4.8 Article

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

Journal

NANO RESEARCH
Volume 16, Issue 4, Pages 5619-5625

Publisher

TSINGHUA UNIV PRESS
DOI: 10.1007/s12274-022-5080-1

Keywords

carbon nanotubes; doping; charge carriers; phonons; electron-phonon coupling

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This article investigates the mid-infrared charge signatures of heavily p-type doped polymer-wrapped single-walled carbon nanotubes (s-SWCNTs). The study finds that hole charge carriers induce strong Fano anti-resonances in mid-infrared transmission spectra and analyzes the relative intensities, energies, and sources of all observed anti-resonances.
In one-dimensional semiconductors such as conjugated polymers and semiconducting single-walled carbon nanotubes (sSWCNTs), 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 C-13 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 sSWCNTs. 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.

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