Influence of Atomic Hydrogen, Band Bending, and Defects in the Top Few Nanometers of Hydrothermally Prepared Zinc Oxide Nanorods

Abstract

We report on the surface, sub-surface (top few nanometers) and bulk properties of hydrothermally grown zinc oxide (ZnO) nanorods (NRs) prior to and after hydrogen treatment. Upon treating with atomic hydrogen (H*), upward and downward band bending is observed depending on the availability of molecular H2O within the structure of the NRs. In the absence of H2O, the H* treatment demonstrated a cleaning effect of the nanorods, leading to a 0.51 eV upward band bending. In addition, enhancement in the intensity of room temperature photoluminescence (PL) signals due to the creation of new surface defects could be observed. The defects enhanced the visible light activity of the ZnO NRs which were subsequently used to photocatalytically degrade aqueous phenol under simulated sunlight. On the contrary, in the presence of H2O, H* treatment created an electronic accumulation layer inducing downward band bending of 0.45 eV (~1/7th of the bulk ZnO band gap) along with the weakening of the defect signals as observed from room temperature photoluminescence spectra. The results suggest a plausible way of tailoring the band bending and defects of the ZnO NRs through control of H2O/H* species.

Stabilization of the Surface of ZnO Films and Elimination of the Aging Effect

“…The FWHM of the peaks increases (Table 1), and the intensity of the peaks decreases. Possible explanations for the decrease in peak intensity are related to the surface potential [32] and the presence of a thin contaminating layer on the surface. However, the presence of a surface potential should cause a shift not only of the Zn lines, but also of the oxygen lines.…”

Dye wastewater treatment enabled by piezo-enhanced photocatalysis of single-component ZnO nanoparticles

“…The green P3 emission is attributed to the singly ionized oxygen vacancies. 41,47 Both blue and green emissions were observed in the as-synthesized ZnO TW-0.20 and the calcined sample with comparable peak intensities, implying that the calcination did not signicantly affect the presence of native defects. However, the orange-red P4 peak disappeared in the PL spectra of calcined ZnO TW-0.20 .…”

“…On the other hand, blue (P2), green (P3), and orange-red (P4) emissions of ZnO have been well described by various reports. 41,47,48 The blue P2 peak is oen corresponded to oxygen vacancies 49 or Zn interstitials 47 which are the native defects of ZnO. The green P3 emission is attributed to the singly ionized oxygen vacancies.…”

Elucidating the growth mechanism of ZnO films by atomic layer deposition with oxygen gas via isotopic tracking

“…The two structures around 4 eV and 7.5 eV are mainly due to electrons in the O 2p orbitals and the O 2p-Zn 4sp hybridized state respectively. [31][32][33] An increase of the O 2p-Zn 4sp states, meaning these orbitals are more populated, is observed when oxygen gas is added during the synthesis process and is linked to a higher number of zinc atoms surrounded by oxygen atoms (O and/or OH) in the final wurtzite structure, thus decreasing the vacancy density in the film. Furthermore, the valence band positions of the two samples (determined without any energy calibration) clearly show a shift of 0.5 eV.…”