Photoelectric Properties Of Embedded Nanocomposites

Ion implantation is a versatile method to prepare nanoparticles embedded in insulators. Embedded metallic nanoparticles have two pronounced properties, surface plasmon resonance (SPR) absorption and nonlinear optical effect. Oriented, single-domain ferromagnetic nanoparticles may represent the future for high-density magnetic data recording. Excellent luminescence of oxide nanoparticles has good applications in light emission devices in different wavebands. However, the effects of substrate, ion flux and fluence on the formation, microstructure and property of nanoparticles are not so clear. The mechanism of interaction between ions and substrates needs further investigation.In this work, nanoparticles in different substrates and different nanoparticles in the same substrates have been studied. For the first time, metallic Ni, Zn, Sn and oxide NiO, ZnO, SnO₂ nanoparticles have been fabricated in single crystals, e.g., Al₂O₃. The microstructures, optical and magnetic properties have been studied for the metallic and oxide nanoparticles. Based on these researches, the main results are as follows:1. Microstructures and properties of Ni-ion-implanted Al₂O₃, MgO, YSZ and TiO₂ single crystals have been studied before and after thermal annealing. (1) Metallic Ni nanoparticles are observed in crystals except YSZ after ion implantation. The implanted areas of substrates are amorphous except YSZ. It seems that amorphous substrates are helpful for the formation of nanoparticles. (2) The wavelength of SPR absorption of metallic nanoparticles increases with the increasing refractive index of substrates and size of nanoparticles. (3) Metallic Ni naoparticles exhibit a stronger ferromagnetism and a larger coercivity than those of bulk Ni. (4) Transmission electron microscopy (TEM) results show that NiO nanoparticles in annealed samples except MgO. The absorption of NiO nanoparticles are observed in annealed Al₂O₃. (5) Ion flux is responsible for the formation of nanoparticles. For example, metallic Ni nanoparticles formed in Al₂O₃ when an ion flux of 5μA/cm² is used. However, spinel NiAl₂O₄ formed in Al₂O₃ when an ion flux of 10μA/cm²is used.2. Optical absorption spectra of Zn-ion-implanted Al₂O₃, MgO, YSZ and CaF₂ single crystals have been studied before and after thermal annealing. Al₂O₃ is selected for microstructures and photoluminescence (PL) investigations due to its good SPR absorption of metallic Zn and exciton absorption of ZnO. (1) SPR absorption of metallic Zn nanoparticles is observed in crystals except YSZ. (2) The SPR absorption of Zn nanoparticles disappeares and the exciton absorption of ZnO nanoparticles appears in Al₂O₃ after annealing at 600℃. After annealing at higher temperatures, the exciton absorption of ZnO becomes weaker and weaker due to the formation of spinel ZnAl₂O₄. (3) ZnO nanoparticles in Al₂O₃ exhibit two PL bands, one at 370 nm (UV) and the other at 500 nm (green). The former is due to recombination of free excitons and the latter is due to deep level defects. Compared with previous studies, the size of ZnO nanoparticles in this paper is smallest and ZnO naoparticles have a strong green PL band. (4) The size of metallic Zn nanoparticles is proportional to fluence. According to quantum-confinement effects, a bigger particle size will result in a bigger SPR wavelength. (5) The Zn-ion-implanted area is amorphous. After annealing, the amorphous area begins to recrystallize firstly at the interface of amorphous and crystalline zones. The recrystallized Al₂O₃ grains have different orientation relationship with the original matrix.3. Optical properties of Sn-ion-implanted Al₂O₃, MgO and YSZ single crystals have been studied before and after thermal annealing. Al₂O₃ is selected for microstructures investigations. (1) There is no SPR absorption of metallic Sn nanoparticles in the three as-implanted crystals due to dielectric function of metallic Sn. (2) The optical absorption at 280 nm of SnO₂ nanoparticles is observed in the three samples after annealing. (3) Three clear PL bands are observed in the three annealed samples. The three bands lie at 410 nm, 520 nm and 700 nm, repectively. The PL bands at 410 nm and 520 nm are similar to those of the previous studies, which are due to deep level defects in the SnO₂ semiconductor. The newly observed one at 700 nm should be related to the new trapped states from the surface states and interface states of SnO₂ nanoparticles embedded in Al₂O₃.