Powering Small Devices

Doesn’t that sound nifty?

Carbon Nanotubes as Nanoscale Mass Conveyors

B. C. Regan et al. Nature. 2004, 428, 924.

•Carbon nanotubes: hollow cores, possible conduits for nanoscale amounts of material•Indium nanoparticles on carbon nanotubes, apply current to nanotube:controllable, reversible atomic scale mass transport along carbon nanotubes,using indium metal •By applying appropriate current to the carbon nanotube pictured, indium is moved from left (a) to right (b) and back again (c).

Points of Interest

•Assembly

•Range of Motion

•Painful Physics Numbers

Assembly

•Nanomotor is constructed and operated in TEM

•Indium is evapourated onto the surface of arc-grown carbon nanotubes (ex situ)

•Assembled using custom-built nanomanipulation stage: two MWNT are alligned in an overlapping parallel arrangement with an indium nanoparticle present near the overlap

Assembly

•Nanomotor is constructed and operated in TEM

•I ndium is evapourated onto the surf ace of arc-grown carbon nanotubes(ex situ)

•Assembled using custom-built nanomanipulation stage: two MWNT are alligned in an overlapping parallel arrangement with an indium nanoparticlepresent near the overlap

Applying the Principle of Transport

•External electronics: apply voltage across the MWNT lever arm junction •Electrical current through the lever arms and the junction•Electrically directed indium surface diffusion: indium atoms from the atomreservoir are transported to the junction region: a single nanocrystal (ram) is grown directly between the lever arms

Range of Motion

•Apply current: nanocrystal grows in length, pushes MWNT lever arms apart

•Reversible: control voltage (upper panel) is switched sequentially between +0.9 and -0.9 V, the ram grows and shrinks

•Cycles with a stroke of 45 nm and a speed of 1 nm/s. Increasing the drive voltage increases rate

Conclusions

•Pressure exerted by the ram is calculated to be 20 bar; with ram cross-sectional area of 36 nm2, force is 2.6 nN

•Nanocrystal ram compares favourably with competing motor technologies for power density:

•With extension velocities > 1900 nm/sec, power output capability of 5 fW. Available power density is initially 8 GW/m3

•The power density of an internal combustion engine is around 50 MW/m3 (calculated for a Toyota Camry 210 hp V6, where the 3L displacement has been taken as the working volume).