Periodic Reporting for period 1 - IMAGINE (Indirect Magnetic Interactions: Tuning by Electric Field)
Période du rapport: 2021-09-01 au 2023-08-31
Within this project, we have made some crucial steps towards this goal. Specifically, we have demonstrated that various 2D magnetic metal-organic frameworks (MOFs) can be synthesized atop graphene supports with different doping levels. We have also demonstrated that these systems are remarkably stable, and even though their synthesis requires ideal conditions of ultrahigh vacuum, they remain stable and atomically-defined even in ambient. Most of the current knowledge of atomically-defined 2D MOFs has been learned on metal supports, therefore we invested a great effort to unravel how the change from metal support to graphene affects the main system parameters, i.e. physical and electronic structure, chemical reactivity, and magnetic ordering. Lastly, we studied how the different doping level of the graphene changes the charge distribution within the MOF. Overall, the main objectives of the project have been fulfilled, and our work clearly contributes to the development of spintronics applications based on 2D metal-organic materials.
The second important task was to characterize the properties of the 2D MOFs atop graphene supports. Prior literature studied similar systems in detail on metal supports, and our initial assumption was that these systems should behave very similarly also on graphene. This turned out to be only partially true, and our detailed study comparing Fe-TCNQ on graphene and on gold supports indeed revealed similarity in the main bonding motifs, but significant structural differences in the local coordination environment of the Fe2+ cation. This leads to different occupancy of the individual d-orbitals, and consequently to vastly different properties, both in electronic structure and in chemical reactivity. Overall, we found that the weaker interaction with the graphene support renders the 2D MOFs much more representative of the free-standing models commonly screened in computational studies. Thus, our work shows that synthesis of 2D MOFs on graphene is a convenient way to narrow the gap between experiment and theory, which is a vital requirement for efficient materials research. These findings are summarized in our manuscript currently in revision for publication in the Journal of the American Chemical Society, and were presented by oral or poster presentations at three international conferences and seminars.
Next, we studied the effects of graphene doping on the properties of supported 2D MOFs. We compared the properties of Ni-TCNQ on undoped graphene/Ir(111) with a Ni-TCNQ network synthesized on an n-doped graphene prepared by intercalation of the graphene/Ir(111) system. We clearly identified significant differences in the structure of these two Ni-TCNQ systems, which are most likely linked to the different charge distribution between the 2D MOF and the support. We have also studied the properties of Ni-TCNQ atop n-doped graphene prepared on SiC crystals, and we have explored the possibilities of remote graphene doping by X-Ray or UV irradiation. Lastly, we have studied the magnetic properties of the Ni-TCNQ and Fe-TCNQ networks in collaboration with our partners, and we explored the possibilities of synthesizing multilayer metal-organic structures. As of now, these collaborative experimental efforts and the supporting computational work are still ongoing. Some results were presented in one invited seminar talk, and a part will be published in a currently prepared manuscript. Overall, it is expected that at least two more publications will be published within next year, summarizing our work on graphene doping and properties of multilayer metal-organic frameworks.