2025
|
| 10. | S. Mearini, D. Brandstetter, Y. Y. Grisan Qiu, D. Baranowski, I. Cojocariu, M. Jugovac, P. Gargiani, M. Valvidares, L. Schio, L. Floreano, A. Windischbacher, P. Puschnig, V. Feyer, C. M. Schneider Substrate Stabilized Charge Transfer Scheme In Coverage Controlled 2D Metal Organic Frameworks Journal Article In: Small, vol. 2500507, 2025. @article{Mearini2025,
title = {Substrate Stabilized Charge Transfer Scheme In Coverage Controlled 2D Metal Organic Frameworks},
author = {S. Mearini and D. Brandstetter and Y. Y. Grisan Qiu and D. Baranowski and I. Cojocariu and M. Jugovac and P. Gargiani and M. Valvidares and L. Schio and L. Floreano and A. Windischbacher and P. Puschnig and V. Feyer and C. M. Schneider},
url = {https://onlinelibrary.wiley.com/doi/10.1002/smll.202500507?af=R},
doi = {10.1002/smll.20250050},
year = {2025},
date = {2025-02-17},
urldate = {2025-02-17},
journal = {Small},
volume = {2500507},
abstract = {Recently, 2D metal-organic frameworks (2D MOFs), characterized by complexcharge transfer mechanisms, have emerged as a promising class of networksin the development of advanced materials with tailored electronic andmagnetic properties. Following the successful synthesis of a 2D MOF formedby nickel (Ni) linkers and 7,7,8,8-tetracyanoquinodimethane (TCNQ) ligands,this work investigates how the Ni-to-ligand ratio influences the electroniccharge redistribution in an Ag(100)-supported 2D MOF. The interplaybetween linker-ligand and substrate-MOF charge transfer processes leads to astable equilibrium, resulting in a robust electronic structure that remainsindependent of stoichiometric ratios. This stability is primarily based on theelectron transfer from the metal substrate, which compensates for chargeimbalances introduced by the metal-organic coordination across differentMOF configurations. Despite minor changes observed in the magneticresponse of the Ni centers, these findings emphasize the robustness of theelectronic structure, which remains largely unaffected by structural variations,highlighting the potential of these 2D MOFs for advanced applications inelectronics and spintronics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recently, 2D metal-organic frameworks (2D MOFs), characterized by complexcharge transfer mechanisms, have emerged as a promising class of networksin the development of advanced materials with tailored electronic andmagnetic properties. Following the successful synthesis of a 2D MOF formedby nickel (Ni) linkers and 7,7,8,8-tetracyanoquinodimethane (TCNQ) ligands,this work investigates how the Ni-to-ligand ratio influences the electroniccharge redistribution in an Ag(100)-supported 2D MOF. The interplaybetween linker-ligand and substrate-MOF charge transfer processes leads to astable equilibrium, resulting in a robust electronic structure that remainsindependent of stoichiometric ratios. This stability is primarily based on theelectron transfer from the metal substrate, which compensates for chargeimbalances introduced by the metal-organic coordination across differentMOF configurations. Despite minor changes observed in the magneticresponse of the Ni centers, these findings emphasize the robustness of theelectronic structure, which remains largely unaffected by structural variations,highlighting the potential of these 2D MOFs for advanced applications inelectronics and spintronics. |
| 9. | Y. Y. Grisan Qiu, D. Brandstetter, S. Mearini, D. Baranowski, I. Cojocariu, M. Jugovac, G. Zamborlini, P. Gargiani, M. Valvidares, A. Windischbacher, P. Puschnig, V. Feyer, C. M. Schneider Conformation-Driven Nickel Redox States and Magnetism in 2D Metal–organic Frameworks Journal Article In: Adv. Funct. Mater., vol. 2418186, 2025. @article{Qiu2025,
title = {Conformation-Driven Nickel Redox States and Magnetism in 2D Metal–organic Frameworks},
author = {Y. Y. Grisan Qiu and D. Brandstetter and S. Mearini and D. Baranowski and I. Cojocariu and M. Jugovac and G. Zamborlini and P. Gargiani and M. Valvidares and A. Windischbacher and P. Puschnig and V. Feyer and C. M. Schneider},
url = {https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202418186?af=R},
doi = {10.1002/adfm.202418186},
year = {2025},
date = {2025-01-29},
urldate = {2025-01-29},
journal = {Adv. Funct. Mater.},
volume = {2418186},
