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Direct Imaging of Photo-Switching Molecular Conformations Using Individual Metal Atom Markers
摘要： Photo-switching behavior of individual organic molecules was imaged by annular dark-field scanning transmission electron microscopy (ADF-STEM) using a highly electron beam transparent graphene support. Photo-switching azobenzene derivatives with ligands at each ends containing single transition metal atoms (Pt) were designed (Pt-complex), and the distance between the strong ADF-STEM contrast from the two Pt atoms in each Pt-complex is used to track molecular length changes. UV irradiation was used to induce photo-switching of the Pt complex on graphene, and we show that the measured Pt-Pt distances within isolated molecules decreases from ~2.1 nm to ~1.4 nm, indicative of a trans-to-cis isomerization. Light illumination of the Pt-complex on the graphene support also caused their diffusion out from initial clusters to the surrounding area of graphene, indicating that the light-activated mobilization overcomes the inter-molecular van der Waals interactions. This approach shows how individual isolated heavy metal atoms can be included as markers into complex molecules to track their structural changes using ADF-STEM on graphene supports, providing an effective method to study a diverse range of complex organic materials at the single molecule level.
关键词： annular dark-field scanning transmission electron microscopy,photo-switch,direct imaging,graphene support,heavy atom marker,azobenzene
更新于2025-09-09 09:28:46
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A 4H-SiC BJT as a Switch for On-chip Integrated UV Photodiode
摘要： This paper presents the design, fabrication and characterization of a 4H-SiC n-p-n bipolar junction transistor as a switch controlling an on-chip integrated p-i-n photodiode. The transistor and photodiode share the same epitaxial layers and topside contacts for each terminal. By connecting the collector of the transistor and the anode of the photodiode, the photo current from the photodiode is switched off at low base voltage (cut-off region of the transistor) and switched on at high base voltage (saturation region of the transistor). The transfer voltage of the circuit decreases as the ambient temperature increases (2 mV/?C). Both the on-state and off-state current of the circuit have a positive temperature coef?cient and the on/off ratio is >80 at temperature ranged from 25 ?C to 400 ?C. It is proposed that the on/off ratio can be increased by ～1000 times by adding a light blocking layer on the transistor to reduce light induced off-state current in the circuit.
关键词： photodiode,switch,BJT,4H-SiC,UV,high temperature
更新于2025-09-08 13:48:38
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[IEEE 2018 48th European Microwave Conference (EuMC) - Madrid, Spain (2018.9.23-2018.9.27)] 2018 48th European Microwave Conference (EuMC) - Characterization of Phase Change Material Germanium Telluride for RF Switches
摘要： This paper presents the simulation and measured results of a phase-change material (PCM) based radio-frequency (RF) switch optimized to improve the ratio between OFF-state and ON-state resistivity. Various samples having germanium telluride (GeTe) films are developed and imaged using Atomic Force Microscope (AFM) and are compared with cross-wafer resistance measurement results to determine the optimum sputtering conditions of the GeTe films. A simple four-layer fabrication process for GeTe based switches is presented. Several switches with different micro-heater dimensions are compared to investigate the performance of heater and its impact on the isolation performance of switch. A compact RF series switch has been measured, demonstrating an insertion loss of only 0.29 dB and an OFF-state isolation better than 23 dB over DC–26 GHz frequency range, yielding a relatively high Roff/Ron ratio.
关键词： SPST,Latching RF Switches,Phase Change Material (PCM),RF Switch,Germanium Telluride (GeTe)
更新于2025-09-04 15:30:14
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Charge Carrier Polarity Modulation in Diketopyrrolopyrrole–Based Low Band Gap Semiconductors by Terminal Functionalization
摘要： Organic semiconductors with variable charge carrier polarity are required for optoelectronic applications. Herein, we report the synthesis of three novel diketopyrrolopyrrole (DPP) based D–A molecules having three different terminal groups (amide, ester and dicyano) and studied their electronic properties. Increase in electron acceptor strength from amide to dicyano, leads to a bathochromic shift in absorption. Photoconductivity and field–effect transistor (FET) measurements confirmed that a small increase in acceptor strength can results in a large change in the charge transport properties from p–type to n–type. The molecule with amide group, DPP–Amide, exhibited a moderate p–type mobility (1.3 × 10–2 cm2V?1s?1), whereas good n–type mobilities were observed for molecules with an ester moiety, DPP–Ester (1.5 × 10–2 cm2V?1s?1) and with a dicyano group, DPP–DCV (1 × 10–2 cm2V?1s?1). The terminal functional group modification approach presented here is a simple and efficient method to alter the charge carrier polarity of organic semiconductors.
