|
Zinc Oxide (ZnO) is an inexpensive n-type semiconductor having a direct band gap of 3.3eV with a large exciton
binding energy of 60meV. Noble metal nanoparticles show a surface plasmon resonance in the visible region due to
collective oscillations of electrons at the surface of metal nanoparticles. The unique features in the composite system of
dielectrics-metal nanoparticles have potential applications in optoelectronic devices such as transparent conductive films,
solar cells, photocatalysts and so on. In this study, ZnO thin films dispersed with Ag or Au nanoparticles were
synthesized using a sol-gel technique. X-ray diffraction peaks of ZnO films exhibited a pattern corresponding to the
hexagonal wultzite structure. In the TEM analysis of ZnO-Au composite films, spherical Au nanoparticles were
observed within the ZnO crystalline matrix. The distribution of the diameter of Au nanoparticles was centered at around
20nm and broadened with the half width of about 20nm. In the ZnO-Ag composite films, Ag nanoparticles grow larger
as the annealing temperature becomes higher and various shape of Ag precipitations like triangular and square plates
were observed in ZnO-Ag (50:50) composite films. The optical absorption peaks were observed at 580nm and 410nm
due to the surface plasmon resonance of gold and silver nanoparticles, respectively. The absorption spectra were
analyzed using a typical effective medium approximation of Maxwell-Garnett model and good fitting was obtained for a
ZnO-Au composite film assuming spherical Au nanoparticle. The spectra were discussed relating with the size and
shape of the nanoparticles, and the refractive index of the matrix.
|
