Anomalous adsorption behaviors in carbon nanotube assembly and its applications

Abstract

Carbon nanotubes (CNTs) have become attractive materials due to their superior physical and mechanical properties. However, the major problem for their practical applications is a lack of a mass production method. Since most of nanostructures are first synthesized in solution or powder forms, one has to pick up and assemble individual nanostructures onto substrates to build functional devices. In this dissertation, we propose surface-programmed assembly method for large-scale CNT and nanowire (NW) assembly guided by self-assembled monolayer patterns. Significantly, our method is compatible with conventional microfabrication process. We studied the selective adsorption and precision alignment behaviors of CNTs on self-assembled monolayer (SAM), bare Au, and bare SiO2 surfaces. Double walled carbon nanotubes (dwCNTs) and multi walled carbon nanotubes (mwCNTs) exhibited strong adsorption onto bare Au, SiO2, and polar SAM, while nonpolar SAM efficiently blocked their adsorption. Smaller CNTs were found to have higher adsorption probability to polar surfaces than larger CNTs. And the dipole-induce dipole interaction is a dominant force in CNT adsorption. We present experimental results revealing the new adsorption kinetics of single walled carbon nanotubes (swCNTs), where rotational and sliding motions of swCNTs are crucial in describing final structures. The sliding chamber experiment shows that swCNTs can slide right above SAM surfaces and form aligned structures. A model based on the diffusion and free energy argument is proposed to explain the motion of swCNTs, where adsorbed swCNTs assembled onto the surface patterns in the formation which minimizes the total energies of the system. Significantly, recent report regarding V2O5 nanowires implies that this new adsorption kinetics can be a general phenomenon for 1-dimensional nanostructures such as CNTs and NWs. This process can be a mean to assemble and align general nanowires onto substrates to fabricate desired device structures without relying on external forces. As a proof of concept, CNT based functional devices such as CNT field effect transistors (FETs), bio-sensors and gas sensors were fabricated and characterized by electrical measurement.