关键词： FP-TRMC,self-assembly,p-n switch,low band gap,Diketopyrrolopyrrole
更新于2025-09-04 15:30:14
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Analysis and design of a multi-function metasurface
摘要： In this paper, based on phase gradient principle, a multi-function dual-layer reflective metasurface is proposed for linear-to-circular (LTC) polarization conversion, beam control and gain improvement. The rotation of reflected circularly polarized wave is switched by the electric field direction of incident linearly polarized waves. At the same time, the reflective circularly polarized wave emerges anomalous refraction (45.6°). The maximum gain of the reflected wave is increased by 3.6dB (70%). The measured results and simulation results are in a reasonable agreement. The presented multi-function metasurface may offer unprecedented potentials for real-time, fast polarization conversion and beam control.
关键词： switch,phase gradient,metasurface,anomalous reflection
更新于2025-09-04 15:30:14
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The reliability of solar energy generating system with inverters in series under common cause failure
摘要： With the shortage of nonrenewable energy, renewable energy resources play an important role in practice. One of the most promising renewable energy is viewed as solar energy resources due to its cleanliness and the inexhaustibility. However, the quantitative assessment method on the reliability of a complicated solar energy generating system has been a considerable challenge. In this paper, we propose a Markov model to imitate a solar energy generating system with inverters in series, unreliable by-pass change-over switches, and common cause failure. Employing the renewal point technique and the Semi-Markov process theory, we build the quantitative reliability models of the system. Further, we develop a new algorithm to obtain the explicit form solution of reliability indices. An example illustrates that the proposed models and the algorithm are e?cient and concise.
关键词： Common cause failure,Switch failure,Micro-inverters,Reliability,Solar energy generating system
更新于2025-09-04 15:30:14
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Synthesis Technique for Low-Loss mm-Wave T/R Combiners for TDD Front-Ends
摘要： A time-division duplex (TDD) transmit/receive (T/R) millimeter-wave (mm-wave) front-end comprises a power amplifier (PA), a low-noise amplifier (LNA), an antenna switch, and appropriate passive matching and combining networks. In this paper, a synthesis methodology is proposed that minimizes the overall losses by combining the PA output and the LNA input matching networks together with the T/R switch into one network. The technique improves mm-wave transceiver performance in terms of PA efficiency and LNA noise figure. The proposed T/R combiner can achieve high linearity and can handle large PA output voltage swings. The architecture can be implemented in any process which provides high integration capability. A Ka-band implementation is demonstrated using 45 nm CMOS silicon-on-insulator that includes a high power, four-stack-based PA and an inductively source-degenerated cascode-based LNA. Within the front-end, the PA achieves saturated output power of 23.6 dBm with peak power added efficiency of 28%, while the LNA achieves NF of 3.2 dB. The overall chip area is 0.54 mm2, including pads.
关键词： transmit/receive (T/R) switch,low-noise amplifier (LNA),power amplifier (PA),5G transmitters,stacked power amplifier,silicon-on-insulator (SOI),time-division duplex (TDD),CMOS,millimeter-wave (mm-wave),Ka-band
更新于2025-09-04 15:30:14
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A new method of accurately measuring photoconductive performance of 4H-SiC photoconductive switches
摘要： A new method of accurately measuring the photoconductive performance of photoconductive semiconductor switch (PCSS) was proposed. By this method, we succeeded extracting the photoconductivity of 4H-SiC substrate free from the obstruction of parasitic inductance in the test circuit. Photoconductive performance of the PCSS were precisely measured, where a maximum on-state photoconductivity of 6.26 (Ω · m)?1, a minimum on-state resistivity of 0.16 Ω · m and an accurate minimum resistance of 1.71 Ω were obtained for SiC substrate. The quantitative relationship between the on-state resistance and the reciprocal of area of laser trigger region was proved. The performance of PCSSs can be continuously adjusted to adapt different application requirements just by changing the area of laser excitation region.
关键词： pulse-power system switches,silicon carbide,Photoconductive switch,on-state resistance,intrinsic photoconductivity
更新于2025-09-04 15:30:14
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Target-switched triplex nanotweezer and synergic fluorophore translocation for highly selective melamine assay
摘要： This paper describes a triplex DNA nanotweezer to specifically capture melamine (MEL). The triplex-forming oligonucleotide (TFO) arm can be switched from the open state to the closed state once MEL binds to the abasic site (AP site) in duplex via the bifacial hydrogen bonding with thymines. Following this nanotweezer operation, the AP site-bound fluorophore is translocated to the terminal triplet to subsequently light up the nanotweezer. The TFO arm is found to be pivotal for permitting the AP site binding. The synergic processes of target competition and fluorophore translocation support a high selectivity for the MEL assay even against the inherent adenosine and the MEL hydrolysis products. Chelerythrine is employed as the fluorescent probe. The detection limit of MEL was estimated to be about 140 nM assuming a signal-to-noise ratio of 3. It was applied to the determination of MEL in spiked milk samples without any separation procedure. Conceivably, this method opens a new avenue towards highly selective triplex-based sensors by making use of other commercially available DNA modifications for recognizing other analytes.
关键词： Milk,Chelerythrine,Switch,Fluorescence,Hydrogen bonding,DNA,Fluorometry,Abasic site
更新于2025-09-04 15:30:14