Electronic structure of a subnanometer wide bottom-up fabricated graphene nanoribbon: End states, band gap, and dispersion

Abstract

Angle-resolved two-photon photoemission and high-resolution electron energy loss spectroscopy are employed to derive the electronic structure of a sub-nanometer atomically precise quasi-onedimensional graphene nanoribbon (GNR) on Au(111). We resolved occupied and unoccupied electronic bands including their dispersion and determined the band gap, which possesses an unexpected large value of 5.1 eV. Supported by density functional theory (DFT) calculations for the idealized infinite polymer and finite size oligomers an unoccupied non-dispersive electronic state with an energetic position in the middle of the band gap of the GNR could be identified. This state resides at both ends of the ribbon (end state) and is only found in the finite sized systems, i.e. the oligomers.

Suppression of electron–vibron coupling in graphene nanoribbons contacted via a single atom

“…S1). The end state is located at positive bias, implying the GNR to be hole doped by the Au(111) substrate 13,16,17,22 . Its spatial shape can be imaged by taking dI/dV maps in the constant-height mode (Fig.…”

Electronic states in finite graphene nanoribbons: Effect of charging and defects

“…[30][31][32] In the experiments, 15,17,18 the zigzag end state peak is observed at positive bias, suggesting that the ribbons are hole-doped. Recently, the interface between Au(111) electrodes and finite armchair GNRs with rounded termini was studied using DFT, and a charge transfer of up to 0.05 electrons per carbon atom from the ribbon to the electrode was found.…”

“…2 It is well known that the PBE-functional underestimates band gaps, and thus the calculated bulk states are at lower energies on the unoccupied side than expected based on the experimentally determined band gap (2.3-5.1 eV). 13,15,16,18 Using the PBE functional, the onset of the occupied and unoccupied bulk states occurs at −0.8 to −1.1 eV and at 0.3 to 1.0 eV, respectively, for the different edge terminations. The use of the B3LYP hybrid functional increases the energy level spacing.…”

“…12 The electronic structure of these ribbons has been widely studied, [13][14][15][16][17][18] finding a bulk band gap of 2.3-5.1 eV using scanning tunneling spectroscopy (STS), [13][14][15][16][17] angle-resolved photoelectron spectroscopy (ARPES), 13 and optical methods. 16,18 Within the bulk gap, states localized at the ribbon zigzag ends have been observed. 14,17,18 A double-peak structure resembling the spin-split zigzag end states was indeed recently found in STS measurements.…”

Identification of pristine and defective graphene nanoribbons by phonon signatures in the electron transport characteristics

“…Furthermore, several groups have succeeded in atomically precise bottom-up fabrication of armchair GNRs (AGNR) [14,15], chiral GNRs [16], and AGNR heterojunctions [17] grown on metal surfaces. Experimentally, the vibrational properties have been investigated by Raman spectroscopy and the electronic structure has been mapped out by STM, angle-resolved (two-photon) photoemission and * mads.brandbyge@nanotech.dtu.dk high-resolution electron energy loss spectroscopy [8,18,19]. Signatures of phonon excitation were observed by STM in the differential conductance spectroscopy performed at the zigzag termini state of AGNRs adsorbed on Au(111), and these signatures were shown to be sensitive to modifications in the local atomic geometry [20].…”