Novel vapor phase method for making ultra thin conformal films of polytetrafluoroethylene (PTFE)
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Novel vapor phase method for making ultra thin conformal films of polytetrafluoroethylene (PTFE) Sushant Gupta1, Arul Arjunan Chakkaravarthi1, Rajiv Singh1, Jeff Opalko2, and Deepika Singh2 1 Materials Science & Engineering, University of Florida, 100 Rhines Hall, Gainesville, FL, 32611 2 Sinmat Inc., 2153 Hawthorne Road, Suite 129 (Box 2), Gainesville, FL, 32641 ABSTRACT Ultra-thin conformal polytetrafluoroethylene (PTFE) films were prepared by a novel physical vapor technique i.e., pulsed electron deposition (PED) technique. Prepared PTFE or Teflon thin films show high degree of conformity on patterned substrates. Under optimized deposition conditions the films exhibit superhydrophobicity. The PED processed films were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM) micrographs and the surface morphology and the conformal nature of the films were studied. The chemical nature and hydrophobicity were studied by FTIR and contact angle measurements, respectively. INTRODUCTION Ultra thin conformal coatings with tailored surface properties are required to achieve high performance microfluidic devices. Surfaces with contrasting wetting properties allow the precise control and manipulation of small volumes of fluids in such devices [1]. Moreover, the hydrophobicity of the channel surface reduces the capillary forces thereby the fluid drag is minimized. Various surface treatments such as conventional coating processes and surfacemodification including spraying or dipping [2, 3], laser ablation of organic polymers [4, 5], plasma processes [6, 7], hydrogel encapsulation [8, 9] and chemical plating [10] are used to prepare the hydrophobic surfaces. However, the coating must be conformal to ensure uniform deposition on the micro-channels. To address such issues in microfluidic devices we developed an alternative vapor phase technique for fabrication of ultra thin conformal films of polytetrafluoroethylene (PTFE). This technique is based on the use of a pulsed electron beam generated by channel spark discharge. Unlike pulse laser deposition (PLD), the PED can be used for optically transparent and reflective targets. The low investment involved with the electron source, makes this process viable for large-scale applications. These attributes have made pulse electron deposition (PED) a promising tool for deposition of inorganic thin films over PLD [11-14]. In this study, we use these advantages for deposition of organic thin films (of PTFE). Ultra-thin, superhydrophobic conformal films were deposited on various patterned structures using aforementioned technique. The films deposited using this technique were characterized by SEM, AFM, FTIR and contact angle measurements.
EXPERIMENTAL Patterned silicon substrate was used for deposition of PTFE (Teflon) films. The nanosecond (100 ns) pulse electron gun, PEBS-20 model from Neocera Inc. was used for the ablation of the target (figure 1). Teflon sheet (12x12x 116 inch3) from Fisher Scientific was cut into circular disc of 1î diame
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