Jung-Hwan Song
Research Scientist
Assistant professor of Electrical and Computer Engineering at the National University of Singapore
Recent news
Publications
Skyler P Selvin; Majid Esfandyarpour; Anqi Ji; Yan Joe Lee; Colin Yule; Jung-Hwan Song; Mohammad Taghinejad; Mark L Brongersma
Acoustic wave modulation of gap plasmon cavities Journal Article
In: Science, vol. 389, iss. 6759, pp. 516-520, 2025.
@article{selvin2025acoustic,
title = {Acoustic wave modulation of gap plasmon cavities},
author = {Skyler P Selvin and Majid Esfandyarpour and Anqi Ji and Yan Joe Lee and Colin Yule and Jung-Hwan Song and Mohammad Taghinejad and Mark L Brongersma},
url = {https://brongersma.stanford.edu/wp-content/uploads/2025/08/science.adv1728-2.pdf
https://www.science.org/stoken/author-tokens/ST-2800/full},
doi = {10.1126/science.adv1728},
year = {2025},
date = {2025-07-31},
urldate = {2025-07-31},
journal = {Science},
volume = {389},
issue = {6759},
pages = {516-520},
abstract = {The important role of metallic nanostructures in nanophotonics will expand if ways to electrically manipulate their optical resonances at high speed can be identified. We capitalized on electrically driven surface acoustic waves and the extreme light concentration afforded by gap plasmons to achieve this goal. We placed gold nanoparticles in a particle-on-mirror configuration with a few-nanometer-thick, compressible polymer spacer. Surface acoustic waves were then used to tune light scattering at speeds approaching the gigahertz regime. We observed evidence that the surface acoustic waves produced mechanical deformations in the polymer and that ensuing nonlinear mechanical dynamics led to unexpectedly large levels of strain and spectral tuning. Our approach provides a design strategy for electrically driven dynamic metasurfaces and fundamental explorations of high-frequency, polymer dynamics in ultraconfined geometries.},
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pubstate = {published},
tppubtype = {article}
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The important role of metallic nanostructures in nanophotonics will expand if ways to electrically manipulate their optical resonances at high speed can be identified. We capitalized on electrically driven surface acoustic waves and the extreme light concentration afforded by gap plasmons to achieve this goal. We placed gold nanoparticles in a particle-on-mirror configuration with a few-nanometer-thick, compressible polymer spacer. Surface acoustic waves were then used to tune light scattering at speeds approaching the gigahertz regime. We observed evidence that the surface acoustic waves produced mechanical deformations in the polymer and that ensuing nonlinear mechanical dynamics led to unexpectedly large levels of strain and spectral tuning. Our approach provides a design strategy for electrically driven dynamic metasurfaces and fundamental explorations of high-frequency, polymer dynamics in ultraconfined geometries.
Lauren Hoang; Marc Jaikissoon; Çağıl Köroğlu; Zhepeng Zhang; Robert KA Bennett; Jung-Hwan Song; Jerry A Yang; Jung-Soo Ko; Mark L Brongersma; Krishna C Saraswat; Eric Pop; Andrew J Mannix
Understanding the Impact of Contact-Induced Strain on the Electrical Performance of Monolayer WS2 Transistors Journal Article
In: Nano Letters, 2024.
