Dual-Electromagnetic Field Enhancements And Quantum Plasmons Through Metallic Nanofingers

The research of surface plasmon optics of metal micro-nano structures is a frontier cross-cutting hot spot in photo-physics,materials and information science.The excitation of the plasmon resonance mode will selectively absorb and scatter the incident light of a certain frequency;at the same time,the energy of the incident light field will be concentrated in the sub-wavelength spatial range,and a locally enhanced electromagnetic field will be formed near the metal surface.Improving the efficiency of the optical processes located near it has shown important application potential in the fields of nonlinear optical enhancement and photoelectric conversion.Compared with the resonance excitation of a single nanostructure,the metal coupling structure can obtain a stronger enhanced electromagnetic field due to the coupling effect between the structures.The realization of the optimal coupling electromagnetic field in the metal coupling structure is determined by the classic electromagnetic theory and quantum effect.Classical electromagnetic theory shows that the smaller the gap in the coupling structure,the coupling electromagnetic field strength continues to increase exponentially;while the quantum effect shows that the smaller the gap,the quantum tunneling of electrons on the metal surface in the gap is obvious,which will significantly reduce the coupling electromagnetic field strength,so it is inevitable.There will be an optimized gap to maximize the coupled electromagnetic field.Therefore,it is of great scientific significance and application value to study the regulation and precise preparation of coupled electromagnetic fields in metal coupling structures.However,due to the limitation of physical micromachining resolution,the minimum gap size is only 5nm,which is much larger than the optimal gap under the control of quantum plasmon(for metal/air/metal coupling structure,the optimal gap is 0.6nm).In addition,the gap structure formed by the bottom-up metal film/medium/nanoparticles is constructed by molecular layer self-assembly to construct an extreme gap with a step size of 0.5 nm,but the excitation has limitations and the manufacturing cost is high.In response to this scientific problem,this paper proposes a new type of metal coupling structure,that is an ordered structure of flexible metal nanofinger.This structure is prepared by techniques such as nanoimprinting,by depositing a dielectric film on the nanofinger and then titrating The solvent,using its surface tension during the volatilization process,causes two or two nanometer fingers to collapse against each other to form a metal/medium/metal ordered coupling structure.In this coupling structure,the gap size is determined by twice the thickness of the dielectric film.Since the film deposition technology has reached the atomic level of regulation,the gap size can be precisely adjusted from a few Angstroms to a few nanometers.On this basis,this paper mainly carried out the following research.First,from the point of view of in-situ dynamics,the physical mechanism of the quantum effect on the coupled electromagnetic field is accurately studied.See below for details:First,we use the large-area flexible metal nanofinger ordered array structure we developed,by titrating the high surface Tension-free absolute ethanol,through the surface tension during its volatilization process,causes the nanofinger to collapse with each other,thereby constructing a zero-gap metal/metal coupling structure.Then use the principle of the plate capacitor to add the same charge between the metal nanofingers that are in contact with each other,and use the electrostatic repulsion changes caused by different voltages to adjust the gap to gradually increase from zero.Experimentally,we studied the coupling mechanism of the coupling electromagnetic field strength with the gap through in-situ micro-region reflectance measurement.As the voltage increases,we observe the preliminary results of the redshift of the BDP resonance mode,which matches the predictions of quantum theory.Related research results provide guidance for the design of metal coupling structures.Second,the double-local coupling enhanced electromagnetic field effect of the suspended flexible metal nanofinger array was studied.In the metal micro-nano structure,since the substrate has a larger dielectric constant than free space,therefore,where it is combined with the substrate,it will cause the localization of the enhanced electric field into the dielectric substrate,so that this part of the electric field It cannot be used to enhance the efficiency of optical processes,such as Raman.Therefore,on the basis of flexible metal nanofinger,we use selective etching of oxygen plasma,so that the edge of the metal nanodisk can be separated from the contact of the polymer nanopillar,and the local field at the bottom of the nano-disk can also be removed from the polymer nanometer.The column is decoupled into free space.Through the deposition of 1nn ultra-thin ta-C medium,the finger collapsed under the action of high surface tension,and the metal/medium/metal coupling system under the extreme gap was successfully constructed.Under the effect of near-field coupling,the coupling strong field at the gap is greatly At the same time,it can be diffused into the free space of the upper and lower surfaces through the ta-C film.For the double local field enhancement effect of the suspended system,we mainly carry out multiple verifications through optical experiments and numerical simulation based on COMSOL.