| Benefiting from increasing advances in nanotechnology,the peculiar optical properties of nanostructures and its applications have attracted widespread attention of the researchers recently.We can manage and control the basic optical process,such as light transmission,scattering,and absorption by using the metal and dielectric nanostructures with certain morphology,which have important applications in the fields of energy,communications and even biomedical.Where the use of dielectric nanostructures to achieved light management in the photoelectric device,the surface plasmon enhanced optical process of noble metal nanostructure and metamaterial absobers based on metal/dielectric composite nanostructures are all the current focus.Effective refractive index is a key parameter in optical property characterization of dielectric nanostructures,and the effective refractive index is closely related to the certain morphology of nanostructures.Therefore,controllable fabrication of nanostructures is the key to achieving light management processes.For noble metal nanostructures,which enhanced optical effects come from the surface plasmon resonance.The surface plasmon resonance of metal nanstructures have applied in many fields,for instance,surface enhanced Raman,enhanced light absorption in semiconductor and enhanced photoluminescence/light extraction.However,most of the physical mechanism of enhanced optical process remains to be further explored,obviously,the enhanced optical effects and the nature of the metal nanostructures are inseparable,including materials,morphology,etc.In addition,plasmonic metamaterials have aroused wide interests and investigation,which prompting researchers to launch massive discussions of the perfect electromagnetic wave absorption mechanism as well as a variety of metastructures design.The metamaterial perfect absorbers have many applications in photoelectric device,highly sensitive sensors,detection chip and stealth coating.This thesis based on more than a few issues to do targeted research,mainly include:(1)in the aspect of nanstructures fabrication,we explore the preparation of the metal and dielectric nanostructures by performing cluster beam deposition;(2)in the investigation of the physical mechanisms,we mainly discuss the anti-reflection and light extraction mechanisms of the porous dielectric nanostructures with tunable refractive index,the near field/far field transformation mechanisms by using the silver nanoparticle arrays and the perfect absorption mechanisms of the plasmonic metasurface;(3)in the application of nanostructures,we optimized the optical performance of the light emitting device by using porous dielectric nanostructures and metal nanoparticle arrays,in addition,the plasmonic metastructure was also used for the surface enhance Raman scattering study.The main results are as follows:Porous dielectric nanostructures with tunable porosity and refractive index were fabricated with cluster beam deposition.Due to self-shadowing effects,the nanoparticles couldn't deposit on the shadow region of the deposited nanoparticles,which induced porous structures and formations of column-like structures.The porosity and refractive index of the nanostructures can be tuned by change the deposition angles.On the other hand,we prepared Ag nanoparticle arrays by performing cluster beam deposition and solid-state dewetting process.Cluster beam deposition has its natural advantages in the preparation of nanoparticle arrays,however,which is not efficient in preparing sparse as well as large size nanoparticle arrays,the solid-state dewetting method can just to make up for this shortfall.In addition,after the structural analysis of more than 50 samples,we obtained a structural-phase diagram of nanostructure formation in the solid-state dewetting process.According to the structural-phase diagram,we can fabricate Ag nanoparticle arrays with certain morphology by confirming thickness of the film and annealing temperature.In this thesis,two types of light management process were investigated,light anti-reflection and light extraction of the porous nanostructure and concluded that:(1)The TiO2 nanoparticle films show broadband transmittance enhancement,the light transmittance of the coated glass slide increases 2%by average in the wavelength range of 400?800 nm,which due to the graded-refractive index effect.The broadband transmittance enhancement is polarization dependent.Angular selective optical transmittance is observed for p-polarized light,which comes from the anisotropy of the nanoparticle assembling.(2)The TiO2 nanoparticle layers were deposited on the bottom surface of the hemispherical glass prism to investigate the light extraction under total internal reflection.Effective extraction of the light trapped in the substrate due to TIR with the TiO2 nanoparticle layers was demonstrated.The transmittance of the light under the TIR conditions was found to increase rapidly with the porosity,which can be raised by adopting a larger incident angle of cluster deposition.The transmission spectrum was found to vary inversely with the fourth power of the wavelength,indicating that the mechanism for light extraction is based on Rayleigh scattering.(3)The porous TiO2 nanoparticle coatings were fabricated on the surface of GaN LEDs to enhance their light output power.A nearly 92%enhancement of the PL intensity as well as a 30%enhancement of the EL intensity was observed.The strategy of our current enhanced light extraction demonstrates an alternative mechanism for LED light output enhancement,which has the advantage that it induces no alterations in the electrical properties of the LEDs and can function with the microscale surface texturing in parallel to generate an additional enhancement.In addition,we fabricated two kinds of hierarchical structures,multiple beveled surface/ZnO and polystyrene/ZnO micro-nano structure on the surface of the LEDs and the light output power is improved by 59.1%and 77%compared to the original planar LEDs,respectively.In this thesis,we also systematically studied the mechanism of the Ag nanoparticle arrays scattered evanescent field into a far-field radiation.Firstly,we quantitatively measured the light extraction efficiency of the Ag nanoparticle arrays with different size and density,and found that the light extraction was highly efficient for the sparse large size nanoparticle arrays.From the FDTD calculations,we conclude that the resonant scattering of the evanescent waves induced by total internal reflection of light on Ag NP layers under SPR was the dominant mechanism in the light extraction process.For the Ag nanoparticle arrays,two kinds of modes can be excited by the incident evanescent field,radiation mode and wave-guiding mode.The radiation mode can be excited under the condition of large inter-particle distance,and when the inter-particle distance is very small,the plamonic wave-guiding will be occurs.In addition,from the experiments we found that when the Ag nanoparticle arrays scattered evanescent field into a far-field radiation,especially,the back scattering is more effective,which could be applied for improving the light extraction efficiency of light emitting devices.By fabricating Ag nanoparticle arrays on the bottom face of the device substrate,a nearly 122%enhancement on the PL intensity was observed without any obvious change of the peak position.We also studied the optical properties of Ag nanoparticles/dielectric layer/Ag film metasurface and its application in surface enhanced Raman scattering.Here we demonstrated a simple method to create a metamaterial absorber by randomly depositing Ag nanoparticles onto an Ag film coated by a dielectric spacer layer,making no effort to control the spatial arrangement of the nanoparticles on the film.We show that the film-coupled nanoparticles provide a reflectance spectrum that can be tailored by varying the geometry(the coverage of the nanoparticles and/or the thickness of the spacer).By carefully controlling the spacer thickness and nanoparticle coverage,near-total power absorption at visible wavelengths was achieved,which can be partly attributed to an interferometric effect.The film-coupled nanoparticle metasurface supports magnetic and electric resonances.These can be considered to generate effective electric and magnetic currents that generate far-fields that cancel,leading to zero reflection and complete absorption.As one might intuitively expect,the total absorption property is accompanied by very strong local field enhancement.We demonstrate that this is highly advantageous for SERS and the measurements show that the SERS enhancement factor is about 109. |
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