Dispersion of gold nanoparticles into a nylon 11 thin film during heat treatment: in situ optical transmission study

Changes in the optical absorption spectra of Au/nylon 11 thin films during the dispersion of Au nanoparticles caused by heat treatment have been investigated by means of in situ optical transmission measurements using a multi-channel charge coupled device spectrophotometer attached to an integrating sphere. Temperature-dependent spectral changes of the surface plasmon resonance absorption of the Au nanoparticles were obtained by the measurement of total transmittance through the sample. It has been found that the peak wavelength of the plasmon band shifted to shorter wavelength and its intensity decreased in the temperature range 40-70 degrees C, corresponding to the temperature at which the nylon 11 matrix relaxed. In order to investigate the cause of this behaviour, we have measured the depth distribution of the Au particles in the film, crystallite size Of the Au particles and refractive index of the nylon 11 matrix film by using XPS, XRD and ellipsometry, respectively. While the size of the Au particles and refractive index of the nylon 11 were nearly constant with heat treatment up to 100 degrees C, the Au particles have penetrated into the nylon 11 layer for the heat treatment at 50 degrees C and further dispersed more deeply above 70 degrees C. The change of the volume fraction of the Au particles caused by the penetration from the surface into the bulk phase of the nylon 11 matrix is suggested to be mainly responsible for the shift of the plasmon band. The dependence of the heating rate on the shift of the plasmon band was also observed.