Figure 4.

(a) Cross-section SEM images of pore diameter modulations in NAA introduced by Lee et al. by switching MA and HA regimes (adapted from [4]); (b) cross-section SEM and optical images of multilayered NAA produced by Lee et al. by pulse anodisation (adapted from [29]); (c) cross-section SEM images of funnel-like NAA produced by Santos et al. by combining multiple anodisation and pore widening steps in a sequential fashion (adapted from [38]). AAO, anodic aluminium oxide.