They look like blades of grass sticking up from the ground. But the vertical
structures in this image are actually soap-like molecules called alkylthiols
acting in a surprising way - instead of lining up like orderly soldiers
on a parade ground, as expected, they are scattered about like restless
children on a playground. The reason seems to be the "ground"
on which they're standing, a pool of liquid mercury (horizontal layers)
whose own lack of organization has thrown off the alkylthiols' usual orderly
tendencies. Physicists at Brookhaven National Laboratory and their collaborators
deduced this model from experiments using X-rays at the lab's powerful National
Synchrotron Light Source. They carefully glanced the X-rays off the mercury-alkylthiol
layers to reveal the disordered structure seen here.
The structure is in stark contrast to the strictly aligned alkylthiols previously seen on gold, suggesting that the strong interactions between the yellow end groups on the chains and the underlying disordered liquid mercury are enough to overcome the order-producing interactions between neighboring chains.
Being able to control the structure of organic thin films is important in areas as diverse as nanoscale electronics and corrosion resistance.
The scientists published their findings in the November 21 issue of Nature.
O.M. Magnussen*, B.M. Ocko*, M. Deutsch^, M. Regan~, P.S. Pershan~, D. Abernathy+, G. Grübel+, J-F. Legrand+|, Nature 384, 6606, pp. 250-252
* Brookhaven National Laboratory, ^ Bar-Ilan University, ~ Harvard University, + European Synchrotron Radiation Facility, | Laboratoire de Spectrometrie Physique