Chirality-specific growth of single-walled carbon nanotubes on solid alloy catalysts

Abstract

Carbon nanotubes have many material properties that make them attractive for applications. In the context of nanoelectronics, interest has focused on single-walled carbon nanotubes (SWNTs) because slight changes in tube diameter and wrapping angle, defined by the chirality indices (n, m), will shift their electrical conductivity from one characteristic of a metallic state to one characteristic of a semiconducting state, and will also change the bandgap. However, this structure-function relationship can be fully exploited only with structurally pure SWNTs. Solution-based separation methods yield tubes within a narrow structure range, but the ultimate goal of producing just one type of SWNT by controlling its structure during growth has proved to be a considerable challenge over the last two decades. Such efforts aim to optimize the composition or shape of the catalyst particles that are used in the chemical vapour deposition synthesis process to decompose the carbon feedstock and influence SWNT nucleation and growth. This approach resulted in the highest reported proportion, 55 per cent, of single-chirality SWNTs in an as-grown sample. Here we show that SWNTs of a single chirality, (12, 6), can be produced directly with an abundance higher than 92 per cent when using tungsten-based bimetallic alloy nanocrystals as catalysts. These, unlike other catalysts used so far, have such high melting points that they maintain their crystalline structure during the chemical vapour deposition process. This feature seems crucial because experiment and simulation both suggest that the highly selective growth of (12, 6) SWNTs is the result of a good structural match between the carbon atom arrangement around the nanotube circumference and the arrangement of the catalytically active atoms in one of the planes of the nanocrystal catalyst. We anticipate that using high-melting-point alloy nanocrystals with optimized structures as catalysts paves the way for total chirality control in SWNT growth and will thus promote the development of SWNT applications.

Understanding the “Activation” of the Nanocluster [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)98-y(EtOH)y] for Low Temperature Growth of Carbon Nanotubes

“…Thus, the use of catalyst promoters likely serves two roles, (1) to replenish the number of metal atoms lost to sublimation, and (2) to reduce the reduction temperature of procatalyst FeMoC into an ''active'' catalyst. Future work will study the catalyst pre-treatment influence on the resulting phase(s) of FeMoC's Fe-Mo catalyst system; akin to the work of Li et al [13][14][15] …”

“…Considering the problems in controlling the composition and size of binary metal oxide nanoparticles [12] single molecular precursors would be considered an ideal solution: given the unique composition and hence size of the final nanoparticle. Recently, Li et al used the molecular nanocluster Na 15 [Na 3 ,{Co(H 2 O) 4 (12,6), (14,4), and (16,0) CNTs in efficiencies of 92, 97, and 80% respectively [13][14][15]. They propose the high chiral selectivity arises from two key factors: 1) the excellent matching between the (n,m) nanotube chirality and the Miller (plane) indices of the l-phase W 6 Co 7 alloy, and 2) the stability of the high melting point alloy that maintains its well-defined structure under CVD conditions.…”

Carbon nanotubes for ultrafast fibre lasers

“…The first approach of the selective growth of CNT was realised by the controlled CVD method [82,130]. Later, numerous works were focused on the production of single geometry nanotubes [130][131][132]. However, presented methods are very complicated and cannot be used for mass production.…”

Nanogap‐Engineerable Electromechanical System for Ultralow Power Memory

“…In previous studies using cantilevered carbon nanotube devices, multiwalled carbon nanotubes rather than SWNTs are often used because they are metallic and the SWNTs are usually a mixture of metallic and semiconducting nanotubes 14. As shown later in this work, the SWNT memory devices reported in this work are applicable for both metallic or semiconducting SWNTs, resolving the challenge of separation of semiconducting SWNTs from metallic ones 31, 32…”