J. De Baerdemaeker

Room-temperature grain growth in sputter-deposited Cu films

The microstructure of sputter-deposited Cu films is shown to be unstable at room temperature (RT). The average grain size increases significantly during RT storage for a couple of hours after deposition. This RT grain growth is shown to be very dependent on the deposition parameters (substrate temperature and sputter gas pressure) and hence on the microstructure of the as-deposited film. The microstructure of sputter-deposited films is usually summarized in a structure-growth-zone model. It is found that significant RT grain growth only occurs for Cu layers with a zone-T-type, as-deposited microstructure.

Influence of carbon on the microstructure of a Fe-Mn-Si-Cr-Ni alloy

The influence of the addition of C to the Fe-Mn-Si-Cr-Ni base material is investigated at room temperature. Steel samples were deformed during a tensile experiment up to a strain of 17%. Light optical microscopy (OM) and x-ray diffraction (XRD) gave information about the different micro-structural phases that exist in the deformed and the undeformed alloys. The evolution of the defect structure is followed by positron annihilation techniques such as Doppler broadening of annihilation radiation spectroscopy (DBAR) and the positron annihilation lifetime spectroscopy (PALS). During deformation a martensitic ε-phase is induced. The size of the martensite plates increases with increasing deformation.

Composition and self-irradiation effects on the positron annihilation lifetime properties of poly(ethylene-co-vinyl acetate).

Abstract The behavior of the copolymer poly(ethylene-co-vinyl acetate), with different amounts of vinyl acetate (VA) (2, 4.5, 9 and 19 w/w%, respectively), has been studied by performing positron lifetime measurements as a function of temperature. An overall reduction of the ortho-positronium formation probability I3 with increasing VA content is observed. The copolymers with 2, 4.5 and 9 w/w% VA show a V-shaped I3 evolution with temperature, caused by positron irradiation induced ionization, whereas the copolymer with 19 w/w% VA has become practically inert to self-irradiation effects.

A study of positronium formation in anodic alumina

Al2O3 samples grown with natural well-ordered channels (having sizes of 30–90 nm in diameter) perpendicular to the surface, one side closed, were measured by means of Doppler broadening (DB) by variable energy positron (VEP) beam and positron annihilation lifetime (PAL) spectroscopy. The samples annealed at 300 and 560 °C showed amorphous structure and no positronium (Ps) formation. The sample annealed at 850 °C showed γ-phase polycrystalline structure and Ps formation. We were not able to prove from the PAL spectroscopy results themselves whether Ps is confined to the channels. We discuss the results of decomposition of the DB annihilation peak into four Gaussians. We conclude that the greater Ps fraction is confined to the channels. From the Compton-to-peak ratio analysis, the fraction of all the injected positrons which form o-Ps and in this form escape from the sample (for a VEP experiment, we have e+ injected from the open side of the channels) has been estimated as being ~20%.