Photoluminescence spectral imaging of ultralong single-walled carbon nanotubes: Micromanipulation-induced strain, rupture, and determination of handedness

We have applied photoluminescence (PL) microscopy with scanning laser excitation wavelength for imaging and characterizing individual, millimeter-long, single-walled carbon nanotubes (SWNTs) grown by chemical-vapor deposition on structured Si/SiO₂ substrates. Trenches etched into the substrates allowed a direct comparison of the PL properties of air-suspended (across the trenches) and on-SiO₂ segments of the same semiconducting nanotubes. For the on-SiO₂ segments, we found an ∼10–20-fold decrease in PL intensity and redshifts of the emission and excitation transitions by 7–27 meV and 5–24 meV, respectively, compared to air-suspended regions of the same SWNTs. Furthermore, PL imaging was applied to SWNTs fractured by dragging an atomic force microscope tip across on-SiO₂ segments. Strong, localized changes in the emission properties were observed. These included the appearance of PL blinking at the fracture site and evidence for residual axial and to a lesser extent torsional strain extending tens of microns away from the fracture site. We also discuss how PL measurements of torsional strain can be used to determine the handedness of a luminescent nanotube.