Controlled stress – thermally inducing strain in graphene

Abstract

This thesis investigates the effects of thermal strain on single to few layer graphene on silicon substrates below room temperature. Three graphene device designs and two directions of temperature change were explored to determine the differences these cause in graphene undergoing strain. Biaxial strain dependences with temperature were found in all graphene thicknesses and designs, with a magnitude consistent with the difference in thermal expansion coefficient (TEC) predicted between graphene and the substrate. The samples did not show significant variance in strain or dopant concentration dependences that correlated with the manufacturing or measurement methods. The thermal expansion coefficients of single to three layer graphene was measured in the range from 6 K to 296 K and were found to be in good agreement with the predicted theory of single layer graphene. A preliminary study into the effects of ultra-flat, h-BN substrates to observe differences in the graphene strain and TEC was undertaken. It was inconclusive at this stage if any significant differences are caused.