Search

In this work, the effects of proton-induced trap evolution on the electrical performances of AlGaN/GaN metal–insulator–semiconductor (MIS) high-electron-mobility-transistors (HEMTs) have been investigated in detail. Contrary to observed proton-induced degradation in sheet electron density (ns), carrier mobility (μn), and sheet resistance (RSH), a significant improvement in gate leakage current (IG) and off-state drain–source breakdown voltage (BVDS) is found in irradiated devices. The low-frequency noise (LFN) results show that the density of traps in the AlGaN layer and AlGaN/GaN interface increases after irradiation, which leads to a degradation in ns, μn, and RSH and an improvement in BVDS due to enhanced electron trapping and depletion. Furthermore, the measurement results obtained from the frequency-dependent conductance technique show that irradiated devices exhibit decreased trap density (DT) at the insulator/semiconductor interface with hardly changed trap energy level (ET), which confirms the observed proton-induced decrease in IG. An increase in DT at the AlGaN/GaN interface is also found after irradiation, which is consistent with LFN results. These traps with deeper ET induce a serious Coulomb scattering effect. This work provides valuable information for the systematic understanding of the proton irradiation effect of AlGaN/GaN MIS-HEMTs.

This Letter reports two kinds of oxygen-containing plasma treated β-Ga2O3 Schottky barrier diodes (SBDs), including N2O plasma treatment and O2 plasma treatment, and the SBD without plasma is prepared for comparison. I–V characteristics, breakdown characteristics, and trap state characteristics of three devices have been studied. It is found that the turn-on voltage of SBDs with N2O plasma can reduce to 0.6 V, and the better current density of 750 A/cm2 and an on-resistance of 3.5 mΩ cm2 are obtained after the N2O plasma treatment. Moreover, the breakdown voltage of SBDs with N2O plasma is 50.2% higher than the conventional one, whose value reaches 323 V. In addition, the trap states' characteristics of the devices are studied, which show that the oxygen-containing plasma can reduce the deep level trap states density partly in the anode region, which can improve the surface quality effectively.

This letter presents a parallel-feedback dual-frequency oscillator (DFO) with low phase noise. It is achieved based on the filter switching technique. By using four switches to control two oscillator loops with a common active device, the oscillation frequency of the proposed DFO can be switched from one to another. Due to the high isolation level of the employed switches, the two oscillator loops almost operate independently. Thus, there is no intermodulation (IM) spurs generated in the output spectrum of the proposed DFO. In the meantime, to improve the phase noise performance of the DFO, each oscillator loop utilizes a high frequency-selectivity bandpass filter with high group delay (GD) as a frequency selective element. In this way, the low phase-noise DFO is developed. For demonstration, the DFO is designed, fabricated, and tested. As seen from the measurement results, the oscillator can oscillate at 2.04 or 3.092 GHz by controlling the four switches. At 100 kHz and 1 MHz frequency offset from the carrier frequency, the phase noises are -108.5 and -129.7 dBc/Hz for 2.04 GHz, while -112.7 and -135.7 dBc/Hz for 3.092 GHz.

A novel slow wave (SW) substrate-integrated waveguide (SIW) with enhanced SW factor (SWF) and broadened bandwidth is proposed by simultaneously increasing the effective permeability and permittivity. The effective permittivity is increased by the enhanced capacitance between the top plane of the waveguide and the loaded patches which are shorted to the SIW bottom plane by the blind via-holes. The effective permeability is increased by lengthening the current path by adding patches on the blind via-holes. The proposed SW-SIW with simultaneous increased effective permeability and permittivity has two obvious advantages over the reported SW-SIW with only effective permeability or permittivity increased: 1) smaller longitudinal and lateral dimensions resulted from higher SWF and lower cutoff frequency, respectively, and 2) wider bandwidth due to stable wave impedance along the periodical SW structure. The lateral dimension of the proposed SW-SIW is decreased by 53% compared with the normal SIW with the same cutoff frequency. The phase velocity is decreased by 73%, which means the longitudinal length is reduced by 73% consequently. The operation band is 7.0–18.8 GHz (91.5% fractional bandwidth) covering ${X}$ - and Ku -bands. A prototype of the proposed SW-SIW is manufactured and measured, and the measured results agree well with the simulations.

