Ion Milling

Ion milling is a process applied to a sample under vacuum whereby a selected area of the surface can be bombarded by an energetic beam of ions. The bombardment erodes the surface, but can also cause damage by ion implantation which can lead to an amorphous layer being formed. Thus rotation and angle of attack is important. Generally using rotation and grazing bombardment angles promote even erosion of the sample surface and minimizes damage effects. However certain grain orientations, grain boundaries and phases may erode at different rates. Ion milling can give reasonably high rates of material removal and this can be enhanced by the use of reactive gases, such as Iodine in the reaction chamber. Exhaust gases are a safety hazard and should be safely exhausted. Follow the manufacturer's instructions. Ion milling can produce surfaces suitable for electron microscope examaination with minimal prior preparation, especially on materials that are difficult to prepare by conventional metallography, such as zirconium and zircalloy.

Note that ion milling can be an aggressive process, possibly giving rise to damage at the specimen surface. Tilting and rotating the sample is usually employed to minimise this effect. However, in the case shown above, considerable erosion and generation of surface relief has occurred as the ion milling time has progressed. Follow the manufacturers advice and instructions.














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