Self-assembled monolayers of eicosanethiol on palladium and their use in microcontact printing

Abstract

We investigate self-assembled monolayers on polycrystalline Pd composed of eicosanethiol (ECT). X-ray photoelectron spectroscopy reveals a composition and structure of the ECT monolayer on Pd similar to those on Au the sulfurs are close to the Pd and underneath the alkyl chains. Monolayers formed from a 0.4 mM solution of ECT in ethanol are 2.8 nm thick and have advancing and receding contact angles with water of ∼115° and ∼90°, respectively. They are 0.3 nm thicker than those on Au and have a surprisingly low receding contact angle. Monolayers of ECT microcontact printed onto 100-nm-thick evaporated Pd films confer good protection of the Pd in a ferrichloride wet etch. It is therefore possible to create Pd patterns with high contrast and with lateral dimensions smaller than 200 nm. The Pd patterns can initiate electroless deposition of NiB, NiP, or Cu but are difficult to use as a mask for etching a less noble metal such as Cu due to the formation of a galvanic cell during etching. Instead, this galvanic cell is helpful to accelerate strongly the etch of Cu underneath Pd to produce suspended, deformable Pd structures.