Hydrogen collisions with transition metal surfaces: Universal electronically nonadiabatic adsorption

Inelastic scattering of H and D atoms from the (111) surfaces of six fcc transition metals (Au, Pt, Ag, Pd, Cu, and Ni) was investigated, and in each case, excitation of electron-hole pairs dominates the inelasticity. The results are very similar for all six metals. Differences in the average kinetic energy losses between metals can mainly be attributed to different efficiencies in the coupling to phonons due to the different masses of the metal atoms. The experimental observations can be reproduced by molecular dynamics simulations based on full-dimensional potential energy surfaces and including electronic excitations by using electronic friction in the local density friction approximation. The determining factors for the energy loss are the electron density at the surface, which is similar for all six metals, and the mass ratio between the impinging atoms and the surface atoms. Details of the electronic structure of the metal do not play a significant role. The experimentally validated simulations are used to explore sticking over a wide range of incidence conditions. We find that the sticking probability increases for H and D collisions near normal incidence-consistent with a previously reported penetration-resurfacing mechanism. The sticking probability for H or D on any of these metals may be represented as a simple function of the incidence energy, E_in, metal atom mass, M, and incidence angle, 𝜗_in. S=(S₀+a⋅E_in+b⋅M)*(1-h(𝜗_in-c)(1-cos(𝜗_in-c)^d⋅h(E)), where h is the Heaviside step function and for H, S₀ = 1.081, a = -0.125 eV^-1, b=-8.40⋅10^-4 u^-1, c = 28.88°, d = 1.166 eV^-1, and e = 0.442 eV; whereas for D, S₀ = 1.120, a = -0.124 eV^-1, b=-1.20⋅10^-3 u^-1, c = 28.62°, d = 1.196 eV^-1, and e = 0.474 eV.