The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform
Shao Zhi Deng - One of the best experts on this subject based on the ideXlab platform.
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Electron emission and structure stability of carbon nanotube Cold Cathode driven by millisecond pulsed voltage
Vacuum, 2020Co-Authors: Yu Zhang, Jun Chen, Yuanming Tan, Lizhou Wang, Meixiang Liao, Shao Zhi DengAbstract:Abstract The carbon nanotube (CNT) Cold Cathode can provide a high current and current density for microwave devices, which normally work under pulse mode. In this work, we studied the electron emission characteristics and strucutre stability of a CNT Cold Cathode in millisecond pulse mode. Peak current and average current are both key parameters for the performance of Cold Cathode. Increasing the duty ratio proved an effective way to increase the average current and average power of the Cold Cathode. The pulsing field emission characteristics of CNT Cold Cathode was optimized by modulating the pulse width, pulse interval time, and duty ratio. The average current in millisecond pulse mode was three orders of magnitude greater than that when using microsecond pulses. The average current also linearly increased with the duty ratio. The morphology of CNT films after pulsing and DC field emission was investigated to reveal the stability and the vacuum breakdown mechanism. The thermal equilibrium of the CNT was analyzed to reveal its underlying mechanism. This work provides a practical strategy for the application of CNT Cold Cathodes in high-power microwave devices.
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design and realization of microwave frequency multiplier based on field emission from carbon nanotubes Cold Cathode
IEEE Transactions on Electron Devices, 2018Co-Authors: Yang Xing, Jun Chen, Yu Zhang, Juncong She, Haijie Huang, Shao Zhi DengAbstract:This paper reports for the first time the theoretical analysis, design, and realization of a microwave (MW) frequency multiplier based on a field emission from carbon nanotube (CNT) Cold-Cathode. The nonlinear characteristic of field emission from CNT Cold-Cathode is utilized for generating field emission current with the harmonics of input signal and achieving frequency multiplication. We demonstrated both theoretically and experimentally that an MW electric field is capable of inducting current with harmonics from CNT Cold-Cathode and that a direct-current (dc) electric field can effectively increase the amplitudes of the harmonics. A reentrant resonant cavity structure was designed and fabricated to deliver the desired combined MW and dc electric fields onto CNT Cold-Cathode and realize the MW frequency multiplier. The device has the target second harmonic at a frequency of 1.868 GHz and a third harmonic at 2.802 GHz with a driving signal at frequency of 0.934 GHz. By simply increasing dc bias, a 12.43-dB increase of the amplitude of target second harmonic is successfully obtained. With such a device, directly modulated electron beam with MW frequency harmonics is obtained. Both the principle and the design can find applications in frequency tunable vacuum electron devices.
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Low‐Temperature Fabrication of Cold Cathode WO2 Nanowire Arrays on Glass Substrate and Improvement of their Working Performance
Advanced materials and technologies, 2017Co-Authors: Yan Tian, Jun Chen, Xun Yang, Tongyi Guo, Luxi Peng, Haibo Gan, Huanjun Chen, Fei Liu, Shao Zhi DengAbstract:WO2 nanowires have great potential as Cold Cathode materials because they exhibit excellent field-emission properties in terms of their low work function and high conductivity. Considering the requirements of the practical applications in large-area Cold-Cathode devices, such as X-ray source and panel display, these nanostructures are desired to be fabricated on glass substrate and integrated into devices. It is best known that the studies on WO2 nanowire Cold Cathode arrays grown on glass-substrate are absent so far, which remains a challenge for the researchers. In the current study, procedures for fabrication of WO2 nanowire Cold Cathode arrays, which consist of 22000 separated patterns on 1.2 in. glass wafer are developed. It is found that the turn-on and threshold field of the nanowire arrays are, respectively, 6.6 and 9.3 V µm−1. In addition, the performance of the Cold Cathode arrays is strongly affected by the distribution of the nanowire density as well as the thickness of Al electrode. By modifying the fabrication techniques, over 82% patterns can contribute to the emission, whereby a maximum current density can reach 1.89 mA cm−2. Such a value can fulfill the basic requirement of the large-area Cold Cathode devices. The research can pave the way for fabrication of high-performance Cold Cathode devices using glass-substrates.
