Doping of semiconductors, such as single-wall carbon nanotubes (SWNTs), by the introduction or removal of charges can be used for modification of their electronic and optical structure. This offers unique opportunities for the fabrication of versatile materials with new properties. However, despite a broad body of work,¹⁻³ the control and spectroscopic assessment of the doping of SWNTs is still being developed^4,5 in order to be able to reproducibly tailor semiconductor properties.

Here, we have studied the photophysical properties of chemically doped SWNTs by absorption and photoluminescence spectroscopy. Polychiral samples of purified HiPCO soot were charged by oxidation with gold chloride. Thanks to very well-resolved and narrow exciton bands in these samples, the trionic signatures induced by charges could be resolved for up to five distinct nanotube species. An investigation of spectral changes in absorption measurements as a function of gold chloride concentration reveals that tubes with smaller bandgaps are doped at lower gold chloride concentrations. The trion binding energy with respect to the dipole-allowed first sub-band exciton transition was also found to increase systematically with decreasing diameter in agreement with previous findings.^1,2 In addition, we find that SWNT oxidation potentials decrease nearly linearly with increasing nanotube diameter. Lastly, a surprisingly abrupt change of exciton oscillator strengths at redox potentials near the nanotube band edge provides evidence for band gap renormalization.

References

1. R. Matsunaga, K. Matsuda, Y. Kanemitsu, Phys. Rev. Lett. 2011, 106, 037404.

2. J. S. Park, Y. Hirana, S. Mouri, Y. Miyauchi, N. Nakashima, K. Matsuda, JACS 2012, 134, 14461−14466.

3. S. M. Santos, B. Yuma, S. Berciaud, J. Shaver, M. Gallart, P. Gilliot, L. Cognet, B. Lounis, Phys. Rev. Lett. 2011, 107, 187401.

4. H. Hartleb, F. Späth, T. Hertel, ACS Nano 2015, 9, 10461−10470.

5. M. Yoshida, A. Popert, Y. K. Kato, Phys. Rev. B 2016, 93, 041402.