Ion beam modification of carbon nanotube yarn in air and vacuum

We studied the effects ion beam irradiation on carbon nanotube (CNT) yarns. CNT yarn was fabricated by drawing and spinning CNT sheets from a vertically aligned CNT forest. The yarn was irradiated by 2.5 MeV protons in either vacuum or air. Irradiation in air was achieved by directing the proton beam through a 0.025 mm thick Ti window. Irradiation in vacuum occurred at a pressure of < 10^-6 torr at room temperature and at an elevated temperature of 600 °C. Tensile testing revealed that CNT yarn irradiated in air increased in tensile strength with increasing proton fluence. For yarn irradiated in vacuum, however, the strength decreased with increasing fluence. We believe that irradiation-induced excitation and trapping/bonding of gas atoms between tubes may play a role for the mechanical property changes.