Manifestation of ripples in free-standing graphene in lattice images obtained in an aberration-corrected scanning transmission electron microscope

The shape of ripples in free-standing graphene is derived from bond length distributions in high-angle annular-dark-field (Z-contrast) images, obtained in an aberration-corrected scanning transmission electron microscope (superSTEM). Local undulation patterns can readily be visualized by applying fast Fourier transform procedures to the lattice images, using a spatial frequency Mer which passes the precise graphitic a-plane spacing. Using aberration-corrected STEM presents the unique opportunity to correlate atomic resolution imaging with the undulations. Values for projected bond lengths, and hence bond inclinations, can be obtained by adjusting the fill to the appropriate band pass. Ripples with amplitude similar to 0.2 in and width similar to 5 nm were observed. Their patterns mod in repeated image scans, with prolonged scanning introducing vacancies. These, in conjunction with adatoms which re also revealed in Z-contrast, induce highly localized Change in the mechanical properties of graphene. Ripples in defected graphene remain dynamic, with changes occurring together with redistribution of defects. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim