Electron Backscatter Pattern Quality as a Tool for Improving FIB Preparation of Oxides
FIB milling is a commonly used technique for the preparation of TEM specimens for a wide variety of materials. The quality of the resulting TEM lamellae and hence the quality of TEM results are determined by the amount of surface damage induced by the ion beam during the preparation. The damaging processes due to the interaction between the ion beam and surface atoms is well known for metals and semiconductors, yet, there are limited number of investigations on surface damage of minerals and compounds with more complex lattice structures like oxides. Since oxide-based compounds are our main research interest, the aim of this study is to gain a better understanding of how FIB milling affects the surface of different oxides.
The thickness of the damaged layer due to amorphization is not only influenced by the FIB settings such as acceleration voltage or beam current, but also depends on the crystal structure and atomic bonding of the material to be milled. For this study, MgO, SrTiO3 and Al2O3, all possessing different crystal structures, were selected in order to study their surface damaging behavior under various FIB milling conditions, which are frequently used during the lamella preparation in a FEI Scios dual beam instrument. The amount of surface damage due to FIB milling was measured in two different ways: firstly, the amorphization layer thickness was directly imaged in cross section inside a TEM. Secondly, electron backscatter patterns (EBSP) and electron backscatter diffraction (EBSD) maps were recorded before and after FIB milling with an EDAX Hikari camera. Since the EBSPs typically origin from depths around 10-50 nm below the surface, the quality of EBSP is a very sensitive measure of surface distortions. Thus, the effects of FIB milling with different acceleration voltages, beam currents, and ion incident angles on single EBSPs as well as on image quality and indexing success of EBSD maps have been investigated.
The presentation will summarize the results and discuss effective strategies for obtaining TEM lamella with minimal surface damage.