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Large molecules made by mechanosynthesis can be stiff

Structures like the rod segment shown to the left are stiff, in the sense that displacement of any part in any direction will be opposed by elastic restoring forces. Although each of the carbon-carbon bonds would, in isolation, permit rotation (as seen in floppy carbon-backbone molecules), the presence of additional bonds prevents rotation from occurring. This structure shown is especially stiff — it is closely related to diamond, which at ordinary pressures is the stiffest known solid.

Solution-phase organic synthesis has been used to make diamond-like structures about half as large as the rod segment shown here. Vapor-phase processes can make bulk diamond from smaller reactive molecules, but without precise control of shape and structural irregularities. Mechanical control will enable synthetic steps to be performed at chosen locations, avoiding side-reactions. This, in turn, will enable the construction of stiff structures of large size, like those made in vapor-phase processes, but made with the atomic precision characteristic of the products of organic synthesis.