Subnanometer Scale Mapping of Hydrogen Doping in Vanadium Dioxide.

Pofelski, Alexandre; Jia, Haili; Deng, Sunbin; Yu, Haoming; Park, Tae Joon; Manna, Sukriti; Chan, Maria K Y; Sankaranarayanan, Subramanian K R S et al. · Nano Lett · 2024

basic_science · Level V

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Abstract

Hydrogen donor doping of correlated electron systems such as vanadium dioxide (VO<sub>2</sub>) profoundly modifies the ground state properties. The electrical behavior of H<sub><i>x</i></sub>VO<sub>2</sub> is strongly dependent on the hydrogen concentration; hence, atomic scale control of the doping process is necessary. It is however a nontrivial problem to quantitatively probe the hydrogen distribution in a solid matrix. As hydrogen transfers its sole electron to the material, the ionization mechanism is suppressed. In this study, a methodology mapping the doping distribution at subnanometer length scale is demonstrated across a H<sub><i>x</i></sub>VO<sub>2</sub> thin film focusing on the oxygen-hydrogen bonds using electron energy loss spectroscopy (EELS) coupled with first-principles EELS calculations. The hydrogen distribution was revealed to be nonuniform along the growth direction and between different VO<sub>2</sub> grains, calling for intricate hydrogenation mechanisms. Our study points to a powerful approach to quantitatively map dopant distribution in quantum materials relevant to energy and information sciences.