SUBJECT: Ph.D. Dissertation Defense
BY: David Brown
TIME: Thursday, January 10, 2019, 9:30 a.m.
PLACE: MRDC Building, 3515
TITLE: Experimental Characterization of Thermal Transport in Two-Dimensional Materials and Thin Films
COMMITTEE: Dr. Satish Kumar, Co-Chair (ME)
Dr. Baratunde A. Cola, Co-Chair (ME)
Dr. Samuel Graham (ME)
Dr. Matthew McDowell (ME)
Dr. Eric M. Vogel (MSE)


The power consumption and heat removal in modern microelectronics are limited by the thermal boundary conductance (TBC) at the interfaces and the change in thermal properties for thin films at the nanoscale. A fundamental understanding and characterization of the thermal transport properties is crucial to ensure energy efficient operation and long lifetime. Two-dimensional (2D) graphene and transition metal dichalcogenides (TMDs) are being investigated for applications in next generation devices, but the interfaces play a critical role in their performance. Time-domain thermoreflectance (TDTR) is used to explore the TBC at metal-graphene-metal interfaces. Metals which strongly interact with graphene are expected to exhibit high TBC, but this is prevented by native oxide on the surface. The TBC at the interfaces of 2D hexagonal boron nitride (h-BN) and graphene are estimated using TDTR. The phonon transmission, including the contributions of different phonon modes, and TBC are calculated using two forms of the diffuse mismatch model for highly anisotropic materials. The spatial variation of TBC at the interface of the 2D semiconducting TMD MoSe2 and metal is demonstrated using a modified TDTR technique. The results indicate enhanced TBC at Ti-MoSe2 interface compared to Al-MoSe2. Additional analysis of optical images and 2D TBC maps revealed increased TBC in single-layer regions compared to bilayer. High dielectric constant insulators such as HfO2 are promising for many future applications, but the impact of the thermal properties cannot be overlooked. The thermal conductivity and heat capacity of HfO2 films of varying thickness is estimated using TDTR. A 20% reduction in bulk heat capacity observed for a 215 nm layer is attributed to density differences originating from combined amorphous and crystalline film composition. The thickness-independent thermal conductivity of HfO2 layers from 12 to 215 nm is measured and is close to the bulk value.