Blistering in Molybdenum Foils under Exposure to the Glow Discharge of D2‒N2 Mixtures

Abstract

The evolution of indestructible blistering in molybdenum foils with the Mo {100} texture is investigated in dc glow discharge in a D₂–N₂ mixture with a nitrogen molar fraction in the mixture varying from zero to unity at 100 V potential negative with respect to plasma, a total pressure of 15 Pa, and temperatures of 30–60°C. After the addition of 0.01N₂ to the deuterium discharge, the surface area occupied by the blisters increases from 2 to 5% and reaches its maximum of 11% upon exposure to D₂−0.04N₂ mixture discharge (the fluence is 4 × 10¹⁹ cm^–2). Afterward, the area decreases, and blistering is absent in the pure N₂ discharge. The amount of deuterium desorbed from the samples upon heating also increases with the addition of nitrogen. In accordance with X-ray photoelectron spectroscopy data, a nitride layer about 5 nm thick is formed if small amounts of N₂ are added to D₂. This layer is assumed to slow both the recombination rate of atomic deuterium coming from the material bulk to the surface and the transfer of D₂ molecules into the gas phase. At the same time, the nitride layer increases the diffusion flux of D atoms into the foil bulk, promoting blister growth.