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Polarized-light optical actuation: a new way to a molecular assembler

P. Krecmer*, a, A. M. Moulinb, M. E. Wellandb, and S. R. Elliotta

aDepartment of Chemistry, University of Cambridge, Lensfield Rd., CB2 1EW, UK
bDepartment of Engineering, University of Cambridge, Trumpington Str., CB2 1PZ, UK

This is an abstract for a presentation given at the
Sixth Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is available on the web.

 

We present details of a recently-discovered novel phenomenon of reversible and controllable contraction and dilatation in a solid (a chalcogenide glass) driven by polarized light. This effect could lead towards an optimum means of actuation of a molecular assembler.

We have found that polarized light causes a bilayer cantilever (consisting of an amorphous As50Se50 film, 250nm thick, deposited on a silicon nitride, V-shaped atomic-force microscope (AFM) cantilever 200 µm long and 0.6 µm thick) to bend reversibly either up or down by up to about +/-1mm, depending on whether the E-vector of the incident polarized light and the long axis of the cantilever are parallel or orthogonal, respectively [Fig. 1.].
 

Fig. 1. The relative orientation of the light electric vector Ex,y with respect to the cantilever. Orientation of the electric vector E of the inducing light parallel to the main axis of the cantilever causes contraction (> c < ) of the chalcogenide film (A); orientation of E orthogonal to the main axis of the cantilever results in expansion (< e > ) of the chalcogenide film (B). The chalcogenide film is evaporated on the top of the cantilever.
 

This is the first observation that an anisotropic mechanical response can result from a polarized light stimulus. Thus, this smart material (a chalcogenide glass) can be incorporated into an optical actuator, and is seen thereby as the basis of the future construction of a general-purpose molecular assembler.

Five distinct features make the phenomenon of polarized-light induced optical actuation much more advantageous than other kinds of actuation for use in an assembler. The first is that the opto-mechanical effect is reversible and non-hysteretic [1], unlike the piezoelectric effect. The second is that since light is used as the stimulus, and not electricity as in piezoelectric devices, noise (e.g. due to electrical pick-up) is greatly reduced; moreover, since the stimulus -polarized light- can be carried over a long distance, the design of an assembler would be greatly simplified (with respect to wiring, vibrations, safety). Thirdly, it is cheap and readily fabricable using current technology. Fourthly, the effect is wavelength-selective (the maximum response is for light having an energy equal to the chalcogenide bandgap). Finally, and most importantly, the optical actuators lend themselves to miniaturization unmatched in resolution by present sources of actuation. Large arrays of independent cantilevers can be envisaged for applications requiring massively parallel processing. Present knowledge of the phenomenon even suggests speculation of polarized-light driven motions on atomic range length scale, thus providing a way to drive molecular machines consisting of a few hundred atoms. It is believed, that proper materials and mechanical design and control of the polarization state of the inducing light can enhance this cantilever deflection with sub-nanometer resolution.

 

Results regarding our current state of understanding of the phenomenon on microscopic and macroscopic levels, future studies and possible applications will be given.

 References

  1. P. Krecmer, A.M. Moulin, R.J. Stephenson, T. Rayment, M.E. Welland and S.R. Elliott, Science 277, 1799-1802 (1997). Reversible nanocontraction and dilatation in a solid induced by polarized light

*Corresponding Address:

P. Krecmer
Department of Chemistry, University of Cambridge, Lensfield Rd., CB2 1EW, UK.



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