Plasmonic Photothermal Effects Of Metal Nanoislands

Surface plasmons are the collective coherent oscillation effect of free electrons on the metal surface.When the frequency of the incident light is the same as the electron collective oscillation frequency,it will cause the surface plasmon resonance.The surface plasmon resonance of metal nanostructures can confine the light field to the sub-wavelength scale,thereby breaking the optical diffraction limit and enhancing the interaction between light and matter.The plasmon resonance relaxation of metal nanostructures produces local field enhancement,hot electrons and thermal effects,which can be widely used in the fields of photocatalysis,material growth,biotherapy,environmental governance,and energy engineering.Metal nanostructures worked as heat sources can not only catalyze molecular reactions,but also drive the transformation of micro-nano crystals.Based on the design and development of nanoislands and their composite systems,our work focuses on the study of plasmonic photothermal effect in micro-nano crystal transformation,molecular catalysis,as well as the optimization design of semiconductor photocatalysts.The main research contents and results are summarized as follows:1.The fast transformation of rare-earth doped luminescent sub-microcrystal is achieved by the photothermal effect and catalytic effect of plasmonic nanoislands.NaYF4 polycrystal can be quickly transformed into Y2O3 single crystal within tens of milliseconds under the plasmon resonance excitation of Au nanoislands,accompanied by the optimization of the crystal structure and a significant increase in luminescence.The rate of crystal transformation is controlled not only by the power and wavelength of laser irradiation,but also by changing the size and gap of the nanoislands.In addition,plasmon-driven crystal transformation is also achieved at very low temperature,which breaks through the technical bottlenecks of traditional methods that rely on high temperature,long cycle and high energy consumption,and realizes a new technology with high resolution,strong targeting and environmental friendliness.Compared with Au nanoislands system,a higher crystal transformation efficiency is realized by Ag nanoislands.However,Ag is easily oxidized in air,resulting in poor stability of photothermal efficiency,which needs to be further improved.2.Design a heat-trapping structure to enhance the photothermal effect of plasmon-driven crystal transformation.The introduction of the heat-trapping layer Al2O3 on the surface of the Au nanoislands can significantly improve the efficiency of crystal transformation,thereby enhancing the plasmonic photothermal effect.Due to the enhanced light absorption and effective heat utilization,the crystal transformation efficiency induced by the heat-trapping structure can be increased by 10 times compared with the pure Au nanoislands system.A relatively high and stable photothermal conversion efficiency is also achieved by heat-trapping structure at very low temperature.Moreover,the introduction of the heat-trapping layer can also improve the photothermal stability of the plasmonic Ag nanoislands.It provides an efficient pathway for the design and development of plasmonic photothermal structure and photothermal manipulation of plasmons at nanoscale.3.The role of photothermal effects in the plasmon-induced catalytic reaction is studied by in-situ monitoring SERS spectra of 4-NTP and 4-ATP molecules.With assistance of plasmonic Ag nanoislands,both the 4-NTP and 4-ATP molecules can be catalyzed into DMAB molecules.And the catalytic efficiency of Ag nanoislands gradually increases with the increase of environment temperature.Moreover,the 4-NTP molecule is hardly to transform to DMAB molecule at nitrogen liquid temperature,while the 4-ATP molecule is easily to transform to DMAB at such extremely low temperature.The SERS spectra investigations by Ag NIs demonstrate that the thermal effect is a key to driving the catalytic reaction of 4-NTP while the hot electrons play an important role in catalytic reaction of 4-ATP.Therefore,the plasmon-induced photocatalytic reaction is not only depends on the hot electrons generated by the metal nanostructure,but also the thermal effect plays an important role in catalytic process.These results provides certain reference and guiding significance for the photothermal application of plasmonic nanomaterials.4.Light-excited semiconductor photocatalysts can induce carrier transitions to participate in redox reactions.The mechanism and regulation characteristics of defect-induced photocatalysis of BiOI semiconductor materials have been studied through theoretical simulations.By introducing oxygen vacancies and I self-doping defects into the BiOI bulk phase and {001} surface structures,the absorption of visible light can be enhanced and photocatalytic activity can be improved.The electronic structure and optical properties of the BiOI {001} monolayer is further controlled by applying biaxial strain.It is found that the utilization of visible-light region is broadened under tensile strain.The research based on the photocatalytic mechanism of BiOI provides a theoretical support and new insights for the structural design of the photocatalyst and its practical application.