Understanding of STFs has grown dramatically since the concept was first proposed in the mid 1990s, with vigorous activity still continuing in STF research. In addition to unsolved problems, new developments continue to bring additional opportunities. For instance, the recent combination of STF and electron beam lithography techniques by Horn et al. (2004) to produce STFs with transverse architecture with consistent characteristics over large areas opens up a whole new line of possible applications. Fig. 15.5 shows examples of simple lines of chiral STF produced by this technique. More complex 2-D patterns such as checkerboards have also been produced. In their most recent work (Horn et al. 2004), they have been able to control the locations of individual nanowires on the substrate by creating a regular array of circular posts 60 nm in diameter which serve as nucleation sites.
Some areas of existing research are surely to see more activity. To date, most work on the optical properties of STFs has focused on frequency domain results. As society reaches forever faster rates of data transmission, pressure to pursue an understanding, in the time domain, of short pulse propagation in STFs will undoubtedly increase. Some work in this area has already begun (Geddes and Lakhtakia 2001; 2003). The ultrasonic use of STFs has been explored theoretically, but, due to the unavailability of STFs with sufficiently large scale features, experimental work is non-existent. With continual improvements and new techniques in STF fabrication, this is also likely to change.
Other areas for potential development (biological, electronic, and chemical applications for examples) are interdisciplinary in nature. With time, the right parties will come together to carry out more work in these exciting areas. Whatever the focus - basic understanding, new applications, or commercial implementation of existing ideas - new and unexpected developments in sculptured thin films are sure to continue at least into the near future.
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