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The growth of integrated photonics has driven the need for efficient, high-bandwidth electrical-to-optical (EO) signal conversion over a broad range of frequencies (MHz–THz), together with efficient, high bandwidth photodetection. Efficient signal conversion is needed for applications including fiber/wireless telecom, data centers, sensing/imaging, metrology/spectroscopy, autonomous vehicle platforms, etc., as well as cryogenic supercomputing/quantum computing. Diverse applications require the ability to function over a wide range of environmental conditions (e.g., temperatures from <4 to >400 K). Active photonic device footprints are being scaled toward nanoscopic dimensions for size compatibility with electronic elements. Nanophotonic devices increase optical and RF field confinement via small feature sizes, increasing field intensities by many orders of magnitude, enabling high-performance Pockels effect materials to be ultimately utilized to their maximum potential (e.g., in-device voltage-length performance ≤0.005 V mm). Organic materials have recently exhibited significant improvements in performance driven by theory-guided design, with realized macroscopic electro-optic activity (r33) exceeding 1000 pm/V at telecom wavelengths. Hybrid organic/semiconductor nanophotonic integration has propelled the development of new organic synthesis, processing, and design methodologies to capture this high performance and has improved understanding of the spatial distribution of the order of poled materials under confinement and the effects of metal/semiconductor-organic interfaces on device performance. Covalent coupling, whether from in situ crosslinking or sequential synthesis, also provides a thermally and photochemically stable alternative to thermoplastic EO polymers. The alternative processing techniques will reduce the attenuation of r33 values observed in silicon organic hybrid and plasmonic organic hybrid devices arising from chromophore-electrode electrostatic interactions and material conductance at poling temperatures. The focus of this perspective is on materials, with an emphasis on the need to consider the interrelationship between hybrid device architectures and materials. [ABSTRACT FROM AUTHOR]

Atomic-level prediction combined with machine learning (ML) and density functional theory (DFT) is carried out to accelerate the fast discovery of potential photovoltaics from the 2D perovskites. Based on the ML prediction, stability test, optical absorption, and the theoretical power conversion efficiency (PCE) evaluation, two promising photovoltaics, i.e., Sr2VON3 and Ba2VON3, are discovered with PCE as high as 30.35% and 26.03%, respectively. Cu, Ag, C, N, H, and He ion implantation are adopted to improve the photovoltaic performance of the high-efficiency and best stable perovskite Sr2VON3. The time-dependent DFT electronic stopping calculations for energetic ion implanted Sr2VON3 indicate that the excited electrons from the valence band contribute to the electron–phonon coupling, the evolution and formation of the defects, and the photovoltaic performance. This work opens the way to the high-accuracy fast discovery of the high-efficiency and environmentally stable 2D perovskites solar cells and the further engineering improvement in photovoltaic performance by ion implantation. [ABSTRACT FROM AUTHOR]

Memristive-based electro-optical neuromorphic hardware takes advantage of both the high-density of electronic circuits and the high bandwidth of their photonic counterparts, thus showing potential for low-power artificial intelligence applications. In this Perspective paper, we introduce a class of electro-optical memristors that can emulate the key properties of synapses and neurons, which are essential features for the realization of electro-optical neuromorphic functionalities. We then describe the challenges associated with existing technologies and finally give our viewpoint on possible developments toward an energy-efficient neuromorphic platform. [ABSTRACT FROM AUTHOR]

The nanosize confined effect is believed to contribute to improving the resistance drift in nanophase change devices. However, the smaller dimension of device designs is limited by plane lithography techniques. Phase change memory with a confined thickness of ultrathin GeTe layers is fabricated to overcome the limit of current plane lithography. Those memory cells composed of two-dimensional materials present a suppressed resistance drift in their amorphous phase. The drift exponent ν is reduced to 0.05 for 3 nm GeTe layers. Combined with Raman spectroscopy and ab initio molecular dynamics simulations, the structural relaxation process is described as the decay of tetrahedral-bonded sites. Tetrahedrons in ultrathin films are more stable than those in bulk materials. The local motifs of amorphous GeTe ultrathin films are covalently bonded and highly ordered in a short range. The majority of highly ordered tetrahedral clusters prevents spontaneous structural relaxation and leads to high stability in amorphous states, which helps to stop intrinsic fluctuations in physical properties of SET and RESET states, without an extra processing cost. [ABSTRACT FROM AUTHOR]

(001)-epitaxial (Ba0.5Sr0.5)TiO3 (BST) thin films with different magnitudes of compressive strain were fabricated on SrRuO3/SrTiO3 substrates by pulsed laser deposition, and their electro-optic (EO) properties were characterized by modulation ellipsometry at different temperatures. All fabricated films showed an increased paraelectric-to-ferroelectric phase transition temperature upon compressive strain and revealed c-domain structures in the ferroelectric phase. We experimentally clarified that the EO properties of compressively strained BST thin films are enhanced toward the phase transition temperature modified by the strain. The experimental results were compared with the theoretical prediction based on a phenomenological thermodynamic model. Although the measured EO coefficient r c was less than that theoretically predicted, the experimentally observed strain effect on the EO properties is in good qualitative agreement. [ABSTRACT FROM AUTHOR]

Laser communication is a promising way of achieving effective communication during reentry. This paper focuses on the phase characteristics and information transmission of laser signals in plasma sheaths. First, propagation of the laser signals through the sheaths is analyzed theoretically. Next, phase characteristics of the periodic laser signals are studied by ground simulation experiments in shock tube. Further, experiments of the pseudorandom amplitude and phase modulated signals are conducted. Finally, information transmission is tested. This paper is the basic research of laser transmission characteristics in plasma sheaths and has experimentally realized successful information transmission in the plasma generated by shock tube. The results could provide reference for the future ground and flight experiments. [ABSTRACT FROM AUTHOR]

