Electrochemical Atomic Layer Deposition (E-ALD) of Pt Nanofilms Using SLRR Cycles

Abstract

This paper describes platinum nanofilm formation via the electrochemical form of atomic layer deposition (E-ALD), where the E-ALD cycles are based on surface limited redox replacement (SLRR) reaction. SLRR is where an atomic layer (AL) of a reactive (sacrificial) metal is exchanged for a more noble metal. In the present study both Cu and Pb AL were investigated as sacrificial atomic layers for replacement with both Pt(II) and Pt(IV) precursors. 25 E-ALD cycles were used to form Pt nanofilm deposits. Initial deposits contained an order of magnitude more Pt than expected, evidenced by a factor of 7 increase in surface roughness. Overly positive potentials achieved during the exchange promoted excess deposition and surface roughening. It is proposed that anionic Pt precursors adsorbed more strongly at high potentials, making them difficult to rinse from the cell. Those remaining adsorbed Pt anions are then reduced to Pt o when the potential was shifted negative for deposition of the sacrificial element. The result was Pt o formation at a large overpotential, which, contributed to excessive Pt deposits and roughening. Increased rinsing of the anionic Pt precursors from the cell eliminated the excess Pt deposition and roughening, resulting in the expected layer by layer growth of an ALD process.

Metal deposition via electroless surface limited redox replacement

“…Introduced by Brankovic et al [7], SLRR utilizes the monolayer limited nature of underpotential deposition (UPD) of a sacrificial metal coupled with a subsequent galvanic displacement of that layer by a more noble metal of interest. To date SLRR has been applied to the realization of monolayer Pt coatings on a variety of metals and alloy nanoparticles [1] and to the deposition of epitaxial films of Ag, Cu, Au, Pt, Ru, and Pd on noble metal substrates [7][8][9][10][11][12][13].…”

“…Conventionally SLRR has been carried out through a multiple immersion approach [7,8] flow cell set-up [10,13,14] and more recently in a one-cell approach developed by our group [9]. The one-cell approach has been effectively applied to the growth of Cu [9], Ag [8], Au [11], and Pt [12,15].…”

“…Traditionally SLRR utilizes the application of a potential by an external source (i.e. potentiostat) in order to realize the formation of the UPD sacrificial layer (SL) [7][8][9][10][11][12][13], and subsequent open circuit displacement of the SL [9]. However, recent scaling of SLRR up to the production of industrial quantities of state-of-the-art catalysts renders this protocol energy intensive and difficult to implement without the use of a high-power potentiostat/rectifier.…”

Electrochemical Atomic Layer Deposition of Cobalt Enabled by the Surface-Limited Redox Replacement of Underpotentially Deposited Zinc

“…Over the last two decades, electrochemical ALD (or e-ALD) has been utilized for deposition of a variety of metals, 23,24 including Pt, [25][26][27][28] Cu, [29][30][31] Pd, 32 Ru, 33 Ag, [34][35][36] Au, 37 Ge, 38 and semiconductor compounds. [39][40][41] In the following introductory discussion, the process of e-ALD of Cu is described as a representative example.…”

The Spontaneous Deposition of Au on Pt (111) and Polycrystalline Pt

“…Because of this, strategies such as surface limited redox replacement (SLRR), 6,[18][19][20][21][22][23][24][25][26][27][28][29][30] or limited ion adsorption on the substrate. [18][19][20][21][22][23][24][25][26]28,29,50,51 These factors ultimately result in the operation of a cyclic process that allows for the deposition of a strict amount of material (usually limited to a ML) per cycle rendering the deposit thickness finely controllable. An additional benefit of these methods is associated with the naturally existing short period of deposition inactivity between cycles that prevents the establishment steady mass transport controlled growth.…”