Mechanism of NO2 detection in carbon nanotube field effect transistor chemical sensors

Zhang, Jian; Boyd, Anthony K.; Tselev, Alexander; Paranjape, Makarand; Barbara, Paola

doi:10.1063/1.2187510

Cited by 171 publications

(144 citation statements)

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“…While one of the reasons for the electrical conductance change is thought to be charge transfer, it has been confirmed that the adsorbed gas molecules on isolated CNT walls have little effect on electrical conductance. 21,22,25 In addition, we confirmed that the temperature dependence of the resistance of the MWCNT film followed the FIT model, i.e., the energy barrier at the CNT junction plays an important role in the conductance of the film. Therefore, it can be inferred that the adsorption energy calculated here is that of the water molecules adsorbed on CNT junctions and is due to charge transfer at the CNT junction.…”

Section: Resultssupporting

confidence: 58%

“…Electronic mail: shu18@hiroshima-u.ac.jp contact interface between the CNT and the electrode, changed due to gas molecules. [20][21][22] In contrast, other groups used CNT networks or films and showed that charge transfer between the CNT and the adsorbed gas has an influence on the electrical conductance. 23,24 Despite these conflicting observations, Boyd et al 25 reported an interesting result.…”

Section: Introductionmentioning

confidence: 99%

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Estimation of adsorption energy for water molecules on a multi-walled carbon nanotube thin film by measuring electric resistance

2016

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Gas sensors based on carbon nanotube (CNT) films have attracted attention owing to their low power consumption. For further development of these sensors, we need to understand the surface interaction of the films with gas molecules. In our previous research, we investigated the influence of water molecules on the electrical conductance of multi-walled CNT films and explained this phenomenon using a two-layer adsorption model. This work motivated us to measure the adsorption energy of CNT-H2O. In this study, we focused on the first-layer adsorption and investigated the sheet resistance to water vapor pressure at various temperatures using the transmission line method (TLM). The results were fitted to Langmuir adsorption model and the adsorption equilibrium constant was determined. The temperature dependence of the sheet resistance followed a model of fluctuation induced tunneling (FIT), in which the energy barrier at the CNT junction is regarded as the main factor influencing the electrical conductance of the CNT film. The sheet resistance and equilibrium constant decreased as temperature increased. This result was consistent with the adsorption phenomenon. Finally, the adsorption energy was determined to be 0.22–0.31 eV, which is larger than the previously calculated value. It was also reported that the adsorption energy of the gas molecules in the interstitial site between two carbon nanotubes was larger than that on the CNT surface. These results indicate that the CNT junction plays a key role in the detection of gas molecules.

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Section: Resultssupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Estimation of adsorption energy for water molecules on a multi-walled carbon nanotube thin film by measuring electric resistance

2016

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“…Therefore the change of the junction characteristics after exposure to a gas is related to the modulation of the contact resistance and not of the channel conductance [14]. Recently, these results have been confirmed by other teams [15] [16] theoretically confirmed that NH 3 molecules have only a weak interaction with carbon nanotubes and graphite: their binding energy is very low and there is little charge transfer with no change in the nanotube band gap Fermi level (plutot que band gap). This last conclusion confirms that gas species do not dope the carbon nanotubes.…”

Section: Theorysupporting

confidence: 69%

Gas fingerprinting using carbon nanotubes transistor arrays

Bondavalli

Legagneux

Pribat

et al. 2008

Journal of Experimental Nanoscience

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This paper deals with the fabrication of carbon nanotube field effect transistors (CNTFETs) for gas sensing applications. Such devices exploit the extremely sensitive change of the Schottky barrier heights between carbon nanotubes (CNTs) and drain/source metal electrodes: the gas adsorption creates an interfacial dipole that modifies the metal work function and so the band bending and the height of the Schottky barrier at the contacts. Our aim is to achieve the fingerprinting of a specific gas using a CNTFET based sensor array. This fingerprinting concept is based on the fact that the change of the metal electrode work function strictly depends on the metal/gas interaction. Consequently the CNTFET transfer characteristics will change specifically as a function of this interaction. To demonstrate this new concept, we have fabricated arrays of CNTFETs with different metal contacts: Au, Pd, Ti and Pt. Using these transistors, we have shown that a particular gas, in our case DiMethylMethyl-Phosphonate (DMMP, a sarin simulant), interacts specifically with each metal: 1 ppm of DMMP (15 min of exposure) reduces the transistor ON current by about 20% for Pt contacted CNTFETs and by nearly one order of magnitude for Pd contacted CNTFETs. We believe that this new approach can be applied for highly selective sensing of various gases, using ultra-compact, room temperature and very low power devices.

