Charge Exchange Processes during the Open-Circuit Deposition of Nickel on Silicon from Fluoride Solutions

Abstract

The open-circuit potential deposition of nickel on silicon from fluoride solutions has been studied under potentiostatic control for two extreme values of pH. At pH 1.2, nickel ions are unable to exchange charge with the silicon substrate, and thus deposition is not observed. At pH 8.0, nickel ions in solution can exchange electrons with both the conduction band and the valence band of the silicon substrate in order to be reduced and deposit on the surface. The results are interpreted in terms of the coupling between the anodic dissolution of silicon in fluoride media and two competing cathodic reactions, hydrogen evolution and nickel deposition. The role of silicon surface states as dissolution intermediates is recalled and their interplay with the cathodic reactions is discussed as a function of solution pH. Surface states must also be relevant in the deposition process from other metallic ion solutions of high technological interest whose energy levels lie within the silicon bandgap.