The effect of rapid thermal annealing on characteristics of carbon coatings on optical fibers

Carbon films are deposited on silica glass fibers by radiofrequency plasme enhanced chemical vapor deposition (rf-PECVD), and the properties of these fibers are improved by rapid thermal annealing. The annealing temperatures are set to 100, 200, 300, 400, 500, 550, 600, and 700 degrees C. Experimential results show that the thickness and surface roughness of carbon films decrease with increasing annealing temperature, ranging from as deposited to 500 degrees C, while the sp(2) carbon bonding, sp(3) CH3 bonding optical bandgap and water contact angle (CA) of carbon films increase. As the annealing temperature increases from 500 to 700 degrees C, parts of the carbon films are delaminated. The sp(3) CH3 bonding in carbon films is shifted to the sp(3) CH2 bonding, and the sp(3) CH2 bonding is subsequently transferred to the sp(2) CH bonding. Meanwhile, the amount of the sp(2) carbon bonding in carbon films increases, while the optical bandgap decreases. Based on the evaluation of water repellency and low- temperature morphology of carbon films, the carbon film annealed at a temperature of 500 degrees C is the best for production of carbon-coated optical fibers. As compared to conventional thermal annealing (CTA), rapid thermal annealing (RTA) is more effective to improve the properties of carbon-coated optical fibers. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim