Finite size effects on the metamagnetic phase transition in a thick B2 FeRh nanocluster film.

FeRh alloys in the CsCl-type (B2) chemically ordered phase present an antiferromagnetic to ferromagnetic order transition around 370 K observed in bulk and continuous films but absent in nanoclusters. In this study, we investigate the thermal magnetic behavior of a thick film composed of assembled FeRh nanoclusters preformed in the gas phase. This work reveals a broad and asymmetric metamagnetic transition with a consequent residual magnetization at low temperature. Due to the coexistence of different grain sizes in the sample, we confront the results with a description that involves two populations of B2-FeRh particles, and the existence of a discriminating size below which the magnetic order transition does not take place.

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers.

Copper indium gallium diselenide-based technology provides the most efficient solar energy conversion among all thin-film photovoltaic devices. This is possible due to engineered gallium depth gradients and alkali extrinsic doping. Sodium is well known to impede interdiffusion of indium and gallium in polycrystalline Cu(In,Ga)Se2 films, thus influencing the gallium depth distribution. Here, however, sodium is shown to have the opposite effect in monocrystalline gallium-free CuInSe2 grown on GaAs substrates. Gallium in-diffusion from the substrates is enhanced when sodium is incorporated into the film, leading to Cu(In,Ga)Se2 and Cu(In,Ga)3Se5 phase formation. These results show that sodium does not decrease per se indium and gallium interdiffusion. Instead, it is suggested that sodium promotes indium and gallium intragrain diffusion, while it hinders intergrain diffusion by segregating at grain boundaries. The deeper understanding of dopant-mediated atomic diffusion mechanisms should lead to more effective chemical and electrical passivation strategies, and more efficient solar cells.

Mixtures of hyaluronic acid and liposomes for drug delivery: Phase behavior, microstructure and mobility of liposomes.

Hyaluronic acid liposomal gels have previously demonstrated in vivo their great potential for drug delivery. Elucidating their phase behavior and structure would provide a better understanding of their use properties. This work evaluates the microstructure and the phase behavior of mixtures of hyaluronic acid (HA) and liposomes and their impact on the vesicle mobility. HA concentration and surface properties of liposomes (positively or negatively charged, neutral, with a polyethylene glycol corona) are varied while the liposome concentration remains constant. Below the entanglement concentration of HA (0.4%), the mixtures exhibit a depletion phase separation except for positively charged liposomes that interact with anionic HA through attractive electrostatic interactions. At high HA concentration, no macroscopic phase separation is observed, except a slight syneresis with cationic liposomes. The microstructure shows aggregates of liposomes homogeneously distributed into a HA network except for PEGylated liposomes, which seem to form bicontinuous interpenetrating networks. The diffusion of liposomes is controlled by HA concentration and their surface properties. Finally, PEGylated liposomes display the highest mobility at high HA concentration (2.28%) both macro- and microscopically. The microstructure of HA-liposomes mixtures and the diffusion of liposomes are key parameters that must be taken into account for drug delivery.