| Ion irradiation as an effective and mature technique for modifying and analyzing the properties of materials,is widely used as key technology in various fields such as semiconductor,information,medicine,physics and chemistry.Among them,ion implantation technology has become one of the major doping methods for semiconductor devices in integrated circuits.When applied in aluminum alloy,metal and ceramic,the material surface modification technology by ion irradiation can significantly improve the wear resistance,corrosion resistance,catalytic performance,superconductivity and optical properties of the workpiece.Based on the interaction between atoms,ion irradiation technology also has very important value and significance in optical material modification,preparation of waveguide structures for light transmission and generation,and two-dimensional materials for light modulation.The integrated optical system mainly involves light generation,transmission and modulation.As an information processing and transmission system,integrated optics devices have the advantages of small size,strong stability,high efficiency,low loss and convenient application,to make them superior in optical information processing and optical communications.Thus optical waveguide has played a crucial role as the basic components of integrated optics.In this dissertation,the ion irradiation technique was applied in several kinds of crystals and successfully prepared optical waveguide structures.Two-dimensional(2D)materials are of great value in the fields of transistors,supercapacitors,photodetectors,sensors and DNA sequencing due to their excellent properties.However,2D materials often require certain features to meet different requirements in practical applications.Therefore,it is necessary to modify 2D materials to achieve specific functions.Ion beam technology has also proven to be a very effective way to modify or design 2D materials.Moreover,the impurities and defects introduced by the ion beam show an important value in the application of two-dimensional materials.The material involved in this dissertation can be divided into two categories:optical crystal and two-dimensional selenide material.The optical crystal materials mainly include LaAlO3,(La,Sr)(Al,Ta)O3,Nd:GdVO4 and Nd:YLiF4 crystal Two-dimensional selenide materials mainly include WSe2 and ReSe2.Due to the different characteristics of the above materials,the ion irradiation process may induce different changes in refractive index,optical absorption and some other features.Thus,it is significant to design the irradiation conditions with different materials for different application purpose.The main contents of this dissertation are as follows:(1)The optical waveguide structures were fabricated by ion irradiation technology,and their structural properties and light transmission characteristics were scientifically studied.(2)Two-dimensional selenide materials were irradiated by carbon ions and their bandgap and luminescent properties were modified to prepare two-dimensional materials for light modulation.In this dissertation,experimental tests and theoretical simulations were applied with different materials to study the change of related properties induced by ion irradiation.Prism coupling and end-face coupling method were used to study the dark mode characteristics and near-field light intensity profile of crystal materials;SRIM software was used to simulate the ion range,distribution,dispersion,doping concentration and energy loss of during the irradiation;the refractive index profile of irradiated crystals were reconstructed by inverse Wentzel-Kramer-Brillouin(iWKB)and Reflectivity Calculation Method(RCM);the optical field transmissions of waveguide devices were simulated by Finite-Difference Beam Propagation Method(FD-BPM);Rutherford backscattering and channel analysis(RBS/channeling)was used to analyze the damage of crystals after ion irradiation process;by means of confocal micro-Raman spectroscopy,absorption spectroscopy and photoluminescence(PL)spectroscopy,the molecular vibration,absorption rate and band gap change before and after ion irradiation were analyzed,respectively;X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and nanoindentation were used to study the structure,elemental composition,chemical state and mechanical properties of the materials after ion irradiation;the morphology of 2D materials were characterized by atomic force microscopy(AFM)and scanning electron microscopy(SEM).Based on the above techniques and simulation methods,the obtained research contents are as follows:Lanthanum aluminate(LaAlO3)crystal is hexagonal structure at room temperature,and changes into cubic structure when the temperature is higher than 813 K.The lattice constants are a = b = 5.36 A and c = 13.11 A for the hexagonal system at room temperature and a = b = c = 3.821 A for cubic system(temperature>813 K).Its melting point is 