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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 (≤5% variation) of response toward tested organic vapors of acetone, ethylacetate, and toluene. © 2008 IEEE.

In this work, carbon nanomaterials have been prepared by CVD technology onto alumina substrates, coated by nanosized Co-catalyst at different thickness (2.5 nm and 7.5 nm) and used for a simple gas sensor device. The surface has been functionalized with sputtered Pt-nanocluster at a tuned loading of 8, 15 and 30 nm. The response of the chemiresistors in terms of p-type electrical conductance has been investigated as a function of the thickness of the Pt-nanoclusters towards different gases (NO 2, NH 3, CO, CH 4, CO 2). Furthermore, the effect of the temperature ranging from 20°C to 250°C on the sensor response has been addressed as well. Additionally, a short-term stability of the carbon nanomaterials based sensor towards NO 2 gas detection has been investigated for a 2-month period. The gas sensors based on Pt-modified carbon nanomaterials exhibit higher sensitivity compared to unmodified material, fast response, reversibility, repeatability, moderate drift of the baseline signal, sub-ppm range detection limit. © 2012 Springer Science+Business Media, LLC.

A Quartz Crystal Microbalance (QCM) gas sensor coated with carbon nanotubes (CNTs) layered films as chemically interactive nanomaterial is described. A QCM resonator integrated on AT-cut quartz substrate has been functionally characterized as oscillator at the resonant frequency of 10 MHz. The CNTs have been grown by chemical vapor deposition (CVD) system onto alumina substrates, coated with 2.5 nm thick Fe catalyst, at a temperature of 750°C in H 2/C 2H 2 gaseous ambient as active materials for gas sensors. CNTs multilayers, with and without buffer layer of cadmium arachidate (CdA), have been prepared by the Langmuir-Blodgett (LB) technique to coat at the double-side the QCM sensors for organic vapor detection, at room temperature. It was demonstrated that the highest mass sensitivity has been achieved for CNTs multilayer onto CdA buffer material due to the greatest gas adsorbed mass. The sensing properties of the CNTs-sensors at enhanced mass sensitivity have been investigated for different vapors of ethanol, methanol, acetone, m-xylene, toluene and ethylacetate in a wide range of concentration from 10 to 800 ppm. The CNTs-based QCM-sensors exhibit high sensitivity (e.g., 5.55 Hz/ppm to m-xylene of the CNTs-multilayer) at room temperature, fast response, linearity, reversibility, repeatability, low drift of the baseline frequency, potential sub-ppm range detection limit. © 2012 Springer Science+Business Media, LLC.

Carbon nanotubes (CNTs) networked films have been grown by chemical vapor deposition (CVD) technology onto miniaturized low-cost alumina substrates, coated by nanosized Co-catalyst for growing CNTs, to perform chemical detection of toxic gasses (NO2 and NH3), greenhouse gasses (CO 2 and CH4) and domestic safety gasses (CO and C 2H5OH) at an operating sensor temperature of 120 °C. The morphology and structure of the CNTs networks have been characterized by scanning electron microscopy (SEM). A dense network of bundles of multiple tubes consisting of multi-walled carbon nanostructures appears with a maximum length of 1-5 μm and single-tube diameter varying in the range of 5-40 nm. Surface modifications of the CNTs networks with sputtered Platinum (Pt) nanoclusters, at tuned loading of 8, 15 and 30 nm, provide higher sensitivity for significantly enhanced gas detection compared to un-decorated CNTs. This could be caused by a spillover of the targeted gas molecules onto Pt-catalyst surface with a chemical gating into CNTs layers. The measured electrical conductance of the functionalized CNTs upon exposures of a given oxidizing and reducing gas is modulated by a charge transfer model with p-type semiconducting characteristics. The effect of activated carbons as chemical filters to reduce the influence of the domestic interfering alcohols on CO gas detection has been studied. Functionalized CNT gas sensors exhibited better performances compared to unmodified CNTs, making them highly promising candidates for functional applications of gas control and alarms. © 2011 Elsevier B.V. All rights reserved.

A Quartz Crystal Microbalance (QCM) gas sensor coated with carbon nanotubes (CNTs) layered films as chemically interactive nanomaterial is described. A QCM resonator integrated on AT-cut quartz substrate has been functionally characterized as oscillator at the resonant frequency of 10 MHz. The CNTs have been grown by chemical vapor deposition (CVD) system onto alumina substrates, coated with 2.5 nm thick Fe catalyst, at a temperature of 750°C in H 2/C2H2 gaseous ambient as active materials for gas sensors. CNTs multilayers, with and without buffer layer of cadmium arachidate (CdA), have been prepared by the Langmuir-Blodgett (LB) technique to coat at the double-side the QCM sensors for organic vapor detection, at room temperature. It was demonstrated that the highest mass sensitivity has been achieved for CNTs multilayer onto CdA buffer material due to the greatest gas adsorbed mass. The sensing properties of the CNTs-sensors at enhanced mass sensitivity have been investigated for three different vapors of ethylacetate, acetone and m-xylene in the range of gas concentration from 10 to 800 ppm. The CNTs-based QCM-sensors exhibit high sensitivity (e.g., 5.55 Hz/ppm to m-xylene of the CNTs-multilayer) at room temperature, fast response, linearity, reversibility, repeatability, low drift of the baseline frequency, potential sub-ppm range detection limit. © 2011 Springer Science+Business Media B.V.

