Application of various methods for the determination of adsorption lifetime and desorption energy of oxygen on tungsten

The adsorption lifetime τ and the desorption energy Q of oxygen atoms on a polycrystalline tungsten surface have been determined as functions of the coverage θ by using a uhv mass spectrometer. A method based on contact potential and sticking probability measurements (T=1200–2500 K), a combined study of steady state and transient state desorption processes (T=2000–2600 K), and three different types of flash desorption measurements under single flight detection conditions (T=1900–2600 K) were employed. Satisfactory agreement of the results obtained from the different methods was observed. A compensation effect, depending on the coverage θ, was found between the pre-exponential factor of τ and the desorption energy Q which varies between 6.3 eV at θ=0 to 3.4 eV at θ=1. A further experiment employing a pulsed molecular beam method is in progress.