Jeonghyeon Kim | EPFL Graph Search

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Optical manipulation of plasmonic nanoparticles: Applications in surface chemistry and nano-optics

Jeonghyeon Kim

Optical tweezers are devices that can manipulate nano- and microparticles using a laser. The principle of optical tweezers is to apply a force to an object using the momentum of light. This force is very small, but it is sufficient to move things in the microscopic world. Consequently, optical tweezers can grab, move, and even assemble objects on a much smaller scale, just like human hands.Optical tweezers have revolutionized the way scientists experiment with small particles in many fields of science, and their utility as a tool for understanding nanoscale processes is continuously expanding. In this dissertation, we discuss the new application possibilities of optical tweezers in two distinct disciplines: surface sciences and nano-optics. We first employ optical tweezers in surface science by trapping gold nanoparticles at an interface and observing their motion. Due to their strong scattering and absorption, gold nanoparticles are a superb optical probe and a nanoscale heater that can be remotely controlled by light. They can provide heat to the molecules adsorbing on the surrounding surfaces and stimulate further interactions. We compare these findings to those obtained using non-thermal dielectric probes and find that heat-induced effects are indeed present in our experiments. This study demonstrates that gold nanoparticles are highly effective probes that can apply heat locally and examine the resulting interaction in real time. Thermal phenomena exist in many scientific disciplines; hence, the optically trapped gold nanoparticles can serve as a valuable tool for investigating these phenomena at the nanoscale.We then assemble gold nanoparticles into a complex structure using optical tweezers. Individually, gold nanoparticles possess exceptional optical properties. However, when two or more of them are arranged adjacently, their properties become even more intriguing due to the strong interaction of the near fields, which is one of the most vital areas of nano-optics. Optical tweezers offer a unique method for organizing these particles in a controlled manner, producing a strong near-field coupling. We examine this coupling behavior by numerically simulating and experimentally realizing optical assemblies. This concept of tweezer-organized assemblies can create exciting opportunities for constructing three-dimensional nanoscale architectures beyond the current technologies that have evolved from conventional semiconductor device fabrication processes. Moreover, optical tweezers enable the flexible combination of structures derived from distinct methods, such as colloidal particles and lithographically defined nanostructures.

EPFL2023

Trap-and-Track for Characterizing Surfactants at Interfaces

Jeonghyeon Kim, Olivier Martin

Understanding the behavior of surfactants at interfaces is crucial for many applications in materials science and chemistry. Optical tweezers combined with trajectory analysis can become a powerful tool for investigating surfactant characteristics. In this study, we perform trap-and-track analysis to compare the behavior of cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC) at water–glass interfaces. We use optical tweezers to trap a gold nanoparticle and statistically analyze the particle’s movement in response to various surfactant concentrations, evidencing the rearrangement of surfactants adsorbed on glass surfaces. Our results show that counterions have a significant effect on surfactant behavior at the interface. The greater binding affinity of bromide ions to CTA+ micelle surfaces reduces the repulsion among surfactant head groups and enhances the mobility of micelles adsorbed on the interface. Our study provides valuable insights into the behavior of surfactants at interfaces and highlights the potential of optical tweezers for surfactant research. The development of this trap-and-track approach can have important implications for various applications, including drug delivery and nanomaterials.

2023

A Low-Temperature Annealing Method for Alloy Nanostructures and Metasurfaces: Unlocking a Novel Degree of Freedom

Jeonghyeon Kim, Olivier Martin, Debdatta Ray, Christian Santschi, Hsiang-Chu Wang

The material and exact shape of a nanostructure determine its optical response, which is especially strong for plasmonic metals. Unfortunately, only a few plasmonic metals are available, which limits the spectral range where these strong optical effects can be utilized. Alloying different plasmonic metals can overcome this limitation, at the expense of using a high-temperature alloying process, which adversely destroys the nanostructure shape. Here, a low-temperature alloying process is developed where the sample is heated at only 300 degrees C for 8 h followed by 30 min at 450 degrees C and Au-Ag nanostructures with a broad diversity of shapes, aspect ratios, and stoichiometries are fabricated. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses confirm the homogeneous alloying through the entire sample. Varying the alloy stoichiometry tunes the optical response and controls spectral features, such as Fano resonances. Binary metasurfaces that combine nanostructures with different stoichiometries are fabricated using multiple-step electron-beam lithography, and their optical function as a hologram or a Fresnel zone plate is demonstrated at the visible wavelength of lambda = 532 nm. This low-temperature annealing technique provides a versatile and cost-effective way of fabricating complex Au-Ag nanostructures with arbitrary stoichiometry.

WILEY-V C H VERLAG GMBH2022