Tuesday, June 30, 20153:30 PM - 5:00 PMCNLS Conference Room (TA-3, Bldg 1690)|
Carbon Nanotube Photophysics: The Era of Targeted Single-Species Ensembles
Erik H. HarozCenter for Integrated Nanotechnologies (MPA-CINT)
Since their discovery in 1993, single-wall carbon nanotubes (SWCNT) have fascinated physicists, chemists, engineers, and material scientists because of the impressive array of mechanical, chemical, electronic, and optical properties, a direct result of their quasi-one-dimensional structures. However, despite their various properties, which should have been a springboard for a host of applications, application development has been slow, due in large part to the mixture of different diameters, lengths, and twist (chiral) angles inherent in as-produced SWCNT material. This heterogeneity of structure leads to bulk material with mixed and often poorer physical properties. For example, optical properties of different SWCNT species such as transition energies, excited-state lifetimes, phonon frequencies, etc. can be obscured in mixed ensemble samples by other species due to spectral overlap.
In this presentation, I will highlight the progress in SWCNT photophysics over the past 13 years and how each major advance in spectroscopy was precipitated by an advance in sample quality through the use of post-synthesis separation strategies to remove sample heterogeneities from bulk material and hence produce samples with high structural uniformity. This structural uniformity subsequently has lead to enhancing our understanding of the fundamental optical processes present in such materials. Specifically, I will discuss the use of the aqueous two-phase extraction technique to produce scalable amounts of highly pure single-electronic-type, narrow-diameter ensemble samples. This method is generalizable to any carbon nanotube material and by careful selection of certain separation parameters such as surfactant composition and concentration, temperature, redox chemistry, etc. ultimately leads to the isolation of single species (chirality) of SWCNTs. Armed with such samples, we explore their optical properties through a combination of absorption, photoluminescence, and resonant Raman spectroscopies to study phenomena such as absorptive and emissive phonon sidebands, nuclear coordinate dependencies of optical transition dipole moments, and SWCNT structural dependencies of phonon frequencies, and extended intertube electronic coupling through delocalized excitonic states. All these phenomena are observed as a consequence of the structural simplicity of these new single-species ensemble samples and only the tip of the iceberg for carbon nanotube research and applications.
Host: Mila Adamska