Catalytic Chemical Vapor Deposition of Single-Wall Carbon Nanotubes at Low Temperatures

Abstract

We report surface-bound growth of single-wall carbon nanotubes (SWNTs) at temperatures as low as 350°C by catalytic chemical vapor deposition from undiluted C 2 H 2 . NH 3 or H 2 exposure critically facilitates the nanostructuring and activation of sub-nanometer Fe and Al/Fe/Al multilayer catalyst films prior to growth, enabling the SWNT nucleation at lower temperatures. We suggest that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.Carbon nanotubes (CNTs) have been a driving force for current advances in nanotechnology, both on an applied and on a fundamental level. Single-wall carbon nanotubes have shown the highest Young's modulus and highest axial thermal conductivity of any solid. Moreover, SWNTs have the highest current carrying capacity of any conductor, which makes them an attractive electronic, sensing, or heat sinking material for nano-electromechanical systems (NEMS) and future (hybrid) integrated circuitry. 1,2Defect-free SWNT synthesis is generally thought to require high temperatures (T). 3 This belief arises from the success of high-T deposition processes. Arc-discharge, laser ablation, and high-pressure CO conversion with inherent (local) temperatures in the order of 1000-4000°C have been optimized mainly for bulk CNT production. 3 For device fabrication, these techniques heavily rely on purification from other carbon allotropes and an indirect postgrowth assembly via stable suspensions. In comparison, catalytic chemical vapor deposition (CVD) allows selective, aligned CNT growth directly onto a substrate and thus presently is the only economically viable process for integrating CNTs into a device. 1,[4][5][6] This approach, however, exposes the substrate to the CNT growth temperature and atmosphere, which creates a need for less aggressive, low T processing conditions. Present back-end CMOS technology allows a maximum temperature of 400-450°C, the limit being set by the mechanical integrity of low dielectric constant intermetal dielectrics. 7 Thermal CVD of SWNTs has been reported at 550°C in furnace 8 and cold wall systems. 9 In situ environmental transmission electron microscopy (TEM) experiments show SWNT nucleation at 480°C. 10 Random-network FETs have been fabricated with SWNTs grown at 450°C by remote plasma-enhanced (PE) CVD.11 However, the high temperatures of bulk production techniques still dominate growth model considerations with the assumption that the catalyst cluster has to be liquefied and that the catalyst bulk is ratecontrolling.12,13 These considerations are also transferred to surface-bound CVD. 14 CNT growth below 500°C is not thought to be possible based on calculations of size-corrected melting points 14 and carbon saturation. 15In this Letter, we report SWNT growth at temperatures below 450°C by thermal CVD at cold wall conditions and demonstrate field effects in as-integrated SWNT FETs. We use evaporated thin catalyst films, which allow accurate patterning by standard lithography techniques and thus compa...

Carbon nanotubes for ultrafast fibre lasers

“…For the carbon source gas, several hydrocarbons were studied, for example, methane [105], ethylene [107], benzene [108] or the most recent one, camphor (C 10 H 16 O), which moreover appeared to be environment friendly [109]. A substrate is covered with catalytic metal particles, like Fe, Ni, Co or their combination.…”

Local heating method for growth of aligned carbon nanotubes at low ambient temperature

“…Typically, temperatures in the range 600-900 o C are required, depending on the details of the growth conditions and catalyst preparation. Although nanotubes can be grown at lower temperatures [5], their structural integrity deteriorates rapidly as the growth temperature is decreased and their mechanical and electrical properties suffer as a consequence. In order to grow good quality carbon nanotubes on CMOS chips (aiming for temperatures below 450 o C) or on other temperature-sensitive substrates such as polymers, it is necessary to find ways to overcome this severe limitation.…”

Influence of Mo on the Fe:Mo:C nanocatalyst thermodynamics for single-walled carbon nanotube growth

“…Furthermore, the presence of small concentrations of Mo reduce the lower size limit of low-temperature steady-state growth from ∼0.58nmf orpureF eparticlesto ∼ 0.52nm. Our ab initio-thermodynamic modeling explains experimental results and establishes a new direction to search for better catalysts.Critical factors for the efficient growth of single walled carbon nanotubes (SWCNTs) via catalytic chemical vapor deposition (CCVD) 1,2,3 are the compositions of the interacting species (feedstock, catalyst, support 4,5,6,7,8,9,10 ), the preparation of the catalysts, and the synthesis conditions 11,12,13,14,15,16,17,18 . Efficient catalysts must have long active lifetimes (with respect to feedstock dissociation and nanotube growth), high selectivity and be less prone to contamination 19,20,21,22,23 .…”

“…chemical poisoning or coating with carbon), thermal sintering (e.g. caused by highly exothermic reactions on the clusters surface 13,14,24 with insufficient heat transfer 25,26 ) and solid-state reactions (nucleation of inactive phases in the cluster 22,23,25 ).…”