Pulsed-laser deposition of polytetrafluoroethylene
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Lancy Tsung Philips Electronic Instruments Company, 85 McKee Drive, Mahwah, New Jersey 07430
J. Thomas Dickinson Department of Physics, Washington State University, Pullman, Washington 99164-2814 (Received 25 August 1994; accepted 12 December 1994)
Thin films of polytetrafluoroethylene have been deposited on amorphous substrates by the pulsed-laser deposition technique. By transmission electron microscopy, the polymer films were shown to consist of both amorphous and crystalline components. The data for the crystalline component are consistent with it being highly ordered with the long helical molecular chains aligned parallel to the film-substrate interface plane. The fraction of crystalline material in the films was found to be related to the substrate temperature during deposition with the maximum amount of crystalline material occurring when the substrate temperature was close to the melting temperature of the polymer.
I. INTRODUCTION Polytetrafluoroethylene (PTFE) has many advantageous physical properties which makes it a material of interest for numerous applications. For certain applications, thin films of PTFE are desirable, and a number of techniques have been used to deposit such films (e.g., Refs. 1-4). Studies of PTFE film formation via plasma-assisted polymerization have demonstrated that the presence of radical and ionic species is a necessary requirement for polymerization.3'5'6 The species that have been proposed as major reactive participants include CF, CF 2 , CF 3 , CF 3+ , C 3 F 5+ , F, and C. Several groups studying the laser ablation of polymers have identified the presence of these and other species, in addition to the monomer, emitted as a result of UV laser irradiation of PTFE targets.7^13 Energy distributions of the positive ions were shown to extend up to 10 eV.11 Thus, laser irradiation of PTFE produces all the essential species for polymerization and film growth. The first reported growth of PTFE films by pulsed-laser deposition (PLD) was by Blanchet and Shah.14 In this article, the influence of substrate temperature on the morphology and crystallinity of laser-deposited PTFE films is reported.
and the pulse repetition rate was 30 Hz. The films were deposited in vacuum (base pressure 10 6—10~7 Torr) onto either glass microscope slides (Gold Seal® Micro Slides) or 3-mm-diameter carbon-coated copper grids. The latter were used for examination of the microstructure of the films by transmission electron microscopy (TEM). The substrates were mechanically clamped onto the stainless steel plate of a small resistive heater (U.S. Incorporated model US-200) and were positioned parallel to the target. A thin piece of copper foil was placed between the heater plate and the glass substrate to improve the thermal contact. The distance between the target surface and the substrate was ~ 5 cm. The temperature of the substrate heater was monitored by a thermocouple embedded into the heater block at a position just behind the substrate. All the temperatures reported here are those of the substrate hea
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