{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,12]],"date-time":"2026-03-12T03:31:08Z","timestamp":1773286268796,"version":"3.50.1"},"reference-count":23,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2026,3,11]],"date-time":"2026-03-11T00:00:00Z","timestamp":1773187200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003725","name":"National Research Foundation of Korea","doi-asserted-by":"publisher","award":["RS-2025-02233037"],"award-info":[{"award-number":["RS-2025-02233037"]}],"id":[{"id":"10.13039\/501100003725","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Advancement of Technology","award":["RS00411221"],"award-info":[{"award-number":["RS00411221"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Micromachines"],"abstract":"<jats:p>In this study, a highly crystalline 2H (hexagonal)-phase MoS2 sensing layer with a precisely controlled crystal structure was realized through a combination of DC sputtering and sulfurization annealing processes, and subsequently integrated with a D-shaped optical fiber to develop a highly sensitive carbon dioxide (CO2) sensor. Conventionally sputtered MoS2 thin films often suffer from the presence of unstable metallic 1T (tetragonal) phases and a high density of sulfur vacancies, which significantly degrade sensor reversibility and long-term stability. Here, high-temperature annealing under a sulfur-rich atmosphere was employed to induce a complete phase transition from the metastable 1T phase to the stable semiconducting 2H phase, while simultaneously healing sulfur vacancies. Enhanced crystallinity was confirmed by Raman spectroscopy. The fabricated sensor exhibited excellent linearity (R2 &gt; 0.99) and markedly improved repeatability over a CO2 concentration range of 1000\u201310,000 ppm. This significant performance enhancement is attributed to reversible charge transfer induced by sulfur vacancy passivation, which modulates the complex refractive index of the MoS2 layer and optimizes optical interaction with the evanescent field of the D-shaped fiber. The phase engineering and defect-healing strategy presented in this work effectively addresses the drift issues commonly observed in conventional electrical gas sensors and provides a crucial pathway toward the realization of high-performance optical gas sensors.<\/jats:p>","DOI":"10.3390\/mi17030341","type":"journal-article","created":{"date-parts":[[2026,3,11]],"date-time":"2026-03-11T11:44:52Z","timestamp":1773229492000},"page":"341","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["CO2 Sensing Characteristics of 2H-MoS2-Coated D-Shaped Optical Fiber Sensors"],"prefix":"10.3390","volume":"17","author":[{"given":"Han-Mam","family":"Kang","sequence":"first","affiliation":[{"name":"Department of Photonic Engineering, Chosun University, Gwangju 61452, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hyung-il","family":"Jang","sequence":"additional","affiliation":[{"name":"Department of Photonic Engineering, Chosun University, Gwangju 61452, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tae-Jung","family":"Ahn","sequence":"additional","affiliation":[{"name":"Department of Photonic Engineering, Chosun University, Gwangju 61452, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7084-0377","authenticated-orcid":false,"given":"Min-Ki","family":"Kwon","sequence":"additional","affiliation":[{"name":"Department of Photonic Engineering, Chosun University, Gwangju 61452, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,3,11]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1222","DOI":"10.1038\/s41561-024-01580-5","article-title":"Estimated human-induced warming from a linear temperature and atmospheric CO2 relationship","volume":"17","author":"Jarvis","year":"2024","journal-title":"Nat. Geosci."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1031","DOI":"10.1021\/acssensors.4c00429","article-title":"Gas Sensors for Climate Change","volume":"9","author":"Kang","year":"2024","journal-title":"ACS Sens."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Ughade, Y., Mehta, S., Patel, G., Gowda, R., Joshi, N., and Patel, R. (2025). Progress in CO2 Gas Sensing Technologies: Insights into Metal Oxide Nanostructures and Resistance-Based Methods. Micromachines, 16.","DOI":"10.3390\/mi16040466"},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Butt, M.A. (2024). Topic Editorial on Fiber-Optic Sensors. Micromachines, 15.","DOI":"10.3390\/mi15121452"},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Khonina, S.N., Kazanskiy, N.L., and Butt, M.A. (2023). Optical Fibre-Based Sensors-An Assessment of Current Innovations. Biosensors, 13.","DOI":"10.3390\/bios13090835"},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Pendao, C., and Silva, I. (2022). Optical Fiber Sensors and Sensing Networks: Overview of the Main Principles and Applications. Sensors, 22.","DOI":"10.3390\/s22197554"},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Qu, W.W., Chen, Y.X., Liu, S.Q., and Luo, L. (2025). Advances and Prospects of Nanomaterial Coatings in Optical Fiber Sensors. Coatings, 