2025
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| 7. | 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 = {Orbital Cinema},
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. |
| 6. | 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 = {Orbital Cinema},
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. |
| 5. | 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 = {Orbital Cinema},
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
|
| 4. | 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 = {Orbital Cinema},
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. |
| 3. | W. Bennecke, A. Windischbacher, D. Schmitt, J. P. Bange, R. Hemm, C. S. Kern, G. D’Avino, X. Blase, D. Steil, S. Steil, M. Aeschlimann, B. Stadtmüller, M. Reutzel, P. Puschnig, G. S. M. Jansen, S. Mathias Disentangling the multiorbital contributions of excitons by photoemission exciton tomography Journal Article In: Nature Communications, vol. 15, no. 1804, pp. 10, 2024. @article{Bennecke2024,
title = {Disentangling the multiorbital contributions of excitons by photoemission exciton tomography},
author = {W. Bennecke and A. Windischbacher and D. Schmitt and J. P. Bange and R. Hemm and C. S. Kern and G. D’Avino and X. Blase and D. Steil and S. Steil and M. Aeschlimann and B. Stadtmüller and M. Reutzel and P. Puschnig and G. S. M. Jansen and S. Mathias},
url = {https://www.nature.com/articles/s41467-024-45973-x},
doi = {10.1038/s41467-024-45973-x},
year = {2024},
date = {2024-02-28},
urldate = {2024-02-28},
journal = {Nature Communications},
volume = {15},
number = {1804},
pages = {10},
abstract = {Excitons are realizations of a correlated many-particle wave function, specifi-cally consisting of electrons and holes in an entangled state. Excitons occurwidely in semiconductors and are dominant excitations in semiconductingorganic and low-dimensional quantum materials. To efficiently harness thestrong optical response and high tuneability of excitons in optoelectronics andin energy-transformation processes,access to the full wavefunction of theentangled state is critical, but has so far not been feasible. Here, we show howtime-resolved photoemission momentum microscopy can be used to gainaccess to the entangled wavefunction and to unravel the exciton’s multiorbitalelectron and hole contributions. For the prototypical organic semiconductorbuckminsterfullerene (C60), we exemplify the capabilities of exciton tomo-graphy and achieve unprecedented access to key properties of the entangledexciton state including localization, charge-transfer character, and ultrafastexciton formation and relaxation dynamics.},
keywords = {Orbital Cinema},
pubstate = {published},
tppubtype = {article}
}
Excitons are realizations of a correlated many-particle wave function, specifi-cally consisting of electrons and holes in an entangled state. Excitons occurwidely in semiconductors and are dominant excitations in semiconductingorganic and low-dimensional quantum materials. To efficiently harness thestrong optical response and high tuneability of excitons in optoelectronics andin energy-transformation processes,access to the full wavefunction of theentangled state is critical, but has so far not been feasible. Here, we show howtime-resolved photoemission momentum microscopy can be used to gainaccess to the entangled wavefunction and to unravel the exciton’s multiorbitalelectron and hole contributions. For the prototypical organic semiconductorbuckminsterfullerene (C60), we exemplify the capabilities of exciton tomo-graphy and achieve unprecedented access to key properties of the entangledexciton state including localization, charge-transfer character, and ultrafastexciton formation and relaxation dynamics. |
2023
|
| 2. | A. Adamkiewicz, M. Raths, M. Stettner, M. Theilen, L. Münster, S. Wenzel, M. Hutter, S. Soubatch, C. Kumpf, F. C.Bocquet, R. Wallauer, F. S. Tautz, U. Höfer Coherent and Incoherent Excitation Pathways in Time-Resolved Photoemission Orbital Tomography of CuPc/Cu(001)-2O Journal Article In: J.Phys. Chem. C, vol. 127, pp. 20411, 2023. @article{Adamkiewicz2023,
title = {Coherent and Incoherent Excitation Pathways in Time-Resolved Photoemission Orbital Tomography of CuPc/Cu(001)-2O},
