Research Fields
Surface nanotechnology and material science for sensing and photoenergy applications
Research fields: Photonics Nano-Engineering group focuses on the study of novel functionalities originating from interfacial electronic/vibronic excitations and photonic properties in nano and micrometer-scale systems.
Outline of Our Research
We study rational design of the devices and synthesis of wavelength conversion and photoenergy converted devices adopting lithographic dielectric nanostructures and chemical nano-synthesis routes. For example we study high-sensitivity and precise sensing methods working in the near to the mid infrared region, including surface-enhanced infrared spectroscopy supported by all-dielectric nanophotonic materials. We also develop infrared photothermal spectroscopic devices as well as UV and NIR photodetectors and light emitters.
Fig. 1. Schematics of nano-structured high-sensitivity bio sensors and photothermal converters working in the mid-to-near infrared and ultraviolet region.
Recent Research Topics
Development of Infrared Photothermal Devices
We realized a narrowband thermal emitter when it is fabricated with refractive dielectrics and highly conductive refractory boron-based ceramics that can sustain well above 1000 deg C. The combination with appropriate perfect absorber design and low-loss metals will open a new avenue for innovative technologies not only in true-temperature thermography, but also create industry seeds for low-temperature rapid heating by material-specific infrared heaters. One of promising candidate material is Ni–based intermetallic compounds as high-temperature materials for infrared (IR) thermophotonic applications. We investigated by using density functional theory calculations, experimental characterization, and microdevice simulations to evaluate the optical performance of several Ni–Al compounds. Among the investigated materials, NiAl demonstrates the most favorable optical properties in the IR region, comparable to those of conventional plasmonic materials, serving as a promising robust material platform for high-temperature IR thermophotonics.
Fig. 2. Thermal emitter based on boron-based low-loss plasmonic ceramics and refractory dielectric multilayer device.
Fig. 3. Electromagnetic simulations for different types of thermal emitters using NiAl. Copied from Figure 5 in [5] (CC BY 4.0).
Materials Discovery for Infrared Photonics/Plasmonics
We presents our extensive research on the high-throughput screening of more than 2,000 plasmonic compounds to optimize the performance of infrared and thermophotonic microdevices. The materials database was collected using the AtomWork-Adv provided by the Materials Data Platform (MDPF) of the National Institute for Materials Science (NIMS). By systematically calculating and evaluating the optical properties of candidate materials, this approach efficiently isolates candidates with excellent optical performance from a vast compositional space. Especially, this comprehensive methodology delivers clear, actionable guidelines for the rational selection and benchmarking of high-performance materials in infrared photonics.
Figure 4: Screening workflow for infrared plasmonic candidates.
Discovery of bioinspired carbonized-polymer microemitters
Our bioinspired carbonized-polymer microspheres provide solid-state fluorescence across the visible spectrum and an optical cavity in the same structure. Excitation-dependent emission is sharpened by whispering-gallery resonances, enabling adaptable full-color output without changing the material or geometry. This integrated photonic-chemical platform supports white-light generation, sensitive chemical sensing, and encrypted anti-counterfeiting [1].
Fig. 5. A single carbonized-polymer microsphere provides excitation-tunable full-color resonances for lighting, sensing, and security. Copied from Visual Abstract in [1] (CC BY 4.0).
Photon recycling and chromaticity-adaptable white light emission
We integrate single-component, metal-free luminescent carbon materials with photonic microcavities to redistribute their emission toward the yellow and red. Resonant photons are confined, reabsorbed, and recycled, producing efficient white light without rare-earth emitters or chemical modification. Tuning the cavity stop band provides cool, pure, and warm white emission along the black-body locus [2].
Fig. 6. Photon recycling in a photonic microcavity converts the blue/cyan emission of metal-free carbon materials into chromaticity-adaptable white light. Copied from Figure 1 in [2] (CC BY 4.0).
Materials technology for anticounterfeit and covert printing
We developed gram-scale, rare-earth-metal-free carbonized-polymer microspheres by hydrothermal processing with natural peptide cross-linking. Their microstructure suppresses aggregation-induced quenching, while extended conjugated emitters generate strong deep-red-to-near-infrared fluorescence. Each sphere also acts as a whispering-gallery microresonator, yielding excitation-tunable spectral barcodes for unclonable security labels [3].
Fig. 7. Biomass-derived carbonized-polymer microspheres combine red-to-NIR fluorescence with whispering-gallery spectral barcodes. Copied from Figure 7 in [1] (CC BY 4.0)
Development of New Dielectric Metasurfafces
Quasi-bound states in the continuum (qBICs) have attracted considerable research interest across a wide range of applications owing to their high quality (Q) factors and strong electric-field enhancement. In our group, we develop BIC-based metasurfaces with Q factors exceeding 100,000, enabling enhanced light–matter interactions at the nanoscale for applications including single-molecule biosensing/imaging, infrared spectroscopy, vibrational strong coupling, and light-emitting devices. The strong interaction between the localized electric field of a qBIC and a virus-sized nanoparticle enables the experimental observation of step-like resonance-wavelength shifts, providing a signature of individual particle-binding events. Combined with their free-space accessibility, BIC metasurfaces offer a user-friendly platform for real-time investigation of nanoscale binding dynamics and label-free biosensing at the ultimate single-entity limit.
Fig. 8. BIC-based metasurfaces.
Surface-enhanced vibrational spectroscopy using silicon metasurfaces
We use low-loss silicon metasurfaces to couple high-Q quasi-bound states in the continuum (qBICs) with molecular vibrations in the mid-infrared. Adjusting structural asymmetry controls radiative loss and continuously tunes the interaction from weak to strong coupling. An optimal asymmetry maximizes the PMMA vibrational signal, providing a CMOS-compatible route to highly sensitive surface-enhanced infrared spectroscopy [4].
Fig. 9. Structural-asymmetry control tunes qBIC–molecule coupling and enhances infrared vibrational fingerprints. Copied from Figure 1 in [4] (CC BY 4.0).
References
-
[1] B. K. Barman, D. Hernández-Pinilla et al., ACS Appl. Mater. Interfaces 16(17), 22312 (2024)
DOI: https://doi.org/10.1021/acsami.3c18035 -
[2] B. K. Barman, D. Hernández-Pinilla et al., Advanced Science 11(41), 2407090 (2024)
DOI: https://doi.org/10.1002/advs.202407090 -
[3] B. K. Barman, Hiroyuki Yamada, Keisuke Watanabe et al., Advanced Science 11(30), 2400693 (2024)
DOI: https://doi.org/10.1002/advs.202400693 -
[4] K. Watanabe, H. R. Devi, M. Iwanaga, and T. Nagao, Adv. Opt. Mater. 12(6), 2301912 (2024)
DOI: https://doi.org/10.1002/adom.202301912 -
[5] T. D. Ngo, T. P. Tran, H. D. Ngo, and T. Nagao, Advanced Photonics Research 6(4), 2400093 (2025)
DOI: https://doi.org/10.1002/adpr.202400093