Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Physics

First Advisor's Name

Wenzhi Li

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Xuewen Wang

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Chunlei Wang

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Prem P. Chapagain

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Yi Xiao

Fifth Advisor's Committee Title

Committee member

Keywords

Vertically aligned Carbon nanotubes (VACNTs), Filled-VACNTs, Direct synthesis, Metal substrates, Tin-oxide nanoparticles, Field emission, Electrochemical lithiation, Lithium-ion battery

Date of Defense

3-26-2021

Abstract

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.

Identifier

FIC009716

Comments

This is the final version of my dissertation.

Previously Published In

[1]. 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.

[2]. 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.

[3]. 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.

[4]. 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.

[5]. Arun Thapa, Xuewen Wang, Wenzhi Li, “Synthesis and field emission properties of Cu-filled vertically aligned carbon nanotubes”, Applied Surface Science 537 (2021) 148086.

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