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A truncated-cone carbon nanotube Cold-Cathode electron gun
Carbon, 2017Co-Authors: Xuesong Yuan, Richard Parmee, Ning Sheng Xu, William I. Milne, Xiaoyun Li, Jianqiang Wu, Matthew T Cole, Yang Yan, Yu Zhang, Shao Zhi DengAbstract:A concurrently high beam current and high current density carbon nanotube (CNT) Cold Cathode electron gun is herein developed. A radial electron source has been realized, formed from CNTs synthesized directly on the side walls of a stainless steel truncated-cone electron gun. Experimental results evidenced a 35 kV/50 mA electron beam can achieve a beam transparency of nearly 100% through the use of double anodes and crossed electric and magnetic fields. A maximum beam current density of 3.5 A/cm2was achieved. These results demonstrate the potential impact of coupling novel Cold Cathode gun architectures and emerging nanomaterials and their collective role in augmenting the performance of incumbent electron gun technologies, alongside allowing for the realization new types of field emission vacuum electron radiation sources.
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A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron
Scientific Reports, 2016Co-Authors: Xuesong Yuan, Yang Yan, Jun Chen, Yu Zhang, Weiwei Zhu, Yan Shen, Juncong She, Shao Zhi DengAbstract:Gigahertz to terahertz radiation sources based on Cold-Cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) Cold-Cathode. It is reported here in first time that a fully-sealed CNT Cold-Cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT Cold-Cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT Cold-Cathode electron gun.
Yu Zhang - One of the best experts on this subject based on the ideXlab platform.
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Electron emission and structure stability of carbon nanotube Cold Cathode driven by millisecond pulsed voltage
Vacuum, 2020Co-Authors: Yu Zhang, Jun Chen, Yuanming Tan, Lizhou Wang, Meixiang Liao, Shao Zhi DengAbstract:Abstract The carbon nanotube (CNT) Cold Cathode can provide a high current and current density for microwave devices, which normally work under pulse mode. In this work, we studied the electron emission characteristics and strucutre stability of a CNT Cold Cathode in millisecond pulse mode. Peak current and average current are both key parameters for the performance of Cold Cathode. Increasing the duty ratio proved an effective way to increase the average current and average power of the Cold Cathode. The pulsing field emission characteristics of CNT Cold Cathode was optimized by modulating the pulse width, pulse interval time, and duty ratio. The average current in millisecond pulse mode was three orders of magnitude greater than that when using microsecond pulses. The average current also linearly increased with the duty ratio. The morphology of CNT films after pulsing and DC field emission was investigated to reveal the stability and the vacuum breakdown mechanism. The thermal equilibrium of the CNT was analyzed to reveal its underlying mechanism. This work provides a practical strategy for the application of CNT Cold Cathodes in high-power microwave devices.
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Theoretical Research on 300GHz Carbon Nanotube Cold Cathode Gyrotron
2019 44th International Conference on Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2019Co-Authors: Lulu Shao, Xuesong Yuan, Weifeng Li, Bin Wang, Yu Zhang, Hailong LiAbstract:In order to develop the terahertz vacuum electronic radiation source devices with field emission Cold Cathodes, a 300GHz carbon nanotube (CNT) Cold Cathode gyrotron is investigated in this paper. The electron gun is designed by particle-in-cell (PIC) simulation software. A magnetic injection CNT Cold Cathode electron gun with 35kV/200mA is developed. Electron gun simulation results show that the velocity ratio of electron beam is 1.3, the average beam radius in the cavity is 0.845 mm. The spread of perpendicular and parallel velocities are 3% and 4.5%, respectively. Results of beam-wave interaction simulation show that the TE03 mode at the frequency of 301 GHz is oscillated. An output power of 450 W is obtained.
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design and realization of microwave frequency multiplier based on field emission from carbon nanotubes Cold Cathode
IEEE Transactions on Electron Devices, 2018Co-Authors: Yang Xing, Jun Chen, Yu Zhang, Juncong She, Haijie Huang, Shao Zhi DengAbstract:This paper reports for the first time the theoretical analysis, design, and realization of a microwave (MW) frequency multiplier based on a field emission from carbon nanotube (CNT) Cold-Cathode. The nonlinear characteristic of field emission from CNT Cold-Cathode is utilized for generating field emission current with the harmonics of input signal and achieving frequency multiplication. We demonstrated both theoretically and experimentally that an MW electric field is capable of inducting current with harmonics from CNT Cold-Cathode and that a direct-current (dc) electric field can effectively increase the amplitudes of the harmonics. A reentrant resonant cavity structure was designed and fabricated to deliver the desired combined MW and dc electric fields onto CNT Cold-Cathode and realize the MW frequency multiplier. The device has the target second harmonic at a frequency of 1.868 GHz and a third harmonic at 2.802 GHz with a driving signal at frequency of 0.934 GHz. By simply increasing dc bias, a 12.43-dB increase of the amplitude of target second harmonic is successfully obtained. With such a device, directly modulated electron beam with MW frequency harmonics is obtained. Both the principle and the design can find applications in frequency tunable vacuum electron devices.
