2025
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| 6. | 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.202500507},
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. |
| 5. | 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. |
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 = {},
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. | D. Baranowski, M. Thaler, D. Brandstetter, A. Windischbacher, I. Cojocariu, S. Mearini, V. Chesnyak, L. Schio, L. Floreano, C. Gutiérrez Bolaños, P. Puschnig, L. L. Patera, V. Feyer, C. M. Schneider Emergence of Band Structure in a Two- Dimensional Metal−Organic Framework upon Hierarchical Self-Assembly Journal Article In: ACS Nano, vol. 18, pp. 19618−19627, 2024. @article{nokey,
title = {Emergence of Band Structure in a Two- Dimensional Metal−Organic Framework upon Hierarchical Self-Assembly},
author = {D. Baranowski and M. Thaler and D. Brandstetter and A. Windischbacher and I. Cojocariu and S. Mearini and V. Chesnyak and L. Schio and L. Floreano and C. Gutiérrez Bolaños and P. Puschnig and L. L. Patera and V. Feyer and C. M. Schneider},
url = {https://pubs.acs.org/doi/10.1021/acsnano.4c04191#},
doi = {10.1021/acsnano.4c04191},
year = {2024},
date = {2024-07-17},
urldate = {2024-07-17},
journal = {ACS Nano},
volume = {18},
pages = {19618−19627},
abstract = {Two-dimensional metal−organic frameworks (2D-MOFs) represent a category of atomically thin materials that combine the structural tunability of molecular systems with the crystalline structure characteristic of solids. The strong bonding between the organic linkers and transition metal centers is expected to result in delocalized electronic states. However, it remains largely unknown how the band structure in 2D-MOFs emerges through the coupling of electronic states in the building blocks. Here, we demonstrate the on-surface synthesis of a 2D-MOF exhibiting prominent π-conjugation. Through a combined experimental and theoretical approach, we provide direct evidence of band structure formation upon hierarchical self-assembly, going from metal−organic complexes to a conjugated two-dimensional framework. Additionally, we identify the robustly dispersive nature of the emerging hybrid states, irrespective of the metallic support type, highlighting the tunability of the band structure through charge transfer from the substrate. Our findings encourage the exploration of band-structure engineering in 2D-MOFs for potential applications in electronics and photonics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Two-dimensional metal−organic frameworks (2D-MOFs) represent a category of atomically thin materials that combine the structural tunability of molecular systems with the crystalline structure characteristic of solids. The strong bonding between the organic linkers and transition metal centers is expected to result in delocalized electronic states. However, it remains largely unknown how the band structure in 2D-MOFs emerges through the coupling of electronic states in the building blocks. Here, we demonstrate the on-surface synthesis of a 2D-MOF exhibiting prominent π-conjugation. Through a combined experimental and theoretical approach, we provide direct evidence of band structure formation upon hierarchical self-assembly, going from metal−organic complexes to a conjugated two-dimensional framework. Additionally, we identify the robustly dispersive nature of the emerging hybrid states, irrespective of the metallic support type, highlighting the tunability of the band structure through charge transfer from the substrate. Our findings encourage the exploration of band-structure engineering in 2D-MOFs for potential applications in electronics and photonics. |
| 2. | 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 = {},
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
|
| 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 = {https://doi.org/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 = {},
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. |
