Observation of Diffusion and Desorption of Hydrogen in Molybdenite.

Diffusion and desorption of hydrogen in a bulk of molybdenite crystal are studied by measurement of gas emitted from the bulk crystal during cleavage experiment for observation of gases in a bulk, electron stimulated desorption (ESD) for measurement of hydrogen concentration on the surface and temperature programmed desorption (TPD) for estimating ion of an activation energy of diffusion and desorption process. The cleavage and ESD experiments are performed to observe the change of hydrogen concentration in the bulk and on the surface by the sample heating. These experiments show that a mount of hydrogen in the bulk reduces at about 500°C and that the hydrogen concentration on the surface and thermal desorption of hydrogen from the bulk also begin to increase around 500°C. The increase of hydrogen concentration on the surface suggests that the activation energy for thermal desorption is lager than the diffusion energy in the bulk to (0001) surface. However, in this case this may not be applicable because of similar temperature behavior of surface hydrogen and desorbed hydrogen. The mechanism of the diffusion and the desorption process is discussed. The activation energy for the desorption induced by diffusion of hydrogen in the bulk to (0001) surface is about 76 kJ/mol.