Objective: This study aims to explore the relationship between exercise persistence (EA), personal growth initiative (PGI), mindfulness and subjective well-being (SWB), which is beneficial to improve the subjective well-being of college students and promote the development of physical and mental health.Methods: A total of 894 college students (average age =19.51 years, SD = 0.85 years) were sampled by stratified cluster sampling. EA, mindfulness, PGI, and SWB were assessed using standard scales. Data were analyzed by Pearson correlation analysis, structural equation model test and bias-correction percentile Bootstrap method. Results: (1) There was a significant positive correlation between EA and SWB (r= 0.353), and the direct path between EA and SWB was significant (β= 0.592, t = 5.480, p < 0.01). (2) EA positively predicted mindfulness (β= 0.104, t = 8.964, p < 0.01) and PGI (β= 0.251, t = 8.743, p < 0.01); mindfulness positively predicted SWB (β= 0.915, t = 2.775, p < 0.01) and PGI (β= 1.349, t = 16.985, p < 0.01); and PGI significantly positively predicted SWB (β= 1.080, t = 8.924, p < 0.01). (3) Mindfulness and PGI played a significant mediating role in the relationship between EA and SWB. Specifically, the intermediary effect is composed of three path of indirect effect: EA→ mindfulness→ SWB (mediating effect value is 0.095), EA→ PGI→ SWB (mediating effect value is 0.271), EA→ mindfulness→ PGI→ SWB (mediating effect value is 0.152). (4) There is no gender difference in the chain mediation effect.Conclusion: (1) EA performance significantly positively predicts college students' mindfulness, PGI and SWB, which means that EA can promote college students' mindfulness, PGI and SWB; (2) EA can not only directly affect SWB, but also indirectly affect SWB through the separate intermediary role of mindfulness and PGI, as well as the chain intermediary role of both. It further explains the reasons why EA has an effect on College Students' SWB, which is of great significance to improve and intervene college students' SWB.

A novel low-loss suspended-line gap waveguide (SLGW) supporting transverse electromagnetic (TEM) propagation is presented for millimeter-wave applications for the first time. The suspended line is composed of two parallel strips connected by metal via holes. Periodic stacked-mushroom electromagnetic band gap (SM-EBG) structures are used to package the suspended line by creating a stopband for all parallel-plate modes. According to the different packaging requirements of the circuit, the SM-EBG unit cell can be composed of several stacked mushrooms and metal covers. The air gaps’ thickness between face-to-face patches of the adjacent mushrooms is near zero, confining more power in the air-filled guiding region of the SLGW. Furthermore, the SM-EBG structures with near-zero thick air gaps can provide more stable mechanical support for the multilayer structure. Therefore, SLGW has a lower loss and more robust gap stability compared with the conventional air-filled printed versions of GWs, such as printed ridge gap waveguide (PRGW) and inverted microstrip gap waveguide (IMGW). On the other hand, compared with the self-packaged double-sided interconnected strip line (DSISL), the proposed SLGW packaged with SM-EBG structures has the advantage of no electrical contact, avoiding the power leakages in the gap between plates at discontinuities and simplifying the assembly. The design and analysis of the SM-EBG structure, the design of SLGW, and the microstrip-to-SLGW transition design are given in this article. A prototype of the proposed SLGW with back-to-back transition is fabricated packaged with SM-EBG structures to prove the concept.

