Subnanometer Scale Mapping of Hydrogen Doping in Vanadium Dioxide

Abstract

Hydrogen donor doping of correlated electron systems such as vanadium dioxide (VO 2 ) profoundly modifies the ground state properties. The electrical behavior of H x VO 2 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 x VO 2 thin film focusing on the oxygen−hydrogen bonds using electron energy loss spectroscopy (EELS) coupled with firstprinciples EELS calculations. The hydrogen distribution was revealed to be nonuniform along the growth direction and between different VO 2 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.

Analytical electron microscopy analysis of insulating and metallic phases in nanostructured vanadium dioxide

“…40 Several studies have already exploited EELS near-edge fine structure to identify different stoichiometries of V x O y samples 41–48 or to study the hydrogenation of VO 2 . 49 However, to the best of our knowledge, studies using (S)TEM in combination with EELS were up to one exception 31 restricted to room temperature without the possibility of observing the changes when the material is switched to the high-temperature phase. Similarly, temperature-dependent low-loss STEM-EELS data that can be directly linked to optical properties are missing.…”