A Global-Optimization Study of the Phase Diagram of Free-Standing Hydrogenated Two-Dimensional Silicon

We perform a comprehensive study of the phase space of two-dimensional hydrogenated silicon. To scan the composition space, we employ an efficient constrained global structural prediction method, capable of exploring all possible bonding patterns on an equal footing. We find an interesting landscape of crystalline geometries, among which hydrogenated versions of mono- and bilayer silicene and haeckelites. The lowest energy phases, however, are buckled, with geometrical features similar to those of surface reconstructions. We observe that many structures can be described as connected nanowires exhibiting shared silicon pentagons. All studied systems are semi-conducting with sizable band gaps. Considering the similarity of some of these structures with recently synthesized 2D silicon phases and their low formation energies, we expect that these 2D materials can be produced experimentally.

Automated summary

A comprehensive study on the phase space of two-dimensional hydrogenated silicon reveals a variety of crystalline geometries, including mono- and bilayer silicene. The lowest energy phases are buckled with similarities to surface reconstructions, with many structures described as connected nanowires exhibiting shared silicon pentagons. All studied systems are semiconducting with sizable band gaps, indicating potential for experimental production of these 2D materials.