Functional Thin Films
Most semiconductors significantly change their bandstructure upon the influence of elastic strain, with consequences in transport improvement in silicon and the ability of turning germanium into a direct bandgap material and thus to allow for the fabrication of a laser. The high elastic strains necessary can only be achieved in absolutely perfect materials, which can more likely be found at small length scales.
Ultrathin semiconductors can be penetrated by visible light and give rise to beautiful and switchable colors. Ionic crystals can be used as sensors for plastic strains as theirs dislocations can be charged.