Abstract
Carbon : nickel (C : Ni) nanocomposite templates (NCTs) were used as catalyst precursors for diameter-controlled growth of single-walled carbon nanotubes (SWCNTs) by chemical vapor deposition (CVD). Two NCT types of 2 nm thickness were prepared by ion beam co-sputtering without (type I) or with assisting Ar(+) ion irradiation (type II). NCT type I comprised Ni-rich nanoparticles (NPs) with defined diameter in an amorphous carbon matrix, while NCT type II was a homogenous C : Ni film. Based on the Raman spectra of more than 600 individual SWCNTs, the diameter distribution obtained from both types of NCT was determined. SWCNTs with a selective, monomodal diameter distribution are obtained from NCT type I. About 50% of the SWCNTs have a diameter of (1.36 ± 0.10) nm. In contrast to NCT type I, SWCNTs with a non-selective, relatively homogeneous diameter distribution from 0.80 to 1.40 nm covering 88% of all SWCNTs are obtained from NCT type II. From both catalyst templates predominantly separated as-grown SWCNTs are obtained. They are free of solvents or surfactants, exhibit a low degree of bundling and contain negligible amounts of MWCNTs. The study demonstrates the advantage of predefined catalysts for diameter-controlled SWCNT synthesis in comparison to in situ formed catalysts.
Highlights
Carbon nanotubes have been known for more than 20 years[1] and since the very first reports on their synthesis fascinating electronic properties of CNTs were predicted
In our previous work on SWCNT growth[48] we reported the successful growth of individual SWCNTs with a Gaussian-like, non-selective diameter distribution of (1.6 ± 0.4) nm from 10 nm thick templates consisting of columnar Ni NPs of (4.0 ± 1.0) nm diameter before the chemical vapor deposition (CVD) growth process
The microstructure of the original nanocomposite templates (NCTs) type I is heterogeneous and consists of Ni-rich particles embedded in an amorphous carbon (a-C) matrix (Fig. 1)
Summary
Carbon nanotubes have been known for more than 20 years[1] and since the very first reports on their synthesis fascinating electronic properties of CNTs were predicted. In currently commercialized applications CNTs are mainly used as additives to improve the mechanical, thermal, and electrical properties of bulk materials (resins, plastics, polymers).[9] Semiconducting SWCNTs are well suited for transistors because of their low electron scattering and small bandgap.[10] For “high-tech” applications, precisely-defined electronic properties are needed. This requires eventually one specific diameter and chiral angle of SWCNTs.[11,12] There are several methods of CNTs synthesis,[13,14,15] and among them CVD is the most versatile and most scalable one. 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, Ni17,23,46–53 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.[16,20,21,25,26,32,35,41,51,54]
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