@article{hoang2024understanding,
title = {Understanding the Impact of Contact-Induced Strain on the Electrical Performance of Monolayer WS2 Transistors},
author = {Lauren Hoang and Marc Jaikissoon and \c{C}a\u{g}ıl K\"{o}ro\u{g}lu and Zhepeng Zhang and Robert KA Bennett and Jung-Hwan Song and Jerry A Yang and Jung-Soo Ko and Mark L Brongersma and Krishna C Saraswat and Eric Pop and Andrew J Mannix},
doi = {10.1021/acs.nanolett.4c02616},
year = {2024},
date = {2024-10-04},
journal = {Nano Letters},
abstract = {Two-dimensional (2D) electronics require low contact resistance (RC) to approach their fundamental limits. WS2 is a promising 2D semiconductor that is often paired with Ni contacts, but their operation is not well understood considering the nonideal alignment between the Ni work function and the WS2 conduction band. Here, we investigate the effects of contact size on nanoscale monolayer WS2 transistors and uncover that Ni contacts impart stress, which affects the WS2 device performance. The strain applied to the WS2 depends on contact size, where long (1 μm) contacts (RC ≈ 1.7 kΩ·μm) show a 78% reduction in RC compared to shorter (0.1 μm) contacts (RC ≈ 7.8 kΩ·μm). We also find that thermal annealing can relax the WS2 strain in long-contact devices, increasing RC to 8.5 kΩ·μm. These results reveal that thermo-mechanical phenomena can significantly influence 2D semiconductor\textendashmetal contacts, presenting opportunities to optimize device performance through nanofabrication and thermal budget.},
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pubstate = {published},
tppubtype = {article}
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Two-dimensional (2D) electronics require low contact resistance (RC) to approach their fundamental limits. WS2 is a promising 2D semiconductor that is often paired with Ni contacts, but their operation is not well understood considering the nonideal alignment between the Ni work function and the WS2 conduction band. Here, we investigate the effects of contact size on nanoscale monolayer WS2 transistors and uncover that Ni contacts impart stress, which affects the WS2 device performance. The strain applied to the WS2 depends on contact size, where long (1 μm) contacts (RC ≈ 1.7 kΩ·μm) show a 78% reduction in RC compared to shorter (0.1 μm) contacts (RC ≈ 7.8 kΩ·μm). We also find that thermal annealing can relax the WS2 strain in long-contact devices, increasing RC to 8.5 kΩ·μm. These results reveal that thermo-mechanical phenomena can significantly influence 2D semiconductor–metal contacts, presenting opportunities to optimize device performance through nanofabrication and thermal budget.
Ludovica Guarneri; Qitong Li; Thomas Bauer; Jung-Hwan Song; Ashley P Saunders; Fang Liu; Mark L Brongersma; Jorik van de Groep
Temperature-Dependent Excitonic Light Manipulation with Atomically Thin Optical Elements Journal Article
In: Nano Letters, 2024.
@article{guarneri2024temperature,
title = {Temperature-Dependent Excitonic Light Manipulation with Atomically Thin Optical Elements},
author = {Ludovica Guarneri and Qitong Li and Thomas Bauer and Jung-Hwan Song and Ashley P Saunders and Fang Liu and Mark L Brongersma and Jorik van de Groep},
doi = {10.1021/acs.nanolett.4c00694},
year = {2024},
date = {2024-04-05},
journal = {Nano Letters},
abstract = {Monolayer 2D semiconductors, such as WS2, exhibit uniquely strong light\textendashmatter interactions due to exciton resonances that enable atomically thin optical elements. Similar to geometry-dependent plasmon and Mie resonances, these intrinsic material resonances offer coherent and tunable light scattering. Thus far, the impact of the excitons’ temporal dynamics on the performance of such excitonic metasurfaces remains unexplored. Here, we show how the excitonic decay rates dictate the focusing efficiency of an atomically thin lens carved directly out of exfoliated monolayer WS2. By isolating the coherent exciton radiation from the incoherent background in the focus of the lens, we obtain a direct measure of the role of exciton radiation in wavefront shaping. Furthermore, we investigate the influence of exciton\textendashphonon scattering by characterizing the focusing efficiency as a function of temperature, demonstrating an increased optical efficiency at cryogenic temperatures. Our results provide valuable insights into the role of excitonic light scattering in 2D nanophotonic devices.},
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pubstate = {published},
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Monolayer 2D semiconductors, such as WS2, exhibit uniquely strong light–matter interactions due to exciton resonances that enable atomically thin optical elements. Similar to geometry-dependent plasmon and Mie resonances, these intrinsic material resonances offer coherent and tunable light scattering. Thus far, the impact of the excitons’ temporal dynamics on the performance of such excitonic metasurfaces remains unexplored. Here, we show how the excitonic decay rates dictate the focusing efficiency of an atomically thin lens carved directly out of exfoliated monolayer WS2. By isolating the coherent exciton radiation from the incoherent background in the focus of the lens, we obtain a direct measure of the role of exciton radiation in wavefront shaping. Furthermore, we investigate the influence of exciton–phonon scattering by characterizing the focusing efficiency as a function of temperature, demonstrating an increased optical efficiency at cryogenic temperatures. Our results provide valuable insights into the role of excitonic light scattering in 2D nanophotonic devices.
