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The Role of Secondary Electron Emission in the Charging of Thin-Film Phase Plates
摘要： In the past few years, physical phase plates (PP) have become a viable tool to enhance the contrast of weak-phase objects in transmission electron microscopy (TEM). Thin-film PPs, such as the Zernike and Hilbert PP, are based on the mean inner potential of microstructured thin films [1,2]. Typically, a thin amorphous carbon (aC)-film is applied, whose thickness is adjusted to induce a well-defined phase shift between unscattered and scattered electrons. However, the illumination with high-energy electrons initiates an irreversible degeneration of the aC-film, which causes electrostatic charging and affects the phase-shifting properties. Taking even advantage of charging, hole-free PPs were recently developed [3,4]. Electrostatic charging plays a central role in the application of thin-film PPs. However, the mechanisms of charging are not well-understood. This work shows that charging is dominated by secondary electron emission. For this purpose, Hilbert PPs were fabricated from different materials to study their charging behavior under electron beam illumination. Besides aC-films, thin films of the metallic glass alloy Pd77.5Cu6.0Si16.5 (PCS) were used for PP fabrication. The PCS-alloy is characterized by an amorphous structure and a high electrical conductivity, which is three orders of magnitude higher than that of aC [5,6]. Moreover, the PCS-alloy exhibits a strong resistance towards oxidation, which suggests less charging of PCS-films.
关键词： transmission electron microscopy,thin-film,secondary electron emission,charging,phase plates
更新于2025-11-21 11:20:48
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Direct patterned growth of intrinsic/doped vertical graphene nanosheets on stainless steel via heating solid precursor films for field emission application
摘要： Vertical graphene nanosheets (VGNs), normally consisting of one to several graphene layers vertically aligned on substrates, are promising in a variety of applications including field electron emitters, gas sensors and energy storage devices. Herein, we report a simple, green, easily scalable and cost-effective strategy of growing both intrinsic and nitrogen (N)-doped VGNs on stainless steel (SS) just by heating the solid thin layers of glucose and/or urea in a resistance-heating furnace. It is interesting that VGNs mainly grow on the roughened regions, which can be attributed to the more nucleation and catalyzing sites on such regions than smooth SS. Meanwhile, the N doping concentration can be adjusted by varying the urea addition. Field electron emission measurement indicates that the obtained N-doped VGNs exhibit excellent field emission with a relatively low turn-on electric field strength (~2.6 V μm?1 at the current density of 10 μA cm?2), large field enhancement factor (~9428) and high stability.
关键词： Green synthesis,Nitrogen doping,Vertical graphene nanosheets,Field electron emission,Direct patterned growth
更新于2025-09-23 15:23:52
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Fabrication of Stable Carbon Nanotube Cold Cathode Electron Emitters with Post-Growth Electrical Aging
摘要： We fabricated carbon nanotube (CNT) cold cathode emitters with enhanced and stable electron emission properties and long-time stability with electrical aging as a post-treatment. Our CNT field emitters showed improved electrical properties by electrical aging. We set the applied bias for effective electrical aging, with the bias voltage defined at the voltage where Joule heating appeared. At the initial stage of aging, the electron emission current started to increase and then was saturated within 3 h. We understood that 5 h aging time was enough at proper aging bias. If the aging bias is higher, excessive heating damages CNT emitters. With the electrical aging, we obtained improved electron emission current from 3 mA to 6 mA. The current of 6 mA was steadily driven for 9 h.
关键词： carbon nanotube,electrical aging,electron emission,Joule heating,field emitters
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Hangzhou, China (2018.8.13-2018.8.17)] 2018 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Nanofabrication Techniques Used for Suppressing Multipactor in Space Applications
摘要： A significant trouble in high power microwave (HPM) systems is multipactor discharge – an avalanche of electrons resulting from the secondary electron emission (SEE). It would cause serious problems and limits the attainable power. Nano fabrication techniques, such as sputtering, photolithography, etching and Graphene, are adopted to reduce the secondary electron yield (SEY) of a material to improve multipactor discharge threshold. It is clearly demonstrated that these fabrications can suppress the SEY efficiently. The influence of surface characteristic on SEY is discussed to find that increase porosity and aspect ratio will reduce SEY. These results provided a criterion to determine nanofabrication techniques for multipactor suppression.
关键词： nanofabrication techniques,secondary electron emission,suppression,multipactor
更新于2025-09-23 15:23:52
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Exact Evaluation of K. Jensen's General Thermal-Field-Photoemission Integral
摘要： Jensen has developed a general expression for the current density JGT F emitted from a surface by thermal or field emission, or by a combination of these processes; he has also shown how the same expression may be analytically extended to compute the current density due to photoemission. JGT F is expressed as a single integral, which Jensen evaluates analytically in certain limits and numerically outside those limits. In this paper, we show how the integral may be expressed generally as convergent series that are easily evaluated numerically for all values of the physical parameters. No real or apparent singularities, like those that appear in the function Z defined by Jensen occur in the series obtained here.
关键词： photoemission,field emission,thermal emission,Electron emission
更新于2025-09-23 15:22:29
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[IEEE 2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV) - Greifswald (2018.9.23-2018.9.28)] 2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV) - Improved Surface Flashover Characteristics of Ceramic Vacuum Interface by Surface Treatment
摘要： In this paper, influences of surface Cr2O3 coating treatment on ceramic vacuum interface under a long pulse-duration voltage are reported. The surface properties of the treated ceramics have been measured by SEM, LSCM and XRD methods. Compared with the original untreated ceramics, the treated ceramic has a smoother surface, a lower SEE coefficient and a lower surface resistivity. As a result, a higher surface flashover voltage has been obtained. The surface treatment is an easy and convenient method to improve surface flashover characteristics of ceramic vacuum interface under a long pulse-duration high voltage.
