Patterned Deposition from Compressed Carbon Dioxide
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PATTERNED DEPOSITION FROM COMPRESSED CARBON DIOXIDE C. K. Luscombe*, W. T. S. Huck*, A. B. Holmes*, T. Lu**, G. A. Leeke**, R. C. D. Santos**, B. Al-Duri**, J. P. K. Seville** *Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K. **Supercritical Fluid Technology Group, Centre for Formulation Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
ABSTRACT Compressed CO2 is employed as the solvent for the deposition of polymers onto patterned surfaces created by a lithographic technique. This deposition technique should have wide applicability in the deposition of organic and polymeric materials for optoelectronic devices. The advantage of controlled deposition confers a further benefit in the control of the patterned surface. In a specific example a perfluorinated polymer was dissolved in liquid carbon dioxide. The polymer solution was deposited by use of a nozzle onto a pre-patterned surface. The resulting polymer film showed a clear image of the original pattern as measured by optical microscopy.
INTRODUCTION Recently, there has been much interest in optoelectronic devices made from organic light emitting diodes [1, 2, 3] and organic transistors [4]. Traditionally, the organic materials are either deposited by spin coating if they are polymeric materials [5], or they are deposited by vacuum sublimation if they are small molecules [6, 7, 8]. Both methods are rather time consuming and in the case of fabricating organic light emitting diode (OLED) devices, the patterning of the multicolor pixels is also complicated. Inkjet printing (IJP) technology is a popular technology for printing computer data onto paper. The application of IJP technology has emerged as an attractive patterning technique due to its low cost, large area processing and multicolor addressing capabilities and it has been used for the patterning of conjugated polymers in light-emitting diodes [9, 10] and also for transistor circuits [4]. Supercritical CO2, readily accessible with a Tc of 31°C and Pc of 73 atm (figure 1), has excellent potential for achieving the goal of an environmentally friendly, economical reaction and processing medium [11]. It is abundant, inexpensive, non-flammable, non-toxic and environmentally benign. Non-polar organic compounds are often highly soluble in this medium. Although its ability to dissolve polar, ionic, or polymeric compounds is exceedingly limited, small amounts of a polar entrainer or an appropriate surfactant can dramatically change the microenvironment to greatly increase the solubility of such substances. Perfluorinated compounds are particularly effective for this purpose, expanding greatly the applicability of CO2. Considerable progress has been made in recent years in using compressed CO2 for deposition of fluorinated coatings on surfaces [12, 13]. One particularly attractive application is
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SCF liquid
PC 73 atm
C
solid
gas T
TC 31°C Temperature
Figure 1. A schematic pressur
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