Hydrogen retention in beryllium: concentration effect and nanocrystalline growth

Abstract

We herein report on the formation of BeD2 nanocrystalline domes on the surface of a beryllium sample exposed to energetic deuterium ions. A polycrystalline beryllium sample was exposed to D ions at 2 keV/atom leading to laterally averaged deuterium areal densities up to 3.5 10(17) D cm(-2), and studied using nuclear reaction analysis, Raman microscopy, atomic force microscopy, optical microscopy and quantum calculations. Incorporating D in beryllium generates a tensile stress that reaches a plateau at ≈1.5 10(17) D cm(-2). For values higher than 2.0 10(17) cm(-2), we observed the growth of ≈90 nm high dendrites, covering up to 10% of the surface in some zones of the sample when the deuterium concentration was 3 × 10(17) D cm(-2). These dendrites are composed of crystalline BeD2, as evidenced by Raman microscopy and quantum calculations. They are candidates to explain low temperature thermal desorption spectroscopy peaks observed when bombarding Be samples with D ions with fluencies higher than 1.2 10(17) D cm(-2).

Preparing the future post-mortem analysis of beryllium-based JET and ITER samples by multi-wavelengths Raman spectroscopy on implanted Be, and co-deposited Be

“…In a recent study we found the same groups of bands at 270, 615, 909 cm -1 , but we also observed a group of two bands at 1710 cm -1 which could be related to surface modes, as the surface to volume ratio was high in our sample, as measured by atomic force microscopy [38] , The 270, 615 and 909 cm -1 groups may be due to a BeD 2 close to a body centered orthorhombic structure with I bam symmetry.…”

“…the answer is not necessarily "yes". For example in [27] we were not able to detect Be-N nor Be-D bonds whereas we were able to do so in [38] by identifying BeD 2 hydrides. Then, here by "defects", we mean every kind of defects that can modify the long range crystallographic order of a pristine crystal, the holy grail to reach with this technique being to be defect-sensitive for every material studied.…”

“…Be, an illustration of this complementarity, in [38], is that we have identified with laboratory experiments the growth of BeD 2 with dendritic forms appearing subsequently to 2 keV ion implantation when the Be layer is saturated by implanted D ions. The width of the bands recorded by…”

“…By taking into account the volume probed by the laser for BeD 2 , (100-200 nm depth penetration as evidenced in [38]) and compared to the monoatomic layer of graphene, then we can conclude that the Raman cross section is ≈300 times smaller in the case of BeD 2 than in the case of graphene.…”

“…In [38], we have showed that these dendrites appear when the amount of deuterium in the material is higher than ≈ 2 10 17 D.cm -2 , when the ≈ 40 nm under surface layer is saturated by D.…”