Thermal properties of few-layer graphene crystallites: role of stacking faults

Layered 2D materials such as graphene have attracted great interest in thermal management applications. In this work we examined thermal properties of few-layer graphene crystallites arranged vertically with stacking disorder. Thermal conductivity and total interface conductance are obtained using Raman optothermal technique together with finite-element simulation. Multi-layer films consisting of vertically assembled few-layer graphene stacks were prepared using CVD technique and stacking disorder was confirmed using Raman spectroscopy and atomic force microscopy measurements. Thermal conductivity was determined to be in the order of 150 W/mK and it was 70% lower when compared to exfoliated multi-layer graphene that lacked stacking faults. Usually a significant decrease in thermal conductivity in graphitic systems is associated with a decrease in the grain size, whereas the defect density in our samples was very small. We discuss the decrease in thermal conductivity based on increased rate of phonon-phonon scattering due to stacking faults. Furthermore, the negative thermal expansion coefficient was estimated as ~ 3.46 ×10^-6 K^-1 near room temperature, and the phonon modes contributing to the same will be discussed.