Enhancing the sensitivity of chemiresistor gas sensors based on pristine carbon nanotubes to detect low-ppb ammonia concentrations in the environment (original) (raw)
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Room Temperature Single Walled Carbon Nanotubes (SWCNT) Chemiresistive Ammonia Gas Sensor
Single walled carbon nanotubes were functionalized with carboxyl (–COOH) group using simple acid treatment process. Thin films of functionalized SWCNTs were fabricated using drop cast technique from the dispersion prepared in de-ionized water. These films were characterized using FE-SEM, FTIR, Raman spectroscopy techniques and current-voltage measurements were carried at room and elevated temperature. SWCNT chemiresistor gas sensor devices on silicon substrate were fabricated using conventional microfabrication technology with pristine and functionalized SWCNTs. Fabricated gas sensors were exposed to ammonia in an in-house developed gas sensor characterization system and response was measured at ammonia concentration up to 50 ppm at room temperature. Functionalized SWCNTs chemiresistor showed an impressive ammonia response of 20.2 % compared with 2.9 % of pristine counterpart. Response enhancement mechanisms are discussed in terms of defects and gas molecule adsorption on CNT surfac...
ACS sensors, 2018
Fabrication and comparative analysis of the gas sensing devices based on individualized single-walled carbon nanotubes of four different types (pristine, boron doped, nitrogen doped, and semiconducting ones) for detection of low concentrations of ammonia is presented. The comparison of the detection performance of different devices, in terms of resistance change under exposure to ammonia at low concentrations combined with the detailed analysis of chemical bonding of dopant atoms to nanotube walls sheds light on the interaction of NH with carbon nanotubes. Furthermore, chemoresistive measurements showed that the use of semiconducting nanotubes as conducting channels leads to the highest sensitivity of devices compared to the other materials. Electrical characterization and analysis of the structure of fabricated devices showed a close relation between amount and quality of the distribution of deposited nanotubes and their sensing properties. All measurements were performed at room t...
An effective monitoring of the air quality in an urban environment requires the capability to measure polluting gas concentrations in the low-ppb range, a limit so far virtually neglected in most of the novel carbon nanotube (CNT)-based sensors, as they are usually tested against pollutant concentrations in the ppm range. We present low-cost gas sensors based on single-walled CNT (SWCNT) layers prepared on plastic substrates and operating at room temperature, displaying a high sensitivity to [NH3]. Once combined with the low noise, the high sensitivity allowed us to reach an ammonia detection limit of 13 ppb. This matches the requirements for ammonia monitoring in the environment, disclosing the possibility to access the ppt detection limit. Furthermore, a blend of SWCNT bundle layers with indium-tin oxide (ITO) nanoparticles resulted in a threefold sensitivity increase with respect to pristine CNT for concentrations above 200 ppb. Finally, the peculiar response of the ITO-SWCNT blend to water vapor provides a way to tailor the sensor selectivity with respect to the relevant interfering effects of humidity expected in outdoor environmental monitoring.
2015
In the last two decades several scientists proposed a new carbon based technology, against the usual silicon based one, and the allotropes of carbon, i.e. carbon nanotubes, single atomic layers of graphite (graphene), fullerene molecules and diamond, as new electronic materials with unique properties. Carbon nanotubes (CNTs), since their discovery attributed to Iijima [10] more than 20 years ago, are well known and studied systems for many applications by now. Of course, gas sensing is one of these applications. With respect to commercial electrochemical sensors for environmental monitoring (mostly based • strategies explored to enhance ammonia sensitivity and response timescales analysis of SWCNT-based gas sensors on ceramic (Al 2 O 3) substrates are described in chapter 3; • in chapter 4 the effects of functionalization with metal oxide nanoparticles of SWCNT layers, deposited on plastic substrates, on the selective response to other gases, i.e. NO 2 and water vapor, are discussed; • finally, in chapter 5 we report the gas sensing response of hybrid material of nanostructured carbon grown on ZnO nanorods or ITO substrates.
