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Effects of Contact Resistance and Finite Young’s Modulus on the Field Emission Properties of Carbon Nanotube Based Emitters

Tripathi, Geet
http://orcid.org/0000-0003-2135-2753
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1712913505135596

Abstract Details

2024, PhD, University of Cincinnati, Engineering and Applied Science: Electrical Engineering.
This dissertation work deals with the development of refined models of field emission (FE) from carbon nanotubes (CNTs). The first project described focuses on an efficient algorithm computing the temperature distribution along a CNT during FE, considering the substrate as a perfect heat sink at temperature T₀. It incorporates Joule heating effects, radiative losses, and recently reported analytical expressions for emission current density and heat exchange at the CNT tip, including Nottingham-Heating and Henderson-Cooling effects. Temperature dependencies of CNT's electrical resistivity and thermal conductivity are also included. Simulation times for calculating CNT FE characteristics and temperature distribution were found to be about two orders of magnitude faster compared to numerical methods accounting for both current and energy exchange at the CNT tip. The algorithm was adapted to analyze the impact of thermal contact resistance on the FE properties of a CNT. Using a boundary condition from literature, thermal contact resistance effects at a CNT/chuck interface were accounted for, with the chuck assumed as a perfect heat sink at temperature T₀. Results demonstrate that current constriction at the CNT/chuck contact point induces self-heating effects, which escalate with higher thermal contact resistance values. Consequently, this increases the temperature profile along the CNT, including its tip temperature, and augments the FE current beyond values presumed with the CNT/chuck interface at T₀. The fractional change of emission current with applied external electric field was calculated for increasing thermal resistivity values of the CNT/chuck interface. Next, the effect of electrostatic forces on the FE properties of flexible emitters as a function of the strength of the applied (macroscopic) external electrostatic field are investigated. Results show that deflection of a flexible metallic CNT due to an externally applied electrostatic field increases its tip field enhancement factor (FEF) as the CNT tip is pulled away from the cathode with increasing field strengths. A numerical integration of solutions to the Euler-Bernoulli (EB) and Laplace equations using COMSOL reveal the presence of nonlinearities in the CNT FE characteristics which are related to the change in the CNT FEF with the applied electrostatic field. Detailed investigation of the bending is carried out as a function of its physical dimensions and the initial angle Θ₀ it makes with its attached base. The results stress the importance of including the effects of bending of CNTs when calculating the FE characteristics of CNT arrays such as from a CNT fiber whose FE properties are primarily determined by the FE properties of the array of CNTs at the tip of the fiber. Finally, the FE characteristics of various non-uniform CNT array configurations as a function of the spacings between the CNTs were investigated using COMSOL. Study included the effects of true randomization in CNT physical parameters (heights, radii, and positions) within the arrays and implementation of a more accurate Murphy-Good FE current estimation model on the average value and standard deviation of the FE current as a function of the size of the CNT array.
Marc Cahay, Ph.D. (Committee Chair)
Tao Li, Ph.D. (Committee Member)
Mark Schulz, Ph.D. (Committee Member)
Tyson Back, Ph.D. (Committee Member)
Yeongin Kim, Ph.D. (Committee Member)
Je-Hyeong Bahk, Ph.D. (Committee Member)
105 p.
Electrical Engineering
Field Electron Emission; Nanomaterials; Carbon Nanotubes; Vacuum Emission Physics; Modeling/Simulations; Iterative Scripts

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Citations

  • Tripathi, G. (2024). Effects of Contact Resistance and Finite Young’s Modulus on the Field Emission Properties of Carbon Nanotube Based Emitters [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1712913505135596

    APA Style (7th edition)

  • Tripathi, Geet. Effects of Contact Resistance and Finite Young’s Modulus on the Field Emission Properties of Carbon Nanotube Based Emitters. 2024. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1712913505135596.

    MLA Style (8th edition)

  • Tripathi, Geet. "Effects of Contact Resistance and Finite Young’s Modulus on the Field Emission Properties of Carbon Nanotube Based Emitters." Doctoral dissertation, University of Cincinnati, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1712913505135596

    Chicago Manual of Style (17th edition)

ucin1712913505135596
83
© 2024, some rights reserved.Creative Commons License Effects of Contact Resistance and Finite Young’s Modulus on the Field Emission Properties of Carbon Nanotube Based Emitters by Geet Tripathi is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Cincinnati and OhioLINK.