Fabrication of metal nanowires using microcontact printing

Abstract

Microcontact printing (μCP) is a versatile soft-lithographic technique to pattern substrates using an elastomeric stamp. We demonstrate the high-resolution capabilities of this technique for the fabrication of metal nanowires using either subtractive or additive patterning strategies. The subtractive method relies on printing a self-assembled monolayer (SAM) to protect a metal substrate selectively in a wet-chemical etch process. We applied this approach to pattern Au, Ag, Cu, and Pd using eicosanethiol (ECT), and Al by printing hexadecanephosphonic acid (HDPA) as the resist-forming compound. As the etch process has to be selective and reliable, optimization of the etch chemistries is essential to obtain nanowires with excellent lithographic definition. The additive method involves the formation of wire template structures that can direct the electroless deposition (ELD) of a metal on a substrate. One variation of this approach entailed the patterning of a thin Au layer that was printed and etched to initiate ELD of Ag, Cu, and NiWP. Printing a colloidal Pd/Sn catalyst directly onto a substrate constitutes another variation of this patterning strategy. The use of a defined colloidal suspension as the ink, the derivatization of the stamp with poly-(ethylene glycol) (PEG), and the pretreatment of the substrate with an amino-functionalized silane were the key elements of this approach, which was demonstrated for the fabrication of NiB and CoP nanowires. Devices with arrays consisting of 400-μm-long wires with 1 μm pitch were produced with these patterning strategies, and wire dimensions of 150-500 nm in width were achieved depending on the fabrication parameters. We have characterized the resulting nanowires using atomic force microscopy (AFM), determined their morphological properties, and addressed their electrical performance.