Carbon nanotube synthesis, processing and spintronics

Covalent molecules can be designed to be the ultimate electronic circuits. Carbon nanotubes (CNT) have a curved, aromatic structure, with electronic properties of metals to semiconductors of varying band gaps as a function of chirality, as well as extreme mechanical, thermal and chemical stability. Due to the covalently bonded structure, metallic CNTs are ballistic conductors over 1mum lengths and can carry current densities of 109A/cm 2. Thus, single-walled carbon nanotubes (SWNT) have been regarded as the most promising electronic material as silicon devices reach their fundamental scaling limitations. More than a decade since their discovery, synthesizing useful quantities of analytically pure carbon nanotubes as well as characterizing and processing into forms suitable for specific applications are largely unsolved problems. In this dissertation, a rational route towards developing single-walled carbon nanotubes for applications based on their electronic structure is demonstrated.; We study SWNTs grown using the dc-arc technique. By systematic characterization of chemically processed SWNTs, we aim at differentiating between the reactivity of SWNTs and the impurities. Spectroscopic methods were developed, to study the electronic structure of SWNTs close to the Fermi level as well as in the near-IR region where it shows prominent electronic transitions and correlated with the effect of impurities and different processing conditions. This allows us to rationally design processing methods for SWNTs with reproducible characteristics. Chemical modifications of the electronic structure are then pursued towards isolating analytically pure SWNTs.; To realize the potential advantages of carbon nanotubes in electronic circuits, besides controlling the materials characteristics, methods to assemble a large density of functional devices need to be developed. Due to low spin-orbit coupling and long spin diffusion lengths (>100nm), CNTs are very promising spintronics materials. In a CNT spin-valve device, spin-polarized electrons are generated at the FM/CNT interface and the CNT provides a coherent path for the polarized electron, which can be detected at the other FM electrode. A versatile method for assembling carbon nanotubes on ferromagnetic (FM) metal contacts from solution was developed. A route to form transparent FM/CNT interfaces as demonstrated. The devices assembled using this technique predominantly exhibit inverse magnetoresistance effect due to spin-polarized transport.