Stanford University PhD Defense Announcement

Transport phenomena in carbon nanomaterials

Amitesh Jayaraman

Advisor: Professor Hai Wang

Department of Mechanical Engineering

Date: September 30, 2025

Time: 9:00 am

Location: Building 520, Room 131

Abstract:

Carbon nanomaterials from nanoparticles and graphene are important to a range of applications, from battery anodes, supercapacitor electrodes, quantum dots for photovoltaics, to graphene-based electronic and photonic devices. At-scale synthesis of functional carbon nanomaterials often requires gas-phase techniques that begin from the formation of polycyclic aromatic hydrocarbons (PAHs). Molecular transport phenomena are relevant in the synthesis of nanoparticles and graphene materials. Gas-phase transport through molecular diffusion of PAHs influences the formation and microstructure of carbon nanoparticles and graphene, and electron transport in large PAHs and graphene impacts their applications. In this dissertation work, a gas-kinetic transport theory is developed for the molecular diffusion of planar and arbitrarily-shaped carbon particles.  In the area of electron transport, a phonon amplitude-enhanced electron tunneling theory is developed for bulk graphite and graphitic nanostructures. Both theories are anchored on the fluctuation-dissipation theorem, where macroscopic transport phenomena provide information about, and can be controlled by, molecular-level fluctuations. It is shown that for nonspherical molecules, anisotropic drag effects result in preferential molecular motion along directions of lower drag, which manifests as a diffusion enhancement. Classical Boltzmann transport is used to describe molecular diffusion, and quantum transport considerations are shown to be relevant in understanding electron tunneling in graphite. The interaction between electrons and out-of-plane phonons is necessary to describe the temperature dependence of electric conductivity in graphite; large amplitude phonons provide electrons a means to short-circuit interlayer tunneling through the equilibrium separation distance. Furthermore, it is shown that for nanostructures and metal-graphene junctions, finite-size effects modify electron tunneling through quantum confinement and Heisenberg uncertainty effects. Finally, the electron tunneling theory is used to describe interlayer electron transport and yield insights into the microstructure of battery-relevant graphite intercalation compounds.