Effect of radiation damage on ion-induced electron emission from highly oriented pyrolytic graphite

The dependences of ion-electron emission yields γ for highly oriented pyrolytic graphite (HOPG) under 30 keV N₂⁺ ion irradiation on target temperature at different ion incidence angles (0-80°) have been measured. The fluences were 10¹⁸-10¹⁹ ion/cm² and irradiation temperatures were varied from room temperature to 400 °C. At normal ion incidence a step-like increase of yield, analogous to the γ-behaviour for polygranular graphites, has been found at an annealing temperature T_a. This effect and the changes of γ(T) with ion incidence angle are discussed in terms of the change of electron path length and the transparency of the lattice for ion beams with increasing degree of lattice order.     

Monitoring the structure-phase changes in graphites using temperature regularities of ion-induced electron emission

The correlation between the temperature dependences of ion-induced electron emission yield, modified surface crystalline structure and morphology of isotropic graphite MPG-8 and highly oriented pyrolytic graphite (HOPG) UPV-1T under high-fluence (F = 10¹⁸-10¹⁹ ion/cm²) 6-30 keV Ar⁺ ion irradiation has been studied and discussed. The target temperature has been varied during continuous irradiation from room temperature to 400 °C. Surface analysis has been performed by the RHEED and SEM techniques. A strong influence of electron transport anisotropy for HOPG has been observed.     

The study of graphite disordering using the temperature dependence of ion-induced electron emission

The temperature dependences of ion-induced electron emission yield γ(T) under 6-30 keV N₂⁺, Ne⁺, Ar⁺ and 15 keV N⁺ high-fluence ion irradiation of polycrystalline graphite at normal ion incidence have been analyzed to trace the structure change dependence depending on irradiation temperature and the level of radiation damage v measured in dpa (displacements per atom). It has been found that, under irradiation at room temperature, the threshold value for graphite lattice disordering equals v_d ≈ 60 dpa for noble gas ions (Ar⁺, Ne⁺) and ν_d ≈ 40 dpa for N₂⁺.     

Excited xenon density and ion-induced secondary electron emission coefficient for vacuum ultraviolet luminous efficiency in alternating current plasma display panel

It is shown for Xe content ratio of 10% that the excited xenon atom density for the 1s₅ metastable state is 3.0 × 10¹² cm^− 3 with a gap distance of 50 μm under a fixed gas pressure of 5.3 × 10⁴ Pa in alternating current plasma display panels. It is observed that the VUV emission of 173 nm continues after its peak and lasts much longer than 147 nm emission. We also found that the time of VUV peak emission intensity for higher xenon mole fraction is longer. It is also concluded that the luminous efficiency is strongly dependent on the ion-induced secondary electron emission coefficient.     

Angular and temperature dependences of ion-induced electron emission of polycrystalline graphite

The dependences of ion-induced electron emission yields γ for MPG-8 graphite under high fluence 30 keV N₂⁺ and Ar⁺ ion irradiation on target temperature at different incidence angles (0-80°) have been measured. At normal incidence a step-like increase of the electron yield has been found at the defect annealing temperature T_a≈190°C. This effect and the changes of γ(T) with incidence angle are discussed in terms of electron path length rise due to decrease of the degree of amorphisation as a result of a phase-transition type of re-crystallisation and radiation damage annealing.     

Secondary electron emission in scanning Ga ion, He ion and electron microscopes

The secondary electron (SE) emission for Ga ion, He ion and electron impact have been calculated using Monte-Carlo simulations, in which the trajectories of all the collision partners (i.e., primary ions, recoiled target atoms, and excited electrons (electron cascade) along which SEs are excited) have been simulated. The SE yields for Ga ion impact show a gradual decrease with increasing Z₂ which is opposite to that found for electron impact. The main reasons for the decrease in SE yield for Ga are the decrease in number and energy of electrons excited by the primary ions and the decrease in contribution of the recoiled atoms to the SE yield with increasing Z₂. For electron impact, both primary electrons and backscattered electrons (BSEs) excite the SEs. The additional SE excitation created by the electron cascade by BSEs is enhanced for high-Z₂ metals especially at E > a few keV. For He ion impact, the Z₂-dependence is between that for the Ga ions and the electrons and is weak because the He ion is light but still much heavier than an electron. As to the lateral resolution, the electron excitations by trapped He ions dominate the SE yield, so that the SE excitation volume is narrower than for electron and Ga impacts. This small contribution of BS He ions to the SE yield does not increase the information depth determined by the trapped He ions, in contrast with the large contribution of BSEs to the SE yields for SEM imaging. The simulated incident-angle dependence in SE yields shows that the topography contrast for He-SIM imaging is clearer than that obtained by SEM and Ga-SIM imaging.     

