Compaction, distribution, and chemical bonding of tungsten-implanted glassy carbon

Abstract

The composition, distribution, and chemical bonding of tungsten-implanted glassy carbon have been studied for ion doses between 3.5×1014 and 1.5×1017 ions/cm2. The implantations were performed using a metal-vapor vacuum arc ion source which for an extraction potential of 20 kV yields a mean implant energy of 60 keV. The implanted layer was examined by Rutherford backscattering spectrometry and Auger profiling spectroscopy. In addition, volume effects were assessed by measuring the step height between implanted and unimplanted regions. It has been established that the implanted tungsten is bonded in a carbidic configuration. This is in agreement with thermodynamic data which favors carbide formation rather than separate phases of metallic tungsten and graphitic carbon. For the highest dose studied, 1.5×1017 ions/cm2, the tungsten distribution was found to be nearly constant near the surface followed by a decrease at larger depths. For ion doses up to 3.6×1016 ions/cm2, the maximum tungsten distribution was found to occur at a depth 300±100 Å and the implanted and retained doses were found to be equal. For tungsten ion doses between 7.35×1014 and 1×1016 ions/cm2, the implanted region was found to be compacted by 300±100 Å. The latter is attributed to an irradiation-induced densification of glassy carbon from 1.5 to 2.1 g/cm3. This compaction effect is also found to occur upon C+ (30 keV) implantation for ion doses between 3×1016 and 1.3×1017 ions/cm2. In this case the implanted layer was compacted by 400±100 Å. For higher tungsten doses, a steep increase in compaction of the tungsten implanted layer was observed. This is attributed to chemical and sputtering effects.