Application Note for Leica EM RES102 – Most metal films already have a thickness that requires no further mechanical pre-preparation. Frequently, however, they are also domed, which can lead to undefined milling angles. This is a disadvantage, particularly for films that contain inclusions, and that therefore mostly require very flat milling angles. Metal sheets are thicker than 100 µm. Mechanical pre-preparation is necessary to obtain an acceptable initial thickness and a good surface quality for ion milling.