Grain Boundaries and Twin Boundaries in Cu(111) Thin Films

Twin boundaries (TBs) are one of the defects that form in most single-crystal growth. Although they are usually considered as one of the grain boundaries (GBs) that satisfy a symmetry operation, the properties and formation mechanism of TBs are very different from those of GBs. In particular, in bulk crystals, TBs are usually analogous to ferroelastic domains. TBs are formed to relieve structurally occurring strain when a phase transitions from a high-temperature phase to a low-temperature phase. They are formed in thin films when two islands with different stacking orders at nucleation meet. At this point, TBs are formed when single-crystal islands meet coherently with a coplanar layer. By contrast, GBs are formed when arbitrarily oriented islands meet incoherently. The effects of TBs and GBs on physical properties are greatly different.