Professor in Department of Micro- and Nanotechnology at DTU Nanotech
Recent news
Publications
Keisuke Ozawa; Hiroshi Sugimoto; Daisuke Shima; Tatsuki Hinamoto; Mojtaba Karimi Habil; Yan Joe Lee; Søren Raza; Keisuke Imaeda; Kosei Ueno; Mark L Brongersma; Minoru Fujii
Routing Light Emission from Monolayer MoS2 by Mie Resonances of Crystalline Silicon Nanospheres Journal Article
In: ACS Applied Optical Materials, vol. 3, iss. 2, pp. 375-382, 2025.
@article{ozawa2025routing,
title = {Routing Light Emission from Monolayer MoS2 by Mie Resonances of Crystalline Silicon Nanospheres},
author = {Keisuke Ozawa and Hiroshi Sugimoto and Daisuke Shima and Tatsuki Hinamoto and Mojtaba Karimi Habil and Yan Joe Lee and S\oren Raza and Keisuke Imaeda and Kosei Ueno and Mark L Brongersma and Minoru Fujii},
doi = {10.1021/acsaom.4c00495},
year = {2025},
date = {2025-02-15},
journal = {ACS Applied Optical Materials},
volume = {3},
issue = {2},
pages = {375-382},
abstract = {A dielectric Mie-resonant nanoantenna is capable of controlling the directionality of the emission from nearby quantum emitters through the excitation of multiple degenerate Mie resonances. A crystalline silicon nanosphere (Si NS) is a promising candidate for a dielectric nanoantenna because crystalline Si has a large refractive index (3.8 at 650 nm) and the small imaginary part of a complex refractive index (0.015 at 650 nm) as an optical material. In this work, we control the emission directionality of excitons supported by monolayer transition metal dichalcogenides (1L-TMDCs) using a Si NS. We first discuss the condition to extract the emission preferentially toward the Si NS side from the analytical calculations. We then study the photoluminescence (PL) of 1L-TMDCs on which differently sized single Si NSs are placed. We show that the PL spectral shape strongly depends on the emission direction, and that the emission toward the Si NS side (top) with respect to the opposite side (bottom) is the largest at a wavelength between the magnetic dipole and electric dipole Mie resonances of a Si NS. Finally, we quantitatively discuss the spectral shape of the top-to-bottom ratio from numerical simulations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A dielectric Mie-resonant nanoantenna is capable of controlling the directionality of the emission from nearby quantum emitters through the excitation of multiple degenerate Mie resonances. A crystalline silicon nanosphere (Si NS) is a promising candidate for a dielectric nanoantenna because crystalline Si has a large refractive index (3.8 at 650 nm) and the small imaginary part of a complex refractive index (0.015 at 650 nm) as an optical material. In this work, we control the emission directionality of excitons supported by monolayer transition metal dichalcogenides (1L-TMDCs) using a Si NS. We first discuss the condition to extract the emission preferentially toward the Si NS side from the analytical calculations. We then study the photoluminescence (PL) of 1L-TMDCs on which differently sized single Si NSs are placed. We show that the PL spectral shape strongly depends on the emission direction, and that the emission toward the Si NS side (top) with respect to the opposite side (bottom) is the largest at a wavelength between the magnetic dipole and electric dipole Mie resonances of a Si NS. Finally, we quantitatively discuss the spectral shape of the top-to-bottom ratio from numerical simulations.
Artyom Assadillayev; Tatsuki Hinamoto; Minoru Fujii; Hiroshi Sugimoto; Mark L. Brongersma; Søren Raza
Plasmon Launching and Scattering by Silicon Nanoparticles Journal Article
In: ACS Photonics, vol. 8, iss. 6, pp. 1582-1591, 2021.
