Mechanical property of nanoscale ZnO/Al2O3 multilayers: An investigation by nano-indentation

Nanoscale ZnO/Al
₂
O
₃
multilayers were prepared on Silicon substrates by atomic layer deposition (ALD) method at 200°C. To understand the size effect of ZnO nanoscale layers on hardness, the mechanical properties of the ZnO/Al
₂
O
₃
multilayers were investigated using nano-indentation technique. As the bilayer period decreases from 60 to 2 nm, the micro-structures of ZnO layers changed from polycrystalline to amorphous. In the bilayer period interval of 60 to 6 nm, the variation of hardness versus bilayer period is similar to Hall-Patch relation, with maximum hardness and elastic modulus of ~10.69GPa and ~138.1GPa, respectively. However when the bilayer period is smaller than 6 nm, the nanolaminates became softer than the single ZnO film.