Cryo-electron energy loss spectroscopy: observations on vitrified hydrated specimens and radiation damage.

Abstract

Valence-band EELS was applied to characterize frozen-hydrated specimens in electron microscopy. Energy-loss fine structure below 30 eV allowed discrimination between vitreous and crystalline ice phases, interpreted through molecular orbital transitions in water and solid-state excitons. Quantitative water content estimation in hydrated biological specimens was achieved by spectral decomposition into ice and organic contributions. Radiation chemistry under electron beam exposure was also investigated: detection of the hydrogen K-edge near 13 eV indicated that molecular hydrogen bubbles form at doses exceeding 10⁴ nm⁻², with internal gas pressures calculated to surpass one thousand atmospheres.

Mechanism

Electron beam irradiation at doses above 10⁴ nm⁻² causes radiolytic decomposition of water molecules in frozen-hydrated specimens, generating molecular hydrogen bubbles detectable via the H K-edge at ~13 eV, with internal pressures exceeding 1000 atmospheres.