TY  - JOUR
A1  - Utecht, Manuel Martin
A1  - Palmer, Richard E.
A1  - Klamroth, Tillmann
T1  - Quantum chemical approach to atomic manipulation of chlorobenzene on the Si(111)-7 x 7 surface
BT  - Resonance localization, vibrational activation, and surface dynamics
JF  - Physical review materials
N2  - We present a cluster model to describe the localization of hot charge carriers on the Si(111)-7 x 7 surface, which leads to (nonlocal) desorption of chlorobenzene molecules in scanning tunneling microscope (STM) manipulation experiments. The localized charge carriers are modeled by a small cluster. By means of quantum chemical calculations, this cluster model explains many experimental findings from STM manipulation. We show that the negative charge is mainly localized in the surface, while the positive one also resides on the molecule. Both resonances boost desorption: In the negative resonance the adatom is elevated; in the positive one the chemisorption bond between the silicon surface adatom and chlorobenzene is broken. We find normal modes promoting desorption matching experimental low-temperature activation energies for electron-and hole-induced desorption.
Y1  - 2017
U6  - https://doi.org/10.1103/PhysRevMaterials.1.026001
SN  - 2475-9953
VL  - 1
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
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  -