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Rosi, Paolo, (2021)  - Controllo e misura sperimentale del momento angolare orbitale di elettroni in un microscopio elettronico a trasmissione (TEM)  - , Tesi di dottorato - (, , Universitą degli studi di Modena e Reggio Emilia ) - pagg. -

Abstract: In optics structuring light or electron beams is the coherent control of the wavefunction aimed to impart any arbitrary amplitude and phase structure. A smart choice of the wavefunction can be used to enhance or inhibit parts of the beam sample interaction or to optimize the measurement. For this reason, beam shaping is nowadays used in many fields such as information encoding, communication, material science, life science and fundamental physics. Furthermore, this idea can allow to overcome the limits of classical light and electron optics techniques and it is at the forefront of the research. This thesis will focus on the more recently developed field of electron beam shaping with particular reference to the Orbital Angular Momentum (OAM) degree of freedom. The eigenstates of OAM are the electron vortex beams (EVBs) whose early experimental demonstration in a transmission electron microscope (TEM) was in 2010-2011 The striking property of EVBs is that they open new ways to study materials with a chiral structure such as magnetic materials, plasmonic materials and proteins. Given the natural cylindrical symmetry of the microscope and of the electron-atom interaction at high energies, the OAM is a natural observable in the scattering event and the selection rules of the scattering can be typically directly measured projecting on OAM states. However, both the measurement and the flexible creation of arbitrary OAM states is complicated with the present electron optics. My thesis is therefore a contribution in the creation of innovative devices and ideas for the generation and the measurement of OAM states in an electron microscope. I will mainly focus on the OAM measuring device called “quantum sorter” or “OAM sorter”. In the first chapter I will describe the instrumentation. First the functioning of a transmission electron microscope (TEM) and why it is among the best and most quantitative instruments to study fundamental material properties at the nanoscale, but also a very interesting optical bench for electrons. Then I will explain the working principle of SEM (Scanning Electron Microscope) and FIB (Focused Ion Beam), as these machines are the main instruments I used to create the new electron optics devices. In the following chapter I will describe the theory of the electron microscopy techniques, mainly phase related ones, that I and the research team that I am part of used during the testing and characterization steps of our devices. Furthermore, I will provide the theoretical framework with some practical examples for electron beam shaping, both holographic and electrostatic, focusing mainly on vortex beams. Lastly, I will show the original research results of my PhD, which comprise mainly of experimental works regarding both the generation and measurement of EVBs by means of synthetic holographic phase plates and novel electrostatic devices based on nanofabricated MEMS, and even the theoretical design study for a functioning OAM-sorter based on magnetic fields. Outside of the main topic of this PhD thesis I delved in other topics, whose results will be shown at the end of the thesis.