Towards nanotube linear servomotors

Abstract

Nanoscale linear servomotors with integrated position sensing are investigated from experimental, theoretical, and design perspectives. Prismatic motion is realized using the interlayer motion of telescoping multiwalled carbon nanotubes (MWNTs). Position sensing can be achieved by monitoring field emission or by measuring resistance change between an MWNT and a gold substrate during sliding movement. Experimental results demonstrate resolution in the nanometer range. Actuation experiments demonstrate the feasibility of a linear nanoservomotor with integrated position sensing based on field emission. A local "kink"-like fluctuation of emission current is observed, which is caused by the change of the protruding length of the nanotube core, thus demonstrating the potential of using emission as a "linear encoder." The complete extension of the inner core is observed and the electrostatic force is calibrated to be tens of nano-Newtons for individual nanotubes-16.5 nN under a 30-V bias. These results demonstrate the possibility of fabricating linear servomotors at the nanometer scale with integrated position sensing. Note to Practitioners-Nanometer scale actuators and sensors that can provide motion and measurement with nanometer-order resolution will enable new industrial applications in which only a few atoms or molecules are measured, transported, or processed. Linear servomotors will play a significant role in such applications because they provide precision prismatic motion directly without requiring a conversion from rotary to linear motion. Nano linear servomotors are experimentally and theoretically investigated in this paper. The devices take advantage of the ultra-low interlayer friction of a multiwalled carbon nanotube (MWNT). Position sensing feedback is achieved by monitoring field emission, which depends on interelectrode distance, or by measuring resistance change between an MWNT and a gold substrate during sliding movement. Whereas this paper targets long-term nanotechnology contributions, some intermediate results are ready for applications in the near future. The interlayer sliding motion demonstrated would enable the building of devices, such as Gigahertz oscillators and attolitter nanosyringes, and the sensors used for position feedback could find applications independently in a macro or microscale machine for detecting proximity, touch, displacement, or orientation.