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.