CN106033059B - Electric-field-enhancement structure - Google Patents

Abstract

The present invention provides an electric field enhancement structure, comprising a base layer and a dielectric layer disposed on the surface of the base layer, and further comprising an isolation layer disposed on the surface of the dielectric layer and a dielectric particle layer disposed on the surface of the isolation layer, The dielectric particle layer is formed of a plurality of dielectric particles having a higher refractive index than the isolation layer. The advantage of the present invention is that the high-refractive index dielectric particles can interact with the incident electromagnetic field to generate a resonant electromagnetic coupling mode, and the heat loss can be greatly reduced; the dielectric particles are close to the metal, and a certain low-refractive-index isolation layer is maintained, and the dielectric The electromagnetic resonance mode of the particle can interact with the plasmon mode of the adjacent metal, resulting in the formation of a huge electromagnetic field between the dielectric particle and the metal; the existence of a low refractive index isolation layer can avoid direct contact between the metal and the probe, Effectively prevent the occurrence of quenching phenomena such as Raman signals and fluorescence signals of the probe.

Description

electric field enhancement structure

technical field

The invention relates to the field of photoelectric field enhancement, in particular to an electric field enhancement structure for enhancing incident photoelectric field intensity.

Background technique

The collective oscillation of surface electrons generated by metal particles under the excitation coupling of electromagnetic waves shows a singular optical property, which is the so-called localized plasmon resonance property. This resonance of light and electrons can confine light to a range of tens of nanometers or even smaller on the surface of metal particles, and form a strong local electromagnetic field. The localized plasmons of metal particles have super strong optical localization and light fields. The enhanced properties make it a great application prospect in biosensors, surface-enhanced Raman spectroscopy, and fluorescence-enhanced spectroscopy.

Surface-enhanced Raman spectroscopy based on metal particles is a well-known spectroscopic application technology. Its principle mainly uses the rough surface of the metal prepared in the experiment or the enhanced electric field near the metal particles to increase the Raman signal from the probe molecule. In surface-enhanced Raman experiments, probe molecules are adsorbed on or placed adjacent to activated metal surfaces or structures. Light of a certain frequency is used to irradiate detection molecules and metal surfaces or metal particles, and electromagnetic waves excite surface plasmons on the metal surfaces or metal particles. The detection molecule can produce a 10 ⁵ -10 ¹⁰ times Raman scattering signal enhancement effect through the enhanced localized plasmon electric field. For some nanoscale metal nanoneedles, nanoantenna structures, their super-strong optical field enhancement can even be used to detect Raman signals of single molecules. In addition to the application of enhanced Raman, the optical field enhancement of metal nanoparticles can also be used in biosensors, fluorescence lifetime enhancement, and nanolasers.

Plasmonic photoelectric field enhancement of metal particles has attracted much attention, but its application prospects are also limited. The most critical technical problem is that the local electromagnetic field enhancement generated by free electron plasmon resonance in metal particles is usually accompanied by large electromagnetic energy absorption, resulting in a large amount of metal heat loss, which eventually leads to an increase in the temperature of metal particles and the surrounding environment. . Theoretical and experimental studies (Nano Totay, 2007, 2, 30) reported that the temperature of metal particles can be increased by 50K under the excitation of a continuous light source, and the temperature can be increased by 1000K under the irradiation of a pulsed light source. The increase in the temperature of the metal particles will not only cause the degradation of its Raman signal enhancement performance in the detection of molecules in Raman spectroscopy, but also may change the properties of the metal particles and their surrounding detection substances, thereby enhancing the electric field of the metal particles. Some biomedical applications are limited.

Contents of the invention

In order to solve the above technical problems, the present invention provides an electric field enhancement structure, which can greatly reduce heat consumption.

In order to solve the above problems, the present invention provides an electric field enhancement structure, which includes a base layer and a dielectric layer arranged on the surface of the base layer, and also includes an isolation layer arranged on the surface of the dielectric layer and an isolation layer arranged on the surface of the isolation layer. The dielectric particle layer is formed of a plurality of dielectric particles, and the refractive index of the dielectric particles is greater than the refractive index of the isolation layer.

