2020
|
| 66. | C. Metzger, M. Graus, M. Grimm, G. Zamborlini, V. Feyer, M. Schwendt, D. Lüftner, P. Puschnig, A. Schöll, F. Reinert Plane-wave final state for photoemission from nonplanar molecules at a metal-organic interface Journal Article In: Phys. Rev. B, vol. 101, iss. 16, pp. 165421, 2020. @article{Metzger2020,
title = {Plane-wave final state for photoemission from nonplanar molecules at a metal-organic interface},
author = {C. Metzger and M. Graus and M. Grimm and G. Zamborlini and V. Feyer and M. Schwendt and D. Lüftner and P. Puschnig and A. Schöll and F. Reinert},
doi = {10.1103/PhysRevB.101.165421},
year = {2020},
date = {2020-04-01},
journal = {Phys. Rev. B},
volume = {101},
issue = {16},
pages = {165421},
publisher = {American Physical Society},
abstract = {In recent years, the method of orbital tomography has been a useful tool for the analysis of a variety of molecular systems. However, the underlying plane-wave final state has been largely expected to be applicable to planar molecules only. Here, we demonstrate on photoemission data from the molecule C60 adsorbed on Ag(110) that it can indeed be a valid approximation for truly three-dimensional molecules at a metal-organic interface. A comparison of the experimental data supported by density functional theory (DFT) calculations of the full interface and simulations of the photoemission process with a more exact final state enables the determination of the adsorption geometry and orientation of the C60 molecules in a monolayer on the Ag(110) surface. Additionally, charge transfer into the molecules is used to confirm the lifting in degeneracy of the t1u molecular orbitals as predicted by DFT calculations.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
In recent years, the method of orbital tomography has been a useful tool for the analysis of a variety of molecular systems. However, the underlying plane-wave final state has been largely expected to be applicable to planar molecules only. Here, we demonstrate on photoemission data from the molecule C60 adsorbed on Ag(110) that it can indeed be a valid approximation for truly three-dimensional molecules at a metal-organic interface. A comparison of the experimental data supported by density functional theory (DFT) calculations of the full interface and simulations of the photoemission process with a more exact final state enables the determination of the adsorption geometry and orientation of the C60 molecules in a monolayer on the Ag(110) surface. Additionally, charge transfer into the molecules is used to confirm the lifting in degeneracy of the t1u molecular orbitals as predicted by DFT calculations. |
| 65. | N. Haag, D. Lüftner, F. Haag, J. Seidel, L. L. Kelly, G. Zamborlini, M. Jugovac, V. Feyer, M. Aeschlimann, P. Puschnig, M. Cinchetti, B. Stadtmüller Signatures of an atomic crystal in the band structure of a C60 thin film Journal Article In: Phys. Rev. B, vol. 101, iss. 16, pp. 165422, 2020. @article{Haag2020,
title = {Signatures of an atomic crystal in the band structure of a C60 thin film},
author = {N. Haag and D. Lüftner and F. Haag and J. Seidel and L. L. Kelly and G. Zamborlini and M. Jugovac and V. Feyer and M. Aeschlimann and P. Puschnig and M. Cinchetti and B. Stadtmüller},
doi = {10.1103/PhysRevB.101.165422},
year = {2020},
date = {2020-04-01},
journal = {Phys. Rev. B},
volume = {101},
issue = {16},
pages = {165422},
publisher = {American Physical Society},
abstract = {Transport phenomena in molecular materials are intrinsically linked to the orbital character and the degree of localization of the valence states. Here we combine angle-resolved photoemission with photoemission tomography to determine the spatial distribution of all molecular states of the valence band structure of a C60 thin film. While the two most frontier valence states exhibit a strong band dispersion, the states at larger binding energies are characterized by distinct emission patterns in energy and momentum space. Our findings demonstrate the formation of an atomic crystal-like band structure in a molecular solid with delocalized π-like valence states and strongly localized σ states at larger binding energies.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
Transport phenomena in molecular materials are intrinsically linked to the orbital character and the degree of localization of the valence states. Here we combine angle-resolved photoemission with photoemission tomography to determine the spatial distribution of all molecular states of the valence band structure of a C60 thin film. While the two most frontier valence states exhibit a strong band dispersion, the states at larger binding energies are characterized by distinct emission patterns in energy and momentum space. Our findings demonstrate the formation of an atomic crystal-like band structure in a molecular solid with delocalized π-like valence states and strongly localized σ states at larger binding energies. |
| 64. | A. Haags, A. Reichmann, Q. Fan, L. Egger, H. Kirschner, T. Naumann, S. Werner, T. Vollgraff, J. Sundermeyer, L. Eschmann, X. Yang, D. Brandstetter, F. C. Bocquet, G. Koller, A. Gottwald, M. Richter, M. G. Ramsey, M. Rohlfing, P. Puschnig, J. M. Gottfried, S. Soubatch, F. S. Tautz Kekulene: On-Surface Synthesis, Orbital Structure, and Aromatic Stabilization Journal Article In: ACS Nano, vol. 14, pp. 15766-15775, 2020. @article{Haags2020,
title = {Kekulene: On-Surface Synthesis, Orbital Structure, and Aromatic Stabilization},
author = {A. Haags and A. Reichmann and Q. Fan and L. Egger and H. Kirschner and T. Naumann and S. Werner and T. Vollgraff and J. Sundermeyer and L. Eschmann and X. Yang and D. Brandstetter and F. C. Bocquet and G. Koller and A. Gottwald and M. Richter and M. G. Ramsey and M. Rohlfing and P. Puschnig and J. M. Gottfried and S. Soubatch and F. S. Tautz},
doi = {10.1021/acsnano.0c06798},
year = {2020},
date = {2020-01-01},
journal = {ACS Nano},
volume = {14},
pages = {15766-15775},
abstract = {We revisit the question of kekulene’s aromaticity by focusing on the electronic structure of its frontier orbitals as determined by angle-resolved photoemission spectroscopy. To this end, we have developed a specially designed precursor, 1,4,7(2,7)-triphenanthrenacyclononaphane-2,5,8-triene, which allows us to prepare sufficient quantities of kekulene of high purity directly on a Cu(111) surface, as confirmed by scanning tunneling microscopy. Supported by density functional calculations, we determine the orbital structure of kekulene’s highest occupied molecular orbital by photoemission tomography. In agreement with a recent aromaticity assessment of kekulene based solely on C–C bond lengths, we conclude that the π-conjugation of kekulene is better described by the Clar model rather than a superaromatic model. Thus, by exploiting the capabilities of photoemission tomography, we shed light on the question which consequences aromaticity holds for the frontier electronic structure of a π-conjugated molecule.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
We revisit the question of kekulene’s aromaticity by focusing on the electronic structure of its frontier orbitals as determined by angle-resolved photoemission spectroscopy. To this end, we have developed a specially designed precursor, 1,4,7(2,7)-triphenanthrenacyclononaphane-2,5,8-triene, which allows us to prepare sufficient quantities of kekulene of high purity directly on a Cu(111) surface, as confirmed by scanning tunneling microscopy. Supported by density functional calculations, we determine the orbital structure of kekulene’s highest occupied molecular orbital by photoemission tomography. In agreement with a recent aromaticity assessment of kekulene based solely on C–C bond lengths, we conclude that the π-conjugation of kekulene is better described by the Clar model rather than a superaromatic model. Thus, by exploiting the capabilities of photoemission tomography, we shed light on the question which consequences aromaticity holds for the frontier electronic structure of a π-conjugated molecule. |
| 63. | P. Hurdax, M. Hollerer, L. Egger, G. Koller, X. Yang, A. Haags, S. Soubatch, F. S. Tautz, M. Richter, A. Gottwald, P. Puschnig, M. Sterrer, M. G. Ramsey Controlling the electronic and physical coupling on dielectric thin films Journal Article In: Beilstein J. Nanotechnol., vol. 11, pp. 1492-1503, 2020. @article{Hurdax2020a,
title = {Controlling the electronic and physical coupling on dielectric thin films},
author = {P. Hurdax and M. Hollerer and L. Egger and G. Koller and X. Yang and A. Haags and S. Soubatch and F. S. Tautz and M. Richter and A. Gottwald and P. Puschnig and M. Sterrer and M. G. Ramsey},
doi = {10.3762/bjnano.11.132},
year = {2020},
date = {2020-01-01},
journal = {Beilstein J. Nanotechnol.},
volume = {11},
pages = {1492-1503},
abstract = {Ultrathin dielectric/insulating films on metals are often used as decoupling layers to allow for the study of the electronic properties of adsorbed molecules without electronic interference from the underlying metal substrate. However, the presence of such decoupling layers may effectively change the electron donating properties of the substrate, for example, by lowering its work function and thus enhancing the charging of the molecular adsorbate layer through electron tunneling. Here, an experimental study of the charging of para-sexiphenyl (6P) on ultrathin MgO(100) films supported on Ag(100) is reported. By deliberately changing the work function of the MgO(100)/Ag(100) system, it is shown that the charge transfer (electronic coupling) into the 6P molecules can be controlled, and 6P monolayers with uncharged molecules (Schottky–Mott regime) and charged and uncharged molecules (Fermi level pinning regime) can be obtained. Furthermore, it was found that charge transfer and temperature strongly influence the orientation, conformation, and wetting behavior (physical coupling) of the 6P layers on the MgO(100) thin films.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
