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Low-energy ion irradiation of 2D materials 
DFG research grant 

In fundamental studies we investigate how a supported 2D material behaves under a variety of irradiation conditions using noble gas ions up to a few keV in energy. The experiments uncover damage formation and recovery in 2D materials at the atomic scale. As an example, we investigated how ion beams induce phase transitions in 2D layers. A reversible ion beam induced crystalline-to-amorphous phase transformation of an MoS2 monolayer resting on a graphene sheet was uncovered (compare figure). Using STS it was learned that the structural transformation is accompanied by a semiconductor-to-metal transition. This research has shown that it is possible to selectively change the defect concentration or even to amorphize the top layer of a heterostructure assembled from 2D materials, without disturbing or damaging the rest of the stack. In a combination with a thermal treatment and a reactive vapour, this opens up the possibility to widely tune the properties of a single 2D layer in a stack.

Our experiments oriented towards practical applications investigate, for instance: how wrinkle formation during 2D layer growth can be suppressed through ion irradiation [more]; how a 2D layer can be ‘punched’ by ions to create a regular lattice of nm-sized vacancy cluster holes, which would be useful for applications like water desalination; or whether ion implantation underneath supported 2D layer materials can be used for high pressure chemistry or isotope separation.

Top left: STM topography of monolayer MoS2 islands on graphene. Top right: Same sample after amorphization through grazing-incidence Xe+ ion irradiation. Middle: Corresponding low-energy electron diffraction patterns visualizing the amorphization – diffraction spots are absent after ion irradiation. Bottom: Molecular dynamics simulation of grazing-incidence Xe+ ion irradiation of MoS2 (sulfur: yellow; Mo: blue) [more