PMMA-BN composites incorporated with Au nanoparticle fabricated by laser ablation

As a class of layered materials, two dimensional (2D) materials have attracted great attention all around the world due to their inherent use for next generation nano technology devices. We can see 2D materials including carbon in our daily life and at many places, for instance, graphite, diamond and so on. New study is also being conducted to produce new functional materials by combining 2D material and polymer. Hexagonal boron nitride (h-BN) which is one kind of 2D material is dispersed in Poly methyl methacrylate (PMMA) or poly styrene (PS). The composite material of h-BN coated with polymer shows an improvement in the properties such as the higher thermal conductivity and higher mechanical strength. In this study, the composite material of PMMA, h-BN and gold nanoparticles has been synthesized. Boron nitride nano-structures were prepared by nanosecond laser ablation in acetone and was carried out at room temperature with laser ablation time of 120 min. The PMMA films were made by PMMA granules dissolved in acetone solvent and then mix with h-BN and gold colloid solution. The prepared composite films were characterized by scanning electron microscopy (SEM), and UV-vis spectroscopy. Such type of unique 2D nano-composite materials make their mark for the future exploitation in electronics and nanocomposite-related applications

Photothermal dynamics of micro-glass beads coated with gold nanoparticles in water : Fine bubble generation and fluid-induced laser trapping

In this study, gold nanoparticles were heterogeneously deposited onto the surface of glass beads through a gold ion reduction method to obtain “plasmonic beads.” The plasmonic beads in pure water were illuminated with a visible continuous-wave laser through an objective lens. Using relatively lower-powered laser, the plasmonic beads were optically trapped and aggregated the other beads over an area much greater than the focal point. On the other hand, using a high-powered laser (> 20 mW/µm2) produced microbubbles in water. Thus, the plasmonic beads studied herein can act as optically controllable fluid and microbubble generators

Photoelectron detection from transient species in organic semiconducting thin films by dual laser pulse irradiation

An Nd3+:YAG pulsed laser was employed as a light source for two-photon photoemission from organic semiconducting thin films in low vacuum and air. Photoionization by the two-photon process was confirmed in both the environments by measuring photoemission current. By constructing a pump–probe system, photoemissions from transient species formed by the pump light irradiation were detected by probe light irradiation as a result of a linear increase in the photocurrent with the pump power via a one-photon process. Thus, we propose a novel method called two-photon photoelectron yield spectroscopy to determine the excited-state energy levels in ambient environments

Femtosecond transient absorption spectroscopy of laser-ablated graphite and reduced graphene oxide for optical switching behavior

Carbon based materials are considered as a rewarding contestant for optical devices due to its novel properties. In this study, graphite is laser-ablated and different analytical methods such as XRD and Raman spectroscopy are used to evaluate the crystalline nature. In XRD, it indicates the decreased intensity after laser ablation but no change in peak positions resulted as graphite is very strong and hard material. Scanning electron microscopy (SEM) used to evaluate structural characteristics shows the overlapping layered structure after ablation. Reduced graphene oxide (rGO) is prepared by using modified Hummers' method and reduced it by thermal reduction method. UV–Vis spectra confirmed the peaks of graphite and rGO at 274 nm and 267 nm, respectively. To study the carrier relaxation dynamics of graphite and rGO, ultrafast Visible-pump/NIR-probe femtosecond transient absorption spectroscopy was used. Carrier relaxation occurred between 260 and 309 fs even after laser ablation damage, which is useful for future application of optical switching under high laser repetition

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

Effects of the solvent during the preparation of MoS2 nanoparticles by laser ablation

Pulsed laser ablation in liquid is a well-known and effective method which can be used to prepare the various nanostructures. However, ablated samples have various problems such as wide size distribution, and effect of solvent to sample during laser ablation in liquid has not been well understood. In response to these problems, in this study, we prepared nanoparticles by irradiating nanosecond laser to samples using different solvents. The experimental results of prepared samples were compared, and we evaluated how the different solvents affect to their morphological and optical properties. The morphology, crystal structures and optical properties of the MoS2 nanoparticle were characterized by Scanning electron microscopy, X-ray diffraction, and UV-Vis absorption spectroscopy. Upon the laser ablation of the samples, the absorbance of UV-Vis spectra increased as approaching the shorter wavelength side. From the SEM images, it confirmed that the particle size became smaller for laser ablated MoS2 sample, which is good agreement with the result of UV-Vis spectra. The XRD spectra shows the appearance of new peak for laser ablated MoS2 in methanol as compared to those samples ablated in ethanol and N-methyl-2-pyrrolidone. It can be said that the crystal structure of the sample has changed after ablation. It suggested that because the particle size became smaller after ablation and the band gap increased. Such MoS2 nanostructure has its own importance for optoelectronics devices

Steady‐State and Time‐Resolved Optical Properties of Multilayer Film of Titanium Dioxide Sandwiched by Gold Nanoparticles and Gold Thin Film

We proposed metal-insulator (MI) and metal-insulator-metal (MIM) structures of titanium dioxide (TiO2) sandwiched by gold nanoparticles (AuNPs) layer and gold sputtered thin film (only for the MIM film) to couple localized plasmon mode of AuNP with multi-reflection mode and/or cavity resonator mode of TiO2. The optical extinctions of MI and MIM with differing TiO2 thickness were studied theoretically by finite-element method simulation and experimentally by optical spectrometry. The extinction peaks of MI and MIM shifted by exchanging the surrounding medium from air to TiO2. The interference of TiO2 in MI structure also affected the extinction spectra showing the oscillation along the spectrum of AuNP in TiO2. Then, the extinction degree of MIM was higher than that of MI because of the coupling between cavity resonance mode with localized plasmon mode and interband transition in AuNPs. In addition, the cross section of MI and MIM films were observed by scanning electron microscopy. The surface of thinner film was rough because TiO2 heterogeneously grew from AuNP. The irregular growth of TiO2 might have induced the wide-range extinction in 300-2500 nm after Au thin film deposition. The transient absorption spectra using a femtosecond laser were also carried out under the condition of 800 nm for excitation laser and 950 nm for probe laser. The long-lived electron (~1 ns) was observed in thick MIM film as a result of hot electron transfer from the gold nanostructure in the film