Structural investigation of xenon-ion-beam-irradiated glassy carbon.

Abstract

Raman spectroscopy, cross-sectional transmission electron microscopy, and electron-energy-loss spectroscopy have been used to monitor the ion-beam-induced transformation in glassy carbon irradiated with 320-keV Xe ions to doses between 5\ifmmode\times\else\texttimes\fi{}${10}^{12}$ and 6\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ions/${\mathrm{cm}}^{2}$. It was found that (i) the ion beam amorphizes the glassy carbon structure; (ii) the amorphization is accompanied by a compaction of the glassy carbon from an initial density of 1.55 to 2.2\ifmmode\pm\else\textpm\fi{}0.2 g/${\mathrm{cm}}^{3}$; and (iii) approximately 15% of the graphitelike bonds in glassy carbon are converted to diamondlike bonds in the amorphization process. The transformation of glassy carbon to an amorphous state occurs in two distinct stages as a function of ion dose. For damage levels up to 0.2 displacements per atom (dpa) the effect of the ion beam is to decrease the average graphitic crystallite size. Above 0.2 dpa, disorder in bond length and bond angle away from ideal graphitic threefold coordination occurs leading to complete amorphization at high doses. The amorphization, compaction, and presence of \ensuremath{\approxeq}15% ${\mathit{sp}}^{3}$ bonds in the implanted layer of glassy carbon results in a surface layer which is significantly more resistant to abrasion than as-grown glassy carbon.