EPR Characterization of Carbon Coated Fiber
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EPR CHARACTERIZATION OF CARBON COATED FIBER DARYL INNISS AT&T Bell Laboratories, 07974
600 Mountain Avenue,
Murray Hill,
N.J.
ABSTRACT An amorphous carbon coating has been developed to improve fatigue and the resistance of silica optical fibers to static hydrogen permeation. The carbon coated optical fibers are characterized by electron paramagnetic resonance spectroscopy. A Lorentzian lineshape is observed, centered at the g value of 2.002. Intensity measurements as a function of temperature suggest that localized spin centers contribute to the spin resonance. It is shown that atmospheric control of the carbonaceous environment results in the removal of these EPR active sites.
INTRODUCTION An amorphous carbon coated optical fiber has been developed to improve the resistance of the fiber to static fatigue and hydrogen permeation.[l] Complete characterization of the carbon coated fiber is essential in understanding how carbon protects the fiber from molecular attack, in optimizing the performance of the carbon coating and in designing new hermetic jackets. The report presented herein delineates structural characteristics of the carbon film via electron paramagnetic resonance spectroscopy (EPR). EPR absorptions are well known for carbon, graphite, coals, and chars. Considerable effort has been made towards the characterization of these resonances. For example, Wagoner[2] showed that charge carriers are responsible for the EPR absorption in pure graphite crystals. The Dysonian line shape[3], which is characteristic of conduction electron spin resonance, was observed. In contrast, Mrozowski[4] showed that neutron irradiated polycrystalline graphite exhibited both localized centers and conduction carriers. In another report, Mrozowski[5] showed that the localized spin centers are sensitive to the gases in contact with the carbon sample. For samples impermeable to air, a partly air sensitive EPR absorption may be observed, implying localized spin centers at the surface, whereas the EPR line of the localized spin centers disappears for samples with open structures. In situ EPR measurements made on carbon coated optical fibers are reported. Intensity measurements as a function of temperature are used to study the origin of the spin centers (i.e., conduction vs. localized electrons). These results are used to infer structural information of the carbon film.
Mat. Res. Soc. Symp. Proc. Vol. 172. ©1990 Materials Research Society
98
EXPERIMENTAL Carbon coated fibers were prepared as described previously.[lJ Approximately 100 fibers, 5 cm long, were placed The polymer coating was in a standard 4 mm o.d. EPR tube. removed with hot sulfuric acid. The fibers were washed with To demonstrate that the distilled water and allowed to air dry. origin of the spin resonance was from the carbon coating, intensity measurements for carbon coated fibers with and without In addition, standard, non-carbon polymer coating were compared. coated fibers were examined. Preliminary examination showed an irreversible response of the EPR intens
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