FIG. 7.

(a) Schematic illustration of uniform ALD coating on a single conical nanochannel (not to scale). Insets show SEM images of the tip side (top) and the base side (bottom) of an ALD Al2O3-coated polymeric conical nanochannel. Scale bar = 100 nm. (b) SEM images of conical Al2O3replicas obtained by coating the conical nanochannels by 150 cycles of ALD Al2O3 and then treating with RIE to partially remove the PET polymer matrix. A broken part of the Al2O3 replica (blue arrow) revealed that the ALD coating was only on the pore wall, indicating excellent step coverage inside the nanochannels. Adapted with permission from Wang et al., Anal. Chem. 87, 16 (2015). Copyright 2015 American Chemical Society.¹⁸³