In Situ Deposition and Patterning of Single-Walled Carbon Nanotubes by Laminar Flow and Controlled Flocculation in Microfluidic Channels

摘要

The remarkable electrical, mechanical, and chemical properties of single-walled carbon nanotubes (SWNTs) create interest in their potential use as semiconducting or conducting elements in sensors, nanoscale transistors, and in large-area electronic systems. As a result, considerable research focuses on developing techniques for depositing and patterning SWNTs from solution, as individuals or aggregates, with well-controlled coverage and alignment. Langmuir-Blodgett techniques[1]-[4] and various schemes of deposition from solution[5]-[15] have been studied extensively. Although these methods exhibit attractive features, they each have some combination of disadvantages, such as low deposition rate, inability to control tube alignment and/or to deposit over large areas, required chemical modification of the SWNTs or substrates, or the need for organic solvents that are incompatible with plastic device components (organic electrodes, semiconductors, or substrates). A recently described alternative technique uses a controlled flocculation process to drive individual tubes out of an aqueous suspension and onto a substrate.[16] The deposition speed of this approach can be high, the tube coverage (i.e. the number of tubes per unit area) can be controlled over a wide range, and the form of the tubes (isolated individual tubes or bundles) can be defined by the processing conditions. The approach is also compatible with a wide range of substrates and it does not require chemical modification of the tubes or the substrates. However, this method does not allow the local orientation of the deposited nanotubes to be defined in a spatially dependent manner. Depositing and patterning SWNTs in a single step are also difficult, and secondary procedures must be used to transfer the nanotubes onto substrates incompatible with spin coating (e.g., curved surfaces).