Pyrolytic properties of di- n -butyltin(IV) diacetate as a precursor for sprayed SnO 2 thin films
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Eiichiro Ikedaa) and Yasuo Kuniya Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, Kasuga 1-13-27, Bunkyo-ku, Tokyo 112, Japan (Received 6 September 1993; accepted 28 October 1993)
The saturated vapor pressure and pyrolytic properties of di-n-butyltin(iv) diacetate have been investigated with and without oxygen in order to understand the orientational growth of SnO 2 thin films by spray pyrolysis. The dependence of the saturated vapor pressure on temperature was determined: log P(evap.)Torr = —2.827 X 103/T + 7.687. It has been found that the pyrolysis of this compound consisted of two stages: elimination of the «-butyl groups in a temperature range between about 280° and 310 °C, and of the acetoxy groups above 320 °C. Such decompositions were shifted toward lower temperatures under oxygen. It was also found that oxygen in air in addition to intramolecular oxygen contributed to the formation of SnO2 crystal phase. Moreover, it was suggested that pyrolized chemical species preserving the S n - 0 bond probably related the orientational growth of the (200) plane of sprayed SnO 2 thin films.
I. INTRODUCTION SnO 2 thin films have been of great interest for their high electrical conductivity, optical transparency, and chemical stability. In fact, the films have been applied to antiabrasive coating, optical selective coating, resistor, transparent heater, transparent electrode, and gas-sensing devices.1 Moreover, the SnO 2 thin films together with ITO recently have been recognized as one of the most significant electrode materials for the sophisticated electro/opto devices such as electroluminescence devices, liquid crystal devices, and solar cells.1 Although vacuum evaporation,2"4 sputtering,5"8 and chemical vapor deposition techniques9"16 have been generally used for the preparation of those films, ever-increasing demand in coating a large area leads to the further development of the chemical preparation techniques such as dip coating17"19 and spray pyrolysis. Among the techniques, spray pyrolysis is a simple and low cost processing one and is successful in forming films on a large scale. In fact, after the successful formation of CdS thin films for solar cells in 1966, the spray pyrolysis has been used for forming a variety of thin films such as metals, oxides, and chalcogenides.20 As in a conventional usage of antiabrasive SnO2 coating on glass materials such as glass containers, a
'Present address: Laser Laboratory, Akishima, Tokyo 196, Japan.
HOYA,
Musashino
3-1,
J. Mater. Res., Vol. 9, No. 3, Mar 1994
http://journals.cambridge.org
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has been mostly used as a typical source compound for forming SnO 2 thin films by spray pyrolysis.21"33 It, however, produces harmful by-products, Cl2 and HC1, in hydrolysis reaction with moisture water in air, which are quick to rust spray pyrolysis apparatus and hazardous to air conservation. Moreover, it easily decomposes to tin hydroxide or tin oxide in air before forming intact films without hazes. Organometallics,
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