posted on 2020-09-18, 14:11authored byYun Do Kim, Seungwook Choi, Ansoon Kim, Woo Lee
Synthetic
nanofluidic diodes with highly nonlinear current–voltage
characteristics are currently of particular interest because of their
potential applications in biosensing, separation, energy harvesting,
and nanofluidic electronics. We report the ionic current rectification
(ICR) characteristics of a porous anodic aluminum oxide membrane,
whose one end of the nanochannels is closed by a barrier oxide layer.
The membrane exhibits intriguing pH-dependent ion transport characteristics,
which cannot be explained by the conventional surface charge governed
ionic transport mechanism. We reveal experimentally and theoretically
that the space charge density gradient present across the 40-nm-thick
barrier oxide is mainly responsible for the evolution of ICR. Based
on our findings, we demonstrate the formation of a single 5–8-nm-sized
pore in each hexagonal cell of the barrier oxide. The present work
would provide valuable information for the design and fabrication
of future ultrathin nanofluidic devices without being limited by the
engineering of the nanochannel geometry or surface charge.