Modification of the mechanical properties of carbon nanotube arrays using electron irradiation induced oxidation

This paper describes a method of altering the compliance and adhesion of nominally vertically aligned multi-walled carbon nanotube (CNT) arrays (“turfs”) using oxidation caused by electron irradiation from typical imaging conditions in a scanning electron microscope. A combination of electron microscopy and infrared spectroscopy demonstrates that typical imaging conditions lead to the deposition and further oxidation of amorphous carbon on CNT turfs. The elastic modulus of the turfs, as measured by nanoindentation, decreases from approximately 100 to 50 MPa after irradiation and exposure to ambient laboratory conditions. The adhesion between the diamond indenter tip and turf is effectively eliminated once the amorphous carbon coated the turfs. In addition, the CNT turf exhibits decreased energy dissipation capabilities and a decreased viscoelastic response during contact loading. This suggests that further research on characterization of CNT turfs should consider the possibility that electron beam exposure during imaging may impact the subsequently measured properties, and that to lessen these effects, imaging times and accelerating voltages should be minimized.