Laser-controlled synthesis and manipulation of carbon nanotubes

This document presents novel laser-based strategies for controlled synthesis, manipulation, and fabrication of carbon nanotubes (CNTs) and CNT-based devices. CNTs are fascinating materials with extraordinary optical and electrical properties that make them potential candidates for a number of applications. However, integration of CNTs into functional devices is a great challenge in conventional CNT growth techniques. Additionally, applications of CNTs in electronic and optoelectronic devices are limited by variations in their types, chiralities and diameters. During the course of my dissertation project, the main objective of my research has been focused on self-integration of CNTs into functional devices and controlling the structural, electrical and optical properties of CNTs with laser-based strategies. Self-aligned growth and integration of CNTs across the contact electrodes were successfully achieved via optical field enhancement at the tips of silver nanoantennas resulting in selective heating and activation of catalyst nanoparticles for CNT growth. CNT-integrated plasmonic nanoantenna arrays were fabricated for infrared bolometers. We showed that strong concentration of optical fields and the small volume of CNTs in the gaps of the nanoantenna arrays resulted in an enhanced light-CNT interaction and hence improved photoresponse of the bolometers. Due to the inability to selectively synthesize CNTs of a given electronic type, both semiconducting and metallic CNTs exist in the CNT-based devices. Since most electronic and optoelectronic devices depend on semiconducting behavior, the presence of metallic CNTs hinders CNT device development. We presented a method to selectively remove metallic CNTs from the CNT mixtures by coupling a laser beam from an optical parametric oscillator (OPO) into their free electrons to selectively heat and burn the metallic CNTs. Furthermore, electronic and optical properties of semiconductive single-walled carbon nanotubes (SWNTs) were successfully manipulated through the modulation of their diameters in a laser-assisted chemical vapor deposition (LCVD) process. Due to inverse relationship between the diameter and bandgap of semiconducting-SWNTs, modulation of their diameter resulted in unique optical and electronic behaviors. Finally, a laser-based single-step approach was developed for synthesis of CNT/silicon core/shell structures. This was achieved through laser-induced melting and evaporation of CNT-deposited Si substrates using a continuous wavelength CO 2 laser