A Combined Scanning Tunneling Microscopy and Electrochemical Study of Nickel Electrodeposition on β-Brass

J Morales,A J Arvia,P Esparza,R C Salvarezza,S González,S M Krijer,L Vázquez

doi:10.1021/la9505780

Abstract

The electrodeposition of Ni on β-brass from Watt's bath was studied by using electrochemical techniques, scanning tunneling microscopy (STM) imaging, and X-ray diffraction. As the electrodeposition current density j was increased from 0.01 to 0.25 A cm-2, both the Ni crystal size (d) and the root mean square roughness of the deposit (ξ) decreased. For j > 0.25 A cm-2 the deposit became rougher due to the growth of large Ni crystals over a background of small Ni crystals. This change in the growth mode appears as a transition in the value of ξ which is promoted by strongly adsorbed intermediates involved in the discharge of Ni2+ ions. The analysis of the dynamic and static roughening exponents resulting from the application of the dynamic scaling theory to the STM images of Ni deposits indicates that the growth of Ni at high current density, i.e. far from the thermodynamic equilibrium, can be described as an aggregation process with a significant contribution of Ni atom surface diffusion.

Highlights

The electrodeposition of Ni on foreign substrates from different acid plating baths has been considered as a model system for establishing a correlation between the electrochemical parameters involved in the plating process and the Ni coating characteristics.[1,2,3,4,5,6,7,8] The early stages of Ni electrodeposition on a foreign substrate have been modeled as a nucleation and threedimensional (3D) growth under charge transfer control[1] involving either circular cones or hemispherical centers.[2]
The morphology of Ni electrodeposits from acid baths has been extensively studied by transmission electron microscopy and scanning electron microscopy on the μm scale, whereas only scarce information has been obtained from scanning tunneling microscopy (STM) and atomic force microscopy (AFM)
Our results show that the increase in the Ni electrodeposition rate from 0.01 to 0.25 A cm-2 results in a decrease in the deposit crystal size and roughness and in an increase in surface disorder

Summary

Introduction

The electrodeposition of Ni on foreign substrates from different acid plating baths has been considered as a model system for establishing a correlation between the electrochemical parameters involved in the plating process and the Ni coating characteristics.[1,2,3,4,5,6,7,8] The early stages of Ni electrodeposition on a foreign substrate have been modeled as a nucleation and threedimensional (3D) growth under charge transfer control[1] involving either circular cones or hemispherical centers.[2]. The morphology of Ni electrodeposits from acid baths has been extensively studied by transmission electron microscopy and scanning electron microscopy on the μm scale, whereas only scarce information has been obtained from scanning tunneling microscopy (STM) and atomic force microscopy (AFM) These new techniques provide real 3D images of solid surfaces at a greater resolution. The application of nanoscopies to the study of metal deposits allowed us to advance in the quantitative interpretation of surface roughness development and its dependence on sample size[9] from the analysis of STM and AFM images. Nickel Electrodeposition on -Brass analysis of the dynamic and static roughening exponents derived from the application of the dynamic scaling to STM images,[10] it can be concluded that Ni electrodeposits grown far from equilibrium conditions behave as self-affine fractals The growth of these coatings can be described by growth models developed for aggregation processes incorporating surface diffusion.[10]

Experimental Section

Results

Discussion