Atom Probe Assist for Grain Boundary Segregation Analysis

Atom probe tomography (APT) is a material analysis method that offers 3D chemical composition and imaging at the atomic scale. It is suitable for analysis of grain boundary segregation. Sample preparation that is similar to transmission electron microscopy (TEM) is required for APT analysis, but it requires needle geometry rather than a thin lamella.

For the study of site specific features, the feature has to be within ~500 nm of the tip apex. A focused ion beam (FIB) tool is used to set up this type of specimen. In the last stages of specimen sharpening, the contrast in the FIB tends to become negligible or very low, making site specific testing difficult.

The Atom Probe Assist (APA) tool offers an original way to observe grain boundary position between FIB milling steps. As the APA sample tip is a small 3D cone, transmission-EBSD (t-EBSD) can be applied to measure and image the crystallographic orientation and establish grain boundary position.

This tool is improved for t-EBSD measurements of APT tips, including default map shapes next to APT tip profiles and images processing methods to improve t-EBSD patterns from samples with diverse sample thickness.

Conventional EBSD can be used to establish the grain boundary position and character of a sample before primary site specific FIB liftout preparation, thereby allowing for testing of specific grain boundary types. This is significant as diverse boundary types have varied segregation behavior impacting material performance.

By gathering t-EBSD datasets between milling steps, the grain boundary position can be easily detected, and the milling method is stopped when the boundary is within 200 nm of the sample tip. Preparation and validation can be accomplished in the FIB, removing the need to transfer the sample.

Key Features

The main features of the APA are listed below:

  • Smart camera optimization - Automated installation of camera parameters for gathering of superior quality t-EBSD patterns from APT specimens for precise data collections
  • Smart background processing - t-EBSD background processing is designed specifically for improved patterns from APT specimens of varying thickness to allow precise grain boundary position and characterization of orientation
  • Hikari Plus EBSD Camera - High performance/high sensitivity EBSD camera for operation across the broadest range of operational conditions
  • APT specimen tip mapping mode -
    • Map shape template designed to suit APT specimen tip shape for rapid and efficient installation and data collection
    • Map shape easily modifiable for stable mapping after specimen milling
    • Spatial indication of mapping dimensions to establish if grain boundary is within the required distance from specimen tip apex
  • Smart indexing - t-EBSD pattern analysis using innovative triplet indexing for better spatial resolution on APT specimens and indexing rates.
  • Transmission-EBSD mode
    • t-EBSD mode installs acquisition parameters to automatically gather good data from t-EBSD specimens
    • Easily switch from t-EBSD to conventional EBSD collection to manage both APT specimen analysis and site section analysis.

Conclusion

The Atom Probe Assist allows users to both prepare specimens for and to gain quality results from APT analysis quicker and more easily than using basic techniques. This tool allows the choice of specific grain boundary types for preparations as APT specimen tips and observes the grain boundary position during the FIB preparation to guarantee APT analysis of the preferred region of interest. The Atom Probe Assist enables APT users to go beyond the boundaries of grain boundary segregation research much faster.

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