Understanding the interaction between atomic hydrogen and solid tungsten is important for the development of fusion reactors in which proposed tungsten walls would be bombarded with high energy particles including hydrogen isotopes. Here, we report results from periodic density-functional theory calculations for three crucial aspects of this interaction: surface-to-subsurface diffusion of H into W, trapping of H at vacancies, and H-enhanced decohesion, with a view to assess the likely extent of hydrogen isotope incorporation into tungsten reactor walls. We find energy barriers of (at least) 2.08 eV and 1.77 eV for H uptake (inward diffusion) into W(001) and W(110) surfaces, respectively, along with very small barriers for the reverse process (outward diffusion). Although H dissolution in defect-free bulk W is predicted to be endothermic, vacancies in bulk W are predicted to exothermically trap multiple H atoms. Furthermore, adsorbed hydrogen is predicted to greatly stabilize W surfaces such that decohesion (fracture) may result from high local H concentrations.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400006075

Hydrogen in tungsten: Absorption, diffusion, vacancy trapping, and decohesion

Structural analysis of surfaces by LEED

Reconstruction of Clean and Adsorbate-Covered Metal Surfaces.

https://escholarship.org/content/qt0t7356ch/qt0t7356ch.pdf?t=p0t0uv

Directed search methods for surface structure determination by LEED

High-resolution helium-atom-scattering measurements of angular distributions and time-of-flight spectra are reported for W(001) in the temperature range from 200 to 1900 K. Angular variations in the total intensity show a reconstruction related superstructure peak whose angular position and intensity are temperature dependent in the range from 400 to 220 K. At 220 K the peak intensity is maximum and its position corresponds to that expected for a reconstructed (√2×√2) R45 o low-temperature phase

Helium-atom-scattering study of the structure and phonon dynamics of the W(001) surface between 200 and 1900 K.

A LEED structure analysis is performed for the W(100) c(2*2) surface reconstruction. Models with pure vertical displacements of the surface atoms can be clearly ruled out while others with predominant lateral displacements in the (11) and (01) directions result in a very good agreement with the experimental curves. However, a clear discrimination between these models is prevented by the insensitivity of normal incidence spectra to the direction of atomic displacements parallel to the surface. A minimum Pendry r-factor of r=0.26 is achieved for a refined model suggested by Debe and King (1979) with a multilayer relaxation (first inter-layer spacing d12=witht1.47 AA second inter-layer spacing d23=1.60 AA, and a reconstruction in the first and second layer with lateral displacements in the (11) direction (first layer: 0.24 AA; second layer: 0.02 AA).

G. Schmidtlein

Papers

LEED intensity analysis of the clean W(100) c(2×2) surface reconstruction

A disordered model for the W(100)1×1 surface