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  • AIP Publishing  (26)
  • 1
    Online Resource
    Online Resource
    Electron-optical system for dual radial sheet beams for Ka-band cascaded angular log-periodic strip-line traveling wave tube
    AIP Publishing ; 2021
    In:  AIP Advances Vol. 11, No. 3 ( 2021-03-01)
    Details
    In: AIP Advances, AIP Publishing, Vol. 11, No. 3 ( 2021-03-01)
    Abstract: A novel electron-optical system is proposed for dual azimuthally stacked radial sheet electron beams (ARSEBs). The two sheet beams are emitted from curved surfaces of two cathodes and are focused by a focusing electrode, which is carefully designed to produce a symmetric field distribution for the two beams and to avoid interference between the beams. A common tunable periodic cusped magnetic focusing system is also designed to focus the two ARSEBs. The dual sheet beams are used in a traveling wave tube (TWT) consisting of a cascade of two azimuthally supported angular log-periodic strip-line (ASALS) slow-wave structures (SWSs). The transmission efficiency in the presence of beam–wave interaction is 93%. The particle-in-cell simulation results show that for a beam voltage of 4400 V and a current of 0.39 A, the proposed cascaded TWT has a maximum gain of 32.5 dB at 35 GHz and a maximum output power of 180 W; this is a significant gain improvement over a TWT using a single ASALS SWS.
    Type of Medium: Online Resource
    ISSN: 2158-3226
    URL: Article
    DOI: 10.1063/5.0037161
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2021
    detail.hit.zdb_id: 2583909-3
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  • 2
    Online Resource
    Online Resource
    Investigation of angular log-periodic folded groove waveguide slow-wave structure for low voltage Ka-band TWT
    AIP Publishing ; 2020
    In:  AIP Advances Vol. 10, No. 3 ( 2020-03-01)
    Details
    In: AIP Advances, AIP Publishing, Vol. 10, No. 3 ( 2020-03-01)
    Abstract: In this paper, a novel angular log-periodic folded groove waveguide (ALFGW) slow-wave structure (SWS) has been investigated theoretically and experimentally for application in Ka-band traveling-wave tubes (TWTs). The dispersion relation for the ALFGW is derived analytically, and the dispersion characteristics are calculated for a Ka-band design. The designed SWS is fabricated using oxygen-free-copper that is silver electroplated. The measured cold-test parameters show good agreement with the simulation results, with S21 varying from −2.7 dB to −4.8 dB and S11 better than −13.6 dB over the frequency range of 30–38 GHz. Simulations of beam–wave interactions using a 4850 V and 0.4 A sheet beam with a high aspect ratio of 28:1 indicate an output power of 128 W, corresponding to a maximum gain and electronic efficiency of 18.1 dB and 6.6%, respectively. Due to the log-periodic form, a higher output power, higher efficiency, wider bandwidth, and lower operating voltage are achieved as compared to a TWT based on the conventional folded groove waveguide (FGW) SWS. These results show that the proposed ALFGW SWS has good potential for application in relatively high-power wideband TWTs.
    Type of Medium: Online Resource
    ISSN: 2158-3226
    URL: Article
    DOI: 10.1063/1.5145346
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 2583909-3
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  • 3
    Online Resource
    Online Resource
    Study of a miniaturized dual-beam TWT with planar dielectric-rods-support uniform metallic meander line
    AIP Publishing ; 2018
    In:  Physics of Plasmas Vol. 25, No. 6 ( 2018-06-01)
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 25, No. 6 ( 2018-06-01)
    Abstract: A dual-beam planar dielectric-rod-support uniform metallic meander line slow-wave structure (SWS) for high-efficiency Ka-band traveling wave tube (TWT) is proposed in this paper. Two dielectric rods are placed on both sides of metallic meander line to support it, instead of the dielectric substrate in the conventional microstrip meander line. Furthermore, it can not only solve the problem of the electron charge accumulation on microstrip but also leads to a bigger interaction impedance. According to particle-in-cell simulation results, a dual-sheet-beam planar dielectric-rod-support uniform metallic meander line TWT can get an output power of 330.2 W at 38 GHz under the case of 10.6 kV beam voltage and 0.2 A beam current. The corresponding maximum gain and electron efficiency are 23.4 dB and 15.5%, respectively, where the length of whole SWS is only 20 mm.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.5023776
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 1472746-8
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  • 4
    Online Resource
    Online Resource
    Zn vacancy induced room-temperature ferromagnetism in Mn-doped ZnO
    AIP Publishing ; 2007
    In:  Applied Physics Letters Vol. 91, No. 6 ( 2007-08-06)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 91, No. 6 ( 2007-08-06)
    Abstract: X-ray absorption fine structure (XAFS) and first-principles calculations were employed to study the structure and ferromagnetism origin of Zn0.97Mn0.03O thin film grown by metal organic chemical vapor deposition. The magnetization measurements indicate that this sample is ferromagnetic at room temperature. The Mn ions are located at the substitutional Zn sites as revealed by the Mn K-edge XAFS spectroscopy. Moreover, the O K-edge XAFS analysis indicated the existence of numerous Zn vacancies. Based on first-principles calculations, the authors propose that the Zn vacancy can induce the room-temperature ferromagnetism in Mn-doped ZnO.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.2769391
