{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,7]],"date-time":"2026-09-07T08:09:33Z","timestamp":1788768573942,"version":"build-2803163510"},"reference-count":45,"publisher":"Wiley","issue":"50","license":[{"start":{"date-parts":[[2026,6,12]],"date-time":"2026-06-12T00:00:00Z","timestamp":1781222400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2026,6,12]],"date-time":"2026-06-12T00:00:00Z","timestamp":1781222400000},"content-version":"tdm","delay-in-days":0,"URL":"http:\/\/doi.wiley.com\/10.1002\/tdm_license_1.1"}],"funder":[{"DOI":"10.13039\/100000181","name":"Air Force Office of Scientific Research","doi-asserted-by":"publisher","award":["FA9550\u201023\u20101\u20100134"],"award-info":[{"award-number":["FA9550\u201023\u20101\u20100134"]}],"id":[{"id":"10.13039\/100000181","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000006","name":"Office of Naval Research","doi-asserted-by":"publisher","award":["N000142412533"],"award-info":[{"award-number":["N000142412533"]}],"id":[{"id":"10.13039\/100000006","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000001","name":"National Science Foundation","doi-asserted-by":"publisher","award":["CMMI\u20102306039"],"award-info":[{"award-number":["CMMI\u20102306039"]}],"id":[{"id":"10.13039\/100000001","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000104","name":"National Aeronautics and Space Administration","doi-asserted-by":"publisher","award":["80NSSC25K7278"],"award-info":[{"award-number":["80NSSC25K7278"]}],"id":[{"id":"10.13039\/100000104","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["advanced.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Advanced Science"],"published-print":{"date-parts":[[2026,9]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n                  <jats:p>Hexagonal boron nitride (hBN) is a widely studied van der Waals material that supports highly confined phonon polaritons\u2014hybrid light\u2010matter quasiparticles arising from the coupling of infrared photons with optical phonons. While prior works\u2014primarily using scattering\u2010type near\u2010field optical microscopy (s\u2010SNOM)\u2014have explored the effect of hBN layer number on the wavelength and propagation characteristics of phonon polaritons, the direct spectroscopic investigation of their resonance energy as a function of layer number has remained largely unaddressed. In this study, we present the first systematic spectroscopic analysis of layer\u2010dependent phonon polariton resonance frequencies in hBN, using photo\u2010induced force microscopy (PiFM). By probing hBN with layer numbers ranging from approximately 10 to 60, we uncover clear and opposing trends in the resonance behavior of the two principal Reststrahlen bands. Specifically, we observe that the in\u2010plane phonon polariton resonance exhibits a blue shift with increasing layer number, while the out\u2010of\u2010plane resonance shows a red shift. Additionally, the peak intensity in the out\u2010of\u2010plane band increases with layer number, whereas the in\u2010plane resonance becomes weaker and broader. These findings reveal critical insights into the optical response of hBN across different layer regimes and underscore the importance of layer number as a tuning parameter in nanophotonic applications.<\/jats:p>","DOI":"10.1002\/advs.76087","type":"journal-article","created":{"date-parts":[[2026,6,12]],"date-time":"2026-06-12T19:28:32Z","timestamp":1781292512000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Layer\u2010Dependent Phonon Polaritons in hBN Resolved by Photo\u2010Induced Force Spectroscopy"],"prefix":"10.1002","volume":"13","author":[{"given":"Amin","family":"Hajarian","sequence":"first","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering University of California  Irvine California 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