Brandon Born; Sung-Hoon Lee; Jung-Hwan Song; Jeong Yub Lee; Woong Ko; Mark L Brongersma
Off-axis metasurfaces for folded flat optics Journal Article
In: Nature Communications, vol. 14, iss. 1, pp. 5602, 2023.
@article{born2023off,
title = {Off-axis metasurfaces for folded flat optics},
author = {Brandon Born and Sung-Hoon Lee and Jung-Hwan Song and Jeong Yub Lee and Woong Ko and Mark L Brongersma},
doi = {10.1038/s41467-023-41123-x},
year = {2023},
date = {2023-09-12},
urldate = {2023-09-12},
journal = {Nature Communications},
volume = {14},
issue = {1},
pages = {5602},
abstract = {The overall size of an optical system is limited by the volume of the components and the internal optical path length. To reach the limits of miniaturization, it is possible to reduce both component volume and path length by combining the concepts of metasurface flat optics and folded optics. In addition to their subwavelength component thickness, metasurfaces enable bending conventional folded geometries off axis beyond the law of reflection. However, designing metasurfaces for highly off-axis illumination with visible light in combination with a high numerical aperture is non-trivial. In this case, traditional designs with gradient metasurfaces exhibit low diffraction efficiencies and require the use of deep-subwavelength, high-index, and high-aspect-ratio semiconductor nanostructures that preclude inexpensive, large-area nanofabrication. Here, we describe a design approach that enables the use of low-index (n ≈ 1.5), low-aspect ratio structures for off-axis metagratings that can redirect and focus visible light (λ = 532 nm) with near-unity efficiency. We show that fabricated optical elements offer a very large angle-of-view (110°) and lend themselves to scalable fabrication by nano-imprint lithography.},
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pubstate = {published},
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The overall size of an optical system is limited by the volume of the components and the internal optical path length. To reach the limits of miniaturization, it is possible to reduce both component volume and path length by combining the concepts of metasurface flat optics and folded optics. In addition to their subwavelength component thickness, metasurfaces enable bending conventional folded geometries off axis beyond the law of reflection. However, designing metasurfaces for highly off-axis illumination with visible light in combination with a high numerical aperture is non-trivial. In this case, traditional designs with gradient metasurfaces exhibit low diffraction efficiencies and require the use of deep-subwavelength, high-index, and high-aspect-ratio semiconductor nanostructures that preclude inexpensive, large-area nanofabrication. Here, we describe a design approach that enables the use of low-index (n ≈ 1.5), low-aspect ratio structures for off-axis metagratings that can redirect and focus visible light (λ = 532 nm) with near-unity efficiency. We show that fabricated optical elements offer a very large angle-of-view (110°) and lend themselves to scalable fabrication by nano-imprint lithography.
Qitong Li; Jung-Hwan Song; Fenghao Xu; Jorik van de Groep; Jiho Hong; Alwin Daus; Yan Joe Lee; Amalya C Johnson; Eric Pop; Fang Liu; Mark L Brongersma
A Purcell-enabled monolayer semiconductor free-space optical modulator Journal Article
In: Nature Photonics, vol. 17, iss. 10, pp. 897-903, 2023.
