Alkane Encapsulation Induces Strain in Small-Diameter Single-Wall Carbon Nanotubes

Encapsulation of linear alkane molecules in the endohedral volumes of small-diameter single-wall carbon nanotubes (SWCNTs) is shown to induce diameter-dependent strain on the hexagonal lattice of carbon atoms composing the tubular structure. For the smallest diameter nanotubes, such as the (6,5), (9,1), (8,3), and (10,0), encapsulation leads to expansive radial strain. This effect is demonstrated through precision measurements of induced shifts in the energy of the intrinsic optical transitions of single-chirality nanotube populations. The effect on the optical transitions from strain is found to exceed that of the effective dielectric medium change when comparing the same SWCNT population filled with an alkane versus those filled with water. This differs from encapsulation of alkanes into larger-diameter nanotubes, for which dielectric effects dominate because of the relative sizes of the guest molecules and the SWCNT cavity. For the SWCNT species examined in this work, the interior cavity diameters are ...