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A proton induced γ-ray emission method for depth profiling Si in the surface regions of materials is described. The method utilizes the resonance at 3098 keV in 28Si(p,p′γ)28Si nuclear reaction and involves the measurement of the characteristic 1778 keV γ-rays. The yield curves of the γ-rays are constructed in 3.0–3.8 MeV proton energy region using different Si targets to determine the analytical capabilities of the resonance. The resonance has a width of ∼12 keV (depth resolution: ∼600 nm in Si), a large probing depth (∼11 μm in Si) and a detection sensitivity of ∼0.7 at.%. A procedure for quantification based on Breit-Wigner formula that encompasses corrections for off-resonance cross-sections is also outlined. Depth profiling of Si in silicon carbide crystals and also in a silicon nitride film with <10% combined uncertainty shows that this method is well suited for probing Si in silicon bearing materials. [ABSTRACT FROM AUTHOR]

Abstract: The paper reports the diffusion coefficients of grain boundary diffusion and grain boundary assisted lattice diffusion of Pd in Mg in Pd/Mg/Si system, a useful material for hydrogen storage, at 473K in vacuum. The grain boundary diffusivity is measured by Whipple model and grain boundary assisted lattice diffusivity by plateau rise method using Pd depth profiles constructed by Rutherford backscattering spectrometry. It is established that grain boundary diffusivities are about six orders of magnitude faster than lattice diffusivities. Fine grained microstructure of Pd film, high abundance of defects in Mg film and higher stability associated with Pd–Mg intermetallics are responsible for the diffusion of Pd into grain boundaries and subsequently in the interiors of Mg. Besides the indiffusion of Pd, annealing also brings about an outdiffusion of Mg into Pd film. Examination by nuclear reaction analysis involving 24Mg(p,p′γ)24Mg resonance reaction shows the occurrence of Mg outdiffusion. Minimization of surface energy is presumably the driving force of the process. In addition to Pd/Mg interface, diffusion occurs across Mg/Si (substrate) interface as well on increasing the annealing temperature above 473K. These studies show that dehydrogenation of films accomplished by vacuum annealing should be limited to temperatures less than 473K to minimize the loss of surface Pd, the catalyst of the hydrogen absorption–desorption process and Mg, the hydrogen storing element, by way of interfacial reactions. [Copyright &y& Elsevier]

Abstract: Intermixing and the formation of Pd–Mg intermetallics on annealing Pd/Mg/Si films in vacuum and hydrogen atmosphere in 348–473K temperature range are studied using Rutherford backscattering spectrometry (RBS) and glancing incidence X-ray diffraction (GI-XRD). Mg films, ∼300nm in thickness were deposited by thermal evaporation whereas Pd layers measuring 10 or 50nm, by electron-beam evaporation. No significant intermixing or formation of an intermetallic is observed in films annealed in hydrogen atmosphere. On the other hand, annealing in vacuum results in the formation of Mg6Pd or Mg5Pd2 and brings about significant intermixing as well. These two are independent processes with the nucleation of Mg6Pd preceeding the occurrence of intermixing. The extent of interaction, in general, is higher in films with 10nm Pd layer at a particular temperature. Mg6Pd is formed in Pd (10nm)/Mg (300nm)/Si films at such low annealing temperature as 423K. It is formed in relatively larger quantities in Pd (50nm)/Mg (300nm)/Si films on annealing at 473K with its content increasing progressively upto 3.5h. The formation of Mg6Pd results from the diffusion of Pd into the grain boundaries of Mg films. RBS vividly shows the prevalence of such a diffusion. The other process, intermixing, occurs initially in the interfacial regions but extends over larger thicknesses on annealing for longer durations. A 5h anneal leads to the formation of Mg5Pd2 in Pd (50nm)/Mg (300nm)/Si films. These compositional and structural changes associated with vacuum annealing are important considerations in improving the hydrogen storage behaviour of Pd–Mg system. [Copyright &y& Elsevier]