Pulsed Laser-Ablation-Induced Fabrication of Metal Nanoparticles in Liquids

This review deals with mechanistic aspects of pulsed laser-induced fabrication of noble metal nanoparticles. This fabrication method is developed over the past two decades and has attracted much attention of researchers in various fields including laser chemistry, materials chemistry and nanobiotechnology. Highlights of this review are advantages and disadvantages inherent to the fabrication method involving complex processes such as vapor bubble generation under high-intensity laser irradiation of microscopic metal surfaces, leading to nanoparticle formation

コウIF ロンブン ジュリ オ メザシタ ヒカリ ナノ テクノロジー ケンキュウ ネットワーク ケイセイ

We made various attempts to publish high impact factor papers. Here we describe such efforts and research activities carried out in fiscal year 2010. As a research, pulsed laser-induced morphological transformation and size-reduction of colloidal gold nanoparticles in the aqueous phase were investigated using transient absorption spectroscopy and transmission electron microscopy (TEM). Femtosecond laser-induced fragmentation of gold nanoparticles within 100 ps after the laser pulse is interpreted in terms of the Coulomb explosion mechanism. On the other hand, nanosecond laser-induced size-reduction of gold nanoparticles is in good agreement with the photothermal evaporation mechanism that is based on heating of particles to temperatures above the boiling point of gold (3100 K). Here, the experimentally observed fragmentation thresholds were well-reproduced by simulations based on electron and lattice temperature models and by considering the dissipation of heat into the surrounding medium. The numerical method described herein has the advantage of identifying the fragmentation mechanism by considering pulse duration- and energy-dependent thresholds

Metallic Nanoparticle Plasmonic Nanoheater

Plasmonic nanoparticles have emerged as unique nanoheaters that selectively heat the local environment of the particles. This local heating finds various applications - from photothermal cancer therapy and photothermal imaging to photothermally-enhanced catalytic activity and photothermal thermoelectric devices. This review deals with the interactions of lasers with plasmonic nanoparticles – from fundamental aspects of plasmonic heating to practical applications such as drug delivery, phase separation of thermoresponsive polymers, hydrothermal reactions, and glass nanoprocessing, to name a few. Plasmonic heating helps to reveal fundamental physics such as phase transition and phase separation at the nanoscale. Besides, plasmonic heating is valuable for microscale fabrication and manipulation. Further, plasmonics incorporating photothermal effects can be a powerful technique for temperature sensing

Flow-Induced Transport via Optical Heating of a Single Gold Nanoparticle

Optothermal trapping has gained increasing popularity in manipulation such as selecting, guiding, and positioning submicron objects because of a few mW laser power much lower than that required for optical trapping. The optotothermal trapping uses thermal gradient-induced phoretic motions, but the underlying physics of driving force has not been fully understood. In this study, we performed optotothermal trapping of 500-nm-diameter colloidal silica via a continuous laser illumination of a single gold nanoparticle from the bottom in a closed chamber. Under illumination, the tracer particles were attracted to the gold nanoparticle and trapped. Notably, the direction of migrating particles was always to hot gold nanoparticle regardless of the configuration of gold nanoparticle placed at two opposite sides of the chamber, on the bottom surface of an upper substrate (ceiling) or on the top surface of a lower substrate (floor). The previous interpretation based on thermal convective flow from the bottom to the top and circulating inside the chamber was only applicable to floor configuration and failed to explain our observation for ceiling. Instead, temperature-induced Marangoni effect at the water/superheated water interface is likely to play a role. This study promoted a better understanding of the driving mechanism in optothermal trapping. Moreover, as an application of the single-particle platform, we showed the photothermal phase separation-induced microdroplet formation of thermoresponsive polymers and the coating of non-thermoresponsive polymers on nanoparticles

