Doctor of Philosophy (PhD)
First Advisor's Name
First Advisor's Committee Title
Second Advisor's Name
Second Advisor's Committee Title
Third Advisor's Name
Third Advisor's Committee Title
Fourth Advisor's Name
Prem P. Chapagain
Fourth Advisor's Committee Title
Fifth Advisor's Name
Fifth Advisor's Committee Title
Vertically aligned Carbon nanotubes (VACNTs), Filled-VACNTs, Direct synthesis, Metal substrates, Tin-oxide nanoparticles, Field emission, Electrochemical lithiation, Lithium-ion battery
Date of Defense
Carbon nanotubes (CNTs) represent one of the critical inventions that have triggered new science and technology in many fields because of their distinctive mechanical, thermal, electrical, electrochemical, and optical properties. Despite the tremendous potential of CNTs, challenges in synthesizing and processing continue to hinder their applications. This dissertation is devoted to synthesizing vertically aligned CNT arrays on metal substrates via plasma-enhanced chemical vapor deposition and the study of their electron field emission (FE) and electrochemical lithiation properties.
Vertically aligned CNTs (VACNTs) are promising electron field emitters for vacuum micro/nano-electronics. Improved control over the morphology and a successful direct-growth of the VACNTs on a metal substrate will greatly improve their emission current and temporal stability. Coating the VACNTs with metal oxides or filling the interior hollow channels of the VACNTs with metals will boost both their mechanical strength and electrical conductivity. The first part of this dissertation is focused on the controlled synthesis, surface modification, metal filling, and FE properties measurement of VACNT arrays grown over several metal substrates, including stainless steel, copper, and nickel. Compared to pristine VACNT array, the SnO2 coated VACNTs (SnO2-VACNTs), VACNT pillars, and copper-filled VACNT array exhibited enhanced FE properties because of the unique structural change caused by the coating procedure, the protection against the structural failure of VACNTs provided by SnO2 nanoparticles, the low contact resistance between the substrate and the VACNTs, the increased active electron emitting sites in pillar structures, and the improved thermal and electrical conductivities of VACNTs caused by a highly conductive copper core filled inside the VACNTs.
Vertically aligned CNTs have great potential applications for developing high-energy and high-power density lithium-ion batteries (LIBs). In the second part of the dissertation, the electrochemical lithiation property of the free-standing binder-free SnO2-VACNTs was investigated. Compared to the conventional graphite-based LIB anode, the SnO2-VACNTs exhibited superior Li+ storage performance with a high specific capacity of 1891 mAh/g at a current density of 0.1 Ah/g after 100 cycles and 900 mAh/g at the current density of 1 A/g after 200 cycles with excellent coulombic efficiency and rate capability, showing potential anode material for developing future LIBs.
Previously Published In
. Arun Thapa, Suman Neupane, Rui Guo, Katherine K. Jungjohann, Doug Pete, Wenzhi Li, “Direct growth of vertically aligned carbon nanotubes on stainless steel by plasma enhanced chemical vapor deposition”, Diamond and Related Materials, 90 (2018) 144-153.
. Arun Thapa, Jing Guo, Katherine L. Jungjohann, Xuewen Wang, Wenzhi Li, “Density control of vertically aligned carbon nanotubes and its effect on field emission properties”, Materials Today Communications 22 (2020) 100761.
. Arun Thapa, Katherine L. Jungjohann, Xuewen Wang, Wenzhi Li, “Improving field emission properties of vertically aligned carbon nanotube arrays through a structure modification”, Journal of Materials Science 55(5) (2020) 2101-2117.
. Arun Thapa, Yuba R. Poudel, Rui Guo, Katherine L. Jungjohann, Xuewen Wang, Wenzhi Li, “Direct synthesis of micropillars of vertically aligned carbon nanotubes on stainless-steel and their excellent field emission properties”, Carbon 171 (2021) 188-200.
. Arun Thapa, Xuewen Wang, Wenzhi Li, “Synthesis and field emission properties of Cu-filled vertically aligned carbon nanotubes”, Applied Surface Science 537 (2021) 148086.
Thapa, Arun, "Electron Field Emission and Electrochemical Lithiation Properties of Vertically Aligned Carbon Nanotube Arrays Grown Directly on Metal Substrates" (2021). FIU Electronic Theses and Dissertations. 4615.
Available for download on Monday, April 15, 2024
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