Deuterium Retention and Release Behavior from Beryllium Co-Deposited Layers at Distinct Ar/D Ratio

Abstract

Beryllium-deuterium co-deposited layers were obtained using DC magnetron sputtering technique by varying the Ar/D2 gas mixture composition (10/1; 5/1; 2/1 and 1:1) at a constant deposition rate of 0.06 nm/s, 343 K substrate temperature and 2 Pa gas pressure. The surface morphology of the layers was analyzed using Scanning Electron Microscopy and the layer crystalline structure was analyzed by X-ray diffraction. Rutherford backscattering spectrometry was employed to determine the chemical composition of the layers. D trapping states and inventory quantification were performed using thermal desorption spectroscopy. The morphology of the layers is not influenced by the Ar/D2 gas mixture composition but by the substrate type and roughness. The increase of the D2 content during the deposition leads to the deposition of Be-D amorphous layers and also reduces the layer thickness by decreasing the sputtering yield due to the poisoning of the Be target. The D retention in the layers is dominated by the D trapping in low activation binding states and the increase of D2 flow during deposition leads to a significant build-up of deuterium in these states. Increase of deuterium flow during deposition consequently leads to an increase of D retention in the beryllium layers up to 300%. The resulted Be-D layers release the majority of their D (above 99.99%) at temperatures lower than 700 K.

Deuterium Retention in Mixed Layers with Application in Fusion Technology

“…This is emphasized by the morphology of the W33 sample (Figure 2d), where surface voids and defects are observed. These surface characteristics were also noticed for Be layers deposited on tungsten substrates in a previous work performed by the authors [41]. As it was underlined there the main cause can be the chemical and roughness difference between the Si and W substrates.…”

“…BeD 2 formation was only observed for the W33 sample and one can argue that the high Be concentration in this sample is the main reason. However, a crystalline phase corresponding to BeD 2 was not observed for the Be layers presented in this study or in previous studies where the layers were produced using the direct current magnetron sputtering technique [36,38,41]. Thus, the formation of these compounds here is not clearly understood.…”

“…The D trapping mechanisms are similar to thoseobserved for the sample with the highest Be content among the mixed layers (W33), namely BeO-D and D trapping in defects. In a previous study, the authors investigated the D retention in Be in relation to the D 2 flow introduced into the chamber [41]. The resulting samples showed minimum O contamination (2 at %) and one of the Be layers was obtained with the exact deposition conditions as the one in our current study (pressure, temperature, D 2 and Ar flow) in the same coating facility [41].…”

“…During TDS measurements, the release of multiple gaseous species from the sample was monitored with an emphasis on mass 3 and mass 4, corresponding to HD and D2, respectively. As was observed in an earlier study [41], the release of D atoms from the codeposited samples was mainly dominated by D2, unlike the HD dominated release from implanted layers [36]. To quantify the D2 release, calibrations were performed by leaking known amounts of D2 into the TDS chamber.…”

“…In a previous study, the authors investigated the D retention in Be in relation to the D 2 flow introduced into the chamber [41]. The resulting samples showed minimum O contamination (2 at %) and one of the Be layers was obtained with the exact deposition conditions as the one in our current study (pressure, temperature, D 2 and Ar flow) in the same coating facility [41]. These provide us with the opportunity to compare both samples given the identical deposition conditions and to assess the influence of oxygen on D release.…”