Properties of a weakly ionized NO gas sensor based on multi-walled carbon nanotubes

Abstract

Nitric oxide NO is one of the major targets for environmental monitoring, but the existing NO sensors are limited by their low sensitivity and narrow test range. Here, a NO gas sensor employing multiwalled carbon nanotubes (MWCNTs) was fabricated, and its properties in NO–N2 mixture were investigated from both emission and ionization. The current Ie passing through the nanotubes cathode was found to decrease with increasing NO concentration and increase linearly in different slopes with the extracting voltage Ue. It is shown that the Schottky barrier of the MWCNTs calculated by Ie increased with NO concentration due to the adsorption of NO gas, which restrained the electron emission and consequently weakened the ionization. The positive ion currents Ic passing through the collecting electrode at different voltages of Ue were found to monotonically decrease with increasing NO concentration, which was induced by both of the reduced electron emission and the consumption of the two excited metastable states N2(A3∑u+) and N2(a′1∑u−) by NO. The sensor exhibited high sensitivity at the low temperature of 30 °C. The calculated conductivity was found to be able to take place of Ic for NO detection in a wide voltage range of 80–150 V Ue.

Ionic Current Extraction in an Electrostatic-Fluid-Based Tripolar System for Ethanol Sensing

“…When an additional collection electrode layer is stacked onto the microbipolar system, ions would be extracted from the discharge region to form the ionic current. − The ionic current was demonstrated to be sensitive and selective to the analytes owing to the charge and mass information of the analyte molecules in the ions in our previous work . In the stacked tripolar system, the electric field plays a vital role in the ion drift and extraction process.…”

“…The IGSs using I s as the gas-sensing parameter were demonstrated to be sensitive to kinds of target gases. , 3 μL of the liquid mixture of methanol, ethanol, and acetic acid at a volume ratio of 1:1:1 was injected into the GC with a split ratio of 49:1. The retention time of the organic vapors would be fixed values in this work , and is qualitatively analyzed by GC, as shown in Figure S12.…”

Sensing Properties of a Novel Temperature Sensor Based on Field Assisted Thermal Emission

“…S area is the total cross-sectional area of all nanotubes on the film, and was calculated according to Figure 1d (Figure S3 in reference [15]); S area = 3.04 × 10 −6 m 2 . Eight least squares straight lines were fitted to the curves of ln j e −1/ T at different U e , and the coefficients R - Sq were calculated (Figure 2c) R-Sq = 1 − (Σ( y i − f i ) 2 )/(Σ( y i − y av ) 2 ) where y i denotes ln j e , f i denotes the fitting value to ln j e , y av denotes the mean value of all ln j e , and subscript i denotes the sequence number.…”

MEMS-Based Ionization Gas Sensors for VOCs with Array of Nanostructured Silicon Needles

“…Recently many researches are focused on application of nanostructured materials and novel electrode structures. − The silicon-based nanostructure is demonstrated to be one kind of the effective nanomaterials to induce a non-uniform electric field for gas molecule ionization in spite of the low working pressure. , Both the microneedle structure and the nanostructure would both enhance the electric field around the micro gas gap. The side-wall microneedle arrays allow the nanostructures to be arranged as tip to tip, which could provide the maximum effective ionization area of the nanolayers.…”