One of the biggest advantage of the on-surface synthesis of graphene nanoribbons (GNR) with respect to other top-down approaches lies on the capability to synthesize atomically precise GNRs with complex shape and edge structure. These beyond conventional zig-zag and armchair GNRs provide a new route for tailoring electronic and chemical properties. In this work, we report the synthesis and the structural, electrical and chemical characterization of periodically modulated armchair graphene nanoribbons by means of scanning tunneling microscopy and spectroscopy (STM/STS) and X-ray photoemission spectroscopy (XPS). By using the home-designed precursor displayed in Fig. 1a on Au(111), we obtain GNRs were the width is modulated by alternating pairs of 7 and 13 carbon atom chains (Fig.1b). An unconventional surface reconstruction-guided growth leads to ultra-long (~100 nm), parallel GNRs that can even cross monoatomic steps (Fig 1c). At high enough coverage GNRs tend to self-assemble by the lateral interaction between the benzene rings that constitute the 13 AGNR regions (Fig 1d). The tunneling spectra reveal a band gap of 2.5 eV, and the spatial mapping of the HOMO and LUMO orbitals follows the 7-13 modulation of the GNR. The two observations indicate that the electronic confinement seems to be dominated by the inner 7 AGNR, and the band structure modulated by the periodic arrays of the external benzene rings of the 13 A-GNR regions.

Resumen del póster presentado a la 10th Conferencia Fuerzas y Túnel, celebrada en Girona (España) del 5 al 7 de septiembre de 2016.-- et al.

Peer reviewed