velocity and frequency. However, to date modulation on the ML is very limited within several to a few hundred hertz low-frequency actuation range, due to the paucity of high-frequency mechanical excitation apparatus. The universality of temporal behavior and frequency response is an important aspect of ML phenomena, and serves as the impetus for much of its applications. Here, we push the study on ML into high-frequency range (∼250 kHz) by combining with piezoelectric actuators. Two representative ML ZnS:Mn and ZnS:Cu, Al phosphors were chosen as the research objects. Time-resolved ML of ZnS:Mn and ZnS:Cu, Al shows unrevealed frequency-dependent saturation and quenching, which is associated with the dynamic processes of traps. From the point of applications, this study sets the cut-off frequency for ML sensing. Moreover, by in-situ tuning the strain frequency, ZnS:Mn exhibits reversible frequency-induced broad red-shift into near-infrared range. These findings offer keen insight into the photophysics nature of ML and also broaden the physical modulation of ML by locally adjusting the excitation frequency.     

WXAMPS theoretical study of the bandgap structure of CZTS thin film to improve the device performance

The carrier recombination was one of the factors limiting the further improvement of the Cu2ZnSnS4 (CZTS) thin film solar cells. In this paper, a proper bandgap structure was designed to solve this problem. The effects of the different bandgap structure on the CZTS thin film solar cells were studied by the solar cell performance simulation software wxAMPS. A graded bandgap structure was designed and optimized. The bandgap with a front bandgap gradient and a flat bandgap gradient had a favorable effect on the CZTS thin film solar cells. Finally, the fill factor (FF) and conversion efficiency (η) of the CZTS thin film solar cell were increased from 36.41% to 42.73% and from 6.85% to 10.03%, respectively. In addition, the effect of donor and acceptor defect densities in CZTS absorber layer near the CdS/CZTS interface on the device performance was studied, η of the CZTS thin film solar cell was increased from 5.99% to 7.55% when the acceptor defect concentration was 1012—1013 cm-3. Moreover, the thicknesses of the CZTS absorber layer were optimized. The FF and η of the CZTS thin film solar cell were increased to 63.41% and 15.04%, respectively.     

Multi-pulse operation in an actively Q-switched Er-doped fiber laser based on electro-optic modulator

In this paper, we report an experimental observation of different states of multi-pulse operation in an actively Q-switched Er-doped fiber laser, which has applications in pulse coding in optical communications. The Q factor is switched by an electro-optic modulator. Completely separated multiple pulses are obtained due to the short response time of the modulator. The influence of pump power and modulation frequency on output pulse state is investigated. In the experiment, the repetition rate of Q-switched pulse is not always consistent with the modulation signal. Single-pulse, single-dual-pulse, dual-pulse, dual-triple pulse, and multiple pulses are observed in one modulation period by increasing pump power. Single-pulse is also observed in two or three modulation periods by increasing the frequency of modulation signal. In addition, the waveform of modulating signal and the polarization state of modulated signal also affect the multi-pulse operation accordingly.     

Blue and red light photoluminescence emission at room temperature from CaTiO3 decorated with α-Ag2WO4

CaTiO₃ (CT) and α-Ag₂WO₄ (AW) semiconductors are widely known for their interesting electrical and photoluminescence (PL) properties. In this study, we decorated CT with AW for obtaining CaTiO₃:α-Ag₂WO₄ (CT:AW), and investigated the properties of the produced materials, especially their PL properties. The X-ray diffraction peaks of the synthesized microcrystals were well indexed to the orthorhombic phase for all the samples. Two morphologies: cube-like for CT and rod-like for AW were observed by field-emission scanning electron microscopy (FE-SEM). The FE-SEM and transmission electron microscopy (TEM) studies indicated the presence of rod-shaped AW deposited on the surfaces of cube-shaped CT morphology. PL emission of the decorated samples overlaps all the visible region spectra because of the contribution from both the constituent materials that induce maximum emissions in the blue and red regions. The examination of Commission internationale de ĺéclairage (CIE) coordinates confirmed that the decorated samples exhibit favored emission the red wavelength region.