Pixelated detectors and improved efficiency for magnetic imaging in STEM differential phase contrast

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.

Optimizing disk registration algorithms for nanobeam electron diffraction strain mapping

“…Since the Sobel filter is a simple matrix, it can be applied across datasets without concern for effects caused by changing user defined thresholds, and is much faster and impartial than an iterative method. Sobel filtering has been shown to improve cross correlation accuracy of the forward scattered disk, useful in differential phase contrast imaging, but has not been robustly tested with diffracted disks containing dynamical contrast [26].…”

The EIGER detector for low-energy electron microscopy and photoemission electron microscopy

“…The recent progress in electron detectors, in particular in pixelated detectors with direct single-electron counting capabilities, have led recently to a new paradigm in transmission electron microscopy by improving the detection efficiency by orders of magnitude (Kü hlbrandt, 2014;McMullan et al, 2009). Indeed, the excellent results from McMullan et al (2007) and Nederlof et al (2013) have driven the very recent developments and the commercialization of hybrid pixel detectors in transmission electron microscopes (Quantum Detectors, 2017;Dectris, 2017;Amsterdam Scientific Instruments, 2017) and scanning transmission electron microscopes (Krajnak et al, 2016;Raighne et al, 2011) at high kinetic energies (40-300 keV) and less stringent vacuum constraints. Also, single-photon-counting pixel detectors like PILATUS (Kraft et al, 2009), EIGER (Dinapoli et al, 2011) and Medipix (Llopart et al, 2002;Gimenez et al, 2015) are widely used in photon science and synchrotron experiments.…”

Controlled Individual Skyrmion Nucleation at Artificial Defects Formed by Ion Irradiation

“…This diffraction contrast completely masks the magnetic contrast in standard DPC, however, the more advanced processing enabled by pixelated detectors can reduce this contrast and allow for successful quantitative imaging with DPC. [44][45][46] As outlined in existing studies, [45,46] the beam Lorentz deflection angle β from perpendicularly magnetized materials depends on the sample tilt and is proportional to B s . Figure 5a shows a DPC image from a 5 × 10 16 ions per cm 2 defect site on sample 1 in a field of 10 mT.…”