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 semiconducting 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.

我们针对二维氢化硅的相空间开展了系统性全面研究。为遍历其组分空间，我们采用了一种高效的约束全局结构预测方法，该方法可无差别地探索所有可能的成键模式。我们发现了一类颇具研究价值的晶体几何结构谱系，其中包含氢化形式的单层硅烯、双层硅烯以及海克尔型硅烯（haeckelite）。然而，能量最低的相态均为褶皱结构，其几何特征与表面重构结构高度相似。我们观察到，诸多结构可被描述为共享硅五边形的互连纳米线。所有被研究的体系均为具有可观带隙的半导体。鉴于其中部分结构与近期合成的二维硅相具有相似性，且其形成能较低，我们预计此类二维材料可通过实验手段成功制备。