G. Cassano

Enhancement of sensitivity in gas chemiresistors based on carbon nanotube surface functionalized with noble metal (Au, Pt) nanoclusters

Multiwalled carbon nanotube (MWCNT) films have been fabricated by using plasma-enhanced chemical vapor deposition system onto Cr–Au patterned alumina substrates, provided with 3nm thick Fe growth catalyst, for NO2 and NH3 gas sensing applications, at sensor temperature in the range of 100–250°C. Nanoclusters of noble metal surface catalysts (Au and Pt) have been sputtered on the surface of MWCNTs to enhance the gas sensitivity with respect to unfunctionalized carbon nanotube films. It was found that the gas sensitivity of Pt- and Au-functionalized MWCNT gas sensors significantly improved by a factor up to an order of magnitude through a spillover effect for NH3 and NO2 gas detections, respectively. The metal-functionalized MWCNT sensors exhibit very high gas sensitivity, fast response, reversibility, good repeatability, and sub-ppm range detection limit with the sensing properties of the MWCNT films tailored by surface catalyst used to functionalize the MWCNT sensors.

Alcohol detection using carbon nanotubes acoustic and optical sensors

We demonstrate the integration of single-walled carbon nanotubes (SWCNTs) onto quartz crystal microbalance (QCM) and standard silica optical fiber (SOF) sensor for alcohol detection at room temperature. Different transducing mechanisms have been used in order to outline the sensing properties of this class of nanomaterials, in particular the attention has been focused on two key parameters in sensing applications: mass and refractive index changes due to gas absorption. Here, Langmuir–Blodgett (LB) films consisting of tangled bundles of SWCNTs without surfactant molecules have been successfully transferred onto QCM and SOF. Mass-sensitive 10MHz QCM SWCNTs sensor exhibited a resonant frequency decreasing upon tested alcohols exposure; also the normalized optoelectronic signal (λ=1310nm) of the refractive index-sensitive SOF SWCNTs sensor was found to decrease upon alcohols ambient. Highly sensitive, repeatable and reversible responses of the QCM and SOF SWCNTs sensors indicate that the detection, at room t...

Carbon nanotube acoustic and optical sensors for volatile organic compound detection

Carbon nanotube coated acoustic and optical sensors have been successfully studied for volatile organic compound (VOC) sensing applications, at room temperature. Here, Langmuir?Blodgett (LB) films consisting of tangled bundles of single-walled carbon nanotubes (SWCNTs) have been transferred onto different transducing sensors by using a linker?buffer LB multilayered material of cadmium arachidate pre-deposited on the sensor surface to promote adhesion of SWCNTs. Two different kinds of sensors have been designed, fabricated and utilized: quartz crystal microbalance 10?MHz AT-cut quartz resonators and standard silica optical fibre sensors based on light reflectometry at a wavelength of 1310?nm. The proposed detection techniques are focused on two key parameters in gas sensing applications: mass and refractive index, and their changes induced by gas molecule absorption. The results indicate high sensitivity, good repeatability and reversibility. Signals from each sensor type have been analysed and processed by using pattern recognition techniques such as principal component analysis and use of artificial neural networks. The recognition of the hybrid system is successfully performed, improving the data fusion from acoustic and optical sensors with SWCNT-functionalized sensors that are highly discriminating. To our knowledge, this is the first reported study of combined hybrid integration of acoustic sensors with optical fibre sensors using nanostructured materials as single-walled carbon nanotubes for VOC detection, at room temperature.

Classification of food, beverages and perfumes by WO3 thin-film sensors array and pattern recognition techniques

Abstract We have designed and fabricated a sensors array using WO3 thin films operating at the temperature of 180°C for food and perfume analysis purposes. The sensing surface of the rf sputtered WO3 thin films has been differently activated by evaporated Pd, Au, Bi, Sb catalysts. Pattern recognition (PARC) techniques as principal components analysis (PCA) and cluster analysis (CA) have been used in order to classify and identify different classes of flavours samples such as olive oils and seed oils, fruit juices, tomato sauces, perfumes. Good separation among flavours samples belonging to homogeneous and comparable classes has been obtained by PARC methods. The headspace sampling has been referenced off-line by qualitative chromatograms of the volatile compounds constituent the odour under test. The preliminary results show the feasibility of the electronic nose system to discriminate various flavours for food analysis and perfumes quality control.

Effect of growth catalysts on gas sensitivity in carbon nanotube film based chemiresistive sensors

Multiwalled carbon nanotube (MWCNT) films have been deposited by using plasma enhanced chemical vapor deposition (PECVD) system onto Cr–Au patterned alumina substrates for NO2 and NH3 gas sensing applications, at operating temperature of 200°C. Nanoclusters of different MWCNT-growth catalysts (Fe and Co) have been predeposited onto substrates to promote the growth of the carbon nanotube films with different structural properties. It is demonstrated that the gas sensitivity of the MWCNT films depends on catalyst used for their growth with highest gas sensitivity achieved for Co-grown MWCNT films. The chemiresistor gas response is attributed to the p-type conductivity in semiconducting MWCNTs and the electrical charge transfer is found to be the major sensing mechanism. The results obtained demonstrate that the MWCNT-based sensors exhibit high gas sensitivity, fast response and reversibility, good repeatability and reproducibility, and sub-ppm range detection limit with the gas sensing properties of the MWC...

