I. Nasti

Sub-PPM Nitrogen Dioxide Conductometric Response at Room Temperature by Graphene Flakes Based Layer

The two-dimensional nature of graphene, allowing a total exposure of all its atoms to the adsorbing gas molecules, provides the greatest sensor area per unit volume and outlines the possibility to employ this material as a powerful sensing layer. The synthesis and manipulation of graphene as well as the device fabrication are still challenging due to several technological limits. In the present work we report on a simple approach to fabricate chemiresistive sensors based on chemically exfoliated natural graphite. The devices show the ability to detect a toxic gas, such as NO2, down to few ppb at room temperature in controlled environments.

Silicon infrared diffuser for wireless communication

We show what we believe to be a novel way to use silicon in infrared radio communication as a suitable material for the realization of optical diffusers in the range of 850-1600 nm. A crystalline silicon wafer is made porous by means of electrochemical etching. The porous silicon produced is optically characterized, and measurements report a high reflectance in the band of interest. We also study the angular distribution of diffused radiation by the porous silicon surface at different angles of incident radiation. Measurements show that radiation diffuses in a quasi-Lambertian manner, confirming the good performance of this material as an incident radiation diffuser.

UV Lithography On Graphene Flakes Produced By Highly Oriented Pyrolitic Graphite Exfoliation Through Polydimethylsiloxane Rubbing

Graphene is a promising candidate in sensing applications; indeed thanks to its two-dimensionality, it provides the highest surface volume ratio, allowing all its atoms to be totally exposed to the adsorbing gas molecules. Due to several technological limits in production and manipulation of graphene as well as the device fabrication, the synthesis of graphene is still far from a well-settled process. This work aims to illustrate an approach for the graphene preparation that is based on the mechanical exfoliation and circumvents some difficulties encountered in a graphene based nanodevice production. Relying on that fabrication technique a chemiresistive sensor device was prepared. Preliminary findings showed that the device responds to a toxic gas such as \(\hbox{NO}_2,\) up to a few ppm, and reducing gases, such as \(\hbox{NH}_3,\) to few hundred ppm, at room temperature in controlled environments.

Chemically Derived Graphene for Sub-ppm Nitrogen Dioxide Detection

One of the most extraordinary properties of the graphene, the high sensitivity to the adsorption/desorption of gas molecule, is still at the very beginning of its exploitation. The ability to detect the presence even of a single interacting molecule relies on the two-dimensional nature of graphene, that allows a total exposure of all its atoms to the adsorbing gas molecules, thus providing the greatest sensor area per unit volume. Nevertheless, due to the complexity of the entire process, starting from the graphene synthesis and/or isolation up to the introduction into the proper device architecture, the fabrication of the single graphene flake based chemical sensor is still challenging. Herein a simple approach to fabricate a sensitive material based on chemically exfoliated natural graphite is presented. The devices were tested upon sub-ppm concentrations of \(\hbox{NO}_2\) and show the ability to detect this toxic gas at room temperature in actual environmental conditions.

OPTICAL STRAIN SENSOR BASED ON POLYMERIC DIFFRACTION GRATINGS

We look at an innovative method for the strain, stress measurement on surface. Our project is a simple imaging technique illuminating a polymer (PDMS) grid, attached on specimen, with a large spectra light source, and recording, with a ccd camera, the grid image obtained by diffracting light. Image acquired under stress is subtracted from one without stress giving a colour map of the surface correlated to the stress intensity. This technique arises from asserted optical techniques. Moreover, taking in account the technological progress (polymer, ccd, LEDs), we make the hardware setup very simple because it doesn’t need coherent light source and the detector may be a commercial colour ccd.

CHEMICAL SENSORS BASED ON CARBON NANOTUBES: COMPARISON BETWEEN SINGLE AND BUNDLES OF ROPES

A chemical gas sensor based on a single rope of single walled carbon nanotubes (SWCNTs) has been fabricated first isolating the rope on a silicon/Si3N4 substrate and then realizing, at its ends, two platinum microelectrodes by means of a Focused Ion Beam (FIB). Its electrical behaviour at room temperature in toxic gas environments has been investigated and compared to sensors based on bundles of SWCNT ropes. For all the devices upon exposure to NO2 and NH3 the conductance has been found to increase or decrease respectively. Response time in NO2 is however faster for device based on the single rope. A mechanism for molecular sensing is proposed.

Polymeric Replicas from Porous Silicon Template (and Its Response to Vapour)

Polystyrene replica is realized preparing polystyrene and depositing the polymer onto a nanostructured porous silicon matrix used as a template. The thin polymer film is peeled off from the substrate and exposed to organic vapours. Swelling affects the optical reflectance and, by a specially adjusted set-up, the kinetic of the vapour desorption is measured in ordcr to investigate replicas as drug delivery systems.

Fabrication and Characterization of a Hydrogen Sensor Based on Palladium Nanowires

A hydrogen sensor based on an array of palladium nanowires has been realized starting from a silicon substrate coated with a Si3N4 where an interdigitated electrode pattern has been fabricated using photolithography. Saturated palladium solution has been prepared and array of palladium nanowires has been formed applying at the electrodes a voltage signal. As grown Pd nanowires are conductive and do not exhibit any response to hydrogen. Their response can be activated after a treatment which modifies physical properties of Pd nanowires, improving their response. The array has been tested towards 4% H2 in nitrogen carrier. We have observed that the device response, at room temperature, is quite strong and reversible so that the sensor device seems to be useful for those applications where the Lower Explosive Limit needs to be controlled.