Abstract
The application of differential phase contrast imaging to the study of polycrystalline magnetic thin films and nanostructures has been hampered by the strong diffraction contrast resulting from the granular structure of the materials. In this paper we demonstrate how a pixelated detector has been used to detect the bright field disk in aberration corrected scanning transmission electron microscopy (STEM) and subsequent processing of the acquired data allows efficient enhancement of the magnetic contrast in the resulting images. Initial results from a charged coupled device (CCD) camera demonstrate the highly efficient nature of this improvement over previous methods. Further hardware development with the use of a direct radiation detector, the Medipix3, also shows the possibilities where the reduction in collection time is more than an order of magnitude compared to the CCD. We show that this allows subpixel measurement of the beam deflection due to the magnetic induction. While the detection and processing is data intensive we have demonstrated highly efficient DPC imaging whereby pixel by pixel interpretation of the induction variation is realised with great potential for nanomagnetic imaging.
Highlights
The application of differential phase contrast imaging to the study of polycrystalline magnetic thin films and nanostructures has been hampered by the strong diffraction contrast resulting from the granular structure of the materials
Problems with diffraction contrast from polycrystalline films have long been a problem for scanning transmission electron microscopy (STEM) Differential phase contrast (DPC) imaging of magnetic thin films
Hardware improvements such as an annular quadrant detector help to an extent, we have shown in this paper that the combination of a pixelated detector and software processing of the bright field disk images gives a huge improvement in the efficiency with which the magnetic phase information can be imaged
Summary
The application of differential phase contrast imaging to the study of polycrystalline magnetic thin films and nanostructures has been hampered by the strong diffraction contrast resulting from the granular structure of the materials. Further hardware development with the use of a direct radiation detector, the Medipix, shows the possibilities where the reduction in collection time is more than an order of magnitude compared to the CCD We show that this allows subpixel measurement of the beam deflection due to the magnetic induction. The geometries employed include bi-split [4], quadrant [7] and annular quadrant [8] with significant performance improvements being gained for imaging of polycrystalline magnetic thin film structures with the latter In such films contrast arising at grain boundaries can produce contrast variations as strong, or stronger, than those arising from the intrinsic magnetisation and contributes unwanted signal variation in the differential phase image.
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