Electron-hole pair excitation determines the mechanism of hydrogen atom adsorption

Abstract

How much translational energy atoms and molecules lose in collisions at surfaces determines whether they adsorb or scatter. The fact that hydrogen (H) atoms stick to metal surfaces poses a basic question. Momentum and energy conservation demands that the light H atom cannot efficiently transfer its energy to the heavier atoms of the solid in a binary collision. How then do H atoms efficiently stick to metal surfaces? We show through experiments that H-atom collisions at an insulating surface (an adsorbed xenon layer on a gold single-crystal surface) are indeed nearly elastic, following the predictions of energy and momentum conservation. In contrast, H-atom collisions with the bare gold surface exhibit a large loss of translational energy that can be reproduced by an atomic-level simulation describing electron-hole pair excitation.

Communication: Hot-atom abstraction dynamics of hydrogen from tungsten surfaces: The role of surface structure

“…For hydrogen atoms and molecules interacting with metallic surfaces at low coverage, for which collisions with pre-adsorbed species are unlikely, the main energy dissipation channel in the picosecond time scale is the excitation of low lying e-h pairs. [45][46][47][48][49][50][51][52] As such an effect depends on the surface electronic structure, its sensitivity to the crystal face is a relevant issue that we address in the present study. To this end, we compare, in the following, the dynamics of H 2 formation by abstraction of pre-adsorbed H atoms upon H atom scattering at finite coverage for the W(100) and W(110) surfaces.…”

“…In the latter, electronic nonadiabaticity is introduced through a dissipative force in the classical equations of motion for the hydrogen atoms. This approach has already been used to investigate non-adiabatic effects in gas-surface elementary processes 46,[48][49][50][51][61][62][63] and allows a good compromise between accuracy and simplicity. 51,64 The friction force, acting independently on each H atom, is approximated as the one corresponding to a homogeneous free electron gas with electronic density equal to that of the bare surface at the atom position.…”

“…This approach has already been used to investigate non-adiabatic effects in gas-surface elementary processes 46,[48][49][50][51][61][62][63] and allows a good compromise between accuracy and simplicity. 51,64 The friction force, acting independently on each H atom, is approximated as the one corresponding to a homogeneous free electron gas with electronic density equal to that of the bare surface at the atom position. This approximation has been recently used to rationalize the adsorption and relaxation of H, N, and N 2 on bare metallic surfaces, 46,48,50 as well as for recombinative H 2 desorption induced by fs-laser pulses.…”

Ab-<i>initio</i> studies of adsorbate-surface interactions

“…If we repeat the above procedure for the spatial derivative with respect to the nuclear position, i.e., ∇ n β β * = 0, we get the following identity: 48) where…”

“…Investigating this problem is important because, even though we know that the Hydrogen atom colliding against a metallic surface has a huge technological applications and importance for many fields of science [45][46][47] , we still do not have a deep knowledge of how this phenomenon happens. 48 This investigation is also instructive, as yet, no practical application of the newly developed formalism has been presented, although the method of exact factorization has been used to compute the time-dependence potential energy surfaces for problems that can be solved, either analytically or numerically, by alternative procedures.…”