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Activation energy for thermal desorptioii of potassium from clean and sulfur covered surfaces of nickel was determined by means of the field emission method. For the low potassium coverage limit (θK 0.02) the desorption was detected from the whole emitter surface in the temperature range of 825-1000 K for the atoms and of 725-825 K for the species of atoms and ions of the potassium. The activation energies of neutral desorption were found to be EaNi = 3.8 eV for the clean nickel and Es /Ni = 3.0 eV for the sulfur covered nickel, θs 0.5. The activatioii energies for the desorptioii of the species of atoms and ions increased from E ti = 2.5 eV for the clean nickel to Ea+iS/Ni = 2.9 eV for the sulfur covered nickel θs 0.5. Also, a value of Ea+iS'/Ni = 4.1 eV was found for a higher coverage of sulfur, θs 1. The results are discussed in terms of Gurney model.

Interaction of hydrogen with vanadium layers preadsorbed on a thermally cleaned tungsten field emitter was studied at room temperature and 78 K through measurements of the total work function changes. An increase in the work function followed by its slight decrease at higher exposure can be understood taking into account the possibility of negatively (β -) and positively (β+) polarized adspecies formation on thin vanadium layer. This process leads to vanadium hydride formation. The work function results suggest that hydrogen diffusion into the vanadium layer is meaningful at room temperature. Thermal desorption of hydrogen adsorbate carried out within the temperature range 409-461 K from thin va^iadium layer (θv = 40) provided a value of 127 ± 6 kJ/mol for the activation energy for desorption.

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