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Dichroism in electron energy-loss spectroscopy
Ošmera, Martin ; Lourenço-Martins, Hugo (oponent) ; Konečná, Andrea (vedoucí práce)
Vortex electron beams (VEBs) are a class of chiral free electron states carrying orbital angular momentum (OAM). Right-handed and left-handed VEBs, acting as probes, can interact differently with chiral objects, yielding measurably different results in electron energy-loss spectroscopy (EELS) experiments. This nontrivial behavior is usually referred to as dichroism. In this theoretical thesis, we considered two different (chiral) samples. First, we reviewed the theory of phonon excitation in 2D hexagonal crystals and studied the possibility of the prediction of vibrational-EEL signal. We then followed with a theoretical model of localized surface plasmon excitation on a prototype of a chiral plasmonic nanoantena -- single-twist helix. We proposed an experiment, in which the EEL spectrum is resolved in pre-interaction and post-interaction OAM. We treated this problem both analytically and numerically and showed conditions necessary for the emergence of dichroism, as well as the possibility of optimizing the experimental parameters for maximization of the dichroism.
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Optical dichroism in vortex electron energy-loss spectroscopy
Ošmera, Martin ; Dub, Petr (oponent) ; Konečná, Andrea (vedoucí práce)
Vortex electron beams (VEBs) carry orbital angular momentum and when they interact with a chiral specimen, dichroism can be observed. In electron energy loss spectroscopy, left-handed VEBs yield different spectra than right-handed VEBs. This could be utilized in the analysis of chiral molecules or nanostructures. We present a semianalytical fully-retarded model for the interaction of a non-focused VEB with a point-like particle, and a numerical quasistatic model for the interaction of a non-focused VEB with a \enquote{macroscopic} chiral nanostructure.
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Optical dichroism in vortex electron energy-loss spectroscopy
Ošmera, Martin ; Dub, Petr (oponent) ; Konečná, Andrea (vedoucí práce)
Vortex electron beams (VEBs) carry orbital angular momentum and when they interact with a chiral specimen, dichroism can be observed. In electron energy loss spectroscopy, left-handed VEBs yield different spectra than right-handed VEBs. This could be utilized in the analysis of chiral molecules or nanostructures. We present a semianalytical fully-retarded model for the interaction of a non-focused VEB with a point-like particle, and a numerical quasistatic model for the interaction of a non-focused VEB with a \enquote{macroscopic} chiral nanostructure.
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