| Noble metallic nanoparticles (NPs) have been paid more attentions and applied extensively in solar cells, light emitting diode and biosensors due to their distinct optical and electrical properties. It is well known that the optical and electrical properties of noble metal NPs depend on the shape, size, refractive index, surface coverage rate and etc. Therefore, preparation of NPs with controllable size and shape, especially by the physical method, is valuable for their potential application. Herein, we performed the study on the fabrication, formation mechanism and optical properties of Ag and Au NPs.In this thesis, Ag and Au NPs were fabricated via magnetron sputtering with subsequent thermal annealing methods, and the influence of processing parameters, such as annealing temperature, annealing modes and dielectric environment, on the shape and optical properties of Ag NPs were investigated. Moreover, single crystalline Au nanoprisms with regular hexagonal shape were firstly fabricated by magnetron sputtering with subsequent rapid thermal annealing treatments. Several works have been developed and following significant results have been attained.1. The morphology of Ag NPs’greatly relies on the annealing modes. The results confirm that the in-situ annealing mode favors the formation of NPs with a great number of small sized NPs (D<50) while the rapid thermal annealing mode is more likely to generate NPs with uniform size and a gauss like size distribution.2. The agglomeration behaviors of Ag films follow different mechanisms when annealed under in-situ and ex-situ treatment process. A comparison study on the shape evolutions of 9 nm-thick Ag films deposited by magnetron sputtering with in-situ heating and ex-situ rapid thermal annealing treatments at different temperatures (200, 250,300,400℃) was exploited, respectively. The former agglomerates via nucleation of voids, and the latter obeys the grain boundary grooving mechanism. We speculate the heating rate plays a key role during the annealing process, namely, the slow heating treatments is favorable for forming of void while the rapid one is beneficial for Ag film gaining enough energy and rupturing at grain boundary.3. The optical properties of Ag NPs greatly rely on the thickness of SiO2 film. Our findings identify that the surface coverage ratio of Ag NPs decreases while the average particle diameter increases as the thickness of SiO2 film increases, and the minimum surface coverage ratio is 33.2% and the maximum average particle diameter is 68.98 nm. The dipole extinction peak of Ag NPs shows a 86.0 nm red shift after introducing SiO2 film, but the peak intensity decreases greatly. Moreover, we found that the scattering number of photons by Ag NPs is decreased by as much as 2x 1018 after inserting a SiO2 layer.4. Single crystalline Au nanoprisms with regular hexagonal shape were firstly fabricated by magnetron sputtering with subsequent rapid thermal annealing treatments. Our results confirm that the morphology of Au NPs greatly depends on the annealing temperature. Au nanorods with aspect ratio of 1.8 and 1.2 are produced respectively for a 7.5 nm Au film annealed at 700 and 800℃. When the annealing temperature increases to 900℃, Au regular hexagonal nanoprisms are formed, and a thermodynamic model is adopted to explain the shape transition of Au NPs. |
PDF Full Text Request