Chemical Sensors Based on Carbon Nanotubes: Comparison Between Single and Bundles of Ropes (original) (raw)
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Focused Ion Beam Nanopatterning for Carbon Nanotube Ropes based Sensor
Un ni iv ve er rs si it tá á d di i B Br re es sc ci ia a, , I It ta aly Abstract: Focused Ion Beam (FIB) technology has been used to realize electrode patterns for contacting Single Walled Carbon Nanotubes (SWCNTs) ropes for chemical gas sensor applications. Two types of transducers, based on a single rope and on bundles, have been realized starting from silicon/Si 3 N 4 substrate. Electrical behaviour, at room temperature, in toxic gas environments, has been investigated and compared to evaluate contribution of a single rope based sensor respect to bundles one. For all the devices, upon exposure to NO 2 and NH 3, the conductance has been found to increase or decrease respectively. Conductance signal is stronger for sensor based on bundles, but it also evident that response time in NO 2 is faster for device based on a single rope. FIB technology offers, then, the possibility to contact easily a single sensitive nanowire, as carbon nanotube rope.
Electrochemically Functionalized Single-Walled Carbon Nanotube Gas Sensor
Electroanalysis, 2006
We demonstrate a facile fabrication method to make chemical gas sensors using single-walled carbon nanotubes (SWNT) electrochemically functionalized with polyaniline (PANI). The potential advantage of this method is to enable targeted functionalization with different materials to allow for creation of high-density individually addressable nanosensor arrays. PANI-SWNT network based sensors were tested for on-line monitoring of ammonia gas. The results show a superior sensitivity of 2.44% DR/R per ppm v NH 3 (which is more than 60 times higher than intrinsic SWNT based sensors), a detection limit as low as 50 ppb v , and good reproducibility upon repeated exposure to 10 ppm v NH 3 . The typical response time of the sensors at room temperature is on the order of minutes and the recovery time is a few hours. Higher sensitivities were observed at lower temperatures. These results indicate that electrochemical functionalization of SWNTs provides a promising new method of creating highly advanced nanosensors with improved sensitivity, detection limit, and reproducibility.
Water-responsive carbon nanotubes for selective detection of toxic gases
Ammonia plays an important role in our daily lives and hence its quantitative and qualitative sensing has become necessary. Bulk structure of carbon nanotubes (CNTs) has been employed to detect the gas concentration of 10 ppm. Hydrophobic CNTs were turned to hydrophilic via the application of a ramp electric field that allowed confinement of a controlled amount of water inside CNT microstructure. These samples were then also used to detect different gases. A comparative study has been performed for sensing three reducing gases, namely, ammonia, sulphur-di-oxide, and hydrogen sulphide to elaborate the selectivity of the sensor. A considerable structural bending in the bulk CNT was observed on evaporation of the confined water, which can be accounted to the zipping of individual nanotubes. However, the rate of the stress induced on these bulk microstructures increased on the exposure of ammonia due to the change in the surface tension of the confined solvent. A prototype of an alarm system has been developed to illustrate sensing concept, wherein the generated stress in the bulk CNT induces a reversible loss in electrical contact that changes the equivalent resistance of the electrical circuit upon exposure to the gas.
TOPICAL REVIEW: Recent progress in carbon nanotube-based gas sensors
Nanotechnol, 2008
The development of carbon nanotube-(CNTs-)based gas sensors and sensor arrays has attracted intensive research interest in the last several years because of their potential for the selective and rapid detection of various gaseous species by novel nanostructures integrated in miniature and low-power consuming electronics. Chemiresistors and chemical field effect transistors are probably the most promising types of gas nanosensors. In these sensors, the electrical properties of nanostructures are dramatically changed when exposed to the target gas analytes. In this review, recent progress on the development of different types of CNT-based nanosensors is summarized. The focus was placed on the means used by various researchers to improve the sensing performance (sensitivity, selectivity and response time) through the rational functionalization of CNTs with different methods (covalent and non-covalent) and with different materials (polymers and metals).
Journal of Sensors, 2012
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 N2as 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...
Carbon nanotubes as new materials for gas sensing applications
Journal of The European Ceramic Society, 2004
Carbon nanotubes (CNTs) deposited by plasma enhanced chemical vapor deposition on Si3N4/Si substrates provided with Pt electrodes have been investigated as resistive gas sensors towards NO2. The electrical response has been measured exposing the films to sub-ppm NO2 concentrations (10–100 ppb in dry air) at different operating temperatures ranging between 25 and 250 °C. The response to NO2 has been found to be at maximum at around 165 °C. Upon exposure to NO2 the electrical resistance of randomly oriented CNTs is found to decrease. The prepared films show reasonable dynamic of the electrical response and high reproducibility of the electrical properties. The resistance decrease of the CNTs when exposed to NO2 gas and the sensor response to concentrations as low as 10 ppb NO2, suggest the possibility to utilize CNTs as new sensors for air-quality monitoring.
Nanotube Molecular Wires as Chemical Sensors
Science, 2000
Chemical sensors based on individual single-walled carbon nanotubes (SWNTs) are demonstrated. Upon exposure to gaseous molecules such as NO 2 or NH 3 , the electrical resistance of a semiconducting SWNT is found to dramatically increase or decrease. This serves as the basis for nanotube molecular sensors. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by slow recovery under ambient conditions or by heating to high temperatures. The interactions between molecular species and SWNTs and the mechanisms of molecular sensing with nanotube molecular wires are investigated.
The gas sensing properties of single-walled carbon nanotubes deposited on an aminosilane monolayer
Sensors and Actuators B-chemical, 2008
This paper presents our study on the effects of an aminosilane monolayer on the gas sensing properties of single-walled carbon nanotubes (SWCNTs). A gas sensor for nitrogen dioxide (NO2) detection was fabricated by conventional photolithography process on an oxidized silicon wafer functionalized with 3-aminopropyltriethoxysilane (APTES). Such a CNT-based gas sensor was found to result in high sensitivity and fast response time compared with the sensor fabricated on a non-silanised surface. The amine groups in the APTES monolayer, electron donating in nature, played a role of charge transfer to the semiconducting SWCNTs, and hence the amount of electrons transferred from SWCNTs to NO2 molecules increased. Our results suggest that the APTES intended originally for selective placement of individual SWCNTs could be used to enhance the gas sensing properties of the SWCNTs.
Single-Walled Carbon Nanotube Thin-Film Sensor for Ultrasensitive Gas Detection
Japanese Journal of Applied Physics, 2005
We demonstrated a gas sensor fabricated by growing a single-walled carbon nanotube (SWNT) thin film directly on a conventional sensor substrate. NO 2 and Cl 2 were detected down to the ppb level under room-temperature operation with a fast response. Using an electrical breakdown technique, gas response sensitivity was improved by an order of magnitude. The relationship between gas concentration and sensor response was derived based on the Langmuir adsorption isotherm, predicting a detection limit of 8 ppb for NO 2 . The SWNT thin-film gas sensor exhibits merits over other types of sensors by virtue of its simplicity in fabrication and feasible application.