Ultrathin dielectric/insulating films on metals are often used as decoupling layers to allow for the study of the electronic properties of adsorbed molecules without electronic interference from the underlying metal substrate. However, the presence of such decoupling layers may effectively change the electron donating properties of the substrate, for example, by lowering its work function and thus enhancing the charging of the molecular adsorbate layer through electron tunneling. Here, an experimental study of the charging of para-sexiphenyl (6P) on ultrathin MgO(100) films supported on Ag(100) is reported. By deliberately changing the work function of the MgO(100)/Ag(100) system, it is shown that the charge transfer (electronic coupling) into the 6P molecules can be controlled, and 6P monolayers with uncharged molecules (Schottky–Mott regime) and charged and uncharged molecules (Fermi level pinning regime) can be obtained. Furthermore, it was found that charge transfer and temperature strongly influence the orientation, conformation, and wetting behavior (physical coupling) of the 6P layers on the MgO(100) thin films. |
| 62. | P. Hurdax, M. Hollerer, P. Puschnig, D. Lüftner, L. Egger, M. G. Ramsey, M. Sterrer Controlling the Charge Transfer across Thin Dielectric Interlayers Journal Article In: Adv. Mater. Interfaces, vol. 7, pp. 2000592, 2020. @article{Hurdax2020,
title = {Controlling the Charge Transfer across Thin Dielectric Interlayers},
author = {P. Hurdax and M. Hollerer and P. Puschnig and D. Lüftner and L. Egger and M. G. Ramsey and M. Sterrer},
doi = {10.1002/admi.202000592},
year = {2020},
date = {2020-01-01},
journal = {Adv. Mater. Interfaces},
volume = {7},
pages = {2000592},
abstract = {Whether intentional or unintentional, thin dielectric interlayers can be found in technologies ranging from catalysis to organic electronics. While originally considered as passive decoupling layers, recently it has been shown that they can actively promote charge transfer from the underlying metal to adsorbates. This charging can have profound effects on the surface chemistry of atoms, atomic clusters, and molecules, their magnetic moments, and charge injection at the contacts of organic devices. Yet, controlled studies required to understand the charge transfer process in depth are still lacking. Here, a comprehensive analysis of the phenomenon of charge transfer using the atomically controlled system of pentacene on ultrathin MgO(100) films on Ag(100) is presented. It is shown that the charge transfer process is governed by the charged and uncharged molecular species with distinct energy levels in the first monolayer. The experimental approach applied in this work allows to observe and control their ratio through direct tuning of either the work function or the thickness of the dielectric interlayer.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
Whether intentional or unintentional, thin dielectric interlayers can be found in technologies ranging from catalysis to organic electronics. While originally considered as passive decoupling layers, recently it has been shown that they can actively promote charge transfer from the underlying metal to adsorbates. This charging can have profound effects on the surface chemistry of atoms, atomic clusters, and molecules, their magnetic moments, and charge injection at the contacts of organic devices. Yet, controlled studies required to understand the charge transfer process in depth are still lacking. Here, a comprehensive analysis of the phenomenon of charge transfer using the atomically controlled system of pentacene on ultrathin MgO(100) films on Ag(100) is presented. It is shown that the charge transfer process is governed by the charged and uncharged molecular species with distinct energy levels in the first monolayer. The experimental approach applied in this work allows to observe and control their ratio through direct tuning of either the work function or the thickness of the dielectric interlayer. |
| 61. | H. M. Sturmeit, I. Cojocariu, M. Jugovac, A. Cossaro, A. Verdini, L. Floreano, A. Sala, G. Comelli, S. Moro, M. Stredansky, M. Corva, E. Vesselli, P. Puschnig, C. M. Schneider, V. Feyer, G. Zamborlini, M. Cinchetti Molecular anchoring stabilizes low valence Ni(I)TPP on copper against thermally induced chemical changes Journal Article In: J. Mater. Chem. C, vol. 8, pp. 8876-8886, 2020. @article{Sturmeit2020,
title = {Molecular anchoring stabilizes low valence Ni(I)TPP on copper against thermally induced chemical changes},
author = {H. M. Sturmeit and I. Cojocariu and M. Jugovac and A. Cossaro and A. Verdini and L. Floreano and A. Sala and G. Comelli and S. Moro and M. Stredansky and M. Corva and E. Vesselli and P. Puschnig and C. M. Schneider and V. Feyer and G. Zamborlini and M. Cinchetti},
doi = {10.1039/D0TC00946F},
year = {2020},
date = {2020-01-01},
journal = {J. Mater. Chem. C},
volume = {8},
pages = {8876-8886},
abstract = {Many applications of molecular layers deposited on metal surfaces, ranging from single-atom catalysis to on-surface magnetochemistry and biosensing, rely on the use of thermal cycles to regenerate the pristine properties of the system. Thus, understanding the microscopic origin behind the thermal stability of organic/metal interfaces is fundamental for engineering reliable organic-based devices. Here, we study nickel porphyrin molecules on a copper surface as an archetypal system containing a metal center whose oxidation state can be controlled through the interaction with the metal substrate. We demonstrate that the strong molecule–surface interaction, followed by charge transfer at the interface, plays a fundamental role in the thermal stability of the layer by rigidly anchoring the porphyrin to the substrate. Upon thermal treatment, the molecules undergo an irreversible transition at 420 K, which is associated with an increase of the charge transfer from the substrate, mostly localized on the phenyl substituents, and a downward tilting of the latters without any chemical modification.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
Many applications of molecular layers deposited on metal surfaces, ranging from single-atom catalysis to on-surface magnetochemistry and biosensing, rely on the use of thermal cycles to regenerate the pristine properties of the system. Thus, understanding the microscopic origin behind the thermal stability of organic/metal interfaces is fundamental for engineering reliable organic-based devices. Here, we study nickel porphyrin molecules on a copper surface as an archetypal system containing a metal center whose oxidation state can be controlled through the interaction with the metal substrate. We demonstrate that the strong molecule–surface interaction, followed by charge transfer at the interface, plays a fundamental role in the thermal stability of the layer by rigidly anchoring the porphyrin to the substrate. Upon thermal treatment, the molecules undergo an irreversible transition at 420 K, which is associated with an increase of the charge transfer from the substrate, mostly localized on the phenyl substituents, and a downward tilting of the latters without any chemical modification. |
2019
|
| 60. | D. Brandstetter Photoemission tomography: experimental data evaluation by fitting to simulated momentum maps Bachelor Thesis 2019. @bachelorthesis{Brandstetter2019,
title = {Photoemission tomography: experimental data evaluation by fitting to simulated momentum maps},
author = {D. Brandstetter},
url = {https://homepage.uni-graz.at/en/peter.puschnig/theses/},
year = {2019},
date = {2019-08-01},
abstract = {Orbital tomography is a new method of analysis in surface science, developed in the last decade. It uses the data from angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) to clarify or even reconstruct orbitals of more complex organic molecules like bisanthene. The conservation of momentum parallel to the surface for an escaping photoelectron provides a basis for this. Using Fermi’s golden rule, it can be shown that the differential cross-section is proportional to the Fourier transformation of the initial state of the electron.
Thus, comparing experimental data and the data of a DFT-simulation, applying a ”plane wave” approximation for the final state of the electron, information about the initial state can be gained.
The practical part of this thesis was concerned with the extension of the functionality provided by a program written for said comparison. Besides implementing a “brute-force” algorithm to find the optimal orientation of the molecule in the simulation, multiple features to manipulate the data were added.},
keywords = {},
pubstate = {published},
tppubtype = {bachelorthesis}
}
Orbital tomography is a new method of analysis in surface science, developed in the last decade. It uses the data from angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) to clarify or even reconstruct orbitals of more complex organic molecules like bisanthene. The conservation of momentum parallel to the surface for an escaping photoelectron provides a basis for this. Using Fermi’s golden rule, it can be shown that the differential cross-section is proportional to the Fourier transformation of the initial state of the electron.
Thus, comparing experimental data and the data of a DFT-simulation, applying a ”plane wave” approximation for the final state of the electron, information about the initial state can be gained.
