Hydrogen- and corrosion-induced defect characterization of ZnO single crystal: A slow positron beam study

Abstract

Hydrogen-and corrosion-induced microstructure and defects of ZnO single crystal under acidic conditions have been studied by using slow positron beam spectroscopy and microscopy techniques. Slow positron beam measurements revealed that a near-surface damaged region with a high concentration of defects was formed after hydrogen charging, but not after corrosion. The formation of hexagonal pyramids was found after electrochemical charging with hydrogen, while the formation of stepped hexagonal pits was observed after direct immersion in the solution. The incorporation of hydrogen by electrochemical charging enhanced the near-band-edge (NBE) emission intensity.

Interaction of hydrogen with defects in ZnO nanoparticles – studied by positron annihilation, Raman and photoluminescence spectroscopy

“…Electrochemical charging with hydrogen into ZnO single crystals leads to the formation of hexagonal pyramids at the surface, 24 and the enhancement of near-band-edge (NBE) emission is ascribed to H O . 25 The diffusion of hydrogen into a solid via annealing in H 2 gas is a process close to thermodynamic equilibrium. Formation of a hydroxyl group was seen when ZnO nanoparticles were exposed to 3% H 2 in N 2 at 300 °C.…”

Importance of doping, dopant distribution, and defects on electronic band structure alteration of metal oxide nanoparticles: Implications for reactive oxygen species

“…Furthermore, rigorous and detailed characterizations of dopants and/or defects also are critical. Such characterization can be performed with X-ray diffraction (Wang et al, 2006), nano beam diffraction with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) (Ward et al, 2014), slow positron beam spectroscopy (Xue et al, 2013), photo-luminescent (PL) emission (Sekiguchi et al, 2000;Zhang et al, 2014), X-ray absorption spectroscopy (XAS) (Brown and Parks, 2001;Rossi et al, 2014;Waychunas and Zhang, 2008), X-ray standing wave measurements , and X-ray spectromicroscopy (STXM) (Chen et al, 2014;Myneni et al, 1999;Warwick et al, 1998). Not only material scientists but also nanotxicologists can add these characterization tools to the routine assessment sequence, depending on the ROS-generation ability of the MONPs (predicted or characterized by the material scientists).…”