Selective Synthesis of Subnanometer Diameter Semiconducting Single-Walled Carbon Nanotubes

Abstract

Subnanometer single-walled carbon nanotubes (sub-nm SWNTs) were synthesized at different temperatures (600, 700, and 800 degrees C) using CoMn bimetallic catalysts supported on MCM-41 silica templates. The state of the catalyst was investigated using X-ray absorption, and the (n,m) indices of the sub-nm SWNTs were determined from Raman spectroscopy and photoluminescence measurements. We find that the size of the metallic particles that seed the growth of sub-nm SWNTs (diameter approximately 0.5-1.0 nm) is highly sensitive to the reaction temperature. Low reaction temperature (600 degrees C) favors the growth of semiconducting tubes whose diameters range from 0.5 to 0.7 nm. These results were also confirmed by electrical transport measurements. Interestingly, dominant intermediate frequency modes on the same intensity scale as the Raman breathing modes were observed. An unusual "S-like" dispersion of the G-band was present in the Raman spectra of sub-nm SWNTs with diameters <0.7 nm.

Investigation of growth dynamics of carbon nanotubes

“…Since then, chirality selective growth of SWCNTs was succeeded on a number of different catalysts: CoMo [106–108], FeCo [109], FeRu [110], NiFe [111], Co [112–114], FeCu [115], Au [116], CoMn [117], Ni [118], Fe [119–120], CoPt [121], Co x Mg 1−x O [122], CoSO 4 [123], WCo alloy [124–125] and Mo 2 C [126]. SiO 2 or MgO were used as catalyst support.…”

“…SiO 2 or MgO were used as catalyst support. The synthesis was conducted using different carbon precursors: CO [105–108 112–115 117–119 122–123], C 2 H 5 OH [107,109,120–121 124–126], CH 3 OH [107], CH 4 [110,116] and C 2 H 2 [111]. Table 1 summarizes the reports on the chirality selective synthesis of SWCNTs.…”

“…It was shown that chirality selectivity is influenced by the synthesis parameters: gaseous carbon source [106–107], its pressure [108], catalyst composition [111], type of support [106] and synthesis temperature [106,109–110 112,115,117,121–122]. The authors of [107] synthesized SWCNTs using four different carbon precursors: CO, C 2 H 5 OH, CH 3 OH and C 2 H 2 on CoMo catalyst.…”

“…In most works, it was observed that the increase in the synthesis temperature led to increase in the nanotube diameters and broadening of the chirality distribution [106,109–110 112,115,117,121–122]. The (6,5) nanotube dominated in the samples synthesized at temperatures around 500–700 °C, whereas such selectivity disappeared at higher temperatures.…”

Heteroepitaxial Growth of Single-Walled Carbon Nanotubes from Boron Nitride

“…It is recognized that the structure of a SWCNT is largely determined by the size, morphology, and composition of the catalyst from which it nucleates and grows345. Great efforts have been made to control the structure of SWCNTs by catalyst engineering, and notable progress has been made on positioning6, alignment7, length8 and diameter9 control and the preferential production of specific conductivities1011121314 and chiralities15161718. However, the synthesis of SWCNTs with a predefined and precisely controlled structure still remains a big challenge.…”