Highlights
Abstract +
The experimental study of precision spectroscopy of dielectronic recombination (DR) of highly charged ions is not only important for astronomical plasma and fusion plasma, but also can be used as a new precision spectroscopy to test the strong-field quantum electrodynamic effect, measure isotope shift, and extract the radius of atomic nuclei. An specially designed electron beam energy detuning system for electron-ion recombination precision spectroscopy experiments has been installed on the heavy ion storage ring CSRe in Lanzhou, China, where the electron-ion collision energy in the center-of-mass system can be detuned to 1 keV, and an independently-developed plastic scintillator detector and multiwire proportional chamber detector have been installed downstream of the electron cooler of the CSRe for detecting recombined ions. The multiwire proportional chamber detector has the ability to non-destructively monitor the profile of the ion beam in real-time while acquiring the recombined ion counts, providing guidance for optimizing the ion beam. On this basis, the first test experiment on dielectronic recombination of Kr25+ ions is carried out at the CSRe, and the dielectronic recombination rate coefficients in a range of 0–70 eV in the frame of center-of-mass are measured. In order to fully understand the experimental results, we calculate the dielectronic recombination rate coefficient of the Kr25+ ion by using the flexible atomic code (FAC) and make a detailed comparison with the experimental result, showing that they are in good agreement with each other, and only the resonance energy values of the two resonance peaks at 1.695 eV and 2.573 eV are significantly different. In addition, the DR resonance energy values and intensities are obtained by fitting the experimental results in a range of 0–35 eV, and we find that the transition 3s→4l (∆n = 1) contributes significantly to the experimental spectral lines. Furthermore, we compare the plasma rate coefficients derived from the DR rate coefficients with those derived from the AUTOSTRUCTURE and FAC theories, which differ by 20 percent in a temperature range less than 106 K. The experimental results show that the DR experimental platform of the CSRe has very good stability and reproducibility, and can provide support for the future DR experiments of highly charged ion, i.e. for testing strong-field quantum electrodynamics effect and measuring the properties of atomic nuclei.
EDITOR'S SUGGESTION
2024, 73 (12): 124201.
doi: 10.7498/aps.73.20240339
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In view of the fact that high-frequency electromagnetic waves mainly enter buildings through windows and glass doors, switchable optically-transparent shielding with broad stopband is increasingly needed. Herein, a novel design for a switchable and optically transparent frequency selective surface (FSS) with ultrawide-stopband is presented in this study. The structure consists of a polymethyl methacrylate (PMMA) layer sandwiched between polydimethylsiloxane (PDMS) layers which contain liquid metal microchannels arranged in an orthogonal Ω-shaped configuration. The mobility of the liquid metal can switch the FSS response from an all-pass to an ultrawide bandstop behavior. The proposed FSS achieves a rejection bandwidth of 18.1 GHz, covering P, L, S, C, X and Ku bands, while maintaining a transparency of 81% and high angular stability up to 80°, regardless of polarization. Furthermore, the mechanism behind the ultrawide stopband and high angular stability is explored through an analysis of reflection and absorption for both TE polarization and TM polarization. Experimental validation under both normal and oblique incidence demonstrates the ultrawide-stopband performance of the fabricated FSS.
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Complex networks serve as indispensable instruments for characterizing and understanding intricate real-world systems. Recently, researchers have delved into the realm of higher-order networks, seeking to delineate interactions within these networks with greater precision or analyze traditional pairwise networks from a higher-dimensional perspective. This effort has unearthed some new phenomena different from those observed in the traditional pairwise networks. However, despite the importance of higher-order networks, research in this area is still in its infancy. In addition, the complexity of higher-order interactions and the lack of standardized definitions for structure-based statistical indicators, also pose challenges to the investigation of higher-order networks. In recognition of these challenges, this paper presents a comprehensive survey of commonly employed statistics and their underlying physical significance in two prevalent types of higher-order networks: hypergraphs and simplicial complex networks. This paper not only outlines the specific calculation methods and application scenarios of these statistical indicators, but also provides a glimpse into future research trends. This comprehensive overview serves as a valuable resource for beginners or cross-disciplinary researchers interested in higher-order networks, enabling them to swiftly grasp the fundamental statistics pertaining to these advanced structures. By promoting a deeper understanding of higher-order networks, this paper facilitates quantitative analysis of their structural characteristics and provides guidance for researchers who aim to develop new statistical methods for higher-order networks.
