Influence of helium-ion bombardment on the surface properties of pure and ammonia-adsorbed water thin films

摘要

The influence of the ion bombardment on the surface properties of water-ice films has been investigated. The films are irradiated with 1.5 keV He~+ ions and analyzed sequentially on the basis of time-of-flight secondary-ion mass spectrometry (TOF-SIMS). In order to minimize any temperature-induced effects, the measurements were made at 15 K. The damage of the films, as estimated from the H/D exchange between NH_3 and the D_2O ice and the intermixing of NH_3 with the H_2~(18)O ice, is recognized at the fluence above 2 x 10~(14) ions/cm~2. The sputtering yield of the D_2O ice is determined as 0.9 ± 0.2 molecules per incoming He~+ ion. The temperature-programmed TOF-SIMS analysis of the water-ice films has been completed within the fluence of 5.8 x 10~(12) ions/cm~2, so that no appreciable damage of the film should be induced during the measurement.