Materials engineering in flatland (2D-MOFs)

Figure 1. Real space structure representations of the relaxed structured for the Ni-MOF, b) valence band spectra. Green, cyan and orange lines refer to the Ni-, Co- and Fe-MOFs, respectively, momentum map of the hybrid states in Ni-MOF, c-e) Experimental (left) and simulated (right) valence band maps represented as binding energy vs momentum cuts along the direction of the Ag(100) substrate: c) Ni-MOF, d) Co-MOF, e) Fe-MOF.

Aiming at ever thinner materials, one eventually reaches the two-dimensional (2D) limit, where the material ultimately becomes just a few atoms, or even only one atom, thin. In this "flatland", the materials acquire unique mechanical, electronic and optical properties that promise great potential for future innovative technologies, for example as materials for energy conversion and storage. Famous examples of such 2D materials are semi-metallic graphene or semiconducting molybdenum disulphide (MoS2).

In collaboration with our colleagues from Institute of Physics, University of Graz we have reported a significant breakthrough in engineering and characterizing the electronic structure of so-called 2D metal-organic frameworks (2D-MOFs). Such 2D-MOFs are a special type of 2D materials, that are made up of metal atoms connected by organic (carbon-based) molecules. They combine the best of both worlds, metals and organic materials, and they hold promise for a wide range of advanced technologies, making our devices smaller, smarter, and more efficient.

Using a synergistic approach that combines experimental and theoretical methodologies, the researchers provide direct evidence for the emergence of band structure upon the hierarchical assembly of 1,2,4,5-tetracyanobenzene (TCNB) organic linkers and transition metal centers into a 2D-MOF lattice (see Figure 1).

However, the studies show not only the formation of the band structure, but also the associated multifunctional electronic and magnetic properties of 2D MOFs: these are largely independent of the underlying substrate. The findings offer a new perspective on how to tailor electronic band structures in 2D MOFs and pave the way for the integration of these materials into future electronic and photonic devices.

The momentum-resolved photoemission experiments were conducted at the Elettra synchrotron facility in Trieste, Italy, where our group operates NanoESCA beamline. All theoretical investigations for this project were performed by Dominik Brandstetter, Dr. Andreas Windischbacher and Prof. Peter Puschnig from the University of Graz, Austria.

Additional experiments were carried out in close collaboration with Prof. Laerte L. Patera and Marco Thaler from the University of Innsbruck, Dr. Luca Floreano and Dr. Luca Schio from the Italian National Research Council, and Dr. Pierluigi Gargiani and Dr. Manuel Valvidares from the BOREAS beamline at the ALBA synchrotron. The research was conducted in close collaboration with Dr. Iulia Cojocariu from the University of Trieste.

Original publications:

1. 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”, Adv. Sci. 11 (2024) 2404667, https://doi.org/10.1002/advs.202404667

2. 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”, ACS Nano 18 (2024) 19618, https://doi.org/10.1021/acsnano.4c04191

Letzte Änderung: 05.03.2025