Matrix of rectangular pores obtained by AFM nanoindentation and electrolytic oxidation of Al

AFM nanoindentation is used for pretexturing of Al sample intended for anodic oxidation in porous film-forming electrolytes. The rectangular quadratic and non-quadratic matrices of nanoindents were made by means of an AFM with diamond tip. The period of the 2D array of nanoindented concaves ranged from ∼50 to ∼370 nm. The pitch of the holes ranged from 13 to 170 nm. After anodization in water solutions of three different acids (0.3 M sulfuric, 0.3 M oxalic and 0.3 M phosphoric) at voltages chosen according to matrix period (20, 30 and 160 V), the well-arranged matrices of rectangular pores were obtained. The rectangular symmetry of the pretextured Al surface almost ideally transferred on porous alumina matrix, maintaining the highly ordered arrangement of the pores and rectangular cross section trough the whole film thickness with high pore depth to aperture size aspect ratio. During prolonged anodization in phosphoric acid, standard cells on the boundary of nanoindented area disturbed the arrangement and shape of quadratic cells.