Mechanical properties of atomic layer deposited Al2O3/ZnO nanolaminates

• Al2O3/ZnO nanolaminates deposited by atomic layer deposition.
• Decrease in bilayer period λ led to decrease of ZnO crystallite size.
• Decrease in ZnO crystallite size led to higher hardness.
• Highest hardness was reached for the nanolaminate with λ = 25 nm (1 nm Al2O3/24 nm ZnO).

Nanoscale structures of aluminium oxide (Al2O3) and zinc oxide (ZnO) multilayers (nanolaminates) were prepared by atomic layer deposition (ALD) on silicon substrates at 120 °C. The focus of this work was to study the effects of bilayer period on mechanical properties and the effect of the ratio between the thicknesses of each material with bilayer period kept constant. We found that reduction of bilayer period led to an increase in hardness of the nanolaminates, which was explained by the Hall–Petch effect. The influence on hardness of the thickness ratio between Al2O3 and ZnO, where it increased by 50% for Al2O3/ZnO = 1:24 with bilayer period = 25 nm was observed. Progressive scratch tests revealed that the highest critical load for delamination and the highest toughness was observed for samples with Al2O3/ZnO = 24:1 with bilayer period = 25 nm.