Backscattered Electron Imaging with an EBSD Detector

In the scanning electron microscope (SEM), backscattered electrons (BSEs) can be used as a complement to secondary electrons (SEs) for imaging bulk sample surfaces. If the sample is steeply tilted, as is the case in electron backscatter diffraction (EBSD) measurements, the usual backscattered electron detectors above the sample are ineffective. The EBSD detector by itself, however, can be used as a software selectable multi-array BSE detector for imaging. Such BSE microstructure images provide information that may be useful to an EBSD analysis. The EBSD pattern itself need not be indexed, therefore BSE imaging using an EBSD system is applicable to non-crystalline and bioscience materials as well. The technique is fast, convenient, and inexpensive. This article describes the system and gives some application examples. Although specimen surfaces are more commonly imaged in the SEM by collecting low-energy SEs, a signal derived from BSEs at energies close to that of the primary beam can also contain valuable information [1]. The number of electrons that are backscattered from a certain spot of the specimen is dependent on the local inclination of the surface, the local elemental composition, and the crystallographic orientation in the near-surface region of the specimen. These signals give rise to topographical contrast, atomic number contrast, and orientation contrast (also known as channeling contrast), respectively. Images produced with BSEs are less affected by minor specimen charging than SEs because the BSEs are of high energy.