Stepwise change in Gibbs free energy curve observed in Si(111) DAS domain growth

The formation and the annihilation rates of stacking fault (SF) half-units were precisely determined from the high-temperature scanning tunneling microscopy (STM) observation of dimer-adatom-stacking-fault (DAS) domains grown on quenched Si(111) surface at 485°C, as a function of the number of corner holes shared by a preexisting large domain and a newly born single SF triangle. In contrast to the general nucleation and growth with a single atom as a building unit, in the nucleation and growth of a nXn DAS domain with a single SF half-unit as a building unit, Gibbs free energy as a function of the number of SF half-units has discrete values. This feature is reflected in the behavior of a newly born SF half-unit adjacent to a larger DAS domain. For the SF half-units sharing one corner hole, the formation rate was lower than the annihilation rate due to the greater contribution of periphery strain to the increase in the Gibbs free energy than that of area increase. For the formation of the SF half-unit sharing two corner holes, the annihilation rate was negligibly small, suggesting that the addition of this single SF triangle increases the domain area keeping the periphery length constant, which results in Gibbs free energy reduction.