Figure 1: Epitaxial growth of C₈-BTBT molecular crystals on graphene.

(a) Cartoon illustration of the molecular structure of C₈-BTBT (left panel) and their packing on graphene (right panel). (b–e) Sequential AFM snapshots of a sample at different stages during a 95-min growth. Scale bar, 2 μm. The complete sequence of the growth process is shown in Supplementary Fig. 4. (f) Histogram of layer thickness of C₈-BTBT molecular crystals on graphene, taken from over 10 samples. (g–j) AFM (g), Raman mapping (h) and cross-polarized optical micrographs (i,j) of a uniform 1L C₈-BTBT crystal grown on graphene. Scale bar, 3 μm. Inset of g is the height profile along the dashed line. The total thickness of graphene and the crystal is 3.7 nm, confirming 1L C₈-BTBT (2L would have made the total thickness greater than 5.3 nm). The Raman spectrum of the C₈-BTBT crystal is plotted in Supplementary Fig. 13b. (k) Normalized intensity of the 1L C₈-BTBT crystal under cross-polarized optical microscope as a function of rotation angle. The data are taken at the marked spot in i and j. (l–o) Patterned growth of C₈-BTBT crystal on graphene. Scale bar, 7 μm. (l,m) Optical microscopy image of a plasma-patterned graphene before and after C₈-BTBT growth, respectively. (n,o) Cross-polarized optical micrographs of the same area after C₈-BTBT growth. The uniform colour change over the entire area confirms that C₈-BTBT forms a single crystal.