Gas phase synthesis of non-bundled, small diameter single-walled carbon nanotubes with near-armchair chiralities

Abstract

We present a floating catalyst synthesis route for individual, i.e., non-bundled, small diameter single-walled carbon nanotubes (SWCNTs) with a narrow chiral angle distribution peaking at high chiralities near the armchair species. An ex situ spark discharge generator was used to form iron particles with geometric number mean diameters of 3–4 nm and fed into a laminar flow chemical vapour deposition reactor for the continuous synthesis of long and high-quality SWCNTs from ambient pressure carbon monoxide. The intensity ratio of G/D peaks in Raman spectra up to 48 and mean tube lengths up to 4 μm were observed. The chiral distributions, as directly determined by electron diffraction in the transmission electron microscope, clustered around the (n,m) indices (7,6), (8,6), (8,7), and (9,6), with up to 70% of tubes having chiral angles over 20°. The mean diameter of SWCNTs was reduced from 1.10 to 1.04 nm by decreasing the growth temperature from 880 to 750 °C, which simultaneously increased the fraction of semiconducting tubes from 67% to 80%. Limiting the nanotube gas phase number concentration to ∼105 cm−3 prevented nanotube bundle formation that is due to collisions induced by Brownian diffusion. Up to 80% of 500 as-deposited tubes observed by atomic force and transmission electron microscopy were individual. Transparent conducting films deposited from these SWCNTs exhibited record low sheet resistances of 63 Ω/□ at 90% transparency for 550 nm light.

Roles of sulfur in floating-catalyst CVD growth of single-walled carbon nanotubes for transparent conductive film applications

“…Floating catalyst chemical vapor deposition (FC-CVD) is a single-step, continuous, scalable method in which the entire process of catalyst and SWCNTs formation takes place in a gaseous environment [9,33]. The aerosol nanoparticles suspended in non-reacting carrier gases without any support act as catalyst particles.…”

“…Our group first time introduced the synthesis of SWCNTs in FC-CVD technique from pre-made catalysts. The purpose of pre-made catalyst synthesis is to get a precise control on size and NC of catalyst, and thus, SWCNT NC during growth [10,33]. In this technique, catalyst particles are pre-produced through the physical evaporation of the electrodes using hot wire generation (HWG) [9] or spark discharge generation techniques [33] (Fig.…”

“…axial or transverse) of the carrier gas and jet speed at the point of spark generation. Conventional rod-to-rod (R-R) electrode configuration with the transverse flow of the carrier gas was previously employed by Mustonen et al for the synthesis of SWCNTs [33]. However, it has been observed that at higher NC agglomeration of the nanoparticles is a major problem for less than 40 lpm of the carrier gas with this geometry.…”

All‐Carbon Thin‐Film Transistors as a Step Towards Flexible and Transparent Electronics

“…[85,86] If given individual, i.e., non-bundled, CNTs, the TCFs treated with a strong solution of HNO 3 exhibit a sheet resistance of 63 Ω sq -1 at a transmission of 90%. [87] In addition, the as-grown CNTs usually contain both metallic CNTs and semiconducting CNTs, so preferential growth of metallic CNTs in the floatingcatalyst CVD method would be helpful to further improve the electrical conductivity of CNT networks. [88] Recently, singlewall CNT TCFs, made by Canatu Inc., with free of reflection and haze have started to enter market for flexible, ultrathin and wearable touch displays and sensors.…”

Phonon contribution to electrical resistance of acceptor-doped single-wall carbon nanotubes assembled into transparent films

“…The sheet resistance of pristine SWCNT films depends on the purity of the samples, the length and diameter of the nanotubes, and the size of the SWCNT bundles [13,15]. The best value of R sq = 89 ohm/sq has been obtained for 90%-transparent SWCNT films fabricated using aerosol technology, which leads to an almost complete elimination of SWCNT bundling (known for such technique as arc discharge [17]) and a substantial increase in SWCNT lengths via the suppression of bundling-induced growth termination [16] The sheet resistance of SWCNT films can be significantly decreased by acid(HNO 3 ) treatment that results in a high level of p-type doping [9,14,18,19]. The other examples of strong acceptors for p-type doping are iodine and cuprous chloride (CuCl) [20][21][22][23][24].…”