Effects of light-ion low-fluence implantation on the pressure response of double-walled carbon nanotubes

Abstract

Low-fluence light-ion $(^{11}\mathrm{B}^{+})$ medium-energy (150 keV/ion) implantation preprocessing of double-walled carbon nanotubes (DWCNTs) has been effected to ``decorate'' them with defects. These are intended to serve as nucleation sites for potential $s{p}^{3}$ interlinking between tube walls in close proximity, following on strong deformation of the tube cross sections under cold compression to 20--25 GPa in diamond anvil cells. The pressure response of such implanted DWCNTs has been monitored in situ using Raman spectroscopy, and compared with those of unimplanted reference DWCNTs. Pressure dependences of the ${G}^{+}$ mode frequency and D to ${G}^{+}$ band intensity ratio, and radial breathing modes, have been monitored. These Raman signatures show that some degree of mechanical softening occurs in the implanted tube bundles, without major disruption to tube integrity in both samples. Consequently, the collapse pressure to racetrack or peanut shaped cross-sectional profiles is lowered substantially, from ${P}_{\mathrm{c}}\ensuremath{\sim}18\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ in the reference tube bundles to ${P}_{\mathrm{c}}\ensuremath{\sim}11\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ in the implanted case. Defect structures also proliferate more readily in the implanted sample under pressure. Therefore, the light-ion low-fluence implantation lowers the threshold pressure for deformation of tube cross sections to high-curvature profiles decorated with defects. Considerations of whether irreversible $s{p}^{3}$ interlinking at low volume fractions is discerned in the Raman data from implanted tube bundles under compression, and the stability of such bonding is discussed.