Asian Research Thesis Index

Abstract

A detailed study of the formation and fragmentation patterns of sp2 bonded carbon nano and micro structures has been carried out. Nanotubes and graphite are the extended and composite structures formed by the curved and flat sheets of graphene. Their structural stabilities and subtle differences have shown to be responsible for their characteristic fragmentation patterns under different forms of irradiations. Various techniques were employed for imparting energy to these structures. These include arc discharge, magnetron sputtering, energetic ion induced sputtering, and ablation with electronic and ionic pulses. Emission spectroscopy as well as the velocity and momentum analyzers was employed for the identification of the fragments. Arc discharge and magnetron sputtering of graphite delivered C1, C2, C3 and higher clusters which subsequently coalesced to form two types of thin films. Raman, Fourier transform infra red spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses relates the sp2 character of these two types of films to the relative ratios of C2 versus all these clusters used in their respective formation. C2 is shown to be the essential component of formation as well as fragmentation of the sp2-bonded structures. Detailed mass spectrometric investigations were performed on Cs+ irradiated SWCNTs, MWCNTs and graphite as a function of Cs+ energy (E(Cs+)) ranging from few tens of eV to 5000 eV. C2, C3 and C4 emission are shown to be the main fragmentation channels for irradiated and pristine single and MWCNTs while C1 shows a linearly increasing relative number density as a function of E(Cs+) thus indicating C1 to be the by-product of the dissociation of C2 and C3. Relative stability of C2 and C3 in energetic collisions with N2 demonstrates that C2 and C2+ dissociate at relatively small collision energies as compared with C3 which has superior survival probabilities even at much higher energies. Sputtering of C2, C3 and C1 under broad energy ranges and doses of Cs+ has been modeled to visualize the breaking of multiple bonds in direct and secondary recoils. The prevalence of C2 among the sputtered species from the irradiated SWCNTs, MWCNTs and graphite targets identify the dominant role that recoil sputtering plays, where a double bonded pair of carbon breaks its four single bonds with four C2 neighbors on sp2– bonded surface.

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