A stretch-fit template

For films of organic and inorganic molecules. Many biological processes, such as bone formation, require hard inorganic materials to grow on a soft macromolecular substrate, although precisely how the two mesh has been something of a mystery. To examine that issue, physicists at Northwestern University floated a two-dimensional array of a fatty acid (a Langmuir monolayer) on a supersaturated solution of barium fluoride (BaF₂), which then crystallized at the interface. Separately, the two lattices are incommensurate. Using x-ray diffraction, the researchers observed that both lattices adapted in order to register with each other. The lattice of the BaF₂ thin film contracted by a few percent and the organic lattice expanded by tilting the molecules. The result was that the facial areas of the unit cells fell into a commensurate ratio of 1.5. BaF₂ is not a biologically important mineral, but Pulak Dutta says he and his fellow group members expect to look directly at biomineralization in an upcoming phase of their work. (J. Kmetko et al., Phys. Rev. Lett. 89 , 186102, 2002 http://dx.doi.org/10.1103/PhysRevLett.89.186102 .)