Dark-field electron holography for strain and composition measurement with a sub-nanometre spatial resolution
نویسندگان
چکیده
Transmission electron microscopy (TEM) is a well-established tool for strain measurement that combines an excellent precision with a high spatial resolution. Strain maps can be obtained by different TEM techniques such as high-resolution transmission electron microscopy (HRTEM), high-resolution scanning transmission electron microscopy (HR-STEM), convergent beam electron diffraction, nanobeam electron diffraction, or dark-field electron holography (DFEH). All of the above-mentioned techniques provide high measurement precision in the range of 10 -3 10 -4 , but only HRTEM and HR-STEM are able to measure strain with a sub-nanometre resolution. Processing of HR(S)TEM images is done either in real or in reciprocal spaces, the latter approach called "Geometric Phase Analysis" (GPA) is widely used thanks to an efficient noise reduction. The highest possible spatial resolution available with GPA equals to a double interatomic distance. The highest spatial resolution of a strain map obtained with DFEH is limited by a double spacing between the hologram fringes, which can be tuned within certain limits by changing the biprism voltage. However a decrease of the fringe spacing is accompanied by a reduction of the hologram contrast, which leads to a drastic drop of the measurement precision. Consequently a spatial resolution of strain measurement with DFEH is typically in the range of 4 6 nm, with the best to our knowledge reported value of 1 nm. 1
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