Study of structural morphology of electrodeposited Ni thin film on Au(111) substrate.

Our central aim is to understand the microstructure and surface morphology (grain boundaries, growth rate) of polycrystalline electrodeposited metal films. Electrodeposited metal films have multiple applications where microstructure and surface morphology play key role to their performance, from ornamental and corrosion-resistant coatings to connectors in ultra-large-scale integrated circuits. Electrical and chemical resistance can also be controlled by microstructures. Specially, electrodeposited Ni has special attraction in electrodeposited polycrystalline metal thin films because of its many applications and unique features. Ni coatings are widely used to improve corrosion and wear resistance, and its mechanical properties make Ni especially useful for micro-electromechanical systems (MEMS) fabricated by electrodeposition. Ni is also of great interest because although Ni shares the fcc crystal structure with Cu, its study introduces new features. Atomic mobilities are significantly lower for Ni than Cu at room temperature which was critically assessed by diffusion coefficient, which suppresses grain coarsening and leads to a more pronounced columnar texture, and unlike Cu, Ni deposition usually takes place at potentials where hydrogen evolution is important, which can strongly modify the texture via surface adsorption. However, despite their significance, the problem of what determines the microstructure and surface morphology of a polycrystalline electrodeposited metal film is still largely unsolved. The detailed mechanism for growth driven grain coarsening or nucleation of new grains at defect still need attention to understand. Our project will overcome this experimental bottleneck by exploiting two major technical advances, high speed atomic force microscopy (HS-AFM) and Xe plasma focussed ion beam (plasma FIB) milling. We shall investigate the relation between microstructure and surface morphology of Ni electrodeposited thin film. In-situ HS-AFM will provide high-resolution surface topography during growth, while plasma FIB milling will be used to section the resulting film to characterize the grain structure at different depths by electron backscatter diffraction (EBSD). Combining HS-AFM and EBSD data will enable us to correlate surface structure evolution with the post-deposition microstructure of the same area of film and to will do so using exceptionally rapid and convenient measurement techniques. Our linked bulk and surface data will provide key aspects of electrodeposition to quantitative study. For example, the relation between crystallographic alignment and growth rate has never been established experimentally under realistic electrodeposition conditions, despite it being fundamental to understanding polycrystalline growth. By comparing successive HS-AFM images we can measure local growth rates and correlate them with the orientations of the basal grains. By changing the electrolyte composition, we shall be able to observe the effect of different adsorbates on orientation-dependent growth rate, providing beneficial insight into the role of additives to control film morphology and texture.
This project falls within the EPSRC Physical science research area.