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  - Raoufi, Meysam
A1  - Hörmann, Ulrich
A1  - Ligorio, Giovanni
A1  - Hildebrandt, Jana
A1  - Pätzel, Michael
A1  - Schultz, Thorsten
A1  - Perdigón-Toro, Lorena
A1  - Koch, Norbert
A1  - List-Kratochvil, Emil
A1  - Hecht, Stefan
A1  - Neher, Dieter
T1  - Simultaneous effect of ultraviolet radiation and surface modification on the work function and hole injection properties of ZnO thin films
JF  - Physica Status Solidi.  A , Applications and materials science
N2  - The combined effect of ultraviolet (UV) light soaking and self-assembled monolayer deposition on the work function (WF) of thin ZnO layers and on the efficiency of hole injection into the prototypical conjugated polymer poly(3-hexylthiophen-2,5-diyl) (P3HT) is systematically investigated. It is shown that the WF and injection efficiency depend strongly on the history of UV light exposure. Proper treatment of the ZnO layer enables ohmic hole injection into P3HT, demonstrating ZnO as a potential anode material for organic optoelectronic devices. The results also suggest that valid conclusions on the energy-level alignment at the ZnO/organic interfaces may only be drawn if the illumination history is precisely known and controlled. This is inherently problematic when comparing electronic data from ultraviolet photoelectron spectroscopy (UPS) measurements carried out under different or ill-defined illumination conditions.
KW  - charge injection across hybrid interfaces
KW  - energy-level alignments
KW  - hybrid metal oxides
KW  - organic interfaces
Y1  - 2020
U6  - https://doi.org/10.1002/pssa.201900876
SN  - 1862-6300
SN  - 1862-6319
VL  - 217
IS  - 5
SP  - 1
EP  - 6
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Schmidt, Roland
A1  - Hagen, Sebastian
A1  - Brete, Daniel
A1  - Carley, Robert
A1  - Gahl, Cornelius
A1  - Dokic, Jadranka
A1  - Saalfrank, Peter
A1  - Hecht, Stefan
A1  - Tegeder, Petra
A1  - Weinelt, Martin
T1  - On the electronic and geometrical structure of the trans- and cis-isomer of tetra-tert-butyl-azobenzene on Au(111)
N2  - Near edge X-ray absorption. ne structure and X-ray photoelectron spectroscopy have been employed to follow the reversible trans to cis isomerization of tetra-tert-butyl-azobenzene (TBA) adsorbed on Au(111). For one monolayer the molecules adopt an adsorption geometry characteristic of the trans-TBA isomer. The azo-bridge (N = N) is aligned nearly parallel to the surface and the phenyl rings exhibit a planar orientation with a small tilt angle <= 4 degrees with respect to the surface normal. Illumination of the molecular layer at 455 nm triggers the trans to cis isomerization which is associated with a pronounced change of the geometrical and electronic structure. The N1s to pi* transition of the central azo-bridge shifts by 0.45 +/- 0.05 eV to higher photon energy and the transition dipole moment (TDM) is tilted by 59 +/- 5 degrees with respect to the surface normal. The pi-system of one phenyl ring is tilted by about 30 degrees with respect to the surface normal, while the second ring plane is oriented nearly perpendicular to the surface. This reorientation is supported by a shift and broadening of the C-H resonances associated with the tert-butyl legs of the molecule. These findings support a configuration of the photo-switched TBA molecule on Au(111) which is comparable to the cis-isomer of the free molecule. In the photo-stationary state 53 +/- 5% of the TBA molecules are switched to the cis configuration. Thermal activation induces the back reaction to trans-TBA.
Y1  - 2010
UR  - http://pubs.rsc.org/en/content/articlehtml/2010/cp/b924409c
U6  - https://doi.org/10.1039/B924409c
SN  - 1463-9076
ER  -