The practical part of this thesis was concerned with the extension of the functionality provided by a program written for said comparison. Besides implementing a “brute-force” algorithm to find the optimal orientation of the molecule in the simulation, multiple features to manipulate the data were added. |
| 59. | A. Wachter Vergleich von Oligoacenen mit fluorinierten Versionen dieser Moleküle Bachelor Thesis 2019. @bachelorthesis{Wachter2019,
title = {Vergleich von Oligoacenen mit fluorinierten Versionen dieser Moleküle},
author = {A. Wachter},
url = {https://homepage.uni-graz.at/en/peter.puschnig/theses/},
year = {2019},
date = {2019-05-29},
abstract = {One of the most important types of organic semiconductors are molecules with linear condensed ring systems, which the oligoacenes are part of. But it ́s very hard to make oligoacene n-type conductive. To face this problem one could perfluorinate those oligoacene, which would swap the hydrogen with those of fluorine atoms. This would lead to a ring system with only C-C and C-F bonds, which will have different conductive properties. This work focuses on the impacts of the perfluorination on the oligoacene, which go up to seven carbon rings. To do this, density functional theory (DFT) calculations have been performed, which were aimed to assess information regarding the structure changes of those perfluorinated oligoacene. Those DFT calculations where performed at the B3LYP/6-31G* level. Further, the energies of the frontier molecular orbitals (MOs) around the gap, as well as the photoemission angular distribution (PAD) were calculated, which should give a good comparison of those structures. Finally, the gap distance was evaluated, which showed a maximal decrease for a single carbon ring of 0.28 eV after it was perfluorinated.},
keywords = {},
pubstate = {published},
tppubtype = {bachelorthesis}
}
One of the most important types of organic semiconductors are molecules with linear condensed ring systems, which the oligoacenes are part of. But it ́s very hard to make oligoacene n-type conductive. To face this problem one could perfluorinate those oligoacene, which would swap the hydrogen with those of fluorine atoms. This would lead to a ring system with only C-C and C-F bonds, which will have different conductive properties. This work focuses on the impacts of the perfluorination on the oligoacene, which go up to seven carbon rings. To do this, density functional theory (DFT) calculations have been performed, which were aimed to assess information regarding the structure changes of those perfluorinated oligoacene. Those DFT calculations where performed at the B3LYP/6-31G* level. Further, the energies of the frontier molecular orbitals (MOs) around the gap, as well as the photoemission angular distribution (PAD) were calculated, which should give a good comparison of those structures. Finally, the gap distance was evaluated, which showed a maximal decrease for a single carbon ring of 0.28 eV after it was perfluorinated. |
| 58. | M. Unzog Adsorption of Oligoacenes and Their Derivatives on Metal Surfaces: A Density Functional Study Masters Thesis 2019. @mastersthesis{Unzog2019,
title = {Adsorption of Oligoacenes and Their Derivatives on Metal Surfaces: A Density Functional Study},
author = {M. Unzog},
url = {https://homepage.uni-graz.at/en/peter.puschnig/theses/},
year = {2019},
date = {2019-05-07},
abstract = {In this thesis we investigate oligoacaenes and their derivatives on metal surfaces by means of density functional theory (DFT). In the first chapter we review density functional theory and how it is used in practice. There, we also discuss topics which come up often in this thesis: the workfunction and its changes, the projected density of states, simulation of photoemission tomography maps and finally the theory of scanning tunneling microscopy (STM). In the second chapter we investigate four different adsorption geometries of tetracene on Ag(110). For each of those geometries we investigate the electronic structure by calculating the workfunction, the respective workfunction change and the projected density of states. For two of those geometries we simulate angle-resolved photoemission maps using the one-step model and compare them with experimentally available maps. In the second chapter we investigate dihydrotetraazapentacene on Cu(110)-(2x1)O. We determine the optimal adsorption site by first locally relaxing the molecules on different adsorption sites and then comparing the energies of the relaxed geometries. Furthermore we calculate the diffusion barrier between two adjacent optimal adsorption sites. We also simulate STM images for these different geometries by using the Tersoff-Hamann approximation and compare the simulated STM image of the optimal adsorption geometry with experimentally available STM data.},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
In this thesis we investigate oligoacaenes and their derivatives on metal surfaces by means of density functional theory (DFT). In the first chapter we review density functional theory and how it is used in practice. There, we also discuss topics which come up often in this thesis: the workfunction and its changes, the projected density of states, simulation of photoemission tomography maps and finally the theory of scanning tunneling microscopy (STM). In the second chapter we investigate four different adsorption geometries of tetracene on Ag(110). For each of those geometries we investigate the electronic structure by calculating the workfunction, the respective workfunction change and the projected density of states. For two of those geometries we simulate angle-resolved photoemission maps using the one-step model and compare them with experimentally available maps. In the second chapter we investigate dihydrotetraazapentacene on Cu(110)-(2x1)O. We determine the optimal adsorption site by first locally relaxing the molecules on different adsorption sites and then comparing the energies of the relaxed geometries. Furthermore we calculate the diffusion barrier between two adjacent optimal adsorption sites. We also simulate STM images for these different geometries by using the Tersoff-Hamann approximation and compare the simulated STM image of the optimal adsorption geometry with experimentally available STM data. |
| 57. | M. Hollerer Charge transfer through thin dielectric films: organic molecules on MgO(001)/Ag(001) PhD Thesis 2019. @phdthesis{Hollerer2019b,
title = {Charge transfer through thin dielectric films: organic molecules on MgO(001)/Ag(001)},
author = {M. Hollerer},
url = {https://resolver.obvsg.at/urn:nbn:at:at-ubg:1-137820},
year = {2019},
date = {2019-02-01},
abstract = {The investigation of epitaxially grown, ultra-thin dielectric films on metal substrates is of great interest in the fields of catalysis and organic electronics. Here, we explore the energy alignment of adsorbates on top of dielectric/metal systems and their resulting charge state. Finally, we demonstrate the impact of charge transfer on fundamental physical and chemical. Organic and inorganic adsorbates are therefore systematically investigated on pristine silver single crystals (Ag(001)) and on Ag(001) supported magnesium oxide (MgO) ultra-thin films.We demonstrate integer charge transfer to the Lowest Unoccupied Molecular Orbital of pentacene (5A) adsorbed on MgO(001)/Ag(001) and fractional charge transfer of 0.7 electrons per molecule on pristine Ag(001). We identify the individual energy level alignment contributions and roughly quantify them. By varying the initial workfunction of the MgO(001)/Ag(001) substrate the equilibration mechanism, leading to the final, constant workfunction, is investigated.Charge transfer to 2-dimensional gold (Au) islands on MgO(001)/Ag(001) enables the catalytic formation of oxalates from carbon-dioxides. Here, we find a morphological transition from 2D to 3D Au-islands upon annealing to elevated temperatures that coincides with a significant decrease of the oxalate formation We conclude that the catalytic reactivity is facilitated by excess charges located on the rim of 2-dimensional Au-islands. In a related topic, we demonstrate that charge transfer controls the self-metalation reaction of free-base porphyrin (2H-TPP) to Mg-TPP on MgO(001)/Ag(001). We achieve this by tuning of the initial substrate workfunction, either enabling or inhibiting charge transfer, and monitoring of the N 1s XPS signal of the porphyrins. Furthermore, we present a scanning tunneling microscopy study on the monolayer formation of water on MgO(001)/Ag(001) and a combined-method growth study on Para-Sexiyphenyl (6P) on pristine Ag(001).},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
The investigation of epitaxially grown, ultra-thin dielectric films on metal substrates is of great interest in the fields of catalysis and organic electronics. Here, we explore the energy alignment of adsorbates on top of dielectric/metal systems and their resulting charge state. Finally, we demonstrate the impact of charge transfer on fundamental physical and chemical. Organic and inorganic adsorbates are therefore systematically investigated on pristine silver single crystals (Ag(001)) and on Ag(001) supported magnesium oxide (MgO) ultra-thin films.We demonstrate integer charge transfer to the Lowest Unoccupied Molecular Orbital of pentacene (5A) adsorbed on MgO(001)/Ag(001) and fractional charge transfer of 0.7 electrons per molecule on pristine Ag(001). We identify the individual energy level alignment contributions and roughly quantify them. By varying the initial workfunction of the MgO(001)/Ag(001) substrate the equilibration mechanism, leading to the final, constant workfunction, is investigated.Charge transfer to 2-dimensional gold (Au) islands on MgO(001)/Ag(001) enables the catalytic formation of oxalates from carbon-dioxides. Here, we find a morphological transition from 2D to 3D Au-islands upon annealing to elevated temperatures that coincides with a significant decrease of the oxalate formation We conclude that the catalytic reactivity is facilitated by excess charges located on the rim of 2-dimensional Au-islands. In a related topic, we demonstrate that charge transfer controls the self-metalation reaction of free-base porphyrin (2H-TPP) to Mg-TPP on MgO(001)/Ag(001). We achieve this by tuning of the initial substrate workfunction, either enabling or inhibiting charge transfer, and monitoring of the N 1s XPS signal of the porphyrins. Furthermore, we present a scanning tunneling microscopy study on the monolayer formation of water on MgO(001)/Ag(001) and a combined-method growth study on Para-Sexiyphenyl (6P) on pristine Ag(001). |
