Albert Sacco Jr., Katherine S. Ziemer
Vincent G. Harris, Juliusz Warzywoda
Date of Award
Master of Science
Department or Academic Unit
College of Engineering. Department of Chemical Engineering.
Chemical engineering, Chemical vapor deposition (CVD)
Nanotubes, Field emission
With the flat panel display industry eclipsing $101 Billion in 2007 and consumer demand for improved picture quality ever growing, field emission has received increased attention. Traditional field emitters have higher pixel density than current displays, but their contrast ratio suffers due to insufficient emission current. An ordered array of multi-wall carbon nanotubes (MWCNTs) should produce much higher emission currents due to their >100x increase in aspect ratio. However, such a device has not yet been demonstrated due, in part, to the challenge of fabricating an ordered vertical array of straight, uniform diameter MWCNTs. MWCNTs were grown in a chemical vapor deposition (CVD) reactor by exposing nickel nanoparticles, formed by annealing thermally evaporated nickel thin films under 20 cm³/s (STP) hydrogen flow at 1173 K for 5 minutes, to a mixture of 6 gases (CH4, CO2, CO, H2, and H2O) with a gas phase carbon activity of 20 at 900 K and a total flow rate of 20 cm³/s (STP) for 90 minutes. Spaghetti-like MWCNTs grew on substrates with 10.2 ± 1 nm nickel nanoparticles in a gas mixture with O/H ratio 0.1. An increase in the O/H ratio to 0.5 resulted in the formation of both spaghetti-like MWCNTs and straight MWCNTs. Substrates with 6.1 ± 1 nm nickel nanoparticles and the same O/H ratio, resulted in preferential growth of straight, uniform diameter MWCNTs. Thus, the fabrication of straight, uniform diameter MWCNTs with CVD requires a nickel nanoparticle diameter less than 10 nm and an O/H ratio of 0.5. Arrays of 43 nm wells were obtained through electron-beam lithography (EBL) after optimization of the thickness of the resist layers and e-beam dosages in addition to hard-baking of the resist. Subsequently, catalyst was deposited within the wells to enable site-specific growth of the MWCNTs. Hard-baking prevented the resist layer from collapsing during the EBL process, but also prevented its removal during lift-off. Electrical characterization of candidate devices within a custom-built high vacuum chamber showed the need for voltages above 162 V in order to achieve measurable emission.
Jonathan Gar-Sing Leong
Leong, Jonathan Gar-Sing, "Controlled growth of uniform diameter multi-wall carbon nanotube arrays via chemical vapor deposition for application in field emission devices" (2008). Chemical Engineering Master's Theses. Paper 3. http://hdl.handle.net/2047/d10018633
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