New Approach to Light-based Nanomotors

It has been shown in multiple experiments that light can influence the motion of small-scale structures. One such example was the "optical tweezers" that was brought up in class at the beginning of the semester. In addition to holding objects in place, the technology has advanced to a point where the laser can transfer angular-momentum to objects that do not already have a motor mechanism. Thus, otherwise stationary objects can be made to rotate under the influence of a laser beam. Until recently, the approach to instigating rotation was altering the angular momentum of photons; a photon's angular momentum would be transfered to the object as it is absorbed.

A new development is that light without angular momentum is being used to rotate nanomotors. Instead of relying on the absorbed photon as a source of angular momentum, a gammadion-shaped gold propeller re-emits photons that have angular momentum. By the law of conservation of angular momentum, the motor after re-emitting a photon must have angular momentum equal and opposite of that of the new photon. This means that structures are now being developed that cater to the type of light available to the researchers, be it photons with angular momentum or without. This approach also allows the amount of total angular momentum to increase and permits the direction of rotation to be altered by the wavelength of the light.

I find this article interesting because it offers a different way of producing nano-scale movement: altering the properties of the nano-structure instead of the light. By changing the structure so it allows light without angular momentum to induce rotation, it permits the properties of the light to be less specific in the respect of angular momentum. Rather than tuning the angular momentum to affect rotation, it allows the light wavelength to control this property, allowing for different and possibly cheaper equipment to be used. Although not in the scope of the article, one possible implication is that the shape and properties of the propeller can be altered by chemical factors. Thus, if the environment of a nanobot implementing this technology were to change, the nanobot would be able to react in a different way even if the light is not altered. This can be used in a way that mimics chemotaxis.

Article:http://www.nature.com/nnano/journal/v5/n8/pdf/nnano.2010.156.pdf

-Austin Butts