| 56. | J. Felter, J. Wolters, F. C. Bocquet, F. S. Tautz, C. Kumpf Momentum microscopy on the micrometer scale: photoemission micro-tomography applied to single molecular domains Journal Article In: J. Phys.: Condens. Matter, vol. 31, pp. 114003, 2019. @article{Felter2019,
title = {Momentum microscopy on the micrometer scale: photoemission micro-tomography applied to single molecular domains},
author = {J. Felter and J. Wolters and F. C. Bocquet and F. S. Tautz and C. Kumpf},
doi = {10.1088/1361-648X/aafc45},
year = {2019},
date = {2019-01-25},
journal = {J. Phys.: Condens. Matter},
volume = {31},
pages = {114003},
abstract = {Photoemission tomography (PT) is a newly developed method for analyzing angularresolved photoemission data. In combination with momentum microscopy it allows fora comprehensive investigation of the electronic structure of (in particular) metal-organicinterfaces as they occur in organic electronic devices. The most interesting aspect in thiscontext is the band alignment, the control of which is indispensable for designing devices.Since PT is based on characteristic photoemission patterns that are used as fingerprints,the method works well as long as these patterns are uniquely representing the specificmolecular orbital they are originating from. But this limiting factor is often not fulfilledfor systems exhibiting many differently oriented molecules, as they may occur on highlysymmetric substrate surfaces. Here we show that this limitation can be lifted by recording thephotoemission data in a momentum microscope and limiting the probed surface area to onlya few micrometers squared, since this corresponds to a typical domain size for many systems.We demonstrate this by recording data from a single domain of the archetypal adsorbatesystem 1,4,5,8-naphthalenetetracarboxylic dianhydride on Cu(0 0 1). This proof of principleexperiment paves the way for establishing the photoemission μ-tomography method as anideal tool for investigating the electronic structure of metal-organic interfaces with so farunraveled clarity and unambiguity.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Photoemission tomography (PT) is a newly developed method for analyzing angularresolved photoemission data. In combination with momentum microscopy it allows fora comprehensive investigation of the electronic structure of (in particular) metal-organicinterfaces as they occur in organic electronic devices. The most interesting aspect in thiscontext is the band alignment, the control of which is indispensable for designing devices.Since PT is based on characteristic photoemission patterns that are used as fingerprints,the method works well as long as these patterns are uniquely representing the specificmolecular orbital they are originating from. But this limiting factor is often not fulfilledfor systems exhibiting many differently oriented molecules, as they may occur on highlysymmetric substrate surfaces. Here we show that this limitation can be lifted by recording thephotoemission data in a momentum microscope and limiting the probed surface area to onlya few micrometers squared, since this corresponds to a typical domain size for many systems.We demonstrate this by recording data from a single domain of the archetypal adsorbatesystem 1,4,5,8-naphthalenetetracarboxylic dianhydride on Cu(0 0 1). This proof of principleexperiment paves the way for establishing the photoemission μ-tomography method as anideal tool for investigating the electronic structure of metal-organic interfaces with so farunraveled clarity and unambiguity. |
| 55. | T. G. Boné Organic Molecules on Alkali Halide Interlayers - A Characterisation of Energy Levels and Charge Transfer Masters Thesis 2019. @mastersthesis{Bone2019,
title = {Organic Molecules on Alkali Halide Interlayers - A Characterisation of Energy Levels and Charge Transfer},
author = {T. G. Boné},
year = {2019},
date = {2019-01-01},
urldate = {2019-01-01},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
|
| 54. | M. Hollerer, D. Prochinig, P. Puschnig, E. Carrasco, H. -J. Freund, M. Sterrer Scanning Tunneling Microscopy of the Ordered Water Monolayer on MgO(001)/Ag(001) Ultrathin Films Journal Article In: J. Phys. Chem. C, vol. 123, pp. 3711-3718, 2019. @article{Hollerer2019,
title = {Scanning Tunneling Microscopy of the Ordered Water Monolayer on MgO(001)/Ag(001) Ultrathin Films},
author = {M. Hollerer and D. Prochinig and P. Puschnig and E. Carrasco and H. -J. Freund and M. Sterrer},
doi = {10.1021/acs.jpcc.8b12256},
year = {2019},
date = {2019-01-01},
journal = {J. Phys. Chem. C},
volume = {123},
pages = {3711-3718},
abstract = {Two-dimensionally ordered monolayers of water on MgO(001) have been extensively studied in the past using diffraction and spectroscopic and computational methods, but direct microscopic imaging has not been reported so far. Here, we present a scanning tunneling microscopy (STM) study, supported by infrared and X-ray photoelectron spectroscopy, of the c(4 × 2)-10H2O and p(3 × 2)-6H2O structures prepared on ultrathin MgO(001)/Ag(001) films. For the applied tunneling conditions, the contrast in the STM images originates from the hydroxyl groups, which result from water dissociation within the monolayer. The observed periodicities match the structures for the energetically most favorable c(4 × 2) and p(3 × 2) monolayer phases obtained from density functional calculations. Although the molecular water species within the monolayers, which are essential for the stabilization of the hydroxyl groups, could not be resolved, the STM results presented in this study provide further confirmation of the predicted structural models of the c(4 × 2)-10H2O and p(3 × 2)-6H2O monolayers.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
Two-dimensionally ordered monolayers of water on MgO(001) have been extensively studied in the past using diffraction and spectroscopic and computational methods, but direct microscopic imaging has not been reported so far. Here, we present a scanning tunneling microscopy (STM) study, supported by infrared and X-ray photoelectron spectroscopy, of the c(4 × 2)-10H2O and p(3 × 2)-6H2O structures prepared on ultrathin MgO(001)/Ag(001) films. For the applied tunneling conditions, the contrast in the STM images originates from the hydroxyl groups, which result from water dissociation within the monolayer. The observed periodicities match the structures for the energetically most favorable c(4 × 2) and p(3 × 2) monolayer phases obtained from density functional calculations. Although the molecular water species within the monolayers, which are essential for the stabilization of the hydroxyl groups, could not be resolved, the STM results presented in this study provide further confirmation of the predicted structural models of the c(4 × 2)-10H2O and p(3 × 2)-6H2O monolayers. |
| 53. | L. Egger, B. Kollmann, P. Hurdax, D. Lüftner, X. Yang, S. Weiß, A. Gottwald, M. Richter, G. Koller, S. Soubatch, F. S. Tautz, P. Puschnig, M. G. Ramsey Can photoemission tomography be useful for small, strongly-interacting adsorbate systems? Journal Article In: New J. Phys., vol. 21, pp. 043003, 2019. @article{Egger2018,
title = {Can photoemission tomography be useful for small, strongly-interacting adsorbate systems?},
author = {L. Egger and B. Kollmann and P. Hurdax and D. Lüftner and X. Yang and S. Weiß and A. Gottwald and M. Richter and G. Koller and S. Soubatch and F. S. Tautz and P. Puschnig and M. G. Ramsey},
doi = {10.1088/1367-2630/ab0781},
year = {2019},
date = {2019-01-01},
journal = {New J. Phys.},
volume = {21},
pages = {043003},
abstract = {Molecular orbital tomography, also termed photoemission tomography, which considers the final state as a simple plane wave, has been very successful in describing the photoemisson distribution of large adsorbates on noble metal surfaces. Here, following a suggestion by Bradshaw and Woodruff (2015 New J. Phys. 17 013033), we consider a small and strongly-interacting system, benzene adsorbed on palladium (110), to consider the extent of the problems that can arise with the final state simplification. Our angle-resolved photoemission experiments, supported by density functional theory calculations, substantiate and refine the previously determined adsorption geometry and reveal an energetic splitting of the frontier π-orbital due to a symmetry breaking which has remained unnoticed before. We find that, despite the small size of benzene and the comparably strong interaction with palladium, the overall appearance of the photoemission angular distributions can basically be understood within a plane wave final state approximation and yields a deeper understanding of the electronic structure of the interface. There are, however, noticeable deviations between measured and simulated angular patterns which we ascribe to molecule-substrate interactions and effects beyond a plane-wave final state description.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
