Conventional gyrotron backward-wave oscillators (gyro-BWOs) operate in a low-order mode, e.g., TE 0,1 mode. As the operating frequency extends to the terahertz (THz) band, the transverse size of low-order mode cavity shrinks, and the power capability is reduced, consequently. A solution to adopt an overmoded interaction cavity with a significantly enlarged index of the operating mode is valid on the condition that the challenging problem of mode competition can be controlled during the broadband frequency tuning. In this paper, a high-order whispering-gallery mode (WGM) THz gyro-BWO with a cathode-end output circuit is investigated. A segment-tapered circuit is applied to suppress the Q factors of competing modes and to obtain a the competition-free stable start-oscillation scenario. The theoretical result predicts that the effective frequency tuning range continuously covers between 252.3 and 260 GHz when the B-field is changed from 9.41 to 9.96 T. Our studies are beneficial to the development of high-performance sources for THz biomedical and material science applications.
Ternary solar cells have been proven to be an effective way to increase the power conversion efficiency (PCE) of organic solar cells (OSCs). Up to now, research effort has mostly focused on fullerene derivatives and acceptor–donor–acceptor (A–D–A) type non-fullerene acceptor-based ternary solar cells, while perylene diimide (PDI)-based ternary devices have been rarely studied. In this contribution, we introduced a new type of ternary solar cell based on a PDI-based small-molecule acceptor (PBI-Por) and a polymer donor (PTB7-Th) with a third PDI-based polymer acceptor (PDI-V). The introduction of PDI-V into the ternary blends not only broadens the absorption of blend films but also increases the electron mobilities. As a result, a high efficiency of 9.43% was obtained for the ternary OSC, which is 20% higher than that of the binary OSC. Detailed studies indicate that PDI-V showed good compatibility with PBI-Por in the blend films, which demonstrates a promising way to fabricate high-performance PDI-based OSCs.
Abstract 2D materials have attracted much interest over the past decade in nanoelectronics. However, it was believed that the atomically thin layered materials are not able to show memristive effect in vertically stacked structure, until the recent discovery of monolayer transition metal dichalcogenide (TMD) atomristors, overcoming the scaling limit to sub-nanometer. Herein, the nonvolatile resistance switching (NVRS) phenomenon in monolayer hexagonal boron nitride (h-BN), a typical 2D insulator, is reported. The h-BN atomristors are studied using different electrodes and structures, featuring forming-free switching in both unipolar and bipolar operations, with large on/off ratio (up to 107). Moreover, fast switching speed (\textless15 ns) is demonstrated via pulse operation. Compared with monolayer TMDs, the one-atom-thin h-BN sheet reduces the vertical scaling to ≈0.33 nm, representing a record thickness for memory materials. Simulation results based on ab-initio method reveal that substitution of metal ions into h-BN vacancies during electrical switching is a likely mechanism. The existence of NVRS in monolayer h-BN indicates fruitful interactions between defects, metal ions and interfaces, and can advance emerging applications on ultrathin flexible memory, printed electronics, neuromorphic computing, and radio frequency switches.
Three-dimensional numerical simulation is performed to study the formation mechanism and influencing factors of droplets in a microfluidic flow-focusing device (MFFD). Three types of liquid-liquid two-phase flow patterns include squeezing, dripping and jetting. Through the level-set method, the two-phase interface is tracked and the process of droplet generation is obtained. The key factors influencing droplet formation size and frequency are studied in MFFD. The results show that the formation of droplets is divided into three stages: Filling stage, Necking stage and Detachment stage, respectively. The formation of droplets is mainly that the continuous phase has flow-focusing effect on the dispersed phase. The flow rate ratio of two phases, the viscosity of the continuous phase and interfacial tension between two phases are the key factors that influence droplet size and frequency. As the flow rate ratio increases, the droplet size becomes larger and the frequency decreases. As the viscosity of the continuous phase increases, the size of the droplets becomes smaller and the frequency increases. When the two-phase interfacial tension becomes larger, the size of the droplets becomes larger and the frequency decreases.
In response to the ongoing challenges for health care and human motion monitoring, this work proposes a three-electrode multi-module sensor (TEMS) integrating proximity feedback, compression sensing and stretching perception. With the assist of the porous carbon nanotubes (CNTs)-polydimethylsiloxane (PDMS) patch in optimized parameters, the unification of the device's out-of-plane non-contact sensing and in-plane contact segmental detection is realized. Besides, coordinated with a set of symmetrically patterned Ag nanowires (NWs) electrodes with specified initial conductivity, the device is highly-sensitive to two-dimensional strains and qualified for recognizing the horizontal tension strain as small as 0.077% and the vertical pressure exerted by a piece of scrip (0.18 Pa) in fast response (millisecond level). The anti-interference ability of the signals is ensured by the PDMS encapsulation and regional stiffness of the device. Furthermore, the simplified fabrication process based on PDMS doping/modification is suitable for human skin-attachable applications, especially as the accurate differentiation of similar motions and the time-phased judgment of continuous movements through collaboration among acquisition results.