The experimental and theoretical work presented in this Thesis is about the realization of an experimental setup for Ultrafast Scanning Electron Microscopy: at first the assembling and the installation of a new sourge has been carried out, and this step was followed by a characterization of the source itself to understand its method of operation and its operative parameters, afterwards an analysis of the environmental noise on the source performances was carried out, and countermeasures were taken to counteract its effect. Known the main characteristics of the assembly, a modeling of the behaviour of a dense electron bunch was done, by the means of both numerical calculations and simulations. The scientific interest in this topic is about the realization of an instrument with a nanometric spatial resolution and an enhanced temporal resolution given by the total broadening of the electron packet in order to observe and comprehend not only the temporal evolution of a phenomena, but also to observe extensively the spatial dynamics by reconstructing those transients which are difficult to point out by the means of a pure optical setup. The data collection of the data has been conducted by reading the Current impinging on a Faraday cup inside the Measurement Chamber of the microscope, whereas the imaging capabilities and the calibration was conducted on a test sample constituted by Sn beads on a C substrate, while the numerical calculation of the pulse duration and the simulation of the trajectories were conducted in a MATLAB environment and in with COMSOL, showing how the cylindrical pulse approximation works fine in both the situation, and for what concerns the propagation in a system with Magnetic Optics an oscillatory behaviour was predicted: for both the propagation the duration was calculated, with an increment of a factor around $10^4$ with magnetic fields applied. For what concerns the future development, which could include a refinement of the model with other charge distribution, the realization of an Electrostatic or Radiofrequency to compress these bunches might be carried out.
Il lavoro sperimentale e teorico presentato in questa tesi riguarda la realizzazione di un setup sperimentale per esperimenti di Microscopia a Scansione Ultraveloce: dapprima si è proceduto all'assemblaggio e installazione della nuova sorgente e ad una sua caratterizzazione per comprenderne il funzionamento e i parametri operativi, al quale ha fatto seguito l'analisi sull'impatto del rumore ambientale sulle sue prestazioni e le contromisure adottate. Inoltre note le caratteristiche della sorgente si è cercato di modellizzare, sia attraverso calcolo numerico che attraverso simulazioni il comportamento di un impulso di elettroni denso in una regione simile a quella della strumentazione esistente. L'interesse principale risiede nella realizzazione di uno strumento in grado di avere una risoluzione spaziale nanometrica ed una risoluzione temporale data dalle dimensioni del pacchetto elettronico, in modo da poter osservare non solo l'evoluzione temporale in maniera dettagliata, ma anche le dinamiche spaziali ricostruendo quei transienti legati alle variazioni di struttura che sono difficilmente rilevabili mediante un setup puramente ottico. La raccolta dei dati sulla sorgente è stata effettuata tramite la lettura delle correnti incidenti su una gabbia di Faraday sita all'interno della camera di misura del microscopio, menre le proprietà di imaging della medesima sono state testate su un campione di prova costituito da sfere di Sn su substrato in C, mentre il calcolo della durata dell'impulso e la simulazione delle traiettorie sono state condotte in ambiente MATLAB e in ambiente COMSOL, mostrando come nella propagazione libera l'approssimazione di impulso cilindrico dia gli stessi risultati, mentre per quanto riguarda la propagazione all'interno di una regione di campo magnetico si registra un comportamento oscillante ove il campo è non nullo: in entrambi i casi è stato possibile calcolare la durata dell'impulso, con un incremento di un fattore 10000 in presenza di campi magnetici Per quanto riguarda gli sviluppi futuri, oltre a possibili aggiornamenti del modello con differenti distribuzioni di carica, sarà possibile realizzare una cavità di compressione elettrostatica o a Radiofrequenza per comprimere tali impulsi.
Development of a setup for ultrafast scanning electron microscopy
FACCHI, GUGLIELMO
2013/2014
Abstract
The experimental and theoretical work presented in this Thesis is about the realization of an experimental setup for Ultrafast Scanning Electron Microscopy: at first the assembling and the installation of a new sourge has been carried out, and this step was followed by a characterization of the source itself to understand its method of operation and its operative parameters, afterwards an analysis of the environmental noise on the source performances was carried out, and countermeasures were taken to counteract its effect. Known the main characteristics of the assembly, a modeling of the behaviour of a dense electron bunch was done, by the means of both numerical calculations and simulations. The scientific interest in this topic is about the realization of an instrument with a nanometric spatial resolution and an enhanced temporal resolution given by the total broadening of the electron packet in order to observe and comprehend not only the temporal evolution of a phenomena, but also to observe extensively the spatial dynamics by reconstructing those transients which are difficult to point out by the means of a pure optical setup. The data collection of the data has been conducted by reading the Current impinging on a Faraday cup inside the Measurement Chamber of the microscope, whereas the imaging capabilities and the calibration was conducted on a test sample constituted by Sn beads on a C substrate, while the numerical calculation of the pulse duration and the simulation of the trajectories were conducted in a MATLAB environment and in with COMSOL, showing how the cylindrical pulse approximation works fine in both the situation, and for what concerns the propagation in a system with Magnetic Optics an oscillatory behaviour was predicted: for both the propagation the duration was calculated, with an increment of a factor around $10^4$ with magnetic fields applied. For what concerns the future development, which could include a refinement of the model with other charge distribution, the realization of an Electrostatic or Radiofrequency to compress these bunches might be carried out.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/94453