Electrical Monitoring of sp³ Defect Formation in Individual Carbon Nanotubes

Many carbon nanotube (CNT) applications require precisely controlled chemical functionalization that is minimally disruptive to electrical performance. A promising approach is the generation of sp³ hybridized carbon atoms in the sp²-bonded lattice. We have investigated the possibility of using a carboxylic acid-functionalized diazonium reagent to introduce a defined number of sp³ defects into electrically contacted CNTs. Having performed real-time measurements on individually contacted CNTs, we show that the formation of an individual defect is accompanied by an upward jump in resistance of approximately 6 kΩ. Additionally, we observe downward jumps in resistance of the same size, indicating that some defects are unstable. Our results are explained by a two-step reaction mechanism. Isolated aryl groups, formed in the first step, are unstable and dissociate on the minute time scale. Stable defect generation requires a second step: the coupling of a second aryl group adjacent to the first. Additional mechanistic understanding is provided by a systematic investigation of the gate voltage dependence of the reaction, showing that defect formation can be turned on and off. In summary, we demonstrate an unprecedented level of control over sp³ defect formation in electrically contacted CNTs, and prove that sp³ defects are minimally disruptive to the electrical performance of CNTs