Validation of kinematically simulated pattern HR-EBSD for measuring absolute strains and lattice tetragonality

Abstract

Cross correlation techniques applied to EBSD patterns have led to what has been termed “high-resolution EBSD” (HR-EBSD). The technique yields higher accuracy orientation and strain data which is obtained by comparing a given EBSD pattern with either a real or a simulated reference pattern. Real reference patterns are often taken from a “central” position in a given grain, where it is hoped that the material is “strain-free”, and they enable the determination of relative changes in orientation and strain from that present in the lattice at the reference position. Simulated patterns, on the other hand, enable comparison of the sample lattice with that of a perfect lattice, resulting in a measure of absolute strain and orientation. However, the simulated pattern method has several drawbacks, including the need to accurately specify microscope geometry, the lower fidelity/detail of simulated patterns compared with real patterns, and the potential for microscope-specific bias in the measured patterns (such as due to optical distortion).These drawbacks have led to much debate about the utility of the cross-correlation technique using simulated patterns. This paper is the first to assess the accuracy of the simulated pattern method relative to the real pattern approach in a setting where accuracy can be reasonably determined, thus providing a fair assessment of the potential of the simulated pattern technique.Based upon recent developments towards a standard material for assessing strain mapping techniques, this paper assesses the overall accuracy of the simulated pattern technique. Mismatch strains are calculated using both the real and simulated pattern techniques for a SiGe film deposited on a Si substrate. While the simulated pattern technique is not as accurate or precise as the real pattern technique for providing relative strains, it provides an estimate of absolute strain that is not available via the real pattern approach.