Studies of Electronic Excitations in Wurtzite ZnO and AlN with Valence Electron Energy-Loss Spectroscopy

  • 黃 榮喜

Student thesis: Doctoral Thesis

Abstract

The main theme of this dissertation is to investigate the fundamental electronic properties of wurtzite semiconductors including zinc oxide (ZnO) and aluminum nitride (AlN) using electron energy-loss spectroscopy (EELS) in conjunction with scanning transmission electron microscopy (STEM) Performance of the recently acquired probe-Cs-corrected JEOL 2100F TEM system is preliminarily evaluated showing routinely achievable optimal spatial and EELS energy resolution of 1 ? and 0 6 eV respectively Such superb capability can also be attributed to the specifically designed laboratory which effectively isolates the environmental interference and provides excellent stability By scanning the probe across the specimen from bulk interior to vacuum four spectral features associated with the surface excitation can be readily recognized According to the gradual transition of the volume plasmon with decreasing thickness the surface plasmon (SP) of ZnO at about 16 eV is assigned Most importantly the criterion for SP excitation with a negative real part of the dielectric function is met within this energy regime The occurrence of surface exciton polaritons (SEPs) under the relaxed condition of εi > | εr | > 0 are clearly observed at 9 5 and 13 5 eV in grazing incidence Furthermore surface guided light modes coupled to the confined ?erenkov radiation just above the bandgap has also been successfully identified which is well consistent with the theoretical simulations The low-loss spectrum of AlN has also been studied by STEM-EELS with the emphasis on the influence of surface oxidation Contrary to intrinsic bulk AlN the oxidized AlN exhibits considerable spectral broadening in the full width at half maximum (FWHM) of volume plasmon as well as in the subsidiary features The modification in the low-loss lineshapes because of oxidation significantly complicates the determination of the dielectric function of intrinsic AlN Simulations based on dielectric theory qualitatively conform to the experimental results while thick overlayers are incorporated further suggesting that the surface oxide of AlN can be quite rough and porous in nature
Date of Award2014 Feb 13
Original languageEnglish
SupervisorChuan-Pu Liu (Supervisor)

Cite this

Studies of Electronic Excitations in Wurtzite ZnO and AlN with Valence Electron Energy-Loss Spectroscopy
榮喜, 黃. (Author). 2014 Feb 13

Student thesis: Doctoral Thesis