We have observed optical activity in thin solid films composed of nanometre-scale helical columns. These films rotate the plane of polarization of light in a manner analogous to cholesteric liquid crystals and other structurally chiral media. This rotation demonstrate the optical activity of the helical structured films and indicates that these films possess other significant optical properties such as circular dichroism (the effect currently exploited in cholesteric liquid-crystal displays). Our measurements demonstrate the value of a new thin-film deposition technique called glancing angle deposition (GLAD), which allows three-dimensional control of film structure on a scale of less than 10 nm.
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