Field Emission Device Made from Multiwalled Carbon Nanotube Sheet
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Field Emission Device Made from Multiwalled Carbon Nanotube Sheet Hai H. Van, Mei Zhang, Ben Wang, and Chuck Zhang Department of Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering; High-Performance Materials Institute, Florida State University, 2525 Pottsdamer Street, Tallahassee, FL 32310, U.S.A. ABSTRACT A new type of cathode for electron field emission (FE) was fabricated. The cathode was made from ultra-thin multiwalled carbon nanotube (CNT) sheets. These sheets were drawn directly from a CNT forest, stacked layer-by-layer together and densified by isopropyl alcohol. CNT emitters were formed by utilizing laser beam to cut the sheet. The FE performance of the proposed devices has been enhanced dramatically. The threshold field for electron emission (at which the emission current is 10 mA/cm2) was 0.88 V/μm. The current density of 36 A/cm2 was achieved at the electric field of 2 V/μm. The enhanced performance is the result of the thin, uniformly distributed and aligned array of the CNT emitters. INTRODUCTION Due to the advantage of nanoscale tubular structure and high thermal and electrical conductivity, carbon nanotubes (CNTs) have been studying for practical applications in various fields, such as sensors, conductors, semiconductors, and composites [1]. Field emission (FE) is also a noticeable application of CNTs [2]. The performance of FE devices is immensely affected by the characteristics of CNTs, such as the work function and the conductivity. Besides, the geometry of the CNT emitter array, such as the length, the orientation, and the distribution of emitters, is also an important factor for the total performance of the FE devices. Based on the structures of FE devices, there are two main types of FE devices, the planar emitter device and the point emitter device. In the case of the planar emitter device, the CNTs are sprayed, deposited, or grown directly on substrates [3-6]. By using these methods, CNTs are randomly distributed over a broad area, thus the orientation and distribution of the emitters are usually not uniform. The screen effect, i.e. a negative effect appearing when emitters are packed too close together, heavily reduces the total field emission performance. With point emitter devices, a single CNT, CNT bundle, or CNT yarn is utilized as an single and unique emitter for each device [7-10]. Because of the nanoscale diameter of CNT tip, the emitting area is very small, resulting in the extremely high current density. However, the emission current of this type of FE devices is relatively low due to the low number of emitters. Additionally, with CNT yarns, the screen effect has impact on reduction of the total FE performance. To increase the number of effective FE emitters and to lessen the screen effect at the same time are important to improve the total performance of FE devices. In this paper, a new methodology is approached to fabricate FE devices for achieving high performance. EXPERIMENT The CNT forest was synthesized on a silicon wafer by chemical vapor deposition (CV
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