IEEE Sensors Letters
CNTs based chemiresistive gas sensors are known to not fully recover to the baseline after gas exposure. This is why often heat is applied to thermally activate the sensor and improve the gas desorption process occurring at the surface. In this paper, we combine single-walled CNTs (SWCNTs) with conjugated polymers (CPs) i.e., Poly(3-hexylthiophene)(P3HT), to realize chemiresistive gas sensors with improved recovery. Five configurations were fabricated with diverse positions of the sensing material layers with respect to the interdigitated electrodes (IDEs), namely: SWCNTs/IDEs and P3HT/IDEs as controls for the CNTs and P3HT singular materials; SWCNTs/P3HT/IDEs, SWCNTs/IDEs/P3HT and P3HT/SWCNTs/IDEs as combined sensing materials layers configurations. The results show that in particular, the P3HT/SWCNTs/IDEs sensors exhibit better performance with respect to the other configurations when exposed to 5, 25, and 50 ppm NH 3. Improvements in terms of response time (103 seconds faster at 5 ppm), sensor response (+26.83% at 50 ppm), and improved recovery to the baseline (+25.69% and +11.34% at 5 and 50 ppm respectively) were obtained when evaluated against SWCNTs/IDEs sensors. These findings suggest that addition of CPs (i.e. P3HT) may be a promising approach to enhance the performance and stability of SWCNTs-based chemiresistive gas sensors, providing a new direction for future research in this field. Future research to investigate the effect of others CPs on the CNTs based chemiresistive gas sensors will be needed to realize more efficient and reliable ammonia gas sensors.
Carbon, 2014
This paper reports the successful experimental demonstration of the localized growth of horizontal, dense carbon nanotube (CNT) arrays in situ and at the wafer scale. The selectivity and directionality of the CNT catalytic growth process along with the adequate design and fabrication of the catalyst support enables the direct integration of nanotubes arrays into heterogeneous devices. This novel CNT integration method is developed to manufacture conductance based gas sensors for ammonia detection and is demonstrated to produce a yield above 90% at the wafer scale. Owing to its flexibility, the integration process can be useful for a wide range of applications and complies with industrial requirements in terms of manufacturability and yield, requirements for the acceptance of CNTs as alternate materials. A state-of-the-art CNT array resistivity of 1.75 · 10 À5 X m has been found from the CNT characterization. When exposed to low NH 3 concentrations, the CNT sensors show good repeatability, long-term stability, and high design robustness and tackle the reproducibility challenge for CNT devices. Individual device calibration is not needed.
A comparative study of single- and multiwalled carbon nanotube sensitivity to ammonia
Journal of Applied Physics, 2009
We interpret the measured sensitivity difference of single walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) used as dielectric sensors of ammonia gas traces in terms of adsorption sites and effective coverages. The dielectric constant of a regular set of SWNTs deposited on a plane is compared to that of a single MWNT having the same size when the same pressure of ammonia molecules is applied on them. The corresponding resonance frequency shifts in the two sensors display an enhanced sensitivity of SWNT over the MWNT in excellent agreement with the experimental measurements.
Journal of Physics D: Applied Physics, 2012
Electrochemically controllable functionalization of single-walled carbon nanotubes (SWNTs) with poly(N-methyl pyrrole) (P[NMP]) is demonstrated for room temperature gas sensing applications. Comparative investigations reveal that the loading content of the functionalization entity has prominent effects on the sensing characteristics of SWNTs. The optimized sensing backbone (P[NMP]-functionalized SWNTs with 5 µC deposited charge) exhibited a lower detection limit of 10 ppb and excellent linearity for a detection window of 10 ppb-01 ppm concentration of NH 3. The typical response and recovery time of the optimized sensor is on the order of minutes. Finally, a performance comparison of the P[NMP]-functionalized SWNT sensing backbones with the pristine P[NMP] nanowire sensor ensured the well-defined role of SWNTs in the functionalized structure. The proposed sensing mechanism suggests that the synthesis parameters can be manoeuvered for the highest operational efficiency of the sensors.
Sensors and Actuators B-chemical, 2007
In this study, an ammonia gas sensor structure for mass production is realized with an array of carbon nanotubes synthesized on an anodic aluminum oxide (AAO) template. The device is expected to yield a uniform performance due to the regular and uniform nano channels in the AAO. It is a vertical structure made with open-ended multi-wall carbon nanotubes through deposition on the inside wall of the AAO so that the gas would diffuse into the nano channels for adsorption. The carbon nanotubes are in the form of flaked carbons having many defect sites. The results show that the sensor has high sensitivity, fast response time of less than 1 min and good reproducible recovery behaviors in atmospheric pressure at room temperature.