Fig. 2: Experimental characterization of the aligned GNR heterojunctions on Au(788).

a STM topographic image of fused 7-AGNRs (sample bias V_s = −1.3 V, tunneling current I_t = 1.8 nA). The black lines outline one possible conducting path through the GNR heterojunctions: quasi-metallic 14- and 21-AGNRs connected by 7-AGNR segments. The inset shows an example of a typical 14-/7-/14-AGNR heterojunction with a short (~3 nm) 7-AGNR segment. See also Supplementary Note 1. b Calculated electronic band structure of 7-AGNRs (blue) and 14-AGNRs (red) shown in the second Brillouin zone of GNRs, where the ARPES scans were acquired. The first and the second valence sub-bands of 14-AGNRs (7-AGNRs) are labeled as VB\({\,}_{1}^{14\mbox{-}{\rm{AGNR}}}\) (VB\({\,}_{1}^{7\mbox{-}{\rm{AGNR}}}\)) and VB\({\,}_{2}^{14\mbox{-}{\rm{AGNR}}}\) (VB\({\,}_{2}^{7\mbox{-}{\rm{AGNR}}}\)), respectively. The valence band maxima in the calculations are aligned to the ARPES data. c Second derivative with respect to momentum of the ARPES scan (to enhance the contrast) of fused GNRs on Au(788) measured along the GNR axis (k_∥) with fixed in-plane momentum perpendicular to the axis (k_⊥)³⁷. To maximize the photoemission intensity from VB\({\,}_{1}^{14\mbox{-}{\rm{AGNR}}}\), we used k_⊥ = 1.1 Å⁻¹. At this k_⊥, the intensities from VB\({\,}_{2}^{14\mbox{-}{\rm{AGNR}}}\) and VB\({\,}_{2}^{7\mbox{-}{\rm{AGNR}}}\) overlap (Supplementary Note 2). The Au sp bands that are from the substrate are also indicated. d UHV Raman spectra (300 K, 633 nm) of GNRs on Au(788) before and after fusion. The frequencies of the respective Raman peaks are indicated (values in cm⁻¹). e Calculated Raman spectra of 7-AGNR and 14-AGNR. The structure of 7-AGNR and 14-AGNR unit cells with the eigenvectors of selected phonon modes are shown (see also Supplementary Note 4). The arrows indicate the atomic displacement. The RBLM3₇ and RBLM3₁₄ are the third overtones of RBLM₇ and RBLM₁₄, respectively.