Nanopatterning of oxide 2-dimensional electron systems using low-temperature ion milling.

We present a 'top-down' patterning technique based on ion milling performed at low-temperature, for the realization of oxide two-dimensional electron system devices with dimensions down to 160 nm. Using electrical transport and scanning Superconducting QUantum Interference Device measurements we demonstrate that the low-temperature ion milling process does not damage the 2DES properties nor creates oxygen vacancies-related conducting paths in the STO substrate. As opposed to other procedures used to realize oxide 2DES devices, the one we propose gives lateral access to the 2DES along the in-plane directions, finally opening the way to coupling with other materials, including superconductors.

Magnetic behavior of Ni nanoparticle films produced by two laser irradiations in vacuum.

Ni Nanoparticle assembled thin films were prepared using an unconventional approach based on the use of a secondary nanosecond (ns) ultraviolet (UV) laser irradiation interacting with the plume of ablated nanoparticles (NPs) during the femtosecond pulsed laser deposition (fs-PLD). The secondary laser beam determines the reduction of the NPs size and their dispersion by partial vaporization of the NPs during their flight from the target to the substrate. The proper selection of the time delay between fs and ns laser pulses allows the latter to interact selectively with different parts of the NPs plume, controlling, to a certain degree, the reduction of the NPs size and dispersion. Another original effect of the UV laser irradiation is the change in the deposited films topology, due to a reduction of the NP-aggregates density and size, fostering non-uniform dense assemblies of NPs with concentration well above the percolation threshold, with the consequent reduction of the influence of the exchange interactions on the macroscopic magnetic properties. The magnetic behavior of the films prepared using two laser beams with respect to that obtained in the case of fs-PLD only is characterized by higher H(c) values (up to approximately 70%) and a good compromise between the hysteresis loops squareness and moderate exchange interactions, strongly correlated with the NPs topology.

Stepwise behaviour of magnetization temperature dependence in iron nanoparticle assembled films.

An unusual stepwise behaviour is reported in the temperature dependence of the zero field cooled magnetization in iron nanoparticle dense films produced by ultra-short pulsed laser deposition assisted by irradiation of nanoparticles with a nanosecond UV laser pulse, appropriately delayed, during their flight from the target to the substrate. This behaviour, induced by the particle system's morphology, characterized by clusters of tightly coupled nanoparticles as well as by some voids between them, is ascribed to the competition between Zeeman energy density, intracluster anisotropy energy density and intercluster exchange energy density. A phenomenological model and Monte Carlo simulations are reported, which support the proposed interpretation.

Sol-gel synthesis, characterization and bioactivity of poly(ether-imide)/TiO2 hybrid materials.

Novel organic-inorganic hybrid materials were synthesized by the sol-gel method from a multicomponent solution containing titanium butoxide, 6 weight % (wt%) or 12 wt% poly(ether-imide) (PEI), water and chloroform. The structure of the interpenetrating network is realized by hydrogen bonds between the Ti-OH group (H-donator) in the sol-gel intermediate species and the carboxylic group (H-acceptor) in the repeating units of the polymer. By Fourier transform infrared (FTIR) analysis the presence of hydrogen bonds between organic-inorganic components of the hybrid materials were proved. The morphology of the hybrid materials was studied by scanning electron microscopy (SEM). The structure of a molecular level dispersion was disclosed by an atomic force microscope (AFM), pore size distribution and surface measurements. The AFM and SEM analyzes confirmed that the PEI/TiO2 samples can be considered homogenous organic/inorganic hybrid materials because in both the compositions studied the average domains were less than 400 nm in size. The bioactivity of the synthesized hybrid materials was demonstrated by the formation of a layer of hydroxyapatite on the surface of the PEI/TiO2 samples soaked in a fluid simulating the composition of human blood plasma (SBF), demonstrated by SEM and energy dispersive spectroscopy (EDS) microscopy.