abstract = {2D metal–organic frameworks (2D MOFs) attract considerable attention because of their versatile properties and as potential candidates for single-atom catalysis, high-density information storage media or molecular electronics and spintronics devices. Their unique characteristics arise from an intricate interplay between the metal center, the surrounding ligands and the underlying substrate. Here, the intrinsic magnetic and electronic properties of a single-layer MOF on graphene is investigated with a combination of spectroscopic techniques and theoretical modeling. Taking advantage of the weak interaction between the MOF and graphene substrate, it is specifically focused on the influence of the coordination environment on these properties. Notably, two distinct coordination configurations are observed for the transition metal centers within the 2D MOF, and clarify how axial distortions in the ligand field affect the hybridization between the Ni 3d states and the π-symmetric molecular orbitals of 7,7,8,8-tetracyanoquinodimethane ligands, leading to the coexistence of two Ni redox states with different spin configurations. Furthermore, the transition from a nearly free-standing MOF is examined to metal-supported frameworks, elucidating the impact of substrate interactions on the electronic and magnetic properties. The findings advance the understanding of MOFs and offer insights into developing functional materials with tailored magnetic and electronic properties.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2D metal–organic frameworks (2D MOFs) attract considerable attention because of their versatile properties and as potential candidates for single-atom catalysis, high-density information storage media or molecular electronics and spintronics devices. Their unique characteristics arise from an intricate interplay between the metal center, the surrounding ligands and the underlying substrate. Here, the intrinsic magnetic and electronic properties of a single-layer MOF on graphene is investigated with a combination of spectroscopic techniques and theoretical modeling. Taking advantage of the weak interaction between the MOF and graphene substrate, it is specifically focused on the influence of the coordination environment on these properties. Notably, two distinct coordination configurations are observed for the transition metal centers within the 2D MOF, and clarify how axial distortions in the ligand field affect the hybridization between the Ni 3d states and the π-symmetric molecular orbitals of 7,7,8,8-tetracyanoquinodimethane ligands, leading to the coexistence of two Ni redox states with different spin configurations. Furthermore, the transition from a nearly free-standing MOF is examined to metal-supported frameworks, elucidating the impact of substrate interactions on the electronic and magnetic properties. The findings advance the understanding of MOFs and offer insights into developing functional materials with tailored magnetic and electronic properties. |
| 8. | A. Haags, D. Brandstetter, X. Yang, L. Egger, H. Kirschner, A. Gottwald, M. Richter, G. Koller, F. C. Bocquet, C. Wagner, M. G. Ramsey, S. Soubatch, P. Puschnig, F. S. Tautz Tomographic identification of all molecular orbitals in a wide binding energy range Journal Article Forthcoming In: ArXiv, Forthcoming. @article{Haags2025,
title = {Tomographic identification of all molecular orbitals in a wide binding energy range},
author = {A. Haags and D. Brandstetter and X. Yang and L. Egger and H. Kirschner and A. Gottwald and M. Richter and G. Koller and F. C. Bocquet and C. Wagner and M. G. Ramsey and S. Soubatch and P. Puschnig and F. S. Tautz},
url = {https://arxiv.org/abs/2501.05287},
year = {2025},
date = {2025-01-09},
urldate = {2025-01-09},
journal = {ArXiv},
abstract = {In the past decade, photoemission orbital tomography (POT) has evolved into a powerful tool to investigate the electronic structure of organic molecules adsorbed on surfaces. Here we show that POT allows for the comprehensive experimental identification of all molecular orbitals in a substantial binding energy range, in the present case more than 10 eV. Making use of the angular distribution of photoelectrons as a function of binding energy, we exemplify this by extracting orbital-resolved partial densities of states (pDOS) for 15 π and 23 σ orbitals from the experimental photoemission intensities of the prototypical organic molecule bisanthene (C28H14) on a Cu(110) surface. In their entirety, these experimentally measured orbital-resolved pDOS for an essentially complete set of orbitals serve as a stringent benchmark for electronic structure methods, which we illustrate by performing density functional theory (DFT) calculations employing four frequently-used exchange-correlation functionals. By computing the respective molecular-orbital-projected densities of states of the bisanthene/Cu(110) interface, a