Boron-Doped\nGraphene Nanoribbons: Electronic Structure\nand Raman Fingerprint

Abstract

We investigate the electronic and\nvibrational properties of bottom-up\nsynthesized aligned armchair graphene nanoribbons of <i>N</i> = 7 carbon atoms width periodically doped by substitutional boron\natoms (B-7AGNRs). Using angle-resolved photoemission spectroscopy\nand density functional theory calculations, we find that the dopant-derived\nvalence and conduction band states are notably hybridized with electronic\nstates of Au substrate and spread in energy. The interaction with\nthe substrate leaves the bands with pure carbon character rather unperturbed.\nThis results in an identical effective mass of ≈0.2 <i>m</i>₀ for the next-highest valence band compared\nwith pristine 7AGNRs. We probe the phonons of B-7AGNRs by ultrahigh-vacuum\n(UHV) Raman spectroscopy and reveal the existence of characteristic\nsplitting and red shifts in Raman modes due to the presence of substitutional\nboron atoms. Comparing the Raman spectra for three visible lasers\n(red, green, and blue), we find that interaction with gold suppresses\nthe Raman signal from B-7AGNRs and the energy of the green laser (2.33\neV) is closer to the resonant E₂₂ transition. The hybridized\nelectronic structure of the B-7AGNR–Au interface is expected\nto improve electrical characteristics of contacts between graphene\nnanoribbon and Au. The Raman fingerprint allows the easy identification\nof B-7AGNRs, which is particularly useful for device fabrication.