L. Quercia

Nanostructured porous silicon for gas sensor applications

Abstract The response of two different types of nanostructured gas sensor to oxygen has been investigated. The first (optical) is based on the photoluminescence quenching effect of a porous silicon sample, the second on the changes of the electrical conductance v. environment of a porous silicon free standing membrane on an insulating neutral substrate. The response of both the devices to oxygen have been measured and compared. The optical based gas sensor exhibits a quenching following the Stern-Volmer model. The corresponding reactivity rate constant is found to depend on a characteristic nanodimension of the wire. The electrically operated sensor is more sensitive to oxygen and shows an opposite behavior if exposed to a reducing environment.

Innovative Diodes based on Amorphous-Porous Silicon Heterojunction

In this paper the authors present an innovative diode based on the heterojunction between amorphous silicon and porous silicon grown on crystalline silicon. The device architecture gives several advantages. Deposition of amorphous silicon on porous material realizes high performance junction at temperature less than 250 C and it passives the porous layer against the natural oxidation due to aging in the environment. Porous technology allows to obtain a controlled textured silicon surface independently from crystalline silicon orientation just to give the opportunity to reduce surface reflectivity and the blue shift of the absorption spectra in solar cell application. Solar cells were characterized by I-V dark/light and quantum yield measurements. Under standard AM 1.5 light they obtained photovoltaic conversion efficiency greater than 10%. Change in photoluminescence in different gas environments showed for gas sensor applications give rise to encouraging results. In dark condition they found the typical diode behavior.

ON THE FABRICATION PROCESS OF POLYMER-COMPOSITES BASED SENSORS

The results of investigations of the effects of two organic solvents of preparation, tetrahydrofuran (THF) and 1,1,1,3,3,3 Hexafluoro-2-propanol (HFIP), and of three different electrical geometry of devices on drop-coated poly (methyl-methacrylate)/ carbon black (PMMA/CB) composites gas sensors are presented. Using HFIP solvent, it is possible to obtain a good dispersion of the CB filler in the polymeric matrix but the thermodynamic responses of devices to acetone and ethanol vapours are independent from their morphology and from the geometry of devices. The highest sensor responses are to acetone vapor. This behavior could be probably attributed to the higher chemical affinity of less polar molecule as acetone towards PMMA. The filler dispersions, the current-voltage (I/V) characteristics and the stability of devices in the time were also studied and discussed.

Towards an All Polymeric Electronic Nose: Device Fabrication and Characterization, Electronic Control, Data Analysis

In this work, a wireless electronic nose prototype, called TinyNose, hosting an array of four different polymeric-composite sensors developed at ENEA, is presented. Sensors are fabricated using a carbon black conducting phase dispersed in different polymeric matrices. The prototype has shown interesting results for VOC compounds detection and discrimination purposes during a measurement campaign.