Jacques Chevallier

Observation of the growth mode of TiN during magnetron sputtering using synchrotron radiation

The heteroepitaxial growth of TiN on MgO(001), deposited by reactive magnetron sputtering, has been studied in situ. Using real-time specular x-ray reflectivity, layer-by-layer growth was observed, with the surface roughening decreasing with an increase in the deposition temperature. Higher temperatures also resulted in lower growth rates. The film thickness was measured with specular x-ray reflectivity. Using off-plane Bragg–Brentano as well as grazing incidence in-plane wide angle scattering, the pseudomorphic growth of TiN to the underlying MgO(001) was established. Transmission electron microscopy reveals atomic planes passing through the MgO–TiN boundary, thus confirming heteroepitaxial growth.

The nanostructure evolution during and after magnetron deposition of Au films

Abstract The evolution of the nanostructure of magnetron sputtered Au films has been experimentally studied. At a synchrotron-radiation beam line, during growth and subsequent annealing, in-situ X-ray diffraction has been carried out to follow the texture, the grain size, the microstrain and lattice-plane distances. With Bragg–Brentano geometry, only (111) grains, having a (111) plane parallel to the film surface, have been observed, while, with glancing incidence and exit X-ray diffraction, (111)* grains, having one of their (111) planes perpendicular to the film surface, have also been observed. Both during growth and subsequent annealing, the (111) texture changed, and some (111)* grains recrystallized and/or the orientation of the grains changed. The microstrain decreased drastically during the first few minutes of growth (300 A) while, simultaneously, the size of the coherently diffracting domains increased. Subsequently, the microstrain became constant, and the rate of increase of the size of coherently diffracting domains leveled off. Initially, during the first few minutes of annealing, a large decrease in the microstrain was observed simultaneously with a dramatic rise of the size of the coherently diffracting domains. After this initial annealing period, as during film growth, the microstrain became constant, and the rate of increase of the size of coherently diffracting domains leveled off. The activation energy for the initial growth of the coherent diffracting domains was found to be Q =0.25±0.03 eV, and the activation energy for normal grain growth was found to be Q =0.99±0.04 eV. Finally, the thin-film stress was followed during growth and subsequent annealing. A tensile contribution to the stress was observed during island coalescence.

Interface stress in Au/Ni multilayers

The effect of intermixing on the apparent interface stress is studied in 〈111〉-textured dc-magnetron sputtered Au/Ni multilayers by use of two methods commonly used for determining interface stress. The method using profilometry and in-plane x-ray diffraction does not take intermixing into account and yields an apparent interface stress of −8.46±0.99 J m−2. However, observed discrepancies between model calculations and measured high-angle x-ray diffractograms indicate intermixing, and by use of the profilometry and sin2 ψ method the real interface stress value of −2.69±0.43 J m−2 is found. This method also reveals a significant and systematic change of the stress-free lattice parameter of both constituents as a function of modulation period which is shown to account for the difference between the two findings. The method using in-plane diffraction is thus shown to be inapplicable to interface stress determinations in systems exhibiting a modulation period-dependent stress-free lattice parameter. Finally, ...

Interactions between hydrogen and group VI donors in GaAs and GaAlAs

GaAs and GaAlAs layers doped with different group VI donors (S, Se, Te) have been exposed to hydrogen plasma. By secondary ion mass spectroscopy, it is shown that, as in Si‐doped materials, the hydrogen diffusion strongly depends on the AlAs content. Electronic transport measurements indicate that after hydrogen diffusion the electron concentration systematically decreases and their mobility increases, demonstrating clearly the passivation of the group VI donors by hydrogen.

A rectifying tungsten-molybdenum foil for positron remoderation

We report the use of a layered foil as a positron rectifying device for transmission geometry positron moderation and remoderation, thereby increasing the efficiency of such devices. Positron transmission through foils consisting of a 10 nm W layer on top of a 100 nm Mo foil has been measured. The measurements are compared with similar results for a 100 nm W foil. A strong rectifying effect with a forward to reverse current ratio of more than 10 is observed making this type of well matched layered foils an obvious candidate for positron remoderation. Retarding energy spectra of the transmitted positrons were obtained and measurements of Doppler broadening and surface branching ratios were performed to further characterize the foils. The obtained transmission results again reveal the discrepancy in positron implantation profiles for thin foils between experiments and existing theory.