Franck Fortuna

Bismuth-catalyzed and doped silicon nanowires for one-pump-down fabrication of radial junction solar cells.

Silicon nanowires (SiNWs) are becoming a popular choice to develop a new generation of radial junction solar cells. We here explore a bismuth- (Bi-) catalyzed growth and doping of SiNWs, via vapor-liquid-solid (VLS) mode, to fabricate amorphous Si radial n-i-p junction solar cells in a one-pump-down and low-temperature process in a single chamber plasma deposition system. We provide the first evidence that catalyst doping in the SiNW cores, caused by incorporating Bi catalyst atoms as n-type dopant, can be utilized to fabricate radial junction solar cells, with a record open circuit voltage of V(oc) = 0.76 V and an enhanced light trapping effect that boosts the short circuit current to J(sc) = 11.23 mA/cm(2). More importantly, this bi-catalyzed SiNW growth and doping strategy exempts the use of extremely toxic phosphine gas, leading to significant procedure simplification and cost reduction for building radial junction thin film solar cells.

Widely tunable two-colour seeded free-electron laser source for resonant-pump resonant-probe magnetic scattering

The advent of free-electron laser (FEL) sources delivering two synchronized pulses of different wavelengths (or colours) has made available a whole range of novel pump–probe experiments. This communication describes a major step forward using a new configuration of the FERMI FEL-seeded source to deliver two pulses with different wavelengths, each tunable independently over a broad spectral range with adjustable time delay. The FEL scheme makes use of two seed laser beams of different wavelengths and of a split radiator section to generate two extreme ultraviolet pulses from distinct portions of the same electron bunch. The tunability range of this new two-colour source meets the requirements of double-resonant FEL pump/FEL probe time-resolved studies. We demonstrate its performance in a proof-of-principle magnetic scattering experiment in Fe–Ni compounds, by tuning the FEL wavelengths to the Fe and Ni 3p resonances.

Stability and evolution of low-surface-tension metal catalyzed growth of silicon nanowires

Low-surface-tension metals were predicted to be insufficient to catalyze the growth of silicon nanowires (SiNWs) in vapor-liquid-solid (VLS) mode while counter examples do exist, for example, in the tin- or indium-catalyzed SiNWs. This puzzle remains largely unresolved. We first examine the local tension-force-balance in a tin-catalyzed SiNW by using a cross-section analysis. We found that the existence of an ultrathin sidewall-spreading catalyst layer helps to stabilize the catalyst drop during growth. The predicted contact-angle evolution, by an energetic balance model, is also supported by the experimental data. These results bring critical understanding on the low-surface-tension catalyzed VLS process.

Hubbard band versus oxygen vacancy states in the correlated electron metal SrVO3

Strong electron correlations in solids are at the heart of fascinating phenomena such as high temperature superconductivity, whose understanding remains a prominent open problem in Physics. A central prediction of dynamical mean field theory (DMFT) is the breaking of Landaus Fermi liquid, which describes extremely well simple metals like copper, into itinerant heavy quasiparticles and localized Mott-Hubbard states. To test it, electronic structure calculations based on DMFT are usually benchmarked against the photoemission spectra of SrVO

Guided growth of in-plane silicon nanowires

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Irreversible transformation of ferromagnetic ordered stripe domains in single-shot infrared-pump/resonant-x-ray-scattering-probe experiments

, a cubic perovskite with one

Magnetic imaging by Fourier transform holography using linearly polarized x-rays

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Temperature and field dependent magnetization in a sub-µm patterned Co/FeRh film studied by resonant x-ray scattering

electron per unit cell that is considered the gold standard in this field. However, the present study shows that the UV synchrotron radiation used in the photoemission experiments creates oxygen vacancies, resulting in a strong peak of defect states essentially on top of the SrVO

IRMA-2 at SOLEIL: a set-up for magnetic and coherent scattering of polarized soft x-rays

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Perpendicular Magnetic Anisotropy in Fe–N Thin Films: Threshold Field for Irreversible Magnetic Stripe Domain Rotation

Hubbard band. As recent works found that the same peak of vacancy states occurs in noncorrelated wide-gap