Accelerating Gas Adsorption on 3D Percolating Carbon Nanotubes

Abstract

In the field of electronic gas sensing, low-dimensional semiconductors such as single-walled carbon nanotubes (SWCNTs) can offer high detection sensitivity owing to their unprecedentedly large surface-to-volume ratio. The sensitivity and responsivity can further improve by increasing their areal density. Here, an accelerated gas adsorption is demonstrated by exploiting volumetric effects via dispersion of SWCNTs into a percolating three-dimensional (3D) network in a semiconducting polymer. The resultant semiconducting composite film is evaluated as a sensing membrane in field effect transistor (FET) sensors. In order to attain reproducible characteristics of the FET sensors, a pulsed-gate-bias measurement technique is adopted to eliminate current hysteresis and drift of sensing baseline. The rate of gas adsorption follows the Langmuir-type isotherm as a function of gas concentration and scales with film thickness. This rate is up to 5 times higher in the composite than only with an SWCNT network in the transistor channel, which in turn results in a 7-fold shorter time constant of adsorption with the composite. The description of gas adsorption developed in the present work is generic for all semiconductors and the demonstrated composite with 3D percolating SWCNTs dispersed in functional polymer represents a promising new type of material for advanced gas sensors.

Enhanced sensing of gas molecules by a 99.9% semiconducting carbon nanotube-based field-effect transistor sensor

“…5,[10][11][12][13][14] Thus, the electrical properties of CNTs can be extremely sensitive to charge transfer and chemical doping effects by various molecules. For instance, adsorption of electron-withdrawing (e.g., NO 2 , O 2 ) [10][11][12][13][14] or donating (e.g., NH 3 ) 11,16,17 molecules on CNTs can cause charge transfer between the CNTs and gas molecules. Notably, if semiconducting CNTs are employed for sensing, the charge transfer can lead to dramatic changes in their electrical conductance (or resistance), which serves as the basis for highly sensitive CNT-based gas sensors.…”

“…Using the reactions of gas molecules with CNTs themselves and the gas-sensitive metal electrodes, a significant change in current flow can occur, resulting from the respective intermolecular charge transfer and SBH modulation. The detection of various gas molecules in CNTbased FET gas sensors has been reported, 6,11,[13][14][15][16][19][20][21] but enhanced sensing methods for gas molecules having different sensing mechanisms, i.e., reacting with CNTs and/or gassensitive metal electrodes, have not yet been reported sufficiently. Controlling the operating regime, i.e., the operating bias conditions in CNT-based FET gas sensors, could be a good method to enhance the sensor operations, depending on the gas molecules to be detected.…”

“…Moreover, we performed the same experiment for the NO 2 response, as shown in Fig. 2(b), where 0.006% NO 2 was injected for 150 s. Oxidizing gases such as NO 2 adsorb on the CNT surfaces and can likely extract electrons from semiconducting CNTs, [11][12][13][14] thereby leading to an expansion of the conducting channel, i.e., decreased CNT resistance.…”

“…NO 2 À . [11][12][13][14] This extraction leads, in turn, to an expansion of the hole accumulation layer, i.e., a decrease in the resistance of the semiconducting CNTs, which means that a high sensitivity can be obtained in the subthreshold regime (also called depletion regimes) at the V GS values shifting to the positive direction, where the gating effect of the gas molecules bound on the channel surface of FET-based sensors is most effective due to the reduced screening of carriers in the channel. This is in sharp contrast to the H 2 responses.…”

Comparison of the adsorption of H2S by ZnO–TiO2 and Ni–ZnO–TiO2 nanoparticles: An adsorption isotherm and thermodynamic study

“…[20][21][22] Nano-structures are nanoscale particles of organic or inorganic materials that have a high affinity to adsorb substances. 23 Because of their high porosity, small size, and active surface, nano-structure sorbents can not only sequester contaminants of varying molecular size, hydrophobicity, and speciation behavior but also enable manufacturing processes to consume raw materials efficiently without releasing a toxic payload. [24][25][26] Nano-structure sorbents work rapidly and have considerable pollutant-binding capacities.…”