Diameter-Controlled Synthesis of Horizontally Aligned Carbon Nanotube Arrays via S-Apphire Interface Engineering

Precise control over the size and dispersion of supported metal nanoparticles is a fundamental issue in heterogeneous catalysis, governing both reaction activity and selectivity. However, regulating these parameters remains challenging due to thermodynamically driven sintering, particularly under high-temperature conditions. This challenge is acutely exemplified in the growth of horizontally aligned carbon nanotube (HACNT) arrays, where the catalyst size dictates the CNT diameter, and consequently the electronic properties for integrated circuit applications. Here, we report a deterministic sulfur-modified sapphire (S-apphire) interface engineering strategy to regulate catalyst dispersion and the resulting CNT diameter. We establish cohesive energy (Ecoh) as a quantitative descriptor of metal-metal versus metal-support interactions and show that sulfur modification selectively tunes Ecoh to control nanoparticle size predictably. This strategy achieves a diameter reduction to ∼1.26 nm using Ti catalysts, meeting the requirements for the 3 nm technology node of CNT integrated circuits, while preserving high array density and good alignment. Top-gated field-effect transistors fabricated on these arrays exhibit on/off current ratios approaching 107, superior to devices with uncontrolled diameters. Beyond CNT electronics, this work offers a generalizable thermodynamic framework for designing stable, size-controlled metal nanostructures via interface engineering.