UC Riverside

Graphene and single-walled carbon nanotubes (SWNTs) are new low dimensional carbon allotropes discovered in recent decades. They have attracted attention because of their unique features from the standpoint of new science and engineering applications. My thesis is focused on the chemical functionalization and applications of these new materials.

The covalent chemical functionalization of graphitic surfaces usually leads to the conversion of sp2 carbon to sp3, thus introducing defects and decreasing the charge carriers mobility. Recently, we discovered that the organometallic chemistry of graphitic surfaces results in the formation of an electronically conjugating, organometallic bis-hexahapto-graphene junction while maintaining the electronic structure of the individual graphene nanostructures; such bonds involve minimal (structural) rehybridization.

Reduction of graphene oxide has been studied as promising method to produce graphene in a large scale, while the conjugation is usually not completely recovered. The characterization of the graphene derived materials and their degree of conjugation remains an important topic in carbon sciences. We have applied absorption spectroscopy and conductivity measurements to measure the conjugation degree of graphene derived materials.

The high thermal conductivity of a graphene layer makes graphite nanoplatelets (GNPs) promising fillers in thermal interface materials. As 2D materials, the orientation of GNPs in thermal composite was investigated. The electrical and thermal properties in in-plane and through-plane directions were measured, showing that the in-plane conductivity is higher than that in through-plane direction. Scanning electron microscopy (SEM) reveals that the anisotropy in the transport properties is due to the in-plane alignment of the GNPs which occurs during the formation of the thermal interface layer. Because the alignment in the thermal interface layer suppresses the through-plane component of the thermal conductivity, the anisotropy strongly degrades the performance of GNPs-based composites in the geometry required for typical thermal management applications and must be taken into account in the development of GNPs-based TIMs. Spherical microparticles were applied to disrupt the GNPs alignment. The hybrid filler formulations reported herein resulted in a synergistic enhancement of the through-plane thermal conductivity of GNP/Al2O3 and GNP/Al filled TIM layers confirming that the control of GNP alignment is an important parameter in the development of highly efficient GNP and graphene-based TIMs.