Publications (39) View all
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Article: Study of titania nanorod films deposited by matrix-assisted pulsed laser evaporation as a function of laser fluence
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ABSTRACT: Chemically synthesized brookite titanium dioxide (TiO2) nanorods with average diameter and length dimensions of 3–4nm and 35–50nm, respectively, were deposited by the matrix-assisted pulsed laser evaporation technique. Atoluene nanorod solution was frozen at the liquid-nitrogen temperature and irradiated with a KrF excimer laser (λ=248nm, τ=20ns) at the repetition rate of 10Hz, at different fluences (25 to 350mJ/cm2). The deposited films were structurally characterized by high-resolution scanning and transmission electron microscopy. 〈100〉 single-crystal Si wafers and carbon-coated Cu grids were used as substrates. Structural analyses evidenced the occurrence of brookite-phase crystalline nanospheres coexisting with individually distinguishable TiO2 nanorods in the films deposited at fluences varying from 50 to 350mJ/cm2. Nanostructured TiO2 films comprising only nanorods were deposited by lowering the laser fluence to 25mJ/cm2. The observed shape and phase transitions of the nanorods are discussed taking into account the laser-induced heating effects, reduced melting temperature and size-dependent thermodynamic stability of nanoscale TiO2.Applied Physics A 04/2012; 105(3):605-610. · 1.63 Impact Factor -
Article: Matrix assisted pulsed laser evaporation: the surface cluster problem
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ABSTRACT: The unexpected presence of agglomerates in polymer films deposited by the Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique is discussed. Many experimental and theoretical works suggest that the simple model of individual molecule evaporation must be abandoned. Solute concentration, boiling temperature and vapor pressure of solvents, laser pulse number, and laser light penetration depth are important parameters to be considered to explain the morphology of the MAPLE deposited films. Nanorods films, which can be efficiently deposited on rough surfaces using the MAPLE technique, present more or less large surface droplets, also. Here, the reduced melting temperature of nanostructured materials can explain agglomeration even at low laser fluences.Applied Physics B 04/2012; 105(3):503-508. · 2.19 Impact Factor -
Article: Zinc oxide nanostructured layers for gas sensing applications
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ABSTRACT: Various kinds of zinc oxide (ZnO) nanostructures, such as columns, pencils, hexagonal pyramids, hexagonal hierarchical structures, as well as smooth and rough films, were grown by pulsed laser deposition using KrF and ArF excimer lasers, without use of any catalyst. ZnO films were deposited at substrate temperatures from 500 to 700°C and oxygen background pressures of 1, 5, 50, and 100 Pa. Quite different morphologies of the deposited films were observed using scanning electron microscopy when different laser wavelengths (248 or 193 nm) were used to ablate the bulk ZnO target. Photoluminescence studies were performed at different temperatures (down to 7 K). The gas sensing properties of the different nanostructures were tested against low concentrations of NO2. The variation in the photoluminescence emission of the films when exposed to NO2 was used as transduction mechanism to reveal the presence of the gas. The nanostructured films with higher surface-to-volume ratio and higher total surface available for gas adsorption presented higher responses, detecting NO2 concentrations down to 3 ppm at room temperature.Laser Physics 04/2012; 21(3):588-597. · 3.61 Impact Factor -
Article: Films of brookite TiO2 nanorods/nanoparticles deposited by matrix-assisted pulsed laser evaporation as NO2 gas-sensing layers
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ABSTRACT: Titanium dioxide (TiO2) nanorods in the brookite phase, with average dimensions of 3–4nm × 20–50nm, were synthesized by a wet-chemical aminolysis route and used as precursors for thin films that were deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. Ananorod solution in toluene (0.016wt% TiO2) was frozen at the liquid-nitrogen temperature and irradiated with a KrF excimer laser at a fluence of 350mJ/cm2 and repetition rate of 10Hz. Single-crystal Si wafers, silica slides, carbon-coated Cu grids and alumina interdigitated slabs were used as substrates to allow performing different characterizations. Films fabricated with 6000 laser pulses had an average thickness of ∼150nm, and a complete coverage of the selected substrate as achieved. High-resolution scanning and transmission electron microscopy investigations evidenced the formation of quite rough films incorporating individually distinguishable TiO2 nanorods and crystalline spherical nanoparticles with an average diameter of ∼13nm. Spectrophotometric analysis showed high transparency through the UV-Vis spectral range. Promising resistive sensing responses to 1ppm of NO2 mixed in dry air were obtained.Applied Physics A 04/2012; 104(3):963-968. · 1.63 Impact Factor -
Article: POLY-(3-HEXYLTHIOPHENE) / [6.6]-PHENYL-C61-BUTYRIC-ACID-METHYL-ESTER BILAYER DEPOSITION BY MAPLE FOR ORGANIC PHOTOVOLTAIC APPLICATIONS
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ABSTRACT: A polymeric poly (3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bilayer structure has been realized, for the first time, by the Matrix-assisted pulsed laser evaporation (MAPLE) technique. Our procedure is based on a single step process in vacuum conditions and uses the same solvent for both the polymers forming the bilayer structure. A proof of concept bilayer P3HT/PCBM solar cell based on the MAPLE deposition has been realized and characterized. The MAPLE technique allows the fabrication of polymeric multilayer device stacks, which is very difficult to realize with the conventional solvent assisted deposition methods. This demonstration qualifies the MAPLE as a general and alternative technique for the implementation of polymeric materials in the hetero-structure device technology.Applied Physics Letters 02/2012; · 3.84 Impact Factor
