In the course of SUPER2D, the interface between different 2D Materials (2DMs) and highly ordered molecular monolayers were investigated. Very different 2DMs were explored: a semiconductor, a superconductor, a layered ferromagnetic material and two compounds which could potentially display intrinsic magnetic ordering. These materials were interfaced to different ultrathin molecular films. A special focus was dedicated to molecules composed of a metal atom coordinated by organic ligands, which possess predictable spin configuration, and generate a net of metallic atoms orderly arranged on the 2DM surface. Additionally, self-assembled monolayers (SAMs) composed of silane-based molecules were employed, which induce predictable doping effects.
Different strategies were explored to obtain high-quality 2DMs. Most 2DMs were grown by molecular beam epitaxy. To confirm the atomic thickness and the desired stoichiometry, the so-obtained single layers were characterized through scanning probe techniques and spectroscopic techniques. Additionally, in some cases 2DMs were obtained by micromechanical exfoliation.
The growth of molecular overlayers was also optimized by following different strategies. Silane-based self-assembled monolayers were grown through a vapor phase deposition. Ultrathin films of organometallic molecules were grown by sublimation in ultra-high vacuum.
Through spectroscopic techniques, it was found that SAMs introduce electric field effects similar to those of a gate terminal, thereby introducing doping effects in the 2DMs. Importantly, the direction of the electric field could be inversed by using different molecules. This effect was exploited in two different studies, leading to two main results:
1. We engineered the charge transport in semiconducting 2DMs, demonstrating high performance p-type or n-type field effect transistors.
2. We showed that the superconducting transition in a single-layer superconductor could be manipulated via the formation of self-assembled monolayers.
Finally, we characterized how the magnetic properties of 2DMs are affected by the presence of a molecular overlayer through X-Ray circular dichroism, which provides information on the magnetic properties with elemental resolution. It was found that (i) VSe2 is not intrinsically ferromagnetic at the single layer limit, in contrast to a previous report reporting ferromagnetism; (ii) the metallic center in organometallic molecules does not couple magnetically to ferromagnetic van der Waals materials.
These results obtained in SUPER2D were presented to the scientific community in four conferences and a workshop, in three occasions as invited contributions. Moreover, to spark interest of the scientific community in the topic of SUPER2D, a perspective and a review paper were published discussing different aspects of 2D materials/molecules interfaces. The results which emerged from the experimental work performed during SUPER2D are described so far in two published works, one focusing on the engineering of charge transport in semiconducting WSe2, and one on the absence of ferromagnetism in VSe2. Other two articles are in preparation.
Moreover, various activities were performed with the purpose of bringing science closer to students/general public, such as Lab visits and demonstrations in front of high-school students and participation to the Science Week.
