TY  - JOUR
A1  - Maass, Friedrich
A1  - Utecht, Manuel Martin
A1  - Stremlau, Stephan
A1  - Gille, Marie
A1  - Schwarz, Jutta
A1  - Hecht, Stefan
A1  - Klamroth, Tillmann
A1  - Tegeder, Petra
T1  - Electronic structure changes during the on-surface synthesis of nitrogen-doped chevron-shaped graphene nanoribbons
JF  - Physical review : B, Condensed matter and materials physics
N2  - Utilizing suitable precursor molecules, a thermally activated and surface-assisted synthesis results in the formation of defect-free graphene nanoribbons (GNRs), which exhibit electronic properties that are not present in extended graphene. Most importantly, they have a band gap in the order of a few electron volts, depending on the nanoribbon width. In this study, we investigate the electronic structure changes during the formation of GNRs, nitrogen-doped (singly and doubly N-doped) as well as non-N-doped chevron-shaped CGNRs on Au(111). Thus we determine the optical gaps of the precursor molecules, the intermediate nonaromatic polymers, and finally the aromatic GNRs, using high-resolution electron energy loss spectroscopy and density functional theory calculations. As expected, we find no influence of N-doping on the size of the optical gaps. The gap of the precursor molecules is around 4.5 eV. Polymerization leads to a reduction of the gap to a value of 3.2 eV due to elongation and thus enhanced delocalization. The CGNRs exhibit a band gap of 2.8 eV, thus the gap is further reduced in the nanoribbons, since they exhibit an extended delocalized pi-electron system.
Y1  - 2017
U6  - https://doi.org/10.1103/PhysRevB.96.045434
SN  - 2469-9950
SN  - 2469-9969
VL  - 96
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Bronner, Christopher
A1  - Utecht, Manuel Martin
A1  - Haase, Anton
A1  - Saalfrank, Peter
A1  - Klamroth, Tillmann
A1  - Tegeder, Petra
T1  - Electronic structure changes during the surface-assisted formation of a graphene nanoribbon
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - High conductivity and a tunability of the band gap make quasi-one-dimensional graphene nanoribbons (GNRs) highly interesting materials for the use in field effect transistors. Especially bottom-up fabricated GNRs possess well-defined edges which is important for the electronic structure and accordingly the band gap. In this study we investigate the formation of a sub-nanometer wide armchair GNR generated on a Au(111) surface. The on-surface synthesis is thermally activated and involves an intermediate non-aromatic polymer in which the molecular precursor forms polyanthrylene chains. Employing angle-resolved two-photon photoemission in combination with density functional theory calculations we find that the polymer exhibits two dispersing states which we attribute to the valence and the conduction band, respectively. While the band gap of the non-aromatic polymer obtained in this way is relatively large, namely 5.25 +/- 0.06 eV, the gap of the corresponding aromatic GNR is strongly reduced which we attribute to the different degree of electron delocalization in the two systems.
Y1  - 2014
U6  - https://doi.org/10.1063/1.4858855
SN  - 0021-9606
SN  - 1089-7690
VL  - 140
IS  - 2
PB  - American Institute of Physics
CY  - Melville
ER  -