Mechanistic study of oxidative chemical vapor deposition of polypyrrole: Effects of the inert gas and deposition time

Abstract

Oxidative chemical vapor deposition (oCVD) is a method for synthesizing uniform and conformal thin films of conductive polymers without any solvents. The structure and properties of oCVD films can be tuned by controlling the process parameters such as the flow rates of the vapor-phase reactants, substrate temperatures, chamber pressure, inert gas flow rate, and deposition time. Although the first three parameters have been studied, the impact of the last two remains as yet unexplored. This study examines how the flow rate of nitrogen gas, an inert gas that assists the oxidant delivered into the reactor chamber, and the deposition time affect the structure and properties of oCVD film. Polypyrrole (PPy) was chosen in this study due to its versatility for many applications. The results showed that nitrogen gas primarily acts as an oxidant carrier gas, impacting the distribution of the oxidant adsorbed onto the substrates. This leads to varying structure and properties of the resultant PPy. Furthermore, nitrogen flow rate and deposition time affect the thickness and conductivity of PPy differently. Increasing nitrogen flow rate significantly improves the distribution of the oxidant, but it can also result in excessive polaronic defects. These defects can severely deteriorate the polymeric structure and reduce the conductivity. Meanwhile, extending the deposition time increases the film thickness linearly due to longer reaction time and initially enhances conductivity until it reaches a plateau. These insights can be beneficial not only for the oCVD method but also for other types of vapor-based polymerization techniques.