Ce诱导Si(111)表面重构和相变机制的研究

Various Cerium-induced reconstructions on Si(111) and their phase transitions were investigated by scanning tunneling microscopy. A √3×√3-R30° reconstruction was observed on the sample at the Ce coverage of 1/3 ML and with sample annealing at 500℃. This surface structure evolved into a 2×3 reconstruction after sample annealing at 850℃. With the annealing temperature rising to 950℃, we observed the coexistence of several reconstructions, including 2×3, 17×6, 11×6 and 5×2. The pure 5×2 phase was obtained by further increasing the annealing temperature to 1150℃. The structural models of the 2×3, 5×2 and (2n+1) ×6 phases composed of honeycomb chains and Seiwatz chains were proposed according to the electron counting rule. The atomic proportion of Si atoms consisting of the honeycomb chains in the 5×2 reconstruction is the largest among the observed reconstructions. As the honeycomb chains are more stable than the Seiwatz chains, the 5×2 reconstruction is the energetically most favorable structure. The phase transition from the √3×√3-R30° reconstruction to the 2×3 reconstruction is driven by the formation of the Seiwatz chains, while the structural evolution to the 5×2 reconstruction is driven by the formation of the honeycomb chains. Our study is of great significance for understanding the physical mechanism and phase transition of rare earth metals-induced reconstructions on the Si(111) surfaces.