2080 ?,density is 6.52 g/cm3,hardness is 6.0-6.5 mohs,and dielectric constant is ? = 21.According to different annealing condition,the color of crystal changes from tawny to brown.Due to its excellent optical and dielectric properties,LaAlO3 crystal has great potential in the integrated optoelectronic devices.LaAlO3 crystals were irradiated by C ion at room temperature,and the irradiation conditions are as follows:(1)at the energy of 6.0 MeV,a fluence of 3.0 R 1015 ions/cm2;(2)at the energy of(6.0 + 5.5)MeV,fluences of(5.0 + 4.0)x 1014 ions/cm2;(3)at the energy of 20.0 MeV,a fluence of 1.0 × 1015 ions/cm2.After C ion irradiation,optical waveguide structures applied to optical transmission were successfully fabricated on LaAlO3 crystals.By detecting the waveguide characteristics of the samples,we deduced that different irradiation conditions induced different guiding modes,refractive indexes,and lattice damages.RBS/channeling spectra,XRD patterns and micro-Raman spectra showed the distribution of lattice damage in near-surface regions of samples.We also found that lattice damages were partly restored after annealing process.After proper annealing,at 633 nm,the propagation loss of samples with the irradiation condition(1)and(2)decreased to 3.59 and 3.57 dB/cm,respectively.These results make it possible to use LaAlO3 crystals in integrated optical systems.The LaAlO3 crystal was irradiated by C and O ion with energy of 6.0 MeV at a fluence of 1.5 × 1015 ions/cm2,respectively.After C ion irradiation,the optical waveguide structure applied to optical transmission was successfully fabricated;after O ion irradiation and proper annealing treatment,the optical waveguide structure was also successfully fabricated.The full width at half maximum and intensity of the Raman peak in waveguide region and substrate region showed the distribution of the disorder degree for samples.By comparing the measured results,we deduced that the waveguide fabricated by C ion irradiation could better limit the light propagation in this experiment.Depending on above conclusions,more accurate and appropriate choices can be made in the integrated photonics system.Strontium aluminate tantalum lanthanum(LSAT)crystal is cubic system at room temperature.The crystal system changes from cubic to quadrature or tetragonal structure when the temperature less than 150 K.The lattice constant is a = b = c ?3.868 A at room temperature,melting point is 1840 ?,density is 6.74 g/cm3,hardness is 6.5 mohs,and dielectric constant is ?= 22.According to the annealing condition,the color of crystal changes from transparent to bight brown.LSAT crystal can be served as a good substrate candidate for thin film deposition.The spectroscopy has also been studied from UV to the near infrared region.Thus,LSAT crystals are of great value in optical or laser related applications.The LSAT crystals were irradiated by C ion with the energy of 6.0 MeV at fluences of 1.0 × 1015 and 2.0 × 1015 ions/cm2,respectively.The optical waveguide structures applied to optical transmission were successfully prepared.The damage and microstructural properties of the samples were investigated by RBS/channeling technology,Raman spectrum and XRD pattern.The obtained dark mode characteristic curves and near-field light intensity profiles showed that the two irradiated samples supported TM0 and TM1 mode propagation.The propagation losses of the two irradiated samples were 1.85 and 2.71 dB/cm,respectively.This experiment showed that the sample irradiated by C ion with energy of 6.0 MeV at the fluence of 1.0 × 1015 ions/cm2 could better limit the light propagation.This experiment results also provides reliable experimental basis for the practical application of LSAT optical waveguide.LSAT crystals were further irradiated by C ions with the energy of 20.0 MeV at a fluences of 1.0 × 1015 ions/cm2.The RBS/channeling spectra,hardness and elastic(Young's modulus)as continuous functions of the depth,and XRD spectra were analyzed.The changes of damage,hardness and structure in the near-surface region of the sample were revealed.After proper annealing,the optical waveguide structure applied to optical transmission was successfully formed in the LSAT.The effects of annealing treatment(at several temperatures)on the optical waveguides were studied by prism coupling and end-face coupling method.The annealing condition which results in the lowest waveguide loss(0.83dB/cm)was chosen as the experimental condition for the following spectroscopic analysis.The Raman spectra showed annealing effect on the recovery of damage for LS AT sample.Nd:GdVO4 crystal with 1%Nd doping concentration(atomic ratio)was used in the experiment.The crystal is tetragonal structures with space group of I41/amd,and its density is 5.47 g/cm3.The refractive index of Nd:GdVO4 crystal is n0 = 1.972,ne =2.192 at 1064 nm wavelength.The Nd:GdVO4 crystal is an efficient diode-pumped laser material with