Protected ultrathin amorphous tin by intercalation at the graphene/Ru interface

Research on two-dimensional (2D) materials has been dominated by crystals, while ultrathin amorphous solids have remained less developed. Accessing metallic glasses near the 2D limit poses challenges in synthesis while also requiring encapsulation against oxidation in air. Here, we discuss a strategy that addresses both issues. Sn intercalation of the graphene/Ru interface at temperatures above the melting point of bulk Sn produces an ultrathin Sn layer that, despite being sandwiched between crystals, resists crystallization down to room temperature. Control experiments on particles suggest such delayed crystallization during cooling from the melt as a common feature of nanoscale particles as well as ultrathin layers of Sn. For graphene, the intercalation by non-crystalline Sn has significant consequences, notably the recovery of the properties of a free-standing sp² carbon monolayer due to a decoupling of the graphene sheet from the underlying Ru support. The amorphous intercalated Sn layer itself is stabilized against oxidation in air by the capping graphene sheet. The combined findings point to avenues for producing ultrathin amorphous metals that are stable in air, enabling investigations of potentially distinct properties of non-crystalline solids near the 2D limit.