Characterization of carbon nanotube nanoswitches with gigahertz resonance frequency and low pull-in voltages using electrostatic force microscopy

An electrostatic force microscope (EFM) was used to characterize single-walled carbon nanotube (SWNT)-based nanoswitches in this paper. A conductive atomic force microscopy (AFM) tip acted as a mechanical probe as well as a positioning electrode in the experiment. The resonance frequency of the SWNT beams was computed from the measured SWNTs' dimension and spring constant. The pull-in voltages and the corresponding gaps were extracted simultaneously from a set of force curves at different EFM probe bias voltages. The adhesive force between the AFM tip and the SWNT beam was measured through the analysis of retract force curves. The relationship between the pull-in voltage and the SWNT nanoswitch gap was in agreement with the electrostatic pull-in theory. Long-range forces such as meniscus force or electrostatic force from surface charges engaged the SWNT beam when the gap was below 6 nm in atmosphere. The SWNT beam with a resonance frequency of 1.1 GHz was actuated by a voltage of 2 V for a gap of 6.5 nm. The average adhesive force between an SWNT beam and a platinum/iridium (PtIr5)-coated tip was found to be about 50 nN. Considering the stiffness of the 1.1 GHz SWNT beam, the elastic restoring force at 6.5 nm exceeds 53 nN, which will overcome the adhesive force and release the 1.1 GHz SWNT beam. Finally, some possible approaches to further improve the behavior of SWNT nanoswitches are discussed.