Isotopic effects in field desorption of hydrogen from tungsten

The observation of a higher brightness of hydrogen FIM images compared to that of deuterium can be interpreted as being due to the different ion rates. By using a pulsed laser atom probe with an additional E × B mass separator and a dual ion detector the field ion rates of the different species of hydrogen as well as the yield by laser stimulated field desorption of surface species were simultaneously recorded. Under the same conditions (temperature, pressure, field strength, monitored area) the rates of hydrogen were a factor of √2 higher, the same ratio was observed for the field dissociation of molecular hydrogen. The binding energy in the field (~ 100 meV) was only slightly higher for hydrogen. In coadsorption experiments the field assisted reaction to H3 was much more pronounced than that of D3. Also, a strong isotopic effect was observed in the temperature dependence of this reaction