Abstract
The Geometrical Phase Analysis (GPA) is an efficient method to measure strain from High Resolution Transmission Electron Microscopy (HRTEM) images. Here we show that it can also be applied efficiently to High Resolution Scanning Transmission Electron Microscopy (HR-STEM) images, which have several advantages: (i) patterns in HR-STEM do not change with thickness and chemical composition (ii) thicker samples can be analysed and (iii) strain and composition can be simultaneously determined. In many situations, the distortions due to the scanning of the beam can be corrected. The strain fields around different threading dislocations in an AlInN layer have been determined from plan view samples prepared by focus ion beam (FIB). Experimental strain maps were compared to analytical calculations that take into account the strain field of dislocations and of the In segregation. Mixed type dislocations are always terminated by an inverse hexagonal pyramidal pit, at the sample surface. The edges of the inverse pyramid are indium rich. The dislocation core is not situated at the centre of the inverse pyramid, which is indium-rich, but slightly shifted.
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