Effects of Hydrogen Post Treatment and Duty Factor on Carbon Nanotube Field Emission Stability
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0963-Q20-50
Effects of Hydrogen Post Treatment and Duty Factor on Carbon Nanotube Field Emission Stability Sigen Wang and Sha Chang Division of Physics & Computing, Department of Radiation Oncology, Medical School, University of North Carolina, Chapel Hill, NC, 27599-7512 ABSTRACT Carbon nanotubes (CNTs) have been investigated as field emission electron sources for a number of applications such as x-ray source and microwave power amplifier. These applications require that nanotubes provide a stable field emission at a high emission current. In this paper, we investigated the emission stability of CNTs as functions of hydrogen post-treatment and duty factor. The experimental results show that the hydrogen plasma treatment and a reduced duty factor from 100% to 35% can noticeably improve the emission stability of CNTs at a high current value of 4000 µA. Our study also shows that emission induced anode heating at high duty factor and high emission current level degrades vacuum level and thus the emission stability of CNTs. Besides, the variation of the working CNT tip numbers at different duty factors, is believed to be another mechanism to affect the emission stability.
INTRODUCTION Carbon nanotubes (CNTs) have attracted considerable attention as electron field emitters owing to their high aspect ratio that leads to large electric field enhancement resulting in high emission current and low operating voltages. 1-4 CNT-based field emission x-ray source has been shown to have several intrinsic advantages over the current x-ray tubes with thermionic cathodes including high temporal resolution and capabilities for spatial and temporal modulation. 4 CNTbased traveling wave tubes can also achieve the same emission current density level as those based on thermionic cathodes, but their dimension can be greatly reduced. 3 Besides emission current, field emission stability is another critical feature for practical applications of the CNT cathodes as high brightness electron sources. 5,6 Some efforts have been made to improve the emission stability including using laser 7 or inert gas 8 to post-treat the CNTs. On the other hand, many electron sources are actually used in a pulse mode, duty factor, which is defined as the ratio of emission time to the total cycle time, is an important parameter for these electron emitters. However, to date little systematic study has been reported on the correlation between the duty factor and the emission stability of CNTs. In this paper, we examine the influence of hydrogen treatment and duty factor on the emission stability of CNTs. It is observed that the hydrogen plasma treated samples exhibit a higher emission stability. Besides, a reduced duty factor (< 35%) can lead to a stable field emission of the CNTs even at a high current value of 4000 µA. The possible mechanisms is discussed based on the characterization results of the CNTs and the observed phenomena during the field emission testing.
EXPERIMENTAL DETAILS The CNTs ( area of 0.79 mm2 ) used in this work were grown on a n-type (10
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