Assessment of (<i>n,m</i>) Selectively Enriched Small Diameter Single-Walled Carbon Nanotubes by Density Differentiation from Cobalt-Incorporated MCM-41 for Macroelectronics

Abstract

Uniformly semiconducting or metallic single-walled carbon nanotube (SWNT) networks are ideal materials for flexible and large-area electronics (macroelectronics). With the goal of developing optimal enrichment and evaluation solutions toward economical production of monodisperse SWNTs for macroelectronics, we selectively enriched SWNTs, which have small diameters (<0.9 nm) and a narrow (n,m) distribution, synthesized on cobalt-incorporated MCM-41 catalysts. The (7,5) enriched SWNTs were obtained from sodium cholate (SC) dispersion, whereas (6,5) were from cosurfactant mixtures of sodium dodecyl sulfate (SDS):SC at 1: 4. Density gradient ultracentrifugation was applied to further refine the separation. Subsequently, SWNT thin-film field effect transistors (FETs) were fabricated using enriched SWNTs. We characterized the chiralities by photoluminescence excitation spectroscopy, optical absorption spectroscopy, Raman spectroscopy, and electrical transport measurements. Among these techniques, results demonstrate that the electrical transport measurement (through Ion/Ioff ratio) of thin-film FETs is the most sensitive technique to evaluate the purity of semiconducting SWNTs. Enriched SWNTs via only SC produced more devices with higher on-/off-current ratios (up to 1 × 106) compared to SWNTs obtained from SDS/SC cosurfactants. These results are different from previous studies using laser-ablation-grown SWNTs (1.1−1.4 nm), encouraging more comprehensive models to explain diameter dependent chirality selection using surfactants.