LEIS analysis of the W surface during water vapor adsorption

The low energy ion spectroscopy (LEIS) experimental results of the steam adsorption by W samples are presented. It is shown that use of the ion scattering spectroscopy has allowed us to measure the thickness of adsorbate water layer on the tungsten surface with good accuracy. Tungsten at room temperature is completely covered by a water monolayer after 20 min (the partial steam pressure p≃2×10−5 Pa) of exposure. The water film thickness can be obtained by analyzing energy spectra of hydrogen ions scattering on surface. To transfer the energy scale (in energy spectra) into the depth scale with 10−15% accuracy one can use the approximation formula confirmed by simulation. In these experiments, the water film thickness on W does not exceed 40−45 Å.