La induced Si trimer bilayer on the Si(111) surface

• Published in: Physical chemistry chemical physics : PCCP 2021-05, Vol.23 (19), p.11466-11471
• Main Authors: Chai, Jun-Shuai, Yang, Guang, Xu, Jing, Wang, Wen-Wu, Xu, Li-Fang, Wang, Jian-Tao
• Format: Article
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d1cp01351c

Using first-principles calculations, we identify a robust R 30° reconstruction of a Si 3 trimer bilayer on the Si(111) surface with a La coverage of 2/3 monolayer. Each surface unit cell contains two Si 3 trimers and two La atoms, where the upper Si 3 trimer is located just above the lower one with a rotation of about 60°, while two La atoms with different heights are distributed between the Si 3 trimers and located on the T 4 top site of the Si(111) surface, forming a honeycomb-like network structure. We find that the two La atoms have different valence states, La 2+ and La 3+ , respectively. The high structural stability is attributed to the lower La atom saturating all the three dangling bonds of the upper Si 3 trimer, while the higher La atom compensates two electrons to the lower Si 3 trimer. The electronic band structure and band-decomposed charge density distribution show a semiconducting characteristic with a small surface band gap of 42 meV. Moreover, simulated STM images show a good structural match with the recent experimental observations. Top view and side view (left) of La/Si(111)- reconstruction and the electronic band structure (right).