author = {A. Adamkiewicz and M. Raths and M. Stettner and M. Theilen and L. Münster and S. Wenzel and M. Hutter and S. Soubatch and C. Kumpf and F. C.Bocquet and R. Wallauer and F. S. Tautz and U. Höfer},
doi = {10.1021/acs.jpcc.3c04859},
year = {2023},
date = {2023-10-09},
urldate = {2023-10-09},
journal = {J.Phys. Chem. C},
volume = {127},
pages = {20411},
abstract = {Time-resolved photoemission orbital tomography (tr-POT) offers unique possibilities for tracing molecular electron dynamics. The recorded pump-induced changes of the angle-resolved photoemission intensities allow one to characterize unoccupied molecular states in momentum space and to deduce the incoherent temporal evolution of their population. Here, we show for the example of CuPc/Cu(001)-2O that the method also gives access to the coherent regime and that different excitation pathways can be disentangled by a careful analysis of the time-dependent change of the photoemission momentum pattern. In particular, we demonstrate by varying photon energy and polarization of the pump light how the incoherent temporal evolution of the LUMO distribution can be distinguished from coherent contributions of the projected HOMO. Moreover, we report the selective excitation of molecules with a specific orientation at normal incidence by aligning the electric field of the pump light along the molecular axis.},
keywords = {Orbital Cinema},
pubstate = {published},
tppubtype = {article}
}
Time-resolved photoemission orbital tomography (tr-POT) offers unique possibilities for tracing molecular electron dynamics. The recorded pump-induced changes of the angle-resolved photoemission intensities allow one to characterize unoccupied molecular states in momentum space and to deduce the incoherent temporal evolution of their population. Here, we show for the example of CuPc/Cu(001)-2O that the method also gives access to the coherent regime and that different excitation pathways can be disentangled by a careful analysis of the time-dependent change of the photoemission momentum pattern. In particular, we demonstrate by varying photon energy and polarization of the pump light how the incoherent temporal evolution of the LUMO distribution can be distinguished from coherent contributions of the projected HOMO. Moreover, we report the selective excitation of molecules with a specific orientation at normal incidence by aligning the electric field of the pump light along the molecular axis. |
| 1. | C. S. Kern, A. Windischbacher, P. Puschnig Photoemission orbital tomography for excitons in organic molecules Journal Article In: Phys. Rev. B, vol. 108, pp. 085132, 2023. @article{Kern2023,
title = {Photoemission orbital tomography for excitons in organic molecules},
author = {C. S. Kern and A. Windischbacher and P. Puschnig},
doi = {10.1103/PhysRevB.108.085132},
year = {2023},
date = {2023-08-22},
urldate = {2023-08-22},
journal = {Phys. Rev. B},
volume = {108},
pages = {085132},
abstract = {Driven by recent developments in time-resolved photoemission spectroscopy, we extend the successful method of photoemission orbital tomography (POT) to excitons. Our theory retains the intuitive orbital picture of POT, while respecting both the entangled character of the exciton wave function and the energy conservation in the photoemission process. Analyzing results from three organic molecules, we classify generic exciton structures and give a simple interpretation in terms of natural transition orbitals. We validate our findings by directly simulating pump-probe experiments with time-dependent density functional theory.},
keywords = {Orbital Cinema},
pubstate = {published},
tppubtype = {article}
}
Driven by recent developments in time-resolved photoemission spectroscopy, we extend the successful method of photoemission orbital tomography (POT) to excitons. Our theory retains the intuitive orbital picture of POT, while respecting both the entangled character of the exciton wave function and the energy conservation in the photoemission process. Analyzing results from three organic molecules, we classify generic exciton structures and give a simple interpretation in terms of natural transition orbitals. We validate our findings by directly simulating pump-probe experiments with time-dependent density functional theory. |
