Publication Date:
2014-12-19
Description:
Publication date: February 2015 Source: Ultramicroscopy, Volume 149 Author(s): B.G. Mendis Two important applications of electron vortex beams are in electron magnetic chiral dichroism (EMCD) measurements and nanoparticle manipulation. In both cases orbital angular momentum (〈 L z 〉) transfer between the vortex beam and the specimen due to dynamic scattering is critical. In general the 〈 L z 〉 pendellösung consists of short and long wavelength oscillations. The former is due to interference between the tightly bound 1s and more dispersive non-1s Bloch states, while the latter is due to interference between the non-1s states. For EMCD experiments with ± ħ angular momentum beams, momentum transfer can be minimised by selecting the appropriate aperture size, so that the probe wavefunction approximately matches that of the 2p-type Bloch states. For manipulating nanoparticles with large angular momentum beams small apertures are required to excite the 1s state and thereby enhance the short wavelength oscillations in 〈 L z 〉. This enables efficient momentum transfer to the specimen, provided the nanoparticle dimension corresponds to a minimum in the 〈 L z 〉 pendellösung.
Print ISSN:
0304-3991
Topics:
Electrical Engineering, Measurement and Control Technology
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Natural Sciences in General
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Physics
