THz Studies of Carrier Dynamics in Single-Walled Carbon Nanotubes and of Optical Activity in Organic Molecular Crystals

Yale University, New Haven CT

Investigators

Abstract

In this award, funded by the Experimental Physical Chemistry Program of the Chemistry Division, Professor Schmuttenmaer of Yale University and his collaborators and students will pursue two interrelated activities: 1. Terahertz (THz) emission spectroscopy from individual single-walled carbon nanotubes (SWCNTs), and 2. THz optical activity in organic molecular crystals and proteins. One of the reasons SWCNTs have received much attention is because they have well defined electrical properties, unlike multi-walled CNTs. An individual SWCNT can be either metallic or semiconducting, depending on the value of its chiral vector (a measure of the manner in which the tube rolls up). They have been recognized as prime candidates for further miniaturization of electronics, i.e., carbon-based electronics. In addition, they are an ideal platform for studying phenomena in one-dimensional (1D) systems. Systems of reduced dimension have provided special opportunities, challenges, and fascination for many years. Their study has given us a deeper understanding of the physics of condensed materials in general. The SWCNT is one of the most fascinating model 1D systems. Another area of the proposed work is to investigate THz optical activity. Optical activity is a fundamental property of chiral molecules. There has been a great deal of recent work using THz time-domain spectroscopy to characterize organic molecular crystals (OMCs). These studies have ranged from amino acid crystals and carbohydrates, to illicit drugs, to pharmaceuticals, to explosives. However, no one has ever reported the THz vibrational circular dichroism (VCD) or optical rotatory dispersion (ORD) spectrum of a molecular system in the THz region. It is uncharted territory. Understanding the characteristics and mechanisms in high speed conductivity in SWCNTs is a critical step toward their utilization in an advanced electronic or optoelectronic device. Given the huge number of scientists studying them, it might seem surprising that no one has yet characterized their THz emission. Studies of THz optical activity will be transformative much in the same way infrared VCD transformed studies of optical activity by opening the IR region of the spectrum to this type of study. THz VCD will obtain information about intermolecular modes that is inaccessible to IR VCD. It will provide rigorous experimental constraints on calculated spectra, whether empirical or ab initio methods are used. Students involved in this project will benefit by interacting with investigators from different fields, namely chemistry (Professor Schmuttenmaer) and physics (Professor Prober). Professors Prober and Schmuttenmaer have a track record of outreach at a variety of levels, and will continue these activities and strengthen them wherever possible.