{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,16]],"date-time":"2026-04-16T16:34:10Z","timestamp":1776357250098,"version":"3.51.2"},"reference-count":45,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2024,6,3]],"date-time":"2024-06-03T00:00:00Z","timestamp":1717372800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Ford university research project grant (URP)","award":["1661"],"award-info":[{"award-number":["1661"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Fabry\u2013Perot interferometers (FPIs), comprising foundry-compatible dielectric thin films on sapphire wafer substrates, were investigated for possible use in chemical sensing. Specifically, structures comprising two vertically stacked distributed Bragg reflectors (DBRs), with the lower DBR between a sapphire substrate and a silicon-oxide (SiO2) resonator layer and the other DBR on top of this resonator layer, were investigated for operation in the near-ultraviolet (near-UV) range. The DBRs are composed of a stack of nitride-rich silicon-nitride (SiNx) layers for the higher index and SiO2 layers for the lower index. An exemplary application would be formaldehyde detection at sub-ppm concentrations in air, using UV absorption spectroscopy in the 300\u2013360 nm band, while providing spectral selectivity against the main interfering gases, notably NO2 and O3. Although SiNx thin films are conventionally used only for visible and near-infrared optical wavelengths (above 450 nm) because of high absorbance at lower wavelengths, this work shows that nitride-rich SiNx is suitable for near-UV wavelengths. The interplay between spectral absorbance, transmittance and reflectance in a FPI is presented in a comparative study between one FPI design using stoichiometric material (Si3N4) and two designs based on N-rich compositions, SiN1.39 and SiN1.49. Spectral measurements confirm that if the design accounts for phase penetration depth, sufficient performance can be achieved with the SiN1.49-based FPI design for gas absorption spectroscopy in near-UV, with peak transmission at 330 nm of 64%, a free spectral range (FSR) of 20 nm and a full-width half-magnitude spectral resolution (FWHM) of 2 nm.<\/jats:p>","DOI":"10.3390\/s24113597","type":"journal-article","created":{"date-parts":[[2024,6,3]],"date-time":"2024-06-03T05:58:00Z","timestamp":1717394280000},"page":"3597","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["SiNx\/SiO2-Based Fabry\u2013Perot Interferometer on Sapphire for Near-UV Optical Gas Sensing of Formaldehyde in Air"],"prefix":"10.3390","volume":"24","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2074-4958","authenticated-orcid":false,"given":"Reinoud","family":"Wolffenbuttel","sequence":"first","affiliation":[{"name":"Laboratory for Electronic Instrumentation, Department of Microelectronics, Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, 2628 CD Delft, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3994-1153","authenticated-orcid":false,"given":"Declan","family":"Winship","sequence":"additional","affiliation":[{"name":"Center for Wireless Integrated MicroSensing and Systems (WIMS2), University of Michigan, Ann Arbor, MI 48109, USA"},{"name":"Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"David","family":"Bilby","sequence":"additional","affiliation":[{"name":"Research and Advanced Engineering, Ford Motor Company, Dearborn, MI 48121, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jaco","family":"Visser","sequence":"additional","affiliation":[{"name":"Research and Advanced Engineering, Ford Motor Company, Dearborn, MI 48121, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4589-4485","authenticated-orcid":false,"given":"Yutao","family":"Qin","sequence":"additional","affiliation":[{"name":"Center for Wireless Integrated MicroSensing and Systems (WIMS2), University of Michigan, Ann Arbor, MI 48109, USA"},{"name":"Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2281-3937","authenticated-orcid":false,"given":"Yogesh","family":"Gianchandani","sequence":"additional","affiliation":[{"name":"Center for Wireless Integrated MicroSensing and Systems (WIMS2), University of Michigan, Ann Arbor, MI 48109, USA"},{"name":"Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2024,6,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"287","DOI":"10.1046\/j.1365-2222.2002.01301.x","article-title":"Effect on formaldehyde on the expression of adhesion molecule in nasal microvascular endothelial cells: The role of formaldehyde in the pathogenesis of sick building syndrome","volume":"32","author":"Kim","year":"2002","journal-title":"Clin. 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