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Influence of ion implantation on the charge storage mechanism of vanadium nitride pseudocapacitive thin films
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International audience. The influence of microstructural or structural defects is seldom investigated in pseudocapacitive electrodes. Indeed, most of the synthesized materials do present defects at every scales which contribute to the improvement of the charge storage. In this study VN thin films were deposited by reactive magnetron sputtering. The as-deposited VN films were compared with similar films implanted with arsenide cations (As+) with energies ranging from 20 keV up to 150 keV. The influence of the ionic implantation on the structure and microstructure of the pristine films was characterized by several techniques. The initial curing of the internal stress of as-deposited VN films observed for low implantation energies was lost with increasing implantation energy. Concomitantly, the electrochemical behaviors of the VN films were investigated. All the VN films show a pseudocapacitive behavior at 2 mV.s−1. At low scan rates, the as-deposited film exhibits the highest areal capacitance (45 mF.cm−2) which drastically decreases upon increasing the scan rate. Only 30% of the initial capacitance is maintained at 100 mV.s−1. Despite lower capacitances at 2 mV.s−1, As+ implanted VN films exhibit better capacitance retention in the same conditions, i.e. up to 65% of the initial capacitance is maintained at 100 mV.s−1. The contributions coming from surface and subsurface reactions have been determined which enable to propose possible origins for the changes occurring in charge storage mechanisms upon ion implantation.
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