Ms. Yulin Liu Profile

Yulin Liu

at Univ of Pittsburgh

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Publications (1)

Proceedings Article | 12 April 2021 Presentation + Paper

Optical-fiber based hydrogen sensing at high temperature using ALD coated oxide sensing layers

Paul Ohodnicki, Jeffrey Wuenschell, Michael Buric, Yulin Liu, Jung-Kun Lee

Proceedings Volume 11739, 117390I (2021) https://doi.org/10.1117/12.2587986

KEYWORDS: Atomic layer deposition, Oxides, Optical sensing, Hydrogen, Titanium dioxide, Environmental sensing, Absorption, Thin films, Sensors, Optical fibers

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Optical fiber-based sensors show unique advantages for high temperature and harsh environment sensing, with off-the-shelf silica fibers being relevant for application environments at temperatures approaching approximately 800oC. Through the integration of oxide-based sensing layers with the optical fiber platform in an evanescent field sensing approach, the optical response of a sensing layer which is modified in response to changing ambient conditions can be directly correlated to the sensor environment. Numerous deposition techniques have been explored in prior publications including sol-gel based wet chemistry deposition and sputtering. As an alternative, atomic layer deposition (ALD) allows for deposition of high quality, nanometer-scale thin films and is uniquely suited for coating of optical fiber-based sensors due to a lack of directionality during the deposition process and compatibility with scalable coating of optical fiber samples. In the current publication, ALD coated TiO₂ sensing layers are demonstrated to show a pronounced optical absorption in the visible range which depends upon subsequent processing temperatures and chemical environments. More specifically, the ALD deposition conditions result in the formation of initially amorphous TiO₂ layers which show a broad absorption band across the visible range due to the amorphous structure. A reversible temperature dependent response is observed, and above a critical temperature (~400-500°C), crystallization of the TiO₂ results in an irreversible change in optical absorption with a sharpened absorption peak associated with the band edge for which the temperature dependence is consistent with prior experiments and theoretical results. Following crystallization of the initially amorphous TiO2 layer, a strong and stable H2 sensing response is also demonstrated for H2 concentrations of various levels ranging from 0-3.9% H₂ in nitrogen balance, and at temperatures up to 800°C. Particularly attractive responses are shown in the telecom wavelengths (1550 nm) indicating potential application for distributed sensing with commercially available techniques.

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