The effect of purification of single-walled carbon nanotube bundles on the alcohol sensitivity of nanocomposite Langmuir?Blodgett films for SAW sensing applications

HiPco (high-pressure CO dissociation process) single-walled carbon nanotube (SWCNT) bundles containing Fe particles were purified in a two-step purification process by thermal annealing in oxygen and post-treatment in HCl. Nanocomposite films of pristine and purified SWCNTs embedded in an organic matrix of cadmium arachidate (CdA) were prepared by a Langmuir?Blodgett (LB) molecular engineering technique with a fixed weight filler content of 75?wt% onto a surface acoustic wave (SAW) transducer operating as an oscillator at a frequency of 433?MHz. The raw and purified samples were characterized at various stages of the purification process using thermogravimetric analysis (TGA), high-resolution transmission electron microscopy (HR-TEM), along with energy-dispersive x-ray spectroscopy (EDS), field emission scanning electron microscopy (FE-SEM) and x-ray diffraction (XRD). Functional characterizations of the SWCNT?nanocomposite-based SAW sensors were investigated towards methanol, isopropanol and ethanol, and demonstrated high sensitivity, reversibility, fast response and ppm level detection at room temperature. Results indicate that the sensitivity of the SAW sensors based on a nanocomposite film of oxygen-annealed SWCNTs is enhanced to the alcohols tested at room temperature. Purification of the SWCNTs in the nanocomposite film affects the SAW sensitivity to alcohol by modulating the sensing properties. The sensing mechanisms are analysed and discussed.

Thin-Film Bulk-Acoustic-Resonator Gas Sensor Functionalized With a Nanocomposite Langmuir–Blodgett Layer of Carbon Nanotubes

A thin-film bulk acoustic resonator (TFBAR) based on a vibrating membrane of AlN/Si3N4 has been fabricated onto a silicon substrate and functionally characterized as gas sensor at a resonating frequency of 1.045 GHz. This novel TFBAR-based gas sensor has been functionalized by a sensing nanocomposite layer, prepared by a Langmuir-Blodgett (LB) technique, of single-walled carbon nanotubes (SWCNTs) embedded in a host matrix of organic material of cadmium arachidate. High-performance gas detection at room temperature of a SWCNT-coated TFBAR sensor has been reported. The sensing device exhibits high sensitivity (e.g., acetone: 12 kHz/ppm; ethylacetate: 17.3 kHz/ppm), fast response (within 2-3 min), slow reversibility (within 1 h), and good repeatability (les 5% variation) of response toward tested organic vapors of acetone, ethylacetate, and toluene.

Acoustic and Optical VOCs Sensors Incorporating Carbon Nanotubes

The authors investigate the sensing properties of single-walled carbon nanotubes (SWCNTs) films, which are used as nanostructured materials for chemical sensors onto three types of transducers using different principles of operation as surface acoustic waves (SAWs), quartz-crystal microbalance (QCM), and a standard silica optical fiber (SOF) for detection of volatile organic compounds at a room temperature. The sensing probes have been configured as 315- and 433-MHz SAW two-port resonator-based oscillator, 10-MHz QCM resonator, and SOF light-reflectometry-based system at a wavelength of 1310 nm. A nanocomposite film of SWCNTs embedded in a cadmium-arachidate matrix was deposited by Langmuir-Blodgett (LB) technique onto the SAW sensors. An LB multilayer of SWCNTs-onto-CdA buffer material was also deposited onto the QCM and SOF sensors. The experiments demonstrate that carbon-nanotubes acoustic and optical sensors are highly sensitive to a wide range of polar and nonpolar organic solvents up to a sub-ppm detection limit at a room temperature

Carbon Nanotubes Coated Acoustic and Optical VOCs Sensors: Towards the Tailoring of the Sensing Performances

This work is focused on the room temperature sensitivities and response times analysis against aromatic volatile organic compounds of both silica optical fiber and quartz crystal microbalance sensors, coated by single-walled carbon nanotubes (SWCNTs) Langmuir-Blodgett multilayers as highly sensitive nanomaterials. The fabricated samples have been characterized by means of X-ray diffraction, high-resolution transmission electron microscopy and scanning electron microscopy, silica optical fiber, and quartz crystal microbalance transducers have been simultaneously exposed at room temperature to toluene and xylene individual vapors in the ppm range. For each transducer type, a time division multiplexing approach has been exploited, enabling the simultaneous interrogation of up to 8 optical and 6 acoustic probes, respectively. The results obtained indicate that both optical and acoustic sensors provide very high reproducibility and sensitivity either towards toluene or xylene, with a resolution of few hundreds of ppb. Furthermore, sensitivities and response times turned out to be dependent on the particular analytes used for the vapors testing. Both transducer types demonstrate a similar response time, while with regard the recovery time, the optical detection seems to be significantly faster than the electrical counterpart. The effect of the SWCNTs monolayers number on sensors sensitivity and response time has also been investigated, demonstrating the possibility to enhance the performances of the proposed transducers by tailoring the geometric properties of the sensitive nanomaterial.

Surface Modification of Carbon Nanotube Networked Films with Au Nanoclusters for Enhanced NO2 Gas Sensing Applications

Multiwalled carbon nanotube (MWCNT) films have been deposited by using plasma-enhanced chemical vapor deposition (PECVD) system onto alumina substrates, provided with 6 nm thick cobalt (Co) growth catalyst for remarkably improved NO2 gas sensing, at working temperature in the range of 100–250∘C. Functionalization of the MWCNTs with nanoclusters of gold (Au) sputtering has been performed to modify the surface of carbon nanotube networked films for enhanced and specific NO2 gas detection up to sub-ppm level. It is demonstrated that the NO2 gas sensitivity of the MWCNT-based sensors depends on Au-loading used as surface-catalyst. The gas response of MWCNT-based chemiresistor is attributed to p-type conductivity in the Au-modified semiconducting MWCNTs with a very good short-term repeatability and faster recovery. The sensor temperature of maximum NO2 sensitivity of the Au-functionalized MWCNTs is found to decrease with increasing Au-loading on their surface, and continuous gas monitoring at ppb level of NO2 is effectively performed with Au-modified MWCNT chemiresistors.