EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Noble gas clusters trapped between two or more graphene layers form two-dimensional noble gas crystallites that are directly observable in an atomically resolved scanning transmission electron microscope (STEM). These otherwise inert atoms appear in both solid- and liquid-like phases, and in our experiments the clusters exhibit size-dependent, electron-beam driven dynamics that include, for instance, “jumps” over distances greater than the dimensions of the crystallites. Atomistic simulations confirm the stability of small clusters and shed light on the observed dynamics.

Ion irradiation is a widely adopted technique for electronic structure engineering in the context of silicon semiconductors. The implantation of hetero-atoms into bulk is thoroughly understood via existing experiments and semi-empirical modelling. However, applying this technique to 2D materials, which have a stopping power much lower than the samples of a greater thickness, necessitates the use of ion energies lower than what is available in most existing experimental setups. In contrast, in the present work we have used initially high-energy Xe$^+$ and Kr$^+$ ions that were decelerate by an electrostatic lens to kinetic energies ranging from a few tens to a few hundreds of eV to trap them in the van der Waals gap of graphene bilayers.