- Sculptured thin film
Sculptured thin films (STFs) are
nanostructure d materials withunidirectional ly varying properties that can be designed and realized in a controllable manner using variants ofphysical vapor deposition . The ability to virtually instantaneously change the growth direction of their columnar morphology, through simple variations in the direction of the incidentvapor flux , leads to a wide spectrum of columnar forms. [ A. Lakhtakiaand R. Messier, "Sculptured Thin Films: Nanoengineered Morphology and Optics" (SPIE Press, Bellingham, WA, USA, 2005).]Forms
These forms can be:
# two-dimensional, ranging from the simple slanted columns and chevrons [K. Robbie, L. J. Friedrich, S. K. Dew, T. J. Smy, and M. J. Brett, "J. Vac. Sci. Technol. A" 13, 1032 (1995).] to the more complex C- and S-shaped morphologies [R. Messier, T. Gehrke, C. Frankel, V. C. Venugopal, W. Otano, and A.Lakhtakia, "J. Vac. Sci. Technol. A" 15, 2148 (1997).]
# three-dimensional, including simplehelix es andsuperhelix es
# combinations of two- and three-dimensional forms.Properties
The column diameter and the column separation normal to the thickness direction of any STF are nominally 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 frominsulators tosemiconductors tometals . Most recently,polymeric STFs have been deposited by combining physical andchemical vapor deposition processes; and deposition on micropatterned substrates has also been carried out.Uses
To date, the chief applications of STFs are in
optics aspolarization filters, Bragg filters, andspectral hole filter s [I. J. Hodgkinson, Q. H. Wu, K. E. Thorn, A. Lakhtakia, and M. W. McCall, "Opt. Commun." 184, 57 (2000).] [A. C. van Popta, M. M. Hawkeye, J. C. Sit, and M. J. Brett, "Opt. Lett." 29, 2545 (2004).] . At visible andinfrared wavelengths, a single-section STF is a unidirectionally nonhomogeneous continuum with direction-dependent properties. Several sections can be grown consecutively into a multisection STF, which can be conceived of as an optical circuit that can be integrated with electronic circuitry on a chip. Being porous, an STF can act as asensor of fluids and can be impregnated withliquid crystals for switching applications too. Applications as low-permittivity barrier layers in electronic chips as well assolar cells have also been suggested.Biomedical applications such astissue scaffold s, drug-delivery platforms,virus traps, and labs-on-a-chip are also in different stages of development.References
* cite book|author=Akhlesh Lakhtakia & Russell Messier|title=Sculptured Thin Films: Nanoengineered Morphology and Optics
publisher=SPIE Press, Bellingham, WA, USA|id=ISBN 0-8194-5606-3
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