Dokument-ID Dokumenttyp Verfasser/Autoren Herausgeber Haupttitel Abstract Auflage Verlagsort Verlag Erscheinungsjahr Seitenzahl Schriftenreihe Titel Schriftenreihe Bandzahl ISBN Quelle der Hochschulschrift Konferenzname Quelle:Titel Quelle:Jahrgang Quelle:Heftnummer Quelle:Erste Seite Quelle:Letzte Seite URN DOI Abteilungen OPUS4-37629 Wissenschaftlicher Artikel Utecht, Manuel Martin; Pan, Tianluo; Klamroth, Tillmann; Palmer, Richard E. Quantum chemical cluster models for chemi- and physisorption of chlorobenzene on Si(111)-7x7 Motivated by recent atomic manipulation experiments, we report quantum chemical calculations for chemi- and physisorption minima of chlorobenzene on the Si(111)-7x7 surface. A density functional theory cluster approach is applied, using the B3LYP hybrid functional alongside Grimme's empirical dispersion corrections (D3). We were able to identify chemisorption sites of binding energies of 1.6 eV and physisorption energies of 0.6 eV, both in encouraging agreement with the trend of experimental data. The cluster approach opens up the possibility of a first-principles based dynamical description of STM manipulation experiments on this system, the interpretation of which involves both the chemi- and physisorbed states. However, we found that special care has to be taken regarding the choice of clusters, basis sets, and the evaluation of the dispersion corrections. Washington American Chemical Society 2014 6 The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory 118 33 6699 6704 10.1021/jp504208d Institut für Chemie OPUS4-54778 Wissenschaftlicher Artikel Utecht, Manuel Martin; Palmer, Richard E.; Klamroth, Tillmann Quantum chemical approach to atomic manipulation of chlorobenzene on the Si(111)-7 x 7 surface 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. College Park American Physical Society 2017 5 Physical review materials 1 2 10.1103/PhysRevMaterials.1.026001 Institut für Chemie OPUS4-37233 Wissenschaftlicher Artikel Utecht, Manuel Martin; Klamroth, Tillmann; Saalfrank, Peter Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers a study based on density functional theory Based on the analysis of optical absorption spectra, it has recently been speculated that the excitonic coupling between individual azobenzene-functionalized alkanethiols arranged in a self-assembled monolayer (SAM) on a gold surface could be strong enough to hinder collective trans-cis isomerization-on top of steric hindrance [Gahl et al., J. Am. Chem. Soc., 2010, 132, 1831]. Using models of SAMs of increasing complexity (dimer, linear N-mers, and two-dimensionally arranged N-mers) and density functional theory on the (TD-) B3LYP/6-31G* level, we determine optical absorption spectra, the nature and magnitude of excitonic couplings, and the corresponding spectral shifts. It is found that at inter-monomer distances of about 20 angstrom and above, TD-B3LYP excitation frequencies (and signal intensities) can be well described by the frequently used point-dipole approximation. Further, calculated blue shifts in optical absorption spectra account for the experimental observations made for azobenzene/gold SAMs, and hint to the fact that they can indeed be responsible for reduced switching probability in densely packed self-assembled structures. Cambridge Royal Society of Chemistry 2011 7 Physical chemistry, chemical physics : a journal of European Chemical Societies 13 48 21608 21614 10.1039/c1cp22793a Institut für Chemie OPUS4-54513 Wissenschaftlicher Artikel Utecht, Manuel Martin; Klamroth, Tillmann Local resonances in STM manipulation of chlorobenzene on Si(111)-7x7 Hot localised charge carriers on the Si(111)-7x7 surface are modelled by small charged clusters. Such resonances induce non-local desorption, i.e. more than 10 nm away from the injection site, of chlorobenzene in scanning tunnelling microscope experiments. We used such a cluster model to characterise resonance localisation and vibrational activation for positive and negative resonances recently. In this work, we investigate to which extent the model depends on details of the used cluster or quantum chemistry methods and try to identify the smallest possible cluster suitable for a description of the neutral surface and the ion resonances. Furthermore, a detailed analysis for different chemisorption orientations is performed. While some properties, as estimates of the resonance energy or absolute values for atomic changes, show such a dependency, the main findings are very robust with respect to changes in the model and/or the chemisorption geometry. [GRAPHICS] . Abingdon Routledge, Taylor & Francis Group 2018 10 Molecular physics 116 13 1687 1696 10.1080/00268976.2018.1442939 Institut für Physik und Astronomie