Date of Award

6-2015

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Dr. John A. Tanis

Second Advisor

Dr. Asghar N. Kayani

Third Advisor

Dr. Thomas W. Gorczyca

Fourth Advisor

Dr. Pnina Ari-Gur

Abstract

The prime motivation of this work is to understand the fundamental transmission process of an electron beam through a funnel-shaped capillary taking into account its shape together with the energy, angular and time dependence of the transmitted electrons produce a microsized electron beam. The utilized capillaries had inlet/outlet diameters of 800/16 μm, 800/100 μm and lengths of 35 mm. Considerable transmission of 800 and 1000 eV electrons for tilt angles up to 1.5o and only small transmission for 500 eV electrons was observed for the capillary with the smaller outlet diameter of 16 μm. Incident electrons with energies of 500 and 1000 eV electrons were successfully transmitted and guided for tilt angles up to ~5o and ~8o, respectively, with respect to the incident beam direction for the capillary with an outlet diameter of 100 μm. The transmitted electrons were found to have both elastic and inelastic behavior. The angular profiles were comprised of up to three peaks for both 500 and 1000 eV energies for the capillary with outlet diameter of 100 μm showing evidence for transmission that goes straight through the capillary without interacting with the walls (direct), and transmission that results from Coulomb deflection by electrons or scattering from nuclei close to the wall surface (indirect). The energy spectra show that elastically transmitted electrons prevail at 500 eV with respect to increasing sample tilt angles, while inelastic processes dominate for 1000 eV already at small tilt angles. The elastic and inelastic components of the transmitted beam caused peaks to occur either individually or together. The transmission was studied as a function of the charge deposition and found to be time dependent. Results suggest fundamental differences between 500 and 1000 eV incident electrons. For 500 eV the transmission slowly increases suggesting charge up of the capillary wall, reaching relative stability. For small tilt angles the transmission shows oscillations in the transmission, which never reached a stable condition. Nevertheless, for larger angles the transmission reached near equilibrium.

Access Setting

Dissertation-Open Access

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