Resreach Of Vacuum Electronic Devices Based On Field Emission Of Carbon Nanotubes

The key technology for application of field emission vacuum electronic devicesis to develop a cathode, electron source, with a long time stability. At present, thereare two kinds of methods that are widely used for fabrication of carbon nanotubes(CNT) cathode, the one is chemical vapor deposition with metal nano membrane ascatalyst, the other is indirect method with CNT attached on conducting substrate byhardener. Both the two methods have the inherent defects caused by thecharacteristics of interface bonding, which causing the fall of CNT membraneultimately. Therefore, the interface bonding performance between CNT and substrateis the central question that restricting the application of these two methods.In this paper, CNT cathode was fabricated on metallic substrate by chemicalvapor deposition (CVD), then two simple field emission vacuum gauges were madewith the CNT cathode. The main contents are as following.(1) CNT films were synthesized by thermal CVD based on the followingconditions: the growth temperature is750℃, the flow ratio of C2H2:Ar is15:200sccm,the growth time is10min, growing pressure is10Torr. Hastelloy sheet, nickel sheet,stainless steel sheet and Hastelloy web were used as the polymetallic catalyst andsubstrate. This process not only removes the deposition of metal nano membrane onsubstrate but also realizes the strong adhesion.(2) The SEM images of CNT show even distribution, moderate density onHastelloy sheet. The HRTEM images show the type of CNT is multi-wall carbonnanotubes (MWNTs), whose diameter is about15nm, and the poly-metal (Ni, Fe, Cretc.) nanoparticles, diameter is about6nm, generally exists in the MWNTs.(3) The MWNTs cathode based on Hastelloy sheet show the best field emissionperformance in diode setup, it’s turn on field is3.15V/μm, threshold field is5.94V/μm, field enhancement factor is1900and it emitting at4.2mA/cm2for20hours without decrease. The transmittance of the MWNTs cathode on Hastelloy sheet testedin triode setup is much higher than that of the Hastelloy web, whose value is about0.61, closing to the physical transmittance of gate,0.77.(4) We have fabricated a novel vacuum gauge based on the the effect of gasadsorption on field emission of the MWNTs on the Hastelloy sheet substrate, andhave demonstrated the gauge posses high sensitivity of field emission in the pressurerange of10-8-10-4Pa by precisely controlling air injection.(5) CNT field emission ion gauge was fabricated based on the ion gauge (IE514)by the cooperation with Lanzhou institute of space physics. The gauge shows goodlinearity in the pressure range of10-6-3.0×10-4Pa.