Three-dimensional sculpturing of columnar morphology is most easily achieved by rotating the substrate about an axis normal to the substrate plane, during physical vapor deposition. The vapor flux density and the substrate rotation velocity have to be maintained at fixed values. Under suitable conditions, helicoidal columns with fixed pitch (i.e., structural period) grow. These are the solid-state analogs of chiral liquid crystals [343, 344], and therefore display optical rotation. Not only can all of the foregoing facts about STFs be traced back to a pioneering paper published by Young and Kowal in 1959 , but their morphological foundation is transparent in an 1898 paper of Bose .
Despite publication in a prestigious journal, the Young-Kowal achievement remained obscure for over three decades. Happily, the technique of rotating the substrate, the helicoidal morphology realized thereby, and the transmission optical activity of the fabricated thin films were rediscovered in the last decade [65-67]. Subsequent progress on their fabrication and optical characteristics has been very rapid.
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