Mechanical properties of amorphous anodic alumina and tantala films using nanoindentation

The hardness and Young's modulus of barrier-type, amorphous anodic oxides have been determined by nanoindentation. The procedure used shallow indents, of 55 nm depth, with alumina, tantala and alumina/tantala 'mixed oxide' films of about 500 nm thickness. The results revealed respective hardnesses of approximately 7.0, 5.3 and 6.5 GPa, and respective Young's moduli of approximately 122, 140 and 130 GPa. Thus, the hardness and Young's modulus followed opposite trends, with alumina having the highest hardness and lowest modulus, and the 'mixed oxide' having intermediate properties. The hardness and Young's modulus of amorphous alumina are factors of about 3.1-3.7 times lower than those of crystalline aluminas.