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Probing the interplay of interactions, screening and strain in monolayer MoS2 via self-intercalation
Our colleagues Iva Šrut Rakić, Dino Novko, and Marko Kralj, together with long term collaborators from the University of Siegen, including an Institute’s alumni Borna Pielić, have published a paper in NPJ 2D Materials and Applications where they demonstrate how self-intercalations of 2D materials can be used to change their electronic properties by manipulating substrate interactions.
Probing the interplay of interactions, screening and strain in monolayer MoS2 via self-intercalation
Borna Pielić, Matko Mužević, Dino Novko, Jiaqi Cai, Alice Bremerich, Robin Ohmann, Marko Kralj, Iva Šrut Rakić, and Carsten Busse, npj 2D Mater Appl 8, 61 (2024).
DOI: https://doi.org/10.1038/s41699-024-00488-3
In this research our colleagues synthesized monolayers of MoS2 on a graphene on Ir(111) substrate using procedures they developed to promote self-intercalation process during synthesis. This non-invasive technique introduces native atoms (in this case Mo or S) between the graphene layer and Ir substrate, significantly altering the electronic structure of MoS2. They find that Mo intercalation strengthens the binding between MoS2 and the graphene substrate, while reducing the band gap. On the other hand, S intercalation weakens the bonding and increases the band gap. In this way graphene modified by either S or Mo intercalation acts as effectively different substrate for MoS2. Observed changes not only significantly affect the morphology and strain of the MoS2 layer, but also lead to notable non-trivial shifts in the material’s electronic band valleys. These shifts are driven by a combination of (i) altered screening of the many-body interactions and (ii) strain, providing new insights into how different substrates impact the electronic structure of 2D materials.
Figure 1. STM image of S (left) and Mo (right) intercalated monolayer MoS2 islands on graphene on Ir(111). Lower panel shows graphic representation of intercalation effects on binding and strain.
This research opens up new possibilities for creating advanced electronics by fine-tuning 2D materials’ properties in a non-invasive fashion during their synthesis. By controlling strain in a material and in parallel the interaction strength with the substrate, one can tailor the electronic properties of 2D heterostructures, paving the way for more efficient devices. In particular, non-rigid band shifts not only change the size of the semiconducting gap but can also switch its character between direct and indirect gap, which opens up possibilities for controlling exciton binding, developing optoelectronic applications, exploring new charge transport regimes, and even superconductivity in 2D systems.
Figure 2. a) STS characterization of MoS2 intercalated by S (orange) and Mo (green) where one can see both the change in the band gap and high symmetry points shifting in energy. b) DFT band structure for freestanding MoS2 calculated for two values of screening ω and five lattice constants a reveals how individual contribution affects band structure.