E. Carria

Novel approach to the fabrication of Au/silica core?shell nanostructures based on nanosecond laser irradiation of thin Au films on Si

We demonstrate the possibility of producing Au/SiO(2) core-shell nanoparticles by nanosecond laser irradiation of thin (5 and 20 nm) Au films on Si. The Au/Si eutectic reaction and dewetting process caused by the fast melting and solidification dynamics induced by the nanosecond laser irradiations are investigated as the origin of the formation of core-shell nanoparticles. Using several microscopic techniques (Rutherford backscattering spectrometry, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and energy filtered transmission electron microscopy) the formation and evolution of the core-shell structures are investigated as a function of the laser fluence in the 500-1500 mJ cm(-2) range for both film thicknesses. In particular, the mean height and diameter and surface density evolution of the core-shell structures are quantified and correlated to the laser fluence and Au film thickness.

High-level incorporation of antimony in germanium by laser annealing

In this work we investigate pulse laser annealing as an alternative approach to reach high-level incorporation of Sb in substitutional location in crystalline germanium. Laser irradiation is demonstrated to recover also those structural defects, like honeycomb structures, that form during high-fluence heavy-ion implantations in Ge and that cannot be eliminated by conventional thermal treatments. Indeed, concentrations of substitutional Sb higher than 1×1021 at./cm3 have been obtained, well above the solid solubility of Sb in Ge. The strain induced on the Ge host lattice is also investigated, evidencing that the obtained Sb doped Ge layer is pseudomorphic to the Ge substrate while positively strained by the substitutional Sb atoms present within the Ge matrix. The kinetics of this Sb-rich Ge alloy phase is finally investigated, showing that most of Sb goes out of lattice with increasing the annealing temperature up to 488 °C, leading to a decrease in the related lattice deformation. These results are very ...

Crystallization of sputtered-deposited and ion implanted amorphous Ge2Sb2Te5 thin films

X-ray diffraction and transmission electron microscopy have been utilized to measure the ion irradiation-induced modification in amorphous Ge2Sb2Te5 thin films. The isothermal crystallization of sputtered-deposited and Sb+ ion irradiated amorphous samples has been studied, focusing on the evolution of the microstructure during the initial stage of the transformation. In both samples, the amorphous to crystal transition occurs through the nucleation of face centered cubic (fcc) crystal domains at the film surface. A fast bidimensional growth of the crystalline nuclei in the sputtered-deposited films occurs by the generation of transrotational grains. The lattice parameter decreases as the crystalline fraction increases above 80%, and it approaches the fcc bulk value at the end of the transformation. Ion irradiation produces a densification of the deposited amorphous film (∼4% vertical shrinkage measured by atomic force microscopy) and an enhancement of the crystallization rate. Even in the irradiated amorp...

Crystallization of ion amorphized Ge2Sb2Te5 thin films in presence of cubic or hexagonal phase

The crystallization kinetics of amorphous Ge2Sb2Te5 (GST) thin films, generated by ion implantation, on top of crystalline GST, either in the cubic or hexagonal phase, was investigated by means of time resolved reflectivity measurements, x-ray diffraction, in situ transmission electron microscopy, and Raman analyses. The crystallization occurred at a lower temperature with respect to a fully amorphous film and in both cases the crystalline phase started growing at the underlying amorphous-crystalline (a-c) interface. However, it was not a solid phase epitaxial growth since cubic GST was always obtained, independent of the phase of the underlying crystal. We speculate that the a-c interface behaves as a continuous region of potential nucleation sites in the crystallization making the crystallization process more efficient.

Role of the strain in the epitaxial regrowth rate of heavily doped amorphous Si films

Solid phase epitaxial regrowth (SPER) of p-doped preamorphized Si was studied by time resolved reflectivity. Strain and dopant concentration were opportunely varied by implanting neutral (Ge) and isovalent (B, Ga) impurities in order to disentangle the two different effects on SPER. Larger SPER rate variations occurred in strained doped Si with respect to undoped samples. The generalized Fermi level shifting model was implemented to include the role of the strain and to fit the experimental data over a large range of temperature for p- and n-type doping. We introduced a charged defect, whose energy level is independent of the dopant species.

A Combined Ion Implantation/Nanosecond Laser Irradiation Approach towards Si Nanostructures Doping

The exploitation of Si nanostructures for electronic and optoelectronic devices depends on their electronic doping. We investigate a methodology for As doping of Si nanostructures taking advantages of ion beam implantation and nanosecond laser irradiation melting dynamics. We illustrate the behaviour of As when it is confined, by the implantation technique, in a SiO2/Si/SiO2 multilayer and its spatial redistribution after annealing processes. As accumulation at the Si/SiO2 interfaces was observed by Rutherford backscattering spectrometry in agreement with a model that assumes a traps distribution in the Si in the first 2-3 nm above the SiO2/Si interfaces. A concentration of 1014 traps/cm2 has been evaluated. This result opens perspectives for As doping of Si nanoclusters embedded in SiO2 since a Si nanocluster of radius 1 nm embedded in SiO2 should trap 13 As atoms at the interface. In order to promote the As incorporation in the nanoclusters for an effective doping, an approach based on ion implantation and nanosecond laser irradiation was investigated. Si nanoclusters were produced in SiO2 layer. After As ion implantation and nanosecond laser irradiation, spectroscopic ellipsometry measurements show nanoclusters optical properties consistent with their effective doping.

Impact of annealing induced structural relaxation on the electrical properties and the crystallization kinetics of amorphous GeTe films

The electrical properties of amorphous GeTe films deposited at room temperature, ion implanted, and melt-quenched have been studied. The activation energy for the mobility gap varies from 0.64, in the melt-quenched, to 0.74 eV, in the as deposited film. In all the types of amorphous, pre-annealing at temperatures below crystallization induces relaxation, increasing the resistance and the mobility gap. Pre-annealing also reduces the nucleation rate for crystallization by a factor up to 4. A model is proposed, describing the competing processes of structural relaxation and crystallization, as governed by a population of sub-critical nuclei formed by medium range ordered regions.