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SEM images (after barrier layer etching) of a porous alumina membrane (PAM) fabricated using etch type I (with area 70 × 70 mm). The barrier layer was first opened on the back side using argon ions followed by the usual bilateral acid pickling. (A) top view (outer surface) and (B) top view (inner surface). The insets show optical images of the PAM and the enlarged SEM top view of the back side before barrier layer etching.
