Francesco Toschi

Role of the Material Electrodes on Resistive Behaviour of Carbon Nanotube-Based Gas Sensors for H 2 SDetection

Miniaturized gas-sensing devices that use single-walled carbon nanotubes as active material have been fabricated using two different electrode materials, namely, Au/Cr and NbN. The resistive sensors have been assembled aligning by dielectrophoresis the nanotube bundles between 40 μm spaced Au/Cr or NbN multifinger electrodes. The sensing devices have been tested for detection of the H2S gas, in the concentration range 10–100 ppm, using N2 as carrier gas. No resistance changes were detected using sensor fabricated with NbN electrodes, whereas the response of the sensor fabricated with Au/Cr electrodes was characterized by an increase of the resistance upon gas exposure. The main performances of this sensor are a detection limit for H2S of 10 ppm and a recovery time of few minutes. The present study suggests that the mechanism involved in H2S gas detection is not a direct charge transfer between molecules and nanotubes. The hypothesis is that detection occurs through passivation of the Au surfaces by H2S molecules and modification of the contact resistance at the Au/nanotube interface.

Conducting polymer/nanodiamond composites: New opportunities and scientific challenges for material science

We present some recent results of a systematic study regarding polymer-based nanocomposites with carbon nanostructures as guest components. This paper is focused on the coupling of conductive polymers, as polyanilines and polythiophenes, with nanodiamond grains. The peculiar properties of such crystalline nanomaterial not only help in improving the mechanical and thermal properties of the host polymeric matrices, but also act on the polymerization mechanism, modifying the morphological features of the polymers. Triggered by the nanodiamond presence, the final nanocomposites show a prominent arrangement of polymer segments into tubular forms and a subsequent structural organization suitable for many technological applications.

Low temperature conductivity of carbon nanotube aggregates

We compare, over wide temperature ranges, the transport properties of single-wall carbon nanotubes arranged in the form of aligned arrays or in the form of fibres. The experimental data show that both the forms of aggregates present a crossover in the transport mechanism from three-dimensional hopping of the electrons between localized states at high temperature to fluctuation-induced tunnelling across potential barriers at low temperature. The role of the junctions formed between the bundles in the array and between the nanotubes inside the fibres is discussed on the basis of the experimental results.

Carbon Nanotubes Guides for Nickel Electrical Interconnects

We present an innovative approach for interconnections based on aligning nanosized nickel particles along single-walled carbon nanotubes bundles. The nanotubes are first deposited to connect normal gold contacts or niobium nitride superconducting pads and a successive step in fabrication, based on an electrochemical method, enables us to “coat” the nanotubes with nickel particles. This technique, as shown by field-emission SEM analysis, generates chains of nickel particles aligned along the nanotubes connecting the contact electrodes. The temperature dependence of the resistance of the chains of Ni nanoparticles evidences the metallic nature of the obtained interconnection and shows values of the resistances up to three orders of magnitudes lower than those of the bare nanotubes bundles. The ease of the fabrication process and its reliability candidate our technique as a possible solution for interconnects applications.

Preparation and Thermal Characterization of Carbon Nanotubes-Based Composites for Applications in Electronics Packaging

The thermal resistance of nanocomposite layers formed by Single Wall Carbon Nanotubes (SWCNT) dispersed in epoxy resins has been measured under conditions similar to the ones used to dissipate heat in microelectronic devices. The variation of thermal conductivity as a function of concentration of SWCNT is reported and discussed with reference to the dispersion state of SWCNT in the layers.