one-to-one comparison with experimental data for an unprecedented number of 38 orbital energies becomes possible. The quantitative analysis of our data reveals that the range-separated hybrid functional HSE performs best for the investigated organic/metal interface. At a more fundamental level, the remarkable agreement between the experimental and the Kohn-Sham orbital energies over a binding energy range larger than 10,eV suggests that -- perhaps unexpectedly -- Kohn-Sham orbitals approximate Dyson orbitals, which would rigorously account for the electron extraction process in photoemission spectroscopy but are notoriously difficult to compute, in a much better way than previously thought. },
keywords = {},
pubstate = {forthcoming},
tppubtype = {article}
}
In the past decade, photoemission orbital tomography (POT) has evolved into a powerful tool to investigate the electronic structure of organic molecules adsorbed on surfaces. Here we show that POT allows for the comprehensive experimental identification of all molecular orbitals in a substantial binding energy range, in the present case more than 10 eV. Making use of the angular distribution of photoelectrons as a function of binding energy, we exemplify this by extracting orbital-resolved partial densities of states (pDOS) for 15 π and 23 σ orbitals from the experimental photoemission intensities of the prototypical organic molecule bisanthene (C28H14) on a Cu(110) surface. In their entirety, these experimentally measured orbital-resolved pDOS for an essentially complete set of orbitals serve as a stringent benchmark for electronic structure methods, which we illustrate by performing density functional theory (DFT) calculations employing four frequently-used exchange-correlation functionals. By computing the respective molecular-orbital-projected densities of states of the bisanthene/Cu(110) interface, a one-to-one comparison with experimental data for an unprecedented number of 38 orbital energies becomes possible. The quantitative analysis of our data reveals that the range-separated hybrid functional HSE performs best for the investigated organic/metal interface. At a more fundamental level, the remarkable agreement between the experimental and the Kohn-Sham orbital energies over a binding energy range larger than 10,eV suggests that -- perhaps unexpectedly -- Kohn-Sham orbitals approximate Dyson orbitals, which would rigorously account for the electron extraction process in photoemission spectroscopy but are notoriously difficult to compute, in a much better way than previously thought. |
2024
|
| 7. | S. Mearini, D. Baranowski, D. Brandstetter, A. Windischbacher, I. Cojocariu, P. Gargiani, M. Valvidares, L. Schio, L. Floreano, P. Puschnig, V. Feyer, C. M. Schneider Band Structure Engineering in 2D Metal–Organic Frameworks Journal Article In: Advanced Science, vol. 11, iss. 38, no. 2404667, 2024. @article{Mearini2024,
title = {Band Structure Engineering in 2D Metal–Organic Frameworks},
author = {S. Mearini and D. Baranowski and D. Brandstetter and A. Windischbacher and I. Cojocariu and P. Gargiani and M. Valvidares and L. Schio and L. Floreano and P. Puschnig and V. Feyer and C. M. Schneider},
url = {https://onlinelibrary.wiley.com/doi/10.1002/advs.202404667},
doi = {10.1002/advs.202404667},
year = {2024},
date = {2024-08-09},
urldate = {2024-08-09},
journal = {Advanced Science},
volume = {11},
number = {2404667},
issue = {38},
abstract = {The design of 2D metal–organic frameworks (2D MOFs) takes advantage ofthe combination of the diverse electronic properties of simple organic ligandswith different transition metal (TM) centers. The strong directional nature ofthe coordinative bonds is the basis for the structural stability and the periodicarrangement of the TM cores in these architectures. Here, direct and clearevidence that 2D MOFs exhibit intriguing energy-dispersive electronic bandswith a hybrid character and distinct magnetic properties in the metal cores,resulting from the interactions between the TM electronic levels and theorganic ligand 𝝅-molecular orbitals, is reported. Importantly, a method toeffectively tune both the electronic structure of 2D MOFs and the magneticproperties of the metal cores by exploiting the electronic structure of distinctTMs is presented. Consequently, the ionization potential characteristic ofselected TMs, particularly the relative energy position and symmetry of the 3dstates, can be used to strategically engineer bands within specificmetal–organic frameworks. These findings not only provide a rationale forband structure engineering in 2D MOFs but also offer promisingopportunities for advanced material design.