Development of Multi-Walled Carbon Nanotubes Film for Ionization based Gas Sensing Application

Nowadays many types of gas sensors have been used to identify and detect the presence of
various gases in industrial plants. However, these gas sensors are still facing the problem of
lack selectivity and sensitivity for gas detection in ambient temperature and also slow in
response time. The objective of this research is to develop multi-walled carbon nanotubes
(MWCNTs) film for ionization based gas sensing application. In this study, MWCNTs film is
proposed to be used as the active component due to its remarkable electronic and field
emission properties for generating ionization mechanism on the gas.
MWCNTs were synthesized by the decomposition of ethylene over metal coated, oxidized
silicon substrate in thermal chemical vapor deposition CVD system. Structure and
morphology of grown MWCNTs were examined using Raman spectroscopy, scanning
electron microscopy (SEM) and transmission electron microscopy (TEM) whilst the
electrical properties of nanotubes film were characterized by Van der Pauw and Hall Eff()ct
technique. Gas sensing properties testing ofMWCNTs film are carried out by identifying gas
breakdown voltage between nanotubes film cathode and aluminum film anode. Gasses that
have been tested are helium, argon, air, hydrogen 2% in air mixture, and ammonia.
MWCNTs grown using this CVD technique are found to have high crystallinity with typical
diameter of 18 nm and length of 1.5 Jlm. Testing the sensing properties at room temperature
reveals that the utilization of MWCNTs film as cathode was able to scale down the air
breakdown voltage by a factor of about 58 % as compared to aluminum cathode. On the I 0
mL gas volume, helium gas gives the lowest breakdown voltage of about 134 V, whilst air
gives the highest value of about 320 V. Further experiment shows that the breakdown volt,.ge
is not significantly affected by the gas volume content in testing chamber. Reducing 'he
interelectrode separation by 60 Jlm results the lowering of the breakdown voltage of helium
gas by 122 V. It is concluded that utilization of MWCNTs film as cathode in the ionization
based gas sensing configuration is capable to detect helium, argon, air, 2% hydrogen in air
mixture, and ammonia at room temperature.