Strain Relief during Growth: CaF2on Si(111)

The growth of thin Ca${\mathrm{F}}_2$ films on Si(111) was studied with in situ low energy electron microscopy and transmission electron microscopy. As the strained epitaxial film passes through the critical thickness, initial dislocations form in triplets (“trigons”). These serve as sources for full edge dislocations which subsequently form a dense network. This unusual dislocation structure provides a natural explanation for a recently proposed “two-dimensional structure modulation” of the Si(111)/Ca${\mathrm{F}}_2$ interface.