Introducing Atom Probe Assist
Enhanced APT specimen preparation for grain boundary segregation analysis
- Atom Probe Tomography (APT) is a material analysis technique that provides 3D chemical composition and imaging at the atomic scale and is uniquely suited to analysis of grain boundary segregation.
- APT analysis requires specimens prepared with a very sharp tip, and analysis of grain boundaries requires these boundaries to be located within approximately 200 nm of the specimen tip for effective characterization.
Traditional APT sample preparation
Traditional preparation of specimens for APT using either electro polishing and analysis in a Transmission Electron Microscope (TEM) or preparation using a Focused Ion Beam (FIB) is often problematic and inefficient.
Atom Probe Assist
Atom Probe Assist provides an innovative means of monitoring grain boundary position between FIB milling steps to ensure that a grain boundary is detected and correctly positioned for subsequent Atom Probe analysis. With Atom Probe Assist, transmission-EBSD (t-EBSD) can be used to measure and image the crystallographic orientation and determine grain boundary position quickly and easily within a single instrument.
Atom Probe Assist is optimized for t-EBSD measurements of APT tips
Atom Probe Assist can:
- Identify different grain boundary types (left below) where random grain boundaries are shaded black and special twin boundaries are shaded white to assist in site-specific FIB liftout sampling.
- Determine grain boundary position between annular FIB milling steps (right below).
The preparation is complete when the grain boundary between the two different orientations (colored yellow and blue) is located within 200 nm of the sample tip.
Smart t-EBSD Pattern Collection
- Conical APT specimens provide a unique challenge for collecting usable t-EBSD patterns due to the constant variation in sample thickness and shape.
- Specialized background corrections have been developed to improve image quality and ensure accurate band detection and pattern indexing from both thin (left) and thick (right) areas of the APT specimens.
- Detector collection parameters are also optimized specifically for t-EBSD collection to reduce the time and effort necessary to obtain the required information.
Specimen Qualification in a Single Instrument
- Atom Probe Assist requires a FIB-SEM, which is used to mill the specimen annularly to the required dimensions for APT analysis.
- The specimen is positioned in the instrument such that the specimen tip is parallel to the FIB beam.
- This configuration allows milling, SEM imaging, and collection of t-EBSD data without moving the specimen.
- This improves specimen yield by eliminating the risk of damage that occurs when transferring between two instruments.
Enhanced Grain Boundary Contrast
- Grain boundary position is determined via t-EBSD mapping.
- By collecting this data between each FIB milling step, the position of the grain boundary can be detected and monitored.
- When the grain boundary is within the required distance from the specimen apex, the specimen is ready for Atom Probe analysis.
- Maps can be collected quickly (≈ 3 minutes) so that the grain boundary position is quickly determined and specimen contamination is minimized.
Orientation map where specific grain boundary types are identified.
Grain Boundary Qualification
- Atom Probe Assist can also be used to collect traditional EBSD data from a sample to determine grain boundary character from a sample of interest.
- Grain boundary character information is important for understanding grain boundary segregation problems, as different grain boundary types exhibit different segregation behavior.
- This translates into different material properties behavior and by revealing grain boundary character, specific boundaries can be easily targeted for Atom Probe preparation and analysis.
Atom Probe Assist is used with a Hikari Plus EBSD Camera
- Data collection rates up to 1,000 indexed points per second
- Orientation precision < 0.1°
- Low noise detector for high quality EBSD and t-EBSD pattern collection
- Phosphor screen optimized for high speed/high sensitivity operation
Atom Probe Assist is used with TEAM™ EBSD Software
- Customized Atom Probe Assist data collection mode
- Transmission-EBSD mode
- Smart systems for consistent optimization of dynamic data collection parameters
- Custom APT map shape with automatic or user-defined step size down to 1 nm