Effect of Catalyst Pretreatment on Chirality-Selective Growth of Single-Walled Carbon Nanotubes

Abstract

We show that catalyst pretreatment conditions can have a profound effect on the chiral distribution in single-walled carbon nanotube chemical vapor deposition. Using a SiO 2 -supported cobalt model catalyst and pretreatment in NH 3 , we obtain a comparably narrowed chiral distribution with a downshifted tube diameter range, independent of the hydrocarbon source. Our findings demonstrate that the state of the catalyst at the point of carbon nanotube nucleation is of fundamental importance for chiral control, thus identifying the pretreatment atmosphere as a key parameter for control of diameter and chirality distributions.

Nitrogen controlled iron catalyst phase during carbon nanotube growth

“…4 In line with our current observations, we argued that this was related to nitrogen-induced changes in the cobalt catalyst structure/faceting, which translate to a change in nucleating SWNT chiralities. 4 In summary, using in-situ X-ray diffractometry, we have directly demonstrated how the addition of a pre-treatmentand add-gas changes the evolution of Fe-catalysts in typical and industrially scalable CNT CVD conditions. Instead of polydisperse catalyst phase mixtures in commonly employed H 2 diluted CVD, the addition of nitrogen (in the form of NH 3 ) controllably leads to phase-pure c-Fe catalysts during pre-treatment and to phase-pure Fe-carbide (Fe 3 C) during growth.…”

“…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.…”

“…2,4,[62][63][64][65][66] In this context, e.g., we have recently shown that the addition of NH 3 to the pretreatment atmosphere for SWNT CVD narrows and downshifts diameter and chiral distributions in cobalt-catalyzed SWNT growth. 4 In line with our current observations, we argued that this was related to nitrogen-induced changes in the cobalt catalyst structure/faceting, which translate to a change in nucleating SWNT chiralities. 4 In summary, using in-situ X-ray diffractometry, we have directly demonstrated how the addition of a pre-treatmentand add-gas changes the evolution of Fe-catalysts in typical and industrially scalable CNT CVD conditions.…”

Carbon : nickel nanocomposite templates – predefined stable catalysts for diameter-controlled growth of single-walled carbon nanotubes

“…There are many reports that catalyst particles must have a suitable size in order to be active for CNT growth and that the control of the catalyst nanoparticles before and during CVD is very important in order to control CNT yield, diameter and chirality. The most used catalysts for CNT growth are Fe, [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Co, 24,[32][33][34][35][36][37][38][39][40][41][42][43][44][45] Ni 17,23,[46][47][48][49][50][51][52][53] and their bimetallic alloys. 38,42,[54][55][56] The CNT synthesis on these catalysts may produce SWCNTs with narrow diameter distribution and few chiralities depending on the catalyst nanoparticle size.…”

Synthesis of Carbon Nanotubes by Catalytic Chemical Vapor Deposition

“…Harutyunyan et al [72] designed cleverly Ar/He/H 2 /H 2 O pretreatment gas effectively to increase the proportion of metallic SWCNTs. In 2014, Bayer et al [73] used Co/SiO 2 to catalyze the growth of SWCNTs with concentrated chiral and pipe diameter distribution. The only explanation for the variation was the effect of ammonia pretreatment on the catalyst's valence state and particle size distribution.…”