Localized Synthesis, Assembly and Application of Carbon Nanotubes

This report describes the localized synthesis, orientation, assembly and application of carbon nanotubes. Synthesis by chemical vapor deposition is activated by means of resistively heating a MEMS structure in a room temperature reaction chamber. Catalyst nanoparticles, created by heating a thin film of NiFe (80%-20% by wt.), activate the breakdown of acetylene gas, which serves as the nanotube precursor. The resulting carbon nanotubes have been seen to grow at rates surpassing 1.5 um/min. These multi-walled nanotubes have diameters between 5 and 50 nm and have grown up to 20 um in length. Since heating is localized to the microstructure, the synthesis process occurs only over a small region of the chip, is scalable for batch fabrication and is compatible with standard on-chip microelectronics or MEMS.

Oriented growth is accomplished by applying a DC electric field between nearby microstructures. Electric fields cause strong nanotube self-alignment and highly directional growth ensues. Oriented nanotube growth continues until contact is made with the second microstructure. The resulting contacts are examined and shown to be mechanically robust and electrically conductive. Testing of the connected nanotubes has shown that their average resistance is between 40 and 100 kohm. Furthermore, this resistance is shown to be dependent on the ambient pressure. A nanoscale hot-wire pressure sensor is demonstrated using the nanotubes. A carbon nanotube electromechanical actuator is also presented. These proof-of-concept devices reveal the applicability of this synthesis method for rapid and simplified manufacturing of nanotube sensors and actuators.

Nanotubes' unique electrical, mechanical, and chemical properties render them applicable in many fields, making this synthesis approach broadly relevant. In particular, this accomplishment makes possible the direct integration of CNT devices with on-chip transduction, readout, processing, and communications circuitry, facilitating the integration of nanostructures with larger-scale systems. It is hoped, therefore, that this pioneering work will facilitate rapid progress toward more integratable and manufacturable nanotube sensors and devices.