Introduction to the Physics of Silicene and other 2D Materials by Seymur Cahangirov Hasan Sahin Guy Le Lay & Angel Rubio

Author:Seymur Cahangirov, Hasan Sahin, Guy Le Lay & Angel Rubio
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

3.2 Growth Mechanism

The subsequent growth of reconstructed silicene after formation of 3×3 silicene was studied by DFT calculations (Cahangirov et al. 2014b). Here we summarize results of that study. As Si atoms are deposited on Ag(111) surface they search for the optimum structure that minimizes the energy. In the absence of the Ag substrate this optimum structure is the cubic diamond structure that has a cohesive energy of 4.598 eV/atom according to DFT calculations. However, in the presence of the Ag substrate a monolayer of silicene that has primarily 3×3 reconstruction is formed. Here, the 3×3 supercell of silicene is matched with the 4×4 supercell of the Ag(111) surface, as shown in Fig. 3.1a. If we remove the Ag substrate and freeze the Si atoms of the 3×3 reconstructed silicene to calculate its cohesive energy, it turns out to be 3.850 eV/atom, which is 108 meV lower than the buckled freestanding silicene. In fact, if we start from the freestanding 3×3 reconstructed silicene and relax the structure, it goes to the buckled structure, meaning that it is not even a local energy minimum in the absence of the Ag substrate. However, the cohesive energy of 3×3 structure surpasses that of the cubic diamond structure when it is placed on the Ag(111) surface, as seen in Table 3.1. This strong interaction between silicene and the Ag substrate explains the growth of monolayer silicene instead of clustering of Si atoms into bulk structures.

Table 3.1Cohesive energies per Si atom and per unit area are given for the 3×3 reconstructed silicene, TDS, LHDS, and HDS structures on the Ag(111) surface

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