Enhanced Electron Field Emission from Carbon Nanotube Matrices
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Enhanced Electron Field Emission from Carbon Nanotube Matrices 2
Archana Pandey1, Abhishek Prasad1, Yoke Khin Yap1, Mark Engelhard , Chongmin Wang 1
2
Department of Physics, Michigan Technological University, 118 Fisher Hall, 1400 Townsend Drive, Houghton, Michigan 49931, U.S.A.
2
EMSL, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA 99354, U.S.A.
ABSTRACT Field emission from as-grown carbon nanotube (CNTs) films often suffered from high threshold electric field, and low emission site density due to screening effects. These problems can be resolved by patterned growth of CNTs on lithographically prepared catalyst films. However, these approaches are expensive and not applicable for future emitting devices with large display areas. Here we show that as-grown CNTs films can have low emission threshold field and high emission density without using any lithography processes. We have reduced screening effects and work function of as-grown CNTs films and created the novel CNT matrices by addition of vapor- and/or liquid- phase deposition. Furthermore, these CNT matrices can continuous emit electrons for 40 hours without significant degradation. The fabrication of our CNT matrices is described as follows. First, CNT films were grown by plasma-enhanced chemical vapor deposition. These vertically-aligned multiwalled carbon nanotubes (VA-MWCNTs) are having typical length and diameter of 4 microns and 40 nm, respectively. Spacing between these CNTs is ~80 nm in average, leading to poor emission properties due to the screening effect. These asgrown samples were then subjected to the deposition of strontium titanate (SrTiO3) by pulsedlaser deposition to reduce both the work function and screening effect of CNTs. The emission properties of these coated samples can be further improved by fully filled the spaces between VA-MWCNTs by poly-methyl metha acrylate (PMMA). The field emission threshold electric field was decreased from 4.22 V/μm for as-grown VA-MWCNTs to 1.7 V/μm for SrTiO3 coated VA-MWCNTs. The addition filling with PMMA and mechanical polishing can further reduce the threshold to 0.78V/μm for the so called PMMA-STO-CNT matrices. Long term emission stability and emission site density were also enhanced. INTRODUCTION Since their discovery CNTs have gained intensive research interest [1-2]. They are novel nanostructured materials with extraordinarily properties. It has been already demonstrated that they are among strongest nanofibres known till date, with Young’s moduli as high as 1 TPa [34]. They also have astonishing electronic properties [5], chemical stability [6] and superior mechanical properties [7]. Because of their very small radius of curvature and high aspect ratio they are expected to have excellent electronic properties [8]. Numerous efforts have been done to develop a better electron source based on field emission of CNTs that could replace the conventional field emission devices at the industrial scale in future. However, in order to do this,
improvements in its field emi
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