arXiv subjects

Prabhat Verma

Publications and source records attributed to Prabhat Verma.

4 recordsLinked to original sources

arXiv2026

Real-time visualization of plasmonic nanoparticle growth dynamics by high-speed atomic force microscopy

Plasmonic nanoparticles generate strongly localized and enhanced light field through localized surface plasmon resonance, thereby playing a central role in plasmonics and nanophotonics. Because the optical properties of plasmonic nanoparticles are highly sensitive to their size and shape, nanoscale visualization of nanoparticle growth is crucial for detailed understanding of growth mechanisms and precise control of particle geometry. However, it is not possible to visualize the rapid growth dynamics using conventional imaging techniques. In this study, we demonstrate in-situ real-time observation of silver nanoparticle (AgNP) growth dynamics at the single-particle level using high-speed atomic force microscopy (HS-AFM). We employed a photoreduction method, which enables reliable control of AgNP formation by laser irradiation. By integrating a stand-alone tip-scan HS-AFM with an optical setup for photoreduction, we successfully captured real-time movies showing the nucleation and subsequent growth of AgNPs at the single-particle level. Furthermore, quantitative single-particle analysis revealed particle-to-particle variations in growth dynamics. The growth dynamics were further studied at different laser intensities, revealing intensity-dependent growth rates and the balance between nucleation and growth. This study establishes HS-AFM as a novel microscopic platform for in-situ visualization of plasmonic nanoparticle growth and will contribute to advances in plasmonics and materials science.

physics.chem-ph↗

arXiv2025

Comparison of near-field light intensities: plasmon nanofocusing vs localized plasmon resonance

The localized surface plasmon resonance of metallic nanostructures produces strongly localized and enhanced near-field light, significantly contributing to nanophotonics research and applications. Plasmon nanofocusing represents another method for generating near-field light through the propagation and condensation of plasmons on tapered plasmonic structures. In both methods, the intensity of near-field light is a critical aspect for many applications. In this study, we numerically inspect and compare the intensities of near-field light generated by either localized plasmon resonance or plasmon nanofocusing. To account for the light-induced changes in the optical properties of plasmonic structures, which in turn influence the near-field light intensity, we couple electromagnetic and thermal calculations to consider in a fully self-consistent manner the effects of the incident light and the light-induced temperature rise within the metal. A gold nanorod and a cone were adopted for exciting the localized plasmon resonance and plasmon nanofocusing, respectively. We find that plasmon nanofocusing generates approximately 1.5 times as strong near-field light as localized plasmon resonance. Our research provides a necessary foundation for generating near-field light, which is crucial for advancing the applications of near-field optics.

physics.optics↗

arXiv2023

In-situ real-time observation of photo-induced nanoscale azo-polymer motions using high-speed atomic force microscopy combined with an inverted optical microscope

High-speed atomic force microscopy (HS-AFM) is an indispensable technique in the biological field owing to its excellent imaging capability for the real-time observation of biomolecules with high spatial resolution. Furthermore, recent developments have established a tip-scan stand-alone HS-AFM that can be combined with an optical microscope, drastically improving its versatility for studying various complex phenomena. Although HS-AFM has mainly been used in biology, it has considerable potential to contribute to various research fields. One of the great candidates is a photoactive material, such as an azo-polymer, which plays a vital role in multiple optical applications because of its unique nanoscale motion under light irradiation. In this study, we demonstrate the in-situ real-time observation of nanoscale azo-polymer motion by combining tip-scan HS-AFM with an optical system, allowing HS-AFM observations precisely aligned with a tightly focused laser position. We successfully observed the dynamic evolution of unique morphologies in azo-polymer films, attributed to photoinduced nano-movements. Moreover, real-time topographic line profile analyses facilitated precise and quantitative investigations of morphological changes, which provided novel insights into the deformation mechanism. This significant demonstration would pave the way for the application of HS-AFM in wide research fields, from biology to material science and physical chemistry.

physics.optics↗

arXiv2022

Nanoscale optical switching of photochromic material by ultraviolet and visible plasmon nanofocusing

Optical control of electronic properties is essential for future electric devices. Manipulating such properties has been limited to the microscale in spatial volume due to the wave nature of light; however, scaling down the volume is in extremely high demand. In this study, we demonstrate optical switching within a nanometric spatial volume in an organic electric material. Photochromic materials such as diarylethene derivatives exhibit semiconducting and insulating properties on ultraviolet (UV) and visible light, respectively, which are promising for optical switching and memory. To control the wavelength between visible and UV light at the nanoscale, we employed plasmon nanofocusing, which allows the creation of a nanolight source at the apex of a metallic tapered structure over a broad frequency range by focusing of propagating plasmons. We utilized an aluminum tapered structure and realized in-situ wavelength control between visible and UV light at the nanoscale. Using this method, nanoscale optical switching between the two states of diarylethene was demonstrated. The switching performance was confirmed for at least nine cycles without degradation. This demonstration would make a significant step forward toward next-generation nanoscale optoelectronic devices and stimulate diverse scientific fields owing to the unique concept of broadband plasmon nanofocusing.

physics.optics↗