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Posted: April 15, 2009
EU-funded researchers align molecules in nanofilms
(Nanowerk News) EU-funded researchers in Denmark, Germany, Israel and the US have found a way to align molecules on the surface of water into nanofilms, making the study of their structure much easier. Their findings, published in the Journal of Chemical Physics, pave the way for advances in the study of cell-membrane proteins and the development of advanced functional materials ("Laser-induced aligned self-assembly on water surfaces").
Nanofilms are created by dissolving the target material in some volatile substance, then splashing it onto the surface of water. The solvent evaporates and the material floats on the water's surface, coming together in a thin crystalline layer.
The problem with this technique is that although the molecules do come together and crystallise, they are all jumbled up, pointing in different directions. Because the orientation of molecules actually dictates the electrical, magnetic, and optical properties of the final film, this '2-D powder' is problematic in the laboratory and impractical for technological applications.
In the new study, the researchers bombarded the film with nanosecond-long laser beam pulses. The laser pulses created an electric field that rotated the molecules slowly. Because the field was polarised, the molecules caught up in it were influenced to line up in the same direction. Although the success rate was 30%, the resulting films were exponentially more useful than any produced to date.
Dr Iftach Nevo, a Marie Curie fellow at the University of Aarhus in Denmark, said, 'To the best of our knowledge, this is the first time aligned films less than a nanometre thick have been produced.'
The team also found that the nature of the volatile substance used to dissolve the original material is extremely important, as both the rate of evaporation and temperature have an effect on the organisation of the original nanofilm.
The technique is a general one, and can be applied to a wide range of molecules. It has not been perfected, but the progress made by the team represents a significant step forward in achieving stable, self-aligned nanofilms. Such films will be of great use in studying the structure of biological tissues and membranes using advanced imaging techniques.
The new knowledge opens the door for nanofilms to be used in the development of molecular electronics and ultra-thin materials, which rely on aligned molecules. They might also have important applications in emerging solar cell technologies. According to co-author Tamar Seideman of Northwestern University in the US, the ability to align the molecules in these devices will be crucial for their effectiveness.