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The design of 2D metal–organic frameworks (2D MOFs) takes advantage ofthe combination of the diverse electronic properties of simple organic ligandswith different transition metal (TM) centers. The strong directional nature ofthe coordinative bonds is the basis for the structural stability and the periodicarrangement of the TM cores in these architectures. Here, direct and clearevidence that 2D MOFs exhibit intriguing energy-dispersive electronic bandswith a hybrid character and distinct magnetic properties in the metal cores,resulting from the interactions between the TM electronic levels and theorganic ligand 𝝅-molecular orbitals, is reported. Importantly, a method toeffectively tune both the electronic structure of 2D MOFs and the magneticproperties of the metal cores by exploiting the electronic structure of distinctTMs is presented. Consequently, the ionization potential characteristic ofselected TMs, particularly the relative energy position and symmetry of the 3dstates, can be used to strategically engineer bands within specificmetal–organic frameworks. These findings not only provide a rationale forband structure engineering in 2D MOFs but also offer promisingopportunities for advanced material design. |
2022
|
| 6. | D. Brandstetter Photoemission Distributions from Time-Dependent Density Functional Theory Masters Thesis 2022. @mastersthesis{Brandstetter2022,
title = {Photoemission Distributions from Time-Dependent Density Functional Theory},
author = {D. Brandstetter},
url = {https://homepage.uni-graz.at/en/peter.puschnig/theses/},
year = {2022},
date = {2022-08-01},
urldate = {2022-08-01},
abstract = {A recent study in photoemission orbital tomography [Science 371, 1056 (2021)] has demonstrated that transiently excited electrons can be traced in time. This has become possible through measuring their signature in the angle-resolved momentum distribution of photoelectrons released by a high-energy probe pulse. Further developing this exciting and powerful new technique, dubbed orbital cinematography, is a desirable track for future experimental development. In this work, we use time-dependent density functional theory to scout ahead and perform an ab-initio simulation of a sub-femtosecond pump-probe angle-resolved photoemission experiment. We investigate potential issues and possible remedies in the description of ARPES within the framework of TD-DFT and conclude with momentum maps of the frontier orbitals.},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
A recent study in photoemission orbital tomography [Science 371, 1056 (2021)] has demonstrated that transiently excited electrons can be traced in time. This has become possible through measuring their signature in the angle-resolved momentum distribution of photoelectrons released by a high-energy probe pulse. Further developing this exciting and powerful new technique, dubbed orbital cinematography, is a desirable track for future experimental development. In this work, we use time-dependent density functional theory to scout ahead and perform an ab-initio simulation of a sub-femtosecond pump-probe angle-resolved photoemission experiment. We investigate potential issues and possible remedies in the description of ARPES within the framework of TD-DFT and conclude with momentum maps of the frontier orbitals. |
| 5. | A. Haags, X. Yang, L. Egger, D. Brandstetter, H. Kirschner, F. C. Bocquet, G. Koller, A. Gottwald, M. Richter, J. M. Gottfried, M. G. Ramsey, P. Puschnig, S. Soubatch, F. S. Tautz Momentum-space imaging of σ-orbitals for chemical analysis Journal Article In: Sci. Adv., vol. 8, pp. eabn0819, 2022. @article{Haags2021,
title = {Momentum-space imaging of σ-orbitals for chemical analysis},
author = {A. Haags and X. Yang and L. Egger and D. Brandstetter and H. Kirschner and F. C. Bocquet and G. Koller and A. Gottwald and M. Richter and J. M. Gottfried and M. G. Ramsey and P. Puschnig and S. Soubatch and F. S. Tautz},
doi = {10.1126/sciadv.abn0819},
year = {2022},
date = {2022-01-01},
journal = {Sci. Adv.},
volume = {8},
pages = {eabn0819},
