Thermal desorption from metal surfaces: A review

Adsorption of hydrogen on Ni(111), (100), and (110) surfaces was studied by means of LEED; energy loss spectroscopy, flash desorption, and work function measurements, as well as by the technique of laser‐induced thermal desorption. Noticeable variations of the LEED intensities for Ni(111) and (100) indicate the formation of disordered adsorbed layers, whereas with Ni(110) the formation of ``streaked'' diffraction patterns and (at high coverages) of a 1×2 structure were observed. Hydrogen adsorption causes a strong damping of the intensity of the surface plasmon excitation and the appearance of an electron loss peak around 15 eV. Flash desorption experiments revealed for Ni(111) and Ni(100) the existence of β1 and β2 states, the former being only filled after completion of the β2 state. Desorption from the β2 state follows a second‐order rate law for Ni(111) and Ni(100), but is of first order with Ni(110). Maximum increases of the work function Δ φ by 0.195, 0.170, and 0.530 eV were observed with Ni(111), ...

Adsorption of hydrogen on nickel single crystal surfaces

Field Emission Energy Distribution (FEED)

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

Displacive surface phases formed by hydrogen chemisorption on W{001}

Total energy distributions of field emitted electrons from the tungsten (110) and (100) planes as a function of coverage by hydrogen and deuterium have been recorded utilizing a spherical deflection energy analyzer. The elastic tunneling resonance spectrum gives a plot of the 'local density of states' in the adsorbate. The inelastic tunneling spectrum reveals those discrete excitation energies available in the adsorbate-substrate complex. These spectroscopic data have been used to infer the chemical nature of the binding states which have been observed in the flash desorption spectrum of hydrogen from tungsten.

A. E. Bell

Papers

Field Emission Energy Distributions of Hydrogen and Deuterium on the (100) and (110) Planes of Tungsten