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2007
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 5
    Online Resource
    Online Resource
    Microscopic formation mechanism of Si/Tl5Al1/TiN ohmic contact on non-recessed i-InAlN/GaN heterostructures with ultra-low resistance
    AIP Publishing ; 2022
    In:  Applied Physics Letters Vol. 121, No. 21 ( 2022-11-21)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 121, No. 21 ( 2022-11-21)
    Abstract: In this work, we use Si/Tl5Al1/TiN for a source/drain ohmic contact to demonstrate an ultra-low contact resistance of 0.11 Ω mm (ρc = 2.62 × 10−7 Ω cm2) on non-recessed i-InAlN/GaN heterostructures. The Ti5Al1 alloy was used to suppress the out-diffusion of Al and extract N from the InAlN layer, which aided the formation of ohmic contact by improving the tunneling efficiency of electrons, as we have reported in the past work. A thin Si inter-layer combined with the Ti5Al1 alloy is proposed to further reduce contact resistance. A heavy n-type InAlN layer was obtained through doping with Si atoms to improve the tunneling transport of electrons. Furthermore, the TiN inclusions penetrated into the GaN channel because the in-diffused Si promoted the decomposition of GaN at a high annealing temperature and the in-diffused Ti reacted with GaN. These TiN inclusions provided direct contact with two-dimensional electron gas, offering an additional path for the injection of electrons into the channel. The tunneling and spike mechanism worked alternately to lower the contact resistance at different annealing temperatures (dividing at 900 °C), implying that the joint effect of tunneling and the spike mechanism was initially promoted in the formation of ohmic contact. The mechanism of this Si/Ti5Al1/TiN ohmic contact was fully understood through microscopic and thermodynamic analyses. These results shed light on the mechanism for the formation of ohmic contact in a gold-free metal stack for GaN-based HEMTs.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/5.0117205
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 6
    Online Resource
    Online Resource
    Baking and plasma pretreatment of sapphire surfaces as a way to facilitate the epitaxial plasma-enhanced atomic layer deposition of GaN thin films
    AIP Publishing ; 2020
    In:  Applied Physics Letters Vol. 116, No. 21 ( 2020-05-26)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 116, No. 21 ( 2020-05-26)
    Abstract: The growth of high-quality epitaxial gallium nitride (GaN) thin films is achieved by using a baking and plasma pretreatment of the substrate prior to the GaN plasma-enhanced atomic layer deposition (PE-ALD). It is found that such pretreatment makes the GaN films grow coherently on sapphire substrates, following a layer-by-layer growth mechanism. The deposited GaN film shows high crystalline quality, a sharp GaN/sapphire interface, and a flat surface. The possibility of growing high-quality GaN epilayers in this way broadens the range of applications for PE-ALD in GaN-based devices.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/5.0003021
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 7
    Online Resource
    Online Resource
    Ballistic transport in sub-10 nm monolayer planar GaN transistors for high-performance and low-power applications
    AIP Publishing ; 2021
    In:  Applied Physics Letters Vol. 119, No. 16 ( 2021-10-18)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 119, No. 16 ( 2021-10-18)
    Abstract: With the constant scaling down of transistors, “More Moore” has put forward requirements for channel materials. Two-dimensional materials are considered as potential next-generation channel materials due to their unique physical properties. Herein, we study the ballistic transport characteristics of sub-10 nm monolayer (ML) planar GaN metal–oxide–semiconductor field-effect transistors (MOSFETs) based on density functional theory and the non-equilibrium Green's function method. The calculation results indicate that n-type ML planar GaN MOSFETs with gate lengths not less than 5 nm exhibit excellent subthreshold characteristics, fast switching speeds, and low switching energies, and the corresponding parameters (off-current, on-current, delay time, and power-delay product) can simultaneously meet the requirements of the International Roadmap for Devices and Systems for the 2028 horizon for high-performance and low-power applications. Therefore, ML planar GaN is predicted to be a reliable next-generation channel material to extend Moore's law.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/5.0070904
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2021
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 8
    Online Resource
    Online Resource
    Size and kink effects on thermal conductivity in nickel nanowires
    AIP Publishing ; 2023
    In:  Applied Physics Letters Vol. 123, No. 8 ( 2023-08-21)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 123, No. 8 ( 2023-08-21)
