Controllation Of Magnetic Field On Field Emission Properties Of Metallized Multiwalled-Carbon Nanotubes

Because of the special electronic structures and outstanding electrical, mechanical, magnetism and optical properties, carbon nanotubes (CNTs) have been regarded as the ideal field emission materials. However, since the wall structure of CNTs is the same as that of graphite, the surface activity of CNTs is low and CNTs are easy to be aggregated in organic solvent or water.The original multi-walled (MW-) CNTs were oxidized by a mixture of concentrated nitric and sulfuric acid in order to remove the impurities and improve their dispersion. After being oxidized, a large number of functional groups were grafted on the surface of MWCNTs, effectively improving the degree of surface defects. Then, the surface metallization of MWCNTs were conducted by a series of processes, including sensitizing, activating and electroless plating under different magnetic fields. And Ni-plated MWCNTs were obtained. Subsequently, a screen printing method was applied to fabricate MWCNTs and MWCNTs/Ni cathodes on the silver electrode. Finally, the cathodes were heat-treated under different magnetic field intensities.The research of electroless plating Ni with and without magnetic showed that the presence of magnetic field is in favor of MWCNTs electroless plating Ni, and the Ni layer on the surface of MWCNTs have a continuous, smooth coating where no nano-tips appeared. On the contrary, without magnetic field, the Ni layer on the surface of MWCNTs was incontinuous and many nano-tips appeared.The field emission performance test of MWCNTs cathodes indicated that the oxidized time of MWCNTs must be appropriate. In a certain time range, lengthening the oxidization time is beneficial to the field emission of MWCNTs. However, an excessive processing time would result in the degradation of field emission. The field emission performance of oxidized MWCNTs cathodes heat-treated for 5 h under different magnetic field was investigated. Our results demonstrated that after the magnetic field assisted heat-treatment the MWCNTs cathodes had better field emission properties than those treated by the usual heat-treatment, giving a turn-on field of 1.10 Vμm-1 and a field enhancement fact β of 13109.The field emission performance test of magnetic-field-assisted heat-treated MWCNTs/Ni cathodes illustrated that the magnetic field help to improve the field emission properties. Under magnetic field of 600 mT, the lowest turn-on field (0.44 V-μm-1), best field emission performance and uniformity would be obtained. Finally, we built a model to analyze the force of signal MWCNTs/Ni under the magnetic field. In theory, the field emission of MWCNTs/Ni cathode improved by magnetic-field-assisted heat-treatment was studied.