关键词： surface treatment,ceramic vacuum interface,surface flashover,secondary electron emission,Cr2O3 coating
更新于2025-09-23 15:22:29
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Electron emission and ultraviolet electroluminescence from valence-band states and defect conduction bands of electroformed Al-Al <sub/>2</sub> O <sub/>3</sub> -Ag diodes
摘要： Electroforming of metal-insulator-metal (MIM) diodes is a soft dielectric breakdown which results in the formation of a conducting filament through the diode. It is a critical step in the development of conducting states between which switching can occur in resistive switching memories. Conduction, electron emission into vacuum (EM), and electroluminescence (EL) have been studied in two groups of electroformed Al-Al2O3-Ag diodes with amorphous anodic Al2O3 thicknesses between 20 nm and 49 nm. EM and EL appear simultaneously with the abrupt current increase that characterizes electroforming of Al-Al2O3-metal diodes. There is voltage-controlled differential negative resistance in the current-voltage (I-V) characteristics after electroforming. There is a temperature-independent voltage threshold for EM, VEM ? 4 V, where VS is the applied voltage, and there is an exponential increase of EM. There is a second exponential increase of EM in region III when VS exceeds a second temperature-independent voltage threshold, UEM. UEM is ～6.6 V for one group of Al-Al2O3-Ag diodes; it is ～7.9 V for the second group. EM is nearly constant in region II for 4 V ? VS ? UEM. Two band-pass filters have been used to characterize EL from electroformed Al-Al2O3-Ag diodes. The long-pass (LP) filter plus photomultiplier responds to photons with energies between ～1.8 eV and ～3.0 eV. The short-pass (SP) filter measures ultra-violet (UV) radiation between ～3.0 eV and ～4.2 eV. Corresponding to region I of EM, there are exponential increases of EL for VS greater than temperature-independent voltage thresholds: VLP ? 2.0 V and VSP ? 2.2 V. There is a second exponential increase of UV with the SP filter in region III for VS greater than a temperature-independent voltage threshold, USP. USP ? 7.9 V for one group of electroformed Al-Al2O3-Ag diodes and USP ? 8.8 V for the second group; USP > UEM. Both groups exhibit EM from valence band states of amorphous Al2O3. The difference in UEM and USP of the two groups of electroformed Al-Al2O3-Ag diodes is attributed to the presence or absence of a defect conduction band formed from the ground state of F0- or F+-centers, oxygen vacancies in amorphous Al2O3. The observation of exponentially increasing EM or EL in the low conductivity state of electroformed Al-Al2O3-metal diodes is not consistent with switching mechanisms of MIM diodes that involve rupture of the conducting filament since rupture that affects diode current, if it occurs, should also cut off EM and EL.
关键词： electroforming,electron emission,electroluminescence,defect conduction bands,resistive switching,Al-Al2O3-Ag diodes
更新于2025-09-23 15:22:29
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Sensitivity-Selectivity Trade-Offs in Surface Ionization Gas Detection
摘要： Surface ionization (SI) provides a simple, sensitive, and selective method for the detection of high-proton affinity substances, such as organic decay products, medical and illicit drugs as well as a range of other hazardous materials. Tests on different kinds of SI sensors showed that the sensitivity and selectivity of such devices is not only dependent on the stoichiometry and nanomorphology of the emitter materials, but also on the shape of the electrode configurations that are used to read out the SI signals. Whereas, in parallel-plate capacitor devices, different kinds of emitter materials exhibit a high level of amine-selectivity, MEMS (micro-electro-mechanical-systems) and NEMS (nanowire) versions of SI sensors employing the same kinds of emitter materials provide significantly higher sensitivity, however, at the expense of a reduced chemical selectivity. In this paper, it is argued that such sensitivity-selectivity trade-offs arise from unselective physical ionization phenomena that occur in the high-field regions immediately adjacent to the surfaces of sharply curved MEMS (NEMS) emitter and collector electrodes.
关键词： selectivity,gas detection,corona discharge,secondary electron emission,sensitivity,surface ionization
更新于2025-09-23 15:22:29
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Investigations on electrical properties and correlations to electron and X-ray energies of pyroelectric LiTaO<inf>3</inf> and LiNbO<inf>3</inf>
摘要： The electrical properties of pyroelectric Lithium Tantalate (LiTaO3) and Lithium Niobate (LiNbO3) were investigated and compared to accessible X-ray energies by using the pyroelectric effect to generate X-rays. The capacitances of different crystals of varying sizes were measured and the resulting permittivities were calculated. A vacuum setup enabled a correlation to the maximum X-ray energies at a variable pressure. The presented results provide an overview of fundamental material properties and the effect on the generated difference of potential.
关键词： Lithium Niobate,pyroelectric crystal,vacuum electron source,X-ray spectrum,permittivity,X-ray energy,electron acceleration,electron emission,capacitance,Lithium Tantalate
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Self-focusing of electrons emitted by rectangular pyroelectric crystals: A study on geometrical conditions for optimized X-ray intensities
摘要： Pyroelectric crystals such as LiTaO3 or LiNbO3 offer the opportunity to produce X-rays with high energy and intensity. These pyroelectric X-ray sources may be used in XRF applications due to particular advantages. This report deals with systematic studies on the behavior of these crystals enabling an optimization of X-ray intensity. Furthermore, the focusing of electrons emitted by rectangular pyroelectric crystals has been studied.
关键词： Lithium Niobate,pyroelectric crystal,vacuum electron source,X-ray intensity,X-ray spectrum,focusing,electron acceleration,electron emission,Lithium Tantalate
更新于2025-09-23 15:21:21