Selective\nGrowth of Subnanometer Diameter Single-Walled\nCarbon Nanotube Arrays in Hydrogen-Free CVD

Abstract

Small diameter single-walled carbon\nnanotube (SWNT) arrays with\nlarger bandgap are more desirable as near-infrared optical absorbers\nfor the fabrication of high performance photovoltaic and photodetector\ndevices. We report herein a rational approach to selective growth\nof well-aligned subnanometer diameter (∼84% between 0.75 and\n0.95 nm) SWNT arrays with a density of 0.3–0.5 tubes/μm\non quartz surfaces using solid Mo₂C catalysts for short-time\ngrowth by low carbon feeding in hydrogen-free CVD. These subnanometer\ndiameter SWNTs have a narrow chirality distribution (the ratio of\n(8,4), (8,5) and (7,6) is higher than 73%). During nanotube growth,\nonly small size Mo nanoparticles are carbonized into stable Mo₂C for catalyzing the growth of SWNTs through low carbon feeding\nrate over short time in the hydrogen-free environment, whereas larger\ncatalysts are inactive due to underfeeding. Meanwhile, solid Mo₂C catalysts are effective in reducing the chirality distributions\nof the as-grown SWNTs. Additionally, combining an annealing process\nafter loading catalyst on the sapphire substrates, the average density\nis increased to ∼15 tubes/μm while maintaining small\ndiameter and narrow chirality distribution. Our results offer more\nchoices for structurally controlled growth of aligned-SWNTs, with\npotential applications in nanoelectronics.