Optical, magnetic, and electrical properties of single-walled carbon nanotubes

In this work we measure the optical, magnetic, and electrical properties of single-walled carbon nanotubes (SWNTs) and carbon nanotube materials. The bare polarized optical absorption cross sections of SWNTs are obtained for the first time, and a large anisotropy is found for light polarized parallel and perpendicular to the nanotube axes. This result validates predicted depolarization effects and also allows rapid measurement of the alignment of nanotube dispersions. Utilizing these calibrated cross sections, the mechanics of SWNTs in a magnetic field are investigated, and alignment of these molecules shows contributions from both the SWNT intrinsic diamagnetic response and external permanent moments. These magnetic alignment measurements are extended using resonant polarized photoluminescence, and we obtain the pure diamagnetic anisotropies for individual (n, m) SWNT species. Magnetic alignment spectroscopy is also used to detect the presence of SWNT bundles, and in all semiconducting SWNT bundles we discover new photoluminescence features providing direct evidence of energy transfer between SWNTs in a bundle. Micro-photoluminescence studies on individual tubes show SWNT emission properties depend strongly upon the SWNT environment. We find energy shifts in the photoluminescence emission can be controlled by varying the excitation power absorbed into the SWNT, and suggest these shifts originate from thermal outgassing of adsorbates on the SWNT sidewalls. Thermal properties of percolated nanotube networks embedded in SWNT-epoxy composites are obtained using a custom thermal conductivity measurement and show enhancements in excess of 50% over pure epoxy. The electrical resistance of novel conducting carbon nanotube aerogels are characterized, and a series of electrical pulses is found to increase the conductivity of polymer-reinforced varieties by several orders of magnitude. Transport and optical measurements on nanotube ensembles show unexplained effects at sub-Tesla magnetic fields with near identical field profiles. We investigate these low field effects as a function of temperature, surfactant, field direction, and discuss the results in the context of mechanisms established for effects in other materials