Improved Field Emission Characteristics of Multi-walled Carbon Nanotube Cathode by Plasma Treatment with a Help of Krypton Fluoride Laser Irradiation

摘要

A screen printing method has been attractive for fabricating multi-walled carbon nanotube (MWNT) cathodes of a field emission display, because of easy mass production and low process cost. However, in case of the as-prepared MWNT cathodes itself, the number of emission site of MWNT cathode was small and special surface treatments such as plasma treatment, focused-ion, laser irradiations, or surface rubbing were inevitably required. In the previous study [1], the number of emission sites in screen printed MWNT cathodes has been increased by Ar plasma treatment due to the formation of dangling bond on the MWNT surface. In this study, laser irradiation in addition to plasma treatment is introduced for the purpose of increase of field emission (FE) characteristics, emission uniformity and emission site density (ESD). MWNTs with a diameter of around 10 nm were mixed with conventional organic binder in order to form MWNT paste. The MWNT paste was screen-printed on an indium tin oxide (ITO) on a glass substrate. The prepared MWNT cathode, then, was loaded between two metal electrodes for the plasma treatment, where the condition for the treatment was as follows: working pressure of 550 mTorr, RF power of 50-250 W and process duration of 1 min. After Ar plasma treatment, the series of plasma treated MWNT cathodes were irradiated with KrF (248 nm) excimer laser in air with an energy density of 100 mJ/cm{sup}2, a pulse width of 20 ns, and a laser irradiation speed of 0.4 mm/s for the purpose of protruding nanotubes from the surface. The spot shape was adjusted using homogenizers as 0.4 mm×50 mm (line beam) with a homogeneity of within 3%. The field emission measurement was performed in a vacuum chamber at a pressure of 10{sup}(-5) Pa. A MWNT cathode and phosphor on ITO glass were used for the cathode and anode electrodes, respectively, where the distance between two electrodes was 75μm, and a dc voltage was applied to measure the FE property.