Experimental And Theoretical Studies Of Syntheses And Modifications Of Metallic Nanoparticles In SiO₂ By Ion Implantation/irradiation

Metallic nanoparticles（NPs） embedded in dielectric media have attracted immense interests in recent years due to their unique optical properties with promising applications in various optoelectronic devices. Among different possible techniques to synthesize such NP-based materials, ion implantation and irradiation combining with subsequent thermal annealing have been proved to be very versatile. In this work, several experimental and theoretical researches were performed with focusing on the syntheses, modifications, and characterizations of metallic NPs in amosphous SiO₂（a-SiO₂） glasses. The main contents and research results are presented as follows.（1） Ag NPs were fabricated in a-SiO₂ glasses by 45 keV Ag ion implantation to a ?uence of 5.0×1016 ions/cm2, and were then subjected to irradiation by 500 keV Xe ions to a fluence of 2.0×1016 ions/cm2. Our results clearly show that Xe ion irradiation could induce transformation of crystalline Ag NPs into polycrystalline ones with various shapes. The modified Ag NPs exhibit a notable shoulder absorption band around 550 nm besides the SPR peak located at about 400 nm. Reduction of the electron mean-free-path and interaction between crystallites in the formed polycrystalline NPs have been proposed to interpret the appearance of the shoulder absorption band. Moreover, our results also show that subsequent thermal annealing at 400 °C for 1h can restore polycrystalline Ag NPs to crystalline ones with spherical shape, which are nearly aligned around the end of the Ag ion range, and contribute a much narrower SPR absorption peak at 400 nm.（2） Cu NPs were fabricated in a-SiO₂ by 45 keV Cu ion implantation at a fluence of 1.0 ×1017 ions/cm2, and were then subjected to implantation of 50 keV Zn ions at fluences of 0.5×1016, 1.0×1016, 5.0×1016 and 10.0×1016 ions/cm2, respectively. It clearly shows that Zn ion implantation at the fluence of 1.0×1016 ions/cm2 could modify the dielectric environment around Cu NPs, significantly enhancing the Cu SPR absorption. However, as Zn ions were post-implanted at the intermediate fluence, Cu-Zn alloy NPs are clearly revealed, which gives rise to unique SPR absorption behaviors. Moreover, phenomena of re-alloying and de-alloying of Cu-Zn NPs have also been demonstrated under subsequent annealing in a flowing nitrogen atmosphere. At higher Zn fluences, Cu NPs are almost sputtered, and only Zn NPs are formed.（3） Silica glasses were pre-implanted with 60 keV Zn ions at different fluences of 1.0×1016 and 1.0×1017 ions/cm2, respectively, and were then subjected to implantation of 45 keV Cu ions at a fluence of 5.0×1016 ions/cm2. Our results clearly show that Zn ion preimplantation at a low fluence of 1.0×1016 ions/cm2 can give rise to the formation of large Cu NPs with a double-layer arrangement, which contribute a greatly enhanced SPR absorption at about 572 nm. As the Zn ion fluence increases to 1.0×1017 ions/cm2, Cu/Cu–Zn core/shell NPs with a high particle density and a narrow size distribution can be obtained, resulting in a strong and broad SPR absorption band around 528 nm. Besides, the dually implanted samples also exhibit excellent third-order nonlinear optical properties comparing with the Cu solely implanted sample.（4） Third-order nonlinear optical properties of Al nanoshells in silica were studied by using the Maxwell-Garnett theory. Simulation results reveal that the third-order nonlinear refraction index neff and absorption coefficient βeff of composite can be remarkably enhanced near the SPR of Al nanoshells. This enhanced third-order nonlinearity can be achieved in the deep-ultraviolet to near-visible-light region by tailoring Al shell thickness. Moreover, the most strongly negative neff occurs on the long wavelength side of SPR, and this deviation becomes larger with decreasing the shell thickness. This has been interpreted by the electron surface scattering dependent on nanoshell thickness.