Abstract:
Glassy carbon is a disordered form of carbon with very high temperature resistance, high
hardness and strength and chemical stability even in extreme environments. Glassy carbon is also
unaffected by nearly all acids and cannot be graphitized even at very high temperature. Because
of these characteristics, there is a possibility that glassy carbon can replace copper, iron, titanium
alloys and other materials employed in making canisters used in nuclear waste storage.
The modification of glassy carbon due to strontium ions implantation and heat treatment is
reported. Glassy carbon (GC) samples were implanted with 200 keV strontium ions to a fluence
of 2×1016 ions/cm2 at room temperature.
Sequential isochronal annealing was carried out on the implanted samples at temperatures
ranging from 200 oC - 900 oC for one hour. The influence of ion implantation and annealing on
surface topography was examined by the scanning electron microscopy (SEM), while Raman
spectroscopy was used to monitor the corresponding structural changes induced in the glassy
carbon. The depth profiles of the implanted strontium before and after annealing were
determined using Rutherford Backscattering Spectroscopy (RBS). Compared to SRIM predictions the implanted strontium profiles was broader. After annealing at
300 oC, bulk and surface diffusion of the strontium atoms took place. Annealing at 400 oC- 700
oC not only resulted in further diffusion of strontium towards the surface, the diffusion was
accompanied with segregation of strontium on the surface of the glassy carbon substrate.
Evaporation of the strontium atoms was noticed when the sample was annealed at 800 oC and
900 oC respectively. These annealing temperatures are higher than the melting point of strontium
(~769 oC).
The Raman spectrum of the virgin glassy carbon shows the disorder (D) and graphitic (G) peaks
which characterize disordered carbon materials. Merging of these two peaks was observed when
the virgin sample was implanted with strontium ions. Merging of these peaks is due to damage
caused by the implantation of strontium. The Raman spectrum recorded after heat treatment
showed that only some of the damage due to implantation was annealed out. Annealing at
20000C for 5 hours resulted in a Raman spectrum very similar to that of virgin glassy carbon
indicating that the damage due to the ion implantation was annealed out.
SEM showed large differences in the surface topography of the polished glassy carbon surfaces
and those of as-implanted samples. Annealing did not significantly change the surface
microstructure of the implanted samples.
