Excellent Electron Emission Characteristics Research Articles

Synthesis of [Ca24Al28O64]4+(4e−) single crystal through xenon lamp melting combined with Ti vapor deoxygenation

In this paper, the high-quality [Ca24Al28O64]4+(4e−) (C12A7:e−) single crystal was synthesized by xenon lamp melting combined with Ti vapor treatment. The relative density of the sample is over 99.7%, and the sample's electron density is 1021 cm−3. The results of electron emission performance show that the sample's emission current density is 1.86 A/cm2 when the applied voltage is 3500 V at 1100 °C, and the fluctuation does not exceed 5%. Theoretical calculation results show that C12A7:e− single crystal has a lower work function (2.36 eV). Also, the free electrons in the cage cavity are mainly distributed around the frame oxygen, which is in a weakly bound state. This makes C12A7:e− single crystal have excellent electron emission characteristics. Theoretical calculations provide support for experiments. These laid the foundation for its application in electron emission.

Effect of Piezoresistive Behavior on Electron Emission from Individual Silicon Carbide Nanowire.

The excellent properties of silicon carbide (SiC) make it widely applied in high-voltage, high-power, and high-temperature electronic devices. SiC nanowires combine the excellent physical properties of SiC material and the advantages of nanoscale structures, thus attracting significant attention from researchers. Herein, the electron vacuum tunneling emission characteristics of an individual SiC nanowire affected by the piezoresistive effect are investigated using in situ electric measurement in a scanning electron microscope (SEM) chamber. The results demonstrate that the piezoresistive effect caused by the electrostatic force has a significant impact on the electronic transport properties of the nanowire, and the excellent electron emission characteristics can be achieved in the pulse voltage driving mode, including lower turn-on voltage and higher maximum current. Furthermore, a physical model about the piezoresistive effect of SiC nanowire is proposed to explain the transformation of electronic transport under the action of electrostatic force in DC voltage and pulsed voltage driving modes. The findings can provide a way to obtain excellent electron emission characteristics from SiC nanowires.

Atomic layer coating of hafnium oxide on carbon nanotubes for high-performance field emitters

Carbon nanotubes coated with hafnium oxide exhibit excellent electron emission characteristics, including a low turn-on voltage, a high field enhancement factor, and exceptional current stability. Their enhanced emission performance was attributed to a decrease in the work function and an increase in the electron density of states at the carbon nanotube Fermi level closest to the conduction band minimum of hafnium oxide. In addition, the enhanced current stability was attributed to the ability of hafnium oxide to protect the carbon nanotubes against ions and free radicals created in the electron field emission process.

Diminish the screen effect in field emission via patterned and selective edge growth of ZnO nanorod arrays

The authors report on the field emission from controlled selective grown zinc oxide (ZnO) nanorod arrays by hydrothermal reaction. With the combined effect from a ZnO seed layer and a passivation layer for nanorod growth, ZnO nanorods could only grow on the edge of a 4 μm diameter circle. The ZnO nanorods hollow arrays present excellent electron emission characteristics duo to its typical morphology which can significantly diminish the screen effect. By calculating the electrostatic field distribution, it was found that the electrostatic field of the ZnO nanorods hollow arrays is significantly higher than that of the solid arrays.

Comparison of field-electron emission from different carbon nanotube array structures

The effect of macroscopic cathode structures, which consisted of an array of the identical vertically aligned carbon nanotube (VACNT) columns in a particular arrangement, on the field emission was investigated. The electric field simulation based on the FEMLAB code showed characteristics of edge-induced U-shaped field distribution on CNT column. It was found that the degree of the field screening was dependent on VACNT-column array patterns, and that the overall field distribution depended on a number of VACNT columns at the periphery for the finite array size. Three different types of VACNT-column array cathodes were fabricated and tested for the field-electron emission: square, hexagonal, and triangular pattern arrays. All these VACNT-column array cathodes showed excellent electron-emission characteristics and a general trend consistent with field distribution simulations.

Electron Field Emission from Self-Organized Micro-Emitters of sp3-Bonded 5H Boron Nitride with Very High Current Density at Low Electric Field

Electron field emission with high current density ∼0.9 A/cm2 at a low electric field of 8.6 V/μm was achieved by self-organized cone-shaped emitters with dimensions on the order of ∼10 μm made of sp3-bonded 5H boron nitride, which was grown by plasma-assisted chemical vapor deposition with the assistance of 193 nm laser irradiation of the surface. The work function of this material proved to be ∼5 eV, whereas the geometrical field enhancement factor amounts to ∼106 cm-1. The known robustness of sp3-bonded BN with its excellent electron emission characteristics and the self-organization of emitter shaped structures may provide new applications for electron emitting devices.

Effects of oxygen and hydrogen on electron field emission from microwave plasma chemically vapor deposited microcrystalline diamond, nanocrystalline diamond, and glassy carbon coatings

Electron field emission from chemically vapor deposited polycrystalline diamond, nanocrystalline diamond, and glassy carbon coatings are reported. Effects of hydrogen-rich or oxygen-containing CVD precursors on electron field emission from CVD carbon coatings are presented. Surface conductivity and negative electron affinity resulting from hydrogen termination of crystalline diamond were found to promote electron field emission for discrete diamond particles and non-continuous diamond films but not for high quality and continuous diamond films as well as nanocrystalline diamond and glassy carbon coatings containing conductive graphitic carbon. Graphitic carbon in nanocrystalline diamond coatings and glassy carbon coatings provided additional conduction paths for electrons and allowed more effective injection of electrons into electron emitters. Nanocrystalline diamond coatings deposited by methanol/ethanol plasmas contained more graphitic carbon than that deposited by hydrogen/methane plasmas resulting in lower turn-on electric field and higher electron field emission current. Glassy carbon coatings deposited by both processes exhibited excellent electron emission characteristics. Low turn-on electric field, i.e., 1 V/μm, for electron field emission was achieved for diamond and glassy carbon coatings deposited under optimized conditions. Among these three classes of carbon coatings, glassy carbon deposited at elevated substrate temperatures were found to exhibit the best electron field emission properties.

Spectro-ellipsometric studies of defective diamond films deposited by MPECVD

Abstract Novel diamond films, which were deposited by microwave plasma enhanced chemical vapour deposition (MPECVD) method using various mixtures of methane and hydrogen gases, and exhibited excellent electron-emission characteristics, have been investigated by X-ray diffraction, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry. The structural investigation has shown that these films are nanocrystalline diamond films and that there are distorted sp 3 -bonded carbons and sp 2 -bonded carbons in the grain boundaries. Moreover, the methane-concentration and the depth-dependent distributions of sp 2 -bonded carbons have been quantified nondestructively by fitting the measured ellipsometric spectra to the three-layer model of the surface layer (diamond+void), the bulk-like layer (diamond+glassy carbon), and the interface layer (diamond+glassy carbon). Interestingly, the relative glassy-carbon fraction in each layer has been found almost invariant for given methane concentration regardless of the thickness. However, regardless of the methane concentration, the interface layers have been found to have a higher glassy-carbon fraction, while the rough surface layers are free from glassy carbon. Finally, it has been found that both the film growth rate and the glassy-carbon fraction increase as a function of methane concentration.