R. Ferragut

Exploring the WEP with a pulsed cold beam of antihydrogen

The AEGIS experiment, currently being set up at the Antiproton Decelerator at CERN, has the objective of studying the free fall of antimatter in the Earth?s gravitational field by means of a pulsed cold atomic beam of antihydrogen atoms. Both duration of free fall and vertical displacement of the horizontally emitted atoms will be measured, allowing a first test of the WEP with antimatter.

The effect of selective interactions at the interface of polymer–oxide hybrid solar cells

The working mechanisms of excitonic solar cells are strongly dominated by interface processes, which influence the final device efficiency. However, it is still very challenging to clearly track the effects of inter-molecular processes at a mesoscopic level. We report on the realization of polymer-based hybrid solar cells made of prototypical materials, namely, poly(3-hexylthiophene) (P3HT) finely infiltrated in a TiO2 scaffold, with power conversion efficiency exceeding 1%. A step-change improvement in the device performance is enabled by engineering the hybrid interface by the insertion of an appropriate molecular interlayer. An unprecedented set of characterization techniques, including time-resolved optical spectroscopy, X-ray photoemission spectroscopy, positron annihilation spectroscopy and atomistic simulations, allows us to rationalize our findings. We show that a suitable chemical structure of the interlayer molecule induces selective intermolecular interactions, and thus a preferential surface energetic landscape and morphological order at the interface which consequently drives a strong improvement in charge generation and a decrease in recombination losses.

Analysis of electron-positron momentum spectra of metallic alloys as supported by first-principles calculations

Electron-positron momentum distributions measured by the coincidence Doppler broadening method can be used in the chemical analysis of the annihilation environment, typically a vacancy-impurity complex in a solid. In the present work, we study possibilities for a quantitative analysis, i.e., for distinguishing the average numbers of different atomic species around the defect. First-principles electronic structure calculations self-consistently determining electron and positron densities and ion positions are performed for vacancy-solute complexes in

Pre-precipitation study in the 7012 Al-Zn-Mg-Cu alloy by electrical resistivity

\mathrm{Al}\text{\ensuremath{-}}\mathrm{Cu}

Hardening nanostructures in an AlZnMg alloy

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Secondary ageing in Al-Cu-Mg

\mathrm{Al}\text{\ensuremath{-}}\mathrm{Mg}\text{\ensuremath{-}}\mathrm{Cu}

A moiré deflectometer for antimatter

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Positronium Formation in Porous Materials for Antihydrogen Production

\mathrm{Al}\text{\ensuremath{-}}\mathrm{Mg}\text{\ensuremath{-}}\mathrm{Cu}\text{\ensuremath{-}}\mathrm{Ag}

On the two-step ageing of a commercial Al - Zn - Mg alloy; a study by positron lifetime spectroscopy

alloys. The ensuing simulated coincidence Doppler broadening spectra are compared with measured ones for defect identification. A linear fitting procedure, which uses the spectra for positrons trapped at vacancies in pure constituent metals as components, has previously been employed to find the relative percentages of different atomic species around the vacancy [A. Somoza et al. Phys. Rev. B 65, 094107 (2002)]. We test the reliability of the procedure by the help of first-principles results for vacancy-solute complexes and vacancies in constituent metals.

Positron annihilation spectroscopy: a new frontier for understanding nanoparticle-loaded polymer brushes

Abstract The early stages of pre-aging at near room temperature in an Al–Zn–Mg–Cu based commercial alloy were studied by electrical resistivity. The resistivity changes can be adequately described in the same terms of a Johnson–Mehl–Avrami (JMA) type function for the volume fraction growth of the Guinier–Preston zones or pre-precipitate solute clusters formed. For one specific case, resistivity results were correlated with those obtained using synchrotron-radiation small-angle X-ray scattering (SR-SAXS). Based on the analysis of the parameters of the JMA equation, the existence of a complex diffusion process during pre-precipitation is deduced. An apparent activation energy of 0.69±0.04 eV for the formation of the above mentioned particles is found. From this energy value, the migration of Mg-vacancy complexes is identified as the main microstructural mechanism responsible for the pre-precipitation.