Unraveling the electronic structures in different phases of gadolinium sesquioxides performed by electron energy loss spectroscopy

Abstract

The gadolinium sesquioxide (Gd2O3) with its bandgap of ∼5.4 eV and high dielectric permittivity and refractive index has been used widely in optics, magnetic resonance imaging, and high k dielectrics. Electron energy loss spectroscopy (EELS) reveals spectral features at 13.5 eV and 15 eV, which can be interpreted as surface and volume plasmons, respectively. The unusual surface exciton polariton, with surface resonances associated with excitonic onsets, was also observed at ∼7.5 eV. Because of the differences in electronic structures between the cubic and the monoclinic phases of Gd2O3, it is straightforward to distinguish the two phases using the low-loss regime and O K-edge as a fingerprint. We further successfully performed EELS and electron diffraction to identify the crystalline phase of a single-crystal Gd2O3 film epitaxially grown on a Si(111) substrate.

Investigation of the excitations of plasmons and surface exciton polaritons in monoclinic gadolinium sesquioxide by electron energy-loss spectroscopy and plasmon spectroscopic imaging

“…Both phase purity and crystallinity of the synthesized m-Gd 2 O 3 were confirmed by X-ray diffraction (XRD) in the previous report. 14 Because the β angle between the (100) and (001) planes for m-Gd 2 O 3 is ∼100.13°, it is essential to obtain electron diffraction (ED) patterns and related TEM and STEM images along the [010] orientation, which displays this characteristic β angle. Fig.…”

“…In contrast, the O K-edge exhibited distinct differences in both the spectral features and energies due to the different Gd and O coordination and Gd–O bond lengths. 14 Furthermore, Shu et al also reported some differences in the low-loss region between c- and m-Gd 2 O 3 , however, without detailed analysis for m-Gd 2 O 3 . 14 Besides, Gd 2 O 3 has a larger bandgap of about 5.3 eV and the interband transitions generating weakly bound delocalized excitons presumably of the Wannier–Mott type readily build up collective resonances at the material surface.…”

“… 14 Furthermore, Shu et al also reported some differences in the low-loss region between c- and m-Gd 2 O 3 , however, without detailed analysis for m-Gd 2 O 3 . 14 Besides, Gd 2 O 3 has a larger bandgap of about 5.3 eV and the interband transitions generating weakly bound delocalized excitons presumably of the Wannier–Mott type readily build up collective resonances at the material surface. Furthermore, the surface resonances associated with transverse excitonic onsets could be assigned to surface exciton polaritons (SEPs).…”

Investigations the Electronic Structure in Monoclinic phase Gadolinium Sesquioxides by Electron Energy Loss Spectroscopy

“…1(d)]. Combining with both STEM-EELS spectra and EFTEM-SI intensity maps, the spectral feature at ~7 eV peak can be considered as a surface resonance associated with excitonic onsets understood as surface exciton-polaritons (SEPs) [4]. In contrast to VP at 15 eV, the spectral intensity at 36 eV peak decreases when position electron probe from the material interior to the specimen edge, and then vanished when the electron probe is positioned at 2 nm away from the material surface as shown in Fig.…”

“…Unlike the exponentially decaying in intensity as a function of q values for both SPs and VPs, the intensity of the spectral peak at ~36 eV increases as a function of q which implies the involving multiple scattering processes as described in ref. [4].…”