Experimental Measurement of Single-Wall Carbon Nanotube Torsional Properties

We report on the characterization of nanometer-scale torsional devices based on individual single-walled carbon nanotubes as the spring elements. The axial shear moduli of the nanotubes are obtained through modeling of device reaction to various amounts of applied electrostatic force and are compared to theoretical values.

Figure 1

(a) Diameter distribution of SWNT material measured by AFM and (b) a suspended SWNT device. Scale bar corresponds to 1 mm.

Figure 2

(a) Sequential SEM images of device 6 at 0, 2, and 4 V applied voltage, respectively. Below each image is the FE calculated electric field potential (in the direction of the SWNT axis) of the device at each bias. (b) Labeled model of the device and overlaid color map of the FE calculated electric potential. Scale bars in (a) correspond to 500 nm and full color scale is 4 V.

Figure 3

(a) Details of the device model, showing the SWNT axis and the six surfaces of interest on the paddle. (b) Diagram of the electrostatic forces (dashed lines) acting on the paddle surfaces and the components of those forces that act as a torque. Moment arm of torques indicated with light gray lines drawn from SWNT axis. Figure drawn out of scale and at small deflection angle for clarity.

Figure 4

(a) Deflection angle vs calculated torque for device 6 where 90° is the maximum deflection attainable by our setup. Inset: measured shear modulus vs calculated torque for the same device. (b) Average shear modulus for each device, normalized to the average theoretical value (0.455 TPa). The shaded region corresponds to the range of theoretical values over all chiralities in Ref. 14.