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Herein we investigate absorption and desorption of hydrogen in the sub-surface of tungsten via density functional theory. Both the near-surface diffusion and recombination of a bulk hydrogen atom with a hydrogen atom adsorbed upon the W(1 1 0) and W(1 0 0) surfaces are investigated at various surface adsorption coverage ratios. This study intends to model the desorption processes occurring during thermal-desorption spectroscopy experiments and the absorption of hydrogen during gaseous or low energy atomic exposure. Since the diffusion and recombination processes are expected to change as the hydrogen coverage of the surface varies, different coverage ratios were investigated on both surfaces. We found that at a saturation coverage of hydrogen on both surfaces, the activation barriers for the recombination of molecular hydrogen are below 0.8 eV. On the contrary, below saturation, the activation barriers for recombination rise to 1.35 eV and 1.51 eV depending on the coverage and on the orientation of the surface. Regarding the absorption of atomic hydrogen from the surface into the bulk, the activation barrier raises from less than 1.0 eV at saturation to around 1.7 eV below saturation on both surfaces. These results indicate that surface mechanisms certainly play a significant role in the kinetics of desorption of hydrogen from tungsten; it is also expected that surface mechanisms affect the total amount on hydrogen absorbed in tungsten during implantation. [ABSTRACT FROM AUTHOR]

This study demonstrates that Raman microscopy is a suitable technique for future post mortem analyses of JET and ITER plasma facing components. We focus here on laboratory deposited and bombarded samples of beryllium and beryllium carbides and start to build a reference spectral databases for fusion relevant beryllium-based materials. We identified the beryllium phonon density of states, its second harmonic and E2G and B2G second harmonic and combination modes for defective beryllium in the spectral range 300–700 and 700–1300 cm−1, lying close to Be–D modes of beryllium hydrides. We also identified beryllium carbide signature, Be2C, combining Raman microscopy and DFT calculation. We have shown that, depending on the optical constants of the material probed, in depth sensitivity at the nanometer scale can be performed using different wavelengths. This way, we demonstrate that multi-wavelength Raman microscopy is sensitive to in-depth stress caused by ion implantation (down to  ≈30 nm under the surface for Be) and Be/C concentration (down to 400 nm or more under the surface for Be+C), which is a main contribution of this work. The depth resolution reached can then be adapted for studying the supersaturated surface layer found on tokamak deposits. [ABSTRACT FROM AUTHOR]