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August 6, 2001
Volume 79, Number 32
CENEAR 79 32 p. 11
ISSN 0009-2347
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Organic Semiconductors Form Large Crystals


The idea of electronics based on organic materials tantalizes researchers with the possibility of designing inexpensive high-tech devices that promise to be flexible, easily molded, and act in other ways just like plastics. But for the most part, plastic electronics have remained an attractive idea with little to show in the way of commercial applications.

SNOWFLAKES Thin-film studies at IBM led researchers to new methods for growing pentacene crystals with roughly 0.1-mm dimensions.
One of the key obstacles has been producing high-quality organic crystals with the requisite electronic properties. In particular, manufacturers would like to be able to grow thin-film organic crystals using the chemical vapor deposition techniques that are so widespread in microelectronics fabrication.

Now, thanks to a crystal-growth study, manufacturers may get their wish. Researchers at IBM's T. J. Watson Research Center have demonstrated that the semiconductor pentacene, a leading candidate for organic electronics applications, can be prepared as thin films with single-crystal grains growing as large as 0.1 mm on a side--nearly 100 times larger than reported previously [Nature, 412, 517 (2001)].

Using an electron microscopy technique, the IBM group, which includes Frank J. Meyer zu Heringdorf, Mark C. Reuter, and Rudolf M. Tromp, shot high-resolution videos that caught pentacene molecules in the act of trying to align themselves into crystals. The team discovered that the molecules bond too tightly to clean silicon substrates to rearrange themselves into orderly formations. But on surfaces modified with a layer of cyclohexene, pentacene molecules have just enough freedom to nestle into one another and form large crystals.

Robert J. Hamers, a professor of chemistry at the University of Wisconsin, Madison, describes the advance as "a technological breakthrough," explaining that, because today's microelectronic devices are just micrometers in size, it ought to be possible to use vapor deposition methods to fabricate high-quality integrated circuits in which each circuit element is made of a single crystal of pentacene.

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