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Synthesis of Stannyl-Substituted Zn4O4 Cubanes as Single-Source Precursors for Amorphous Tin-Doped ZnO and Zn2SnO4 Nanocrystals and Their Potential for Thin Film Field Effect Transistor Applications

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posted on 10.05.2011 by Marianna Tsaroucha, Yilmaz Aksu, Elisabeth Irran, Matthias Driess
The first heterobimetallic alkyl(trimethylstannoxy)zinc clusters with the formula [Me3SnOZnR]4 (R = Me 1, Et 2) are facile accessible by the Brønsted acid−base reaction of trimethyltin hydroxide with the respective zinc dialkyls ZnR2 (R = Me, Et). The resulting products 1 and 2 can be isolated as white solids in high yields (>95%) and were characterized by multinuclear NMR, elemental analysis, FTIR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction analyses. They proved to serve as unprecedented low-temperature single source precursors (SSPs) for the fabrication of tin-containing ZnO as well as zinc stannate semiconducting materials and could be successfully utilized in field effect transistor (FET) applications. The thermal degradation of 1 and 2 under dry synthetic air, monitored by thermogravimetric analysis (TGA and TGA-IR), indicates high volatility of the trimethylstannyl group, which turned out to be the key parameter to control the tin concentration in the final semiconducting product. Low temperatures of degradation as well as low heating rates reduce the rate of tin loss and lead to mainly amorphous, nanosized tin-containing zinc oxide materials. Moreover, degradation at higher temperatures (>350 °C) and higher heating rates produces a homogeneous mixture of zinc stannate Zn2SnO4 and ZnO as major products. Remarkably, calcination of the latter mixtures at 600 °C favors crystallization and increases the surface area up to 298 m2 g−1. This unexpected increase in surface area is accompanied by a decrease in the tin concentration owing to the liberation of SnO2. All of these products were analyzed by multiple techniques including powder X-ray diffraction analysis (PXRD), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) spectroscopy. Finally, semiconducting thin films of tin-doped ZnO with 1.5 wt % tin were produced, without the use of any additive, through spin-coating of a mixture of precursor 1 and homometallic [MeZnOtBu]4 and subsequent degradation at 350 °C in dry air. These films can serve as suitable semiconducting layers in FET applications and show a high performance, that is, high electron mobility and homogeneity after annealing at 350 °C in air.

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