Nb interaction with hydrogen plasma

Abstract

A niobium membrane was immersed in hydrogen plasma and could be electrically biased to vary the energy of bombarding ions in the range of 1–200 eV. The fluxes of plasma driven absorption and permeation were almost entirely governed by incident suprathermal neutrals (mostly, thermal atoms), whose energy does not depend on membrane bias, but the ions of controllable energy do affect the neutral-induced permeation through modifying the membrane surface. At the zero bias a high temperature-independent plasma driven permeation (superpermeation) was observed alongside of an enhanced absorption. Bombardment by ions of an energy higher than 50 eV resulted in a sharp decrease of the plasma driven permeation/retention and in an acceleration of boundary processes of absorption/reemission of thermal molecules. At ion energies below 50 eV, the effect of ion bombardment on the plasma driven permeation and the kinetic coefficients of boundary processes were nonmonotonic in ion energy, having a maximum at ∼10 eV. Both an in situ doping with O of the bulk of Nb and a membrane temperature increase reduced the effects of ion bombardment to their complete disappearance. Responsible for that was the replenishment by means of surface segregation of an oxygen monolayer sputtered by ion bombardment.