Pulsed laser stimulated field desorption of hydrogen from molybdenum
Abstract
The recently developed pulsed laser atom probe has been used to investigate the adsorption and dissociation of molecular hydrogen in high electric fields. The results indicate that at temperatures of 60 K and fields of 2.0 V/Å and higher, hydrogen is field adsorbed on molybdenum surfaces in molecular form. The activation energy of desorption is found to depend on the square of the applied electric field, in agreement with an expression previously derived for noble gas atoms. The desorption mechanism is shown to be a two-step process consisting of thermal release followed by field ionization and/or dissociation above the surface at xc (the critical distance of field ionization). Values of xc are obtained for H+, H2+, and He+, and it is shown that the probability of molecular dissociation at a given field strength can be predicted from simple energetic considerations. An expression relating the number of field adsorbed molecules on a surface with N adsorption sites to various experimental parameters is derived from an empirical rate equation, and data from the present study are shown to be in good agreement with the theoretical predictions.
- Publication:
-
Journal of Chemical Physics
- Pub Date:
- January 1981
- DOI:
- 10.1063/1.441162
- Bibcode:
- 1981JChPh..74.1479K
- Keywords:
-
- Desorption;
- Hydrogen;
- Molecular Ions;
- Molybdenum;
- Pulsed Lasers;
- Abundance;
- Activation Energy;
- Adsorption;
- Atom Concentration;
- Dissociation;
- Electric Field Strength;
- Laser Outputs;
- Atomic and Molecular Physics