Fig. 4: Width distribution of PTCDA-derived seeds.
From: Graphene nanoribbons initiated from molecularly derived seeds
a Large area STM images of nanoribbons initiated from PTCDA-derived seeds after 46 min of CH4 exposure (applied bias = 2 V, tunneling current = 0.1 nA). Scale bar is 200 nm. b High magnification STM image of an individual nanoribbon (applied bias = 2 V, tunneling current = 0.1 nA). Scale bar is 10 nm. Features 1–3 mark GeOx species and/or adsorbates on the bare Ge surface encroaching upon or directly touching the nanoribbon edges (resulting from exposure of the substrate to ambient air during transfer from the CVD reactor to the STM chamber). Feature 4 highlights topographical variation in the Ge underneath the nanoribbons (resembling the shallow hills and valleys that become more prominent in wider nanoribbons because of the nanofaceting of the Ge(001) surface under graphene during synthesis). c High magnification STM image of an individual nanoribbon (applied bias = 0.2 V, tunneling current = 1 nA). Scale bar is 3 nm. Features 5–7 mark honeycomb, intervalley scattering with periodicity of λf (wavelength of electrons near the high symmetry K-point of the first Brillouin zone of graphene), and \(\sqrt 3\) quasiparticle interference patterns, respectively, in the nanoribbon interior. In some instances, these patterns change from scan to scan, likely concurrent with apparent changes in GeOx species and/or adsorbates near the edges or tip (Supplementary Fig. 13). w highlights the nanoribbon width. An additional nanoribbon is characterized by high magnification STM in Supplementary Fig. 14. d–f Width histograms of nanoribbons initiated without seeds, with pentacene-derived seeds, and with PTCDA-derived seeds after 46 min of CH4 exposure. Mean (µ), standard deviation (σ), and polydispersity (σ/µ) are specified, where w = µ ± σ. STM images in a–c are scaled to topographic height, with dark red being lowest and light yellow being highest.
