Highly chiral-selective growth of single-walled carbon nanotubes with a simple monometallic Co catalyst

Abstract

We report on the growth of single-walled carbon nanotubes from a monometallic Co catalyst on an oxidized Si wafer support by the most simple growth recipe (vacuum annealing, growth by undiluted C2H2). Nevertheless, multiwavelength Raman spectroscopy and transmission electron spectroscopy show a remarkable selectivity for chiral indices and thus, e.g., high abundance with a single chirality representing 58% of all semiconducting tubes. In situ x-ray photoelectron spectroscopy monitors the catalyst chemistry during carbon nanotube growth and shows interfacial Co-Si interactions that may help to stabilize the nanoparticle/nanotube diameter. We outline a two-mechanism model explaining the selective growth

Nitrogen controlled iron catalyst phase during carbon nanotube growth

“…% N. 51 ) Thus, by co-feeding nitrogen during pre-treatment we have prevented the formation of the previously 5 obtained a-Fe/c-Fe mixtures during pre-treatment by thermodynamically forcing the system into a defined phase-pure c-Fe state (green area in Figure 3(c)) at otherwise constant CVD conditions and irrespective of initial minor residual carbon contamination. 5 Equally, during exposure to the hydrocarbon source in the growth stage (orange trajectory (III) in Figure 3(c)), we observed phase-pure Fe 3 C catalyst particles when using NH 3 (in contrast to the c-Fe/a-Fe/Fe 3 C mixtures when using H 2 5 ). Thus, co-feeding of nitrogen also drastically changed the phase evolution of the catalyst during the growth stage, indicating that nitrogen addition stabilizes Fe 3 C. This observation is in good agreement with previously published phase stabilities in the ternary Fe-C-N system as a function of nitrogen and carbon activities ("Lehrer diagrams") 52,53 and also with recent first principle calculations on the stabilizing effect of N addition on Fe 3 C. 54 Our own thermodynamic calculations in Figure 3(c) also show that the phase fraction of Fe 3 C is incrementally increasing by N addition for a range of C contents.…”

“…For instance, to date selective growth of CNTs with specific narrow sets of chiralities remains limited. [1][2][3] As the structure of the nanotube is largely defined at the point of nucleation 2,4 and thereby templated by the state of the catalyst at this point, the first requirement for control over nanotube structures is stringent control over the phase and structure of the catalyst. Such control however remains equally limited, as multiple competing active catalyst phases co-exist under typical CVD conditions.…”

Chiral-Selective Growth of Single-Walled Carbon Nanotubes on Lattice-Mismatched Epitaxial Cobalt Nanoparticles

“…As comparisons, SWNTs grown from similar catalytic systems which lack such an epitaxial relationship, e.g. monometallic Co catalyst on an oxidized Si wafer16, SiO 2 -supported Co catalyst13, cobalt-incorporated MCM-41 (Co-MCM-41) catalyst48 and SiO 2 -supported CoMo catalyst9, all display far broader chirality distributions.…”

“…Although significant progress has been made in chirality separation of SWNTs by a number of post-synthesis approaches2, such as density gradient centrifugation34, DNA wrapping chromatography567, and multicolumn gel chromatography8, direct selective growth of SWNTs with a narrow chirality distribution91011121314151617 is still regarded as an irreplaceable approach to achieve the goal without deteriorating the pristine structure and modifying the electronic properties of the SWNTs. Over the last decade, substantial efforts have been devoted to developing various structure-controlled synthesis methods91011121314151617, of which most are based on the catalytic chemical vapor deposition (CVD) method910111213141516, known to be an economic and controllable process for carbon nanotube production. It has been discovered that, in the CVD process, SWNTs nucleate and grow on active catalytic nanoparticles and the size and crystal structure of those nanoparticles play a key role in determining the chiral structures of the produced SWNTs181920.…”

Carbon nanotube growth: First-principles-based kinetic Monte Carlo model

“…Due to their outstanding physical and chemical properties [1][2][3], considerable effort has been made to improve the carbon nanotubes (CNT) yields with various morphologies [4][5][6][7]. For example, by controlling the reaction factors, e.g.…”