Tin (IV) Oxide Coatings with Different Morphologies on the Surface of a Thinned Quartz Fiber for Sensor Application

Thin-film coatings of tin oxide on the surface of a chemically thinned section of a single-mode quartz fiber have been obtained and experimentally characterized. The materials were synthesized on the fiber surface by metal-organic chemical vapor deposition (MOCVD). To change the surface morphology, we used different amounts of tetramethyltin (SnMe₄) supplied by a carrier gas (dried air) to the deposition zone by varying the temperature of the bubbler with the reagent. During deposition, the transmission spectrum of the optical path was recorded in real time, and the temperature of the bubbler in the experiments varied from –20 to +20°С. After studying the surface on a scanning electron microscope, the deposited films were tested for chemical resistance to an aqueous solution of sulfuric acid and the sensitivity of the lossy mode resonance (LMR) to changes in the refractive index of the environment in the range from 1.35 to 1.41 was evaluated. Samples produced at higher reagent flow rates exhibited a greater resonance sensitivity of 3800 nm/refractive index unit (RIU) for the first-order TM component of the resonance, but such coatings dissolve noticeably in concentrated sulfuric acid solutions, in contrast to coatings obtained with low reagent consumption.