arXiv subjects

Hiroshi Sugimoto

Publications and source records attributed to Hiroshi Sugimoto.

9 recordsLinked to original sources

arXiv2026

Probe- and Substrate-Dependent Visibility of Mie Resonances in Silicon Nanospheres

Silicon nanospheres are high-quality optical resonators and promising building blocks for Mie-tronic devices. While the Mie resonances of an isolated sphere are well understood, practical implementations require substrates that inevitably modify the measured optical response. Here, we investigate how substrates alter the observable spectrum of individual nanospheres, focusing on three fundamentally different cases: a thin silicon nitride membrane, that emulates a free-standing particle, bulk silicon, which is common in experiments, and gold, where mirror charges lead to hybrid optical modes. Cathodoluminescence and dark-field spectroscopy, combined with electrodynamic simulations, show that the measured resonances are not intrinsic to the particle but depend strongly on the environment and the excitation mechanism. We find that substrate-induced effects and probe-specific selection rules can suppress, enhance, or even invert the spectral signatures of electric and magnetic modes. These results provide practical guidelines for interpreting and designing substrate-supported dielectric resonators for Mie-tronic applications.

physics.optics↗

arXiv2025

Color Routing and Beam Steering of Single-Molecule Emission with a Spherical Silicon Nanoantenna

Single-photon emitters radiate as electric dipoles, which limits light collection efficiency and complicates integration into flat photonic devices. Developing nanophotonic structures capable of directing photon emission with tunable angular distributions in the visible spectrum has been pursued for applications ranging from integrated optical systems to discrimination of molecular species. To date, such directional control has been achieved using components whose overall footprint is larger than the emission wavelength and often rely on lossy plasmonic components. Here, we employ the DNA origami technique for deterministic nanoscale assembly, positioning single fluorophores in nanometric proximity to a single silicon spherical nanoparticle and demonstrate unidirectional emission with forward-to-backward intensity ratios up to ~7 dB. Furthermore, we show that a single silicon nanosphere antenna can function as a color router or a beam steerer depending on its size, emitter spectral range and emitter-nanoparticle distance.

physics.optics↗

arXiv2025

Polymer-Shell Coating of Mie-Resonant Silicon Nanospheres for Controlled Fabrication of Self-Assembled Monolayer

A polymer shell offers a unique opportunity to tailor structural and optical properties of optically functional nanoparticles and their ensembles. Here, we develop a process to coat Mie-resonant silicon nanospheres (Si NSs) with a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel shell. We show formation of a PNIPAM shell of controlled thickness from the change of the hydrodynamic diameter and study the effect of thermoresponsive shrinkage and expansion of the shell on the Mie resonance of a Si NS. We then demonstrate that Si NSs with PNIPAM shells enable fabrication of cluster-free, self-assembled monolayers of Si NSs, in which distances between NSs are controlled by the PNIPAM shell thickness.

cond-mat.mtrl-sci↗

arXiv2025

Distance dependent interaction between a single emitter and a single dielectric nanoparticle using DNA origami

Optical nanoantennas can manipulate light-matter interactions at the nanoscale, modifying the emission properties of nearby single photon emitters. To date, most optical antennas are based on metallic nanostructures that exhibit unmatched performance in terms of electric field enhancement but suffer from substantial ohmic losses that limit their applications. To circumvent these limitations, there is a growing interest in alternative materials. In particular, high-refractive-index dielectrics have emerged as promising candidates, offering negligible ohmic losses, and supporting both electric and magnetic resonances in the visible and near-infrared range that can unlock novel effects. Currently, the few available studies on dielectric nanoantennas focus on ensemble measurements. Here, we exploit the DNA origami technique to study the interaction between silicon nanoparticles and organic fluorophores at the single molecule level, in controlled geometries and at different spectral ranges within the visible spectrum. We characterize their distance-dependent interaction in terms of fluorescence intensity and lifetime, revealing a significant modification of the decay rate together with minimal quenching and a high fluorescence quantum yield even at short distances from the dielectric nanoparticle. This work demonstrates the advantages of dielectric nanoantennas over their metallic counterparts and paves the way for their applications in single-molecule spectroscopy and sensing.

