Browsing by Author "Wang, Shun-Fa"

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Laser Trapping and Assembling of Nanoparticles at Solution Surface Studied by Reflection Micro-spectroscopy
(2015-01-01)
Wang, Shun-Fa
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Yuyama, Ken-ichi
;
Suigiyama, Teruki
;
Masuhara, Hiroshi
;
應用化學系
We present the laser power dependent behavior of optical trapping assembling of 208-nm polystyrene (PS) nanoparticles at the solution surface layer. The assembling dynamics is examined by reflection microspectroscopy as well as transmission and backscattering imaging. The transmission imaging shows that the laser irradiation at the solution surface layer forms a nanoparticle assembly, whose diameter becomes large with the increase in the laser power. The backscattering image of the assembly gives structural color, meaning that nanoparticles are periodically arranged over the whole assembly region. In reflection microspectroscopy, one band appears at long wavelength and is gradually shifted to the short wavelength with the irradiation. After the blue shift, the reflection band is located at the shorter wavelength under the laser irradiation at the higher power. We discuss these spectral changes from the viewpoint of the inter-particle distance determined by the dynamic balance between attractive optical force and repulsive electrostatic force among nanoparticles.
Laser-Assisted Nanowetting: Selective Fabrication of Polymer/Gold Nanorod Arrays Using Anodic Aluminum Oxide Templates
(1970-01-01)
He, Hung-Chieh
;
Yan, Ai-Ling
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Karapala, Vamsi Krishna
;
Wang, Shun-Fa
;
Shen, Ming-Hui
1D polymer nanomaterials have attracted significant interest in recent years because of their unique properties and promising applications in various fields. It is, however, still a challenge to fabricate polymer nanoarrays with desired sizes and controlled morphologies. Here, an unprecedented approach, the laser-assisted nanowetting (LAN) method, to selectively fabricate polymer nanoarrays is presented. Polystyrene (PS) is blended with gold nanorods (AuNRs), which are used to absorb the energy from the laser. After the blend films are brought in contact with AAO templates, the AuNRs at regions shone by the laser beams absorb the energy and heat the surrounding polymer chains, resulting in the formation of PS/AuNRs arrays in selected areas. This work paves a new research direction for developing template-based polymer nanomaterials.
Optical Trapping-Formed Colloidal Assembly with Horns Extended to the Outside of a Focus through Light Propagation
(2016-05)
Kudo, Tetsuhiro
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Wang, Shun-Fa
;
Yuyama, Ken-ichi
;
Masuhara, Hiroshi
;
應用化學系
We report optical trapping and assembling of colloidal particles at a glass/solution interface with a tightly focused laser beam of high intensity. It is generally believed that the particles are gathered only in an irradiated area where optical force is exerted on the particles by laser beam. Here we demonstrate that, the propagation of trapping laser from the focus to the outside of the formed assembly leads to expansion of the assembly much larger than the irradiated area with sticking out rows of linearly aligned particles like horns. The shape of the assembly, its structure, and the number of horns can be controlled by laser polarization. Optical trapping study utilizing the light propagation will open a new avenue for assembling and crystallizing quantum dots, metal nanoparticles, molecular clusters, proteins, and DNA.
Optically Evolved Assembly Formation in Laser Trapping of Polystyrene Nanoparticles at Solution Surface
(2016-11-29)
Wang, Shun-Fa
;
Kudo, Tetsuhiro
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Yuyama, Ken-ichi
;
Sugiyama, Teruki
;
Masuhara, Hiroshi
Assembling dynamics of polystyrene nanoparticles by optical trapping is studied with utilizing transmission/reflection microscopy and reflection microspectroscopy. A single nanoparticle assembly with periodic structure is formed upon the focused laser irradiation at solution surface layer and continuously grows up to a steady state within few minutes. By controlling nanoparticle and salt concentrations in the colloidal solution, the assembling behavior is obviously changed. In the high concentration of nanoparticles, the assembly formation exhibits fast growth, gives large saturation size, and leads to dense packing structure. In the presence of salt, one assembly with the elongated aggregates was generated from the focal spot and 1064 nm trapping light was scattered outwardly with directions, while a small circular assembly and symmetrical expansion of the 1064 nm light were found without salt. The present nanoparticle assembling in optical trapping is driven through multiple scattering in gathered nanoparticles and directional scattering along the elongated aggregates derived from optical association of nanoparticles, which dynamic phenomenon is called optically evolved assembling. Repetitive trapping and release processes of nanoparticles between the assembly and the surrounding solution always proceed, and the steady state at the circular assembly formed by laser trapping is determined under optical and chemical equilibrium.
Preparation and micropatterning of gold nanoparticles by femtosecond laser-induced optical breakdown
(2017-09-01)
Uwada, Takayuki
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Wang, Shun-Fa
;
Liu, Tsung-Han
;
Masuhara, Hiroshi
;
應用化學系
We fabricated gold nanoparticles (NPs) via a femtosecond (fs) laser-induced cavitation bubbling. By introducing intense fs laser pulses into HAuCI4 aqueous solution containing 1-propanol, optical breakdown and the following cavitation bubble generation occurred at the focus through multiphoton absorption of water, resulting in the formation of gold nanoparticles (Au NPs). Intermediate species such as radicals and solvated electrons produced upon the bubbling contribute to gold ion reduction, while direct ionization of Au-chloride complex, photothermal decomposition and direct optical decomposition are excluded as possible mechanisms. Utilizing the fs laser-induced bubbling we demonstrate in-situ micropatterning of Au NPs on a substrate from the same HAuCI4 aqueous solution containing 1-propanol. (C) 2017 Elsevier B.V. All rights reserved.
Reflection Microspectroscopic Study of Laser Trapping Assembling of Polystyrene Nanoparticles at Air/Solution Interface
(2016-07-28)
Wang, Shun-Fa
;
Yuyama, Ken-ichi
;
Sugiyama, Teruki
;
Masuhara, Hiroshi
;
應用化學系
We present the formation of a single nanoparticle assembly with periodic array structure induced by laser trapping of 200 nm polystyrene nanoparticles at air/solution interface of the colloidal heavy water solution. Their trapping and assembling behavior is observed by monitoring transmission and backscattering images and measuring reflection spectra under a microscope. Upon the laser irradiation into the solution surface layer, nanoparticles are gathered at and around the focal spot, and eventually a nanoparticle assembly with the size much larger than the focal volume is formed. The assembly gives structural color in visible range under halogen lamp illumination, indicating that constituent nanoparticles are periodically arrayed. Reflection spectra of the assembly show a reflection band, and its peak position is gradually shifted to short wavelength and the bandwidth becomes narrow with time, depending on the distance from the focal spot. After the laser is switched off, red-shift is observed in the reflection band. These results indicate that nanoparticles are rearranged into a densely packed periodic array during laser irradiation and diffused out to the surrounding solution after turning off the laser. These dynamics are discussed from the viewpoints of the attractive optical trapping force and the electrostatic repulsive force among nanoparticles.