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Theoretical Study of a 0.22 THz Backward Wave Oscillator Based on a Dual-Gridded, Carbon-Nanotube Cold Cathode
MDPI AG, 2018Co-Authors: Qingyun Chen, Xuesong Yuan, Matthew T Cole, Yu Zhang, Lin Meng, Yang YanAbstract:The carbon nanotube (CNT) Cold Cathode is an attractive choice for millimeter and terahertz vacuum electronic devices owning to its unique instant switch-on and high emission current density. A novel, dual-gridded, field emission architecture based on a CNT Cold Cathode is proposed here. CNTs are synthesized directly on the Cathode surface. The first separating grid is attached to the CNT Cathode surface to shape the CNT Cathode array. The second separating grid is responsible for controlled extraction of electrons from the CNT emitters. The Cathode surface electric field distribution has been improved drastically compared to conventional planar devices. Furthermore, a high-compression-ratio, dual-gridded, CNT-based electron gun has been designed to further increase the current density, and a 21 kV/50 mA electron beam has been obtained with beam transparency of nearly 100%, along with a compression ratio of 39. A 0.22 THz disk-loaded waveguide backward wave oscillator (BWO) based on this electron gun architecture has been realized theoretically with output power of 32 W. The results indicate that higher output power and higher frequency terahertz BWOs can be made using advanced, nanomaterial-based Cold Cathodes
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parametrically optimized carbon nanotube coated Cold Cathode spindt arrays
Nanomaterials, 2017Co-Authors: Xuesong Yuan, Matthew T Cole, Yu Zhang, W I Milne, Yang YanAbstract:Here, we investigate, through parametrically optimized macroscale simulations, the field electron emission from arrays of carbon nanotube (CNT)-coated Spindts towards the development of an emerging class of novel vacuum electron devices. The present study builds on empirical data gleaned from our recent experimental findings on the room temperature electron emission from large area CNT electron sources. We determine the field emission current of the present microstructures directly using particle in cell (PIC) software and present a new CNT Cold Cathode array variant which has been geometrically optimized to provide maximal emission current density, with current densities of up to 11.5 A/cm2 at low operational electric fields of 5.0 V/μm.
Charles A. Spindt - One of the best experts on this subject based on the ideXlab platform.
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Cold Cathode Based Microwave Devices for Current and Future Systems
2018 31st International Vacuum Nanoelectronics Conference (IVNC), 2018Co-Authors: David R. Whaley, Christopher E. Holland, Charles A. Spindt, Carter M. Armstrong, Paul R. SchwoebelAbstract:We report ongoing efforts to achieve reliable field emitter (FE) Cathode operation for high current electron beam generation in RF microwave devices. These efforts include testing of Cold Cathode traveling wave tubes, high average power Cathodeonly testing, and evaluating Cathode emission variation over long operating periods in a microwave device vacuum environment. Finally, looking toward future needs, emittance reduction is being addressed to allow Cold Cathode operation in the mm-wave frequency regime.
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100 W operation of a Cold Cathode TWT
IEEE Transactions on Electron Devices, 2009Co-Authors: David R. Whaley, Colby L. Bellew, Christopher E. Holland, Carter M. Armstrong, Ramon Duggal, Charles A. SpindtAbstract:Recent demonstration of low-voltage high- transconductance field emitter array operation holds promise for the successful development of reliable Cold Cathode vacuum electronics device technologies. This paper reports on the experimental studies of implementation of such field emitter arrays as the electron source for a moderate power traveling wave tube (TWT) operating in the C-band frequency regime. The Cold Cathode TWT has operated for over 150 h at duty factors up to 10%, beam currents up to 121 mA, and RF powers up to 100 W at 5 GHz. High Cathode current densities of 15.4 A/cm2 were achieved concurrent with excellent beam control, resulting in 99.4% beam transmission under zero-RF-drive operating conditions and 97.3% transmission at maximum RF output power. The Cathode is shown to operate with a 72% reduction in the operating voltage from the previous generation of emitters fabricated by SRI International, bringing the operating voltage for full current operation well below 100 V. Extensive device characterization and life testing has been performed, and inter- esting variation in Cathode performance was observed during the high-duty high-current portion of the testing program. The results presented here represent the highest current, highest power, and highest duty factor ever reported for an RF vacuum device employing a field emission Cold Cathode electron source.
Yang Yan - One of the best experts on this subject based on the ideXlab platform.