@article{assadillayev2021plasmon,
title = {Plasmon Launching and Scattering by Silicon Nanoparticles},
author = {Artyom Assadillayev and Tatsuki Hinamoto and Minoru Fujii and Hiroshi Sugimoto and Mark L. Brongersma and S\oren Raza},
doi = {10.1021/acsphotonics.0c01554},
year = {2021},
date = {2021-05-19},
journal = {ACS Photonics},
volume = {8},
issue = {6},
pages = {1582-1591},
abstract = {Resonant optical nanomaterials with a high refractive index, such as silicon, have become key elements for controlling free-space light. Here, we show that silicon nanoparticles can manipulate highly confined guided waves in the form of surface plasmon polaritons (SPPs) on a subwavelength scale. Using electron energy-loss spectroscopy in a transmission electron microscope, we demonstrate that SPPs in ultrathin metal films can be efficiently launched due to the strong coupling between the Mie resonances of the nanoparticle and the SPP modes. We find that the SPP excitation wavelength can be tuned across the entire near-infrared by varying the particle size. For insight into the coupling mechanism, we also measure the electron-beam-induced response of the Mie resonances in isolated silicon nanostructures in a broad size range. Finally, we show that the silicon nanoparticles act as scatterers of the SPPs supported by the film. Our results may pave the way for using high-refractive-index dielectric nanoantennas as compact elements for manipulating highly confined SPPs.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Resonant optical nanomaterials with a high refractive index, such as silicon, have become key elements for controlling free-space light. Here, we show that silicon nanoparticles can manipulate highly confined guided waves in the form of surface plasmon polaritons (SPPs) on a subwavelength scale. Using electron energy-loss spectroscopy in a transmission electron microscope, we demonstrate that SPPs in ultrathin metal films can be efficiently launched due to the strong coupling between the Mie resonances of the nanoparticle and the SPP modes. We find that the SPP excitation wavelength can be tuned across the entire near-infrared by varying the particle size. For insight into the coupling mechanism, we also measure the electron-beam-induced response of the Mie resonances in isolated silicon nanostructures in a broad size range. Finally, we show that the silicon nanoparticles act as scatterers of the SPPs supported by the film. Our results may pave the way for using high-refractive-index dielectric nanoantennas as compact elements for manipulating highly confined SPPs.
Jung-Hwan Song; Søren Raza; Jorik van de Groep; Ju-Hyung Kang; Qitong Li; Pieter G. Kik; Mark L. Brongersma
Nanoelectromechanical modulation of a strongly-coupled plasmonic dimer Journal Article
In: Nature Communications, vol. 12, no. 48, 2021.
@article{song12nanoelectromechanical,
title = {Nanoelectromechanical modulation of a strongly-coupled plasmonic dimer},
author = {Jung-Hwan Song and S\oren Raza and Jorik van de Groep and Ju-Hyung Kang and Qitong Li and Pieter G. Kik and Mark L. Brongersma },
doi = {10.1038/s41467-020-20273-2},
year = {2021},
date = {2021-01-04},
journal = {Nature Communications},
volume = {12},
number = {48},
abstract = {The ability of two nearly-touching plasmonic nanoparticles to squeeze light into a nanometer gap has provided a myriad of fundamental insights into light\textendashmatter interaction. In this work, we construct a nanoelectromechanical system (NEMS) that capitalizes on the unique, singular behavior that arises at sub-nanometer particle-spacings to create an electro-optical modulator. Using in situ electron energy loss spectroscopy in a transmission electron microscope, we map the spectral and spatial changes in the plasmonic modes as they hybridize and evolve from a weak to a strong coupling regime. In the strongly-coupled regime, we observe a very large mechanical tunability (~250 meV/nm) of the bonding-dipole plasmon resonance of the dimer at ~1 nm gap spacing, right before detrimental quantum effects set in. We leverage our findings to realize a prototype NEMS light-intensity modulator operating at ~10 MHz and with a power consumption of only 4 fJ/bit.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The ability of two nearly-touching plasmonic nanoparticles to squeeze light into a nanometer gap has provided a myriad of fundamental insights into light–matter interaction. In this work, we construct a nanoelectromechanical system (NEMS) that capitalizes on the unique, singular behavior that arises at sub-nanometer particle-spacings to create an electro-optical modulator. Using in situ electron energy loss spectroscopy in a transmission electron microscope, we map the spectral and spatial changes in the plasmonic modes as they hybridize and evolve from a weak to a strong coupling regime. In the strongly-coupled regime, we observe a very large mechanical tunability (~250 meV/nm) of the bonding-dipole plasmon resonance of the dimer at ~1 nm gap spacing, right before detrimental quantum effects set in. We leverage our findings to realize a prototype NEMS light-intensity modulator operating at ~10 MHz and with a power consumption of only 4 fJ/bit.
