Commensurate-incommensurate transition and strain relief patterns in monolayer C_(60) on Cd(0001)

摘要

We have studied the commensurate-incommensurate phase transition, rotation epitaxy, and strain relief patterns in C_(60) overlayers grown on Cd(0001) with a low-temperature scanning tunneling microscopy. When deposited at low temperature (～200 K), C_(60) molecules form the 10 × 10 high-order commensurate (HOC) phase with two different half-unit cells, resembling the Si(111)-7 ×7 surface. Postannealing at room temperature (RT) results in the transition from HOC phase to incommensurate phase, in which strain relaxation takes place in the form of periodic vacancies and C_(60) heptamer arrays. In the case of RT deposition, parallel stripe domain walls appeared in the commensurate 2 3~(1/2)×2 3~(1/2) R30° phase. These results provide essential information for understanding the strain relaxation mechanism, and the role of substrate temperatures in the process of C_(60) thin films growth.