Studies of Electronic Excitations of Rectangular ZnO Nanorods by Electron Energy-Loss Spectroscopy

Facile fabrication of ZnO:S/ZnO hetero-nanostructures and their electronic structure investigation by electron energy loss spectroscopy

“…It is documented as the interband transition from O 2p to Zn 3s. 28,32 The different intensity and peak shape of the left shoulder in the low-loss EELS spectrum of the ZnO:S trunk and pure ZnO branches might be caused by the implantation of sulfur. The substitution of oxygen atoms by sulfur would introduce the interband transition of S 3p to Zn 3s and contribute to the related surface guided modes.…”

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.…”

“…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.…”

Comment on ‘Nanoscale mapping of optical band gaps using monochromated electron energy loss spectroscopy’

“…Thirdly, VEELS always shows strong plasmon peaks (for zinc oxide at 18.8eV [9], for zinc at 17.2eV [10]) the long tail components of which have been shown to also influence the numerical fitting results [7]. Moreover, for the specific materials system of zinc oxide under consideration here there are further, weaker valence interband transitions at 3.8, 5.5., 9.5 and 13.5eV [9], and there may be a pronounced surface plasmon peak around 15.8eV [11] in a thin foil sample, so fitting a simple square-root function to a small range which will inevitably contain several weak humps and shoulders makes physically rather limited sense. The underlying fundamental reason is that the free-electron approximation for a threedimensional perfect bulk material implicitly assumed in the derivation of the square-root function for the density of states is not necessarily fulfilled in this crystalline material.…”