Modification Of Optical Waveguides And Two-dimensional Materials By Ion Irradiation

As an important material surface modification and surface characterization technology,ion irradiation has a wide range of applications in the metal materials,semiconductor industry,chemistry,magnetic materials,medicine,physics and other fields.Based on the interaction between ion and solid material,the ion irradiation technique can also be applied to effective doping of semiconductor material and preparation of optical waveguide structure.In 1969,S.E.Miller of the Bell Lab in the United State proposed the concept of "Integrated Optics" which integrates optical components in a small-sized substrate with advantages of low volume,high efficiency,stable performance and convenient use.It has wide application prospect such as optical information storage,optical fiber sensing technology,light radar,material science research and large-capacity and long-distance optical communication.Optical waveguide is basic structure of integrated optics which can carry out optical signal transmission and conversion;therefore the optical waveguide structures directly affect the performance of integrated optical components.At present,ion irradiation technology has become a more mature waveguide preparation method.By controlling the species of irrradiation ions,energy,fluence and temperature,optical waveguides can be prepared on glass,semiconductors,polymers,crystals and other materials.In the process of ion irradiation,irradiated ions lose energy in the process of interaction with the material through electronic and nuclear energy loss,which can result in damage to the structure of the substrate and cause structure distortion and change of refractive index which can directly affect the application value of the integrated optical components.Therefore,it is very important to study the microstructure and optical properties of the waveguide.The elementary excitation,electronic state and various interactions within the nanomaterials are different from solid materials;which make nano-materials have a wide range of applications in energy,chemical,defense,aerospace,medicine,etc.The application of nanomaterials is becoming more and more extensive so that more researchers focus on the structure and properties of nanomaterials in harsh irradiation environments.Ion irradiation can damage the structure of materials,meanwhile it can modify the surface of nano-materials,so that some of the properties of materials can get improved and optimized.Therefore,it is very important to study the irradiation mechanism and macroscopic property of nano-materials for improving the nano-material by using ion irradiation technology in the future.The main work of this paper is ion-irradiated optical crystals?MgAl₂O₄,Y₂SiO₅,Pr:Y2SiO₅?and nano-material thin films?ZnO thin films,multilayer WS₂ nanosheets,multilayer MoSe₂ nanosheets?,which includes:the preparation of planar optical waveguide structure by ion irradiation,the lattice damage and optical and mechanical properties of ion-irradiated optical crystals,and modification of layer numbers,thickness and optical band gap of nano-material thin films;.In this paper,the structure,mechanical and optical properties of optical crystals and nano-material thin films before and after irradiation were studied by means of theoretical simulation and experimental characterization.The SRIM software was used to simulate the electronic energy loss,nuclear energy loss,and ion range distribution during ion irradiation.The refractive index distribution at 633 nm of the samples before and after ion irradiation was measured by prism coupling method.Reflectance Calculation method?RCM?was used to reconstruct refractive index distribution of planar optical waveguide structures.The near-field intensity distribution of the planar optical waveguide structure in the visible light band is tested by the end-facet coupling method,and the transmission loss of the planar optical waveguide structure is tested by backscattering method.FD-BPM is used to simulate the optical transmission of optical waveguide based on the refractive index reconstructed by RCM.The damage,element distribution and film thickness of the samples before and after ion irradiation were tested by backscattering/channel?RBS/Channeling?technique.Elements distribution was analyzed by secondary ion mass spectrometry?SIMS?.The structure,surface morphology,film thickness and layer number and optical properties of samples were tested by X-ray diffraction?XRD?,Raman scattering,absorption/transmission spectra,metallographic microscope,atomic force microscopy?AFM?