InGaN/GaN multi-quantum-well blue (461±4 nm) light emitting diodes with higher electroluminescence intensity are obtained by postgrowth thermal annealing at 720 °C in O2-ambient. Based on our first-principle total-energy calculations, we conclude that besides dissociating the Mg–H complex by forming H2O, annealing in O2 has another positive effect on the activation of acceptor Mg in GaN. Mg can be further activated by the formation of an impurity band above the valence band maximum of host GaN from the passivated MgGa–ON complex. Our calculated ionization energy for acceptor Mg in the passivated system is about 30 meV shallower than that in pure GaN, in good agreement with previous experimental measurement. Our model can explain that the enhanced electroluminescence intensity of InGaN/GaN MQWs based on Mg-doped p-type GaN is due to a decrease in the ionization energy of Mg acceptor with the presence of oxygen. [ABSTRACT FROM AUTHOR]

InGaN/GaN multi-quantum-well blue (461±4 nm) light emitting diodes with higher electroluminescence intensity are obtained by postgrowth thermal annealing at 720 °C in O2-ambient. Based on our first-principle total-energy calculations, we conclude that besides dissociating the Mg–H complex by forming H2O, annealing in O2 has another positive effect on the activation of acceptor Mg in GaN. Mg can be further activated by the formation of an impurity band above the valence band maximum of host GaN from the passivated MgGa–ON complex. Our calculated ionization energy for acceptor Mg in the passivated system is about 30 meV shallower than that in pure GaN, in good agreement with previous experimental measurement. Our model can explain that the enhanced electroluminescence intensity of InGaN/GaN MQWs based on Mg-doped p-type GaN is due to a decrease in the ionization energy of Mg acceptor with the presence of oxygen. [ABSTRACT FROM AUTHOR]

We show in this paper single-shot and multi-shot laser-induced damage thresholds (LIDTs) of HfO2/SiO2 high reflective films (the reflectance = 99.9%) are affected by the presence of a water layer absorbed on the surface of the porous films. When the water layer was removed with the process of pumping, the single-shot LIDT measured in vacuum dropped to ∼48% of that measured in air, while the multi-shot LIDT in vacuum dropped to ∼47% of its atmospheric value for the high reflective films. Typical damage micrographs of the films in air and in vacuum were obtained, showing distinct damage morphologies. Such atmosphere dependence of the laser damage morphology was found to originate from that formation of a water layer on the surface of porous films could cause an increase of horizontal thermal conductivity and a reduction of vertical thermal conductivity. Moreover, laser-induced periodic ripple damages in air were found in the SiO2 layer from the micrographs. A model of deformation kinematics was used to illustrate the occurrence of the periodic ripple damage, showing that it could be attributed to a contraction of the HfO2 layer under irradiation by the 5-ns laser pulses in air. [ABSTRACT FROM AUTHOR]

A comprehensive analysis on the chaos of a high-dimensional wind power system is performed in this study. A high-dimensional wind power system is more complex than most power systems. An 11-dimensional wind power system proposed by Huang, which has not been analyzed in previous studies, is investigated. When the systems are affected by external disturbances including single parameter and periodic disturbance, or its parameters changed, chaotic dynamics of the wind power system is analyzed and chaotic parameters ranges are obtained. Chaos existence is confirmed by calculation and analysis of all state variables' Lyapunov exponents and the state variable sequence diagram. Theoretical analysis and numerical simulations show that the wind power system chaos will occur when parameter variations and external disturbances change to a certain degree. [ABSTRACT FROM AUTHOR]

Green InGaN/GaN multiple quantum wells light-emitting diodes with graded superlattice (GSL) AlGaN/GaN inserting layer are investigated numerically and experimentally. Our simulation results indicate that GSL inserting layer can decrease the effective barrier height of holes by 57 meV, which makes holes more easily inject into the quantum wells. The piezoelectric polarization field near the last barrier is suppressed effectively by introducing of the GSL inserting layer. As a result, the efficiency droop radio is improved from 35.8% to 19.4% at current density of 100 A/cm-2. [ABSTRACT FROM AUTHOR]

We report a novel coherent excitation phenomenon in a heterogeneous network of coupled FitzHugh-Nagumo elements. It is demonstrated that dynamical rewiring in the network can play a constructive role to bring on coherent excitations. The coherence factor as the function of rewiring time interval represents a nontrivial phenomenon which is a fingerprint of coherence resonance. We call this resonant behavior caused by dynamical wiring changes the network-rewiring-induced coherence resonance. The mechanism can be understood by the effective noise played by the rewiring process.

Estimating the focal size and position of a high-intensity focused ultrasound (HIFU) transducer remains a challenge since traditional methods, such as hydrophone scanning or schlieren imaging, cannot tolerate high pressures, are directional, or provide low resolution. The difficulties increase when dealing with the complex beam pattern of a multielement HIFU transducer array, e.g., two transducers facing each other. In the present study we show a novel approach to the visualization of the HIFU focus by using shockwave-generated bubbles and a diagnostic B-mode scanner. Bubbles were generated and pushed by shock waves toward the HIFU beam, and were trapped in its pressure valleys. These trapped bubbles moved along the pressure valleys and thereby delineated the shape and size of the HIFU beam. The main and sidelobes of 1.1- and 3.5 MHz HIFU beams were clearly visible, and could be measured with a millimeter resolution. The combined foci could also be visualized by observing the generation of sustained inertial cavitation and enhanced scattering. The results of this study further demonstrate the possibility of reducing the inertial cavitation threshold by the local introduction of shock wave-generated bubbles, which might be useful when bubble generation and cavitation-related bioeffects are intended within a small region in vivo.