Raman Spectroscopy of Ripple Formation in Suspended Graphene
journal contributionposted on 09.12.2009, 00:00 by Chun-Chung Chen, Wenzhong Bao, Jesse Theiss, Chris Dames, Chun Ning Lau, Stephen B. Cronin
Using Raman spectroscopy, we measure the optical phonon energies of suspended graphene before, during, and after thermal cycling between 300 and 700 K. After cycling, we observe large upshifts (∼25 cm−1) of the G band frequency in the graphene on the substrate region due to compression induced by the thermal contraction of the underlying substrate, while the G band in the suspended region remains unchanged. From these large upshifts, we estimate the compression in the substrate region to be ∼0.4%. The large mismatch in compression between the substrate and suspended regions causes a rippling of the suspended graphene, which compensates for the change in lattice constant due to the compression. The amplitude (A) and wavelength (λ) of the ripples, as measured by atomic force microscopy, correspond to an effective change in length Δl/l that is consistent with the compression values determined from the Raman data.