Two-dimensional materials made of Group 14 elements, graphene’s cousins, have attracted enormous interest in recent years because of their unique potential as useful topological insulators.
In particular, the up-to-now purely theoretical possibility of a lead-based 2D honeycomb material, called plumbene, has generated much attention because it has the largest spin-orbit interaction, due to lead’s orbital electron structure and therefore the largest energy band gap, potentially making it a robust 2D topological insulator in which the Quantum Spin Hall Effect might occur even above room temperature.
For this reason finding a reliable and cheap method of synthesizing plumbene has been considered to be an important goal of materials science research.
Now, Nagoya University-led researchers have created plumbene by annealing an ultrathin lead (Pb) film on palladium Pd(111). The resulting surface material has the signature honeycomb structure of a 2D monolayer, as revealed by scanning tunneling microscopy.
Surprisingly, beneath the plumbene, a palladium-lead (Pd-Pb) alloy thin film forms with a bubble structure reminiscent of a Weaire-Phelan structure (which partitions space into cells of equal volume with the least total surface area of the walls between them, solving the “Kelvin Problem”). The Weaire-Phelan structure was the inspiration for the design of the Beijing National Aquatics Centre (“Water Cube”) of the 2008 Olympics in Beijing.