The architecture of many living creatures combines soft organic tissue
with hard inorganic crystal. How do the hard parts develop while up
against the soft parts?
To examine this issue, physicists at Northwestern University have grown
an inorganic lattice (barium fluoride, BaF2) directly beneath a two-dimensional
crystalline array of organic molecules (a fatty acid).
Using the diffraction of synchrotron radiation from these planar arrays,
the researchers observe the structure of the two lattices and also affirm
that the two become commensurate (that is, they register with each other),
the first time this has been done in an experiment.
Even though the lattice spacings of the BaF2 and the organic
monolayer are different, each contributes toward a compromise, the barium
fluoride structure by contracting just a bit, and the molecules by expanding
their spacing at one end: picture the molecules as a stack of pencils
standing on end and then being tilted a bit, modifying the spacing of
the pencil tips (see figure).
BaF2 is not a biologically important mineral, but the Northwestern
scientists (contact Pulak Dutta, 847-491-5465, email@example.com)
expect to look directly at biomineralization in an upcoming phase of
Furthermore, since growing two or more incommensurate materials next
to each other (an important operation in the microelectronics industry)
is difficult because of the unequal atomic spacings, the new research
might in the long run be able to lessen or end the currently stringent
need for high vacuum to make epitaxially grown materials. (Kmetko
et al., Physical Review Letters, 28 Oct)