Critical domain size of the 7 x 7 structure for nucleation and growth on Si(111) quenched surfaces

Two-speed phase dynamics in the si(111) (7 x7)-(1 x 1) phase transition

We propose a natural two-speed model for the phase dynamics of Si(111) 7 x 7 phase transition to high-temperature unreconstructed phase. We formulate the phase dynamics by using phase-field method and adaptive mesh refinement. Our simulated results show that a 7 x 7 island decays with its shape kept unchanged, and its area decay rate is shown to be a constant increasing with its initial area. Low-energy electron microscopy experiments concerned are explained, which confirms that the dimer chains and corner holes are broken first in the transition, and then the stacking fault is remedied slowly. This phase-field method is a reliable approach to phase dynamics of surface phase transitions.

Surface stress and thermodynamic nanoscale size selection

Using the Si(111) surface as an example, we show how temperature can be used to tune the size of domains during a surface phase transition. From analysis of the measured stable domain sizes, we determine key material parameters and clarify the close relationship between nucleation and thermodynamic size selection. More generally, the model we developed describes nanoscale self-assembly processes in contact with a reservoir (for example, liquid- or vapor-phase epitaxy).

Observations of sudden structural-changes of the faulted-halves of the DAS structure on quenched Si(1 1 1) by STM

We have carried out scanning tunneling microscopy (STM) observations of unreconstructed regions on quenched Si(1 1 1) surfaces at 380 degrees C at a scanning speed of 1.7 s per frame. In the regions, it is found that single faulted-halves of the dimer-adatom-stacking-fault (DAS) structure are formed isolatedly or at the edges of the surrounding DAS domains sharing one corner hole. In such "living" regions, we have succeeded to observe sudden structural changes of the faulted-halves during line scans in single frames of STM images.