Ultrafast dynamics of carrier relaxation determining the quasi-1D and non-1D electronic behaviors in carbon nanostructures

We investigate the relaxation dynamics of photoexcited carriers in bundled few-walled carbon nanotubes (CNTs) and van der Waals (vdW) heterostructures of CNTs covered with boron nitride nanotubes (BNNT) using ultrafast transient absorption spectroscopy from the near-infrared to the ultraviolet spectral range. The relaxation constant of the photoexcited carriers in bundled CNTs decreases with the photon energy of the probe, conversely, that in vdW heterostructures is almost constant with respect to the photon energy. The energy dependence of the relaxation constants for the probing photon energy determines whether the bundled CNT materials show one-dimensional (1D) or non-1D electronic behavior. The bundled CNTs show a non-1D electronic character, and the vdW heterostructures show a quasi-1D electronic one. It suggests that the bundled structure and intercalation of the insulating BNNT layer strongly influence their electronic dimensionality. These insights, offering a precise understanding of material properties, are beneficial for designing future optoelectronic devices based on nanostructured materials.