Andrea Cordaro; Jorik van de Groep; Søren Raza; Emanuele Francesco Pecora; Francesco Priolo; Mark L. Brongersma
Anti-reflection high-index metasurfaces combining Mie and Fabry-Pérot resonances Journal Article
In: ACS Photonics, vol. 6, no. 2, pp. 453–459, 2019.
@article{cordaro2019anti,
title = {Anti-reflection high-index metasurfaces combining Mie and Fabry-P\'{e}rot resonances},
author = {Andrea Cordaro and Jorik van de Groep and S\oren Raza and Emanuele Francesco Pecora and Francesco Priolo and Mark L. Brongersma},
doi = {10.1021/acsphotonics.8b01406},
year = {2019},
date = {2019-01-04},
journal = {ACS Photonics},
volume = {6},
number = {2},
pages = {453\textendash459},
abstract = {Minimizing reflection losses is required for the efficient operation of a wide range of optical components. Anti-reflection coatings supporting Fabry-P\'{e}rot resonances are commonly used to solve this problem and can be applied on an industrial scale. Recent work has shown that reflections can also be reduced by placing an array of high-index nanostructures on a surface. In such coatings, anti-reflection is achieved by tailoring the scattering by optical Mie resonances. Here, we design and fabricate Si metasurfaces that combine both Fabry-P\'{e}rot and Mie resonances in a single metasurface to realize a multi-resonant broadband anti-reflection response. We optically characterize the metasurfaces demonstrating 4.1% AM1.5\textendashaveraged reflectance across the visible spectrum (425\textendash900 nm). Our metasurface design strategy is generally applicable to different materials and frequency ranges, making our approach relevant for a broad variety of applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Minimizing reflection losses is required for the efficient operation of a wide range of optical components. Anti-reflection coatings supporting Fabry-Pérot resonances are commonly used to solve this problem and can be applied on an industrial scale. Recent work has shown that reflections can also be reduced by placing an array of high-index nanostructures on a surface. In such coatings, anti-reflection is achieved by tailoring the scattering by optical Mie resonances. Here, we design and fabricate Si metasurfaces that combine both Fabry-Pérot and Mie resonances in a single metasurface to realize a multi-resonant broadband anti-reflection response. We optically characterize the metasurfaces demonstrating 4.1% AM1.5–averaged reflectance across the visible spectrum (425–900 nm). Our metasurface design strategy is generally applicable to different materials and frequency ranges, making our approach relevant for a broad variety of applications.
Fatih Nadi Gür; Cillian Patrick Thomas McPolin; Søren Raza; Martin Mayer; Diane Joane Roth; Anja Maria Steiner; Markus Löffler; Andreas Fery; Mark L Brongersma; Anatoly V Zayats; Tobias AF Koenig; Thorsten L Schmidt
DNA-Assembled Plasmonic Waveguides for Nanoscale Light Propagation to a Fluorescent Nanodiamond Journal Article
In: Nano Letters, vol. 18, no. 11, pp. 7323–7329, 2018.
