Investigation On Growth And Characterization Techniques Of Field Emission CNTs With High Quality

Carbon nanotubes with typical layered hollow structure and featuresof large aspect ratio, high mechanical strength and stable chemicalproperty have drawn extensive interests and been studied in areas ofelectronic devices for their applications as field emission and energystorage electrolytes. Thermal chemical vapor deposition are widely usedin the fabrication of various CNTs due to its outstanding advantages ofsimple assembles, easy operation, low cost, controllable industrialparameters, high productivity and suitable for large scale production. Inpresent, in situ technique and solid layer methodare mostly adopted togrow CNTs. however, the properties, especially the life span, are impacted because of weak bond between the CNTs and the substratesand the poor conductivity caused by the high contact resistance. hence, toenhance the bonds between the CTs and the substrates may be asignificant way to improve its properties.CNTs with strong adhesion to the substrate were directly grown onmetal coil with catalyst (Ni, Fe) by adopting the vacuum CVD andsurface anodizing techniques in the present study. By investigating thestructure of CNTs, analyzing the bonding structure and the componentsbetween CNT and the surface, the growth mechanism of directlyfabricating CNTs that adhere strongly with the substrates is discussed.Furthermore, the metal substrates were subjected to the porous treatmentthrough anodize process. Homogeneous CNTs with strong adhesion tothe substrates were obtained by optimizing the growing conditionsincluding anodic voltage, anodizing time and concentration of electrolytesolution along with temperature, time, pressure and gas flow during thethermal CVD procedure. Field emission of CNTs was studied.The results show that CNTs on alloy coils are best grown for10minunder60torr at750℃, and that the optimum way is to anodize the coil in0.6mol/l oxalic acid under50V for1min. CNTs on the anodized coilshow an activation electric field of2.8V/μm and a maximum currentdensity of20.7mA/cm2. CNTs on Ni coils are best grown for10minunder30torr at625℃; the adhesion strength for CNTs on Ni coils which are anodized in0.3mol/l oxalic acid under50V for1min is4.1N. It hasbeen improved33%comparing to the ones on Ni without anodizing.Moreover, the CNTs grown on anodized Ni are used as cathode, the fieldemission test shows an improvement of53%in the start electric field,which has decreased from3.9V/μm to2.6V/μm. The maximum currentdensity is10.8mA/cm2. The decay of current density is0.01after a12hours test under an electric field of3.7V/μm.