Source point calibration from an arbitrary electron backscattering pattern

Precise knowledge of the position of the source point is a requirement if e lectron backscattering patterns (EBSPs) are to be used for crystal orientat ion measurements or other types of measurements which demand a geometrical analysis of the patterns. Today, possibly the most popular method for locat ing the source point is a computational technique which uses the positions of a number of indexed Kikuchi bands for calculating the coordinates of the point. A serious limitation of this calibration technique is, however, tha t the localized bands must first be indexed, which is difficult if the loca tion of the source point is not known with reasonable precision. This paper describes a new technique which determines the location of the s ource point from the positions of a number of bands in an arbitrary EBSP. B esides the positions of the Kikuchi bands, the only information which is re quired by this new calibration procedure is the same crystallographic infor mation which is used for normal indexing of EBSPs. The procedure is shown t o work successfully with patterns from a simple cubic crystal, as well as w ith patterns from an orthorhombic BiSCCO superconductor. In the former case , four bands are shown to be sufficient to ensure a unique determination of the source point, whereas five bands are required in the latter case. Once the bands have been localized, the time required for calculating the sourc e point position is of the order of 1 min on a standard PC.