A New Role of a Low-Voltage, Ultra-High Resolution FE-SEM for Corrosion Studies (1)

— Sample Surface Preparation for Ultra-High Resolution FE-SEM —

Abstract

For successful application of low-voltage, ultra-high resolution FE-SEM in corrosion studies, the use of test specimens with clean, smooth and deformation-free surfaces is of critical importance. Otherwise, subtle surface evolutions associated with early stages of corrosion, proceeding both generally over the matrix surface and locally at and around fine inclusions of various sizes and compositions, will never be disclosed clearly. Here, a new and novel approach for the preparation of sample surfaces of required quality is presented. A key feature is the use of radio-frequency powered Glow Discharge (rf-GD) sputtering for final follow-up treatment of mechanically polished sample surfaces. This utilizes its unique sputtering characteristics where both conductive and non-conductive surfaces are sputtered very stably with Ar⁺ ions of very low energies, less than 50 eV, and very high current density of ∼100 mA cm⁻² ; the very low energies of Ar⁺ ions ensure that sputtering proceeds without significant formation of altered surface layers, while high current density allows sputtering to proceed at very high rates, typically 1∼10 μm s⁻¹, making sample preparation time extremely short, normally less than 10 s.