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...

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