Biomedical subjects

M Beleggia

Publications and source records attributed to M Beleggia.

5 recordsLinked to original sources

PubMed2005

Electron optical phase-shifts by Fourier methods: analytical versus numerical calculations.

The theoretical framework for the computation of electromagnetic fields and electron optical phase-shifts in Fourier space has been recently applied to objects with long-range fringing fields, such as reverse-biased p-n junctions and magnetic stripe domains near a specimen edge. In addition to new analytical results, in this work, we present a critical comparison between numerical and analytical computations. The influence of explicit and implicit boundary conditions on the phase shifts and phase-contrast images is also investigated in detail.

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PubMed2004

On the transport of intensity technique for phase retrieval.

The Transport of Intensity technique is becoming a viable alternative to electron holography for phase retrieval in Transmission Electron Microscopy. However, several issues are still to be clarified in order to ascertain the applicability of the technique; among them, the controversy regarding its geometrical or wave-optical nature, as related to the phase detection limit. We show here that the Transport of Intensity is a wave-optical technique that works in a special regime of small defocus where the image intensity is linear with the defocus parameter. By a simple analytical example we show that the Transport of Intensity correctly reconstructs the electron optical phase shift even when the phase is smaller than pi, a value defining the boundary between the geometrical and wave approaches. Another example is given, the reconstruction of a phase jump, accompanied with experimental support showing that phase retrieval by Electron Holography and Transport of Intensity techniques yields results in good agreement.

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PubMed2003

A Fourier approach to fields and electron optical phase-shifts calculations.

The Fourier method is applied to calculate fields and electron optical phase shifts in specimens having long-range electromagnetic fields, like reverse biased p-n junctions or stripe magnetic domains. It is shown that this approach not only allows to take into account rather easily the effect of the fringing fields protruding in the space around the specimen, but also to obtain solutions to interesting models in analytical form.

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PubMed2000

On the calculation of the phase shift of superconducting fluxons: from the isolated to the lattice case

The numerical problems associated to the calculation of the phase shift due to a flux line lattice (FLL) in a thin superconducting specimen are presented and discussed. In order to be able to adequately treat the periodic case, the Fourier transform of the phase shift due to a flux tube is needed. This result is obtained by means of a new approach, where the phase shift is calculated from the beginning in the reciprocal space, treating separately each Fourier coefficient of the magnetic vector potential. The equivalence with the old approach is demonstrated and the utility of the new formulation for calculating the phase shift of closely packed FLL shown.

Journal Article↗

PubMed2000

Electron microscopy of reverse biased p-n junctions

The aim of this paper is to present and discuss the recent results obtained in the investigation of reverse-biased p-n junctions by means of the out-of-focus method. It will be shown how the interpretation of the experimental images is not in agreement with the expectations based on the bulk p-n junction theory. The possible causes of this discrepancy will be discussed: among them a significant reason could be the finite specimen thickness with the associated surface states, which influences the width and shape of the depletion layer in the thinned specimen.

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