Negative charge delivery in ice via proton-hole transfer

Abstract

Water ice has been regarded as a “p-type semiconductor,” with the excess protons in ice serving as the positive charge carrier. Although ice is considered to be an insulator at very low temperatures, we recently found that ice has electrical conductivity via negative charge delivery even at temperatures around 10 K when simultaneously irradiated with ultraviolet photons and electrons, indicating that ice serves as an “n-type semiconductor” as well. Based on experimental and theoretical investigations, we propose that the carrier of the negative charge conductivity is the OH⁻ ion, called the proton-hole, and OH⁻ moves toward the interior of ice by repeated proton abstractions from neighboring H₂O molecules, namely the proton-hole transfer mechanism.