Atomic deuterium (hydrogen) adsorption on thin silver films

Abstract

Atomic deuterium and hydrogen adsorption on thin silver films deposited under UHV conditions on Pyrex glass was studied by means of measurements of the resistance changes Δ R combined with thermal desorption mass spectrometry (TDMS). The roughness factor of thin Ag films of known geometry, textured as a result of sintering, was determined by means of the BET method (xenon adsorption), while their preferential crystallographic orientation (1 1 1) was estimated on the basis of XRD data. Δ R measurements were performed during various exposures of the films maintained at a constant temperature (78 or 89 K) to the flux of atomic deuterium (hydrogen) of known concentration generated on a hot tungsten filament. Every adsorption run was followed by thermal desorption. This gives a link between the Δ R measured directly in the course of adsorption and the coverage Θ determined on the basis of TDMS data, together with the BET and XRD results. It was found that at 78 K the rate of atomic deuterium (hydrogen) adsorption and recombination on the surface of sintered thin Ag films fits the Eley–Rideal (ER) mechanism, while at 89 K its overlapping with the Langmuir–Hinshelwood (LH) recombination starts to play a role. The initial sticking probability reaches 0.41 and 0.65 for D and H atoms, respectively, while the corresponding probabilities for recombination are 0.04 and 0.07. The activation energies for associative desorption of deuterium and hydrogen are 36 and 29 kJ/mol, respectively.