Rossana Gazia

Triazene photopolymer dynamic release layer-assisted femtosecond laser-induced forward transfer with an active carrier substrate

Discs of solid material have been forward transferred from thin films on transparent carrier substrates using femtosecond Ti:sapphire laser-induced forward transfer (fs-LIFT) with a triazene polymer dynamic release layer (DRL). The fluence threshold for fs-LIFT was found to be only ≈20% of the DRL ablation threshold at the laser wavelength. This decrease is attributed to ultrafast shock-wave generation in the constrained polymer layer under femtosecond irradiation being the driving force for fs-LIFT with the polymer DRL. The result is very different from the nanosecond regime, where the LIFT threshold is observed to be slightly above the polymer ablation threshold. White-light continuum generation in a carrier substrate is observed and its influence on the fs-LIFT process is discussed.

Effect of the fabrication method on the functional properties of BaTiO3: PVDF nanocomposites

This paper deals with the preparation and characterization of nanocomposite (NC) materials, comparing different technologies for sample fabrication, in view of their possible application as piezoelectric sensors. Those NCs consist on BaTiO3 nanoparticles embedded into a polyvinylidene fluoride matrix, where both the ceramic and the polymeric phases could exhibit ferroelectricity. In particular, we compare the properties of samples prepared through three different methods, i.e., solvent casting, enabling a fast realization, spin-coating, which allows to realize thin flexible films particularly interesting for large area sensors, and hot embossing, which is exploited to modify the residual porosity in the thick films. The influence of the fabrication techniques on the physical and chemical properties is investigated. Different electrode materials have been tested and compared, ranging from sputtered Pt to an engineered thermally evaporated Ti/Au bilayer. Leakage current, polarization, displacement curves, and piezoelectric coefficient d33 are evaluated by small signal indirect measurements, comparing the properties of different materials and understanding how processing technologies influence the sensor performances by acting on the functional materials.

Smart piezoresistive tunnelling composite for flexible robotic sensing skin

A highly mechanically flexible tactile device based on a metal–elastomer composite material was prepared by an efficient and simple process. The microcasting fabrication technique, used for the preparation of a selfstanding sheet of functional material, gives the possibility of easily fabricating complex-shaped structures suitable for integration on robot surfaces for tactile sensing applications. Under the action of a compressive stress the composite material exhibits a giant piezoresistive effect, varying its electrical resistance by several orders of magnitude. This phenomenon can be tuned by changing the material composition parameters, which directly modify the sensitivity of the sensor. After a comprehensive characterization of the functional properties of the material, an 8 × 8 pressure sensor matrix with dedicated electronics was fabricated and tested.

Nanostructured ZnO Materials: Synthesis, Properties and Applications

Over the last decade ZnO nanostructures were intensively and extensively studied by many research groups all over the world not only for their remarkable chemical and physical properties, but also for their current and future technological applications. The aim of this chapter is to give a comprehensive overview of the synthesis methods and growth mechanisms as well as the diverse properties of ZnO nanostructures. According to the ZnO morphology, the chapter shows the most important applications. In particular, the functional properties of ZnO nanostructures in photovoltaic’s, chemical and gas sensing, electronic, optical, optoelectronic, and energy-harvesting devices are reviewed.

Monitoring the dye impregnation time of nanostructured photoanodes for dye sensitized solar cells

Dye-sensitized solar cells (DSSCs) are getting increasing attention as low-cost, easy-to-prepare and colored photovoltaic devices. In the current work, in view of optimizing the fabrication procedures and understanding the mechanisms of dye attachment to the semiconductor photoanode, absorbance measurements have been performed at different dye impregnation times ranging from few minutes to 24 hours using UV-Vis spectroscopy. In addition to the traditional absorbance experiments, based on diffuse and specular reflectance on dye impregnated thin films and on the desorption of dye molecules from the photoanodes by means of a basic solution, an alternative in-situ solution depletion measurement, which enables fast and continuous evaluation of dye uptake, is presented. Photoanodes have been prepared with two different nanostructured semiconducting films: mesoporous TiO2, using a commercially available paste from Solaronix, and sponge-like ZnO obtained in our laboratory from sputtering and thermal annealing. Two different dyes have been analyzed: Ruthenizer 535-bisTBA (N719), which is widely used because it gives optimal photovoltaic performances, and a new metal-free organic dye based on a hemisquaraine molecule (CT1). Dye sensitized cells were fabricated using a customized microfluidic architecture. The results of absorbance measurements are presented and discussed in relation to the obtained solar energy conversion efficiencies and the incident photon-to-electron conversion efficiencies (IPCE).

