Deposition, characterization and biological application of epitaxial Li:ZnO/Al:ZnO double-layers

Double-layers of lithium doped ZnO (LZO) and aluminum doped ZnO (AZO) are grown on r-cut sapphire (r-Al2O3) crystal substrates by pulsed-laser deposition. The epitaxial double-layers are a-axis lattice oriented to the substrate. The LZO/AZO/r-Al2O3 samples have high optical transmission in the visible range and a bandgap energy of Eg = 3.28 eV according to the absorption edge of ZnO. The AZO bottom layers are electrically conductive (resistivity at room temperature ρ ~ 10− 3 Ω cm) and LZO top layers are highly resistive (ρ ≥ 105 Ω cm). Acoustic shear mode resonances in r-Al2O3 are excited by employing electric fields to the piezoelectric LZO layer (frequency interval 1.5–3 GHz). For biological applications, Madin–Darby canine kidney cells are cultivated on Platinum coated LZO/AZO/r-Al2O3 samples. Osmotic pressure applied to the cells increases or reduces the cell volume depending on the osmolarity of the medium.