Unveiling the Secrets of Interlayer Confinement

In a groundbreaking study published in Nature Materials, Manuel Längle and colleagues have successfully created and directly visualized two-dimensional (2D) noble gas solids, a long-sought goal in the field of condensed matter physics. The researchers achieved this by inserting noble gas atoms, such as xenon and krypton, into the gap between graphene layers using ultralow-energy ion irradiation.

Once inside the 2D container, the noble gas atoms and clusters remain highly mobile, only becoming stationary when pinned to defects associated with negative curvature in graphene. This deformation provides a pocket that exerts pressure on the encapsulated species, keeping the cluster in a 2D shape for a sufficient duration, allowing for image acquisition.

Interestingly, the study revealed that as the cluster size increases, the local curvature change in graphene becomes more even, leading to a decrease in pressure exerted on the clusters and an increase in interatomic distance. When the cluster size is large enough and the corresponding pressure is sufficiently low, clusters undergo a solid-to-liquid transformation and lose their strict 2D shape. This phenomenon, which goes against common sense that smaller clusters have a lower melting point and are more prone to phase transition, is partially attributed to the larger deformation needed to accommodate Xe clusters between graphene layers and the lower pressure required for the solid-liquid transformation of Xe clusters at room temperature.

The creation of 2D noble gas solids provides an opportunity for studies in fundamental condensed matter physics, ranging from atomic arrangements and orientational order to lattice dynamics, symmetry breaking, and phase transition. This research also opens up the possibility of implanting and encapsulating various elements, either gaseous, liquid, or solid phase species, in the gaps between van der Waals layers, stimulating future research on other 2D confined systems.

The precise control of the confined atoms at a particular spatial location could lead to potential applications in electronics, quantum information, energy conversion, and other fields. With this study, Längle and colleagues have taken a significant step towards understanding and harnessing the potential of 2D confined systems.

Source:
<https://www.nature.com/articles/s41563-024-01850-y>