Electronic excitations induced by hydrogen surface chemical reactions on gold

Abstract

Associated with chemical reactions at surfaces energy may be dissipated exciting surface electronic degrees of freedom. These excitations are detected using metal-insulator-metal (MIM) heterostructures (Ta-TaOx-Au) and the reactions of H with and on a Au surface are probed. A current corresponding to 5×10(-5) electrons per adsorbing H atom and a marked isotope effect are observed under steady-state conditions. Analysis of the current trace when the H atom flux is intermitted suggests that predominantly the recombination reaction creates electronic excitations. Biasing the front versus the back electrode of the MIM structure provides insights into the spectrum of electronic excitations. The observed spectra differ for the two isotopes H and D and are asymmetric when comparing negative and positive bias voltages. Modeling indicates that the excited electrons and the concurrently created holes differ in their energy distributions.

Electronic Friction Dominates Hydrogen Hot-Atom Relaxation on Pd(100)

“…Importantly, this is consistent with the fact that chemicurrent intensities measured during the chemisorption of atoms and molecules scale with the adsorption energy [13][14][15]. Chemicurrents have also been observed during the associative desorption of H 2 on metal surfaces [42,43]. Our finding shows that in these experiments a large amount of e-h pair excitation may take place during the motion of the H atoms on the surface prior to recombination.…”

Ab initiomolecular dynamics with simultaneous electron and phonon excitations: Application to the relaxation of hot atoms and molecules on metal surfaces

“…The competition between the e-h pairs and phonon channels governs the relaxation dynamics of the transient hot species, and thus it plays a decisive role in the system reactivity properties. The reason is that it rules the traveled length and relaxation time of a hot atom or molecule on the surface and, consequently, the probability to undergo a recombination reaction with another adsorbate [18][19][20][21][22][23].…”

“…The competition between the e-h pairs and phonon channels governs the relaxation dynamics of the transient hot species, and thus it plays a decisive role in the system reactivity properties. The reason is that it rules the traveled length and relaxation time of a hot atom or molecule on the surface and, consequently, the probability to undergo a recombination reaction with another adsorbate [18][19][20][21][22][23].Recent ab initio molecular dynamics (AIMD) simulations with electronic friction (AIMDEF) have shown that e-h pair excitations are the dominant relaxation mechanism for hot H atoms on Pd(100) that originate from the dissociative adsorption of H 2 [16]. More particularly, this channel dissipates energy at a five times faster rate than the phonon channel [10].…”

Unified description of H-atom–induced chemicurrents and inelastic scattering

“…However, a growing number of examples have been found where electronic and nuclear degrees of freedom are strongly coupled in violation of the BOA (2-6). H-atom interactions at metals offer a remarkable opportunity to test non-BOA theories against experiment, since H-adsorptioninduced chemicurrent experiments (7)(8)(9)(10)(11)(12)(13)(14) offer a direct measure of electronic excitation and H-atom inelastic scattering experiments (15) directly probe nuclear motion. In chemicurrent experiments, exothermic H interactions like adsorption and recombination produce hot electrons that pass over a potential barrier to be collected.…”

“…Hence, the magnitude of the chemicurrent is dependent on both the reaction-induced production of hot electrons and the likelihood of transmission over the barrier. To reduce uncertainties associated with barrier transmission, the ratio of hydrogen-and deuterium-induced chemicurrent is often measured--H-induced chemicurrents are typically two to five times larger than those from D atoms (7,(11)(12)(13). H-atom surface scattering experiments yield H-atom translational energy loss distributions.…”