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“…When the PMMA encapsulated devices were exposed to a humid ambient, the electrical characteristics of the transistors changed due to permeation of water molecules through PMMA. Similarly, Zhang et al 7 used SU-8/PMMA ͑2 m / 200 nm͒ to passivate their CNT FETs. After exposing their devices to an NO 2 environment for 1 h, they have noted that the gas molecules diffused through the SU-8/PMMA layer and caused variations in the transistor behavior.…”

mentioning

confidence: 99%

Parylene-C passivated carbon nanotube flexible transistors

Selvarasah

Busnaina

et al. 2010

Applied Physics Letters

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Carbon nanotubes are extremely sensitive to the molecular species in the environment and hence require a proper passivation technique to isolate them against environmental variations for the realization of reliable nanoelectronic devices. In this paper, we demonstrate a parylene-C passivation approach for CNT thin film transistors fabricated on a flexible substrate. The CNT transistors are encapsulated with 1 and 3 m thick parylene-C coatings, and the transistor characteristics are investigated before and after passivation. Our findings indicate that thin parylene-C films can be utilized as passivation layers for CNT transistors and this versatile technique can be readily applied for the encapsulation of CNT devices such as field effect transistors, p-n diodes, and logic circuits fabricated on flexible substrates. © 2010 American Institute of Physics. ͓doi:10.1063/1.3499758͔Single-walled carbon nanotubes ͑SWNTs͒ with their unique physical, electrical, and mechanical properties are being considered as a potential replacement for existing semiconducting materials in flexible electronics. Their mobility can exceed 10 5 cm 2 / V s −1 , and they have large current carrying ͑10 9 A / cm 2 ͒ capability, higher ON/OFF ratios ͑Ͼ10 5 ͒ and extreme mechanical flexibility. 1 SWNT based field effect transistors ͑FETs͒ exhibit p-type behavior in the ambient environment, and they can be converted to n-type by doping e.g., polymer functionalization. 2 Carbon nanotube ͑CNT͒ flexible devices such as high frequency FETs, p-n diodes, and logic circuits have already been reported. 3 Their large surface area to volume ratios and extreme sensitivity to the molecular species in the environment ͑e.g., oxygen, moisture, etc.͒ can significantly affect the electrical properties of CNT transistors. [4][5][6] To isolate SWNT based flexible transistors from environmental factors, thin and flexible passivation layers need to be investigated prior to deployment of these devices in real world applications.Several groups have already explored passivation of CNT based devices with thin polymeric films yet had limited success. For example, Dai et al. 5 have reported a 1.7 m polymer ͓polymethyl-methacrylate ͑PMMA͔͒ coating for passivating CNT based transistors. When the PMMA encapsulated devices were exposed to a humid ambient, the electrical characteristics of the transistors changed due to permeation of water molecules through PMMA. Similarly, Zhang et al. 7 used SU-8/PMMA ͑2 m / 200 nm͒ to passivate their CNT FETs. After exposing their devices to an NO 2 environment for 1 h, they have noted that the gas molecules diffused through the SU-8/PMMA layer and caused variations in the transistor behavior. In addition to polymeric encapsulants, Kaminishi et al. and Kim et al. 8 ͑15 nm deposited using atomic layer deposition ͑ALD͒ at 300°C͒ layers as passivation layers for CNT FETs. The drawback with both Si 3 N 4 and ALD based deposition methods is that both materials are either deposited at or require annealing steps at elevated temperatures which lim...

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Mechanism of NO2 detection in carbon nanotube field effect transistor chemical sensors

Cited by 171 publications

References 10 publications

Estimation of adsorption energy for water molecules on a multi-walled carbon nanotube thin film by measuring electric resistance

Estimation of adsorption energy for water molecules on a multi-walled carbon nanotube thin film by measuring electric resistance

Gas fingerprinting using carbon nanotubes transistor arrays

Parylene-C passivated carbon nanotube flexible transistors

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