Among the available wide-bandgap semiconductors, silicon carbides (SiC) are suitable for high-temperature applications. However, one-dimensional nanomaterials exhibit new properties different from those of their corresponding bulk materials. This can be attributed to their nanometer size and intriguing properties. Consequently, single-phase SiC nanotubes and C-SiC coaxial nanotubes have been successfully synthesized. As such, different techniques such as ion irradiation have been employed to characterize various microstructural developments of these nanomaterials. Unfortunately, little is known about the microstructural development of C-SiC coaxial nanotubes under ion irradiation.
In most cases, novel-structured and hybrid carbon nanomaterials are expected to have superior physical properties as compared to the typical carbon nanomaterials. This, however, requires the synthesis of carbon nanomaterials with new structures. To this end, Dr. Tomitsugu Taguchi, Dr. Shunya Yamamoto, and Dr. Hironori Ohba at the National Institutes for Quantum and Radiological Science and Technology in Japan reported the synthesis and formation mechanism of novel hybrid carbon nanomaterials inside silicon carbide nanotubes by ion irradiation method. The work is currently published in the research journal, Acta Materialia.
Briefly, the synthesized novel hybrid carbon nanomaterial consisted of one-dimensionally stacked graphene nanodisks with diameters less than 50 nm and cylindrical multiwalled carbon nanotubes inside amorphous SiC nanotubes. Transmission electron microscopy was used to characterize the synthesized hybrid carbon nanomaterials while in situ transmission electron microscopy observations were used to investigate their microstructure developments under ion irradiation at room temperature.
The authors observed that the increase of ion fluence resulted in the increase in the outer diameter of the C-SiC coaxial nanotubes and a corresponding decrease in their inner diameter, which further led to the disappearance of the interior hole. Ion irradiation was the cause of the emergence of the new continuous graphitic layers perpendicular to the nanotube length direction in the microstructure as well as the amorphous nature of the SiC crystals in the C-SiC coaxial nanotube. The critical amorphization dose for SiC crystals was significantly higher than that of the bulk SiC. This was attributed to the large specific surface area of the C-SiC nanotubes which initiated the induced point defects released from the grain boundaries by the irradiation process. Despite the entire amorphization of SiC crystals, the carbon layers remained their crystalline nature even after ion irradiation.
Based on the results, the carbon layers exhibited better resistance against amorphization after ion irradiation, compared with the SiC layer in the C-SiC coaxial nanotube. This was due to the compression stress accrued on the carbon layer, attributed to the SiC layer undergoing configuration change during irradiation, and the restraining of sputtering of the carbon atoms on the outer surface of the carbon layer. The high compression stress which was estimated to be approximately 2GPa was confirmed by the decrease in the lattice plane spacing of the carbon layer after the completion of the SiC crystals amorphization.
For the first time, Tomitsugu Taguchi and his colleagues successfully synthesized a novel hybrid carbon nanomaterial inside silicon carbide by ion irradiation of the C-SiC coaxial nanotube. Through ion irradiation of the C-SiC coaxial nanotube, novel microstructural change that are considered promising processes for the synthesis of novel carbon nanomaterials were developed. The study will, therefore, advance the synthesis of new hybrid carbon nanomaterials and widen their applications in various fields.
Taguchi, T., Yamamoto, S., & Ohba, H. (2019). Synthesis of novel hybrid carbon nanomaterials inside silicon carbide nanotubes by ion irradiation. Acta Materialia, 173, 153-162.Go To Acta Materialia