TEM investigation of barrier‐like anodic oxide films on aluminum

The present study focuses mainly on non‐electrochemical investigation of thin barrier‐like oxide films formed under different pulse frequencies. The TEM investigation principally shows amorphous oxide films, which are dense and free of pores. The various pulse experiments have no influence on these film properties. The oxide growth factor was calculated to 1.06 nmV −1 in all cases. The microstructure (crystallographic orientation, grain boundaries) of the underlying substrate does not affect the oxide films. Independent of the pulse frequency, electrolyte species are not incorporated into the oxide films. The evidenced differences in the film thickness are caused by intrinsic peculiarities of the high‐field mechanism of growing oxide.