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Orientation contrast imaging of microstructures in rocks using forescatter detectors in the scanning electron microscope

Published online by Cambridge University Press:  05 July 2018

David J. Prior ,
Patrick W. Trimby ,
Ursula D. Weber  and
David J. Dingley
David J. Prior
Affiliation:
Department of Earth Sciences, Liverpool University, L69 3BX, UK
Patrick W. Trimby
Affiliation:
Department of Earth Sciences, Liverpool University, L69 3BX, UK
Ursula D. Weber
Affiliation:
Department of Earth Sciences, Liverpool University, L69 3BX, UK
David J. Dingley
Affiliation:
Department of Physics, University of Bristol, UK
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Abstract

We have developed a system using ‘forescatter detectors’ for backscattered imaging of specimen surfaces inclined at 50–80° to the incident beam (inclined-scanning) in the SEM. These detectors comprise semiconductor chips placed below the tilted specimen. Forescatter detectors provide an orientation contrast (OC) image to complement quantitative crystallographic data from electron backscatter patterns (EBSP). Specimens were imaged using two detector geometries and these images were compared to those collected with the specimen surface normal to the incident beam (normal-scanning) using conventional backscattered electron detector geometries and also to an automated technique, orientation imaging microscopy (OIM). When normal-scanning, the component of the BSE signal relating to the mean atomic number (z) of the material is an order of magnitude greater than any OC component, making OC imaging in polyphase specimens almost impossible. Images formed in inclined-scanning, using forescatter detectors, have OC and z-contrast signals of similar magnitude, allowing OC imaging in polyphase specimens.

OC imaging is purely qualitative, and by repeatedly imaging the same area using different specimen-beam geometries, we found that a single image picks out less than 60% of the total microstructural information and as many as 6 combined images are required to give the full data set. The OIM technique is limited by the EBSP resolution (1–2°) and subsequently misses a lot of microstructural information. The use of forescatter detectors is the most practical means of imaging OC in tilted specimens, but it is also a powerful tool in its own right for imaging microstructures in polyphase specimens, an essential asset for geological work.

Keywords

contrast imagesscanning electron microscopybackscattered electrons
Type
Mineralogy
Information
Mineralogical Magazine , Volume 60 , Issue 403 , December 1996 , pp. 859 - 869
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1996

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