Bottom-up fabrication and characterization of graphene nanoribbons

Mardi 17 Avril 2012 à 15h00
Salle "Rémy Lemaire" K 223 (1er étage) bât. K de l'institut Néel/CNRS

Pascal RUFFIEUX (EMPA, Dübendorf, Suisse)

Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
Graphene nanoribbons (GNRs) are predicted to be semiconductors with an electronic band gap that sensitively depends on the ribbon width. For armchair GNRs (AGNRs) the band gap is inversely proportional to the ribbon width. Furthermore, a quantum confinement-related periodic modulation of the band gap is added to the inverse scaling. This modulation has a period of three carbon dimers (∆N=3) in ribbon width and becomes dominant for AGNRs narrower than ~3 nm [1]. This allows, in principle, for the design of GNR-based structures with specific and widely tunable electronic properties, but requires structuring with atomic precision. This is the main reason why experiments accessing the electronic structure of narrow GNRs are largely missing, which is in contrast to an impressive number of GNR-related computational studies. Here, I will report on our recently developed bottom-up approach allowing for the successful fabrication of atomically precise GNRs based on surface-assisted synthetic routes using specifically designed precursor monomers [2], thus making narrow GNRs and related graphene nanostructures available for experimental investigations of their structural and electronic properties. More specifically, we elucidate the critical on-surface chemical reactions by a combined computational and experimental approach allowing for a detailed description of the growth process [3]. The electronic band gap of N=7 AGNRs is determined by means of scanning tunneling spectroscopy (STS) on the as-grown GNRs on Au(111). Furthermore, the fabrication of aligned GNR samples using vicinal Au substrates as templates allows for a determination of the band structure via angle-resolved photoelectron spectroscopy (ARPES). The three highest occupied N=7 AGNR bands are clearly identified and their dispersion mapped with high precision.

[1] Yang, L., Park, C.-H., Son, Y.-W., et al., Phys. Rev. Lett., 99, 186801 (2007).
[2] Cai, J., Ruffieux, P., Jaafar, R., et al., Nature, 466, 470–473 (2010).
[3] Blankenburg, S., Cai, J., Ruffieux, P., et al., ACS Nano, 6, 2020-2025 (2012).

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