an absorption band of about 1.6 nm at 808.4 nm wavelength,which is well matched with the emission band of a GaAlAs laser diode.And it shows excellent spectral properties,such as a large emission cross section and high Raman gain effect.Therefore,as an important functional material,Nd:GdVO4 crystal has attracted a great deal of attention.However,its lattice structure is easily changed by ion irradiation,thus the corresponding optical properties changed.Nd:GdVO4 crystals were irradiated by H and C ions.The waveuigde structures applied to light generation were successfully formed.The irradiation conditions are as follows:(1)H ion irradiation:at the energy of 460.0 keV,a fluence of 5.6 × 10l6 ions/cm;(2)C ion irradiation:at the energy of 6.0 MeV,a fluence of 1.0 × 1015 ions/cm2;(3)C ion irradiation:at the energy of 6.0 MeV,a fluence of 3.0 × 1015 ions/cm2.The dpa distribution,shifts of XRD diffraction peak,hardness and elastic modulus of samples,and micro-Raman spectra indicated that the lattice disorder was induced by the ion irradiation.The peak intensity and position of Raman spectra had obvious changes between the waveguide and substrate region.These provided accurate information for analyzing the lattice structure changes in ion irradiated Nd:GdVO4 crystal.The studies of absorption spectra,fluorescence spectra,refractive index profiles,and the formation of waveguide structure also indicated that damage was generated in the samples.In addition,it was found that lattice damage in near-surface region caused by C ion(medium-mass ion)irradiation was higher than that caused by H ion(light ion)irradiation with similar dpa.Nd:YLF crystal is tetragonal system.The lattice contant is a = 5.26 A,c = 10.94 A,the density is 3.95 g/cm3,the melting point is 825?,the hardness is 4-5 mohs,and light transmission range is 0.1-7.5,?m.The refractive index are n0 = 1.448 and ne =1.47 at 1.053,um wavelength.The laser wavelength is ? = 1.047,?= 1.053,and the fluorescence life is about 485,?s.Due to its large fluorescence line width and natural birefringence,Nd:YLF crystal is a good candidate for low threshold wave(CW)mode-locked laser.It has broad application prospects in ultrafast pulsed laser system.The Nd:YLF crystal was irradiated by 80.0 keV Ga ion with a fluence of 1.0 × 1015 ions/cm.The XRD pattern and fluorescence spectra demonstrated that the overall crystallinity and intrinsic photoluminescence features of the Ga-ion irradiated Nd:YLF were well preserved.The Raman intensity increased at 325 cm-1,which had important potential application value in the actual production.Tungsten diselenide(WSe2),a semiconducting transition-metal dichalcogenides(STMD),has drawn great attention in the recent years,due to its p-type semiconductor properties.Monolayer WSe2 is becoming an attractive choice for photovoltaic and photoconductive device applications.Unlike its bulk materials,monolayer WSe2 is a direct bandgap semiconductor.Thus it is suitable for optoelectronics,light,chemical sensors,spin coupling valleys,and other related applications.In order to explore its defect effect,the monolayer WSe2 on Al2O3 was irradiated with a 1.0 MeV C ion at fluences of 5.0 x 1013 and 5.0 x 1014 ions/cm2.AFM images showed that C ion irradiation could effectively control the sample's shape,size and some other parameters.The Raman spectra showed the vibrational and electronic properties of the monolayer WSe2 sample after C ion irradiation.The PL spectra showed that the bandgap of the sample could be effectively controlled by C ion irradiation,which has important application value in the preparation of two-dimensional materials for light modulation.ReSe2,another kind of STMD material,has been extensively researched because of its excellent optical and electrical properties,and has great potential in applications beyond CMOS devices.Unlike WSe2 and some other STMDs,ReSe2 materials rely less on the number of atom layers in terms of optical and vibrational properties.In order to explore its defect effect,the multilayer ReSe2 samples(grown on single-crystal-Al2O3 substrate by CVD)were irradiated by 1.0 MeV C ions at the fluence rates of 5.0 x 1013 and 5.0 × 1014 ions/cm2,respectively.The results confirmed that the size,thickness,and morphology of the ReSe2 samples could be effectively controlled after 1.0 MeV C ion irradiation from the AFM and SEM images.The crystallinity of the ReSe2 flakes was improved with increasing layer number after 1.0 MeV C ion irradiation by XRD pattern.The redshifts of the Raman modes after 1.0 MeV C ion irradiation indicated that interlayer van der Waals interactions were not strong enough to determine the layer dependence of the phonon behavior.In addition,in photocatalysis,the bending of the surface energy band can be a good way to suppress the recombination of electrons and holes,thus improving the quantum effect of the reaction. |
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