Pb Monolayer Mediated Thin Film Growth of Cu and Co: Exploring Different Concepts

Abstract

We present results exploring different concepts for Pb monolayer mediated thin film growth of Cu on Ru(0001) and Co on polycrystalline Cu substrates. Both systems are of considerable importance in microchip fabrication technology and they exhibit a three dimensional growth at room temperature which somewhat limits their application. The Pb monolayer mediation of the growth process is explored by having its role as a surfactant, flux mediator or as a sacrificial layer in deposition via surface limited redox replacement protocol. Electrochemical and STM results suggest that Pb monolayer induces 2D Cu growth on Ru(0001) and the growth mechanism is very dependent on the Pb mediation role. The surfactant properties of electrolessly deposited Pb monolayer are also studied during electroless deposition of Co on polycrystalline Cu. The benefit of Pb monolayer mediation of the Co growth process was manifested by 2D Co thin film morphology, high quality of the grain boundaries, and improved magnetic properties.

Electroless Pb Monolayer Deposition—Prelude for Further Advances in Catalyst Monolayer Synthesis via Surface Limited Redox Replacement Reaction

“…So far, all substrates which demonstrate the Pb ML e-less deposition also exhibit the Pb UPD phenomenon. [10][11][12]19 Therefore, in situ and ex situ methods employed in UPD studies can be also used to study the Pb ML e-less deposition. The most common one is monitoring of the open circuit potential (OCP) transients.…”

“…The in situ ECQMB measurement is an additional method for studying the Pb ML e‑less deposition. − An example is shown in Figure A where frequency and OCP transients are recorded simultaneously. Both signals have the same qualitative shape.…”

“…For interpretation of the OCP transients, the E vs t model is obtained when the above expression is combined with representative adsorption isotherm. Almost identical surface density, morphology, and stability of the Pb ML e‑less and the Pb ML UPD , − , suggest that the use of UPD isotherms is appropriate. The Swathirajan–Bruckenstein isotherm is applicable to a variety of Pb ML UPD -substrate systems; In this setting, the meaning E θ →0 is the OCP at which the Pb ML e-less approaches zero coverage.…”

“…This can be achieved by a solution-shuffling approach for which the equipment and a solution management setup have been already developed and automated as a part of the efforts in electrochemical ALD studies . Alternatively, the sample-shuffling experimental configuration has been employed as well. − In either case, the simplicity and effectiveness of the e-less ALD have been demonstrated.…”

“…However, recent developments in the area of electroless (e-less) deposition show promising results. They demonstrate that UPD-like monolayers can be synthesized on various catalytically relevant substrates using an e-less deposition with simple experimental routine and solution chemistry. − Several reports indicate that the e-less Pb ML (Pb ML e‑less ) deposition is of particular interest. − It occurs on substrates that do exhibit the Pb UPD phenomenon, and it can be used to modify catalytically active substrates (noble metals), improving their activity for particular reactions. , The Pb ML e‑less can also replace the UPD ML in the SLRR reaction, enabling formation of the catalyst ML on substrates with nonconductive support. In this case, the full deposition cycle requires consecutive immersion of the substrate in the solution for the Pb ML e‑less deposition (first step) and then in the solution for the SLRR, that is, catalyst deposition (second step).…”