Thermal-mismatch-strain relaxation in epitaxial ${\mathrm{CaF}}_2$, ${\mathrm{BaF}}_2$/${\mathrm{CaF}}_2$, and PbSe/${\mathrm{BaF}}_2$/${\mathrm{CaF}}_2$ layers on Si(111) after many temperature cycles

The thermal mismatch strain in stacks containing PbSe, ${\mathrm{BaF}}_2$, and/or ${\mathrm{CaF}}_2$ on Si(111) substrates is relieved by the glide of dislocations in the principal 〈110〉{100} glide system. The strain in the ${\mathrm{BaF}}_2$(111) and ${\mathrm{CaF}}_2$(111) buffer layers is relaxed at room temperature regardless of whether they form the top layer in the stack or are overgrown by other layers. PbSe (as well as ${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sn}}_{\mathit{x}}$Se and PbTe) top layers are capable of relieving the strain induced by the thermal-expansion mismatch even at 77 K, and after many temperature cycles between room temperature and 77 K. Even after 1400 such cycles, plastic relaxation still occurs on each cycle. The x-ray rocking curves, typically 150–190 arc sec wide, do not broaden on cycling. The total cumulative plastic deformation of the layer corresponds to as much as 400%. After the first few thermal cycles, no new thermal-strain-relieving dislocations are created, but the existing ones move back and forth on the same atomic glide planes with each cycle.