Validate New Mineral Discoveries with Tescan Sample Preparation and EBSD Analysis

Why Tescan FIB-SEM is ideally suited to prepare and characterize mineral samples

Geoscientists have access to numerous physical and analytical techniques for both preparing samples and identifying a mineral’s composition and characteristics.

For sample preparation, most laboratories use electropolishing, chemical etching, vibration polishing, laser polishing, Ar broad ion beam milling, and FIB polishing in a FIB-SEM. But, unlike the other methods mentioned above, FIB polishing - can be accurately controlled by the operator. This is critical for preserving the details of mineral grains in the sample volume.

For the structural characterization X-ray diffraction is typically used. However, EBSD allows acquisition of diffraction patterns with submicron lateral resolution.

The advantage to using FIB-SEM instead of other methods is its ability to locate specific mineral grains, polish the sample locally, and perform high resolution structural characterization—in a single instrument workflow.

How Data wascollected

To locate the minerals of interest, SEM imaging was used to navigate to the area of interest. Tescan FIB-SEM instruments navigate using known coordinates, mineral maps from other instruments like TESCAN TIMA, or by identifying features of interest during SEM imaging..

Next, FIB polishing at low accelerating voltage is used to prepare the sample for crystallographic characterization. Local polishing of the mineral grain prior to performing EBSD creates the smooth surface that is essential for obtaining high quality diffraction patterns. The polishing progress can be monitored in real-time to ensure that the sample reaches the desired quality while avoiding loss of the grain of interest. Depending on the sample, preparation can be achieved in the range of 5 to 50 minutes.

Finally, EBSD analysis is used to determine the grain's crystallographic structure and its orientation. A non-destructive technique, because it can be applied to samples without altering their structure or properties, EBSD is fully embedded in the FIB-SEM platform to deliver a complete imaging and characterization workflow

The IMA/CNMNC’s approval of EBSD as a recognized source for crystallographic data for structural comparison opened the door to developing a complete workflow—from sample preparation to final crystallographic data—that can be performed entirely within the FIB-SEM instrument. 

Polishing by focused ion beam in the Tescan AMBER FIB-SEM provides several advantages. The major advantage is in-situ visual monitoring of the FIB polishing process by using live SEM imaging. This workflow allows samples to be coated , since the coating can be locally removed.

This FIB polishing workflow can be applied to EBSD sample preparation for any unique, small-scale features which could be destroyed by using standard non-localized polishing methods like Ar broad ion beam milling or vibration polishing, among other techniques.

Using Tescan AMBER FIB-SEM with embedded EBSD facilitated the discovery and identification of new mineral species occurring in micron-sized grains. Crystallographic data provided by EBSD was used to validate the findings.