Speaker
Description
Two-dimensional (2D) materials provide a unique playground in which reduced dimensionality, surface effects, and interfacial interactions give rise to electronic and structural phenomena absent in bulk systems. Among others we focused on 2D elemental systems based on 15th group α-antimonene, α-bismuthene. Following the synthesis of these systems, we have systematically explored their physical properties, uncovering a range of intriguing phenomena. These include unpinned Dirac states [1], Dirac points enforced by nonsymmorphic symmetries [2], and signatures of topologically protected edge states [3]. More recently, we reported directional structural superlubricity and indications of Lévy-flight-like dynamics in the spontaneous diffusion of Bi nanostructures on graphite [4]. However, these materials are inherently prone to environmental instability, which motivated us to undertake a broader investigation of oxidation processes at the nanoscale, extending our studies to a wider class of 2D systems and exploring strategies for their stabilization.
A key challenge in the study and application of 2D materials is their susceptibility to oxidation, which limits experimental reproducibility and device stability. In this context, we have systematically investigated the oxidation behavior of TMDs, revealing a pronounced thickness dependence near the monolayer limit. Ultrathin layers exhibit oxidation pathways distinct from their bulk counterparts, leading to the formation of structurally and electronically distinct oxide phases.
One strategy to mitigate degradation is the use of protective capping layers. We have explored several such approaches, with particular emphasis on graphene. Beyond its protective role, graphene enables the formation of heterostructures with TMDs, providing a platform to engineer its electronic properties, including attempts to induce a band gap and to investigate twist-dependent phenomena.
At the same time, rather than treating oxidation solely as a detrimental effect, we exploit oxide formation as a route toward functional materials. In particular, we investigated the controlled growth of ultrathin MoO$_3$ layers on graphite [5, 6], demonstrating a substantial increase in its work function (WF), which is essential for applications such as optoelectronic devices. Moreover, MoO$_3$-based systems provide a versatile platform for functional phenomena, including resistive switching, which will also be discussed.
References
[1] Q. Lu et al., Nat. Comm. 13 (2022) 4603
[2] P.J. Kowalczyk et al., ACS Nano 14 (2020) 1888
[3] S. Salehitaleghani et al., 2D Mat. 10 (2022) 15020
[4] M. Le Ster et al., Small 21 (2025) 2408349
[5] D. Kowalczyk et al., 2D Mat. 8 (2021) 25005
[6] D. Kowalczyk et al., ACS Appl. Mat. Int. 14 (2022) 44506
Acknowledgments
This work was supported by National Science Centre, Poland under projects: 2019/35/B/ST5/03956, 2020/38/E/ST3/00293 and 2024/55/B/ST11/01717.