Amplitude-mode spectroscopy of chemically injected and photogenerated charge carriers in semiconducting single-walled carbon nanotubes

• Published in: Nano research Vol. 16; no. 4
• Main Authors: Vardeny, Shai R., Phillips, Alan, Thurman, Kira A., Vardeny, Z. Valy, Blackburn, Jeffrey L.
• Format: Journal Article
• Language: English
• Published: United States Springer 18-11-2022
• Subjects: carbon nanotubes; charge carriers; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; doping; Fano; NANOSCIENCE AND NANOTECHNOLOGY; spectroscopy; vibrational
• ISSN: 1998-0124; 1998-0000

In one-dimensional semiconductors such as conjugated polymers and semiconducting single-walled carbon nanotubes (s-SWCNTs), injected charge carriers (electrons or holes) can have profound impacts on both electronic conductivity and optical spectra, even at low carrier densities. Understanding charge-related spectral features is a key fundamental challenge with important technological implications. Here, we employ a systematic suite of experimental and theoretical tools to understand the mid-infrared charge signatures of heavily p-type doped polymer-wrapped s-SWCNTs. Across a broad range of nanotube diameters, we find that hole charge carriers induce strong Fano anti-resonances in mid-infrared transmission spectra that correspond to defect-related (D-band) and in-plane tangential (G-band) Raman-active vibrational modes, along with anti-resonances arising from infrared (IR)-active polymer and SWCNT modes. We employ 13C isotope-labeled s-SWCNTs and a removable wrapping polymer to clarify the relative intensities, energies, and sources of all observed anti-resonances. Simulations performed with the "amplitude mode model" are used to quantitatively reproduce Raman spectra and also help to explain the outsized intensity of the D-band anti-resonance, relative to the G-band, observed for both moderately and degenerately doped s-SWCNTs. Here, the results provide a framework for future studies of ground- and excited-state charge carriers in s-SWCNTs and a variety of low-dimensional materials.