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  • AIP Publishing  (27)
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  • AIP Publishing  (27)
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  • 1
    In: APL Materials, AIP Publishing, Vol. 10, No. 9 ( 2022-09-01)
    Abstract: Strain engineering has been demonstrated to be an effective knob to tune the bandgap in perovskite oxides, which is highly desired for applications in optics, optoelectronics, and ferroelectric photovoltaics. Multiferroic BiFeO3 exhibits great potential in photovoltaic applications and its bandgap engineering is of great interest. However, the mechanism of strain induced bandgap engineering in BiFeO3 remains elusive to date. Here, we perform in situ ellipsometry measurements to investigate the bandgap evolution as a function of uniaxial strain on freestanding BiFeO3 films. Exotic anisotropic bandgap engineering has been observed, where the bandgap increases (decreases) by applying uniaxial tensile strain along the pseudocubic [100]p ([110] p) direction. First-principles calculations indicate that different O6 octahedral rotations under strain are responsible for this phenomenon. Our work demonstrates that the extreme freedom in tuning the strain and symmetry of freestanding films opens a new fertile playground for novel strain-driven phases in transition metal oxides.
    Type of Medium: Online Resource
    ISSN: 2166-532X
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 2722985-3
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  • 2
    Online Resource
    Online Resource
    AIP Publishing ; 2013
    In:  Review of Scientific Instruments Vol. 84, No. 9 ( 2013-09-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 84, No. 9 ( 2013-09-01)
    Abstract: To generate a relative high frequency mesoband microwave, a compact coaxially fed transmission line switched oscillator with high voltage capability is investigated. The characteristic impedance and voltage capability of the low impedance transmission line (LITL) have been analyzed. It is shown that the working voltage of the oscillator can reach up to 200 kV when it is filled by pressurized nitrogen and charged by a nanosecond driving source. By utilizing a commercial electromagnetic simulation code, the transient performance of the switched oscillator with a lumped resistance load is simulated. It is illustrated that the center frequency of the output signal reaches up to ∼0.6 GHz when the spark gap practically closes with a single channel. Besides, the influence of the closing mode and rapidity of the spark gap, the permittivity of the insulator at the output end of the LITL, and the load impedance on the transient performance of the designed oscillator has been analyzed in quantification. Finally, the good transient performance of the switched oscillator has been preliminarily proved by the experiment.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 3
    Online Resource
    Online Resource
    AIP Publishing ; 2021
    In:  Review of Scientific Instruments Vol. 92, No. 10 ( 2021-10-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 92, No. 10 ( 2021-10-01)
    Abstract: This study investigates the frequency tunability of a coaxial transverse electromagnetic mode (TEM)–linear-polarized TE11 mode tunable turnstile mode converter (TTMC) for high-power microwave applications using a combination of simulation and experiment. In the proposed structure, the sliding folded waveguide can be moved radially to meet the requirement of linear polarization, and the matching structure is designed to eliminate the undesired reflection. The simulation shows that the conversion efficiency of the TTMC can reach over 99% in the frequency range of 1.45–2.35 GHz, corresponding to a frequency tuning bandwidth of about 47.4%. Moreover, the TTMC can maintain a continuous high conversion efficiency at different frequency points by changing the tuning mechanism. The experimental investigation shows that the TTMC can convert the coaxial TEM mode into a circular waveguide TE11 mode with a conversion efficiency of above 95% in the frequency range of 1.55–2.35 GHz. The experimental measurements agree well with the simulation results, implying feasibility of the TTMC design and its superior performance.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2021
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 4
    Online Resource
    Online Resource
    AIP Publishing ; 2019
    In:  Review of Scientific Instruments Vol. 90, No. 4 ( 2019-04-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 90, No. 4 ( 2019-04-01)
    Abstract: A carbon fiber array cathode (CFAC) was presented and tested in a magnetically insulated transmission line oscillator (MILO) in earlier papers; however, the performance of this cathode was not as good as the traditional polymer velvet cathode, and the nonuniform fibers’ distribution on the cathode surface was postulated as the culprit for this. In this paper, this CFAC has been carefully reprocessed, and the performance is improved (efficiency increases from ∼12% to ∼16%) and reaches a level that is as good as the velvet cathode, which means that this CFAC provides a promising substitute for the polymer velvet cathode in MILO.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2019
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 5
    Online Resource
    Online Resource
    AIP Publishing ; 2020
    In:  Review of Scientific Instruments Vol. 91, No. 2 ( 2020-02-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 91, No. 2 ( 2020-02-01)
    Abstract: Evaluation conditions of the minimum circumscribed circle and maximum inscribed circle in Cartesian coordinates are transformed into those in polar coordinates. According to the radius of the measured points, the candidate points for evaluating the minimum circumscribed circle and maximum inscribed circle are divided into three cases which are solved with the corresponding algorithms. Several examples have been used to validate the validity of the proposed algorithm.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 6
    Online Resource
    Online Resource
    AIP Publishing ; 2022
    In:  Review of Scientific Instruments Vol. 93, No. 10 ( 2022-10-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 93, No. 10 ( 2022-10-01)
