Defects in silicene: vacancy clusters, extended line defects, and Di-adatoms.

Shuang Li,Yifeng Wu,Wei Liu,Yonghui Wang,Tong Jiang,Yi Tu,Yonghao Zhao

doi:10.1038/srep07881

Abstract

Defects are almost inevitable during the fabrication process, and their existence strongly affects thermodynamic and (opto)electronic properties of two-dimensional materials. Very recent experiments have provided clear evidence for the presence of larger multi-vacancies in silicene, but their structure, stability, and formation mechanism remain largely unexplored. Here, we present a detailed theoretical study of silicene monolayer containing three types of defects: vacancy clusters, extended line defects (ELDs), and di-adatoms. First-principles calculations, along with ab initio molecular dynamics simulations, revealed the coalescence tendency of small defects and formation of highly stable vacancy clusters. The 5|8|5 ELD – the most favorable extended defect in both graphene and silicene sheets – is found to be easier to form in the latter case due to the mixed sp2/sp3 hybridization of silicon. In addition, hybrid functional calculations that contain part of the Hatree-Fock exchange energy demonstrated that the introduction of single and double silicon adatoms significantly enhances the stability of the system, and provides an effective approach on tuning the magnetic moment and band gap of silicene.

Highlights

Correspondence and requests for materials should be addressed to Defects in Silicene: Vacancy Clusters, Extended Line Defects, and Di-adatoms
Hybrid functional calculations that contain part of the Hatree-Fock exchange energy demonstrated that the introduction of single and double silicon adatoms significantly enhances the stability of the system, and provides an effective approach on tuning the magnetic moment and band gap of silicene
We focused on five architectures of extended line defects (ELDs) embedded in silicene, showing that ELDs have lower formation energies compared to vacancy clusters, which arises from the reconstruction of periodic defects

Summary

Correspondence and requests for materials should be addressed to

Nano Structural Materials Center, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, Jiangsu, China. Silicene forms a slightly buckled monolayer structure that allows more flexibility to tailor their band structures and functions8–12 Despite such single-layer silicon has been theoretically speculated for two decades, the actual fabrication of silicene on many substrates, such as Ag[111]13–14, ZrB2(0001), (2 3 1)-reconstructed Au[110]16, and Ir[111] surfaces, has been reported only very recently. The presence of multi-atom vacancies is of fundamental importance for understanding the formation and operation of layered materials, their configurations, stabilities, and formation mechanisms are far from being fully comprehended In this contribution, we performed density-functional theory (DFT) calculations to investigate the reconstruction, coalescence, and diffusion behaviors of vacancy defects in free-standing silicene. We studied the adsorption and diffusion of silicon atoms on silicene layers, and uncovered that such adsorption process can enhance the stability of the system and open sizeable band gaps in silicene

Results

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Methods

Additional information