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Heating graphene to incandescence and the measurement of its work function by the thermionic emission method

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Nano Research 2014年第4期7卷 553-560页

作者： Feng Zhu State Key Laboratory of Low-Dimensional Quantum Physics Department of Physics and Tsinghua-Foxconn Nanotechnology Research Center Tsinghua University Beijing 100084 China Collaborative Innovation Center of Quanturn Matter Beijing 100084 China

The work function （WF） of graphene is an essential parameter in graphene electronics. We have derived the WF of graphene by the thermionic emission method. Chemical vapor deposition （CVD）-grown single-layered polycrystalline graphene on copper foil is transferred to a cross-stacked carbon nanotube （CNT） film drawn from a super-aligned multiwalled CNT array. By decreasing the pore size of the CNT film, the as-prepared CNT-graphene film （CGF） can be Joule heated to a temperature as high as 1,800 K in vacuum without obvious destruction in the graphene structure. By studying the thermionic emission, we derive the WF of graphene, ranging from 4.7 to 4.8 eV with the average value being 4.74 eV. Because the substrate influence can be minimized by virtue of the porous nature of the CNT film and the influence of adsorbents can be excluded due to the high temperature during the thermionic emission, the measured WF of graphene can be regarded as intrinsic.

关键词： graphene carbon nanotube thermionic emission work function

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

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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

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： Tongyao Zhang Hanwen Wang Xiuxin Xia Chengbing Qin Xiaoxi Li 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

Ultralow Ohmic Contact in Recess-Free Ultrathin Barrier AlGaN/GaN Heterostructures Across a Wide Temperature Range

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Chinese Journal of Electronics 2025年第1期34卷 137-145页

作者： Yuhao Wang Sen Huang Qimeng Jiang Xinhua Wang Jie Fan Haibo Yin Ke Wei Yingkui Zheng Xinyu Liu Key Laboratory of Microelectronic Devices & Integrated Technology Institute of Microelectronics of the Chinese Academy of Sciences Institute of Microelectronics University of Chinese Academy of Sciences

“Ohmic-before-passivation” process was implemented on ultrathin-barrier AlGaN（<6 nm）/GaN heterostructure to further reduce the ohmic contact resistance（Rc）. In this process, alloyed Ti/Al/Ni/Au ohmic metal was f... 详细信息

“Ohmic-before-passivation” process was implemented on ultrathin-barrier AlGaN（thermionic field emission above 200 K and by field emission below 200 K. The “ohmic-before-passivation” process enables the relative stability of ohmic contacts between 50 K and 475 K and significantly improves the direct current characteristics of GaN-metal-insulator-semiconductor-high electron mobility transistor, offering a promising means for scaling down and enabling the utilization of low-voltage GaN-based power devices in extreme environmental conditions.

关键词： Resistance Low voltage thermionic emission HEMTs Ohmic contacts Wide band gap semiconductors Transistors MODFETs Aluminum gallium nitride Thermal stability

Delayed Ionization and Delayed Detachment in Molecules and Clusters

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Chinese Journal of Chemical Physics 2009年第2期22卷 162-170页

作者： F. Lépine B. Baguenard B. Concina M. A. Lebeault C. Bordas Université de Lyon F-69522 Lyon France Université Lyon 1 Villeurbanne CNRS UMR 5579 LASIM

The evolution of a molecular system excited above its ionization threshold depends on a number of parameters that include the nature of the excited states and their couplings to the various continua. The general nature of the processes governing this evolution depends also essentially on the complexity of the molecule, more precisely on its size, density of states, and strength of the couplings among the various internal degrees of freedom. In this paper we address the question of the transition between autoionization that prevails in small molecules, and delayed ionization occurring in larger molecules or clusters. This transition is illustrated by autoionization of Na2 Rydberg states on one hand, delayed ionization in fullerene C60, and delayed detachment in small cluster anions on the other hand. All processes are studied in the case of nanosecond laser excitation, corresponding to a rather slow deposition of the internal energy.

关键词： Autoionization Autodetachment thermionic emission

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： Tianhang MENG Zhongxi NING Daren YU 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

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

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 78-299 K have been interpreted on the basis of thermionic emission across an inhomogeneous Schottky contact. The experiment shows that the apparent barrier height (φap) increases from 0.437 eV at 78 K to 0.698 eV at room temperature. The plot of φap 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 0.012 eV, respectively.

关键词： thermionic emission

Forward Current Transport Mechanisms of Ni/Au-InAlN/AlN/GaN Schottky Diodes

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Chinese Physics Letters 2014年第5期31卷 140-143页

作者：王晓风邵振广陈敦军陆海张荣郑有炓 Key Laboratory of Advanced Photonic and Electronic Materials School of Electronic Science and Engineering Nanjing University Nanjing 210093

We fabricate two Ni/Au-In0.17 Al0.83N/AlN/GaN Schottky diodes on substrates of sapphire and Si, respectively, and investigate their forward-bias current transport mechanisms by temperature-dependent current-voltage mea- surements. In the temperature range of 300-485K, the Schottky barrier heights （SBHs） calculated by using the conventional thermionic-emission （TE） model are strongly positively dependent on temperature, which is in contrast to the negative-temperature-dependent characteristic of traditional semiconductor Schottky diodes. By fitting the forward-bias I V characteristics using different current transport models, we find that the tunneling current model can describe generally the I V 5ehaviors in the entire measured range of temperature. Under the, high forward bias, the traditional TE mechanism also gives a good fit to the measured I-V data, and the actual barrier heights calculated according to the fitting TE curve are 1.434 and 1.413eV at 300K for InAlN/AlN/GaN Schottky diodes on Si and the sapphire substrate, respectively, and the barrier height shows a slightly negative temperature coefficient. In addition, a formula is given to estimate SBHs of Ni/Au-InAlN/AlN/GaN Schottky diodes taking the Fermi-level pinning effect into account.

关键词： SCHOTTKY-barrier diodes SCHOTTKY barrier thermionic emission FERMI level ELECTRON mobility DISLOCATION density