X-ray Photoelectron Spectroscopy of Polytetrafluoroethylene Thin Films Grown By Pulsed Laser Deposition

  • PDF / 372,447 Bytes
  • 6 Pages / 420.48 x 639 pts Page_size
  • 25 Downloads / 210 Views

DOWNLOAD

REPORT


X-RAY PHOTOELECTRON SPECTROSCOPY OF POLYTETRAFLUOROETHYLENE THIN FILMS GROWN BY PULSED LASER DEPOSITION S. ISMAT SHAH AND GRACIELA B. BLANCHET Central Research and Development, Experimental Station, E. I. du Pont de Nemours and Company, P.O. Box 80356, Wilmington, DE 19880-0356.

ABSTRACT: Polytetrafluoroethylene (PTFE) films were prepared by laser ablation of bulk PTFE targets using a Nd-YAG laser (4th. harmonic). Both low and high molecular weight PTFE targets were used. X-ray Photoelectron Spectroscopy of the deposited films indicates that under certain deposition conditions it is possible to transfer the material of correct composition from the target onto the substrate. Films ablated with lower laser fluence were fluorine deficient. Fluorine deficiency leads to the formation of CF, CHF, and crosslinked carbon impurities. The background gas in the deposition chamber does not seem to have much effect on the composition. Films deposited with either Ar or CF 4 as the background gas have similar compositions. The oxygen concentration of the films decreases with the increase in the laser fluence. At the highest fluence used, 1.5 J/cm 2 , the 0 concentration was less than 1% regardless of the molecular weight of the target material. INTRODUCTION: XPS analyses have been extensively utilized in the analyses of the structure and bonding in polymer systems [1,2]. In addition to the surface modification of the polymers [3], surface, subsurface, and bulk polymer properties have been studied and differentiated [4]. Fluoropolymers are an ideal case for XPS investigations owing to the fact that F is the most electronegative element in the periodic table. The reaction between F and C induces the largest chemical shifts in the Cls binding energies. Therefore, there is extensive literature available on the study of fluoropolymers [5]. Recently, Dilkis published various reports to unambiguously assign the binding energies arising from CF 3 , CF 2 , CF, CHF, etc.[6,7] in the fluoropolymer systems. Polytetrafluoroethylene (PTFE) films have been prepared by various techniques including vacuum evaporation [8-9], rf sputtering [10-13], and plasma polymerization [14-15]. Sputtering and evaporation generally produce films that are fluorine deficient; however, stoichiometric films have been deposited by plasma polymerization of monomer gases. UV photoablation was generally considered to be a technique better suited for organic material removal [16-18] rather than for deposition. However, we have recently reported successful deposition of PTFE films by UV laser ablation [19]. In this paper we present results of the XPS analyses of the first PTFE films deposited by the laser ablation technique.

Mat. Res. Soc. Symp. Proc. Vol. 285. 01993 Materials Research Society

600

EXPERIMENTAL: The deposition was carried out in a small vacuum chamber with a background pressure of 10-7 Torr. The chamber was equipped with quartz windows which allowed the laser beam to be incident on the sample at a 450 angle. The targets were prepared by pressing Tefl

Data Loading...