| The unique chemical and physical properties of nanomaterials makes them extremely useful for science and industry,such as catalysis,energy storage or conversion and biological detection.The functions of nanomaterials are strongly dependent on their size,shape and composition.It is highly important to reveal the structure-function correlation for creating novel structures with high activity or even new function.However,the conventional ensemble measurements can only obtain the average signal from a large number of nanoparticles(NPs),which may be influenced by a lot of complex factors and cannot be directly related to structural heterogeneity of NPs.Revealing the particle-specific activity at the single NP level appears to be the most effective way to overcome such a barrier.Recently,electrochemical dark field scattering technique,which enables in situ acquisition of the scattering spectra of single plasmonic nanoparticles in an electrochemical system with a high sensitivity,high throughput and negligible interference,have attracted increasing attentions.However,most of the reported setups suffer from the optical path distortion caused by solution layer,which dramatically deteriorates the time resolution and detection limit of such a technique.Addressing the above issues,we designed a new setup with an ultrahigh sensitivity,which allows for characterization of some challenging electrochemical system.The design can be further applied for improving the spatial resolution and detection sensitivity of the electrochemical Raman spectroscopy.The main results and conclusions of this thesis are listed as follows:1)We designed a completely new setup based on the water immersion objective,which effectively eliminates the optical path distortion and improves the detection sensitivity.We further introduced the supercontinuum white laser to our setup to further improve detection sensitivity and the time resolution above three order of magnitude.For the first time,we were able to obtain the dark field spectrum and image of single Au NP down to the size of 7 nm in the electrochemical environment.2)Such an ultrasensitive setup enabled us to in situ reveal the mechanism of underpotential deposition(UPD)process on single Au NP surfaces.We successfully used the potential-dependent scattering spectra to reconstruct the cyclic voltammograms of single NPs,and clearly identified different underpotential deposition potentials on Au NPs with different facets.Furthermore,we were able to identify the different UPD potentials on different facets of single NP surfaces,and even calculated the area ratio of different facets through spectra shift.3)We further applied the method to study the silver UPD and overpotential deposition(OPD)on the surface of single nanorods.For the first time,we directly observed the silver UPD process on single nanorod,and identified different deposition potentials at different facets.The results show that the facet on the apex is more active than the side surface,for the UPD with a potential difference of 5 mV.Whereas it is the opposite for OPD,in which silver tends to deposit on the side surface at small overpotential.Silver gradually deposits on the whole surface with the increased overpotential.The apex surface becomes dominant site for the deposition at a high overpotential.Tlie above conclusions provide a new understanding of the role of silver ion and pH for the synthesis of Au nanorod.4)Water immersion objective was also successfully applied for designing the novel setup for electrochemical Raman spectroscopy,which dramatically improves the intensity and spatial resolution of Raman spectroscopy.It further allows the extension of the electrolyte layer thickness to 2.0 mm,which can effectively avoid the adverse impact of thin layer on the real electrochemical reaction,such as the hindered diffusion and increased ohmic drop.All these are critical for pushing the electrochemical Raman studies to single nanoparticle level or specific electrochemical reactions with extremely weak signal. |
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