EDITOR'S SUGGESTION
2024, 73 (12): 126401.
doi: 10.7498/aps.73.20240347
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High-performance non-reciprocal photonic devices can improve the efficiency of optical quantum manipulation, information processing, and quantum simulation effectively. The enhanced optical signal can simultaneously amplify the weak signal output by the quantum system and isolate the sensitive quantum system from the back-scattered external noise, which is the core technology of high-performance photonic devices. In our previous work (2023 Opt. Express 31 38228 ), we have achieved dynamic control of unidirectional reflection amplification based on four-wave mixing gain and the use of coupling field intensity varying linearly with position. In this work, we design a simple three-level closed loop coherent gain atomic system, setting the intensity of coupling field to be varying with position step shape to break the spatial symmetry of probe susceptibility, and achieving perfect non-reciprocal reflection light amplification. In contrast, the stepped variation of coupling field intensity is easier to adjust in experiment, greatly reducing the difficulty in the experiment. Specifically, the system introduces phase modulation. By changing the phase, the frequency region of probe gain and absorption can be switched, which makes the modulation of reflection amplification more flexible.
EDITOR'S SUGGESTION
2024, 73 (12): 128501.
doi: 10.7498/aps.73.20240361
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Metal oxide thin film transistor has been widely used in flat panel display industry because of its low leakage current, high mobility and large area uniformity. Besides, with the development of printed display technology, inkjet printing process can fabricate the customizable patterns on diverse substrates with no need of vacuum or lithography to be used, thus significantly reducing cost and receiving more and more attention. In this paper, we use inkjet printing technology to prepare a bottom gate bottom contact thin film transistor (TFT) by using indium-zinc-tin-oxide (IZTO) semiconductor. The surface morphology of the printed IZTO film is modified by adjusting the solvent composition and solute concentration of the printing precursor ink. The experimental result show that the use of binary solvents can effectively overcome the coffee ring shape caused by the accumulation of solute edge in the volatilization process of a single solvent, ultimately presenting a uniform and flat contour surface. Further increase in solute concentration is in favor of formation of convex surface topology. The reason for the formation of the flat surface of the oxide film is the balance between the inward Marangoni reflux of the solute and the outward capillary flow during volatilization. In addition, IZTO thin film transistor printed with binary solvents exhibits excellent electrical properties. The ratio of width/length = 50/30 exhibits a high on-off ratio of 1.21×109, a high saturation field-effect mobility is 16.6 cm2/(V·s), a low threshold voltage is 0.84 V, and subthreshold swing is 0.24 V/dec. The uniform and flat active layer thin film pattern can form good contact with the source leakage electrode, and the contact resistances of TFT devices with different width-to-length ratios are less than 1000 Ω, which can reach the basic conditions of high mobility thin film transistors prepared by inkjet printing. Therefore, using solvent mixture provides a universal and simple way to print oxide films with required surface topology, and present a visible path for inkjet printing of high-mobility thin film transistors.
EDITOR'S SUGGESTION
2024, 73 (12): 120701.
doi: 10.7498/aps.73.20240383
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X-ray free-electron laser (XFEL), as a novel advanced X-ray light source, has excellent properties such as ultra-high brightness, ultra-shot pulse duration, and full coherence. The coherent X-ray diffraction imaging (CDI) has a lot of advantages at high resolution and quantitative imaging compared with the traditional lens based X-ray imaging methods. By combining the excellent properties of XFEL and advantages of CDI, the single-shot imaging has been realized, based on the concept of “diffraction before destruction”. Shanghai soft X-ray free-electron laser facility (SXFEL) is the first XFEL facility operated at the X-ray wavelength in China. The coherent scattering and imaging (CSI) endstation is the first commissioned endstation at SXFEL, focusing on the high spatiotemporal imaging for nano materials and micro materials by using a single-shot imaging method. To realize the single-shot experiment at XFEL, especially for single-shot imaging, the timing system plays a crucial role in ensuring the operation of the equipment in sequence. This paper introduces the design and implementation process of SXFEL single-shot imaging timing. The timing system is implemented with White Rabbit (WR) and digital delay and pulse generator (BNC505). Single-shot imaging is realized by synchronously moving the sample scanning stages and X-ray shutter to select a single pulse to illuminate the sample. At the same time, the X-ray detector is triggered with the timing system to record the single-shot diffraction pattern. During debugging, a gold nanodisks each with a side length of approximately 300 nm and a thickness of about 30 nm, as test samples, are imaged at the CSI endstation. The nanodisks are uniformly dispersed on Si3N4 membranes for single-shot imaging. Because of the ultra-high peak intensity at the focus spot, the samples and membrane are ionized for each XFEL pulse shot. A raster scan is performed on the membranes at intervals of 50 μm to update the sample. With the timing system and X-ray shutter, single-shot diffraction patterns can be recorded by using an X-ray detector. From the image of the Si3N4 membrane after raster scanning, the ionized holes with an interval of 50 μm can be recognized. Finally, phase retrieval is applied to the single-shot diffraction pattern to obtain a real-space image of the sample. The resolution of the reconstructed image is estimated by calculating the phase-retrieval transfer function (PRTF). With a citation of the PRTF curve dropping below $ 1/{\mathrm{e}} $ , the spatial frequency cutoff is determined to be 22.6 μm–1, corresponding to a half period resolution of 22.1 nm. The results show that the designed timing system can accurately control the time sequence of the imaging process, meeting the requirement for single-shot imaging within 50 Hz at SXFEL.
