Thermal Desorption of Potassium from Clean and Sulfur Covered Nickel

Activation energy for thermal desorption 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 (Θ$\text{}_{K}$ ≈ 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 E$\text{}_{Ni}^{a}$ = 3.8 eV for the clean nickel and E$\text{}_{S}\text{}_{/}\text{}_{Ni}^{a}$ = 3.0 eV for the sulfur covered nickel, Θ$\text{}_{s}$ ≈ 0.5. The activation energies for the desorption of the species of atoms and ions increased from E$\text{}_{Ni}^{a+i}$ = 2.5 eV for the clean nickel to E$\text{}_{S}\text{}_{/}\text{}_{Ni}^{a+i}$ = 2.9 eV for the sulfur covered nickel Θ$\text{}_{s}$ ≈ 0.5. Also, a value of E$\text{}_{S'}\text{}_{/}\text{}_{Ni}^{a+i}$ = 4.1 eV was found for a higher coverage of sulfur, Θ$\text{}_{s}$ ≈ 1. The results are discussed in terms of Gurney model.