Growth and Structure of Carbon Nanotube Y-Junctions

Abstract

The effect of a catalyst on the growth and structure of carbon nanotube Y-junctions (CNTYs) using chemical vapor deposition has been investigated. Cobalt-, magnesium-, and calcium-nitrates are utilized as precursors of catalysts Co, Mg, Ca, Co/Mg, Co/Ca, and Mg/Ca for CNTY synthesis. Experimental result shows that Co/Mg or Co/Ca can grow CNTYs with straight branches while Co, Mg, Ca, and Mg/Ca will not grow any CNTYs, indicating that only combinations of Co with Mg or Ca will facilitate the formation of CNTYs. In addition, the effect of the carbon source on the formation of CNTYs has also been studied. It is found that thiophene (C4H4S) can promote the formation of CNTYs, while other sources such as methane (CH4) and acetylene (C2H2) cannot. The result shows that both the catalyst and the carbon source substantially affect the formation of CNTYs.

Formation mechanism of Y-junctions in arrays of multi-walled carbon nanotubes

“…There might be many different mechanisms of formation of Y-junctions according to the experimental conditions; the mechanism reported here is not necessarily the same as in other nanotubes [4][5][6][7] in which bamboo-like structures are not observed. In the frame of the proposed merger scenario, the occurrence of Y-junctions is proportional to the probability of two particles to meet during the growth of the nanotubes.…”

“…In some instances, CNTs are naturally synthesized with junctions, some having unique electrical properties. For instance, Y-junctions of CNTs [4][5][6][7] can be used as nanometer-sized transistors [8]. Other types of junctions -like T-junctions, or H-junctions [9] -could also be useful in the prospect of organizing CNTs into complex networks to make nano-electronics circuits [2].…”

The Intramolecular Junctions of Carbon Nanotubes

“…One of the most used additive elements is sulfur, which would be decomposed from sulfur-containing materials such as thiophene [155,157,[166][167][168][169][170] and octadecanethiol. [49] Sulfur can promote the growth of branched junctions in the pyrolysis of organometallic precursors, such as nickelocene, [157] ferrocence, [166] nickel phthalocyanines, [155,170] iron phthalocyanines, [169,170] and iron pentacarbonyl. [170] This was first reported by Rao et al in 2000.…”

“…[171,172] Moreover, other additives, such as Ca, Mg, Si, Al can also promote the growth of branched junctions. [49,173,174] By pyrolysis of methane over cobalt supported on magnesium oxide, macro-scale Y-junctions with straight arms were synthesized (Fig. 10c), and the catalyst for the Y-junction growth was found to contain Ca, Mg, Si, and O.…”

“…Li et al found that the introduction of sulfurcontaining precursors such as thiophene into the CVD process could largely promote the formation of SWNT/SWNT junctions, as sulfur could change the active site on the catalyst, which caused a change of the CNT growth direction and then the SWNT/SWNT junctions formed. [49] Recently, Yao et al…”