Molecular orbital tomography, also termed photoemission tomography, which considers the final state as a simple plane wave, has been very successful in describing the photoemisson distribution of large adsorbates on noble metal surfaces. Here, following a suggestion by Bradshaw and Woodruff (2015 New J. Phys. 17 013033), we consider a small and strongly-interacting system, benzene adsorbed on palladium (110), to consider the extent of the problems that can arise with the final state simplification. Our angle-resolved photoemission experiments, supported by density functional theory calculations, substantiate and refine the previously determined adsorption geometry and reveal an energetic splitting of the frontier π-orbital due to a symmetry breaking which has remained unnoticed before. We find that, despite the small size of benzene and the comparably strong interaction with palladium, the overall appearance of the photoemission angular distributions can basically be understood within a plane wave final state approximation and yields a deeper understanding of the electronic structure of the interface. There are, however, noticeable deviations between measured and simulated angular patterns which we ascribe to molecule-substrate interactions and effects beyond a plane-wave final state description. |
| 52. | X. Yang, L. Egger, P. Hurdax, H. Kaser, D. Lüftner, F. C. Bocquet, G. Koller, A. Gottwald, P. Tegeder, M. Richter, M. G. Ramsey, P. Puschnig, S. Soubatch, F. S. Tautz Identifying surface reaction intermediates with photoemission tomography Journal Article In: Nat. Commun., vol. 10, pp. 3189, 2019. @article{Yang2019,
title = {Identifying surface reaction intermediates with photoemission tomography},
author = {X. Yang and L. Egger and P. Hurdax and H. Kaser and D. Lüftner and F. C. Bocquet and G. Koller and A. Gottwald and P. Tegeder and M. Richter and M. G. Ramsey and P. Puschnig and S. Soubatch and F. S. Tautz},
doi = {10.1038/s41467-019-11133-9},
year = {2019},
date = {2019-01-01},
journal = {Nat. Commun.},
volume = {10},
pages = {3189},
abstract = {The determination of reaction pathways and the identification of reaction intermediates are key issues in chemistry. Surface reactions are particularly challenging, since many methods of analytical chemistry are inapplicable at surfaces. Recently, atomic force microscopy has been employed to identify surface reaction intermediates. While providing an excellent insight into the molecular backbone structure, atomic force microscopy is less conclusive about the molecular periphery, where adsorbates tend to react with the substrate. Here we show that photoemission tomography is extremely sensitive to the character of the frontier orbitals. Specifically, hydrogen abstraction at the molecular periphery is easily detected, and the precise nature of the reaction intermediates can be determined. This is illustrated with the thermally induced reaction of dibromo-bianthracene to graphene which is shown to proceed via a fully hydrogenated bisanthene intermediate. We anticipate that photoemission tomography will become a powerful companion to other techniques in the study of surface reaction pathways.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
The determination of reaction pathways and the identification of reaction intermediates are key issues in chemistry. Surface reactions are particularly challenging, since many methods of analytical chemistry are inapplicable at surfaces. Recently, atomic force microscopy has been employed to identify surface reaction intermediates. While providing an excellent insight into the molecular backbone structure, atomic force microscopy is less conclusive about the molecular periphery, where adsorbates tend to react with the substrate. Here we show that photoemission tomography is extremely sensitive to the character of the frontier orbitals. Specifically, hydrogen abstraction at the molecular periphery is easily detected, and the precise nature of the reaction intermediates can be determined. This is illustrated with the thermally induced reaction of dibromo-bianthracene to graphene which is shown to proceed via a fully hydrogenated bisanthene intermediate. We anticipate that photoemission tomography will become a powerful companion to other techniques in the study of surface reaction pathways. |
| 51. | X. Yang, L. Egger, J. Fuchsberger, M. Unzog, D. Lüftner, F. Hajek, P. Hurdax, M. Jugovac, G. Zamborlini, V. Feyer, G. Koller, P. Puschnig, F. S. Tautz, M. G. Ramsey, S. Soubatch Coexisting Charge States in a Unary Organic Monolayer Film on a Metal Journal Article In: J. Phys. Chem. Lett., vol. 10, pp. 6438-6445, 2019. @article{Yang2019a,
title = {Coexisting Charge States in a Unary Organic Monolayer Film on a Metal},
author = {X. Yang and L. Egger and J. Fuchsberger and M. Unzog and D. Lüftner and F. Hajek and P. Hurdax and M. Jugovac and G. Zamborlini and V. Feyer and G. Koller and P. Puschnig and F. S. Tautz and M. G. Ramsey and S. Soubatch},
doi = {10.1021/acs.jpclett.9b02231},
year = {2019},
date = {2019-01-01},
journal = {J. Phys. Chem. Lett.},
volume = {10},
pages = {6438-6445},
abstract = {The electronic and geometric structures of tetracene films on Ag(110) and Cu(110) have been studied with photoemission tomography and compared to that of pentacene. Despite similar energy level alignment of the two oligoacenes on these surfaces revealed by conventional ultraviolet photoelectron spectroscopy, the momentum-space resolved photoemission tomography reveals a significant difference in both structural and electronic properties of tetracene and pentacene films. Particularly, the saturated monolayer of tetracene on Ag(110) is found to consist of two molecular species that, despite having the same orientation, are electronically very different—while one molecule remains neutral, another is charged because of electron donation from the substrate.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
The electronic and geometric structures of tetracene films on Ag(110) and Cu(110) have been studied with photoemission tomography and compared to that of pentacene. Despite similar energy level alignment of the two oligoacenes on these surfaces revealed by conventional ultraviolet photoelectron spectroscopy, the momentum-space resolved photoemission tomography reveals a significant difference in both structural and electronic properties of tetracene and pentacene films. Particularly, the saturated monolayer of tetracene on Ag(110) is found to consist of two molecular species that, despite having the same orientation, are electronically very different—while one molecule remains neutral, another is charged because of electron donation from the substrate. |
| 50. | E. Parth Imaging molecular orbitals for ARPES simulations Bachelor Thesis 2019. @bachelorthesis{Parth2019,
title = {Imaging molecular orbitals for ARPES simulations},
author = {E. Parth},
url = {https://homepage.uni-graz.at/en/peter.puschnig/theses/},
year = {2019},
date = {2019-01-01},
keywords = {},
pubstate = {published},
tppubtype = {bachelorthesis}
}
|
2018
|
| 49. | X. Yang, I. Krieger, D. Lüftner, S. Weiß, T. Heepenstrick, M. Hollerer, P. Hurdax, G. Koller, M. Sokolowski, P. Puschnig, M. G. Ramsey, F. S. Tautz, S. Soubatch On the decoupling of molecules at metal surfaces Journal Article In: Chem. Commun., vol. 54, pp. 9039-9042, 2018. @article{Yang2018,
title = {On the decoupling of molecules at metal surfaces},
author = {X. Yang and I. Krieger and D. Lüftner and S. Weiß and T. Heepenstrick and M. Hollerer and P. Hurdax and G. Koller and M. Sokolowski and P. Puschnig and M. G. Ramsey and F. S. Tautz and S. Soubatch},
doi = {10.1039/C8CC03334J},
year = {2018},
date = {2018-01-01},
urldate = {2018-01-01},
journal = {Chem. Commun.},
volume = {54},
pages = {9039-9042},
abstract = {We report a method to achieve physical and electronic decoupling of organic molecules from a metal surface. Oxygen adsorbed on the Cu(100) surface immobilizes the surface electrons in the Cu–O covalent bonds. This results in electronic surface hardening and prevents charge transfer from the metal into perylene-tetracarboxylic dianhydride molecules subsequently deposited on this surface.},
keywords = {DACH},
pubstate = {published},
tppubtype = {article}
}
We report a method to achieve physical and electronic decoupling of organic molecules from a metal surface. Oxygen adsorbed on the Cu(100) surface immobilizes the surface electrons in the Cu–O covalent bonds. This results in electronic surface hardening and prevents charge transfer from the metal into perylene-tetracarboxylic dianhydride molecules subsequently deposited on this surface. |
| 48. | M. Graus, C. Metzger, M. Grimm, V. Feyer, P. Puschnig, A. Schöll, F. Reinert Degeneracy Lifting of Adsorbate Orbitals Imaged by High-Resolution Momentum Microscopy Journal Article In: J. Phys. Soc. Jpn, vol. 87, pp. 061009, 2018. @article{Graus2017,
title = {Degeneracy Lifting of Adsorbate Orbitals Imaged by High-Resolution Momentum Microscopy},
author = {M. Graus and C. Metzger and M. Grimm and V. Feyer and P. Puschnig and A. Schöll and F. Reinert},
doi = {10.7566/JPSJ.87.061009},
year = {2018},
date = {2018-01-01},
journal = {J. Phys. Soc. Jpn},
volume = {87},
pages = {061009},
