THERMAL-DESORPTION OF POTASSIUM FROM CLEAN AND SULFUR COVERED NICKEL

Activation energy for thermal desorption of potassium from clean and s ulfur covered surfaces of nickel was determined by means of the field emission method. For the low potassium coverage limit (Theta(K) approx imate to 0.02) the desorption was detected from tile whole emitter sur face in the temperature range of 825-1000 Ii for the atoms and of 725- 825 Ii for the species of atoms and ions of the potassium. The activat ion energies of neutral desorption were found to be E(Ni)(a) = 3.8 eV for the clean nickel and E(S/Ni)(a) = 3.0 eV for the sulfur covered ni ckel, Theta(S) approximate to 0.5. The activation energies for tile de sorption of the species of atoms and ions increased from E(Ni)(a+1) = 2.5 eV for the clean nickel to E(S/Ni)(a+1) = 2.9 eV for the sulfur co vered nickel Theta(S) approximate to 0.5. Also, a value of E(S'/Ni)(a1) = 4.1 eV was found for a higher coverage of sulfur, Theta(S) approx imate to 1. The results are discussed in terms of Gurney model.