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Nanocrystalline high-entropy hexaboride ceramics enable remarkable performance as thermionic emission cathodes

Fundamental Research 2023年第6期3卷 979-987页

作者： Mengdong Ma Xinyu Yang Hong Meng Zhisheng Zhao Julong He Yanhui Chu School of Materials Science and Engineering South China University of TechnologyGuangzhou 510641China Center for High Pressure Science(CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan UniversityQinhuangdao 066004China School of Materials Science and Engineering Hefei University of TechnologyHefei 230009China

The development of high-entropy borides with combined structural and functional performance holds untold scientific and technological potential,yet relevant studies have been rarely *** this work,we report nanocrystalline(La_(0.25)Ce_(0.25)Nd_(0.25)Eu_(0.25))B6 high-entropy rare-earth hexaboride(HEReB6-1)ceramics fabricated through the high-pressure sintering of self-synthesized nanopowders for the first *** as-fabricated samples exhibited a highly dense(96.3%)nanocrystalline(94 nm)microstructure with major(001)fiber textures and good grain boundaries without any impurities,resulting in a remarkable mechanical,electrical,and thermionic emission *** results showed that the samples possessed outstanding comprehensive mechanical properties and a high electrical resistivity from room temperature to high temperatures;these were greater than the average values of corresponding binary rare-earth hexaborides,such as a Vickers hardness of 23.4±0.6 GPa and a fracture toughness of 3.0±0.4 MPa•m^(1/2)at room *** importantly,they showed high emission current densities at elevated temperatures,which were higher than the average values of the corresponding binary rare-earth *** instance,the maximum emission current density reached 48.3 A•cm^(−2)at 1873 *** superior performance makes the nanocrystalline HEReB6-1 ceramics highly suitable for potential applications in thermionic emission cathodes.

关键词： High-entropy ceramics Hexaborides Nanocrystalline Mechanical properties thermionic emission

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thermionic electron emission in the 1D edge-to-edge limit

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Chinese Physics B 2022年第5期31卷 733-737页

作者：张桐耀王汉文夏秀鑫秦成兵李小茜 State Key Laboratory of Quantum Optics and Quantum Optics Devices Institute of Opto-ElectronicsShanxi UniversityTaiyuan 030006China Collaborative Innovation Center of Extreme Optics Shanxi UniversityTaiyuan 030006China Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China State Key Laboratory of Quantum Optics and Quantum Optics Devices Institute of Laser SpectroscopyShanxi UniversityTaiyuan 030006China

thermionic emission is a tunneling phenomenon,which depicts that electrons on the surface of a conductor can be pulled out into the vacuum when they are subjected to high electrical tensions while being heated hot enough to overtake their work *** principle has led to the great success of the so-called vacuum tubes in the early 20 th *** date,major challenges still remain in the miniaturization of a vacuum channel transistor for on-chip integration in modern solid-state integrated ***,by introducing nano-sized vacuum gaps(~200 nm)in a van der Waals heterostructure,we successfully fabricated a one-dimensional(1 D)edge-to-edge thermionic emission vacuum tube using graphene as the *** the increasing collector voltage,the emitted current exhibits a typical rectifying behavior,with the maximum emission current reaching 200 p A and an ON-OFF ratio of 10;.In addition,it is found that the maximum emission current is proportional to the number of the layers of *** results expand the research of nano-sized vacuum tubes to an unexplored physical limit of 1 D edge-to-edge emission,and hold great promise for future nano-electronic systems based on it.

关键词： vacuum microelectronics thermionic emission graphene electronic transport in nanoscale materials and structures

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Impact of exterior electron emission on the self-sustaining margin of hollow cathode discharge

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Plasma Science and Technology 2020年第9期22卷 2-11页

作者：孟天航宁中喜于达仁 Harbin Institute of Technology Harbin 150001.People's Republic of China

Hollow cathode researches used to focus on the inner cavity or downstream plume,however,rarely on the gap between the throttling orifice plate and the keeper plate(T-K gap),which was found to impact the self-sustaining margin of hollow cathode discharge in this *** the lower margin,the main power deposition and electron emission and ionization regions would migrate from inner cavity and downstream plume to the T-K gap,in which case,the source and destination of each m A current therein matter for the self-sustaining *** the metal surfaces in the T-K gap with emissive materials proved effective in lowering the lower margin by supplementing auxiliary thermionic emission,compensating electron loss on cold absorbing walls and suppressing discharge *** doing so,the lower margin of a 4 A hollow cathode was lowered from 1 to 0.1-0.2 A,enabling it to couple with low power Hall thruster without extra keeper current.