EDITOR'S SUGGESTION
2024, 73 (12): 120704.
doi: 10.7498/aps.73.20240043
Abstract +
In recent years, regulating organic functional molecule has gradually received much attention in the field of materials due to its significant contribution in improving the charge carrier mobility of nanometer optoelectronic device. Molecular configuration and assembly structure of vanadyl phthalocyanine (VOPc) are systemically investigated on pristine and oxidized Cu(110) surface by using low temperature scanning tunneling microscopy. In the initial deposition stage, two molecular adsorption configurations, referring to O-up and O-down, are randomly distributed on the pristine Cu(110) surface. By oxidizing Cu(110) at different oxygen atmospheres and substrate temperatures, two different copper oxide structures are obtained, i.e. CuO-(2×1) and Cu5O6-c(6×2). The VOPc molecules are then deposited on both surfaces via thermal evaporation. For the CuO-(2×1) surface, contrastly, extended molecular chains form in the initial adsorption and subsequently the VOPc molecules assemble into an ordered molecular film involving both configurations. The VOPc molecules shows two packing orientations with a rotation angle of about 36° relative to each other. On Cu5O6-c(6×2), the O-down and O-up molecules are isolatedly adsorbed at the initial coverage. As the coverage increases, molecular assembly film gradually forms a parallelogram-shaped unit cell that involves only the O-up molecules. The molecular film exhibits two distinct molecular orientations with a rotation angle of about 42° relative to each other. The dipole-dipole interaction drives the configuration transition from the O-up configuration to O-down configuration. The O-down VOPc molecules of the second layer tend to be adsorbed on the molecular membrane supported by the Cu5O6-c(6×2) surface. The dipole-dipole interaction between neighboring molecular layers may be responsible for the preferable adsorption of the second-layered molecules. This study suggests the importance of surface oxidization in modifying configurations and orbital distributions of adsorbed molecules that can affect the charge transport in molecular films during fabricating electronic devices.
EDITOR'S SUGGESTION
2024, 73 (12): 123201.
doi: 10.7498/aps.73.20240292
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EDITOR'S SUGGESTION
2024, 73 (12): 125201.
doi: 10.7498/aps.73.20240392
Abstract +
Numerical simulation has become an indispensable tool in the study of gas discharge. However, it is typically used to reveal microscopic properties in a discharge under specific conditions. In this work, a unified fluid model for discharge simulation is introduced in detail. The model includes the continuity equation, the energy conservation equation of the species (electrons and heavy particles), and Poisson’s equation. The model takes into account some processes such as cathode electron emission (secondary electron emission and thermionic emission), reaction enthalpy change, gas heating, and cathode heat conduction. The full current-voltage characteristic (CVC) curve covers a range of discharge regimes, such as the Geiger-Müller discharge regime, Townsend discharge regime, subnormal glow discharge regime, normal glow discharge regime, abnormal glow discharge regime, and arc discharge regime. The obtained CVC curve is consistent with the results in the literature, confirming the validity of the unified fluid model. On this basis, the CVC curves are obtained in a wide pressure range of 50–3000 Torr. Simulation studies are carried out focusing on the discharge characteristics for microgap of 400 µm at pressures of 50 Torr and 500 Torr, respectively. The distributions of typical discharge parameters under different pressure conditions are analyzed by comparison. The results indicate that the electric field in the discharge gap is uniform, and that the space charge effect can be ignored in Townsend discharge regime. The cathode fall region and the quasi-neutral region both appear in glow discharge regime, and the space charge effect is significant. In particular, the electric field reversal occurs in abnormal discharge regime due to the heightened particle density gradient. The electron density reaches about 1022 m–3 in arc discharge regime dominated by thermionic emission and thermal ionization, with the current density increasing. The gas temperature peak is 11850 K when the pressure is 500 Torr, and the cathode surface is heated to nearly 4000 K due to heat conduction. The present model can be used to simulate gas discharge across a wide range of condition parameters, promoting and expanding fluid model applications, and assisting in a more comprehensive investigation of discharge parameter properties.
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