Surface and Internal Reactions of ZnO Nanowires: Etching and Bulk Defect Passivation by H Atoms

Reactions of ZnO nanowires (NWs) with atomic hydrogen were investigated with temperature-programmed desorption (TPD) mass spectrometry, scanning electron microscopy, and photoluminescence (PL) spectroscopy. During TPD, molecular H2, H2O, and atomic Zn desorbed from ZnO NWs pretreated with atomic H at 220 K. Three distinct H2 TPD peaks, two from surface H states and one from a bulk H state, were identified. The TPD assignment of the bulk H state was corroborated by significantly suppressed emission at 564 nm and enhanced emission at 375 nm in PL experiments. Etching of ZnO NWs by atomic H was confirmed by desorption of molecular H2O and atomic Zn in TPD and by electron microscopic images of H-treated ZnO NWs. A mechanistic model for underlying H/ZnO NW reactions is proposed and discussed.