Multiscale Characterization and Two-Stage Assembly Mechanism of Dimension-Limited Self-Aligned Carbon Nanotube Arrays

High-density, semiconducting aligned carbon nanotube arrays (A-CNTs) are essential for next-generation electronics. Dimension-limited self-alignment (DLSA) is a leading route to wafer-scale A-CNT fabrication, yet the instabilities that limit array quality remain poorly understood, hampering targeted process optimization. Here, we establish a multiscale characterization framework combining cross-polarized optical microscopy (xPOM) and scanning electron microscopy (SEM) to evaluate DLSA-prepared A-CNT wafers and identify the underlying film-formation mechanism. Notably, characterization of the entire 4-inch wafer is achieved within approximately 1 h, providing an efficient route for high-throughput macroscopic inspection. Cross-validation across multiple characterization methods reveals a hierarchical morphology comprising four spatial regions and recurring macroscopic defects. These observations, together with in situ measurements of DLSA dynamics, support a two-stage self-assembly mechanism: initial two-dimensional biphasic self-assembly behavior followed by quasi-one-dimensional triphasic self-assembly coupled to continuous transfer. The second stage, imposed by orientational confinement at the air/top-layer/CNT-dispersion interface, is proposed to drive globally consistent alignment. Specific defects are further associated with distinct kinematic processes and mechanical stress states. This mechanistic picture provides a framework for suppressing non-idealities in A-CNTs and supporting their eventual integration into CNT-based logic circuits.