Effects of MeV Ions on Thermal Stability of Single Walled Carbon Nanotubes
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Effects of MeV Ions on Thermal Stability of Single Walled Carbon Nanotubes A. R. Adhikari1, M. B. Huang1, C. Y. Ryu2, P. M. Ajayan3 and H. Bakhru1 1 College of Nanoscale Science and Engineering, State University of New York, Albany, NY12222 2 Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute Troy, NY12180 3 Department of Material Science and Engineering, Rensselaer Polytechnic Institute Troy, NY12180 Abstract The properties of carbon nanotubes (CNTs) are closely dependent on their structures, and therefore may be tailored by controllably introducing defects in the nanotube systems. In this work, we have investigated the effects of energetic ions (H+ and He+) on the thermal stability of single wall nanotubes (SWNTs) against oxidation in air. SWNTs were irradiated with MeV ions to various doses in the range 1013-1016 cm-2. Thermogravimetric analysis (TGA) was used to determine the loss of CNT masses as a result of oxidation processes. As opposed to the case of pristine SWNTs for which the temperature (Tmax) corresponding to maximum oxidation rate was found to be ~ 495 ºC, ion beam processing significantly enhanced the thermal stability of nanotubes, e.g., Tmax increased by about 30 ºC after H+ implantation (dosage: 1015 cm-2) and 17 ºC after He+ implantation (dosage: 1013 cm-2). The activation energies for thermal oxidation under various conditions were also extracted from TGA data, with values ranging from 1.13 eV (for pristine SWNTs) to 1.37 eV, depending on ion doses and species. Raman spectroscopy was used to determine the characteristics of the G band (C-C stretching mode) and D band (disorder induced mode) in CNTs. The work suggests that the SWNTs modifies to more stable structure (may be cross-linked SWNTs) at small doses. Once the number of defects exceeds some critical value (depending on the type and dosage of bombarding ion) the bonding energy in CNTs weakens, leading to the reduced thermal stability of CNTs against oxidation. Introduction Since their discovery [1] in 1993, single-walled carbon nanotubes (SWNTs) have attracted a great attention in the scientific community even in a short span of time. May be due to unusual structure and its relation with various properties, they have become a potential candidate for a wide range of applications [2-5]. In many applications, such as high-strength composites [6] in nuclear reactors or space shuttles, CNTs are expected to expose different types of ion beams followed by interaction between them, where the stability is of primary concern since CNTs are metastable. Instead, this could modify CNTs as the interaction can produce different types of defects, like substitutional, interstitial, single or multiple vacancies, etc. [7] that plays a crucial role in their electronic properties of bulk material. Therefore, it is essential to understand the microstructural change in ion irradiated CNTs. These days ion manipulation has become an essential process in the fabrication of Si or other compound semiconductor devices. This p
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