@article{li2023purcell,
title = {A Purcell-enabled monolayer semiconductor free-space optical modulator},
author = {Qitong Li and Jung-Hwan Song and Fenghao Xu and Jorik van de Groep and Jiho Hong and Alwin Daus and Yan Joe Lee and Amalya C Johnson and Eric Pop and Fang Liu and Mark L Brongersma},
doi = {10.1038/s41566-023-01250-9},
year = {2023},
date = {2023-07-23},
urldate = {2023-07-23},
journal = {Nature Photonics},
volume = {17},
issue = {10},
pages = {897-903},
abstract = {Dephasing and non-radiative decay processes limit the performance of a wide variety of quantum devices at room temperature. Here we illustrate a general pathway to notably reduce the detrimental impact of these undesired effects through photonic design of the device electrodes. Our design facilitates a large Purcell enhancement that speeds up competing, desired radiative decay while also enabling convenient electrical gating and charge injection functions. We demonstrate the concept with a free-space optical modulator based on an atomically thin semiconductor. By engineering the plasmonic response of a nanopatterned silver gate pad, we successfully enhance the radiative decay rate of excitons in a tungsten disulfide monolayer by one order of magnitude to create record-high modulation efficiencies for this class of materials at room temperature. We experimentally observe a 10% reflectance change as well as 3 dB signal modulation, corresponding to a 20-fold enhancement compared with modulation using a suspended monolayer in vacuum. We also illustrate how dynamic control of light fields can be achieved with designer surface patterns. This research highlights the benefits of applying radiative decay engineering as a powerful tool in creating high-performance devices that complements substantial efforts to improve the quality of materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
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Dephasing and non-radiative decay processes limit the performance of a wide variety of quantum devices at room temperature. Here we illustrate a general pathway to notably reduce the detrimental impact of these undesired effects through photonic design of the device electrodes. Our design facilitates a large Purcell enhancement that speeds up competing, desired radiative decay while also enabling convenient electrical gating and charge injection functions. We demonstrate the concept with a free-space optical modulator based on an atomically thin semiconductor. By engineering the plasmonic response of a nanopatterned silver gate pad, we successfully enhance the radiative decay rate of excitons in a tungsten disulfide monolayer by one order of magnitude to create record-high modulation efficiencies for this class of materials at room temperature. We experimentally observe a 10% reflectance change as well as 3 dB signal modulation, corresponding to a 20-fold enhancement compared with modulation using a suspended monolayer in vacuum. We also illustrate how dynamic control of light fields can be achieved with designer surface patterns. This research highlights the benefits of applying radiative decay engineering as a powerful tool in creating high-performance devices that complements substantial efforts to improve the quality of materials.
Jung-Hwan Song; Philippe Lalanne; Min-Kyo Seo; Mark L Brongersma
Transfer Matrix Method-Compatible Model for Metamaterial Stacks Journal Article
In: ACS Photonics, vol. 10, iss. 8, pp. 2948-2954, 2023.
@article{song2023transfer,
title = {Transfer Matrix Method-Compatible Model for Metamaterial Stacks},
author = {Jung-Hwan Song and Philippe Lalanne and Min-Kyo Seo and Mark L Brongersma},
doi = {10.1021/acsphotonics.3c00693},
year = {2023},
date = {2023-07-18},
urldate = {2023-07-18},
journal = {ACS Photonics},
volume = {10},
issue = {8},
pages = {2948-2954},
abstract = {Mean-field theory-based effective refractive index models are widely used to design optical metamaterials and interpret their optical properties. However, emerging applications where metamaterials are embedded into layered device architectures require a detailed consideration of the metamaterial’s dispersive properties and interfacial boundary conditions, which are beyond the scope of the mean-field theory for homogeneous bulk media. Here, we describe an approach to calculate the optical transfer function for one-dimensional optical metamaterials that includes the dispersive properties of the effective index as well as the effective interfacial impedance. We address the boundary conditions at a metamaterial interface by a complex-valued effective interfacial impedance. Combined with the effective refractive index, the effective interfacial impedance enables a description of the optical transfer for 1D optical metamaterials with the transfer matrix method. This opens up scalable design of one-dimensional multilayered structures that include metamaterial layers. We illustrate the approach with the design of a metamaterial-based antireflection coating for a thin-film photodetector.},
keywords = {},
pubstate = {published},
tppubtype = {article}
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Mean-field theory-based effective refractive index models are widely used to design optical metamaterials and interpret their optical properties. However, emerging applications where metamaterials are embedded into layered device architectures require a detailed consideration of the metamaterial’s dispersive properties and interfacial boundary conditions, which are beyond the scope of the mean-field theory for homogeneous bulk media. Here, we describe an approach to calculate the optical transfer function for one-dimensional optical metamaterials that includes the dispersive properties of the effective index as well as the effective interfacial impedance. We address the boundary conditions at a metamaterial interface by a complex-valued effective interfacial impedance. Combined with the effective refractive index, the effective interfacial impedance enables a description of the optical transfer for 1D optical metamaterials with the transfer matrix method. This opens up scalable design of one-dimensional multilayered structures that include metamaterial layers. We illustrate the approach with the design of a metamaterial-based antireflection coating for a thin-film photodetector.
