Structure, Stability, and Electronic Properties of Hydrogenated Monolayer 2D Silicon Allotropes by First‐Principles Calculation

Abstract

Since the theoretical conceptualization of graphene and the experimental separation of single and multiple graphene layers, [1,2] 2D materials have been extensively studied due to their intriguing properties and promising applications. [3][4][5][6][7] Silicene, a representative 2D silicon allotrope, has been demonstrated to be stable and experimentally synthesized on Ag (111) substrates. [8][9][10][11][12][13] The bandgap of pristine silicene was very tiny (1.55 meV) and susceptibly influenced by the interactions with the substrate, which all prevented its practical application as a semiconductor device. [14][15][16][17][18] To eliminate the serious influence of the substrate on the structural stability and electronic properties of layer silicon nanostructure, a series of 2D silicon allotropes, such as honeycomb dumbbell silicene (HDS), [19][20][21] large honeycomb dumbbell silicene (LHDS), [22][23][24] hybrid octagonal tiling pattern and dumbbell-like units (OTDS), [25] and trigonal dumbbell silicene (TDS), [26][27][28] have been proposed to achieve the stability of monolayer structure. It can be found that, to form the stable sp 3 hybridization configuration, all these studies were performed on the basis of the dumbbelllike unit. In addition, it has been demonstrated that the group-IV graphene-like structures completely covered by hydrogen or halogen atoms can form an sp 3 hybridization structure with fourfold-coordinated atoms. [29,30] These structures containing hydrogen or halogen atoms were energetically accessible and should be readily synthesized through the hydrogenation or halogenation processes. Clearly, it should be feasible to generate novel monolayer 2D silicon allotropes with stable sp 3 configurations in hydrogen concentration environments.In this work, we perform the prediction of silicon allotropes containing hydrogen using a systematic ab-initio global structural optimization method under hydrogen concentration conditions, then the monolayer 2D silicon allotropes were picked out and further finely optimized. In particular, we successfully predicted the monolayer 2D silicon allotropes with stable sp 3 hybridization configuration under the ambient conditions of hydrogen concentration and the possible synthesis route for these allotropes was analyzed by comparing their formation energy relative to the corresponding hydrogen-free structures and the hydrogen-free structures on Ag(111) substrate. Furthermore, we investigated the electronic properties of these monolayer 2D silicon allotropes after verifying their dynamic and