Diameter-Dependent Raman and AFM Assessment of Damage in Yttrium-Treated Films of Single-Walled Carbon Nanotubes

Abstract

Conjugated polymer sorting is a widely used route to obtain semiconducting single-walled carbon nanotubes (semi-CNTs), but residual polymer wrappers after deposition can negatively affect surface chemistry, interfacial behaviour, and device performance. Yttrium-assisted purification treatment has been explored as a promising route for removing such wrapper species. However, effects of this purification treatment on different diameter ranges remain a mystery. This work evaluates the yttrium-assisted purification strategy and quantifies how the treatment impacts the structural integrity of different semi-CNT diameter ranges. Three PFO-BPy-sorted diameter windows are studied: CoMoCAT (6,5) (~0.75 nm), HiPCO (075-1.28 nm), and Arc Discharge (1.3-1.7 nm). To enable reliable, diameter-dependent comparisons, a sample-preparation workflow is implemented to reduce substrate, atmospheric, and solvent artifacts in Raman analysis, including passivation layer and nitrogen encapsulation, which together reduce the as-deposited Raman D/G ratio by ~90%. Yttrium-treatment cycles performed repetitively reveal a strong diameter dependence: Arc Discharge semi-CNTs show no damage and even a decrease in the D/G ratio, HiPCO shows a modest increase, while (6,5) semi-CNTs exhibit a pronounced increase of ~400%. A quasi-quantitative comparison to literature is used to bound contributions from doping and strain, supporting defect addition as the dominant origin of the D/G ratio rise in the smallest-diameter tubes. AFM imaging shows no uniform nanotube segmentation or shortening behaviour across all diameters.