Figure 1

SEM cross-section picture of NAA-based DBR sample obtained with Q ₀  = 0.5 C, 50 cycles, and T _anod  = 9°C. ‘a’ interfaces limiting one cycle, ‘b’ pore with conical shape, ‘c’ beginning of a pore branching corresponding to a decreasing anodization voltage, ‘d’ frustrated branch as the voltage increases again, and ‘e’ surviving pore growing in the subsequent cycle.