| Integrated Optics plays an important role in the modern optical communication and information processing applications, and the optical hetero-structure is the key and basis of integrated optics. Optical hetero-structure combines the single crystalline materials with different properties together, in order to realize the special performance which the single crystal cannot achieve, and the optical waveguide structure is the requirement for the hetero-structure formation. Ion-implantation or "smart-cut" method has an advantage in fabricating high-quality optical hetero-structure. However, this method still has some difficulties and challenges in optical applications, the lack of knowledge on material physical process is one of the factors limiting the application of this method, and the study on the defects and lattice damage induced by ion implantation is very important. Through investigating the lattice defects and damage properties in different ion-implanted optical crystals, we try to clarify how the defects and damage influence the optical waveguide structure formation, and find out the optimum condition for the layer-splitting. We tried to explain the evolution of implant-induced defects with experimental conditions and crystal lattice properties, and obtain the optimum implantation and post-processing conditions for the optical material layer-splitting, providing theoretical basis for the layer-splitting with ion implantation on optical materials.There are two parts in this thesis, physics mechanism and layer-splitting fabrication: the physics mechanism is our investigations on the lattice damage properties and optical waveguide structure formation mechanism in ion-implanted Nd:YVO4crystal and KTiOPO4crystal, in order to deduce the possibility of layer-splitting; based on the physics mechanism investigation, we succeeded in fabricating the thin film of KTP with ion implantation method, so the physics mechanism study in the main part of this thesis.Here list the main contents and results of this thesis:The damage analysis of Nd:YVO4crystal implanted by He+ions at low energy.We report the damage properties of the He+ions implanted Nd:YV04crystal. Implantation was carried out at room temperature by He+ions at the doses of1×1016,2×1016, and4×1016ions/cm2with the energy of200keV. The depth of the damage region is about0.85μm beneath the surface. RBS/channeling technique was used to investigate the damage profile of ions implanted samples. Low atomic displacement ratio in as-implanted samples indicates a high irradiative resistance of YVO4crystal and the dynamic annealing effect of He+ions in the implantation process. Post-implant annealing was performed for all the samples at200℃and300℃for an hour, respectively. The height and width of damage peak decreased somewhat after annealing at200℃. Repairing and re-crystallization of damaged lattice was achieved after annealing at300℃. Photoluminescence of ion-implanted samples were measured to investigate effect of implantation on fluorescence properties of Nd3+. The damage on sample surface was analyzed by optical microscopy (OM) and atomic force microscopy (AFM).The study on irradiation effects in heavy ions-implanted Nd:YVO4crystal, including:Analysis of Si+-implanted Nd:YV04crystal:the relation between lattice damage and waveguide formation; and Radiation damage study of MeV ions-implanted Nd:YVO4crystal.We report the lattice damage and annealing properties of the500keV Si+ions implanted Nd:YVO4crystal with different doses. Rutherford Backscattering spectrometry (RBS)/channeling technique was used to analyze the damage profiles of ion-implanted samples. A series of post-implant annealing were performed at temperature from250℃to400℃to investigate the relation between lattice damage profile and the waveguide formation. Implantations at doses of more than5×1014ions/cm2can result in high damage ratio in the near-surface region and the lattice structure can’t be restored even after annealing at400℃. Such seriously damaged lattice is relative stable and contributes to the waveguide structure. Convergence of refractive index at surface region after ion implantation is believed maily due to the elastic collisions with the target atoms caused by nuclear energy loss.Damage formation mechanism of Nd:YVO4implanted with MeV ions is investigated. MeV Si+ions were implanted into Nd:YV04crystal, and the lattice damage was measured using Rutherford backscattering spectroscopy/channeling(RBS/C) method. The damage creation kinetic indicates a significant contribution from electronic energy loss to the surface damage. A detailed analysis allows us to deduce the different contributions from electronic and nuclear stopping powers to the lattice damage production. An obvious difference in extent of damage from1MeV and3MeV Si+ implantations also implies that there exists a threshold value of the electronic energy deposition for damage formation. The exact value of threshold is obtained by comparison with the experimental data obtained from3MeV O+, F+and Si+implantation results, which turns out to be (1.7±0.1) keV/nm.Refractive-index profile in ion implanted Nd:YV04waveguide:the relation between index change and lattice damageA model is presented to explain the refractive-index changes in the ion-implanted Nd:YVO4waveguide region, which is helpful for characterizing index profile dependence on implantation parameters. It indicates that the lattice damage is the main factor for the refractive-index changes. Waveguide structure is formed mainly due to an increase of ordinary refractive index in ion-implanted region. The theoretical results based on this model are in good agreement with the experimental data from500keV Si+ion-implantation and keV He+ion-implantation.Analysis of structural modifications in KTP implanted by He+ion for crystal ion slicingWe report on the lattice structural modifications in He+-implanted KTP in order to analyze the possibility of KTP thin film fabrication with ion implantation method. Rutherford backscattering spectroscopy/channeling (RBS/Channeling), transmission electron microscopy (TEM), and atomic force microscopy (AFM) are used to examine the structural changes caused by200keV He+-implantation followed by thermal annealing. Lattice disruption, He-bubbles or platelets formation and lattice crack production are observed in the implantation region. The implications of these observations for KTP thin film fabrication are discussed.SAXS and TEM Investigations of Swift Heavy Ion Tracks in KTPPotassium titanyl phosphate (KTP) crystals in both x-cut and z-cut were irradiated by Au ions with energies of185MeV and2.2GeV. The morphology of the resulting ion tracks was investigated using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). SAXS measurements indicate the presence of cylindrical ion tracks with abrupt boundaries and a density contrast of1±0.5%compared to the surrounding matrix, consistent with amorphous tracks. The track radius depends on the crystalline orientation, with6.0nm measured for the ion tracks along x-axis and6.3nm for that along z-axis. TEM images in both cross-section and plan-view show amorphous ion tracks with radii comparable to those determined from SAXS analysis. The protruding hillocks covering the sample surface detected by AFM indicate the amorphous material within the ion tracks is less dense than the surrounding matrix. Simulations using an inelastic thermal-spike model are in good agreement with the experimental results, supporting the notion of a melt-quench mechanism is operative during ion track formation.Analysis of Layer Splitting in Z-Cut KTP Implanted by H+ionsPotassium titanyl phosphate (KTP) thin film with thickness～1μm was exfoliated from both z-cut and x-cut single-crystal bulk samples implanted by117keV H+ions with ion fluence of6×1016ions/cm2. Scanning electron microscope (SEM), atomic force microscopy (AFM), and optical microscopy (OM) were used to observe the splitted thin film morphology. Post-implantation annealings were imposed on the samples to see the surface morphology modification. H+-ions with the same implantation condition were also implanted into x-cut KTP for comparison. |
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