Andrew Cardes 2/21/07

1. A presentation of … Batch Fabrication of Carbon Nanotube BearingsA Subramanian, L Dong, J Tharian, U Sennhauser, & B Nelson Andrew Cardes 2/21/07

2. Why MWCNT Bearings? Attributes Possible Applications • Ultra-fast • Fatigue-free • Low friction • Varying resistance with telescoping core motion • Tubular switches • Memories • Nano-servomotors • Integrated position sensing • Resonators/oscillators • Rotational NEMS

3. Nanostructure Array Design (a) Schematic diagram of the MWNT nanostructure. SEM images of the nanostructure at high and low magnification are provided in the top-left and bottom-right insets, respectively. The scale bar in the top-left inset represents 100 nm. (b) Nanoelectrode array design. A lower magnification image in the inset shows the entire array.

4. Batch Fabrication Results (a)–(g) Bearings created by partial electric breakdown. Nanotube thinning in the region between electrodes is clearly visible. Also, the possible degrees of freedom for the engineered nanotubes are shown in the inset of panel (b). (h) Fully broken nanotube with two segments. (i) Partly thinned nanotube, where the breakdown appears to be partial and asymmetric about the core. This may or may not be a bearing. (j) NT with a kink that is partly thinned. (k) Nanotube with improper contacts. (l) Two overlapping nanotubes. The scale bars represent 20 and 100 nm in panels (b)–(f) and (g)–(m), respectively. (m) Full summary of the array.

5. Electrical measurements during shell structuring (a) I –V plots before the onset of shell breakdown; increasing conductance with bias can be seen in the inset. (b) Variation of I0 with biasing cycles. I0 reduces during successive cycles at the same Vmax and increases during the transition from one voltage level to the next higher level. (c) I –V plots measured during biasing cycles 24 to 28 are shown. (d) A closer view of the negative, high bias region of cycles 24 to 28. (e) A closer view of the positive, high bias region of cycles 24 to 28. Current reduction and shell breakdown occurring primarily within these high bias segments are evident from panels (d) and (e). (f) The breakdown of entire NTs in a single step at the start of cycle 5 is shown in this plot. The arrow points to the 844 μA drop in current that occurs at −2.5 V.

6. Batch fabrication results cont. (a)–(h) Bearings created by partial electric breakdown. The NT on the top in panel (e) does not show any visible thinning within the resolution limits of the SEM and hence, it is not clear if this will operate as a bearing. Also, panel (h) shows the NT imaged with a stage tilt of 40◦ and it can be clearly seen that the polyhedral carbon nanoparticle is beneath the NT without affecting its topology. The top view of this NT is shown in the inset in this image. (i) Schematic diagram of the nanoarray design with arrows pointing to FIB machined breaks on the electrode layer. The imperfect nanotubes on these electrodes were thus removed from the electric breakdown circuit. (j) Variation of I0 with successive biasing cycles. (k) Individual I –V plots for cycles 31 to 34 illustrating the gradual reduction in currents. The inset shows a closer view of the high bias regions. The scale bars represent 100 and 50 nm in panels (a)–(g) and (h), respectively. The scale bar in panel (i) represents 10 μm.

7. NB from piecewise engineering of single NTs (a) Illustration of a MWNT assembled by floating electrode DEP. The electrode wiring scheme for parallel shell structuring is also shown. The inset shows an SEM image of the fabricated array at a tilt of 40◦ with the scale bar representing 50 μm. (b) SEM image of a nanobearing formed by this method shown at a stage tilt of 40◦, with the scale bar representing 100 nm. The inset illustrates the degrees of freedom of the NT shell structure.

8. High density NT bearings • (a) MWNT assembled onto five spatially separated metallic contacts and thinned in the regions between contacts. The electrode wiring scheme for current-driven engineering is also shown. The array design can be seen in the top-left inset. (b), (c) High magnification SEM images clearly showing outer shell removal in all segments of this NT. (d) Schematic illustration of high density MWNT rotary motors and independent bearings that can be created by further nanomachining of this structure. (e) Telescoping segments formed with a 220 nm pitch and separated by ∼6–10 nm gaps. The arrows point to the inter-segment gaps in this image taken with a stage tilt of 40◦. (f) Schematic illustration of the core–shell mechanisms formed in panel (e) with the inter-segment gaps exaggerated to reveal the shell structure. The scale bars represent 500 nm in panel (a) and 100 nm in panels (b), (c) and (e). It is important to note that we have assumed all shells with diameters below 10 nm extrude together as a single core. However, unlike in Zhang et al’s report [26, 27], the caps on both sides of our core are open leading

9. Thank you! Thank you!