Control of Proton Propagation and Phase Transition in Hydrogenated VO₂

Proton (H⁺) doping effectively modulates the metal-insulator phase transitions of vanadium dioxide (VO₂) via its reversible incorporation into interstitial sites, providing exotic physical functionalities and emerging applications. Although selective area proton doping is crucial for neuromorphic electronics, the spatial proton propagation and the related phase transitions remain unclear. Herein, we demonstrate the control of proton propagation and the phase transitions of hydrogenated VO₂ films by engineering the size and spacing of platinum (Pt) catalysts. Raman spectroscopy reveals that protons propagate for ∼4 µm, with an accompanying phase transition, in VO₂ films modified with micro-sized Pt catalysts. Together with Kelvin probe force microscopy (KPFM) data, these results demonstrate that hydrogen diffusion induces three distinct phases in the H_xVO₂ film around the Pt catalyst. The electronic phase transitions can be well manipulated by controlling proton propagation. The Pt nanoparticle catalysts with nanometer spacing significantly enhance hydrogen propagation and accelerate the rich phase transitions of H_xVO₂ films at a low hydrogenation temperature (100°C). The proton-doping-induced phase transformation is further confirmed by theoretical calculations of the geometric and electronic structures. The insights into spatial proton propagation provide critical guidance for controlling the electronic phase transitions and optimizing the energy-efficient VO₂-based ionic and electronic applications.