Improved properties of TiAlN coatings through the multilayer structure

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Patterned structures of in situ size controlled CdS nanocrystals in a polymer matrix under UV irradiation.

A method of in situ formation of patterns of size controlled CdS nanocrystals in a polymer matrix by pulsed UV irradiation is presented. The films consist of Cd thiolate precursors with different carbon chain lengths embedded in TOPAS polymer matrices. Under UV irradiation the precursors are photolyzed, driving to the formation of CdS nanocrystals in the quantum size regime, with size and concentration defined by the number of incident UV pulses, while the host polymer remains macroscopically/microscopically unaffected. The emission of the formed nanocomposite materials strongly depends on the dimensions of the CdS nanocrystals, thus, their growth at the different phases of the irradiation is monitored using spatially resolved photoluminescence by means of a confocal microscope. X-ray diffraction measurements verified the existence of the CdS nanocrystals, and defined their crystal structure for all the studied cases. The results are reinforced by transmission electron microscopy. It is proved that the selection of the precursor determines the efficiency of the procedure, and the quality of the formed nanocrystals. Moreover it is demonstrated that there is the possibility of laser induced formation of well-defined patterns of CdS nanocrystals, opening up new perspectives in the development of nanodevices

Experimental-observation of Landau-levels in nonperiodic (fibonacci) superlattices

Contains fulltext : 145234.pdf (publisher's version ) (Open Access

Misure di laboratorio dell'isolamento al calpestio di massetti galleggianti su solai in CLT

La caratterizzazione acustica dei massetti galleggianti viene normalmente eseguita in laboratorio su di un solaio di riferimento in cemento armato, secondo le norme della serie ISO 10140 e non esistono dati di questi massetti su solai in CLT. L\u2019articolo presenta i risultati di uno studio, in laboratorio, compiuto su di un solaio in legno sul quale sono stati posti in opera 15 differenti combinazioni di strati resilienti e massetti a secco o in sabbia e cemento. Si \ue8 indagato anche sull\u2019effetto di diversi sottofondi alleggeriti. Sono stati inoltre presi in considerazione anche i controsoffitti appesi o vincolati all\u2019intradosso del solaio. Allo stesso tempo si \ue8 cercato di trovare una relazione sperimentale che estenda l\u2019efficacia della relazione di Cremer anche al di sopra dei 1000 Hz, tale relazione infatti, lega il potere fonoisolante R dei solai al livello di calpestio normalizzato Ln. L\u2019obiettivo \ue8 quello contribuire al miglioramento delle formule previsionali da utilizzare su strutture leggere, come il CLT, che non possono essere considerate infinitamente rigide come le strutture edilizie comunemente utilizzate

Microstructural characterization of GaAs-AlxGa1-xAs core-shell nanowires grown by Au-catalyst assisted metalorganic vapor phase epitaxy

In this work, we report on the microstructural and morphological characterization of III-V semiconductor nanowires (NWs) epitaxially grown on (111)B-GaAs substrates by Au-catalyst assisted metalorganic vapor phase epitaxy. As-grown dense (10^8-10^9 cm^-2) arrays of few-micron long vertically-aligned (i.e. parallel to the <111> crystallographic axis) GaAs, AlxGa1-xAs and core-shell GaAs-AlxGa1-xAs NWs were investigated, carrying out HRXRD measurements on different (hkl) reflections and by recording reciprocal space maps (RSMs) around the materials (111) reciprocal lattice points (relps). We show that NW diffraction peaks are visible in the RSM by means of characteristic halos. In the case of GaAs NWs, the halo is located at the (111) relp indicating that the NWs are grown along the <111> direction and parallel to the <111> axis of the GaAs substrate. On the contrary, for AlxGa1-xAs NWs or intentional core-shell GaAs-AlxGa1-xAs NWs the halo is displaced (along the momentum transfer normal to the surface, Qz) with respect to the GaAs (111) relp due to the elastic lattice strain associated with the compositional variation, e.g. the Al molar fraction in the AlxGa1-xAs alloy, within the nanostructures

X-RAY-DIFFRACTION STUDY OF CORRUGATED SEMICONDUCTOR SURFACES, QUANTUM WIRES AND QUANTUM BOXES

We show that high-resolution double-crystal X-ray diffraction is not only sensitive to the periodic structural modulation normal to the crystal surface as it occurs in semiconductor superlattices, but is under appropriate experimental conditions also very sensitive to the periodic modulation parallel to the crystal surface (surface grating). This fact allow us to study the structural properties, geometrical parameters and strain state, of quantum wires and quantum boxes. We present experimental results on AlGaAs/GaAs and InAs/GaAs quantum wires and show that the quantum wire period and quantum wire width can be determined very precisely. In addition, we found a partial elastic strain relaxation normal to the quantum wires, resulting in an orthorhombic lattice deformation