We demonstrate that femtosecond laser ablation of silicon targets in vacuum is a viable route to the generation and deposition of nanoparticles with radii of ≈5–10 nm. The nanoparticles dynamics during expansion has been analyzed through their structureless continuum optical emission, while atoms and ions, also present in the plume, have been identified by their characteristic emission lines. Atomic force microscopy analysis of the material deposited at room temperature has allowed the characterization of the nanoparticles size distribution. Taking into account the emissivity of small particles we show that the continuum emission is a blackbody-like radiation from the nanoparticles. Our results suggest that nanoclusters are generated as a result of relaxation processes of the extreme material state reached by the irradiated target surface, in agreement with recently published theoretical studies

Doping of biocompatible nanomaterials with magnetic phases is currently one of the most promising strategies for the development of advanced magnetic biomaterials. However, especially in the case of iron-doped magnetic hydroxyapatites, it is not clear if the magnetic features come merely from the magnetic phases/ions used as dopants or from complex mechanisms involving interactions at the nanoscale. Here, we report an extensive chemical-physical and magnetic investigation of three hydroxyapatite nanocrystals doped with different iron species and containing small or no amounts of maghemite as a secondary phase. The association of several investigation techniques such as X-ray absorption spectroscopy, Mössbauer, magnetometry, and TEM allowed us to determine that the unusual magnetic properties of Fe-doped hydroxyapatites (FeHA) occur by a synergy of two different phenomena: i.e., (i) interacting superparamagnetism due to the interplay between iron-doped apatite and iron oxide nanoparticles as well as to the occurrence of dipolar interactions and (ii) interacting paramagnetism due to Fe ions present in the superficial hydrated layer of the apatite nanophase and, to a lesser extent, paramagnetism due to isolated Fe ions in the apatite lattice. We also show that a major player in the activation of the above phenomena is the oxidation of Fe into Fe, as induced by the synthesis process, and their consequent specific positioning in the FeHA structure.

We construct a theory of the deflection of a bimorph cantilever, applicable to both the isotropic and anisotropic cases, and also including noise effects. The proposed formulation gives the correct expressions for the longitudinal and transverse deflections of a magnetoelastic cantilever for an arbitrary ratio of the thickness of the two components. The optimization of the cantilever as a sensor as a function of the thickness of the two components is discussed and also some results of the cantilever as an actuator are reported.

We have used the technique of femtosecond (fs) laser ablation in a vacuum to produce films of nickel nanoparticles. A peculiarity of this fs laser deposition is the significant shape and orientation anisotropy of the nanoparticles, which are oblate ellipsoids with the major axis parallel to the deposition substrate. The deposited films present unique magnetic properties, and, in specific conditions, very high remanence ratios (up to 0.7) accompanied with relatively low values of saturation and coercive fields can be obtained. We have interpreted these results in terms of the mentioned anisotropies, and of the occurrence of a thermally induced in-plane tensile stress, which is a function of the nanoparticles size

Composite material constituted by Fe micro-particles homogeneously dispersed in a silicone matrix, at a volume concentration slightly above the percolation threshold but separated by a thin silicone layer, was produced. The particle magnetic softness and their average size, have been properly improved with respect to previous investigations in order to maximize the piezo-resistive and the piezo-magnetic effects. The optimal combination of magneto-elasticity and piezo-resistivity enables to achieve a record value of magneto-piezo-resistivity sensitivity. An analytical model is proposed to simulate the theoretically expected behavior of electric resistance vs. the applied induction field gradient, so to predict the magneto-piezoresistive response and explain the obtained material tailoring. The experimental results have been in good agreement with the theoretically predicted behaviors, so validating the employed model and the interpretation of the phenomenon. A simple basic application in position sensing is also reported. The analytical model presented in this paper has demonstrated its potentiality to project further improvements, while the experimental results allow for different innovative applications