An in-situ method for protecting internal cracks/pores from ion beam damage and reducing curtaining for TEM sample preparation using FIB

Xiang Li Zhong; Sarah J Haigh; Xiaorong Zhou; Philip J Withers

doi:10.1016/j.ultramic.2020.113135

An in-situ method for protecting internal cracks/pores from ion beam damage and reducing curtaining for TEM sample preparation using FIB

Ultramicroscopy. 2020 Dec:219:113135. doi: 10.1016/j.ultramic.2020.113135. Epub 2020 Oct 10.

Authors

Xiang Li Zhong¹, Sarah J Haigh², Xiaorong Zhou², Philip J Withers³

Affiliations

¹ Department of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK; Henry Royce Institute, Department of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. Electronic address: xl.zhong@manchester.ac.uk.
² Department of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
³ Department of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK; Henry Royce Institute, Department of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.

PMID: 33129062
DOI: 10.1016/j.ultramic.2020.113135

Abstract

Focused ion beam (FIB) milling has evolved to be one of the most important Transmission Electron Microscope (TEM) site specific sample preparation techniques. However, this technique still poses challenges, such as the structural damage and potential curtaining issues often observed for thin TEM lamella. These artefacts can negatively affect the TEM analysis results. In particular, structures such as internal cracks and pores in FIB prepared TEM samples can often be damaged during sample preparation. This is commonly regarded as an unavoidable problem, even though microstructurally intact thin lamellae TEM samples are widely needed for the investigation of crack tips or pore morphologies in many different materials. This presents a strong driver for the development of innovative methods to overcome damage and curtaining issues during FIB sample preparation. Here we report on a new methodology developed to protect internal cracks and pores from ion beam damage. Our proposed method also mitigates curtaining issues, which often make TEM analysis more difficult. This method uses the FIB to sputter and redeposit material onto the edges of any cracks or pores in order to fill these features in-situ prior to lamella thinning. Case studies showcasing this method are presented, demonstrating the approach on a modular pure iron sample and on a porous laser treated Al/B₄C composite sample. Our proposed 'filling' method has demonstrated a two key benefits; it preserves the integrity of the edges of any cracks and pores and it reducing curtaining. The results also demonstrate that this technique can be an alternative to conventional Gas Injection System (GIS) deposition for protecting the external top surface.

Keywords: FIB (Focused Ion Beam); Internal cracks and pores; Ion beam damage; Porous materials; Redeposition; TEM (Transmission Electron Microscope) sample preparation.