Ionic Current Rectification of Porous Anodic Aluminum Oxide (AAO) with a Barrier Oxide Layer

Abstract

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.

Sustainable power generation for at least one month from ambient humidity using unique nanofluidic diode

“…1a. Besides, the strategy adopting nanofluidic diode-type PN junction has been verified as very feasible both by theory and experiment in hypersaline environment to build an osmotic power generator system 37,38 . But how to use the unique PN junction phenomenon in atmospheric moisture environment still remains a challenge.…”

Influence of Asymmetric Geometry on the Ion Transport of Tandem Nanochannels

“…Since the smallest diameter of the asymmetric nanochannel is 35 nm comparable to the thickness of the double layer in 1 mM KCl, it is expected that the selective ion transport (i.e., ICR) could be observed. The surface charge of AAO is dependent on the solution pH. ,, When the solution pH is lower than the isoelectric point (IEP 6.5) of alumina fabricated in oxalic acid, the hydroxyl group on the surface of AAO displays positively charged as a result of protonation, and when the solution pH is higher than the isoelectric point, the surface hydroxyl group is deprotonated, and the AAO carries negative charges. As displayed in Figure , because of the symmetry structure in the nanochannel with a tandem number of 1, the I – V curves display linear responses.…”

Unraveling the six stages of the current–time curve and the bilayer nanotubes obtained by one-step anodization of Zr

“…These new ideas presented in this paper improve the growth kinetics of metal anodization and help to regulate the structure of various porous anodic oxides. 74–78 …”