Forescattered Image Acquisition with EBSD Detection for Grain Structure Analysis

The Nordlys EBSD detector from Oxford Instruments can be fitted with up to six forescattered detectors, which are positioned around the phosphor screen, as depicted in Figure 1. Two of them are fitted below the phosphor screen, two above and one each on either side.

The diodes are placed to acquire superior quality images without shadowing the EDS detector. The images to be collected by these detectors will be determined their position when the sample is tilted to EBSD geometries.

Figure 1. Positioning of forescattered detectors on the Nordlys EBSD detector

Key Features of Nordlys EBSD Detector

The FSD diodes above the phosphor screen will produce atomic number (or Z) contrast images (Figure 2) by collecting backscattered electrons. The diodes below the screen will provide orientation contrast image (Figure 3) of a sample by collecting forescattered electrons, revealing the grain and subgrain structure of the sample.

Figure 2. Atomic number contrast image taken from a geological sample

Figure 3. Orientation contrast image taken from a geological sample

The Nordlys EBSD detector is a useful tool for EBSD analysis due to its ability to provide a quick overview of the microstructure and show details within the sample that may otherwise be difficult to observe.

The side diodes are capable of collecting images, including components of both types of images. The automatic image optimization is applied prior to acquisition. Default settings are available for both atomic number and orientation contrast images. Manual settings are also possible.

Aztec Interface

Aztec can concurrently acquire an image from each of the FSD diodes mounted on the detector. These individual images reveal features within the sample that may be ignored if a mixed image alone is acquired. The images from the lower two diodes depicted in Figures 4 and 5 reveal a twin structure that is not seen from the other diodes.

Figure 4. Forescattered image acquisition within the AZtec interface

Figure 5. Orientation contrast image from a polished Gabbro, formed by mixing the two lower forescattered images.

It is possible to individually control the brightness and contrast of each image (Figure 6). A mixed image can be constructed by merging any combination of the individual images. The operator can decide the weight of each image in the final image. This option facilitates constructing an image revealing all the required detail.

Figure 6. Images from each of the six diodes can be viewed and controlled independently. This maximises the sample detail visible from these images.

This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments NanoAnalysis.

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