Abstract
The diffusion properties of H+ in ZnO nanorods are investigated before and after 20 MeV proton beam irradiation by using 1H nuclear magnetic resonance (NMR) spectroscopy. Herein, we unambiguously observe that the implanted protons occupy thermally unstable site of ZnO, giving rise to a narrow NMR line at 4.1 ppm. The activation barrier of the implanted protons was found to be 0.46 eV by means of the rotating-frame spin-lattice relaxation measurements, apparently being interstitial hydrogens. High-energy beam irradiation also leads to correlated jump diffusion of the surface hydroxyl group of multiple lines at ~1 ppm, implying the presence of structural disorder at the ZnO surface.
Highlights
Electronic and diffusion properties of hydrogen in ZnO have been extensively studied, since efficient defect engineering is essential to fabricate electronic, ferroelectric, and optical devices[1,2,3,4]
It has been reported that radiation-induced defects cause the threshold voltage shift and the electrical conductance modulation, making them potentially applicable in nanoelectronic devices[7,10]
The hydroxyl groups on ZnO have been recently identified by observing their vibrational modes by infrared spectroscopy[13,14]
Summary
Electronic and diffusion properties of hydrogen in ZnO have been extensively studied, since efficient defect engineering is essential to fabricate electronic, ferroelectric, and optical devices[1,2,3,4]. Previous works addressed effects of proton implantation on electrical properties, it is still far from being well understood from a microscopic point of view. We observe atomic-scale features on protons and their diffusion properties in proton-implanted ZnO nanorods by using proton NMR spectroscopy. The rotating-frame relaxation rate, on the other hand, effectively probes motions occurring at ultralow-frequencies[21]. Mobile and rigid hydrogen species in ZnO have distinct values for the spectral density in the ultralow-frequency region, giving an opportunity to simultaneously investigate their diffusion properties[17,21]. We identify comprehensive hydrogen species in proton-implanted ZnO nanorods and investigate their dynamical properties by employing the rotating-frame spin-lattice relaxation technique. A broad resonance line before irradiation is denoted by H0, which is shifted upfield with increasing temperature. The resonance line at 4.1 ppm after irradiation is denoted by H3
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