MATERIALS SCIENCE AND ENGINEERING SEMINAR Ion Beam Irradiation on Hard Material Surfaces: Nanopatterning of Gallium Antimonide and Silicon Substrates and Irradiation Damage of Ultrafine and Multimodal Tungsten by Osman Jihad El-Atwani Ph.D. Final Exam Advisor Professor J. P. Allain ABSTRACT Several important applications of ion beam irradiation emerged in the last two decades. While being utilized in investigating the irradiation damage to nuclear materials as plasma facing components (PFC), ion beam irradiation is also used in nanopatterning of single and multicomponent semiconductors. In this work, fundamental studies regarding the above two topics are presented. In the first study, formation of multimodal and ultrafine grain tungsten by spark plasma sintering is discussed and the irradiation damage of these materials at low energy irradiation (up to 200 eV) and high temperatures (up to 950 oC) is illustrated. Surface morphology changes and their correlation to grain size, grain boundary grooving, and irradiation enhanced recrystallization are discussed based on ex-situ irradiation/morphology observations. In the second study, several crucial aspects regarding nanostructuring of gallium antimonide (GaSb) surfaces via normal incident argon irradiation are discussed. In-situ surface characterization with x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) during the irradiation of GaSb surfaces at low energy (up to energies near sputtering threshold), was used to determine the surface concentration at different irradiation doses. Comparison with ex-situ characterized samples, where Ga concentrations were proved to be high due preferential reaction with oxygen, elucidated the significance of in-situ irradiation conditions. Moreover, several other aspects regarding the structures evolution and formation mechanism such as preferential sputtering of Sb, morphology evolution behavior, the effect of native oxide, and nanopatterning at energies near sputtering threshold are discussed based on in-situ XPS, ISS, and grazing incidence small angle x-ray scattering (GISAXS) results. In the third study, structuring of silicon substrates via normal incident ion irradiation is discussed. While ion beam irradiation of silicon substrates with no impurity seeding can lead to surface smoothing behavior, irradiation of metal-coated silicon substrates was shown to lead to nanodots formation on silicon substrates that remain even after the removal of the metal film material. Real time GISAXS and x-ray fluorescence (XRF) as well as in-situ XPS and ISS studies were performed during the irradiation of different metal-coated silicon substrates. The results, combined with ex-situ scanning electron microscopy (SEM), elucidated the importance of silicides in the structure formation mechanism. Date: Wednesday, July 18, 2012 Time: 8:30 AM Place: ARMS 3115 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100