abstract = {Tracing the modifications of molecules in surface chemical reactions benefits from the possibility to image their orbitals. While delocalized frontier orbitals with π character are imaged routinely with photoemission orbital tomography, they are not always sensitive to local chemical modifications, particularly the making and breaking of bonds at the molecular periphery. For such bonds, σ orbitals would be far more revealing. Here, we show that these orbitals can indeed be imaged in a remarkably broad energy range and that the plane wave approximation, an important ingredient of photoemission orbital tomography, is also well fulfilled for these orbitals. This makes photoemission orbital tomography a unique tool for the detailed analysis of surface chemical reactions. We demonstrate this by identifying the reaction product of a dehalogenation and cyclodehydrogenation reaction.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Tracing the modifications of molecules in surface chemical reactions benefits from the possibility to image their orbitals. While delocalized frontier orbitals with π character are imaged routinely with photoemission orbital tomography, they are not always sensitive to local chemical modifications, particularly the making and breaking of bonds at the molecular periphery. For such bonds, σ orbitals would be far more revealing. Here, we show that these orbitals can indeed be imaged in a remarkably broad energy range and that the plane wave approximation, an important ingredient of photoemission orbital tomography, is also well fulfilled for these orbitals. This makes photoemission orbital tomography a unique tool for the detailed analysis of surface chemical reactions. We demonstrate this by identifying the reaction product of a dehalogenation and cyclodehydrogenation reaction. |
2021
|
| 4. | R. Wallauer, M. Raths, K. Stallberg, L. Münster, D. Brandstetter, X. Yang, J. Güdde, P. Puschnig, S. Soubatch, C. Kumpf, F. C. Bocquet, F. S. Tautz, U. Höfer Tracing orbital images on ultrafast time scales Journal Article In: Science, vol. 371, pp. 1056-1059, 2021. @article{Wallauer2020,
title = {Tracing orbital images on ultrafast time scales},
author = {R. Wallauer and M. Raths and K. Stallberg and L. Münster and D. Brandstetter and X. Yang and J. Güdde and P. Puschnig and S. Soubatch and C. Kumpf and F. C. Bocquet and F. S. Tautz and U. Höfer},
doi = {10.1126/science.abf3286},
year = {2021},
date = {2021-01-01},
urldate = {2021-01-01},
journal = {Science},
volume = {371},
pages = {1056-1059},
abstract = {Frontier orbitals determine fundamental molecular properties such as chemical reactivities. Although electron distributions of occupied orbitals can be imaged in momentum space by photoemission tomography, it has so far been impossible to follow the momentum-space dynamics of a molecular orbital in time, for example, through an excitation or a chemical reaction. Here, we combined time-resolved photoemission using high laser harmonics and a momentum microscope to establish a tomographic, femtosecond pump-probe experiment of unoccupied molecular orbitals. We measured the full momentum-space distribution of transiently excited electrons, connecting their excited-state dynamics to real-space excitation pathways. Because in molecules this distribution is closely linked to orbital shapes, our experiment may, in the future, offer the possibility of observing ultrafast electron motion in time and space.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Frontier orbitals determine fundamental molecular properties such as chemical reactivities. Although electron distributions of occupied orbitals can be imaged in momentum space by photoemission tomography, it has so far been impossible to follow the momentum-space dynamics of a molecular orbital in time, for example, through an excitation or a chemical reaction. Here, we combined time-resolved photoemission using high laser harmonics and a momentum microscope to establish a tomographic, femtosecond pump-probe experiment of unoccupied molecular orbitals. We measured the full momentum-space distribution of transiently excited electrons, connecting their excited-state dynamics to real-space excitation pathways. Because in molecules this distribution is closely linked to orbital shapes, our experiment may, in the future, offer the possibility of observing ultrafast electron motion in time and space. |
| 3. | D. Brandstetter, X. Yang, D. Lüftner, F. S. Tautz, P. Puschnig kMap.py: A Python program for simulation and data analysis in photoemission tomography Journal Article In: Comp. Phys. Commun., vol. 263, pp. 107905, 2021. @article{Brandstetter2020,
title = {kMap.py: A Python program for simulation and data analysis in photoemission tomography},
author = {D. Brandstetter and X. Yang and D. Lüftner and F. S. Tautz and P. Puschnig},
doi = {10.1016/j.cpc.2021.107905},
year = {2021},
date = {2021-01-01},
journal = {Comp. Phys. Commun.},
volume = {263},
pages = {107905},
