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Ferragut R.,LNESS | Liddicoat P.V.,University of Sydney | Liao X.-Z.,University of Sydney | Zhao Y.-H.,University of California at Davis | And 4 more authors.
Journal of Alloys and Compounds | Year: 2010

Positron annihilation spectroscopy in two variants (coincidence Doppler-broadening CDB and lifetime spectroscopy LT) was used for the characterisation of severely deformed nanocrystalline 7075 Al alloy, with specific attention to the distribution of solute in the proximity of grain boundaries. The 7075 samples were deformed via the high pressure torsion (HPT) technique after solution treatment and quenching. The grain size at the end of the deformation was sub 100 nm. The deformed samples have undergone 3 months of natural ageing post-processing. CDB and LT measurements consistently indicate that the fraction of trapped positrons in these samples is near to 90%. The analysis of CDB data shows that the environment of the positron traps is enriched with solute up to 50 at.%, nearly evenly divided between Mg and transition metals (Zn and Cu). The CDB results indicate an enhancement of solute concentration at grain boundaries associated with HPT deformation. © 2009 Elsevier B.V.

Picco A.,University of Milan Bicocca | Bonera E.,University of Milan Bicocca | Grilli E.,University of Milan Bicocca | Guzzi M.,University of Milan Bicocca | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Raman spectroscopy is commonly used for the optical characterization of structural properties of SiGe alloys but a measurement of the Raman efficiency as a function of excitation wavelength and concentration is still lacking. This information is nevertheless important for the interpretation of data, especially for the analysis of inhomogeneous samples. In this work, the relative Raman efficiency of Si1-xGex alloys has been obtained for several excitation energies as a function of the composition x with steps of Δx∼0.02 across the whole composition range. We observed resonances in correspondence of the E1/E1+Δ1 and E 0/E0+Δ0 transitions. For a fixed excitation energy the efficiency varies of about 2 orders of magnitude vs the composition of the alloy, while, for a fixed composition, we observed a change in efficiency of up to 3 orders of magnitude depending on the excitation energy. The maximum scattering efficiency at resonance decreases by an order of magnitude when moving from silicon-rich to germanium-rich alloys. The data are discussed in terms of the polarizability and compared to the literature relative to pure silicon and germanium. The data reported in this paper can be used to design experiments under resonant conditions to selectively probe different regions in inhomogeneous samples. © 2010 The American Physical Society.

Savoini M.,LNESS | Biagioni P.,LNESS | Finazzi M.,LNESS | Duo L.,LNESS
Physica Status Solidi (B) Basic Research | Year: 2010

The movement of photosensitive azo polymers induced by scanning near-field illumination is studied. As a function of the photon flux illuminating the sample and exposure time, different effects are obtained: from a nanoscopic reorientation, inducing birefringence in the sample, to a macroscopic movement of the photosensitive polymers. It is also shown that this movement is strongly influenced by the state of incident light polarization. The combination of azo polymers and nearfield illumination allows encoding sub diffraction information and can be exploited in applications as nanomachining and nanofabrication. Birefringence signal associated to nanoscopic reorientation of the azomers. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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