Measuring the stress in field-emitting carbon nanotubes

Carbon nanotubes (CNTs) are frequently torn away by the electric field during field emission, which usually results in device failure due to short circuit or discharge. An AFM cantilever is employed to measure the tensile force experienced by individual field-emitting CNTs, from which the Maxwell stress and the local E-field at the CNT tip can be derived. We found that CNTs always initiate field emission at the same tensile stress. The turn-on field strength, however, increased from 2 to 60 V mu m(-1) as the anode - cathode distances decreased from 0.3 mm to several microns. Depositing a thin film of titanium on the CNT tip was shown to effectively decrease the turn-on voltage and stress, a result crucial to the fabrication of CNT-based field emission flat panel displays (FE-FPDs).