| As an excellent cold cathode emission material,carbon nanotube(CNT)films are an important part of the vacuum microelectronic device.However,in strong electric field and medium high-vacuum condition of the intense pulsed emission mode,CNT films are easily damaged by spark or arc discharge in the working process,and it is easily scratched by the external force during the assembly process.This irreversible damage will cause irrecoverable attenuation to the performance of the cold cathode.In this paper,the interfacial property,damage mechanism and improving way of CNT films grown on copper substrate are analyzed,and getting better performance cold cathode material by preparing the CNT/Ag bulk composite material.The effect of the third phase metal on the improvement of the CNT/Cu interfacial property was studied.Cr/Cu composite metal substrate was prepared by doping a certain amount of chromium powder into copper powder by powder metallurgy,and the CNT films grown on the substrate were prepared.The interfacial property and field emission correlation property of CNT films on pure copper and Cr/Cu composite metal substrates were qualitatively compared by field emission test and ultrasonic exfoliation test.The results showed that the CNT films on the copper-chromium substrate exhibited stronger current emission capability and resistance to current damage in the field emission test,showing a positive correlation between interfacial adhesion and field emission characteristics.It indicates that Cr can effectively improve the interfacial property between copper substrate and CNT films,significantly enhancing the capability of interfacial bonding and current emission.In addition,the ultrasonic test results also showed that the CNT films on Cr/Cu composite substrates had better mechanical damage resistance.The ultrasonic exfoliation experimental method proposed in this paper is putting the CNT films in anhydrous ethanol for a certain time in the ultrasonic instrument,and getting the qualitative characterization of the adhesion according to the residual condition of the substrate surface.This method is expected to be developed into a semi-quantitative characterization method by combining with computer graphics analysis,which can expand the characterization method of the weak adhesion property of thin film.In order to further improve the mechanical damage resistance of carbon nanotube cold cathode,a bulk Ag/CNT composite cold cathode was prepared,and the electron emission characteristics under the vacuum environment similar to the condition of strong current pulse emission was studied.The results showed that the increase of CNT content was beneficial to the improvement of field emission performance.The emission repeatability of current density-field strength(J-E)curve of bulk composite cold cathode was significantly better than that of thin film cathode,and the spark damage in the emission process was not easy to cause a significant decline in emission performance.It may even enhance the emission performance by activating a large amount of CNTs inside as new effective emission sites,thus having the ability to self-repair.For the sample prepared in 30:1 mass ratio of Ag to MWCNT with the diameter of20-30 nm,we got the max emission current density of 4.6 mA/cm~2 at the field strength of1.9 V/?m by the first emission test,which was better than carbon nanotube films.The field emission performance tended to be stable after multiple tests.The results of this paper have good application prospects for high power microwave devices,particle accelerators and other vacuum electronic devices. |
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