Trapping hydrogen with a bimetallic interface

We report results of a study on the interaction of hydrogen with thin Au films grown on an Ir{111} surface at $\approx 100\mathrm{K}$, using nuclear reaction analysis and first-principles calculations. We found that H atoms can be confined at the interface between the bulk-Ir surface and the Au thin film, which is realized by increasing the binding energy and the activation barrier for desorption via lattice relaxation of the Au layer.

Figure 1

STM topographic images $(500\times 500{\mathrm{nm}}^2)$ of (a) 1.2 ML and (b) 3.6 ML Au covered Ir{111} at room temperature. Images were taken at sample currents and voltages of (a) $0.21\mathrm{nA}$ and $0.14\mathrm{V}$ and (b) $0.19\mathrm{nA}$ and $0.17\mathrm{V}$.

Figure 2

Intensity profile of the $\gamma$ ray from the ${}^1\mathrm{H}({}^{15}\mathrm{N},\alpha \gamma ){}^{12}\mathrm{C}$ nuclear reaction on 0.5 ML-H covered Ir{111} as a function of the incident ${}^{15}\mathrm{N}$ beam energy. The incidence angle is 60° from the surface normal. Solid curve is a fit to a single Gaussian form.

Figure 3

Intensity profiles of the $\gamma$ ray from the ${}^1\mathrm{H}({}^{15}\mathrm{N},\alpha \gamma ){}^{12}\mathrm{C}$ nuclear reaction as a function of the incident ${}^{15}\mathrm{N}$ beam energy. (a) ${\mathrm{H}}_2$ exposure after 4 ML Au deposition on the clean Ir{111}, (b) ${\mathrm{H}}_2$ exposure after 4 ML Au deposition on the H-saturated Ir{111}. The incidence angle is 65° from the surface normal. Solid curves are fits to Gaussian form [a sum of two Gaussian forms (dashed lines)].

Figure 4

Calculated adsorption energy of a H atom as a function of the position at the interface between Ir (three layers) and Au (one layer). The energy reference corresponds to an isolated H atom. The positions of the octahedral (full circles) and tetrahedral (open circles) sites are defined in the bottom panel. The position of zero corresponds to the first Ir layer. Also shown by full and open squares are the potential curve of H at the interface between Au (three layers) and Au (one layer).