Effect of imaging conditions for reliable measurement of local strain from synthetic High Resolution Transmission Electron Microscope (HRTEM) images by Geometrical Phase Analysis (GPA)

Synthetic HRTEM images are simulated using Jems® simulation software with a model specimen consisting of a film of strained silicon on top of a relaxed Si0.82Ge0.18 alloy substrate in the [110] zone axis, where biaxial tensile strain exists in the strained silicon layer. Two simulated models are created: one with a sudden change in lattice constant (strained Si on a “fat” Si substrate) and another with a sudden change in atomic number (strained Si on a Cl substrate) in order to separate the effects of strain discontinuities from atomic number discontinuities measuring strain using Geometric Phase Analysis (GPA). The simulated models are subjected to image processing using GPA software developed by Chung. Two dimensional strain maps are reconstructed and the local strain is determined. Further, an analysis is done to evaluate the best imaging conditions for strain measurement using GPA at heteroepitaxial interfaces. In addition, the behavior of GPA across a step function in strain or atomic number is examined for information about (a) spatial resolution, (b) the effects of a sudden change in atomic number, (c) instrument parameters, and (d) specimen thickness for a 300KeV TEM.