abstract = {On the topical example of the symmetry splitting of degenerate orbitals due to adsorption we drive the technique of orbital imaging by momentum microscopy (k-PEEM) ahead, demonstrating the potential of the method when performed with high accuracy in terms of experimental quality, energy resolution and data evaluation. Upon adsorption on the twofold symmetric substrate Ag(110), the symmetry of Iron-phthalocyanine reduces from fourfold two twofold, leading to distinct binding energies of the two e1g orbitals which constitute the twofold degenerate lowest unoccupied molecular orbital of the gas-phase molecule. In this combined experimental and theoretical study, we show that by k-PEEM with high energy resolution the individual orbitals can be identified and distinguished by mapping in momentum space.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
On the topical example of the symmetry splitting of degenerate orbitals due to adsorption we drive the technique of orbital imaging by momentum microscopy (k-PEEM) ahead, demonstrating the potential of the method when performed with high accuracy in terms of experimental quality, energy resolution and data evaluation. Upon adsorption on the twofold symmetric substrate Ag(110), the symmetry of Iron-phthalocyanine reduces from fourfold two twofold, leading to distinct binding energies of the two e1g orbitals which constitute the twofold degenerate lowest unoccupied molecular orbital of the gas-phase molecule. In this combined experimental and theoretical study, we show that by k-PEEM with high energy resolution the individual orbitals can be identified and distinguished by mapping in momentum space. |
| 47. | B. Kollmann, Z. Chen, D. Lüftner, O. Siri, P. Puschnig Synthesis and combined experimental and theoretical characterization of dihydro-tetraaza-acenes Journal Article In: J. Phys. Chem. C, vol. 122, pp. 6475-6482, 2018. @article{Kollmann2018,
title = {Synthesis and combined experimental and theoretical characterization of dihydro-tetraaza-acenes},
author = {B. Kollmann and Z. Chen and D. Lüftner and O. Siri and P. Puschnig},
doi = {10.1021/acs.jpcc.8b00985},
year = {2018},
date = {2018-01-01},
journal = {J. Phys. Chem. C},
volume = {122},
pages = {6475-6482},
abstract = {We present a combined experimental and theoretical study of electronic and optical properties of dihydro-tetraaza-acenes (DHTAn). Using solvent-free condensation, we are able to synthesize not only DHTA5 but also the longer DHTA6 and DHTA7 molecules. We then investigate their gas-phase electronic structures by means of ab initio density functional calculations employing an optimally tuned range-separated hybrid functional. By comparing with the parent linear oligoacenes (nA) and based on computed ionization potentials and electron affinities, we predict DHTAn molecules to be more stable than acenes of the same length, where we expect DHTAn molecules to be persistent at least up to n = 7 rings. We further exploit the analogy with nA by analyzing the entire intramolecular π-band structure of the DHTAn molecules. This clearly reveals that the additional two electrons donated by the dihydropyrazine group are delocalized over the entire molecule and contribute to its π-electron system. As a consequence, the symmetry of the frontier orbitals of DHTAn differs from that of the parent nA molecule. This also affects the UV–vis absorption spectra which have been measured for DHTA5, 6, and 7 dissolved in dimethyl sulfoxide and analyzed by means of excited state calculations within a time-dependent density functional theory framework.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present a combined experimental and theoretical study of electronic and optical properties of dihydro-tetraaza-acenes (DHTAn). Using solvent-free condensation, we are able to synthesize not only DHTA5 but also the longer DHTA6 and DHTA7 molecules. We then investigate their gas-phase electronic structures by means of ab initio density functional calculations employing an optimally tuned range-separated hybrid functional. By comparing with the parent linear oligoacenes (nA) and based on computed ionization potentials and electron affinities, we predict DHTAn molecules to be more stable than acenes of the same length, where we expect DHTAn molecules to be persistent at least up to n = 7 rings. We further exploit the analogy with nA by analyzing the entire intramolecular π-band structure of the DHTAn molecules. This clearly reveals that the additional two electrons donated by the dihydropyrazine group are delocalized over the entire molecule and contribute to its π-electron system. As a consequence, the symmetry of the frontier orbitals of DHTAn differs from that of the parent nA molecule. This also affects the UV–vis absorption spectra which have been measured for DHTA5, 6, and 7 dissolved in dimethyl sulfoxide and analyzed by means of excited state calculations within a time-dependent density functional theory framework. |
| 46. | G. Zamborlini, M. Jugovac, A. Cossaro, A. Verdini, L. Floreano, D. Lüftner, P. Puschnig, V. Feyer, C. M. Schneider On-surface nickel porphyrin mimics the reactive center of enzyme cofactor Journal Article In: Chem. Commun., vol. 54, pp. 13423-13426, 2018. @article{Zamborlini2018,
title = {On-surface nickel porphyrin mimics the reactive center of enzyme cofactor},
author = {G. Zamborlini and M. Jugovac and A. Cossaro and A. Verdini and L. Floreano and D. Lüftner and P. Puschnig and V. Feyer and C. M. Schneider},
doi = {10.1039/C8CC06739B},
year = {2018},
date = {2018-01-01},
journal = {Chem. Commun.},
volume = {54},
pages = {13423-13426},
abstract = {Metal-containing enzyme cofactors achieve their unusual seactivity by stabilizing uncommon metal oxidation states with structurally complex ligands. In particular, the specific cofactor promoting both methanogenesis and anaerobic methane oxidation is a porphynoid chelated to a nickel (I) atom via a multi-step biosynthetic path, where the nickel reduction is achieved through extensive molecular hydrogenation. Here, we demonstrate an alternative route to porphyrin reduction by charge transfer from a selected copper substrate to commercially available 5,10,15,20-tetraphenyl-porphyrin nickel(II). X-ray absorption measurements at the Ni L3-edge unequivocally show that NiTPP adsorbed on Cu(100) are stabilized in the highly reactive Ni(I) oxidation state by electron transfer to the molecular orbitals. Our approach highlights how some fundamental properties of synthetically inaccessible biological cofactors may be reproduced by hybridization of simple metalloporphyrins with metal surfaces, with implications towards novel approaches to heterogenous catalysis.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Metal-containing enzyme cofactors achieve their unusual seactivity by stabilizing uncommon metal oxidation states with structurally complex ligands. In particular, the specific cofactor promoting both methanogenesis and anaerobic methane oxidation is a porphynoid chelated to a nickel (I) atom via a multi-step biosynthetic path, where the nickel reduction is achieved through extensive molecular hydrogenation. Here, we demonstrate an alternative route to porphyrin reduction by charge transfer from a selected copper substrate to commercially available 5,10,15,20-tetraphenyl-porphyrin nickel(II). X-ray absorption measurements at the Ni L3-edge unequivocally show that NiTPP adsorbed on Cu(100) are stabilized in the highly reactive Ni(I) oxidation state by electron transfer to the molecular orbitals. Our approach highlights how some fundamental properties of synthetically inaccessible biological cofactors may be reproduced by hybridization of simple metalloporphyrins with metal surfaces, with implications towards novel approaches to heterogenous catalysis. |
| 45. | P. Puschnig, M. G. Ramsey Photoemission Tomography: Valence Band Photoemission as a Quantitative Method for Investigating Molecular Films Incollection In: Encyclopedia of Interfacial Chemistry, pp. 380 - 391, Elsevier, Oxford, 2018, ISBN: 978-0-12-809894-3. @incollection{Puschnig2017,
title = {Photoemission Tomography: Valence Band Photoemission as a Quantitative Method for Investigating Molecular Films},
author = {P. Puschnig and M. G. Ramsey},
doi = {10.1016/B978-0-12-409547-2.13782-5},
isbn = {978-0-12-809894-3},
year = {2018},
date = {2018-01-01},
booktitle = {Encyclopedia of Interfacial Chemistry},
pages = {380 - 391},
publisher = {Elsevier},
address = {Oxford},
abstract = {The frontier orbitals of molecules are the prime determinants of their chemical, optical, and electronic properties. Arguably, the most direct method of addressing the (filled) frontier orbitals is ultra-violet photoemission spectroscopy (UPS). Although UPS is a mature technique from the early 1970s on, the angular distribution of the photoemitted electrons was thought to be too complex to be analyzed quantitatively. Recently angle-resolved UPS work on conjugated molecules, both in ordered thick films and chemisorbed monolayers, has shown that the angular (momentum) distribution of the photocurrent from orbital emissions can be simply understood when a plane wave final state is assumed. This approach, becoming known as orbital or photoemission tomography, relates the emission distribution to the Fourier transform of the ground state orbitals. The examples given will introduce photoemission tomography and demonstrate its potential as a technique to determine both electronic and geometric structures not just complementary but also competitive to methods as diverse as scanning tunneling microscopy and near-edge X-ray absorption spectroscopy.},
keywords = {},
pubstate = {published},
tppubtype = {incollection}
}
