Temperature-dependent Raman investigation on suspended graphene: Contribution from thermal expansion coefficient mismatch between graphene and substrate

Dedicated Raman investigation was performed on the graphene suspended on the round holes, compared with graphene supported on Si/SiO2 substrate, in the temperature range from 173 K to 673 K. We observed an unexpected result that the temperature-dependent Raman frequency shift of suspended graphene was similar as that of supported graphene. This evidenced that the strain caused by thermal expansion coefficient mismatch between graphene and substrate cannot be neglected from suspended graphene. We predicted that the unsupported graphene zone and its surrounding graphene that adhered to substrate should be considered as a whole while studying the thermodynamic properties of this suspended graphene, and thus a semi-quantitative factor was introduced to the estimate the contribution from substrate to the suspended graphene, explaining well this result. Our results suggest that the thermal expansion coefficient mismatch induced strain should be taken into consideration in the study of electronic and transport properties of suspended graphene devices, in which the self-heating effect cannot be eliminated during operation.