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?.In addition,the mechanical properties of the samples before and after ion irradiation were tested by nano-indentation.Magnesium aluminum spinel?MgAl₂O₄?belongs to the cubic crystal system with corrosion resistance,abrasive resistance,high hardness and bending strength,stable physical and chemical properties,and good optical transmittance in the ultraviolet to infrared light band.It is an ideal functional material which is widely used in short wavelength communications,chemical,electronic devices,laser materials and other fields.MgAl₂O₄ single crystal samples were irradiated with O ions with energy of 6.0 MeV and fluence of 1.5 ×1015 ions/cm² to form planar optical waveguide structures.The results show the ion irradiation caused lattice damage,increased the absorbance;a typical "barrier + well" type optical waveguide structure is formed.We fabricated planar optical waveguide structures with carbon ion irradiation of different energy?6.0 MeV??6.0 + 6.0?MeV?and fluence?5 × 1014 ions/cm²?1×1015 ions/cm²?1.5 ×1015 ions/cm²??4 × 1014 + 5 ×1014?ions/cm²?on MgAl₂O₄ crystal.The results show that the refractive index of the waveguide after C ion irradiation is"well + barrier" type distribution.C ion irradiated samples can ideally confine light transmission,and transmission loss is less than O ion irradiated samples.The lattice damage and color centers of the sample produced by the multi-energy and multi-fluence C ion irradiation process changed the lattice structure of the sample and resulted in high light absorption rate in the visible to near-infrared band.As a widely used new type of laser crystal material with strong chemical stability,low thermal expansion,excellent optical properties and thermal conductivity,Y₂SiO₅?YSO?has drawn much attention in recent years.A planar optical waveguide structure was prepared by irradiating Y₂SiO₅?YSO?with energy of 6.0 MeV at a fluence of 1 ×1015 ions/cm².The results show that the full width at half maximum?FWHM?of the sample increased after C-ion irradiation,the peak position shifted to the higher angle?20 value became larger?,and the grain size became smaller.The Raman peak intensity,hardness and Young's modulus of the samples increased after irradiation.In addition,the C ion irradiation had an effect on the absorption characteristics of the YSO samples at the UV band,and no effect in the visible and near-infrared band.Carbon ion irradiation and oxygen ion irradiation with different energy and fluences were used to fabricate planar optical waveguides on YSO and Pr:YSO crystals.The results show different types of optical waveguides were fabricated in both TE and TM modes.The C ion irradiated optical waveguide can support single-mode while the O ion irradiated waveguides support multi-mode.The absorption of the samples in the ultraviolet band was enhanced obviously after ion irradiation.And the absorbance increased with the increase of irradiation fluence.The hardness and Young's modulus of the samples increased with the increase of irradiation fluence,and decreased after O ion irradiation.The non-metallic ion-doped ZnO material can effectively improve the light absorption of the sample in the visible region.N ions have similar ionic structure and ionic radius like O ions.With low ionic energy,easy handling and abundant resources,N ions are often considered as effective doping ions.ZnO nano-films were prepared on sapphire?Al2O3?by magnetron sputtering method.Part of the samples was treated with N ion irradiation with energy of 90 keV and fluence of 1×1015 ions/cm².The irradiated and non-irradiated samples were subjected to an annealing treatment at 100 to 500 ?.The results show that the N-ion irradiation and the increase of the annealing temperature can improve the crystallization quality of the sample.With increasing annealing temperature,the transmittance and the band gap of the non-irradiated sample decreased.High-quality nano-ZnO thin film materials can be prepared by ion irradiation and annealing treatment at a suitable temperature.With a controllable layer number,1-2 eV bandgap range and many other advantages,single atomic layer or several atomic layer two-dimensional transition metal sulfide are widely used in the catalytic,lubricants,optoelectronic devices,energy and functional nano composite materials and other fields.The multi-layer WS₂ nanosheets were irradiated with O ions with energy of 600 keV and 6.0 MeV at a fluence of 1 x 1014 ions/cm² and 1 × 1015 ions/cm².The results show that the number of layers of WS2 nanosheets reduced,the thickness is thinner after ion irradiation,and the high-energy O-ion irradiation breaks the original triangular structure of the multilayer WS₂ nanosheets.The photonic band gap Eg increases with the increase of irradiation energy.Meanwhile,the photonic band gap decreases with the increase of irradiation fluence.Therefore,the layer number and optical band gap of multi-layer WS₂ nanosheet can be effectively controlled by adjust the O-ion irradiation conditions.The multilayer MoSe₂ nanosheets were irradiated with O ions with energy of 600 keV and 6.0 MeV at a fluence of 1 × 1014 ions/cm² and 1 × 1015 ions/cm².The results show that the nanosheets have larger size and the trend of aggregation;its shape is no longer a perfect triangular structure after irradiation.Ion irradiation with high energy and high fluence decreased the thickness of nanosheet,while O-ion irradiation with low energy and high fluence resulted in better crystallization.Ion irradiation destroys the van der Waals forces and their electronic structures betweenlayers of the multilayer MoSe₂ nanosheets.The transmittance of the sample increased,and the band gap of the multilayer MoSe₂ nanosheets changed after ion irradiation.