Oberflächenionisation und desorptionskinetik von indium an reinen und sauerstoffvorbelegten wolframoberflächen

Abstract A mass spectrometric study of surface ionization and desorption kinetics of indium on recrystallized tungsten ribbons is reported. The degree of ionization α and the mean residence time τ were measured as functions of the temperature T between 1000 K and 2800 K and of the oxygen surface coverage θ o at oxygen partial pressures p o 2 between 4 × 10 −10 Torr and 1 × 10 −6 Torr. From the analysis of the In + desorption current in modulated beam experiments values of τ between 10 3 s and less than 10 −4 s could be determined using either a recorder, an oscilloscope or a lock-in amplifier. From simultaneous measurements of τ and α the desorption probabilities per unit time of ionic and atomic desorption of the In adparticles, P i and P a , are determined separately at different values of θ o . From the temperature dependence of these quantities the corresponding desorption energies E i and E a are represented as functions of the surface coverage θ o of the pre-adsorbed oxygen.