Study on effect of oxygen adsorption on characteristics of field electron emission from aligned carbon nanotubes grown by plasma-enhanced hot filament chemical vapor deposition

The characteristics of field electron emission (FE) from aligned carbon nanotubes (ACNTs) in a form of film, which were catalytically grown by plasma-enhanced hot filament chemical vapor deposition, were measured for many cycles. The results indicate that the FE characteristic for every measurement cycle is different and it follows the Fowler–Nordheim model in the low field region, but it deviates from the model in the high field region. The ACNTs were investigated by energy dispersive X-ray (EDX) and the EDX spectrum shows that oxygen is adsorbed on the ACNTs. The theory related to adsorption and space-charge effect was applied to analyze the experimental results.     

Low-field electron emission from carbon cluster films: combined thermoelectric/hot-electron model of the phenomenon

Abstract

Thin carbon films consisting of separate nanometer-scale sp² carbon islands with smooth vacuum boundary deposited on Si wafers were found to be capable of low-field electron emission – starting from macroscopic field magnitudes as low as ～1?V/µm. For such films, we suggest a novel model of emission facilitation by thermoelectric field associated with heat generation concentrated in nanosized areas. Quantitative estimates performed on the basis of this hypothesis for typical experimental conditions gave estimates for local thermoelectric field magnitude and lateral non-uniformity of surface potential as high as ～100?V/μm and a few Volts, respectively. Thus, the suggested model explains the low-field emission capability of smooth-surface nanocarbon films observed in many previous experiments.     

Side electron emission device using a composite of carbon nanofibers and aluminum

A new side electron emission device (SEED) was fabricated with carbon nanofiber/aluminum (CNF/Al) composites prepared by the elastomer precursor method. In the SEED, a cross-sectional side face of the CNF/Al composite plate was perpendicularly placed onto an anode surface by inserting an insulating spacer. Above a certain threshold voltage in a vacuum, field electrons were obtained from the side face of the composite emitter. With increasing content of CNFs in the composite, the threshold voltage decreased and emission currents increased. The current of ~ 8 μA was kept stable up to 93 h under a continuous application of 1 kV. This improved stability as compared to a conventional field emission device was attributed to a reduced damage of CNFs in the SEED structure.     

铁电阴极电子发射研究进展

铁电发射是一种新型强流受激电子发射，本文综述了铁电弱发射和强发射的研究现状及其发射机理，重点分析了不同的铁电体相结构、电压脉冲激励波形、铁电发射结构以及萃取电压的波形等对铁电阴极电子发射特性和工作机理的影响，总结了目前铁电阴极等离子体辅助电子发射机理和模型，最后介绍了铁电阴极的应用前景。     

碳元素的另一种同素异形体——白碳

白碳和金刚石、石墨这两种常见的碳的晶态结构不同,它是sp1杂化的碳元素的另一种晶态同素异形体.白碳具有一维直线碳链的特殊结构.本文对白碳材料的制备方法、结构特点、表征方法进行了综述,并展望了其在纳米器件、分子器件、以及场致电子发射等方面的应用前景.     

Secondary electron emission of TiN-coated alumina ceramics

TiN film is often coated on alumina rf windows to suppress multipactor due to high secondary electron emission (SEE) coefficients. In this paper, SEE coefficients of alumina ceramics and sapphire coated with TiN films of various thicknesses are investigated. The SEE coefficients were measured using a scanning electron microscope with a single-pulse electron beam (100 pA, 1 ms). The SEE coefficients of TiN-coated alumina ceramics were lower than those of uncoated ones and nearly unity for TiN thickness of more than 1 nm, even with incident energy of 1 keV. To emulate multipactor-induced surface heating, the SEE coefficients were also measured at high temperature. The results showed a decrease in the SEE coefficients with temperature for TiN thickness of more than 0.5 nm. TiN coating on an rf window should be as thin as possible, and 0.5-1 nm may be the optimum thickness for suppressing multipactor.     