abstract = {Ultra-violet photoemission spectroscopy is a widely-used experimental technique to investigate the valence electronic structure of surfaces and interfaces. When detecting the intensity of the emitted electrons not only as a function of their kinetic energy, but also depending on their emission angle, as is done in angle-resolved photoemission spectroscopy (ARPES), extremely rich information about the electronic structure of the investigated sample can be extracted. For organic molecules adsorbed as well-oriented ultra-thin films on metallic surfaces, ARPES has evolved into a technique called photoemission tomography (PT). By approximating the final state of the photoemitted electron as a free electron, PT uses the angular dependence of the photocurrent, a so-called momentum map or k-map, and interprets it as the Fourier transform of the initial state’s molecular orbital, thereby gaining insights into the geometric and electronic structure of organic/metal interfaces. In this contribution, we present kMap.py which is a Python program that enables the user, via a PyQt-based graphical user interface, to simulate photoemission momentum maps of molecular orbitals and to perform a one-to-one comparison between simulation and experiment. Based on the plane wave approximation for the final state, simulated momentum maps are computed numerically from a fast Fourier transform (FFT) of real space molecular orbital distributions, which are used as program input and taken from density functional calculations. The program allows the user to vary a number of simulation parameters, such as the final state kinetic energy, the molecular orientation or the polarization state of the incident light field. Moreover, also experimental photoemission data can be loaded into the program, enabling a direct visual comparison as well as an automatic optimization procedure to determine structural parameters of the molecules or weights of molecular orbitals contributions. With an increasing number of experimental groups employing photoemission tomography to study molecular adsorbate layers, we expect kMap.py to serve as a helpful analysis software to further extend the applicability of PT.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ultra-violet photoemission spectroscopy is a widely-used experimental technique to investigate the valence electronic structure of surfaces and interfaces. When detecting the intensity of the emitted electrons not only as a function of their kinetic energy, but also depending on their emission angle, as is done in angle-resolved photoemission spectroscopy (ARPES), extremely rich information about the electronic structure of the investigated sample can be extracted. For organic molecules adsorbed as well-oriented ultra-thin films on metallic surfaces, ARPES has evolved into a technique called photoemission tomography (PT). By approximating the final state of the photoemitted electron as a free electron, PT uses the angular dependence of the photocurrent, a so-called momentum map or k-map, and interprets it as the Fourier transform of the initial state’s molecular orbital, thereby gaining insights into the geometric and electronic structure of organic/metal interfaces. In this contribution, we present kMap.py which is a Python program that enables the user, via a PyQt-based graphical user interface, to simulate photoemission momentum maps of molecular orbitals and to perform a one-to-one comparison between simulation and experiment. Based on the plane wave approximation for the final state, simulated momentum maps are computed numerically from a fast Fourier transform (FFT) of real space molecular orbital distributions, which are used as program input and taken from density functional calculations. The program allows the user to vary a number of simulation parameters, such as the final state kinetic energy, the molecular orientation or the polarization state of the incident light field. Moreover, also experimental photoemission data can be loaded into the program, enabling a direct visual comparison as well as an automatic optimization procedure to determine structural parameters of the molecules or weights of molecular orbitals contributions. With an increasing number of experimental groups employing photoemission tomography to study molecular adsorbate layers, we expect kMap.py to serve as a helpful analysis software to further extend the applicability of PT. |
2020
|
| 2. | 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 = {},
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. |
2019
|
| 1. | 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. |
