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Technology Stocks : Light Emitting Devices, organic and novel

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To: John Finley who wrote (176)	9/14/2000 7:26:10 PM
From: kinkblot	Read Replies (1) of 330

I wondered about that, too. They give this info in a footnote to the first Science paper: Note 10. A 0.8 ± 0.09-µm-thick layer of tellurium (99.99+%; Strem Chemicals) was vacuum evaporated at 106 torr and 7A (Ladd Industries 30000) onto a NaCl 25-mm salt substrate (polished NaCl window; Wilmad Glass). The layer thickness and deposition rate were monitored in situ with a crystal thickness monitor (Sycon STM100). A 10% solution of polystyrene (GoodYear PS standard, 110,000 g/mol) in toluene was spin cast at 1000 rpm onto the tellurium-coated substrate and allowed to dry for a few hours; the polymer layer thickness is 1.65 ± 0.09 µm. The Te has a high refractive index n of about 4.6 in the wavelength range 10-15 microns where they get the omnidirectional reflectivity. This gives a high ratio of ~2.9 to the index of the polystyrene at 1.6. Assuming that one material might be a typical plastic or glass with n in the range 1.4 to 1.7, it's clear from their Fig 3 that choosing a second material of much higher refractive index increases the extent of the omnidirectional reflection wavelength range. They say in their final paragraph that "the possibility of achieving omnidirectional reflectivity itself is not associated with any particular choice of materials and can be applied to many wavelengths of interest." I got the materials in the 9-layer sequence reversed; it's 5 Te layers, 4 PS. I just renewed my lapsed Science Online subscription. It's not a bad deal, $12 for AAAS members. I've already got my money's worth just re-reading the article by Fink et al. I find it easier to read the paper version, but I don't keep them around and that one is long since gone. They pile up quickly at one issue a week. I'd file them, but I'm trying to reduce the flood of paper in here, and they're always available online when I need them. WT

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