Plasmonic hot-electron transfer and nanofabrication

Localized surface plasmon resonance (LSPR) of plasmonic nanoparticles and nanostructures has attracted wide attention because the nanoparticles exhibit a strong near-field enhancement through interaction with visible light, enabling subwavelength optics and sensing at the single-molecule level. The extremely fast LSPR decays have raised doubts that such nanoparticles have use in photochemistry and energy storage. Recent studies have demonstrated the capability of such plasmonic systems in producing LSPR-induced hot electrons that are useful in energy conversion and storage when combined with electron-accepting semiconductors. Due to the femtosecond timescale, hot-electron transfer is under intense investigation to promote ongoing applications in photovoltaics and photocatalysis. Concurrently, hot-electron decay results in photothermal responses or plasmonic heating. Importantly, this heating has received renewed interest in photothermal manipulation, despite the developments in optical manipulation using optical forces to move and position nanoparticles and molecules guided by plasmonic nanostructures. To realize plasmonic heating-based manipulation, photothermally generated flows, such as thermophoresis, the Marangoni effect and thermal convection, are exploited. Plasmon-enhanced optical tweezers together with plasmon-induced heating show potential as an ultimate bottom-up method for fabricating nanomaterials. We review recent progress in two fascinating areas: solar energy conversion through interfacial electron transfer in gold-semiconductor composite materials and plasmon-induced nanofabrication

A Concrete Treatment of Efficient Continuous Group Key Agreement via Multi-Recipient PKEs

Continuous group key agreements (CGKAs) are a class of protocols that can provide strong security guarantees to secure group messaging protocols such as Signal and MLS. Protection against device compromise is provided by commit messages: at a regular rate, each group member may refresh their key material by uploading a commit message, which is then downloaded and processed by all the other members. In practice, propagating commit messages dominates the bandwidth consumption of existing CGKAs. We propose Chained CmPKE, a CGKA with an asymmetric bandwidth cost: in a group of N members, a commit message costs O(N) to upload and O(1) to download, for a total bandwidth cost of O(N). In contrast, TreeKEM costs (log N) in both directions, for a total cost (N log N). Our protocol relies on generic primitives, and is therefore readily post-quantum. We go one step further and propose post-quantum primitives that are tailored to \Chained CmPKE, which allows us to cut the growth rate of uploaded commit messages by two or three orders of magnitude compared to naive instantiations. Finally, we realize a software implementation of Chained CmPKE. Our experiments show that even for groups with a size as large as N = 2^10, commit messages can be computed and processed in less than 100 ms

Liquid-Liquid Interface Can Promote Micro-Scale Thermal Marangoni Convection in Liquid Binary Mixtures

Liquid-liquid phase separation, a physical transition in which a homogeneous solution spontaneously demixes into two coexisting liquid phases, has been a key topic in the thermodynamics of two-component systems and may find applications in separation, drug delivery, and protein crystallization. Here we applied a microscale temperature gradient using optothermal heating of a gold nanoparticle to overcome the experimental difficulties inherent in homogeneous heating: we aimed at highlighting precise structural development by avoiding randomly nucleating/growing microdomains. In response to laser illumination, a single gold nanoparticle immersed in a binary mixture of aqueous 2,6-dimethylpiridine (lutidine) and N-isopropylpropionamide (NiPPA) was clearly sensitive to the phase transition of the surrounding liquid as demonstrated by light scattering signals, spectral red-shifts and bright-spot images. The local phase separation encapsulating the gold nanoparticle resulted in immediate formation and growth of an organic-rich droplet which was confirmed by Raman spectroscopy. Remarkably, the droplet was stable under a non-equilibrium steady-state heating condition because of strong thermal confinement. Microdroplet growth was ascribed to thermocapillary flow induced by a newly formed liquid-liquid interface around the hot gold nanoparticle. Based upon a tracer experiment and numerical simulation, it is deduced that the transport of solute to the high temperature area is driven by this thermocapillary flow. This study enhances our understanding of phase separation in binary mixtures induced by microscale temperature confinement