Surface exciton polariton in monoclinic HfO₂: an electron energy-loss spectroscopy study

Plasmons dispersion and nonvertical interband transitions in single crystal Bi2Se3investigated by electron energy-loss spectroscopy

“…Considering that the EELS features can be generally understood in the framework of the macroscopic dielectric-response theory, 16,18,22 we thus derived the frequency (ω)-dependent dielectric function, ε(ω), of Bi 2 Se 3 from the black spectrum in Fig. 1(a) by performing Kramers-Krönig analysis (KKA), as shown in Fig.…”

“…1(a) and (b)), the spectral features at ~5.5 and ~10 eV are further weaken but still visible, signifying the characteristic of the evanescent wave fields of SPs. 16,18,22,26 The STEM-EELS spectrum imaging, 27 which has been well established to probe SPs in noble metals [28][29][30] and semiconductor 31 , was performed to further confirm the physical origin of the spectral features at ~5.5 and ~10 eV as SPs. Figure 1 (c)- (e) show the STEM-EELS intensity maps, measured from the same area in HAADF image (inset, Fig.…”

Probing the size dependence on the optical modes of anatase nanoplatelets using STEM-EELS

“…12 According to recent findings, surface features that are excited at energies near to interband transitions may be associated to a particular type of surface excitations named surface exciton polaritons (SEPs). [30][31][32][33] SEPs are collective excitations of delocalized Wannier-type excitons originating at the surface of materials. The existence of a surface exciton polariton requires that 2 >1 > 0, a condition 30 satisfied by many semiconductors and insulators above the band gap, including anatase.…”

“…[30][31][32][33] SEPs are collective excitations of delocalized Wannier-type excitons originating at the surface of materials. The existence of a surface exciton polariton requires that 2 >1 > 0, a condition 30 satisfied by many semiconductors and insulators above the band gap, including anatase. In addition to this condition, the thickness of the sample must be small enough to allow the imaginary part, ki, of the complex wavevector k to be negligible, a condition that is also satisfied for a thin platelet.…”

“…In addition to this condition, the thickness of the sample must be small enough to allow the imaginary part, ki, of the complex wavevector k to be negligible, a condition that is also satisfied for a thin platelet. 30 There have been limited investigation of SEPs using EELS, and they have only recently observed in semiconducting nanostructures, such as HfO2 thin films, 30 GaN nanoprisms, 31 and ZnO nanorods 32,33 in aloof geometry where the interband transitions are suppressed and the corresponding surface features enhanced. energy of the SP mode gradually blue shifts with thickness, and eventually reaches the asymptotic value of 9.6 eV in a 10 nm thick slab.…”