Polyaniline Nanothin Film Chemiresistive Gas Sensors
Conducting polymers (CPs) are a group of conjugated polymers offering unique electrical/electronic properties of metals/semiconductors while retaining the attractive mechanical properties and processing advantages of polymers. In particular, polyaniline (PANI), because of its stability in ambient conditions and wide range of tunable electrical conductivity, is one of the most prominent CPs receiving a great deal of attention. The conductivity of PANI can be varied from insulating to nearly metallic by modulating its oxidative state by changing the type of counter ion (dopant) and degree of doping. The ability to switch between the conducting and insulating forms makes PANI responsive to acid/base and reducing/oxidizing compounds, enabling it to be used as sensing element in resistance type sensors known as chemiresistors.
In this dissertation, we demonstrated a novel method for electrochemical growth of conducting polymer polyaniline (PANI) nanothin film across a pair of gold microelectrodes on Si/SiO2 for one step and site-specific fabrication of PANI film based field-effect transistor/chemiresistor sensors. Various instrumentation techniques, including scanning electron microscope (SEM), atomic force microscopy (AFM), field-effect transistors (FET), and X-ray photoelectron spectroscopy (XPS) were applied to acquire physical and electrical properties of the nanothin film.
The film had a thickness of 9-20 nm and a carpet-like morphology offering high surface to volume ratio that enhances gas adsorption and promotes surface perturbation. The sensing performance of the nanothin film device was comparable to that of 1-dimensional (1-D) nanostructure, with a great advantage in ease of processing and durability in post-synthesis functionalization. The film was further functionalized using a dip coating process to introduce recognition material into the polymer domain for enhancing reactivity and selectivity of the film transducer. The nanothin film was functionalized with primary amine, polyethyleneimine, potassium iodide and cupric chloride for highly sensitive and selective detection of formaldehyde, carbon dioxide, ozone and nerve agent sarin simulant dimethyl methylphosphonate, respectively.