18,316 research outputs found
Symmetry-guided nonrigid registration: the case for distortion correction in multidimensional photoemission spectroscopy
Image symmetrization is an effective strategy to correct symmetry distortion
in experimental data for which symmetry is essential in the subsequent
analysis. In the process, a coordinate transform, the symmetrization transform,
is required to undo the distortion. The transform may be determined by image
registration (i.e. alignment) with symmetry constraints imposed in the
registration target and in the iterative parameter tuning, which we call
symmetry-guided registration. An example use case of image symmetrization is
found in electronic band structure mapping by multidimensional photoemission
spectroscopy, which employs a 3D time-of-flight detector to measure electrons
sorted into the momentum (, ) and energy () coordinates. In
reality, imperfect instrument design, sample geometry and experimental settings
cause distortion of the photoelectron trajectories and, therefore, the symmetry
in the measured band structure, which hinders the full understanding and use of
the volumetric datasets. We demonstrate that symmetry-guided registration can
correct the symmetry distortion in the momentum-resolved photoemission
patterns. Using proposed symmetry metrics, we show quantitatively that the
iterative approach to symmetrization outperforms its non-iterative counterpart
in the restored symmetry of the outcome while preserving the average shape of
the photoemission pattern. Our approach is generalizable to distortion
corrections in different types of symmetries and should also find applications
in other experimental methods that produce images with similar features
Numerical correction of anti-symmetric aberrations in single HRTEM images of weakly scattering 2D-objects
Here, we present a numerical post-processing method for removing the effect
of anti-symmetric residual aberrations in high-resolution transmission electron
microscopy (HRTEM) images of weakly scattering 2D-objects. The method is based
on applying the same aberrations with the opposite phase to the Fourier
transform of the recorded image intensity and subsequently inverting the
Fourier transform. We present the theoretical justification of the method and
its verification based on simulated images in the case of low-order
anti-symmetric aberrations. Ultimately the method is applied to experimental
hardware aberration-corrected HRTEM images of single-layer graphene and MoSe2
resulting in images with strongly reduced residual low-order aberrations, and
consequently improved interpretability. Alternatively, this method can be used
to estimate by trial and error the residual anti-symmetric aberrations in HRTEM
images of weakly scattering objects
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