Sculptured thin films (STFs) are nanostructured materials with unidirectionally varying properties that can be designed and realized in a controllable manner using century-old techniques of physical vapor deposition (PVD). The ability to virtually instantaneously change the growth direction of their columnar morphology through simple variations in the direction of the incident vapor flux leads to a wide spectrum of columnar forms. These forms can be (i) 2D, ranging from the simple slanted columns and chevrons to the more complex C- and S-shaped morphologies; and (ii) 3D, including simple helixes and superhelixes. A few examples of STFs are presented in Figs. 2.1 and 2.2.
For most optical applications envisioned, the column diameter and the column separation normal to the thickness direction of any STF should be constant. The column diameter can range from about 10 to 300 nm, while the density may lie between its theoretical maximum value to less than 20% thereof. The crystallinity must be at a scale smaller than the column diameter. The chemical composition is essentially unlimited, ranging from insulators to semiconductors to metals.
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