@article{gur2018dna,
title = {DNA-Assembled Plasmonic Waveguides for Nanoscale Light Propagation to a Fluorescent Nanodiamond},
author = {Fatih Nadi G\"{u}r and Cillian Patrick Thomas McPolin and S\oren Raza and Martin Mayer and Diane Joane Roth and Anja Maria Steiner and Markus L\"{o}ffler and Andreas Fery and Mark L Brongersma and Anatoly V Zayats and Tobias AF Koenig and Thorsten L Schmidt},
year = {2018},
date = {2018-10-19},
journal = {Nano Letters},
volume = {18},
number = {11},
pages = {7323\textendash7329},
abstract = {Plasmonic waveguides consisting of metal nanoparticle chains can localize and guide light well below the diffraction limit, but high propagation losses due to lithography-limited large interparticle spacing have impeded practical applications. Here, we demonstrate that DNA-origami-based self-assembly of monocrystalline gold nanoparticles allows the interparticle spacing to be decreased to ∼2 nm, thus reducing propagation losses to 0.8 dB per 50 nm at a deep subwavelength confinement of 62 nm (∼λ/10). We characterize the individual waveguides with nanometer-scale resolution by electron energy-loss spectroscopy. Light propagation toward a fluorescent nanodiamond is directly visualized by cathodoluminescence imaging spectroscopy on a single-device level, thereby realizing nanoscale light manipulation and energy conversion. Simulations suggest that longitudinal plasmon modes arising from the narrow gaps are responsible for the efficient waveguiding. With this scalable DNA origami approach, micrometer-long propagation lengths could be achieved, enabling applications in information technology, sensing, and quantum optics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Plasmonic waveguides consisting of metal nanoparticle chains can localize and guide light well below the diffraction limit, but high propagation losses due to lithography-limited large interparticle spacing have impeded practical applications. Here, we demonstrate that DNA-origami-based self-assembly of monocrystalline gold nanoparticles allows the interparticle spacing to be decreased to ∼2 nm, thus reducing propagation losses to 0.8 dB per 50 nm at a deep subwavelength confinement of 62 nm (∼λ/10). We characterize the individual waveguides with nanometer-scale resolution by electron energy-loss spectroscopy. Light propagation toward a fluorescent nanodiamond is directly visualized by cathodoluminescence imaging spectroscopy on a single-device level, thereby realizing nanoscale light manipulation and energy conversion. Simulations suggest that longitudinal plasmon modes arising from the narrow gaps are responsible for the efficient waveguiding. With this scalable DNA origami approach, micrometer-long propagation lengths could be achieved, enabling applications in information technology, sensing, and quantum optics.
Ahmet Fatih Cihan; Alberto G. Curto; Søren Raza; Pieter G. Kik; Mark L. Brongersma
Silicon Mie resonators for highly directional light emission from monolayer MoS2 Journal Article
In: Nature Photonics, vol. 12, pp. 284-290, 2018.
@article{CihanMoS2,
title = {Silicon Mie resonators for highly directional light emission from monolayer MoS2},
author = {Ahmet Fatih Cihan and Alberto G. Curto and S\oren Raza and Pieter G. Kik and Mark L. Brongersma},
doi = {10.1038/s41566-018-0155-y},
year = {2018},
date = {2018-04-23},
journal = {Nature Photonics},
volume = {12},
pages = {284-290},
abstract = {Controlling light emission from quantum emitters has important applications, ranging from solid-state lighting and displays to nanoscale single-photon sources. Optical antennas have emerged as promising tools to achieve such control right at the location of the emitter, without the need for bulky, external optics. Semiconductor nanoantennas are particularly practical for this purpose because simple geometries such as wires and spheres support multiple, degenerate optical resonances. Here, we start by modifying Mie scattering theory developed for plane wave illumination to describe scattering of dipole emission. We then use this theory and experiments to demonstrate several pathways to achieve control over the directionality, polarization state and spectral emission that rely on a coherent coupling of an emitting dipole to optical resonances of a silicon nanowire. A forward-to-backward ratio of 20 was demonstrated for the electric dipole emission at 680 nm from a monolayer MoS2 by optically coupling it to a silicon nanowire.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Controlling light emission from quantum emitters has important applications, ranging from solid-state lighting and displays to nanoscale single-photon sources. Optical antennas have emerged as promising tools to achieve such control right at the location of the emitter, without the need for bulky, external optics. Semiconductor nanoantennas are particularly practical for this purpose because simple geometries such as wires and spheres support multiple, degenerate optical resonances. Here, we start by modifying Mie scattering theory developed for plane wave illumination to describe scattering of dipole emission. We then use this theory and experiments to demonstrate several pathways to achieve control over the directionality, polarization state and spectral emission that rely on a coherent coupling of an emitting dipole to optical resonances of a silicon nanowire. A forward-to-backward ratio of 20 was demonstrated for the electric dipole emission at 680 nm from a monolayer MoS2 by optically coupling it to a silicon nanowire.
