Check the Substrate Before You Grow

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Science  05 Oct 2007:
Vol. 318, Issue 5847, pp. 13d
DOI: 10.1126/science.318.5847.13d
CREDIT: CHOONGIK KIM/NORTHWESTERN UNIVERSITY

Organic thin-film transistors (TFTs) can be fabricated by depositing an organic semiconductor layer on a polymeric insulator such as polystyrene (PS) or polymethyl-methacrylate that coats the gate electrode. Kim et al. (p. 76) show that these thin insulating layers have glass transition temperatures, Tg, well below that of the corresponding bulk material and in the range of temperatures normally used for deposition of the semiconductor layer. Pentacene layers grown at temperatures below the surface-depressed Tg exhibited much higher carrier mobilities and grain sizes than those layers grown at higher temperatures, where the material is rubbery and has greater polymer chain motion. Surface treatments that cross-link the chains of the insulating layer, such as oxygen-plasma treatment of PS films, increased the surface Tg and restored higher mobility.

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