The frontier orbitals of molecules are the prime determinants of their chemical, optical, and electronic properties. Arguably, the most direct method of addressing the (filled) frontier orbitals is ultra-violet photoemission spectroscopy (UPS). Although UPS is a mature technique from the early 1970s on, the angular distribution of the photoemitted electrons was thought to be too complex to be analyzed quantitatively. Recently angle-resolved UPS work on conjugated molecules, both in ordered thick films and chemisorbed monolayers, has shown that the angular (momentum) distribution of the photocurrent from orbital emissions can be simply understood when a plane wave final state is assumed. This approach, becoming known as orbital or photoemission tomography, relates the emission distribution to the Fourier transform of the ground state orbitals. The examples given will introduce photoemission tomography and demonstrate its potential as a technique to determine both electronic and geometric structures not just complementary but also competitive to methods as diverse as scanning tunneling microscopy and near-edge X-ray absorption spectroscopy. |
2017
|
| 44. | G. Zamborlini, D. Lüftner, Z. Feng, B. Kollmann, P. Puschnig, C. Dri, M. Panighel, G. Di Santo, A. Goldoni, G. Comelli, M. Jugovac, V. Feyer, C. M. Schneider Multi-orbital charge transfer at highly oriented organic/metal interfaces Journal Article In: Nat. Commun., vol. 8, pp. 335, 2017. @article{Zamborlini2017,
title = {Multi-orbital charge transfer at highly oriented organic/metal interfaces},
author = {G. Zamborlini and D. Lüftner and Z. Feng and B. Kollmann and P. Puschnig and C. Dri and M. Panighel and G. Di Santo and A. Goldoni and G. Comelli and M. Jugovac and V. Feyer and C. M. Schneider},
doi = {10.1038/s41467-017-00402-0},
year = {2017},
date = {2017-01-01},
journal = {Nat. Commun.},
volume = {8},
pages = {335},
abstract = {The molecule–substrate interaction plays a key role in charge injection organic-based devices. Charge transfer at molecule–metal interfaces strongly affects the overall physical and magnetic properties of the system, and ultimately the device performance. Here, we report theoretical and experimental evidence of a pronounced charge transfer involving nickel tetraphenyl porphyrin molecules adsorbed on Cu(100). The exceptional charge transfer leads to filling of the higher unoccupied orbitals up to LUMO+3. As a consequence of this strong interaction with the substrate, the porphyrin’s macrocycle sits very close to the surface, forcing the phenyl ligands to bend upwards. Due to this adsorption configuration, scanning tunneling microscopy cannot reliably probe the states related to the macrocycle. We demonstrate that photoemission tomography can instead access the Ni-TPP macrocycle electronic states and determine the reordering and filling of the LUMOs upon adsorption, thereby confirming the remarkable charge transfer predicted by density functional theory calculations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The molecule–substrate interaction plays a key role in charge injection organic-based devices. Charge transfer at molecule–metal interfaces strongly affects the overall physical and magnetic properties of the system, and ultimately the device performance. Here, we report theoretical and experimental evidence of a pronounced charge transfer involving nickel tetraphenyl porphyrin molecules adsorbed on Cu(100). The exceptional charge transfer leads to filling of the higher unoccupied orbitals up to LUMO+3. As a consequence of this strong interaction with the substrate, the porphyrin’s macrocycle sits very close to the surface, forcing the phenyl ligands to bend upwards. Due to this adsorption configuration, scanning tunneling microscopy cannot reliably probe the states related to the macrocycle. We demonstrate that photoemission tomography can instead access the Ni-TPP macrocycle electronic states and determine the reordering and filling of the LUMOs upon adsorption, thereby confirming the remarkable charge transfer predicted by density functional theory calculations. |
| 43. | D. Lüftner, S. Weiß, X. Yang, P. Hurdax, V. Feyer, A. Gottwald, G. Koller, S. Soubatch, P. Puschnig, M. G. Ramsey, F. S. Tautz Understanding the photoemission distribution of strongly interacting two-dimensional overlayers Journal Article In: Phys. Rev. B, vol. 96, pp. 125402, 2017. @article{Lueftner2017,
title = {Understanding the photoemission distribution of strongly interacting two-dimensional overlayers},
author = {D. Lüftner and S. Weiß and X. Yang and P. Hurdax and V. Feyer and A. Gottwald and G. Koller and S. Soubatch and P. Puschnig and M. G. Ramsey and F. S. Tautz},
doi = {10.1103/PhysRevB.96.125402},
year = {2017},
date = {2017-01-01},
journal = {Phys. Rev. B},
volume = {96},
pages = {125402},
abstract = {Photoemission tomography (PT), the analysis of the photoemission intensity distribution within the plane wave final-state approximation, is being established as a useful tool for extracting the electronic and geometric structure of weakly interacting organic overlayers. Here we present a simple method for extending PT, which until now has been based on the calculations of isolated molecules. By including the substrate and a damped plane-wave final state, we are able to simulate the photoemission intensity distribution of two-dimensional molecular overlayers with both strong intermolecular and molecule-substrate interactions, here demonstrated for the model system 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) on Cu(100). It is shown that the interaction and hybridization of the lowest unoccupied molecular orbital of PTCDA with substrate states leads to its occupation and the formation of a strongly dispersing intermolecular band, whose experimental magnitude of 1.1 eV and k-space periodicity is well reproduced theoretically.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Photoemission tomography (PT), the analysis of the photoemission intensity distribution within the plane wave final-state approximation, is being established as a useful tool for extracting the electronic and geometric structure of weakly interacting organic overlayers. Here we present a simple method for extending PT, which until now has been based on the calculations of isolated molecules. By including the substrate and a damped plane-wave final state, we are able to simulate the photoemission intensity distribution of two-dimensional molecular overlayers with both strong intermolecular and molecule-substrate interactions, here demonstrated for the model system 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) on Cu(100). It is shown that the interaction and hybridization of the lowest unoccupied molecular orbital of PTCDA with substrate states leads to its occupation and the formation of a strongly dispersing intermolecular band, whose experimental magnitude of 1.1 eV and k-space periodicity is well reproduced theoretically. |
| 42. | C. Udhardt, F. Otto, C. S. Kern, D. Lüftner, T. Huempfner, T. Kirchhuebel, F. Sojka, M. Meißner, B. Schröter, R. Forker, P. Puschnig, T. Fritz Influence of Film and Substrate Structure on Photoelectron Momentum Maps of Coronene Thin Films on Ag(111) Journal Article In: J. Phys. Chem. C, vol. 121, pp. 12285-12293, 2017. @article{Udhardt2017,
title = {Influence of Film and Substrate Structure on Photoelectron Momentum Maps of Coronene Thin Films on Ag(111)},
author = {C. Udhardt and F. Otto and C. S. Kern and D. Lüftner and T. Huempfner and T. Kirchhuebel and F. Sojka and M. Meißner and B. Schröter and R. Forker and P. Puschnig and T. Fritz},
doi = {10.1021/acs.jpcc.7b03500},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
journal = {J. Phys. Chem. C},
volume = {121},
pages = {12285-12293},
abstract = {Angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) was measured for one-monolayer coronene films deposited on Ag(111). The (kx,ky)-dependent photoelectron momentum maps (PMMs), which were extracted from the ARUPS data by cuts at fixed binding energies, show finely structured patterns for the highest and the second-highest occupied molecular orbitals. While the substructure of the PMM main features is related to the 4 × 4 commensurate film structure, various features with three-fold symmetry imply an additional influence of the substrate. PMM simulations on the basis of both free-standing coronene assemblies and coronene monolayers on the Ag(111) substrate confirm a sizable molecule–molecule interaction because no substructure was observed for PMM simulations using free coronene molecules.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) was measured for one-monolayer coronene films deposited on Ag(111). The (kx,ky)-dependent photoelectron momentum maps (PMMs), which were extracted from the ARUPS data by cuts at fixed binding energies, show finely structured patterns for the highest and the second-highest occupied molecular orbitals. While the substructure of the PMM main features is related to the 4 × 4 commensurate film structure, various features with three-fold symmetry imply an additional influence of the substrate. PMM simulations on the basis of both free-standing coronene assemblies and coronene monolayers on the Ag(111) substrate confirm a sizable molecule–molecule interaction because no substructure was observed for PMM simulations using free coronene molecules. |
| 41. | P. Puschnig, A. D. Boese, M. Willenbockel, M. Meyer, D. Lüftner, E. M. Reinisch, T. Ules, G. Koller, S. Soubatch, M. G. Ramsey, F. S. Tautz Energy ordering of molecular orbitals Journal Article In: J. Phys. Chem. Lett., vol. 8, pp. 208-213, 2017. @article{Puschnig2016,
title = {Energy ordering of molecular orbitals},
author = {P. Puschnig and A. D. Boese and M. Willenbockel and M. Meyer and D. Lüftner and E. M. Reinisch and T. Ules and G. Koller and S. Soubatch and M. G. Ramsey and F. S. Tautz},
doi = {10.1021/acs.jpclett.6b02517},
year = {2017},
date = {2017-01-01},
journal = {J. Phys. Chem. Lett.},
volume = {8},
pages = {208-213},
