Preparation Of Plasmonic Copper Chalcogenide Semiconductor Nanocrystals

For many years,metal nanomaterials with localized surface plasmon resonances（LSPRs）have been a research hotspot in the field of nanotechnology.Before 2009,almost all plasmon work was based on the metals copper,silver and gold.Until 2009,ZHAO and co-authors proved for the first time that semiconductor nanomaterials also exhibit LSPR properties through groundbreaking theoretical predictions and experimental analysis.This discovery broke the inherent knowledge of previous confinement of plasmons to metal nanomaterials,extending it to the semiconductor nanomaterials.Since then,the research of semiconductor plasmons has begun to enter people’s sight.Among many semiconductor nanomaterials,the environmentally friendly copper chalcogenide(Cu_2-xE,E=S,Se,Te)semiconductor nanocrystals（NCs）have been shown good potential applications in light capture,photovoltaic,photocatalysis,near-infrared（NIR）imaging,photothermal therapy,chemical sensors,radio communications,plasmonic-based solar cells and flexible display devices,which have attracted our attention.Although several studies have been reported on copper chalcogenide semiconductor NCs.However,the current international research on the properties of semiconductor nanocrystalline plasmons is still in its infancy,and there are still many issues that have not been resolved.So a lot of work is still needed to further deepen its mechanism and potential practical applications.Herein,several preliminary studies have been made on the synthesis,properties and applications of plasmonic copper chalcogenide semiconductors.The main research contents and results are as follows:In chapter two,a series of novel highly monodisperse colloidal copper-bismuth-sulfide（Cu_xBi_yS,x,y>0）semiconductor NCs have been synthesized by using standard Schlenk line with Cu Cl and Bi Cl₃ as cation precursors.We systematically study the transformations of morphologies,crystalline phases,sizes,nonstoichiometric compositions of these NCs and their relationships with their NIR LSPR absorption spectra and demonstrate that these ingredients can be tuned radically by adjusting the Cu/Bi precursor molar ratio.Furthermore,the NIR LSPR absorptions of Cu_xBi_yS NCs are relevant to their sizes and nonstoichiometric compositions and blue-shift and increase in the LSPR peak position and intensity,respectively,due to the increment of copper deficiency with increasing the Bi/Cu precursor molar ratio.Subsequently,hydrophilic Cu_xBi_yS NCs are synthesized through a ligand-exchange process by using an amphiphilic ligand 3-mercaptopropionic acid（MPA）and their LSPR bands can be spectrally tuned in the NIR―water window‖region.Hydrophilic MPA-capped Cu_xBi_yS NCs show high photothermal conversion efficiency,negligible cytotoxicity,good photostability and excellent biocompatibility.The feasibilities demonstrate that these NCs can act as an effective photothermal agent for the preliminary study in-vitro photothermal imaging and photothermal therapy.In chapter three,semiconductor plasmonics is a recently emerging field that expands the chemical and physical bandwidth of the hitherto well established noble metallic nanoparticles.Achieving tunable plasmonics from colloidal semiconductor nanocrystals has drawn an enormous interest and is promising for plasmon-related applications.However,realizing this goal of tunable semiconductor nanocrystals is currently still a synthetic challenge.Here,we report a colloidal synthesis strategy for highly dispersed,platelet-shaped antimony?doped copper sulfide（Sb_y-Cu_xS）semiconductor NCs with a dominant LSPR band tunable from the NIR into the mid-visible spectral range.This work presents the synthesis and quantifies the resulting plasmonic features.It furthermore elucidates the underlying carrier concentration requirements to realize a continuum of LSPR spectra.Building on our previous work on binary plasmonics Cu_xS,Cu_xSe,and Cu_xTe NCs,the present method introduces a much wider and finer tunability with ternary semiconductor plasmonics.In chapter four,the synthesis of highly anisotropic multiply-twinned semiconductor NCs with specific properties is highly desirable but still remains a significant challenge.Here,we present a multi-step thermal seed-mediated growth approach for the synthesis of homogeneous copper?antimony?sulfide triangular nanoplates and their subsequently self-assembled into highly anisotropic five-fold twinned NCs.The highly anisotropic copper?antimony?sulfide five-fold twinned NCs exhibit both enhanced LSPR and surface-enhanced Raman scattering（SERS）properties,which might attributed to the strong plasmon coupling effects that enable the enhancements of electromagnetic field at the adjacent internanoplate junctions and sharp corners or edges in these five-fold twinned NCs.Hence,this strategy provides an approach for the design and fabrication of a new class of highly anisotropic multiply-twinned nanostructures for some potential applications,such as plasmonic-based optical modulation,catalysis,sensing,and smart-windows.In chapter five,heterojunction photocatalysts are widely adopted for efficient water splitting,but ion migration can seriously threaten the stability of heterojunctions,as with the well-known low stability of Cd S-Cu_2?xS due to intrinsic Cu^I ion migration.Here,we utilize Cu^I migration to design a stratified Cd S-Cu_2?xS/Mo S₂ photocatalyst,in which a unique Cu^I@Mo S₂（Cu^I-intercalated within the Mo S₂ basal plane）is created by Cu^I migration and intercalation to the adjacent Mo S₂ surface.These epitaxial vertical growth of Cu^I@Mo S₂ nanosheets on the surface of one-dimensional core-shell Cd S-Cu_2?xS nanorods form catalytic and protective layers to simultaneously enhance catalytic activity and stability.Charge transfer is verified by kinetics measurements with femtosecond time-resolved transient absorption spectroscopy（fs-TA）and direct mapping of the surface charge distribution（SCD）with a scanning ion conductance microscope（SICM）.This design strategy demonstrates that the potential of utilizing hybridized surface layers as effective catalytic and protective interfaces for photocatalytic hydrogen production.In chapter six,plasmon-induced hot-electron transfer（PHET）from metallic nanostructures is a new paradigm for enhancing solar light energy conversion efficiency.However,one critical issue limiting the reported efficiencies of devices based on this concept is often the loss of hot electrons via ultrafast electron-electron scattering and thermalization.A new proposed prestissimo charge-transfer mechanism,called the plasmon-induced interfacial charge-transfer transition（PICTT）,that enables a direct,instantaneous transfer of hot electrons from a plasmonic-metal into its strongly coupled interfacial semiconductors,arising from the ultrafast nonradiative plasmon decay.This innovative and ultrafast PICTT process could not only direct the plasmonic energy flow via strong interfacial plasmon coupling,but also overcome the above limitation caused by PHET and simultaneously enhance the photoelectric conversion efficiencies in optoelectronic devices.Despite the fact that impressive progress has been made in studying the mechanism of plasmon coupling,the intrinsic mechanism that governs the energy-or charge-transfer from plasmonic metals to semiconductors remains largely elusive.Several theoretical and experimental studies have concluded that efficient plasmon-induced ultrafast hot-carrier transfer was observed in plasmonic-metal/semiconductor heteronanostructures.The reported PICTT mechanism is potentially a general phenomenon at metal/semiconductor or metal/molecule heterointerfaces.Thus,PICTT may present a new opportunity to limit energy-loss in plasmonic metal nanostructures and increase device efficiencies based on plasmon coupling.