Synthesis Of Silver Nanowires And Their Applications In The Transparent Electrode And Surface-enhanced Raman Scattering

Silver nanowires(Ag-NWs)have received considerable attention because of their outstanding electrical,optical,mechanical properties,and surface plasmon properties.Currently,Ag-NWs have been used in many fields such as transparent electrodes(TEs),surface-enhanced Raman scattering(SERS),catalysis,and micro-nano-electronics device.However,the TEs made from Ag-NWs still face a series of challenges such as large initial sheet resistance and poor chemical stabilities when exposed in the environment,greatly hindering their commercial applications.When used in the field of SERS,the Ag-NW SERS substrate lacks sufficient“hot spots”and moreover their number and distribution are difficult to control.These factors results in poor spectral reproducibility and stability,not satisfing the requirements for practical actual detection.Focusing on the above problems,this thesis mainly carried out the following researches content:1.Photo-assisted polyol synthesis of Ag-NWs with an aspect ratio of 500.Many previsous researche have revealed that increasing the aspect ratios of Ag-NWs is an effective way to improve the optoelectronic performance of TEs.However,Ag-NWs synthesized using traditional polyol reduction method usually have an aspect ratio lower than 300.This thesis reports a modified polyol reduction method to synthesized Ag-NWs with average diameters as thin as 50 nm and an aspect ratio up to 500.The success of this synthesis is based on the employment of optical radiation in the nucleation stage and does not require to change any other experimental conditions.The optical radiation will increase the nucleation rate and then lead to decreasing the size of the nucleus.The decrease of nucleus size will thin Ag-NWs diameter and don't impact the Ag-NWs length,increases the aspect ratios of Ag-NWs.Besides,this thesis have further determined the relationship between the final morphology of the Ag-NWs and copper chloride amount,temperature,the molar ratio of PVP to silver.2.Room temperature welding of Ag-NW TEs to improve their conductivity.Ag-NW TEs have emerged as a promising next-generation transparent electrode.However,the current Ag-NW TEs are often plagued by high NW-NW contact resistance,which can be largely attributed to the ill-defined polyvinylpyrrolidone(PVP)surface ligands and non-ideal Ag-PVP-Ag contact at NW-NW junctions.This thesis report a room temperature direct welding strategy to greatly improve the conductivity of the Ag-NW TEs.Specifically,this thesis use a sodium borohydride(Na BH₄)treatment process to thoroughly remove the PVP ligands and produce a clean Ag-Ag interface that allows direct welding of NW-NW junctions at room temperature,thus greatly improving the conductivity of the Ag-NW films while not affecting their transmittance,outperforming those obtained by thermal or plasmonic thermal treatment.The mechanism study shows that the carbonyl group of PVP bonded with Ag-NW can be displaced by the hydride derived from the hydrolysis of Na BH₄,thereby enabling complete removal of PVP from Ag-NWs surface.3.Electrochemical cleaning of the Ag-NW TEs to improve their carrier transport properties.Based on the hydrogen displacement mechanis m of Na BH₄ to remove PVP from the Ag-NWs surface,this thesis have further proposed a rapid electrochemical cleaning strategy.Similar to the hydrogen displacement mechanism of Na BH₄,the hydrogen adsorption/desorption process in the hydrogen evolution rea ction(HER)can also effectively remove the PVP layer from the Ag-NWs surface.The difference is that the electrochemical removal of PVP in the HER region is a result of the hydrogen displacement process(major role)coupled with the electrostatic desorption process.This thesis show that the removal of the PVP ligands can substantially reduce the sheet resistance of the Ag-NW TEs from 49 to 13 ohm/sq(with90.91%transmittance at 550 nm)and reduce the interfacial resistance at the Ag-NW TE/active layer interface by 94.3%in the vertically stacked devices,the in-plane and out-of-plane carrier transport performance of Ag-NW TEs have been greatly improved.4.Dodecanethiol modification of Ag-NW TEs to improve their long-term stability.Ag-NWs are susceptible to degradation via the vulcanization process when exposed in the ambient environment,resulting in a sharp increase in the sheet resistance of Ag-NW TEs.So,the long-term stability of Ag-NW TEs is another critical issue for practical applications apart from sheet resistance an d transmittance.Considering that the thiol group of dodecanethiol(DT)shows great affinity to silver metal and DT can easily form a dense and ordered monolayer on the Ag surface to prevent Ag from vulcanization.This thesis first use the Na BH₄ treatment process to produce a surface-cleaned Ag-NW TEs,and then decorating it with a dense,ordered,and hydrophobic DT protective layer.As a result,the stability of the Ag-NW TE can be greatly improved by 150-times compared with that of PVP-wrapped ones in the summer air(average relativity humidity,>90%;average temperature,>25°C).Furthermore,the clean Ag-Ag interface at NW-NW junctions has not changed and the thickness of the DT layer is only 1-2 nm so that after decorating the surface-cleaned Ag-NW TEs with the DT protective layer,the conductive,transmittance,and flexible properties of Ag-NW TE is hardly affected.5.Preparation of ordered SERS substrate with improved hot-spots from Ag-NWs.Designing a SERS substrate with highly repeatable and unifor m“hot spots”structure is essential to obtain stable and repeatable SERS signals.This thesis assembly of Ag-NWs into an ordered array arranged side by side through the self-assembly process at the liquid-liquid interface,and then the Ag-NPs with uniform distribution grew on the Ag-NWs surface by the light-induced method.The“hot spots”will be formed at Ag-NP/Ag-NW junctions,thus enhancing the intensity of the local electromagnetic field.Raman measurement results show that our SERS substrate not only can effectively enhance the Raman scattering of Rhodamine 6G molecular but also can obtain consistent Raman spectroscopy at different substra te sites,improving the stable and reliable of SERS signals.Moreover,Ag-NWs has dimensions spanning from nanometer to sub-micrometer length scale.Their large surface areas make them ideal SERS substrates for large-scale sensing applications.This thesis provides a feasible solution for the preparation of high-performance TEs and SERS substrate based on Ag-NWs,greatly facilitating Ag-NWs applications in transparent electrodes and SERS field.