Electrochemical Surface Processes and Opportunities for Material Synthesis

Abstract

Technological advances in the operation and performance of microelectronic, optical, magnetic, and, more recently, energy conversion devices depend in large part on an ever-increasing accuracy of material synthesis and film fabrication methods. In particular, the ongoing miniaturization of devices requires strict control of the crystal structure and microstructure in film as well as patterned structures, often down to the atomic scale.Electrodeposition has an important role to play in this pursuit toward miniaturization and enhanced performance [1]. Underpotential deposition (UPD) [2, 3] and surface-limited redox replacement (SLRR) [4] exploit the low energy of the metal ion precursors in solution (of the order of the thermal energy, 0.025-0.03 eV) to control the formation or replacement of single atomic layers via self-limiting processes. In UPD, a monoatomic layer of metal M is deposited on a conductive substrate S at a potential more positive than the redox potential of M [2]. This shift in redox potential is made possible by the fact that the M-S bond is stronger than the M-M bond; since the effective pair interaction V eff = V MM + V SS − 2V MS is typically in the order of 0.01-0.1 eV, only low energy precursors are sensitive to these energy differences, thus limiting the deposit to one (or sometimes two) atomic layers. SLRR involves UPD monolayer formation, followed by displacement of this layer with a full or partial monolayer of a more noble element, through a cementation process [4]. An analogous process, selective electrodesorption-based atomic layer deposition (SEBALD) consists in the formation at UPD of a sacrificial sulfur monolayer to induce UPD of late transition metals such as Fe, Co, and Ni in the form of monolayers or nanosized islands [5].Underpotential codeposition (UPCD) is a generalization of the UPD process, whereby alloy electrodeposition occurs at potentials more positive than the redox potential of the less noble element [6]. UPCD is made possible by the effective atomic pair interactions in the solid state, or equivalently by the alloying bond enthalpy. In contrast with UPD, UPCD is used to form alloy films of arbitrary

Electrodeposition of Alloys and Compounds in the Era of Microelectronics and Energy Conversion Technology

“…UPD exhibits pronounced sensitivity to the atomistic features of the electrode surface, and has been used to estimate true surface area, in particular surface roughness, and for the decoration of selected surface features, for example in corroded samples. UPD, however, has been mainly used as a method for surface modification for the purpose of improving functional properties, such as catalytic activity and selectivity [51]; in particular, UPD phenomena are used extensively to form nanomaterials with controlled structure and atomic configuration, down to the atomic scale.…”

“…Specifically, the redox potential of the less noble metal during alloy deposition is shifted with respect to the redox potential of Me ion on Me substrate due to the free energy of mixing Gmix; formation of solid solutions in particular results in a redox potential shift in the positive direction; the phenomenon is referred to as underpotential co-deposition (UPCD). The relationship between the free energy of mixing [51]:…”

Editors' Choice—Reaction Kinetics of Metal Deposition via Surface Limited Redox Replacement of Underpotentially Deposited Monolayer Studied by Surface Reflectivity and Open Circuit Potential Measurements

“…The very details of these three protocols and their applications have been discussed elsewhere in the literature. 4,5,10 Still, more work is necessary to unravel the controlling phenomena of this deposition method and to properly define optimum conditions at which the true benefits of this method are fully exploited.In many applications concerned with deposition of only a single monolayer of P or ultra-thin films such as core-shell catalyst synthesis for example 2,3,6 (P = Pt, Pd), the properties of deposited films are * Electrochemical Society Student Member. * * Electrochemical Society Member.…”

“…These include nature of supporting electrolyte in reaction solution, concentration and oxidation state of the metal ions, complexation and temperature. 5,17,18 Therefore, identifying the fundamental relation between the experimental conditions and resulting kinetics of SLRR reaction should help practitioners to exercise a full control over deposit morphology. This will open new applications of this method in broad spectrum of scales from laboratory experiments to industrial synthesis of core-shell catalysts or wafer level ultrathin thin film growth technologies.…”

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.…”