Formation of continuous platinum layer on top of an organic monolayer by electrochemical deposition followed by electroless deposition

A metal–molecule–metal sandwich structure is constructed to wire the molecule to external circuits. A continuous mono-atomic thick metallic layer of platinum is formed on top of a 1,4-benzenedimethanethiol (BDMT) self-assembled monolayer (SAM) on a Au(1 1 1) substrate through electrochemical deposition followed by electroless deposition (ELD). At first, about 1/3 monolayer of Pt is formed on top of the BDMT SAM by electrochemical reduction of pre-adsorbed PtCl 4 2 - complex, then the coverage of Pt layer is increased by ELD. Two approaches for ELD of Pt are examined. In the first approach, the pre-formed sub-monolayer of Pt is used as a nucleation center for ELD of Pt by reducing Pt ions in a solution containing a reducing agent. X-ray photoelectron spectroscopy (XPS), angle resolved X-ray photoelectron spectroscopy (AR-XPS) and electrochemical measurements show that the coverage of Pt increases with the increase of plating time but the metallic Pt penetrates through organic film and deposits between SAM and Au(1 1 1) substrate if the plating time is too long. In the second approach, the electrochemically formed sub-monolayer of Pt is used not only as a nucleation center but also as a catalyst for the selective ELD of Cu. Electrochemical measurements as well as AR-XPS after a spontaneous redox replacement of Cu by Pt confirm that a full layer of Pt is formed on top of the BDMT SAM and no platinum is found underneath the SAM. The latter is a new method for a construction of a metal–molecule–metal sandwich structure, which allows wiring molecules to external circuits.