Chemical interaction of H and D atoms with Ag∕H:p-Si(111) thin film diodes

Abstract

During exothermic reactions of atomic hydrogen or deuterium on a silver surface hot charge carriers are produced which have been observed by using Ag/ p-Si͑111͒ Schottky diodes. Thin film devices provide a means to bring a charge detector as close to the reaction site as the mean free path of the charge carriers. In the case of a p-doped substrate the Schottky barrier works as a high-pass energy filter for hot holes. The authors have therefore produced large area Schottky diodes with film thicknesses of up to 30 nm varying the thickness to rule out any influence of this device parameter. Those diodes were then exposed to beams of hydrogen atoms and deuterium atoms produced in a hot capillary source. Gas exposures do not affect the Schottky barrier height significantly. While exposing the samples to defined atom fluxes, the closed-loop current was monitored in real time. It shows that the current is proportional to the flux of atoms impinging on the surface. The authors have found hydrogen to generate 3.7 times more chemicurrent than is created during reactions with deuterium. Theoretical predictions of nonadiabatic energy dissipation using the electronic friction model agree well with the experimental results.

Energy transfer and chemical dynamics at solid surfaces: The special role of charge transfer

“…Of course, the energy distribution of the endo-electrons is not obtained in such an experiment. More recently, a strong isotope effect between H(3.7 ± 0.7) and D(1) atom chemi-current is seen [324,325]. Assuming a Boltzmann electron energy distribution, this isotopic ratio was used to derive the electron temperature for H on Cu (T eff,H = 1690 ± 300 K), which compares favorably to that calculated from a novel electronic-friction based model [88,110,111], which we now discuss in more detail.…”

“…The current is based on electronically nonadiabatic EHP creation which occurs during exothermic adsorption of hydrogen on Cu surfaces. This phenomenon has since been demonstrated for a wider variety of surface reactions and replacing silicon by germanium [293,[317][318][319][320][321][322][323][324][325][326]. In similar devices, others have also observed chemi-current, for example produced by the catalytic oxidation of CO to CO 2 [327][328][329][330][331][332][333][334].…”

Hydrogen Oxidation-Driven Hot Electron Flow Detected by Catalytic Nanodiodes

“…1a. Non-catalytic metal-semiconductor diodes have been used to prove that hot electrons are generated in adsorption reactions in ultrahigh vacuum (UHV) at temperatures below 150 K [18][19][20] . By using catalytic metal-semiconductor diodes such as Pt/TiO 2 or Pt/GaN, it has also been possible to detect steady chemicurrent from catalytic CO oxidation at atmospheric pressure, between 400 K and 550 K 16,21 .…”

Electron-hole spectra created by adsorption on metals from density functional theory

“…12 A smearing of the occupation factors of 1 mRy using a simple Fermi-Dirac broadening scheme is used, which corresponds roughly to the experimental temperatures. 26 Using the aforementioned parameters we obtained a lattice constant of 4.061 Å for bulk Al, while the experimental value is 4.050 Å. Figure 1 shows the Kohn-Sham band structure of an Al͑111͒ slab with a ͑1 ϫ 1͒ unit cell resulting from our calculations.…”