Ion Beam Synthesis Of Ag Nanoparticles In SiO₂and Heavy Ion Irradiation Induced Modifications

Ion implantation into insulators at high fluence is one of important ways tosynthesize compounds involved nanoparticles (NPs). These nano-compounds havepotential application in various fields, such as opto-electronic devices, biosensors,optical switches, etc. In this dissertation, we performed the modifications of the sizedistribution and optical properties of Ag nanoparticles embedded in SiO2by postheavy ion irradiation. The main contents and results are given as follows.(1) Ag NPs embedded into SiO2were fabricated by implantation of45keV Agions at a fluence of5×1016ions/cm2, and their structures and optical absorptionproperties were characterized in detail. The formation of Ag NPs into SiO2gives riseto a surface plasma resonance absorption peak at about400nm. Results from XTEMshow that Ag ion implantation induces formation of Ag nanoparticles in the shallowsurface, which mainly have (111) and (200) orientations. The Ag NPs show a bimodaldistribution in their sizes. Large Ag NPs are mainly distributed in the region close tothe surface, while small ones are located around the end of the Ag ion range.Moreover, HRTEM observations of Ag NPs also indicate that most of the NPs arespherical and have good crystalline structure.(2) The synthesized Ag NPs were then subjected to irradiation of Ar and Xe ionsat the same energy of500keV and same fluence of1×1016ions/cm2, respectively. Byusing techniques of XTEM, UV-vis and GXRD, modifications in structures andoptical properties of Ag NPs were investigated. Our results clearly show that post Xeion irradiation could induce intensity increase in the Ag SPR absorption companyingwith remarkable decrease in its full width at half maximum of the SPR absorptionpeak. XTEM results demonstrate that post Xe ion irradiation promotes growth ofsmall Ag NPs around the Ag ion range into larger NPs, which leads to quantityincrease of the large NPs. Moreover, results from HRTEM observations also indicatethat post Xe ion irradiation gives rise to formation of Ag NPs with various damagedstructures. Comparing with Ar ion irradiation at the same conditions, Xe ionirradiation is more effective to modulate the SPR absorption of Ag NPs together withtheir structures. (3) By using Xe ion irradiation of the synthesized Ag NPs at the same energy butat different fluences, the effects of Xe irradiation on structures and optical propertiesof NPs have been studied. Our results clearly show that increasing fluence could giverise to decrease in intensity of Ag SPR absorption accompanying with significantincrease in the530nm shoulder absorption peak. In such case, most of the Ag NPs areheavily damaged. Therefore, NPs with special structures, such as octahedron,“star-like”decahedron and so on, were created. Based on our experimental results, wepropose that the occurrence of shoulder absorption peak at large wavelength could berelated to the formation of damaged Ag NPs due to post Xe ion irradiation. Moreover,the possible mechanisms for heavy ion irradiation induced modifications in structureand size distribution of Ag NPs have also been discussed and presented.Our findings may present experimental and theoretical basis for modulation ofstructure and optical properties of NPs embedded in insulators.