Thermal expansion coefficient of multilayer graphene with rotational stacking faults

Recent studies on twisted bilayer and multi-layer graphene have opened new avenues of research in condensed matter physics. These artificially made superlattices showed very intriguing electrical properties, including superconductivity at certain commensurate rotation angles between the stacked layers. Even though electrical properties are studied to some extent, the effect of rotation angle on the thermal properties has not received adequate attention. In particular, the thermal expansion of these systems is not well understood. In this direction, we have studied thermal expansion coefficient of few-layer graphene samples with rotational misorientation. These samples were synthesized using chemical vapor deposition technique from a solid carbon precursor. The Raman spectra of these samples indicated the presence of rotational stacking faults, which was confirmed by selected area electron diffraction measurements. Finally, the in-plane thermal expansion coefficient of this system was obtained using temperature dependent Raman spectroscopy for T = 4.5 to 300K. Thermal expansion coefficient was determined to be negative in this temperature range and the corresponding room temperature value was obtained to be ≈ -3.47 × 10-6 K-1. This value is comparable to that of few- layer graphene. We suggest that the thermal expansion of multilayer graphene with rotational stacking faults follows the thermal expansion of the individual few-layer crystallites rather than showing bulk graphitic behavior.