Determination of strain fields on two-dimensional images using the STC method

In this paper, a novel method called the Strain Tensor using Computational Fourier transform moire (STC) method is proposed to obtain strain maps in a 2D lattice image such as an HRTEM or HAADF-STEM image. The method is a modification of the CFTM method, but it has two essential merits. Firstly, the method provides a 2x2 strain tensor using two independent Bragg peaks, and can hence be used to calculate both the axial and shear components, whereas the CFTM method can be used to calculate only the axial strain. Secondly, the STC method can provide more reliable results than the CFTM method by excluding the weak Bragg peaks of low signal/noise ratio on a digital diffractogram. In addition, the STC method is better than the GPA method because it does not require an unwrapping process. In this work, the STC method is demonstrated using a computer-generated image, showing that the method matches exactly with the CFTM method. Furthermore, the results for an experimental image reveal that the STC method can be an alternative method for strain analysis when the CFTM method cannot provide reliable results owing to weak Bragg peaks of low signal/noise ratio.