Chirality Assignment of Single-Walled Carbon Nanotubes with Strain

Strain-induced band gap shifts that depend strongly on the chiral angle have been observed by optical spectroscopy in single-walled carbon nanotubes (SWCNTs). Uniaxial and torsional strains are generated by changing the environment surrounding the SWCNTs, using the surrounding ${\mathrm{D}}_2\mathrm{O}$ ice temperature or the hydration state of a wrapping polymer. These methods are used as diagnostic tools to determine the quantum number $q$ and examine chiral vector indices for specific nanotubes.

Figure 1

A data map of $E_{22}$ excitation-$E_{11}$ emission using the semiempirical formula from Bachilo et al. [6]. Three photoluminescence spectra of SDS-suspended SWCNT solution measured at room temperature are shown using selective excitation with 633, 720, and 810 nm radiation.

Figure 2

(a)–(c) The effects of temperature on the band gap luminescence for PVP-wrapped SWCNT sample PCNT1 solution excited with (a) 633, (b) 720, and (c) 810 nm radiation. From our analysis $P3\equiv R3$, $P4\equiv Q3$, $P6\equiv Q4$, and $P7=Q5$. (d) Room temperature photoluminescence spectra excited with 633 nm as a function of drying time for PVP-wrapped SWCNT sample PCNT2. The photoluminescence curves are scaled and shifted in the vertical direction to aid comparison.

Figure 3

The temperature dependence of the strongest luminescence peak positions excited with 633 nm. The energies of most peaks are also shifted by the ice phase transitions at 273 K (phase Ih to liquid) and 72 K (phase XI to Ih).

Figure 4

(a) Fitting of heating induced band gap shifts to Eq. (1) based on Bachilo et al. [6] and Hagen and Hertel's scenario I [11] assignments. (b) Heating and swelling induced band gap shifts versus chiral angle according to the Bachilo et al. assignment. The dashed lines show the best fitted curves.