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Simulation Study of Compact Carbon Nanotube Cold-Cathode Oscillator
2019 International Vacuum Electronics Conference (IVEC), 2019Co-Authors: Xuesong Yuan, Bin Wang, Qingyun Chen, Yang YanAbstract:A compact carbon nanotube Cold-Cathode oscillator operating at terahertz band is designed by PIC simulation software in this paper. The Cathode part is integrated with the high frequency structure. The field emission beam of the Cold Cathode is modulated by the high frequency field in the high frequency structure directly. The simulation results show that a peak output power of 3.4W is obtained at 140GHz, and the emission current modulation depth is 7.7% when the surface electric field strength of the Cathode is $\pmb{12}\mathbf{V}/\pmb{\mu}\mathbf{m}$ .
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Theoretical Study of a 0.22 THz Backward Wave Oscillator Based on a Dual-Gridded, Carbon-Nanotube Cold Cathode
MDPI AG, 2018Co-Authors: Qingyun Chen, Xuesong Yuan, Matthew T Cole, Yu Zhang, Lin Meng, Yang YanAbstract:The carbon nanotube (CNT) Cold Cathode is an attractive choice for millimeter and terahertz vacuum electronic devices owning to its unique instant switch-on and high emission current density. A novel, dual-gridded, field emission architecture based on a CNT Cold Cathode is proposed here. CNTs are synthesized directly on the Cathode surface. The first separating grid is attached to the CNT Cathode surface to shape the CNT Cathode array. The second separating grid is responsible for controlled extraction of electrons from the CNT emitters. The Cathode surface electric field distribution has been improved drastically compared to conventional planar devices. Furthermore, a high-compression-ratio, dual-gridded, CNT-based electron gun has been designed to further increase the current density, and a 21 kV/50 mA electron beam has been obtained with beam transparency of nearly 100%, along with a compression ratio of 39. A 0.22 THz disk-loaded waveguide backward wave oscillator (BWO) based on this electron gun architecture has been realized theoretically with output power of 32 W. The results indicate that higher output power and higher frequency terahertz BWOs can be made using advanced, nanomaterial-based Cold Cathodes
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parametrically optimized carbon nanotube coated Cold Cathode spindt arrays
Nanomaterials, 2017Co-Authors: Xuesong Yuan, Matthew T Cole, Yu Zhang, W I Milne, Yang YanAbstract:Here, we investigate, through parametrically optimized macroscale simulations, the field electron emission from arrays of carbon nanotube (CNT)-coated Spindts towards the development of an emerging class of novel vacuum electron devices. The present study builds on empirical data gleaned from our recent experimental findings on the room temperature electron emission from large area CNT electron sources. We determine the field emission current of the present microstructures directly using particle in cell (PIC) software and present a new CNT Cold Cathode array variant which has been geometrically optimized to provide maximal emission current density, with current densities of up to 11.5 A/cm2 at low operational electric fields of 5.0 V/μm.
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A truncated-cone carbon nanotube Cold-Cathode electron gun
Carbon, 2017Co-Authors: Xuesong Yuan, Richard Parmee, Ning Sheng Xu, William I. Milne, Xiaoyun Li, Jianqiang Wu, Matthew T Cole, Yang Yan, Yu Zhang, Shao Zhi DengAbstract:A concurrently high beam current and high current density carbon nanotube (CNT) Cold Cathode electron gun is herein developed. A radial electron source has been realized, formed from CNTs synthesized directly on the side walls of a stainless steel truncated-cone electron gun. Experimental results evidenced a 35 kV/50 mA electron beam can achieve a beam transparency of nearly 100% through the use of double anodes and crossed electric and magnetic fields. A maximum beam current density of 3.5 A/cm2was achieved. These results demonstrate the potential impact of coupling novel Cold Cathode gun architectures and emerging nanomaterials and their collective role in augmenting the performance of incumbent electron gun technologies, alongside allowing for the realization new types of field emission vacuum electron radiation sources.
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A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron
Scientific Reports, 2016Co-Authors: Xuesong Yuan, Yang Yan, Jun Chen, Yu Zhang, Weiwei Zhu, Yan Shen, Juncong She, Shao Zhi DengAbstract:Gigahertz to terahertz radiation sources based on Cold-Cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) Cold-Cathode. It is reported here in first time that a fully-sealed CNT Cold-Cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT Cold-Cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT Cold-Cathode electron gun.
Xuesong Yuan - One of the best experts on this subject based on the ideXlab platform.
