Preparation And Optical Properties Of SiO₂ Based Composite Thin Films

The study of the composite films of metal (especially Ag, Au and Cu) nanoparticles and dielectric matrices, are of considerable interest in the world of materials science because of their unique physical and chemical properties, including surface plasmon resonance, surface enhanced Raman, surface enhanced fluorescence, metal nanoshells, and semiconductor quantum dots. Such properties provide excellent potential applications in electronics and passive optical components. They are also useful for photonic and magnetic devices and decorative colored glass wares.Ag/SiO2 composite thin films were prepared by means of sol-gel method and deoxidized using UV radiation, and were characterized by XRD, SEM, IR, UV-Vis, PL and Raman spectroscopy. The results of XRD indicate that the sample exhibits a typical face-centered cubic (fcc) silver phase. The results of SEM show that the composite thin films are very homogeneous and the size of Ag nanoparticles is small. The thickness of the films is about 1μm. The results of the optical absorption spectra show that the intensity of the absorption peaks at 420 nm is increasing with the molar ratio of Ag/Si, and the absorption peaks have some red shift. The PL spectra show that the luminescent intensity at 442 nm is very strong and decreases a little with the increase of nAg/nsi. And some blue shift appears. The results of Raman spectra indicate that the surface enhanced Raman scatter aroused by the enhancing of the surface region electromagnetic field of Ag nanoparticles appears.Au/SiO2 composite thin films were prepared by means of sol-gel method and deoxidized using UV radiation, and were characterized by SEM, TEM, XRD and UV-Vis spectroscopy, et al. The results of XRD show that the Au nanoparticles dispersed in amorphous SiO2 exhibit a typical face-centered cubic (fcc) phase. The results of SEM indicate that the composite thin films are very homogeneous and the size of the nanoparticles is small. The results of the optical absorption spectra show that the intensity of the absorption peaks becomes stronger and has some red shift from 585 nm to 600 nm and with the increasing of the temperature and nAu/nSi. And the samples with larger nAu/nSi exhibit absorption at 820 nm,900 nm and 585 nm of near-infrared region.Ag-Au alloys/SiO2 composite thin films (nAg/nAu=1:0,2:1,1:2,0:1)were prepared with AgNO3, HAuCl4 and TEOS by means of sol-gel method and deoxidized using UV radiation. The results of SEM and XRD indicate that the composite thin films are very homogeneous and the size of the nanoparticles is about 10 nm. The results of the optical absorption spectra show that the absorption peaks have some red shift from 430 nm belonged to the SPR absorption peak of Ag nanoparticles to 605 nm and 880 nm belonged to the SPR absorption peaks of Au nanoparticles with the increasing of nAg/nAu.The SPR absorption peaks around 515 nm,730 nm and 550 nm,730 nm belonged to the samples (nAg:nAu=2:1,1:2), respectively, show the formation of Ag-Au Alloys dispersed in the SiO2Structure and photoluminescent properties of the ZnO/SiO2 composite thin films under the influence of different calcined temperature were studied, and the photoluminescent properties of ZnO/SiO2 composite film with different concentration of ZnO were studied too. The result shows that high calcined temperature is good for the crystallization of samples and the reducing of structural defects. The particles become larger as the calcined temperature rise and partly reunion. The highest transmission composite film is calcined at 400℃. There are strong blue emission peaks of samples. The band gap changed and the emission peak intensity at ultraviolet and blue region increased with the concentration of ZnO increased. Ag-ZnO/SiO2 composite thin films with Ag doped in ZnO layer were prepared. And the structure and photoluminescent properties of composite thin films under the influence of different Ag concentration were also discussed. The result shows that there is diffraction peak of Ag after annealed in air at 300℃as the content of Ag increased, the absorption peaks have red shift and widen because of the electron transfer between Ag and ZnO and the particle size of Ag becoming larger. The photoluminescent intensity of the films in the section of ultraviolet and visible region weakened with the content of Ag increased, and this is owing to the reduction of the hole concentration and the compensation of structural defects caused by the doping of Ag.