关键词： hollow cathode self-sustained discharge secondary electron emission ionization oscillations thermionic emission

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Effect of particle size on the polycrystalline CeB_6 cathode prepared by spark plasma sintering

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Journal of Rare Earths 2011年第6期29卷 580-584页

作者：包黎红张久兴周身林 Key Laboratory of Advanced Functional Materials Ministry of Education College of Materials Science and Engineering Beijing University of Technology

The full densification polycrystalline cerium hexaboride （CeB6） cathode material was prepared by using the spark plasma sintering （SPS） method in an oxygen free system. The starting precursor nanopowders with an average grain size of 50 nm were prepared by high-energy ball milling. The ball-milled nanopowder was fully densified at 1550 °C under 50 MPa, which was about 350 °C lower than the conventional hot-pressing method and it was also lower than that of coarse powder under the same sintering condition. The mechanical properties of nanopowder sintered samples were significantly better than that of coarse powder, e.g., the flexural strength and Vickers hardness were 211% and 51% higher than that of coarse powder, respectively. The electron backscattered diffraction （EBSD） result showed that the （100） fiber texture could be fabricated by the ball-milled nanopowder sintered at 1550 °C and the thermionic emission current density was measured to be 16.04 A/cm2 at a cathode temperature of 1873 K.

关键词： cerium hexaboride spark plasma sintering thermionic emission particle size rare earths

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Schottky Barrier Height Inhomogeneity of Ti／n—GaAs Contact Studied by the I—V—T Technique

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Chinese Physics Letters 2002年第4期19卷 553-556页

作者：蒋玉龙陆昉 DepartmentofMicroelectronics ASIC&SystemStateKeyLaboratoryFudanUniversityShanghai200433 StateKeyLaboratoryofAppliedSurfacePhysics FudanUniversityShanghai200433

The current-voltage characteristics of Ti/n-GaAs Schottky diodes measured over a temperature range of 78-299K have been interpreted on the basis of thermionic emission across an inhomogeneous Schottky contact. The experiment shows that the apparent barrier height (ap) increases from 0.437eV at 78K to 0.698eV at room temperature. The plot of ap versus 1/T does not exhibit a simple linear relationship over the whole temperature range, indicating that the barrier height distribution is more complicated than the frequently observed single Gaussian distribution. A new multi-Gaussian distribution model is developed. Our experimental results can be explained by a double Gaussian distribution of the barrier heights. The weight, the mean barrier height, and the standard deviation of the two Gaussian functions are 0.00001 and 0.99999, 0.721 and 0.696, 0.069 and 0.012eV, respectively.

关键词： thermionic emission

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La-Mo film cathode preparation and analysis in situ

La-Mo film cathode preparation and analysis in situ

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The 5th International Vacuum Electron Sources Conference(IVESC2004)

作者： Shiming Hao Zuoren Nie Jiancan Yang Yiman Wang Xiaoli Xi The Key Laboratory of Advanced Function Materials Ministry of Education School of Materials Science and Engineering Beijing University of Technology Beijing 100022 China

Lanthanum-containing cathodes are an attractive alternative to thorium tungsten cathodes because of their low work function and their comparatively low operating temperatures. The function of La element in La-Mo cathode material was studied by using a set of equipment specially designed to cathode research. A La-Mo film cathode was prepared with pulsed laser deposition （PLD） in diverse vacuum condition. For the first time, the electron emission properties have been measured without exposing to the atmosphere. By means of Auger electron spectroscopy, we investigated the surface composition of the cathode in situ. We find out obviously that the cathode emission properties have relation to the surface La/O ratio. As the La/O ratios get higher, the emission properties show better. The excess La element is contributed to thermionic emission. On the basis of experiment result, the emission mechanism of La-Mo cathode has been discussed.

关键词： thermionic emission pulsed laser deposition cathode surface

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Function of Oxygen in Mo-La2O3 Cathode

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Journal of Rare Earths 2006年第4期24卷 446-446页

作者： Hao Shiming Nie Zuoren College of Sciences Henan University of Science and TechnologyLuoyang 471003 China College of Material Science and Engineering Beijing University of Technology Beijing 100022 China

Different atomic ratio La/O film cathodes were prepared by pulsed laser deposition under various vacuum conditions. The emission properties were measured and their surface composition was investigated with in situ AES analyses. The function of oxygen in thermoionic emission of Mo-La2O3 cathode was investigated. Excess oxygen is negative to electron emission because lanthanum is easy to become stable La2O3, but proper proportion oxygen can weaken the evaporation of lanthanum and conduce to cathodes＇ stable work. The formation of oxygen vacancies enhances semiconductor property of La-O compound and improves greatly the performance of cathodes.

关键词： thermionic emission cathode oxygen vacancies rare earths

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