Electron–Proton Co‐doping‐Induced Metal–Insulator Transition in VO2 Film via Surface Self‐Assembled l‐Ascorbic Acid Molecules.

Charge doping is an effective way to induce the metal–insulator transition (MIT) in correlated materials for many important utilizations, which is however practically limited by problem of low stability. An electron–proton co‐doping mechanism is used to achieve pronounced phase modulation of monoclinic vanadium dioxide (VO2) at room temperature. Using l‐ascorbic acid (AA) solution to treat VO2, the ionized AA− species donate electrons to the adsorbed VO2 surface. Charges then electrostatically attract surrounding protons to penetrate, and eventually results in stable hydrogen‐doped metallic VO2. The variations of electronic structures, especially the electron occupancy of V 3d/O 2p hybrid orbitals, were examined by synchrotron characterizations and first‐principle theoretical simulations. The adsorbed molecules protect hydrogen dopants from escaping out of lattice and thereby stabilize the metallic phase for VO2. [ABSTRACT FROM AUTHOR]