Why use low angle in the later stage of ion thinning?

The reason of using low angle in the later stage of ion thinning is that high angle ion beam is easy to destroy the structure and chemical composition of the sample surface. Ion milling is a commonly used sample preparation technology, which uses ion beams to remove materials from the sample surface to obtain the required thickness or shape. The main reason for using low angle in the later stage of ion thinning is that high angle ion beam is easy to destroy the structure and chemical composition of the sample surface. For example, high angle ion beam can cause surface crystal structure rearrangement, ion implantation and surface chemical reaction. These damages may affect the physical and chemical properties of samples, thus affecting the accuracy of sample research. In contrast, the low-angle ion beam can cut the sample more evenly and reduce the damage to the sample surface. Therefore, in the later stage of ion thinning, in order to protect the structure and performance of the sample, low-angle ion beams are generally used for scraping and trimming.