    Abstract: Relativistic magnetron (RM) is a promising high-power microwave source, whose advantages include high efficiency, high power, and compact configuration. Enhancing power efficiency and output power are the most important two development directions for RM. Based on the two targets, a high efficiency and high power RM is presented and investigated numerically and experimentally in this paper. When the diode voltage is 485 kV, the beam current is 6.9 kA, and the magnetic field is 0.34 T, and high power microwave is generated with the power of 1.35 GW, frequency of 1.47 GHz, and power efficiency of 40.3% in the experiments.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 7
    Online Resource
    Online Resource
    AIP Publishing ; 2019
    In:  Review of Scientific Instruments Vol. 90, No. 12 ( 2019-12-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 90, No. 12 ( 2019-12-01)
    Abstract: It is very important to select the initial four candidate points of the minimum zone circles to improve the computational efficiency. According to the radius of the measured points, three models of error evaluation are proposed and corresponding algorithms are given for evaluating the minimum zone circles based on the lower envelope lines, four-point intersection principle, and bisection method. The points constructing the lower envelope lines can be used for the evaluation of the maximum inscribed circle. Several examples have been carried out to validate the validity of the proposed algorithm.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2019
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
    Library Location Call Number Volume/Issue/Year Availability
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  • 8
    Online Resource
    Online Resource
    AIP Publishing ; 2022
    In:  Review of Scientific Instruments Vol. 93, No. 10 ( 2022-10-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 93, No. 10 ( 2022-10-01)
    Abstract: The development of pulsed power technology requires an electron beam accelerator with high output power and repetitive operation. A compact repetitive electron beam accelerator based on a pulse transformer and a pulse forming line of high permittivity liquid, as an essential type of one, has attracted extensive attention at the present time. In this paper, the development of a compact high energy-density electron beam accelerator, viz., HEART-20, based on a propylene carbonate (PC) forming line is presented. The accelerator HEART-20 consists of a primary energy source, a pulse transformer, a PC pulse forming line, a gas spark gap switch, and a vacuum diode. First, the operation principle of the accelerator is described. Second, the design of the accelerator’s parameters is presented. A pulse transformer is developed for rapid charging of the PC-filled pulse forming line. The coupling coefficient is above 0.9, the voltage ratio is about 200, and the operation voltage is about 800 kV. Third, the energy storage characteristics of PC are investigated. The insulation characteristics of PC under positive charging voltage are found to perform better than those under negative charging voltage. The insulating strength of PC can be improved by pressurization. Finally, the development of the accelerator HEART-20 is presented. Across a vacuum diode load, it can steadily operate at a 20 GW output power in 5 Hz rep-rate. Moreover, it can drive a magnetically insulated line oscillator to produce about 2.0 GW microwave. These findings provide a good foundation for the development of a rep-rate intensive electron beam accelerator with promising applications for the future.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 9
    In: Applied Physics Letters, AIP Publishing, Vol. 120, No. 6 ( 2022-02-07)
    Abstract: Benefitting from regrown Ohmic contact with a contact ledge structure, high performance millimeter-wave InAlN/GaN HEMT is fabricated to satisfy low voltage RF applications. Different from the commonly seen fabrication process for regrown Ohmic contact, the scheme proposed in this work features MBE regrowth of n+ GaN on the whole wafer after formation of regrowth well without masks and partial removal of n+ GaN grown on the access region by self-stopping etching. The remaining n+ GaN on the barrier, serving as contact ledges, provides an additional current path to achieve the reduced equivalent source-drain distance and, thus, improved output current, and more current contribution is made by contact ledge as the actual source-drain distance shrinks. With the assistance of contact ledge, the fabricated device demonstrates output current density of 2.8 A/mm, a peak extrinsic transconductance of 823 mS/mm, a knee voltage of 1.6 V, and an on-resistance of 0.47 Ω·mm. Although self-stopping etching is performed on the access region, the device exhibits ignorable current collapse. At 30 GHz and VDS of 6 V, decent power-added-efficiency of 52% together with output power density of 1.2 W/mm is achieved, revealing the great potential of the proposed regrown Ohmic contact with contact ledge structure for low voltage RF applications.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    RVK:
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 10
    Online Resource
    Online Resource
    AIP Publishing ; 2020
    In:  AIP Advances Vol. 10, No. 3 ( 2020-03-01)
    In: AIP Advances, AIP Publishing, Vol. 10, No. 3 ( 2020-03-01)
    Abstract: Relativistic magnetrons (RMs) are one of the most promising high power microwave devices. A high-efficiency relativistic magnetron (HERM) with a novel all-cavity extraction structure is presented and investigated theoretically and numerically in this paper. Compared with conventional RMs with an all-cavity extraction structure, the HERM has three improved features. First, a single stair is introduced into the HERM. Second, the angular width of the extraction structure is bigger than that of the anode slow-wave structure. Third, the extraction port is set behind the anode vanes in the axial direction instead of being set between two anode vanes. These improved features can enhance the extraction efficiency of the HERM. The typical simulation results are as follows: high-power microwaves of the transverse electromagnetic mode are generated with a peak power of 1.65 GW, a frequency of 1.61 GHz, and a power efficiency of 67.6%, when the voltage is 586 kV and the current is 4.19 kA. The simulation results verify the validity of the novel all-cavity extraction structure.
    Type of Medium: Online Resource
    ISSN: 2158-3226
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 2583909-3
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