SUBJECT: Ph.D. Proposal Presentation
BY: Zihao Zhang
TIME: Monday, March 9, 2015, 1:00 p.m.
PLACE: MRDC Building, 4211
TITLE: Investigating the Far- and Near-Field Thermal Radiation in Carbon-Based Nanomaterials
COMMITTEE: Dr. Zhuomin Zhang, Chair (ME)
Dr. Wenshan Cai (ECE)
Dr. Yogendra Joshi (ME)
Dr. Satish Kumar (ME)
Dr. Andrew Peterson (ECE)


Modern nanomaterials made of naturally abundant carbon has paved a path toward developing sensitive thermal detectors, solar energy converters, versatile imaging devices, and many other advanced applications in thermal radiation manipulation. The proposed thesis explores and models the unique electronic properties of carbon nanotubes and graphene, in order to explain their interactions with electromagnetic waves in both classical far-field radiation heat transfer and near-field fluctuational electrodynamics.
The investigation of the optical constants and thermal radiative properties of vertically aligned carbon nanotubes (VACNT) demonstrates the near-perfect absorption in the infrared wavelengths. The dielectric functions of VACNT reveal that hyperbolic dispersion is satisfied in two broad infrared wavelength bands. In the far-field, this hyperbolic behavior suggests collimation of energy rays within the medium. Using the transmission matrix method, the calculation of the Poynting vector gives the energy streamlines within tilted uniaxial media established by the effective medium theory. The near-field radiation heat transfer between semi-infinite VACNT substrates is improved through increased tunneling modes in more evanescent wavevectors. By analyzing the near-field Poynting vector calculations, the penetration depth into the hyperbolic substrate is explained.
This work demonstrates the capabilities of graphene as a radiative heat transfer tuner or enhancer. Graphene, an atomically thin sheet of carbon, possesses interesting properties that give it metal-like conduction by either chemical impurity doping or voltage gating. In the near-field, graphene sheets placed at the interfaces between the vacuum gap and substrates greatly enhances surface plasmon polariton coupling. Graphene in combination with aligned CNT arrays has remarkable promise in creating tunable terahertz plasmonic metamaterials.