Mechanistic Insights into Signal Generation and Probing Depth in Photothermal-Based Atomic Force Microscopy-Infrared (AFM-IR)

Mechanistic Insights into Signal Generation and Probing Depth in Photothermal-Based Atomic Force Microscopy-Infrared (AFM-IR) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Mechanistic Insights into Signal Generation and Probing Depth in Photothermal-Based Atomic Force Microscopy-Infrared (AFM-IR) Georg Ramer, Yide Zhang, Margaux Petay, Alexandre Dazzi, Bernhard Lendl This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9269428/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Photothermal-based atomic force microscopy infrared (AFM-IR) spectroscopy enables nanoscale chemical imaging and subsurface characterization, yet the fundamental mechanisms governing its probing depth remain only partially understood. Classical thermal diffusion model predicts a length scaling of f -1/2 with modulation frequency, whereas recent experiments observed a much stronger confinement of probing depth in AFM-IR close to f -3/2 . To resolve this discrepancy, we develop a unified analytical model that quantitatively links absorbed optical energy to the detected cantilever oscillation amplitude in AFM-IR. The model integrates frequency-dependent subsurface heat deposition, thermoelastic expansion with strain attenuation, and resonance-enhanced cantilever dynamics. Our analysis reveals that the effective probing depth (d probe ) is not governed by thermal diffusion alone but is strongly affected by optical and thermoelastic strain attenuation. These combined effects lead to an inverse frequency scaling (d probe ∝f -1 ), indicating that mechanical transduction processes play a dominant role in determining depth sensitivity. This framework provides a mechanistic basis for the experimentally observed strong confinement of probing depth and offers quantitative guidelines for tuning depth sensitivity through excitation frequency, pulse conditions, sample architecture, and tip–sample coupling. Physical sciences/Optics and photonics Physical sciences/Optics and photonics/Optical techniques Physical sciences/Optics and photonics/Optical techniques/Optical spectroscopy/Infrared spectroscopy Full Text Additional Declarations There is no conflict of interest Supplementary Files SIMechanisticInsightsintoAFMIRSignalFormationandDepthSensitivity.pdf Supplementary materials for Mechanistic Insights into Signal Generation and Probing Depth in Photothermal-Based Atomic Force Microscopy-Infrared (AFM-IR) Cite Share Download PDF Status: Under Review Version 1 posted Review # 1 received at journal 09 May, 2026 Reviewer # 2 agreed at journal 28 Apr, 2026 Reviewer # 1 agreed at journal 27 Apr, 2026 Reviewers invited by journal 23 Apr, 2026 Submission checks completed at journal 23 Apr, 2026 Editor assigned by journal 30 Mar, 2026 First submitted to journal 30 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9269428","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":628300805,"identity":"8de5c5d8-60e4-4e94-8a97-056983dbb64e","order_by":0,"name":"Georg 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