TY - JOUR A1 - Mielke, Johannes A1 - Martınez-Blanco, J. A1 - Peters, M. V. A1 - Hecht, S. A1 - Grill, L. T1 - Observing single-atom diffusion at a molecule-metal interface N2 - The dynamics at the interface between a close-packed porphyrin monolayer and Au(111) is investigated by time-dependent scanning tunneling microscopy, detecting the motion of single-interface adatoms in real space. Imaging sequences reveal predominant switching of the molecular appearance in adjacent molecules, pointing to a spatial correlation that is consistent with adatom diffusion from one molecule to the next. In some cases, the number of switching molecules is drastically increased, indicating collective switching events. In addition to the thermally induced motion of adatoms at the interface, also voltage pulses from the microscope tip can induce the process—revealing different yields in agreement with the model of adatom hopping. KW - STM KW - molecular switch KW - single molecule KW - switching dynamics KW - porphyrin KW - Au(111) PY - 2016 UR - http://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.035416 U6 - https://doi.org/10.1103/PhysRevB.94.035416 VL - 94 IS - 3 SP - 035416-1 EP - 035416-7 PB - American Physical Society AN - OPUS4-37177 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Saywell, A. A1 - Bakker, A. A1 - Mielke, Johannes A1 - Kumagai, T. A1 - Wolf, M. A1 - García-López, V. A1 - Chiang, P.-T. A1 - Tour, J. M. A1 - Grill, L. T1 - Light-Induced Translation of Motorized Molecules on a Surface N2 - Molecular machines are a key component in the vision of molecular nanotechnology and have the potential to transport molecular species and cargo on surfaces. The motion of such machines should be triggered remotely, ultimately allowing a large number of molecules to be propelled by a single source, with light being an attractive stimulus. Here, we report upon the photoinduced translation of molecular machines across a surface by characterizing single molecules before and after illumination. Illumination of molecules containing a motor unit results in an enhancement in the diffusion of the molecules. The effect vanishes if an incompatible photon energy is used or if the motor unit is removed from the molecule, revealing that the enhanced motion is due to the presence of the wavelength-sensitive motor in each molecule. KW - Diffusion KW - Molecular devices KW - Molecular motor KW - Scanning probe microscopy KW - Photoexcitation KW - Photochemistry KW - Molecular machines PY - 2016 UR - http://pubs.acs.org/doi/abs/10.1021/acsnano.6b05650 U6 - https://doi.org/10.1021/acsnano.6b05650 VL - 10 IS - 12 SP - 10945 EP - 10952 PB - ACS Publications AN - OPUS4-39095 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Böckmann, H. A1 - Liu, S. A1 - Mielke, Johannes A1 - Gawinkowski, S. A1 - Walluk, J. A1 - Grill, L. A1 - Wolf, M. A1 - Kumagai, T. T1 - Direct observation of photoinduced tautomerization in single molecules at a metal surface N2 - Molecular switches are of fundamental importance in nature, and light is an important stimulus to selectively drive the switching process. However, the local dynamics of a conformational change in these molecules remain far from being completely understood at the single-molecule level. Here, we report the direct observation of photoinduced tautomerization in single porphycene molecules on a Cu(111) surface by using a combination of low-temperature scanning tunneling microscopy and laser excitation in the near-infrared to ultraviolet regime. It is found that the thermodynamically stable trans configuration of porphycene can be converted to the metastable cis configuration in a unidirectional fashion by photoirradiation. The wavelength dependence of the tautomerization cross section exhibits a steep increase around 2 eV and demonstrates that excitation of the Cu d-band electrons and the resulting hot carriers play a dominant role in the photochemical process. Additionally, a pronounced isotope effect in the cross section (∼100) is observed when the transferred hydrogen atoms are substituted with deuterium, indicating a significant contribution of zero-point energy in the reaction. Combined with the study of inelastic tunneling electron-induced tautomerization with the STM, we propose that tautomerization occurs via excitation of molecular vibrations after photoexcitation. Interestingly, the observed cross section of ∼10–19 cm2 in the visible–ultraviolet region is much higher than that of previously studied molecular switches on a metal surface, for example, azobenzene derivatives (10–23–10–22 cm2). Furthermore, we examined a local environmental impact on the photoinduced tautomerization by varying molecular density on the surface and find substantial changes in the cross section and quenching of the process due to the intermolecular interaction at high density. KW - STM KW - Pophycene PY - 2016 U6 - https://doi.org/10.1021/acs.nanolett.5b04092 SN - 1530-6984 SN - 1530-6992 VL - 16 IS - 2 SP - 1034 EP - 1041 PB - ACS AN - OPUS4-35803 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mielke, Johannes A1 - Hanke, F. A1 - Peters, M.V. A1 - Hecht, S. A1 - Persson, M. A1 - Grill, L. T1 - Adatoms underneath single porphyrin molecules on Au(111) N2 - The adsorption of porphyrin derivatives on a Au(111) surface was studied by scanning tunneling microscopy and spectroscopy at low temperatures in combination with density functional theory calculations. Different molecular appearances were found and could be assigned to the presence of single gold adatoms bonded by a coordination bond underneath the molecular monolayer, causing a characteristic change of the electronic structure of the molecules. Moreover, this interpretation could be confirmed by manipulation experiments of individual molecules on and off a single gold atom. This study provides a detailed understanding of the role of metal adatoms in surface–molecule bonding and anchoring and of the appearance of single molecules, and it should prove relevant for the imaging of related molecule–metal systems. PY - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-324144 UR - http://pubs.acs.org/doi/pdf/10.1021/ja510528x SN - 0002-7863 SN - 1520-5126 VL - 137 IS - 5 SP - 1844 EP - 1849 PB - American Chemical Society CY - Washington, DC AN - OPUS4-32414 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -