Aluminum Hydroxide Nano- and Microstructures Fabricated Using Scanning Probe Lithography with KOH Ink.

Using scanning probe lithography (SPL) with KOH ink, this study fabricates aluminum hydroxide (Al(OH)3) nano- and microfeatures on a gold (Au) film that has been deposited on an aluminum (Al) layer. Hydroxyl ions (OH-) from the KOH ink loaded onto the Au film can react with the underlying Al layer to form Al(OH)3 structures due to the decrease in the pH of the reacting solution.1 In this process, Al(OH)3 solidification is governed by the pH of the KOH ink solution, which is affected by its volume. Suitably small volumes (down to hundreds of attoliters) of the KOH ink solution can be applied to the substrate surface using dip-pen nanolithography (DPN) and polymer-pen lithography (PPL). Using DPN and PPL printing with the solid (i.e., gel) and liquid phases of KOH ink, sub-micron- (minimum ≈300 nm) and micron-sized (≥4 µm) Al(OH)3 features can be obtained, respectively. The fabrication of Al(OH)3 structures using the proposed pH-dependent solidification process can be achieved with relatively small volumes in ambient conditions without requiring a previously reported molding process.1,2.

Can Static Electricity on a Conductor Drive a Redox Reaction: Contact Electrification of Au by Polydimethylsiloxane, Charge Inversion in Water, and Redox Reaction.

We investigated the static charge generation by contact electrification between Au and polydimethylsiloxane (PDMS) and the redox reaction by the static charge in the aqueous phase, to reveal the mechanism of contact electrification and redox reaction which may be applied to mechanical-to-chemical energy harvesting. First, the static charge distribution on the equipotential Au was probed through Kelvin probe force microscopy (KPFM) in air after the contact with patterned PDMS. Positive charges are localized on the contact areas indicating the ion migration while the polarity becomes negative after water contact. Second, the redox reaction by the charged Au was electrochemically monitored using open circuit potential (OCP), stripping voltammetry, and copper underpotential deposition (UPD). All electrochemical experiments consistently resulted in the reduction of the reactant by the charged Au within the highly dielectric water media. We concluded that the reduction is not driven by the discharge of static charge on Au but by reducing radicals.