Small Molecule Additives to Suppress Bundling in Dimensional-Limited Self-Alignment Method for High-Density Aligned Carbon Nanotube Array

Semiconducting single-walled carbon nanotube (CNT) is a promising candidate as a channel material for advanced logic transistors, attributed to the ultra-thin 1-nm cylindrical geometry, high mobility, and high carrier injection velocity. However, the presence of undesired CNT bundles in the CNT arrays for wafer-scale device fabrication, even when utilizing the state-of-the-art dimension-limited self-alignment (DLSA) method, poses challenges. These CNT bundles degrade the transistor gate's efficiency in controlling the flow of charge carriers in the CNT channel, leading to pronounced device-to-device variability. Here, a novel method is introduced to alleviate bundling in CNT arrays assembled via DLSA, by involving small molecule additive to screen the attractive van der Waals force between neighboring CNTs during the DLSA process, resulting in over 50% reduction in CNT bundling. Furthermore, a pioneering methodology for quantifying CNT bundles is presented and employed experimentally to assess bundles in dense CNT arrays assembled by DLSA using transmission electron microscopy. Both experimental data and molecular dynamics simulation reveal that CNT bundling originates from van der Waals attraction between CNTs, and the disturbed liquid-liquid interface by accumulating excess polar molecules. These findings illuminate new pathways for realizing dense, bundle-free CNT arrays.