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Simulation Study of Compact Carbon Nanotube Cold-Cathode Oscillator
2019 International Vacuum Electronics Conference (IVEC), 2019Co-Authors: Xuesong Yuan, Bin Wang, Qingyun Chen, Yang YanAbstract:A compact carbon nanotube Cold-Cathode oscillator operating at terahertz band is designed by PIC simulation software in this paper. The Cathode part is integrated with the high frequency structure. The field emission beam of the Cold Cathode is modulated by the high frequency field in the high frequency structure directly. The simulation results show that a peak output power of 3.4W is obtained at 140GHz, and the emission current modulation depth is 7.7% when the surface electric field strength of the Cathode is $\pmb{12}\mathbf{V}/\pmb{\mu}\mathbf{m}$ .
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Theoretical Research on 300GHz Carbon Nanotube Cold Cathode Gyrotron
2019 44th International Conference on Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2019Co-Authors: Lulu Shao, Xuesong Yuan, Weifeng Li, Bin Wang, Yu Zhang, Hailong LiAbstract:In order to develop the terahertz vacuum electronic radiation source devices with field emission Cold Cathodes, a 300GHz carbon nanotube (CNT) Cold Cathode gyrotron is investigated in this paper. The electron gun is designed by particle-in-cell (PIC) simulation software. A magnetic injection CNT Cold Cathode electron gun with 35kV/200mA is developed. Electron gun simulation results show that the velocity ratio of electron beam is 1.3, the average beam radius in the cavity is 0.845 mm. The spread of perpendicular and parallel velocities are 3% and 4.5%, respectively. Results of beam-wave interaction simulation show that the TE03 mode at the frequency of 301 GHz is oscillated. An output power of 450 W is obtained.
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Theoretical Study of a 0.22 THz Backward Wave Oscillator Based on a Dual-Gridded, Carbon-Nanotube Cold Cathode
MDPI AG, 2018Co-Authors: Qingyun Chen, Xuesong Yuan, Matthew T Cole, Yu Zhang, Lin Meng, Yang YanAbstract:The carbon nanotube (CNT) Cold Cathode is an attractive choice for millimeter and terahertz vacuum electronic devices owning to its unique instant switch-on and high emission current density. A novel, dual-gridded, field emission architecture based on a CNT Cold Cathode is proposed here. CNTs are synthesized directly on the Cathode surface. The first separating grid is attached to the CNT Cathode surface to shape the CNT Cathode array. The second separating grid is responsible for controlled extraction of electrons from the CNT emitters. The Cathode surface electric field distribution has been improved drastically compared to conventional planar devices. Furthermore, a high-compression-ratio, dual-gridded, CNT-based electron gun has been designed to further increase the current density, and a 21 kV/50 mA electron beam has been obtained with beam transparency of nearly 100%, along with a compression ratio of 39. A 0.22 THz disk-loaded waveguide backward wave oscillator (BWO) based on this electron gun architecture has been realized theoretically with output power of 32 W. The results indicate that higher output power and higher frequency terahertz BWOs can be made using advanced, nanomaterial-based Cold Cathodes
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parametrically optimized carbon nanotube coated Cold Cathode spindt arrays
Nanomaterials, 2017Co-Authors: Xuesong Yuan, Matthew T Cole, Yu Zhang, W I Milne, Yang YanAbstract:Here, we investigate, through parametrically optimized macroscale simulations, the field electron emission from arrays of carbon nanotube (CNT)-coated Spindts towards the development of an emerging class of novel vacuum electron devices. The present study builds on empirical data gleaned from our recent experimental findings on the room temperature electron emission from large area CNT electron sources. We determine the field emission current of the present microstructures directly using particle in cell (PIC) software and present a new CNT Cold Cathode array variant which has been geometrically optimized to provide maximal emission current density, with current densities of up to 11.5 A/cm2 at low operational electric fields of 5.0 V/μm.
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A truncated-cone carbon nanotube Cold-Cathode electron gun
Carbon, 2017Co-Authors: Xuesong Yuan, Richard Parmee, Ning Sheng Xu, William I. Milne, Xiaoyun Li, Jianqiang Wu, Matthew T Cole, Yang Yan, Yu Zhang, Shao Zhi DengAbstract:A concurrently high beam current and high current density carbon nanotube (CNT) Cold Cathode electron gun is herein developed. A radial electron source has been realized, formed from CNTs synthesized directly on the side walls of a stainless steel truncated-cone electron gun. Experimental results evidenced a 35 kV/50 mA electron beam can achieve a beam transparency of nearly 100% through the use of double anodes and crossed electric and magnetic fields. A maximum beam current density of 3.5 A/cm2was achieved. These results demonstrate the potential impact of coupling novel Cold Cathode gun architectures and emerging nanomaterials and their collective role in augmenting the performance of incumbent electron gun technologies, alongside allowing for the realization new types of field emission vacuum electron radiation sources.