(color online) (a) Graphene G-band frequency map. Scale bars, 10 μm.^[70] (b) Graphene G-peak averaged over a dark and a bright stripe in panel (a) with the G-band frequency and 1596.8 cm for bright and dark stripes, respectively. Lines correspond to Lorentzian fits to the experimental data (orange diamonds for the bright stripe and dark-red squares for the dark stripe).^[70] (c) Schematic of a top-gated graphene transistor on periodically poled .^[70] (d) Representative gate-dependent Raman G-band frequency averaged over a down-polarized domain (orange diamonds) and an up-polarized domain (dark-red squares). Error bars indicate the s. d. of the frequency within each stripe.^[70] (e) Photocurrent response of a ferroelectricity-induced p–n junction in graphene. The red line represents the photocurrent response of a top-gated graphene transistor with a gate voltage of 400 mV on periodically poled . The simultaneously detected Raman E(TO8) frequency (black) along the same line was used to identify the down polarized (blue) and up-polarized (orange) domains of the . Grey shading corresponds to the Ti/Pd contacts. A schematic band diagram can be constructed based on the experimental observations.^[70]