Two-dimensional (2D) materials have emerged as a versatile platform at the intersection of fundamental physics and applied science. Their atomically thin nature gives rise to distinctive electronic and optical properties, while simultaneously enabling them to function as highly sensitive, readily integrable probes of their local environment. Advanced optical techniques, such as super-resolution microscopy, have opened new opportunities to interrogate these materials at the nanoscale, providing optical access to individual defect behaviors, exciton diffusion and recombination dynamics, and charge transport pathways. Such approaches not only deepen our understanding of intrinsic material behavior but also position 2D systems as powerful sensors capable of resolving local dielectric variations, electric and magnetic fields, and other environmental perturbations.
\r\nCentral to this work is hexagonal boron nitride (hBN), a transparent, wide bandgap semiconductor that serves as a host for optically active defects. These defects function as reaction centers, single-photon emitters, and spatially resolved nanoscale sensors that can be readily integrated into electronic and photonic architectures. Owing to its optical transparency, chemical stability, and compatibility with diverse material platforms, hBN provides an exceptional foundation for optical sensing. Building upon this foundation, we explore material properties and present new methods for spatially resolved in situ optical imaging with hBN to advance dynamic, wide-field optical sensing.
\r\nWe investigate a previously reported class of emitters that arise from interactions between native hBN and organic solvents. These emitters are believed to originate from defect sites that bind transiently to solvent molecules. To study their behavior, we develop a platform for imaging the dynamics of these transient emitters while varying the electrochemical potential and applying electric fields with controlled orientations. By tracking the spectra of individual emitters, we enable multiplexed measurements that allow spatially resolved electrochemical imaging. Through systematic analysis, we rule out modulation mechanisms based on direct electric field effects or charge transfer. Instead, we identify a mechanism driven by changes in H⁺ concentration, which is modulated during the oxidation of trace water present in the solvent. This finding opens the possibility of using this platform for sensitive detection of H⁺ and trace water in methanol fuel cells, where such species critically influence operational efficiency.
\r\nIn the final part of the thesis, we focus on a well-characterized spin defect in hBN, the negatively charged boron vacancy, and explore strategies to enhance its photoluminescence (PL) through heterostructure engineering that facilitates energy and exciton transfer. We demonstrate the coupled structure’s improved utility in optical magnetometry compared to the defect by itself and discuss how improvements in PL could advance the development of wide-field optically detected magnetic resonance (ODMR) imaging using this spin defect. Using a defect in hBN would leverage 2D materials’ exceptional sensing capabilities and planar integrability.
\r\nOverall, this thesis aims to highlight the strengths of integrating 2D materials with optical sensing and to develop transferable techniques for introducing controlled stimuli, such as electrochemical potentials, electric fields, or electromagnetic waves, with high fidelity and minimal artifacts. These advances not only demonstrate the potential of hBN as a versatile sensing platform but also establish methodologies applicable to a wide range of low-dimensional material systems.
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\r\nFor zoom:
\r\n Meeting ID: 611 3428 2068 Passcode: 952027
EPFL racing team will provide an update on the main achievments of this year
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\r\nThis month we will have the pleasure to host Agostino Di Francescantonio, postdoc in the Laboratory of Nanoscience for Energy Technologies (LNET) with the presentation entitled:
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\r\n\"Nonlinear and reconfigurable optical metasurfaces\"
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\r\nFor organizational purposes (if you want to eat pizza!), please confirm your participation using this google form.
\r\nDon’t hesitate to extend the invitation to any postdoc and colleague!
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\r\nHope to see you there,
\r\nThe team of the EPFL Photonics Chapter
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\r\nAbstract:
\r\nOptical metasurfaces -- periodic arrangement of subwavelength nanostructures -- are emerging as suitable platforms for manipulation of free-space optical signals in ultrathin devices. Particular interest is attracted by resonant metasurfaces, where optical modes provide extreme confinement of light in the nanostructures volume and subsequent enhancement of light-matter interaction. This aspect is essential to boost the efficiency of various phenomena, from optical nonlinearities (e.g., multiphoton interaction like in second-harmonic generation) to reconfiguration mechanisms (i.e., dynamic modulation of the refractive index). In this talk I will survey techniques of controlling light at the nanoscale, focusing on nonlinear and reconfiguration processes, what they offer and what are their limitations.
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\r\nYou don't know POBs?
\r\nPOBs (Pizza-Optics-Beer) are monthly seminars organized by the student association EPFL Photonics Chapter.
\r\nA PhD or a postdoc gives a 20-minutes presentation about his/her research in photonics. Discussions continue informally around pizza and beers!
\r\nThe event is free and open to anyone.
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\r\nWe thank the Doctoral Program in Photonics (EPDO), the Society of Photo-Optical Instrumentation Engineers (SPIE.), Optica and SwissPhotonics for their support.
From the earliest dreams of travel imagined in literature to space missions shaping scientific research today, the Moon remains a horizon that is at once scientific, historical, and symbolic.
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\r\nOn the occasion of the Artemis II mission, the Library highlights its collections dedicated to the Moon and to space exploration: Astronauts’ memoirs, scientific works, NASA archives, and works of fiction. Explore the many ways in which the Moon and the Universe have been imagined, studied, and told.
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\r\nAll the documents on display are available to borrow under usual conditions.