Humidity Sensitivity of Multi-Walled Carbon Nanotube Networks Deposited by Dielectrophoresis

Abstract

This paper presents an investigation on the humidity sensitivity of deposited multi-walled carbon nanotube (MWCNT) networks using ac dielectrophoresis (DEP) between interdigitated electrodes (IDEs). MWCNTs dispersed in ethanol were trapped and enriched between IDEs on a Si/SiO2 substrate under a positive DEP force. After the DEP process, the ethanol was evaporated and the MWCNT network on a substrate with IDEs was put into a furnace for repeated thermal annealing. It was found that the resistance stability of the network was effectively improved through thermal annealing. The humidity sensitivity was obtained by measuring the resistance of the MWCNT network with different relative humidity at room temperature. The experimental results show the resistance increases linearly with increasing the relative humidity from 25% to 95% RH with a sensitivity of 0.5%/%RH. The MWCNT networks have a reversible humidity sensing capacity with response time and recovery time of about 3 s and 25 s, respectively. The resistance is dependent on temperature with a negative coefficient of about −0.33%/K in a temperature range from 293 K to 393 K.

Integrated carbon nanotube-based sensor with CMOS processor for monitoring breath

“…MWCNTs used in our experiments were produced by chemical vapour deposition with a diameter of 10-30 nm and a length of 10-20 m. The MWCNTs were purified through a process so-called acid treatment according to the report by Liu et al [14] The acid treatment could greatly enhance the solubility of MWCNTs by introducing carboxylic (-COOH) functional groups to the sidewalls and ends of MWCNTs. [15] Then the production of the sensor was divided into two stages.…”

Synthesis and characterization carboxyl functionalized Multi-Walled Carbon Nanotubes (MWCNT-COOH) and NH2 functionalized Multi-Walled Carbon Nanotubes (MWCNTNH2)

“…This process is repeated for several times until the pH of the solution reaches neutral. The acid treatment can greatly increase the solubility of MWCNTs by introducing the carboxylic functional group (-COOH) to the side wall and the tip of MWCNTs [9]. In this experiment, a multiwalled carbon nanotubes (MWCNTs) functionality process with an amino group (MWCNTs-NH 2 ) was performed under one reaction.…”

“…The use of these nano sensors also varies, some nano sensors are used for the detection of microbial contaminants [18], gas detection such as hydrogen [1,19], air humidity [7,9,20], formalin [2,16,21,22,23].Nanomaterials have a high surface area so that if used as a sensor will have a better response.However, the nanotubes in the CNT material have not been able to respond well if they have not been activated by breaking the carbon bonds on the tube wall and attached to the amino group as material functionalization so it is easy to interact with the gas. Although thismaterial provide safe detection of gas, it still have some limitations and challenges such as low relative resistance changes and selectivity, long-term instability and so on.…”

“…Some forms of CNTs that are often used as feedstocks for the manufacture of nano sensors consist of 2, namely Singlewall Carbon Nanotubes (SWCNT) [2][3][4][5][6] and Multiwall Carbon Nanotubes (MWCNTs) [7][8][9][10][11][12][13][14][15][16][17]. The use of these nano sensors also varies, some nano sensors are used for the detection of microbial contaminants [18], gas detection such as hydrogen [1,19], air humidity [7,9,20], formalin [2,16,21,22,23].Nanomaterials have a high surface area so that if used as a sensor will have a better response.However, the nanotubes in the CNT material have not been able to respond well if they have not been activated by breaking the carbon bonds on the tube wall and attached to the amino group as material functionalization so it is easy to interact with the gas.…”

A flexible humidity sensor based on KC–MWCNTs composites

“…It's found that the chemical treatment makes CNT shorten, more open ends, and more defects, which makes water molecules adsorb tubes easily and then improve the sensing performances. Liu et al [8] presented a resistor-type humidity sensor based on deposited MWCNTs networks using AC dielectrophoresis between interdigitated electrodes on silicon substrate. The sensor exhibits as a promising humidity sensing material with good reversibility, high response and good linearity, etc.…”