Kavli Affiliate: Michael Crommie
| Summary:
Graphene nanoribbons (GNRs) are a highly tunable class of one-dimensional (1D) quantum materials that can be fabricated through bottom-up synthesis. Precise control over GNR band gaps and band-edge alignments has established them as a promising nanoelectronics platform, but forming high-quality electronic interfaces remains challenging. Here we combine sequential on-surface synthesis and scanning tunneling microscopy (STM)-induced dehydrogenation to directly write metallic 7-iGNR segments into otherwise semiconducting H$_2$-7-iGNRs without changing the GNR width or carbon backbone connectivity. The resulting metallic segments exhibit nonzero spectral weight at the Fermi level ($E_mathrmF$) and spatially extended electronic states, consistent with two dispersive bands crossing $E_mathrmF$. The new metallic states are well described by an extended Su–Schrieffer–Heeger zigzag-ladder Hamiltonian. Scanning tunnelling spectroscopy (STS) and first-principles calculations show that the valence band edge of adjacent, connected semiconducting GNR segments lies close to $E_mathrmF$ for the metallic segments. STS spectra recover bulk GNR properties within $sim$1 nm on either side of the metal-semiconductor GNR interface, with no discernible depletion region. The observed GNR band edge alignment is consistent with a small energy barrier for hole injection, thus suggesting a possible route towards atomically precise, low-barrier p-type contacts for future GNR-based electronic devices.
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