Quartz crystal nano-balance for hydrogen sensing at room temperature using carbon nanotubes aggregates

The gas sensor based on carbon nanotubes are presently receiving considerable attention because of the outstanding properties, such as faster response, higher sensitivity, lower operating temperature and robustness of the nanotubes in comparison with the other types of sensing materials. In the present research, we demonstrate detection of hydrogen at room temperature using a Quartz Crystal Nano-balance (QCN) and as sensing material, Single-Walled Carbon Nanotubes (SWCNTs) dispersed in a polythiophene matrix. The experimental determination of H2 in H2/N2 mixtures has been performed by using a counter frequency and observing the frequency shifts induced in a quartz crystal resonator by H2 adsorption and consequent mass variation of the active layer deposited on the quartz. The high sensitivity of the realized nano-balance allows us to observe mass variations up to few nanograms /Hertz and to detect up to 1% of H2. The good sensing performances of the nanotube-based material make unnecessary the use of any catalyst species for H2 detection. Moreover this QCN device is able to work with good efficiency at 23 °C and 1 Atm.

Realization of a carbon nanotube-based triode

We report the design and realization of a carbon nanotube-based integrated triode. Patterned Si/SiO2/Nb/Nb2O5multilayer was successfully realized by means of a photolithographic process. Such structure constitutes the patterned substrate of the successive Hot Filament Chemical Vapour Deposition (HFCVD) process. Selective growth of highly oriented SWCNT arrays was obtained in the predefined locations while survival of the entire structure was achieved. Field emission measurements of such materials were carried out both on a diode and in a triode configuration. Good and reproducible field emission behaviour has been observed in several realized structures. In order to validate the experimental data a first simulation of the behaviour of the integrated vacuum triode with a single field emission CNT was also simulated.

Gold nanoparticles functionalized by rhodamine B isothiocyanate: a new tool to control plasmonic effects

Gold nanoparticles with an average diameter of 10 nm, functionalized by the dye molecule rhodamine B isothiocyanate, have been synthesized. The resulting material has been extensively characterized both chemically, to investigate the bonding between the dye molecules and the nanoparticles, and physically, to understand the details of the aggregation induced by interaction between dye molecules on different nanoparticles. The plasmonic response of the system has been further characterized by measurement and theoretical simulation of the static UV-Vis extinction spectra of the aggregates produced following different synthesis procedures. The model parameters used in the simulation gave further useful information on the aggregation and its relationship to the plasmonic response. Finally, we investigated the time dependence of the plasmonic effects of the nanoparticles and fluorescence of the dye molecule using an ultrafast pump-probe optical method. By modulating the quantity of dye molecules on the surface of the nanoparticles it was possible to exert fine control over the plasmonic response of nanoparticles.

Nanotechnology radar thermal management

Active phased array antennas in state of art radars, adopt many high power amplifiers. High power transmit-receive modules are assembled in dense electronic environments and they have to cope with severe environmental operative condition. Radar state of art systemic signal processing requires growing and enormous power calculation in order to obtain unprecedented hard real-time performances as well as implementing adaptive knowledge based algorithms. Unfortunately the present steady growth of the micro-processors performance are reaching a saturation point due to the approaching limit of miniaturizations. Present and future active phased array antennas and signal processors have large and increasing heat dissipation problems. Nanotechnologies are emerging as enabling technologies that will provide a revolution in the sectors of sensors and radar systems. These innovative technologies could enable new solutions and improve weight, size, speed, power consumption, efficiency, and so on. In addition, the nanotechnologies could solve the increasing heat dissipation problems by adopting carbon nanotubes CNT ropes or arrays for thermal management and interconnection.

Nanotechnology RADAR thermal management

Active phased array antennas in state of art radars, adopt many high power amplifiers. High power transmit-receive modules are assembled in dense electronic environments and they have to cope with severe environmental operative condition. Radar state of art systemic signal processing requires growing and enormous power calculation in order to obtain unprecedented hard real-time performances as well as implementing adaptive knowledge based algorithms. Unfortunately the present steady growth of the micro-processors performance are reaching a saturation point due to the approaching limit of miniaturizations. Present and future active phased array antennas and signal processors have large and increasing heat dissipation problems. Nanotechnologies are emerging as enabling technologies that will provide a revolution in the sectors of sensors and radar systems. These innovative technologies could enable new solutions and improve weight, size, speed, power consumption, efficiency, and so on. In addition, the nanotechnologies could solve the increasing heat dissipation problems by adopting carbon nanotubes CNT ropes or arrays for thermal management and interconnection.