abstract = {Orbitals are invaluable in providing a model of bonding in molecules or between molecules and surfaces. Most present-day methods in computational chemistry begin by calculating the molecular orbitals of the system. To what extent have these mathematical objects analogues in the real world? To shed light on this intriguing question, we employ a photoemission tomography study on monolayers of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) grown on three Ag surfaces. The characteristic photoelectron angular distribution enables us to assign individual molecular orbitals to the emission features. When comparing the resulting energy positions to density functional calculations, we observe deviations in the energy ordering. By performing complete active space calculations (CASSCF), we can explain the experimentally observed orbital ordering, suggesting the importance of static electron correlation beyond a (semi)local approximation. On the other hand, our results also show reality and robustness of the orbital concept, thereby making molecular orbitals accessible to experimental observations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Orbitals are invaluable in providing a model of bonding in molecules or between molecules and surfaces. Most present-day methods in computational chemistry begin by calculating the molecular orbitals of the system. To what extent have these mathematical objects analogues in the real world? To shed light on this intriguing question, we employ a photoemission tomography study on monolayers of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) grown on three Ag surfaces. The characteristic photoelectron angular distribution enables us to assign individual molecular orbitals to the emission features. When comparing the resulting energy positions to density functional calculations, we observe deviations in the energy ordering. By performing complete active space calculations (CASSCF), we can explain the experimentally observed orbital ordering, suggesting the importance of static electron correlation beyond a (semi)local approximation. On the other hand, our results also show reality and robustness of the orbital concept, thereby making molecular orbitals accessible to experimental observations. |
| 40. | M. Hollerer, D. Lüftner, P. Hurdax, T. Ules, S. Soubatch, F. S. Tautz, G. Koller, P. Puschnig, M. Sterrer, M. G. Ramsey Charge Transfer and Orbital Level Alignment at Inorganic/Organic Interfaces: The Role of Dielectric Interlayers Journal Article In: ACS Nano, vol. 11, pp. 6252-6260, 2017. @article{Hollerer2017,
title = {Charge Transfer and Orbital Level Alignment at Inorganic/Organic Interfaces: The Role of Dielectric Interlayers},
author = {M. Hollerer and D. Lüftner and P. Hurdax and T. Ules and S. Soubatch and F. S. Tautz and G. Koller and P. Puschnig and M. Sterrer and M. G. Ramsey},
doi = {10.1021/acsnano.7b02449},
year = {2017},
date = {2017-01-01},
journal = {ACS Nano},
volume = {11},
pages = {6252-6260},
abstract = {It is becoming accepted that ultrathin dielectric layers on metals are not merely passive decoupling layers, but can actively influence orbital energy level alignment and charge transfer at interfaces. As such, they can be important in applications ranging from catalysis to organic electronics. However, the details at the molecular level are still under debate. In this study, we present a comprehensive analysis of the phenomenon of charge transfer promoted by a dielectric interlayer with a comparative study of pentacene adsorbed on Ag(001) with and without an ultrathin MgO interlayer. Using scanning tunneling microscopy and photoemission tomography supported by density functional theory, we are able to identify the orbitals involved and quantify the degree of charge transfer in both cases. Fractional charge transfer occurs for pentacene adsorbed on Ag(001), while the presence of the ultrathin MgO interlayer promotes integer charge transfer with the lowest unoccupied molecular orbital transforming into a singly occupied and singly unoccupied state separated by a large gap around the Fermi energy. Our experimental approach allows a direct access to the individual factors governing the energy level alignment and charge-transfer processes for molecular adsorbates on inorganic substrates.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
It is becoming accepted that ultrathin dielectric layers on metals are not merely passive decoupling layers, but can actively influence orbital energy level alignment and charge transfer at interfaces. As such, they can be important in applications ranging from catalysis to organic electronics. However, the details at the molecular level are still under debate. In this study, we present a comprehensive analysis of the phenomenon of charge transfer promoted by a dielectric interlayer with a comparative study of pentacene adsorbed on Ag(001) with and without an ultrathin MgO interlayer. Using scanning tunneling microscopy and photoemission tomography supported by density functional theory, we are able to identify the orbitals involved and quantify the degree of charge transfer in both cases. Fractional charge transfer occurs for pentacene adsorbed on Ag(001), while the presence of the ultrathin MgO interlayer promotes integer charge transfer with the lowest unoccupied molecular orbital transforming into a singly occupied and singly unoccupied state separated by a large gap around the Fermi energy. Our experimental approach allows a direct access to the individual factors governing the energy level alignment and charge-transfer processes for molecular adsorbates on inorganic substrates. |
| 39. | S. Schröder Structural and electronic characterization of hetero-organic NTCDA-CuPc adsorbate systems on Ag(111) PhD Thesis 2017, ISBN: 978-3-95806-239-9. @phdthesis{Schröder2017,
title = {Structural and electronic characterization of hetero-organic NTCDA-CuPc adsorbate systems on Ag(111)},
author = {S. Schröder},
editor = {Verlag Forschungszentrum Jülich GmbH Zentralbibliothek},
url = {http://hdl.handle.net/2128/14795},
isbn = {978-3-95806-239-9},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
abstract = {Ching Tang and Steven van Slyke invented the first organic light emitting diode (OLED)in 1987 after they discovered that light can be emitted by passing current througha carbon-based material [TV87]. Since then organic molecules have been used additionally in organic field transistors (OFETs) [KTA03] and photovoltaic cells (OPVC)[YSF05]. Organic solar cells are very promising as they have many advantages compared to inorganic devices: 10 times thinner active layers are sufficient, the costs are much less and the production is easier. To compete with inorganic solar cells however the efficiency of the organic solar cells has to be increased by a factor of 2-3 [Kie07]. For further development and an increase of the efficiency of these devices, different materials have been studied as small organic molecules and polymers. This should lead to deeper knowledge of fundamental mechanisms at organic-metal and organic-organic interfaces, in order to find the material of choice. Many different homomolecular prototype systems of semiconducting molecules on metals have therefore been investigated extensively in the last decade [Tau07], [For97], [EBST04], [BLC+10], [SHK+09], [KSS+10], [DGS+07]. Studying the formation of the first layer is necessary as it is crucial for the growth of the subsequent layers [BCK05], in the end defining the properties of the organic device. [...]},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
Ching Tang and Steven van Slyke invented the first organic light emitting diode (OLED)in 1987 after they discovered that light can be emitted by passing current througha carbon-based material [TV87]. Since then organic molecules have been used additionally in organic field transistors (OFETs) [KTA03] and photovoltaic cells (OPVC)[YSF05]. Organic solar cells are very promising as they have many advantages compared to inorganic devices: 10 times thinner active layers are sufficient, the costs are much less and the production is easier. To compete with inorganic solar cells however the efficiency of the organic solar cells has to be increased by a factor of 2-3 [Kie07]. For further development and an increase of the efficiency of these devices, different materials have been studied as small organic molecules and polymers. This should lead to deeper knowledge of fundamental mechanisms at organic-metal and organic-organic interfaces, in order to find the material of choice. Many different homomolecular prototype systems of semiconducting molecules on metals have therefore been investigated extensively in the last decade [Tau07], [For97], [EBST04], [BLC+10], [SHK+09], [KSS+10], [DGS+07]. Studying the formation of the first layer is necessary as it is crucial for the growth of the subsequent layers [BCK05], in the end defining the properties of the organic device. [...] |
| 38. | P. Hurdax Charge transfer to organic molecules promoted by ultrathin insulating layers on metals Masters Thesis 2017. @mastersthesis{Hurdax2017,
title = {Charge transfer to organic molecules promoted by ultrathin insulating layers on metals},
author = {P. Hurdax},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
keywords = {DACH},
pubstate = {published},
tppubtype = {mastersthesis}
}
|
2016
|
| 37. | M. Meyer Orbitaltomographie organischer Moleküle: Experiment und Datenauswertung Bachelor Thesis 2016. @bachelorthesis{Meyer2016,
title = {Orbitaltomographie organischer Moleküle: Experiment und Datenauswertung},
author = {M. Meyer},
year = {2016},
date = {2016-07-28},
keywords = {},
pubstate = {published},
tppubtype = {bachelorthesis}
}
|
