Individual multi-walled carbon nanotubes (MWCNTs) were exposed to the electron beam of 200 kV energy and high resolution transmission electron micrographs were recorded at several time intervals. Interestingly, the nucleation of diamond nanoparticles with in the highly disordered MWCNT matrix upon electron-irradiation is observed. This happens without any assistance of high pressures and temperatures. High pressure X-ray diffraction experiments were performed on core/shell structures which suggest that even the closed structures of carbon resist any inward pressure, thereby ruling out the possibility of a hypothetical internal pressure under the electron irradiation conditions. Our experiments suggest that the transformation of graphitic carbon into diamond in the size window of a few nanometers is possible due to the stability of the diamond and a selective dissolution effect of 200 kV electrons on graphite. A mechanism for the same is proposed.

    Abstract
    1 Introduction
    2 Experimental
        2.1 Electron irradiation and in situ high resolution transmission electron microscopy
        2.2 High pressure X-ray diffraction experiment on coreshell carbon nanostructures
    3 Results and discussion
        3.1 Nucleation of nano-crystalline diamond within co-existing highly defective graphitic matrix
        3.2 Proposed mechanism of diamond nucleation under the present conditions
    4 Conclusions
    Acknowledgements 
    References

• Surakanti Srinivas Reddy(UGC-DAE Consortium for Scientific Research, Kalpakkam Node, University of Madras)
• Balmukund Shukla(Condensed Matter Physics Division, Materials Science Group)
• V. Srihari(High Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre)
• G. M. Bhalerao(UGC-DAE Consortium for Scientific Research)
• N. V. Chandra Shekar(Condensed Matter Physics Division, Materials Science Group)