Paper EM-WeM9
Reliable and Selective Formation of Metallic Contacts to Organic Thin Films: Towards Molecular Electronics

Wednesday, November 11, 2009, 10:40 am, Room B1

We have investigated the selective deposition of copper on alkanethiolate self-assembled monolayers (SAMs) using electroless deposition. This work has important applications in molecular and organic electronics, sensing, biotechnology, photonics and other technologies. We demonstrate that useful deposition rates can be obtained by “self-seeding” - the immersion of the SAM in a solution containing Cu²⁺ ions prior to addition of the reducing agent, formaldehyde. The selectivity of the deposition is achieved by increasing the bath temperature to 45 ºC. At this temperature Cu deposition ceases on –CH₃ terminated SAMs but continues on –COOH terminated SAMs. Finally, and perhaps most importantly, copper penetration through SAMs can be prevented by the addition of adenine to the bath. The addition of adenine also leads to smooth film morphologies. Each of these effects is explained by the formation of complexes with the SAM terminal group. Copper-terminal group complexes lead to useful deposition rates and control of the selectivity of the deposition. The formation of adenine-terminal group complexes prevents Cu penetration through the monolayer. Similarly, we observe that strongly adherent nickel films can be selectively deposited on functionalized SAMs through careful control of the bath conditions, especially temperature and pH.