Transmission and Trapping of Low-Energy (1–10 eV) Electrons in Crystalline Ice Films

Abstract

We studied the interactions between low-energy (1–10 eV) electrons and a crystalline ice film in a low fluence condition, where incident electrons interacted mostly with the pristine ice lattice. The electron beams were irradiated onto an ice film sample of large thickness (>100 monolayers) at 95 K. The kinetic energy and flux of incident electrons were maintained constant by applying an offset bias potential to the sample to compensate the charging voltage of an ice film developed by electron trapping. A Kelvin work-function probe was used to measure the charging voltage and estimate the electron trapping efficiency. The measurements for ice films with different thicknesses showed that low energy electrons transmitted through the ice films very efficiently. When electrons were trapped in the ice films, the trapping occurred preferentially at the surface of ice films. The electron trapping cross-section for the ice surface was estimated to be ≤(2.6 ± 0.3) × 10–23 m2 at the incident electron energy of 1–10 eV. The electron trapping cross-section for the ice interior was below ∼10–25 m2. In comparison, adsorbed SO2 and CFCl3 molecules on the ice surface were able to trap incident electrons much more efficiently than the surface water molecules, with corresponding cross sections of (1.1 ± 0.4) × 10–21 m2 and (2.8 ± 0.3) × 10–21 m2, respectively.

Proton Transport and Related Chemical Processes of Ice

“…They proposed that the negative current results from electron attachment to OH radicals and the transport of resultant OH − ions through ASW via a proton-hole transfer mechanism. The negative current, however, may originate from multiple sources in these experiments, including electron transmission through ASW, 97,98 electron attachment to OH radicals and defect structures in ASW, as well as the proposed OH − transport. These various possibilities weaken the proposal of OH − transport via a proton-hole transfer mechanism.…”

Behavior of Hydroxyl Radicals on Water Ice at Low Temperatures

“…As shown in Figure (b), a negative constant current was observed during the operation of the UV lamp. This was the first finding on the negative current conductivity of ASW below 50 K. We note that transmission of electron is significantly suppressed at temperatures below 50 K. − To further elucidate the role of UV photons, the second experiment depicted in Figure (c) was performed. In this experiment, UV photons were supplied through a glass capillary plate mounted at the top of the guide to block photoelectrons generated within the guide, and electrons were separately provided by an electron gun placed in front of the substrate.…”