Effects of monolayer coverages on substrate sputtering yields

Materials currently being used or considered for plasma-side applications are not entirely satisfactory, particularly in the medium edge temperature (approx. 100 to 300 eV) regime. A new approach to impurity control based on self-sustaining surface segregated low-Z layers with high secondary ion fractions has been suggested and tested in laboratory experiments. A crucial requirement is that substrate sputtering yields be reduced about an order of magnitude by monolayer adsorbate coverages. Theoretical and experimental evidence is adduced to support the contention that overlayer coverages (a monolayer of Li on Cu) result in profound reductions of substrate (e.g., Cu) sputtering yields. The conclusion that a material such as a dilute alloy of Li in Cu could function as a limiter or a divertor plate material is, in part, based on the fact that more than 85% of the sputtered flux originates in the first atomic layer (e.g., Li) of the target