| Electron gun filament,as a key material for electron emission,has an important impact on the performance of electron guns.Carbon nanotubes（CNTs）were proved with excellent field emission properties both in thin film and individual.However,due to their extremely small geometry（diameter is only on the order of nanometer）and uncontrollable length,CNTs are difficult in assembly and weak to resist the damage under high strength operation.So that,they are difficult to be used as standard devices.To solve this problem,in this paper,perfect morphological quasi-macroscopic carbon fibers（QMCFs）with diameters on the order of microns and lengths on the order of centimeters were prepared based on iron-catalyzed pyrolysis of methane.The deviceization technique for standard filament devices based QMCFs was studied.And then QMCFs-based filament devices were developed.After that,the mechanisms,including macroscopization growth,electron emission characteristic,emission fluctuation were analyzed.The main research work and conclusions are as follows:（1）The macroscopization growth of carbon fibers was achieved by chemical vapor deposition（CVD）method under iron-catalyzed conditions,using methane as carbon source.By the aids of optical microscopy,scanning/transmission electron microscopy,Raman and other characterization equipment,we have determined that QMCFs fibrils range in length from a few millimeters to greater than 1 cm,with quasi-cylindrical morphology,hemispherical tips,no entanglement between individuals,visible to the naked eye,and manually manipulable under macroscopy.The microstructure is a solid structure with coaxially curled graphite lamellae and possesses a certain degree of graphitization,and its conductive properties have been tested for excellent performance,which can be used as a single-tip cold cathode emission material.（2）The morphological analysis of the deposition of pyrolysis products reveals the general process of macroscopic growth evolution of CFs:gas-phase carbon atoms-cluster carbon-particulate carbon-merged particulate carbon-chainization（non-linear non-regular morphological chain）-conformation（taking straight and morphologically oriented）-end-state samples.（3）Using QMCF as the emitter and capillary copper tubes as the"support",we designed a filament device scheme and built a device crimping device to standardize the crimping of filament devices.And then,the electrical contact reliability verification of the assembled filament device proves that it is an ohmic contact,which meets the electrical connection requirements of electronic devices and can be used as a reliable standardized single-tip cold cathode filament.（4）Electron emission characteristics tests show that single quasi-macroscopic carbon fibers have excellent electron emission characteristics and repeatability characteristics.The emission current can reach up to more than 1 m A,and the emission current density reaches 744 A/cm~2;the QMCFs have good repeatability test characteristics under the conditions below the limit current;The emission stability of QMCFs with different diameters under different current and anode-to-cathode distance were tested.The results showed that the fluctuation was mainly caused by the shape change of QMCF because of the graphite layer fragment being peeled under the electric field fluctuation;the aging treatment at lower operating currents can improve the stability of QMCFs in the repeatability test at higher operating currents;In addition,the field enhancement effect is directly related to the field emission properties of the material.The test results show that the larger the aspect ratio of QMCFs,the stronger the field enhancement effect is at the same current density.Choosing a suitable aspect ratio can optimize the field emission characteristics to a certain extent. |
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