Comparing the electrochemical mechanisms and microhardness of Ni electrodepositions on multilayer Mo/Si and monolayer Pt films at different temperatures

Abstract

Recently, Ni electroforming is playing an indispensable role in modern optical manufacturing, and multilayer molybdenum/silicon (Mo/Si) film is a promising reflective material with potential applications in soft X–ray/EUV microscopy and astrophysical research. Therefore, the multilayer Mo/Si mirrors (MLMs) fabricated by Ni electroforming is highly expected, where the electrochemical process and deposition quality need to be clarified firstly. In this study, the temperature impacts on the electrochemical reaction dynamics and nucleation mechanisms of Ni electrodepositions on multilayer Mo/Si and monolayer Pt films were compared, and the variations in crystallization growth and microhardness were further discussed. The results showed that the apparent activation energy of Ni electrodepositions on Mo/Si and Pt films was 24.36 kJ/mol and 17.69 kJ/mol, respectively, while the increase in temperature had the similar depolarization influence on both films by positively shifting the reduction potential. In the meanwhile, the 3D instantaneous mechanism remained as the initial nucleation mode for Ni electrodepositions on multilayer Mo/Si film, while as temperature rose, the grain growth gradually changed from a highly coarse and large–sized pyramidal structure to a more refined cluster mode. Nevertheless, the grain texture for Ni electrodepositions on monolayer Pt film evolved from a regularly cone shape to an unevenly elliptical colony–like morphology, primarily ascribed to the progressive nucleation procedure along with higher hydrogen evolution at elevated temperature. Consequently, the appropriate increase in deposition temperature effectively encouraged the rapid development of particular crystal planes and modified the microscopic quality of microhardness, which provided a reference for optimizing fabrication of metallic mirror based on Ni electroforming.