At the end of 2019, A new type of beta-CoV, SARS-CoV-2 emerged and triggered the COVID-19 pandemic, which spread overwhelmingly around the world in less than a year. However, the origin and direct ancestral viruses of SARS-CoV-2 remain unknown. RaTG13, a novel coronavirus found in bats in China’s Yunnan Province, is the closest relative virus of the SARS-CoV-2 identified so far. In this study, a new SARS-CoV-2 related virus, provisionally named PrC31, was discovered in Yunnan province by retrospectively analyse bat next generation sequencing (NGS) data of intestinal samples collected in 2018. PrC31 shared 90.7% and 92.0% nucleotide identities to the genomes of SARS-CoV-2 and the bat SARSr-CoV ZC45, respectively. Sequence alignment of PrC31 showed that several genomic regions, especially orf1a and orf8 had the highest homology with those corresponding genomic regions of SARS-CoV-2 than any other related viruses. Phylogenetic analysis indicated that PrC31 shared a common ancestor with SARS-CoV-2 in evolutionary history. The differences between the PrC31 and SARS-CoV-2 genomes were mainly manifested in the spike genes. The amino acid homology between the receptor binding domains of PrC31 and SARS-CoV-2 was only 64.2%. Importantly, recombination analysis revealed that PrC31 underwent multiple complex recombination events (including three recombination breakpoints) involving the SARS-CoV and SARS-CoV-2 sub-lineages, indicating that PrC31 evolved from yet-to-be-identified intermediate recombination strains. Combined with previous studies, it is revealed that the beta-CoVs may possess a more complex recombination mechanism than we thought.

Interlayered thin-film nanocomposite membranes (TFNi) are an emerging type of membranes with great potential to overcome the permeability-selectivity upper bound of conventional thin-film composite (TFC) nanofiltration and reverse osmosis membranes. However, the exact roles of the interlayer and the corresponding mechanisms leading to enhanced separation performance of TFNi membranes remain poorly understood. This study reports a polydopamine (PDA)-intercalated TFNi nanofiltration membrane (PA-PSF2, PDA coating time of 2 h) that possessed nearly an order of magnitude higher water permeance (14.8 ± 0.4 Lm-2 h-1 bar-1) than the control TFC membrane (PA-PFS0, 2.4 ± 0.5 Lm-2 h-1 bar-1). The TFNi membrane further showed enhanced rejection toward a wide range of inorganic salts and small organic molecules (including antibiotics and endocrine disruptors). Detailed mechanistic investigation reveals that the membrane separation performance was enhanced due to both the direct "gutter" effect of the PDA interlayer and its indirect effects resulting from enhanced polyamide formation on the PDA-coated substrate, with the "gutter" effect playing a more dominant role. This study provides a mechanistic and comprehensive framework for the future development of TFNi membranes.

A compact dual-mode inverted microstrip ridge gap waveguide (IMRGW) resonator and a series of dual-band IMRGW bandpass filters (BPFs) with easily controllable passbands are proposed for the first time in this article. The resonator is embedded into the ridge of the IMRGW without disturbing the placement of the mushroom-type bed of nails. A metalized via-hole is introduced to the center of the IMRGW resonator to ground a central patch, resulting in an inverted microstrip resonance mode and a cavity resonance mode simultaneously. The cavity resonant mode is relatively insensitive to the dimensions of the central patch, while the inverted microstrip resonance is insensitive to the dimensions of the cavity enclosed by electromagnetic band-gaps (EBGs) and two rows of metalized via-holes. Therefore, the resonant frequency of the two modes can be tuned independently. The resonators can be cascaded easily with a short IMRGW transmission line. A series of IMRGW based dual-band BPF with different orders are designed, fabricated, and measured. The third-order BPF’s simulated passbands are 13.07–13.41 and 18.46–18.91 GHz with a fractional bandwidth of 2.5% and 2.3%. Low insertion losses better than 1.7 and 2.1 dB are obtained on the two passbands. The measured passbands are 13.52–13.86 and 18.9–19.34 GHz with a fractional bandwidth of 2.3% and 2.2% while the insertion losses are better than 2.5 and 2.3 dB for the third-order BPF.

