Diameter dependence of the electronic structure of ZnO nanorods determined by x-ray absorption spectroscopy and scanning photoelectron microscopy

Abstract

O K -, ZnL3, and K-edges x-ray absorption near-edge structure (XANES) spectra and scanning photoelectron microscopy (SPEM) spectra were obtained for ZnO nanorods with various diameters. The analysis of the XANES spectra revealed increased numbers of O2p and Zn4p unoccupied states with the downsizing of the nanorods, which reflects the enhancement of surface states when the diameter is decreased. Valence-band photoemission spectra show a significant narrowing of the valence band for the 45nm diameter nanorod. The Zn3d intensities in the Zn3d SPEM spectra are drastically diminished for all nanorods as compared to the ZnO reference film, which can be interpreted as a reduction in density of itinerant final states or in transition probability.

Defect induced ferromagnetism in Co-doped ZnO thin films

“…Zn L 2,3 XAS spectra shown in the inset of Fig. 2 (d) are in agreement with the XAS measurements at ZnO nanorods [21] and crystalline ZnO [22] corroborating that no significant Zn defect related features such as Zn interstitials are present in the samples. The spectroscopic measurements show that oxygen vacancies or oxygen related defects rather dominate than Zn interstitials.…”

Zn K-edge XANES in nanocrystalline ZnO

“…Finally, the increase of the amplitude of the main peak, observed in Zn K-edge XEOL XANES spectra of nanostructured ZnO films [6], can be due to the partial influence of polarization effect, the contribution from the oxygen terminated surfaces or the presence of oxygen vacancies in the first coordination shell of zinc in the bulk. Note that a change of this peak was also observed in the reference [5], devoted to ZnO nanorods of different diameters (d): the peak amplitude increases for nanorods with smaller diameter.…”

“…Zn K-edge XANES in ZnO was calculated using the ab initio FDMNES code and the obtained results were compared with available [3][4][5][6] experimental data. The effects of non-muffin-tin potential correction, cluster size, bulk defects, surface termination and polarization on the shape of the XANES signal were addressed with particular emphases on the variation of the main peak (at about 6 eV above the absorption edge) amplitude.…”

“…The influence of bulk defects, surface and polarization effects on XANES is discussed in attempt to explain few currently available experimental data [3][4][5][6].…”

Techniques for the Study of the Electronic Properties.

“…A general feature shared by all nanostructured oxide materials with size typically below 10-15 nm is that they display broader CRs with respect to well-crystallized references. 19,21,24,25,26,31,33,39 This can be observed in the inset of Figure 6.1; the derivative spectra give evidence of a larger overlap between CRs. The reason for this can be understood in terms of the f-rule.…”