Probing residual strain in epitaxial graphene layers on 4H-SiC(0001¯) with Raman spectroscopy

Raman microspectroscopy was used to measure compressive strain within epitaxial graphene (EG) grown on the carbon-terminated SiC(0001¯) face as a function of annealing time for a growth temperature of 1400 °C. A maximum strain of −0.5% was seen at the longest time of 55 min. This differs from the −0.9% expected for strain caused by cooling from the growth temperature due to the differential thermal contraction between the SiC and EG layer, despite good agreement between this model and data on EG on SiC(0001). We suggest that this is due to the different EG bonding mechanisms on the two SiC faces.