Vertically-aligned carbon nanotubes (CNTs) films have been grown by radiofrequency plasma-enhanced chemical vapor deposition system onto alumina substrates, coated with 2.5 nm thick Fe catalyst, for NO2, H 2 and C2H5OH gas sensing applications, at sensor temperatures from room-temperature to 150°C. The CNTs appear in the form of forest-like structure. Nanoclusters of noble metals with nominal thickness of 5 nm of Pt, Ru and Ag have been sputtered on the top-surface of the vertically-aligned CNTs layers to enhance the gas sensitivity. It was demonstrated that the gas sensitivity of the metal modified CNTs-sensors significantly improved by a factor up to an order of magnitude through a spillover effect, and a broader selectivity was provided. The gas sensing properties of the CNTs-sensors, including the metal-modified CNTs, are characterized by a change of the electrical conductivity in a model of the charge transfer with a semiconducting p-type character. The metal-functionalized CNTs-sensors exhibit high sensitivity, fast response, reversibility, good repeatability, sub-ppm range detection limit. A practical application of the CNTs-sensors for monitoring landfill gas is presented. © 2010 Springer Science+Business Media B.V.

A chemical sensor based on Thin-Film Bulk Acoustic Resonator (TFBAR) structure is designed, fabricated and functionally characterized. A novel acoustic gas microsensor is represented by TFBAR consisting of a piezoelectric A1N thin layer sandwiched between two metallic Al electrodes and excited by a microwave signal to build a vibrating membrane integrated onto silicon substrate and resonating at 1.045 GHz frequency. Nanocomposite film based on Single-Walled Carbon Nanotubes (SWCNTs) with nanostructured properties have been prepared by Langmuir-Blodgett (LB) material processing technique to functionalise the surface of TFBAR devices for gas detection. Based on the excellent integration compatibility with SWCNTs-based TFBAR sensor, the studied sensing device provides the potentiality in high-performance gas detection applications. The sensing characteristics towards vapors of acetone, ethylacetate, toluene, alcohols have been measured at room temperature with high sensitivity, fast response, good reversibility and repeatability of response.

A chemical sensor based on Surface Acoustic Wave (SAW) electro-acoustic structure is designed, fabricated and functionally characterized for gas sensing, at room temperature. A SAW two-port resonator integrated on ST-quartz substrate has been used in dual differential mode at resonant frequency of 433 and 915 MHz. Nanocomposite films based on filler of Carbon Nanotubes (CNTs) with nanostructured properties have been prepared by Langmuir-Blodgett (LB) material processing technique to functionalize the surface of SAW devices for vapor detection. The sensing characteristics towards vapors of ethanol, methanol, acetone, m-xylene, and toluene have been measured at room temperature with good performance of the SAW sensor.

A surface acoustic wave (SAW) gas sensor with multiwalled carbon nanotubes (CNTs) layered films as chemically interactive nanomaterial is presented. A SAW two-port resonator integrated on ST-cut quartz substrate has been functionally characterized as oscillator in dual differential mode at the resonant frequency of 433.92 and 915 MHz. Nanocomposite layers based on filler of CNTs, grown by RF-plasma enhanced chemical vapor deposition, have been prepared by the Langmuir-Blodgett (LB) technique to coat the SAW microdevices for organic vapor detection, at room temperature. Results concerning the SAW sensing performance towards ethanol, methanol, acetone, m-xylene, and toluene are described. These results demonstrate clearly the potential of the SAW CNTs-nanocomposite chemical microsensors at high frequencies for the fabrication of low-cost and highly gas-sensitive devices for promising room-temperature sensing operations.

We demonstrate the successful operation of a chemical microsensor based on Thin Film Bulk Acoustic Resonator (TFBAR) for organic vapor detection at room temperature. The TFBAR consists of a vibrating membrane of AIN/SI 3N4 fabricated on silicon substrate and resonating at the frequency of 1.045 GHz. Using a nanocomposite layer based on Single-Walled Carbon Nanotubes (SWCNTs) and prepared by the Langmuir-Blodgett technique onto the TFBAR device as highly-sensitive nanomaterial, the sensing performance of TFBAR sensor has been evaluated both as a passive device by a network analyzer with phase and insertion loss responses, and as oscillator with frequency response. The vapor sensing characteristics of SWCNTs-based TFBAR sensor are presented illustrating interesting results. © 2007 IEEE.