Research On Structural And Optical Characteristics Of Nanomaterials By Synchrotron Radiation Small Angle X-ray Scattering And Numerical Simulation

In this thesis,we focus on the nanomaterials are metallic plasmonic nanomaterials,under an external electromagnetic field,the collective oscillation of the conducting free electrons of the metallic plasmonic nanomaterials is referred as localized surface plasmon resonance(LSPR).Due to this fascinating optical properties,metallic plasmonic nanomaterials show great promise for use in surface-enhanced Raman scattering(SERS),optoelectronics,solar cell,metamaterial,catalysis and non-linear optics.The LSPR of metallic plasmonic nanomaterials depends on many factors,including materials,size and shape and the local dielectric environment surrounding the metallic nanostructures.The understanding of the interactions between LSPR and these factors is the fundamental issues in the emerging field of plasmonic.Small angle X-ray scattering(SAXS)is very suitable method for studying the structural information of metallic plasmonic nanomaterials,Herein we use the synchrotron-based small angle X-ray scattering and optical techniques along with transmission electron microscopy measurements,together with numerical simulations,present a comprehensive view of the structure and optical properties of metallic plasmonic nanomaterials.In addition,the application of metallic plasmonic nanomaterials to thin films solar cell materials by simulation using finite-difference time-domain(FDTD).Studies involve preparation method,structural characterizations,plasmonic optical properties and applications of metallic plasmonic nanomaterials involved in this thesis.The main works are summarized as follows:1.X-ray scattering technique is widely used in material structural characterizations.The weak scattering nature however makes it susceptible to background noise and can consequently render the final results unreliable.To address the problem,an iterative method to determine X-ray scattering background is introduced with its feasibility demonstrated by small angle X-ray scattering studies of gold nanoparticles.This method solely relies on the correct structural modeling of the sample to separate scattering signal from background during data fitting processes,which allows them to be immune from experimental uncertainties.In addition,the importance of accurate determination of the scaling factor for background subtraction is also illustrated.2.The broken symmetry of Janus nanostructures(JNs)provides distinctive means to express drastically different chemical and physical characters within a single particle and acquire emergent properties usually inconceivable for homogeneous or symmetric nanostructures.In spite of their tremendous application potentials,considerable challenges are encountered in identifying pathways to synthesize or assemble JNs with controllable geometry and morphology.We exploit the reverse process of growth,i.e.silver etching,to quantitatively control over the structure and optical properties of the DNA-mediated Au-Ag JNs.The transmission electron microscopy(TEM)and optical measurements,along with numerical simulations,present a comprehensive view of the etching dynamics and a detailed analysis of the influencing factors that provide handles for regulating the silver etching rate and progress.3.The deviation between experimental study and numerical analysis in optical properties of Au-Ag JNs has not been fully understood.To address the problem,we use the synchrotron-based small angle X-ray scattering and optical techniques along with transmission electron microscopy measurements,together with numerical simulations,present a comprehensive view of the structure and optical properties of Au-Ag JNs.A simple hybrid conductive junction model for the understanding of the spectral features is presented.Our finding of a strong influence of DNA on the optical spectrum suggests that the DNA need to be considered in designing,understanding and utilizing the optical properties of Au-Ag JNs and other ligand mediated plasmonic nanomaterials.4.In terms of application of metallic plasmonic nanomaterials,we introduce periodic Ag nanowire(Ag NWs)structures into perovskite films to optimize their solar absorption efficiency through plasmonic interactions.A remarkable integrated solar absorption enhancement of 25.9% is attained by incorporating properly tailored periodic Ag NWs arrays into perovskite films.The Ag nanocrosses are further introduced into perovskite films to achieve polarization-independent light harvesting capability.The omnidirectional light absorption enhancement ability of metallic plasmonic nanomaterials embedded perovskite films is also demonstrated.These promising results could open a new path for further improving the absorption efficiency of perovskite films and help pave their way into real-world deployments.