Abstract
The decreasing size of modern functional magnetic materials and devices cause a steadily increasing demand for high resolution quantitative magnetic characterization. Transmission electron microscopy (TEM) based measurements of the electron energy-loss magnetic chiral dichroism (EMCD) may serve as the needed experimental tool. To this end, we present a reliable and robust electron-optical setup that generates and controls user-selectable single state electron vortex beams with defined orbital angular momenta. Our set-up is based on a standard high-resolution scanning TEM with probe aberration corrector, to which we added a vortex generating fork aperture and a miniaturized aperture for vortex selection. We demonstrate that atom size probes can be formed from these electron vortices and that they can be used for atomic resolution structural and spectroscopic imaging – both of which are prerequisites for future atomic EMCD investigations.
Highlights
For magnetic materials and in solid state physics in general, the orbital angular momenta (OAM) and spins of atoms and their mutual coupling are of surmounting importance, since due to the correlation of the orbital angular momentum (OAM) with the local electron density distribution and the crystal structure, they are intimately related to anisotropies in particular of the magnetic properties
That the passing single vortex beam can be focused down to angstrom-sizes achieving atomic resolution in scanning transmission electron microscopes (STEM) energy loss spectra (EELS), which is a critical pre-requisite for atomic resolution energy-loss magnetic chiral dichroism (EMCD) measurements
The undiffracted, central beam carries no OAM and is defined as L = 0. Note that since this image of the probe is obtained in STEM mode with switched-off diffraction, it is convoluted with the aberrations of the lower objective lens of the microscope
Summary
For magnetic materials and in solid state physics in general, the orbital angular momenta (OAM) and spins of atoms and their mutual coupling are of surmounting importance, since due to the correlation of the OAM with the local electron density distribution and the crystal structure, they are intimately related to anisotropies in particular of the magnetic properties. EVBs have first been discussed theoretically by Bliokh et al.[25] and were experimentally demonstrated by Uchida and Tonomura[26] using stacked graphene layers, and by Verbeeck et al.[27] and McMorran et al.[28] with the use of holographic masks Since such electron vortices carry discrete orbital angular momenta and can be focused down to sub-nanometer diameters, the use of eVBs for EMCD measurements may pave the way towards the quantitative determination of local magnetic properties with unrivalled lateral resolution in scanning transmission electron microscopes (STEM). EVBs can be generated with a variety of different methods that are all based on shaping the electron beam in the condensor lens system of the TEM by using holographic diffraction masks, phase plates, (switchable) magnetic needles, or aberration correctors All these approaches have their individual advantages and disadvantages. Changing the OAM requires to frequently change the excitation of the corrector lens system, the feasibility of which is not yet explored
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
