Laser hydriding-a novel method to store hydrogen in solids

Abstract

Laser hydriding is a novel technique to incorporate large amounts of hydrogen into the surface layers of materials. The process consists of laser-irradiating the sample in hydrogen atmosphere at elevated hydrogen-gas pressures (1-3 bar). We used up to 256 pulses of a XeCl excimer laser (308 nm, 55 ns pulse duration, <= 5 J/cm(2) laser fluence) to irradiate titanium, amorphous and single-crystalline silicon samples. The hydrogen depth profiles were measured with the 3MV pelletron accelerator MaRPel, using the nuclear reaction H-1(N-15, alpha gamma)C-12 at the 6.385MeV resonance. Titanium samples show hydrogen concentrations of up to 47 at.% after laser hydriding at a fluence of 4 J/cm(2): The laser treatment leads to the formation of the TiH2 phase. Laser hydriding of crystalline silicon samples results in a damaged region near the sample surface and a hydrogen concentration of up to 8 at.%, much higher than the solubility limit in thermodynamic equilibrium. In the case of amorphous silicon, epitaxial recrystallization is observed after the laser treatment, with a smaller hydrogen take-up as compared to crystalline silicon. Thermodynamic simulations were carried out to elucidate the laser-material interaction. Similarities and differences relative to laser nitriding and carburization will be discussed briefly.