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Nanoscale vision


Single metal nanoparticles detected with the 'spatial modulation' technique. Measurement of the spectrum of a single nanoparticle (top right) permits reconstruction of its geometry (top left).


What if you could “see” objects smaller than 10 nanometers in diameter? Two French research teams1 were the first to make this possible by developing a new optical imaging technique called “spatial modulation spectroscopy.”2 The technique, which could revolutionize the field of nanoscale imaging, allows the geometric characteristics of tiny objects to be accurately determined. The method is based on measuring the optical absorption spectrum of a nanoparticle whose position is varied at a frequency of about 1 kilohertz in the focal spot of a light beam. The resulting spectrum is analyzed to build up the shape, size and orientation of the particle. “Our technique makes it possible to 'see' an object much smaller than the visible wavelength,3 which, to our knowledge is not possible using any other optical system,” says Fabrice Vallée, based at the University of Bordeaux-I. Moreover, the method allows nanoparticles in different environments, such a polymers, liquids, and glass, to be observed in situ–something that until now was only possible using electron microscopy.


Isabelle Dumé





Notes :

1. Centre de physique moléculaire optique et hertzienne in Bordeaux (CNRS / Université Bordeaux-I joint lab). Laboratoire de spectrométrie ionique et moléculaire in Lyon (CNRS / Université Lyon-I joint lab).
2. O. L. Muskens et al., “Single metal nanoparticle absorption spectroscopy and optical characterization,” Appl. Phys. Lett. 88: 063109. 2006.
3. The wavelength of visible light (from 400 to 800 nm) used to image an object. It is around 500 nm in these experiments.


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