Investigation of the local electron emission from current-carrying silver nanoparticle films by an emission electron microscope

Emission electron microscopy was used to study the electron emission observed under the passage of a tunnel current through a silver nanoparticle film when a voltage is applied to it. The electron emission originates from separate emission centers emitting photons as well. The electron emission centers are visualized as separate spots in an emission electron microscope. A deformation of shape and size of these spots was studied at various applied voltages. It enables the energy spread of electrons emitted from an individual emission center or at least the width of its most intensive part ε as well as the magnitude of electric field E near this center to be estimated. It has been shown that ε comprises 0.5-0.6 eV, and E < < 10⁷ V/cm. The latter result means that the electron emission is not the field emission.     

Magnetic field enhances the graphitized structure and field emission effect of carbon nanotubes

This study uses a low temperature thermal chemical vapor deposition with an applied external magnetic field to grow carbon nanotubes (CNTs) on Ni/Ag-printed glass substrates. A mixture of C₂H₂ and H₂ gas was used for the growth of the CNTs. A Ni catalyst layer was deposited on the Ag-printed glass substrate by pulse electroplating. Scanning electron micrographs as well as the presence of two sharp peaks at 1320 cm⁻¹ (D band) and 1590 cm⁻¹ (G band) in the Raman spectra indicate that the graphitized structure of CNTs synthesized under a magnetic field has higher quality (i.e., a D-band to G-band intensity ratio of 0.303) than CNTs synthesized without a magnetic field. Transmission electron micrographs show a fine Ni catalyst at the tip of the tube for CNTs synthesized under a magnetic field, exhibiting a CNT “tip-growth” model. The synthesis of CNTs in the presence of a magnetic field also generates better field emission properties and better lighting morphology than without a magnetic field.     

MgO纳米线的制备及其电子发射性能的研究

采用碳热还原-氧化法成功制备大小均匀的MgO纳米线,采用场致发射电子显微镜(FESEM)和X射线衍射(XRD)表征其形貌及晶体结构。采用丝网印刷将MgO纳米线转移到阴极电极,并将阴极电极与印刷有荧光粉的阳极电极组装成二级场致发射器件。场致电子发射测试表明MgO纳米线具有较好的电子发射特性:其阈值电场强度仅为3.82V/μm(1mA/cm2),最高电流密度达到2.68mA/cm2(4.01V/μm),发光亮度为1152cd/m2,4h内没有明显的衰减。MgO有望作为冷阴极材料在场致发射器件上得到应用。     

Monte Carlo study of the ion-induced electron current tunneling through a metal-insulator-metal junction

A Monte Carlo program is developed to investigate the kinetically excited electrons passing through a realistic Ag-Al₂O₃-Al junction when Ar⁺ ions impact on the top Ag layer. The program includes excitation of the target electrons (by projectile ions, recoiling target atoms and fast primary electrons) and subsequent transport of these excited electrons from Ag to bottom Al layer of the metal-insulator-metal (MIM) junction. The calculated tunneling electron yield is consistent with the recently reported experimental results. The simulation, however, enables the calculation of partial tunneling electron yields of the electrons excited by the projectile ions, recoil atoms and cascade electrons, the depth distribution of the electron excitation points in the MIM junction and energy distribution of the tunneling electrons. Our calculation showed that the electrons excited by fast cascade electrons are the major contributor to the tunneling electron yield while the direct contribution of projectile ions to tunneling electron yield is evident only at the projectile energies greater than 10 keV. The tunneling electrons have their origin close to the bottom end of the Ag layer and bulk of the tunneling electrons have energies around 2 eV.     

The trapped ion–electron instability in an electron storage ring with a gap in the bunch train

The trapped ion–electron instability in an electron storage ring is studied for a broad distribution of natural ion oscillation frequencies, termed ion bounce frequencies. A gap in the train of electron bunches may be used to create bands of unstable ion bounce frequencies, so that an ion species is ejected from regions of the ring where its horizontal or vertical bounce frequency is unstable. Expressions are obtained for the reduction in the incoherent tune shifts and trapped ion–electron instability growth rates resulting from the gap.     

A study on the secondary electron emission from Na-ion-doped MgO films in relation to the discharge characteristics of plasma display panels

Using a sol-gel precursor, Na-ion-doped MgO was prepared and applied to alternative current plasma display panels (ac-PDP). The cathodoluminescence spectra showed that the F⁺ center was increased as the concentration of Na⁺ was increased. Numerous pores were found on the printed MgO surface and seemed to give higher memory margin of ac-PDP compared to an electron beam-evaporated MgO film. All doped MgO showed higher secondary electron emission than printed pure MgO, likely owing to the O defect states of MgO. In addition, this result indicated the operational memory margin of the ac-PDP was directly proportional to the grade of surface charging.