Electrochemical generation of metal structures using surface based molecular self-assemblies as templates

Abstract

Exploring electrochemical processes controlled by surface-based molecular assemblies, this thesis studies a coordination-controlled electrodeposition (CCED) scheme, which relies on chemical functionality, i.e., metal coordination, provided by the tail group of a self-assembled monolayer (SAM). Based on the electrochemical reduction of coordinated ions, the scheme is extended by introducing metal ions into the bulk electrolyte. Using a SAM of 3-(4-pyridine-4-yl-phenyl)-propane-1-thiol (BP3N) on Au(111) electrode, the co-deposition of coordinating Pd and non-coordinating Cu has been investigated. Following Pd²⁺-pyridine complexation, the electrochemical deposition was performed in an acidic Cu²⁺-containing electrolyte. Both cyclic voltammetry (CV) and chronoamperometry revealed the promoting effect of coordinated Pd²⁺ on bulk Cu deposition. The process involves three phases, (i) the Pd cluster formation, (ii) the intermix of Pd and Cu, and (iii) the deposition of bulk Cu. Depending on conditions, deposits with morphologies ranging from isolated CuPd nanoparticles to ultrathin metal films were generated and characterised with scanning tunnelling microscopy (STM). The Pd-Cu core-shell nature of these nanoparticles was confirmed by transmission electron microscopy (TEM). To understand the metal nucleation mechanism, density functional theory (DFT) calculations were carried out to clarify the initial stage of Pd aggregation. Furthermore, inspired by the calculation results, the effect of metal-SAM interaction in metal nucleation was illustrated by the reduced particle size for CCED on binary SAMs with protruding phenyl groups.

The exploration of the CCED scheme towards nanostructure generation was investigated using either patterns of CuPd nanoparticles fabricated by selective particle removal based on scanning probe lithography (STM or atomic force microscopy) or patterned SAMs produced by electron beam lithography. Metal films with thickness below 3 nm and metal structures with lateral features down to sub-10 nm were fabricated. Additionally, with SAMs serving to control the adhesion, a cyclic scheme consisting of electrodeposition on a patterned substrate and lift-off was investigated, offering the prospect of replicative nanostructure fabrication.