Optical and magnetic properties of carbon nanotube ensembles

In this work we use optical spectroscopy as a tool to probe the basic properties of carbon nanotubes (CNTs), which include structure-dependent magnetic susceptibility anisotropies Δχ, optical energy transfer between bundled semiconducting CNTs, the energy level splitting between bright singlets and dark K-momentum singlets in (6,5) CNTs, and surfactant-induced photoluminescence (PL) brightening in CNTs. Our polarized and unpolarized measurements of visible and near-infrared Raman scattering, absorbance, and PL are performed on ensembles of CNTs suspended in water, which allows for the high signal-to-noise spectra necessary for detecting weak signals. Additionally, optical techniques are well-suited for ( n, m)-selectivity in heterogeneous samples, since each ( n, m) species has a distinct series of optical resonances. We combine our experimental results with quantum and classical theories to model the response of CNT band structure in a magnetic field, quantify uniaxial and biaxial ordering, predict exciton-phonon coupling, and connect our experimental Δχ values to published calculations within a symmetry-expansion framework