||Collective oscillation of conduction electrons in metallic nanoparticles known as localized surface plasmon resonance has been studied for nano-optics applications. The excitation of localized surface plasmons on nano-structured metal material leads to strong light scattering and absorption. Since the localized surface plasmon resonance is strongly dependent on the shape, size, size distribution, and dielectric property of surrounding environment of nano-structured metal, the dependence can be applied in wide applications. However, the direct and non-destructed observation of nano-structured metal is required to the development of nano-technology, we proposed a real time optical observation due to the optical respons of metal nano-particles system. Furthermore, we proposed a fast and simple method to fabricate a high order metal nano-particles array and used liquid crystal material to directly modulate the surface plasmon effect on the metal nanoparticles. |
The purpose of this work is to study the surface plasmon effect excited on metal nanoparticles. These works are described as follows:
A. The topic of the first work is “Real time absorbance spectra due to optical dynamics of silver nano-particles film”, we report the real time absorbance spectra due to optical dynamics of silver nano-particles film under a heating treatment from 28 to 300 ℃. A 7nm-thicked sliver film was thermally deposited on an indium tin oxide glass substrate. In the process of heating, the real time absorbance spectra of silver nano-particles film were measured by an optical spectrometer. It was noted that the absorbance spectra of the film varied with the heat-treating temperature and time. The peak position in the spectra curve shifted to shorter wavelength below the temperature of 250 ℃, then shifted to red band due to higher temperature treatment. With the comparison of scanning electron micrograph analysis, the real time absorbance spectra exhibited a particular optical property confirmed by the dynamic dark-field optical microscopy system. The real-time absorbance spectra and dark-field micrographs analyses lead to a direct and non-destructed observation of growing evolution of metal nano-particles.
B. The topic of the second work is “Laser pulse induced gold nanoparticles grating”. We report the results of our experimental investigation of laser induced gold nano-particle gratings and their optical diffraction properties. A single shot of a pair of Nd-YAG laser pulses of the same polarization is directed toward a thin gold film of thickness 6 nm on a substrate of polymethyl methacrylate (PMMA). As a result of the laser illumination, the thin gold film is fragmented into an array of nano-particles. Using scanning electron and dark-field optical micrographs, we discovered that the morphology of the gold nanoparticles grating is dependent on the fluence of laser pulse. The spectrum of first order diffraction shows a spectral dependence, possibly due to the presence of the nano-particles of various sizes. The ablation of thin films of nano-thickness via the use of laser pulses may provide a simple and efficient method for the fabrication of nano-scale structures, including 2D arrays of nano-particles.
C. The topic of the second work is “Surface plamons induced extra diffraction band of cholesteric liquid crystal grating”. We investigated the diffraction behavior of cholesteric liquid crystal (CLC) grating with the surface plasmon effect was investigated. One indium-tin-oxide plate of the CLC grating cell was covered with silver nanoparticles. With the application of a proper voltage, a well formed phase grating was constructed in the CLC cell. The CLC grating was probed by a beam of the polarized-monochromatic light, and the wavelength range was from 450 to 700 nm. It was shown that an extra first-order diffraction band was observed around 505 nm. The physical reason of the extra diffraction band could be the surface plasma effect emerged from silver nanoparticles. The extra diffraction band due to the surface plasmon effect can offer potential applications in nano-optics, such as the optical switch function.