physics.optics↗

arXiv2024

Routing Light Emission from Monolayer MoS$_2$ by Mie Resonances of Crystalline Silicon Nanospheres

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 towards 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 wavelengths 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.

physics.optics↗

arXiv2024

Beam Dynamics Issues in the SuperKEKB

This article reviews the beam dynamics issues, such as intra-beam scattering, beam-beam interaction, lattice nonlinearity, and space charge, in SuperKEKB before its commissioning.

physics.acc-ph↗

arXiv2023

Universal click-chemistry approach for the DNA functionalization of nanoparticles

Nanotechnology has revolutionized the fabrication of hybrid species with tailored functionalities. A milestone in this field is the DNA conjugation of nanoparticles, introduced almost 30 years ago, which typically exploits the affinity between thiol groups and metallic surfaces. Over the last decades, developments in colloidal research have enabled the synthesis of an assortment of non-metallic structures, such as high-index dielectric nanoparticles, with unique properties not previously accessible with traditional metallic nanoparticles. However, to stabilize, integrate and provide further functionality to non-metallic nanoparticles, reliable techniques for their functionalization with DNA will be crucial. Here, we combine well-established dibenzylcyclooctyne-azide click-chemistry with a simple freeze-thaw method to achieve the functionalization of silica and silicon nanoparticles, which form exceptionally stable colloids with a high DNA surface density of 0.2 molecules/nm2. Furthermore, we demonstrate that these functionalized colloids can be self-assembled into high-index dielectric optical antennas with a yield of up to 78% via the use of DNA origami. Finally, we extend this method to functionalize other important nanomaterials, including oxides, polymers, core-shell and metal nanostructures. Our results indicate that the method presented herein serves as a crucial complement to conventional thiol functionalization chemistry and thus greatly expands the toolbox of DNA-functionalized nanoparticles currently available.

physics.chem-ph↗

arXiv2022

Disentangling cathodoluminescence spectra in nanophotonics: particle eigenmodes vs transition radiation

Cathodoluminescence spectroscopy performed in an electron microscope has proven a versatile tool for analysing the near- and far-field optical response of plasmonic and dielectric nanostructures. Nevertheless, the transition radiation produced by electron impact is often disregarded in the interpretation of the spectra recorded from resonant nanoparticles. Here we show, experimentally and theoretically, that transition radiation can by itself generate distinct resonances which, depending on the time of flight of the electron beam inside the particle, can result from constructive or destructive interference in time. Superimposed on the eigenmodes of the investigated structures, these resonances can distort the recorded spectrum and lead to potentially erroneous assignment of modal characters to the spectral features. We develop an intuitive analogy that helps distinguish between the two contributions. As an example, we focus on the case of silicon nanospheres, and show that our analysis facilitates the unambiguous interpretation of experimental measurements on Mie-resonant nanoparticles.

cond-mat.mes-hall↗

arXiv2021

Ultraviolet Mie resonances in computationally discovered boron phosphide nanoparticles

Controlling ultraviolet light at the nanoscale using optical Mie resonances holds great promise for a diverse set of applications, such as lithography, sterilization, and biospectroscopy. However, Mie resonances hosted by dielectric nanoantennas are difficult to realize at ultraviolet wavelengths due to the lack of both suitable materials and fabrication methods. Here, we systematically search for improved materials by computing the frequency dependent optical permittivity of 338 binary semiconductors and insulators from first principles, and evaluate their potential performance as high refractive index materials using Mie theory. Our analysis reveals several interesting candidate materials among which boron phosphide (BP) appears particularly promising. We then prepare BP nanoparticles and demonstrate that they support Mie resonances at visible and ultraviolet wavelengths using both far-field optical measurements and near-field electron energy-loss spectroscopy. We also present a laser reshaping method to realize spherical Mie-resonant BP nanoparticles. With a refractive index above 3 and low absorption losses, BP nanostructures advance Mie optics to the ultraviolet.

physics.optics↗