    Abstract: The potential applications of nanowires in thermal management and thermoelectric energy conversion have sparked extensive research on thermal transport in various nanowires. Nickel nanowires, with their unique properties and promising applications, have been extensively studied. However, the influence of size, particularly the impact of kink structures, on the thermal transport behavior in nickel nanowires remains unclear. In this paper, we employed electron-beam lithography and liftoff techniques to fabricate suspended nickel nanowires with varying sizes and kinks to experimentally investigate the size and kink effect on the thermal conductivity. The experimental results revealed that the thermal transport behavior of nickel nanowires is significantly influenced by both size and kink effects. Notably, as the nanowire size decreases, the thermal conductivity also decreases. Furthermore, we discovered that the thermal conductivity can be adjusted by altering the number and angle of kinks. Increasing the number of kinks from 18 to 36 resulted in a significant decrease in thermal conductivity. In contrast, as the kink angle decreased from 157° to 90°, the thermal conductivity also decreased. However, intriguingly, when the kink angle was further decreased from 90° to 43°, the thermal conductivity increases. This non-monotonic change in thermal conductivity with the kink angle provides an interesting insight into the intricate behavior of heat carriers in kinked nickel nanowires. Additionally, we found that varying the alloy elements can profoundly alter the thermal conductivity of nanowires with kinks. These results offer valuable insights into the behaviors of heat carriers, including electrons and phonons, during heat transfer in nickel nanowires.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/5.0159583
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2023
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 9
    Online Resource
    Online Resource
    Comparative study on high-voltage safety performance of LiNixMnyCozO2 cathode with different nickel contents
    AIP Publishing ; 2022
    In:  Applied Physics Letters Vol. 121, No. 20 ( 2022-11-14)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 121, No. 20 ( 2022-11-14)
    Abstract: In this article, systematic comparison of the safety performance of LiNixMnyCozO2 is made to find a balance among nickel content, energy density, and thermal stability. Three kinds of LiNixMnyCozO2 cathodes with different nickel contents are charged to different cut-off voltages from 4.2 to 4.6 V (vs Li+/Li) to obtain different energy densities, and their safety is evaluated through differential scanning calorimetry. Different characteristic temperatures are proposed to describe the cathode safety comprehensively and a relationship between energy density and thermal stability is established. It is found that cathode with lower nickel content (LiNi0.5Mn0.3Co0.2O2 and LiNi0.6 Mn0.2Co0.2O2) charging to high voltage exhibits better thermal stability compared to high nickel cathode (LiNi0.8Mn0.1Co0.1O2) at a conventional voltage. Numerical simulation based on a lumped thermal model is also performed to predict the real thermal behaviors of batteries using different cathodes. The discussion of the impact of the cut-off voltage for NMC cathodes provides a new dimension to further improve the comprehensiveness of battery material safety database and a new viewpoint on the trade-off between cathode energy density and safety.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/5.0123625
    RVK:
    UA 1000
    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
    A new strategy for simultaneous photoluminescence and thermal energy storage/release: Microencapsulated phase change materials via nano-Y2O3 modified PW@CaCO3
    AIP Publishing ; 2023
    In:  Journal of Applied Physics Vol. 133, No. 4 ( 2023-01-28)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 133, No. 4 ( 2023-01-28)
    Abstract: A multifunctional microencapsulated phase change material (PW@CaCO3/Y2O3) with both photoluminescence and thermal energy storage/release properties has been prepared by in situ polymerization. The material is based on the phase change material paraffin wax (PW) as its core, and the highly thermally conductive inorganic material CaCO3 is selected as the shell material to which a nano-Y2O3 material is attached. Five samples with different amounts of nano-Y2O3 incorporated in the shell are prepared. The microscopic morphology, chemical composition, crystal structure, thermal energy storage properties, thermal conductivity, thermal stability, as well as fluorescence spectra and intensities of the samples are experimentally measured and compared. The luminescence properties of nano-Y2O3 and the light enhancement phenomenon of microencapsulated phase change materials are also analyzed. The thermal properties are investigated, and it is found that the PC-Y3 sample (i.e., the mass ratio of PW:CaCO3:nano-Y2O3 is 100:100:3.0) exhibits the best thermal performance among the five samples with a melting enthalpy of (87.5 ± 2.5)  J/g, an encapsulation efficiency of (61.9 ± 1.2)%, a thermal energy storage efficiency of (62.1 ± 1.5)%, an average specific heat capacity of (1.38 ± 0.21) kJ/(kg K) in solid phase (10–20 °C) and (1.46 ± 0.02) kJ/(kg K) in liquid phase (70–80 °C), and a thermal conductivity of (1.55 ± 0.01) W/(m K) in solid phase that is six times that of the solid PW. A study of the optical properties revealed that the microcapsules emitted blue light at an excitation wavelength of 290.0 ± 2.2 nm. The fluorescence intensity appeared to be enhanced with the addition of nano-Y2O3. This microencapsulated phase change material has potential applications in areas where synchronization of fluorescence and thermal modulation is required; for example, some specific fluorescent sensors that are very sensitive to heat should operate at a fixed low temperature.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/5.0127543
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2023
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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