OPUS4-51174 Wissenschaftlicher Artikel Utecht, Manuel Martin; Gaebel, Tina; Klamroth, Tillmann Desorption induced by low energy charge carriers on Si(111)-7 x 7 We use clusters for the modeling of local ion resonances caused by low energy charge carriers in STM-induced desorption of benzene derivates from Si(111)-7 x 7. We perform Born-Oppenheimer molecular dynamics for the charged systems assuming vertical transitions to the charged states at zero temperature, to rationalize the low temperature activation energies, which are found in experiment for chlorobenzene. Our calculations suggest very similar low temperature activation energies for toluene and benzene. For the cationic resonance transitions to physisorption are found even at 0 K, while the anion remains chemisorbed during the propagations. Further, we also extend our previous static quantum chemical investigations to toluene and benzene. In addition, an in depth analysis of the ionization potentials and electron affinities, which are used to estimate resonance energies, is given. Hoboken Wiley 2018 9 Journal of computational chemistry : organic, inorganic, physical, biological 39 30 2517 2525 10.1002/jcc.25607 Institut für Chemie OPUS4-8512 Dissertation Utecht, Manuel Martin Zur Optimierung und dem Auslesen molekularer Schalter 2015 143 Institut für Chemie OPUS4-39338 Wissenschaftlicher Artikel Schulze, Michael; Utecht, Manuel Martin; Moldt, Thomas; Przyrembel, Daniel; Gahl, Cornelius; Weinelt, Martin; Saalfrank, Peter; Tegeder, Petra Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10(-18) cm(2) for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions. Cambridge Royal Society of Chemistry 2015 8 Physical chemistry, chemical physics : a journal of European Chemical Societies 17 27 18079 18086 10.1039/c5cp03093e Institut für Chemie OPUS4-8118 Wissenschaftlicher Artikel Schulze, Michael; Utecht, Manuel Martin; Moldt, Thomas; Przyrembel, Daniel; Gahl, Cornelius; Weinelt, Martin; Saalfrank, Peter; Tegeder, Petra Nonlinear optical response of photochromic azobenzene-functionalized self-assembled monolayers The combination of photochromic and nonlinear optical (NLO) properties of azobenzene-functionalized self-assembled monolayers (SAMs) constitutes an intriguing step towards novel photonic and optoelectronic devices. By utilizing the second-order NLO process of second harmonic generation (SHG), supported by density-functional theory and correlated wave function method calculations, we demonstrate that the photochromic interface provides the necessary prerequisites en route towards possible future technical applications: we find a high NLO contrast on the order of 16% between the switching states. These are furthermore accessible reversibly and with high efficiencies in terms of cross sections on the order of 10−18 cm2 for both photoisomerization reactions, i.e., drivable by means of low-power LED light sources. Finally, both photostationary states (PSSs) are thermally stable at ambient conditions. Cambridge Royal Society of Chemistry 2015 7 Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies 27 17 18079 18086 10.1039/c5cp03093e Institut für Chemie OPUS4-39170 Wissenschaftlicher Artikel Schulze, Michael; Utecht, Manuel Martin; Hebert, Andreas; Rück-Braun, Karola; Saalfrank, Peter; Tegeder, Petra Reversible Photoswitching of the Interfacial Nonlinear Optical Response Incorporating photochromic molecules into organic/inorganic hybrid materials may lead to photoresponsive systems. In such systems, the second-order nonlinear properties can be controlled via external stimulation with light at an appropriate wavelength. By creating photochromic molecular switches containing self-assembled monolayers on Si(111), we can demonstrate efficient reversible switching, which is accompanied by a pronounced modulation of the nonlinear optical (NLO) response of the system. The concept of utilizing functionalized photoswitchable Si surfaces could be a way for the generation of two-dimensional NLO switching materials, which are promising for applications in photonic and optoelectronic devices. Washington American Chemical Society 2015 5 The journal of physical chemistry letters 6 3 505 509 10.1021/jz502477m Institut für Chemie OPUS4-46507 Wissenschaftlicher Artikel Maass, Friedrich; Utecht, Manuel Martin; Stremlau, Stephan; Gille, Marie; Schwarz, Jutta; Hecht, Stefan; Klamroth, Tillmann; Tegeder, Petra Electronic structure changes during the on-surface synthesis of nitrogen-doped chevron-shaped graphene nanoribbons 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. College Park American Physical Society 2017 7 Physical review : B, Condensed matter and materials physics 96 10.1103/PhysRevB.96.045434 Institut für Physik und Astronomie