This study developed a novel strategy for azeotrope separation such as ethanol-water binary system. Distillation-pervaporation hybrid process was employed by using hollow fiber pervaporation composite membranes as structured packing in a single hybrid column rather than using pervaporation as an externally connected unit of the distillation column. The separating limitation of azeotrope challenged in conventional distillation could be readily overcome by continually removing water from the hybrid system via pervaporation. The competition between distillation and pervaporation has been found to be cause of unexpected concentration distribution in the hybrid column. The mass flux of mixture decreased with time whereas the selectivity of water to ethanol first increased then decreased with time. Analysis of this system illustrated that the increase in heating power and membrane area shortened time for obtaining certain content of ethanol in the mixture. However, faster decline in mass flux occurred due to an increase in the removal rate of water. With respect to its simplicity, efficiency and broad applicability, this hybrid process is expected to provide a benchmark for the enhancement of distillation-pervaporation process by hollow fiber membrane packing.

A slow-wave substrate integrated groove gap waveguide (SW-SIGGW) is presented for the first time in this letter. The developed SW-SIGGW consists of three stacked substrate layers with different thickness, in which asymmetric half-height mushroom-type electromagnetic bandgap (EBG) structures are utilized for the convenience of tuning the heights of each layer. The slow-wave effect is achieved by loading periodical metallic via holes inside the groove gap waveguide in the bottom layer separating the magnetic and electric fields. In both lateral and longitudinal dimensions, 41% reductions are achieved through this new topology of SW-SIGGW, since the guided wavelength decreases significantly compared to the normal SIGGW of same width and height. A prototype of the SW-SIGGW is designed, manufactured, and measured. The simulated and measured results are in good agreement, proving the validity and feasibility of the design.

Fabricating nanostructured and nanomaterial enhanced polyamide (PA) selective layer are the trend for next-generation thin-film composite (TFC) membranes for elevated performance. However, the mech...

Superhydrophobic polyvinylidene fluoride (PVDF) membrane is a promising material for membrane distillation. Existing approaches for preparing superhydrophobic PVDF membrane often involve separate manipulation of surface roughness and surface chemistry. Here we report a one-step approach to simultaneously manipulate both the surface roughness and surface chemistry of PVDF nanofibrous membranes for enhanced direct-contact membrane distillation (DCMD) performances. The manipulation was realized in a unique solvent-thermal treatment process, during which a treatment solution containing alcohols was involved. We demonstrate that by using different chain-length alcohols in the treatment solvent, surface roughness can be promoted by creating nanofin structures on the PVDF nanofibers using an alcohol which has moderate affinity with PVDF. Meanwhile, surface chemistry can be tuned by adjusting the fraction distribution of crystal phases (nonpolar α phase and polar β phase) in the membrane using different alcohols. PVDF membranes with different surface wettabilities were used to evaluate the effects of surface roughness and surface energy on the DCMD performances. Combining both low surface energy and multi-scale surface roughness, pentanol-treated PVDF membrane achieved best anti-water property (water contact angle of 164.1° and sliding angle of 8.1°), and exhibited superior water flux and enhanced anti-wetting ability to low-surface-tension feed in the DCMD application.

A β-Ga2O3 Schottky barrier diode (SBD) with a p-type NiOx guard ring was fabricated, and the reverse leakage and subthreshold leakage current reduction was found at high temperatures from temperature-dependent I–V characteristics. The functional mechanisms of NiOx as edge termination on leakage reduction were studied. NiOx can increase the barrier height and passivate the defects at the interface, resulting in the suppression of subthreshold leakage and elimination of current crowding effect confirmed by a thermal emission microscope. From the temperature-dependent x-ray photoelectron spectroscopy characteristics, more holes generated to deplete Ga2O3 at higher temperatures were found. It leads to reduce the reverse leakage current. The small-polaron transportation in NiOx is proposed to argue the implausibility of the leakage conduction in NiOx. This work will offer critical physical insight and a valuable route for developing low-leakage Ga2O3 SBDs.

Thin-film composite (TFC) membranes are attracting wide attention because their ultrathin selective layer usually corresponds to the higher membrane flux for pervaporation. However, the direct preparation of the TFC membranes on ceramic substrates confronted with the great difficulties because the larger pores on ceramic substrate surfaces are detrimental to the formation of an intact polyamide (PA) selective layer produced by interfacial polymerization (IP) reaction. Here, the integrated ZIF-L nanosheets were proposed to be used as an assistance interlayer for the first time to eliminate the existence of the pores of the ceramic support, and provides a better basis for the formation of an intact PA selective layer by IP reaction between TMC and ethylenediamine (EDA). The experimental data obtained in pervaporation (PV) show that the increased flux from 1.1 to 2.9 kg/m2h corresponds to the decreased separation factor from 396 to 110 when the feed concentration of ethanol decreases from 95 wt % to 80 wt % at 50 °C. In addition, the membrane flux increases from 0.8 to 2.5 kg/m2h with a change of the separation factor from 683 to 111 when the operational temperature varies from 30 to 60 °C. These results demonstrate the great potential of the fabricated TFC membranes in practical application for PV dehydration of organic solutions.

In this paper, AlN films grown by magnetron sputtering method have been proposed as the gate insulator layer of AlGaN/GaN high electron mobility transistors (HEMTs) to decrease gate leakage current and suppress the interface trap. The effect of the temperature of substrate on the quality of AlN films have been investigated. By inserting the thin AlN film (35 nm) as a gate insulator layer, the on-state resistance of AlGaN/GaN HEMTs decrease from 11.1 Ω mm to 10.3 Ω mm @V g = 0 V, the current collapse decreases from 16.6% to 3.2%, the gate leakage can be reduced from 1.2 × 10−1A mm−1 to 4.4 × 10−6A mm−1 @V g = 2 V by five orders of magnitude, and the fast interface states disappear and the normal trap density decreases from 0.96–1.3 × 1013 cm−2eV−1 to 1.3–3.4 × 1012 cm−2 eV−1, proving that magnetron-sputtered AlN is an effective way to improve the performance of GaN HEMTs.

In this work, a high linearity AlGaN/GaN HEMT integrated dual threshold coupling (DT) technology and Schottky–Ohmic drain (SOD) were fabricated and analyzed. Since the architecture of DT synthesized planar- and recess-HEMT periodically along the gate width, SOD alleviated the peak electric field (E-field) around the gate region and the peak transconductance ( Gm-max) of 248 mS/mm with the associated transconductance plateau of ∼4.0 V at Vds = 28 V was obtained, which is evidently flatter than that of HEMT without the SOD structure. Attributed to the improved Gm linearity at high E-field, the DT-SOD HEMT exhibits the predicted linearity figure of merit of 5–13 dB when biased at class AB operation, which is ∼10 dB higher than that of DT-HEMT. Moreover, the fabricated device yields a nearly constant fT/ fmax of 47/118 GHz over a wide gate voltage, and load-pull measurements at 30 GHz reveal that these devices deliver output power density ( Pout) of 7.8 W/mm with the associated 1-dB compression point ( P1 dB) of 28.5 dBm at Vds = 28 V. The experimental results indicate that the employment of DT technology and SOD structure is an attractive approach to enhance the linearity at high E-field for millimeter wave devices.

To improve the pervaporation (PV) performance of isopropanol (IPA) dehydration, polyamide (PA) thin-film composite (TFC) membranes were fabricated by interfacial polymerization (IP) of 1,3-diaminopropane (DAPE) and trimesoyl chloride (TMC) on the surface of TiO2 modified ceramic hollow fiber (CHF) substrate. The TiO2 interlayer prepared by the sol-gel method completely cover the rough and macroporous surface of the α-Al2O3 hollow fiber, providing relatively smooth and intact surface but also abundant electrostatic sites (hydroxyl) for better IP. The PA layer prepared on the TiO2 interlayer is thinner, defect-free and exhibited higher smoothness and cross-linking degree than that on the original CHF support. The effects of monomer concentration, immersion time in aqueous phase and contact time of TMC solution were also investigated. The TFC membrane prepared under optimum conditions exhibited the outstanding PV separation index (PSI) value of 7.83 × 107 with separation factor above 12,000 and the permeate flux nearly 6.44 kg/m2 h for PV dehydration of 90 wt% IPA at 60 °C. After 100 h of long-term operation, the PV membrane maintains the high separation performance. This TFC membrane prepared by an effective and simple method provides an alternative for designing high-performance PV membrane in organics dehydration.