Amit Kohn, Ph.D. | FUN 2025

Amit Kohn, Ph.D.

Associate Professor, Department of Materials Science and Engineering

Tel Aviv University

Speech Title:

Mapping Charge Distribution in Nanoscale Ionic Materials by Electron Holography

Abstract:

Charge redistribution in nanoscale ionic crystals has an important role on their functional properties. While theoretical advances in understanding this phenomenon have been achieved, quantitative mapping of charge distribution at the nanoscale is challenging. I will present applications of off-axis electron holography in the transmission electron microscope (TEM) combined with high-resolution TEM imaging and spectroscopy to characterize charge redistribution in two such cases. The first case is a semiconducting hybrid of a PbS core and CdS arms that exhibit epitaxial relations. In these nanoscale structures, fluorescence emission from the CdS arms is quenched, attributed to energy band alignment with respect to the PbS core. Off-axis electron holography of single structures compared to 3-dimensional Poisson simulations indeed show a Type I interface in which the electric field is mostly redistributed on the CdS arm, causing charge carriers to separate and prevent recombination. The second case is non-stoichiometric nano granular spinel, MgO∙Al 2 O 3 , for which we show that the space charge potential and grain boundary segregation are controlled by the excess cation species and also by the grain dimensions with respect to the Debye length. Moreover, by applying an electric field during sintering, the magnitude of the space charge potential is decreased.

Bio:

Amit Kohn is an Associate Professor at the Department of Materials Science and Engineering at Tel Aviv University since last October. Amit’s research projects are in the field of magnetic and electronic materials used for information storage devices. The contribution of the research is to relate between structure and composition of these materials to the magneto-transport properties of the devices. The objective is therefore to improve on, or design new so-called ‘spin-electronic’ devices.
Structural and chemical characterization is mostly achieved by analytical transmission electron microscopy, which probes the properties of the materials at the nanoscale and up to the atomic level. In addition, Amit applies and develops Lorentz electron microscopy and electron holography in order to image magnetic and electrostatic fields in materials and devices at the nanometre scale.
Prof. Kohn holds a Ph.D. in Materials Engineering from the Technion – I. I. T.. He was a Royal Academy of Engineering Research Fellow at the Materials Department, University of Oxford followed by a faculty position at Ben-Gurion University of the Negev.