Research On Optical Characteristic Of Metal Nanoparticle And Its Polymer Composite Film

The researches on optical characteristics and its applications of metal nanoparticles are always a very active topics, which are based on localized surface plasmon resonance (LSPR).When resonance occurs, localized electrical field near the nanoparticle will be greatly enhanced and the resonance wavelength is sensitive to the surrounding medium.As a result, metal nanoparticles can be applied into optical sensing, surface-enhanced Raman scattering and enhanced nonlinear optics etc.This dissertation foucus on optical properties of metal nanoparticle both in theory and experiment, especially for gold nanorod and its polymer composite film.The main research works and conclusions are as follows:1. Gold and silver nanoparticles with different shapes and sizes are prepared using chemical meathod.These particles include nanospheres, nanocubes, nanorods and nanowires etc.They are characterzed by transmission electronic microscope, scanning electronic microscope and UV-vis-NIR spectrophotometer.2. The optical properties of gold nanorod are studied based on the Gans theory, including the relationship between LSPR peak of gold nanorod and aspect ratio or dielectric constant of surrounding medium. The influence of aspect ratio on the refractive index sensitivity of nanorod is analyzed in theory and verified in experiment. The experiment results show that sensitivity increases almost linearly with aspect ratio. It varies from 216nm/RIU (aspect ratio 2.5:1) to 352nm/RIU (aspect ratio 4.2:1) in the monitored wavelength range. The experiment result is in accord with discrete dipole approximation (DDA) simulation result. We calculated the extinction spectrum of gold nanorod with uniform aspect ratio and nomal distributed aspect ratios.The results show that the width of longitudinal LSPR peak of gold nanorod with nomal distributed aspect ratios is about 3 times wider than that with uniform aspect ratio.3. The gold nanorod and poly vinyl alcohol(PVA) composite film is prepared.Gold nanorod in the PVA film is aligned by stretched the film. The effect of stretched length on the 3D order parameter of gold nanorod is studied, which shows that the 3D order parameter is 0.72 when the film is strectched to 6 times longer than its original length.By doping the probe molecule in the above composite film, we studied its application in the polarization dependence of surface-enhanced Raman scattering. The surface enhanced Raman scattering (SERS) intensity of characteristic vibrational band of the probe is observed obviously dependent on the angle (?) between incident polarization and major axis of nanorod. The relationship between them manifests a cos2θ-dependence. The conclusion is illustrated from both the localized field enhancement and optical antenna effect of gold nanorod.4. The third-order nonlinear optical properties of gold nanorod sol and its PVA composite film is investigated by Z-scan technique in 532nm.The experiment results show that both gold nanorod sol and its PVA composite film manifest third-order nonlinear optical characteristic except pure PVA film. The results also reveal that third-order nonlinear susceptibility of the composite film is 2 orders of magnitude larger than that of gold nanorod sol. The result is illustrated from theoretical model of third-order nonlinear susceptibility enhancement.Highlights of the dissertation are as follows:1. The relationship between refactive index sensitivity and its aspect ratio is studied in experiment, which shows a linear relationship.In experiment, the sensitivity of gold nanorod with aspect ratio 4.2 can reach 352nm/RIU.2. The effect of aspect ratio dispersion on the width of longitudinal LSPR peak of gold nanorod is investigated based on Gans theory.We point out that the width of longitudinal LSPR peak of gold nanorod with nomal distributed aspect ratios is about 3 times wider than that with uniform aspect ratio.3. The effect of stretched length on the 3D order parameter of gold nanorod is studied quantitatively. The experiment result shows that the 3D order parameter is 0.72 when the film is strectched to 6 times longer than its original length.We proposed a low cost and effective SERS substrate based on aligned gold nanorod-PVA composite film and demonstrated its application in polarization dependent SERS research.