Growth Direction Dependence Of Mechanical Propertiesof Carbon Nanoflber Probes Fabricated By Ion Irradiation Method

摘要

Linear-shaped single carbon nanofibers (CNFs) were batch-grown onto commercially available Si cantilevers for atomic force microscopy by the Ar~+ ion irradiation method (9 cantilevers/batch). As confirmed by field emission scanning electron microscopy, they were almost uniform in size with standard deviations of less than 20%, and the growth direction of the CNFs was readily controllable by changing the direction of incident Ar~+ ions. The results of force-curve measurements of CNFs thus grown in the direction almost perpendicular to the lever plane of the cantilever chips revealed that long CNF probes (～1 μm in length) were mechanically as soft as the carbon nanotube probes, whereas short CNF probes (～400 nm in length) were as hard as Si probes. In addition, for short CNF probes (～400nm in length), the hardness was more prominent for the CNFs grown in the direction of 10-20° from the normal to the lever plane. For the obliquely grown short CNFs with the growth angle larger than 25° from the normal to the lever plane, buckling was observed. The change in CNF shape was not recognized before and after the force-curve measurements even for the CNFs that buckled during the force-curve measurements. Thus, it was concluded that the mechanical property was controllable from soft to hard by changing the CNF length and was also strongly affected by the growth direction of the CNFs.