Focused high- and low-energy ion milling for TEM specimen preparation

Abstract For atomic-resolution aberration-corrected (Cs-corrected) scanning transmission electron microscopy (STEM) the quality of prepared TEM specimens is of crucial importance. High-energy focused gallium ion beam milling (FIB) is widely used for the production of TEM lamella. However, the specimens after conventional FIB preparation are often still too thick. In addition, damage and amorphization of the TEM specimen surface during the milling process occur. In order to overcome these disadvantages, low-energy Ar ion milling of FIB lamellae can be applied. In this work, we focus on TEM specimen preparation of different thin films (GaN, Ge 2 Sb 2 Te 5 , TiO 2 ) and interface structures (GaN/6H-SiC, SrTiO 3 /TiO 2 , Ge 2 Sb 2 Te 5 /Si) using a combination of FIB with a focused low-energy Ar ion polishing. The results show that this combination enables the routine preparation of high quality TEM lamellae with a smooth surface and uniform thickness, even at the interface region between two different materials and over a lateral range of several micrometres. The prepared lamellae exhibit less surface damage and are well suited for atomic-resolution Cs-corrected STEM/TEM imaging at medium and low accelerating voltages. These results are in a good agreement with Monte Carlo simulations performed by the Stopping and Range of Ions in Matter (SRIM) software.