15.","DOI":"10.3390\/coatings15091008"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"10743","DOI":"10.1364\/OE.25.010743","article-title":"Optimization in nanocoated D-shaped optical fiber sensors","volume":"25","author":"Zubiate","year":"2017","journal-title":"Opt. Express"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Zhang, H.X., Zhou, X., Li, X.G., Gong, P.Q., Zhang, Y.A., and Zhao, Y. (2023). Recent Advancements of LSPR Fiber-Optic Biosensing: Combination Methods, Structure, and Prospects. Biosensors, 13.","DOI":"10.3390\/bios13030405"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"e202414720","DOI":"10.1002\/anie.202414720","article-title":"Molybdenum Disulfide Induced Phase Control Synthesis of Multi-dimensional Co3S4-MoS2 Heteronanostructures via Cation Exchange","volume":"64","author":"He","year":"2025","journal-title":"Angew. Chem. Int. Ed."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Acosta, S., and Quintana, M. (2024). Chemically Functionalized 2D Transition Metal Dichalcogenides for Sensors. Sensors, 24.","DOI":"10.3390\/s24061817"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1771","DOI":"10.1038\/s41598-020-79563-w","article-title":"2D materials coated on etched optical fibers as humidity sensor","volume":"11","author":"Owji","year":"2021","journal-title":"Sci. Rep."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"13440","DOI":"10.1021\/acsanm.1c02937","article-title":"Two-Dimensional MoS2 Nanosheet-Functionalized Optical Microfiber for Room-Temperature Volatile Organic Compound Detection","volume":"4","author":"Yap","year":"2021","journal-title":"ACS Appl. Nano Mater."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1016\/j.optlastec.2016.11.021","article-title":"Recent research progress of optical fiber sensors based on D-shaped structure","volume":"90","author":"Ying","year":"2017","journal-title":"Opt. Laser Technol."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"117750","DOI":"10.1016\/j.apcatb.2019.117750","article-title":"3D flower-like defected MoS2 magnetron-sputtered on candle soot for enhanced hydrogen evolution reaction","volume":"263","author":"Gao","year":"2020","journal-title":"Appl. Catal. B-Environ."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Kumar, R.R., Gupta, S., Anbalagan, A.K., Khan, A., Tai, N.H., Lee, C.H., and Lin, H.N. (2025). Time-Dependent Growth of Sputtered MoS2 Films on ZnO Nanorods for Enhanced NO2 Sensing Performance. Micromachines, 16.","DOI":"10.3390\/mi16060659"},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Hong, G.S., Kim, M.E., Lee, J.S., Kim, J.Y., and Kwon, M.K. (2024). Respiration Monitoring Using Humidity Sensor Based on Hydrothermally Synthesized Two-Dimensional MoS2. Nanomaterials, 14.","DOI":"10.3390\/nano14221826"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Kim, E., Kim, J.Y., and Kwon, M.K. (2023). Synthesis of MoS2 Using Chemical Vapor Deposition and Conventional Hydrothermal Methods: Applications to Respiration Sensing. Appl. Sci., 13.","DOI":"10.3390\/app13106084"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Fu, X.Q., Qiao, Z.R., Zhou, H.Y., and Xie, D. (2024). Defect Engineering in Transition Metal Dichalcogenide-Based Gas Sensors. Chemosensors, 12.","DOI":"10.3390\/chemosensors12060085"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"117185","DOI":"10.1016\/j.trac.2023.117185","article-title":"Recent advances in technologies toward the development of 2D materials-based electronic noses","volume":"166","author":"Parichenko","year":"2023","journal-title":"TrAC-Trend Anal. Chem."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"25291","DOI":"10.1021\/acsami.7b05775","article-title":"Heterogeneous Nanostructure Based on 1T-Phase MoS2 for Enhanced Electrocatalytic Hydrogen Evolution","volume":"9","author":"Liu","year":"2017","journal-title":"ACS Appl. Mater. Inter."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"795","DOI":"10.1016\/j.apsusc.2016.09.007","article-title":"Electronic structure of Ar+ ion-sputtered thin-film MoS2: A XPS and IPES study","volume":"392","author":"Santoni","year":"2017","journal-title":"Appl. Surf. Sci."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"25297","DOI":"10.1021\/acsomega.4c03166","article-title":"Direct or Indirect Sonication in Ecofriendly MoS2 Dispersion for NO2 and NH3 Gas-Sensing Applications","volume":"9","author":"Fadil","year":"2024","journal-title":"ACS Omega"}],"container-title":["Micromachines"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-666X\/17\/3\/341\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,3,11]],"date-time":"2026-03-11T11:49:14Z","timestamp":1773229754000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-666X\/17\/3\/341"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,3,11]]},"references-count":23,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2026,3]]}},"alternative-id":["mi17030341"],"URL":"https:\/\/doi.org\/10.3390\/mi17030341","relation":{},"ISSN":["2072-666X"],"issn-type":[{"value":"2072-666X","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,3,11]]}}}