Multi-beam pulsed laser deposition for advanced thin-film optical waveguides

We discuss our progress in the use of multiple laser beams and multiple targets for the pulsed laser deposition of thin films for waveguide laser and magneto-optic applications. In contrast to the more widely used single-beam/single-target geometries, having more than one laser-produced plume can allow tuning of the material properties and complex engineering of the deposited thin films. For optical applications - the majority of the work reported here - dopants can be selectively introduced, lattice mismatch and residual strain can be compensated, which is an important factor for successful growth of thin films of ~ tens of microns thickness, and refractive index values can be adjusted for fabrication of sophisticated waveguiding structures. We discuss mixed, layered, superlattice and Bragg reflector growth, which involve out-of-plane engineering of the film structure, and in-plane engineered geometries for designs relevant to thin-film disc lasing devices. Finally we briefly discuss our most recent use of multi-plume growth for magneto-optic thin films, which involves compositional tuning of final magnetic properties.

X-Ray Analysis on Ceramic Materials Deposited by Sputtering and Reactive Sputtering for Sensing Applications

Piezoelectric materials have been extensively studied and employed over the last decades with the aim of developing new sensors and actuators to be applied in a wide range of industrial fields. The continuous increase of miniaturization requirements led also to an increasing interest in the synthesis of piezoelectric materials in the form of thin films. As an example, the growth of wireless mobile telecommunication systems favored the expansion of the design and fabrication of high-frequency oscillators and filters (Huang et al., 2005). Within this context, conventional surface acoustic wave (SAW) filters were gradually replaced by film bulk acoustic resonator (FBAR) devices. Their advantage in comparison with SAW devices resides in a higher quality factor (Lee et al., 2003) and lower fabrication costs (Huang et al., 2005). These kinds of devices are based on piezoelectric materials. Thus, an improvement in such material properties can have a strong impact in communication performances. A similar situation exists in the field of sensing. The increase of the sensitivity in piezoelectric sensors is one of the main targets which could be achieved by improving material characteristics. Therefore, the interest in this class of materials is not decreasing with time. On the contrary the enhancement of the piezoelectric material performances, together with the synthesis of new lead-free piezoelectric materials and the integration of ceramic materials with flexible substrates (Akiyama et al., 2006; Wright et al., 2011), is one of the latest research goals. Most piezoelectric materials are metal oxide and few metal nitride crystalline solids and can be single crystals or polycrystalline materials. In both cases, piezoelectric materials are anisotropic and the determination of the response of the material to an external mechanical stress induced along a certain direction on its surface must be performed along different crystallographic axes. Quantitative information about how the material responds to external stresses is given by the piezoelectric constants. Thus, the efficiency of the piezoelectric response can strongly vary with the crystal orientation of the material, and this occurs for bulk materials and thin films (Du et al., 1999; Yue et al., 2003).

Emerging pulsed laser deposition techniques

The use of lasers for the deposition and processing of electronic and photonic materials is becoming increasingly widespread and advances in processing technology are reducing costs and increasing throughput. Laser deposition of photonic materials and laser processing techniques can produce high quality devices with novel properties. Part one covers laser deposition and growth of materials, including pulsed laser deposition and laser-induced self-assembly of semiconductors. Part two describes laser patterning and lithography techniques, such as 3D laser lithography. Part three looks at laser treatments to manipulate properties of photonic materials for applications such as optical storage, laser components, waveguides and displays.