Field Emission Properties of Vertically Aligned Carbon Nanotubes Driven by Polar and Non-Polar Gas Adsorption
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Field Emission Properties of Vertically Aligned Carbon Nanotubes Driven by Polar and Non-Polar Gas Adsorption Youngsik Song1, Brian Usner2, Jaewu Choi1*, Seong-Chu Lim3, and Young Hee Lee3 1
Dept. of Electrical and Computer Engineering, Wayne State University, 5050 Anthony Wayne Dr. #3100, Detroit, MI 48202 2 Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson Hwy, Baton Rouge, LA 70806 3 Dept. of Physics, Center for Nanotubes and Nanostructured Composites, Institute of Basic Science, Sungkyunkwan University, Suwon, 440-746, Republic of Korea *
Corresponding author: [email protected]
ABSTRACT We studied the gas adsorption effects on the field emission properties of vertically aligned multiwalled carbon nanotube films by exposing them to polar (H2O) and nonpolar (N2O) gas molecules. The charge transfer between adsorbates and carbon nanotubes plays an important role in the field emission properties. With bias voltage ~ 1.2V/µm, the field emission properties of the carbon nanotubes are improved by exposing the nitrous oxide while the bias effect with water exposure is less significant. The improvement of the field emission properties by gas exposure is attributed not only to the change in the work function of the carbon nanotubes caused by a charge transfer, but also to the reactivity of the adsorbate gas with localized-cap states. INTRODUCTION Carbon nanotubes have been studied as a field emission electron emitter because of their high aspect ratio, mechanical strength, and metallic properties [1]. Numerous studies on the field emission properties of carbon nanotube have been conducted and aim to develope a point electron source using a single carbon nanotube [2], and a field emission display using carbon nanotube films [3]. However, there are arguments pertaining to the role of the localized-cap states [4] and the adsorbate states on the field emission process [5]. We studied the effect of polar (H2O) and non-polar (N2O) gas exposure on the field emission properties from vertically aligned carbon nanotube films to shed light on the roll of the localized-cap states and the adsorbate states. EXPERIMENTAL DETAILS The vertically aligned mutilwalled carbon nanotubes were grown on Ni-coated Si substrates using a thermal chemical vapor deposition (T-CVD) technique. The carbon nanotube diameter, length, and density are 20-50 nm, ~ 10 µm, and ~ 2 x 104 nm2, respectively. To identify the electronic structure of the carbon nanotube caps, we employed ultraviolet and x-ray photoemission spectroscopy. The angle resolved photoemission study was conducted at a synchrotron radiation center, Center for Z5.8.1
Advanced Microstructures and Devices (CAMD) at Louisiana State University. Monochromatic ultraviolet light was obtained from dispersion of 3m-toroidal grating. To get the ultrahigh vacuum condition (1x 10-10 Torr), the chamber was baked at 450 K for 40 hours. The combined resolution for the photoemission spectroscopy was 100 meV. The aligned samples were annealed for several stag
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