Field Emission of ITO-Coated Vertically Aligned Nanowire Array
© The Author(s) 2010
Received: 25 January 2010
Accepted: 13 April 2010
Published: 29 April 2010
An indium tin oxide (ITO)-coated vertically aligned nanowire array is fabricated, and the field emission characteristics of the nanowire array are investigated. An array of vertically aligned nanowires is considered an ideal structure for a field emitter because of its parallel orientation to the applied electric field. In this letter, a vertically aligned nanowire array is fabricated by modified conventional UV lithography and coated with 0.1-μm-thick ITO. The turn-on electric field intensity is about 2.0 V/μm, and the field enhancement factor, β, is approximately 3,078 when the gap for field emission is 0.6 μm, as measured with a nanomanipulator in a scanning electron microscope.
KeywordsField emission ITO Nanowire Top–down
Field emission is quantum mechanical tunneling of electrons through the surface potential barrier into vacuum , which has been widely exploited in vacuum electronic applications including electron guns, microwave tubes, and flat panel displays . Vertically aligned nanowire array (VANA) shows excellent field emission properties owing to a strong local electric field due to their parallel orientation to the applied electric field . Numerous studies have been carried out on the fabrication of VANAs as field emitters using bottom-up synthesis approaches [4–6]. However, these bottom-up methods have drawbacks such as an expensive process and relatively low fabrication reliability, thus making them unsuitable for mass production.
In this letter, a top–down method of modified conventional UV lithography is suggested for the fabrication of a VANA, thereby resolving the problems of bottom-up methods while allowing control over the VANA’s position and shape. In the lithography process, a photoresist VANA is fabricated with a UV exposure dose control. After the lithography, a carbonization process (pyrolysis process) is followed to provide volume contraction of the array’s structure. The pyrolyzed carbon VANA is coated with a 0.1-μm-thick ITO layer in order to realize a durable field emitter and to provide low turn-on voltage [7, 8]. ITO has good transparence characteristics in the visible region of the electromagnetic spectrum while maintaining high electrical conductivity, thermal stability, and oxidation resistance [4, 9]. In a field emission experiment, a nanomanipulator in a scanning electron microscope (SEM) is used in order to measure field emission while precisely controlling the distance between the anode and cathode (field emitter).
Note that −21.18 is the slope of the red line and −5.76 is the y-intercept of the red line in Fig. 4b. The estimated field enhancement factor of the ITO-coated VANA, β, is 3,078 when the work function of ITO is 4.5 eV . The measured value of the field enhancement factor is comparable with previous research results of field emitters [4, 14, 15].
In summary, an ITO-coated VANA was fabricated by a top–down method using modified conventional UV lithography, and the field emission characteristics were evaluated using a Zyvex nanomanipulator. The top–down method offers many advantages including an economical process, good fabrication reliability, and suitability for mass production. The turn-on electric field intensity of the ITO-coated VANA is about 2.0 V/μm, and the estimated field enhancement factor β is 3,078. These results show that the ITO-coated VANA is a very promising candidate for vacuum electron field emission applications.
This work was partly supported by Brain Korea 21 and Award No KUK-F1-038-02, made by King Abdullah University of Science and Technology (KAUST).
This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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