Further, the ratio of the refractive index of the dielectric particles to the refractive index of the isolation layer is greater than 1.4.

Further, the refractive index of the isolation layer is greater than 1.

Further, the dielectric particles are scattered on the surface of the isolation layer to form a layer of dielectric particles.

Further, the electromagnetic enhancement structure is excited by electromagnetic waves of a certain wavelength, and the ratio of the size of the dielectric particles to the wavelength of the electromagnetic waves is in the range of 0.05-1.

Further, the material of the dielectric particles is one of inorganic materials or organic materials.

Further, the material of the dielectric layer is graphene or metal.

The advantages of the present invention are:

1. High-refractive index dielectric particles can interact with incident electromagnetic fields to generate resonant electromagnetic coupling modes. The generation of this resonant mode is based on the electromagnetic coupling resonance of bound electrons in dielectric particles, compared to the free electrons in metal particles. Plasmon resonance, heat loss can be greatly reduced.

2. The dielectric particles are close to the metal and maintain a certain low refractive index isolation layer. The electromagnetic resonance mode of the dielectric particle can interact with the plasmon mode of the adjacent metal, resulting in a huge gap between the dielectric particle and the metal. Electromagnetically enhanced fields.

3. The existence of the low-refractive-index isolation layer can avoid direct contact between the metal and the detection object, and effectively prevent the quenching phenomenon of the Raman signal and fluorescence signal of the detection object.

Description of drawings

Fig. 1 is the structural representation of the electric field enhancement structure of the present invention;

Fig. 2 is the distribution diagram of the electric field intensity along the XY plane at the center of the silicon dielectric particle of the electric field enhanced structure of the present invention;

Fig. 3 is the function curve of the electric field enhancement between the silicon dielectric particles and the metal silver dielectric layer of the present invention and the electric field enhancement near the silicon dielectric particles in the air at different electromagnetic excitation wavelengths;

Fig. 4 is the variation curve of the electric field enhancement degree of the present invention with different thicknesses of the isolation layer.

Detailed ways

The specific implementation of the electric field enhancement structure provided by the present invention will be described in detail below in conjunction with the accompanying drawings.

The X-axis, Y-axis and Z-axis in FIG. 1 represent the X-axis, Y-axis and Z-axis respectively.

1, the electric field enhancement structure of the present invention includes a base layer 101, a dielectric layer 102 disposed on the surface of the base layer 101, an isolation layer 103 disposed on the surface of the dielectric layer 102, and a dielectric layer disposed on the surface of the isolation layer 103. Electric particle layer 104 .

The dielectric particle layer 104 is formed by a plurality of dielectric particles 105 , and only one dielectric particle 105 is schematically marked in FIG. 1 . The dielectric particles 105 of the present invention are excited by electromagnetic radiation to generate an electromagnetic resonance mode of a certain frequency, and this electromagnetic resonance mode is coupled with the metal plasmons excited by the dielectric layer 102, resulting in the formation of a gap between the dielectric particles 105 and the dielectric layer 102 Enhanced electric field.

The electromagnetic resonance mode of a certain frequency generated by the high-refractive index dielectric particles 105 excited by electromagnetic radiation can interact with the incident electromagnetic field to generate a resonant electromagnetic coupling mode. The generation of this resonant electromagnetic coupling mode is based on the The electromagnetic coupling resonance of bound electrons, compared with the plasmon resonance of free electrons in metal particles, can greatly reduce the heat loss of the electric field enhanced structure of the present invention.

In this specific embodiment, the dielectric particles 105 are scattered on the surface of the isolation layer 103 to form the dielectric particle layer 104 . The scattered arrangement refers to that the dielectric particles 105 are arranged randomly, randomly, and irregularly on the surface of the isolation layer 103 .

The material of the dielectric particle 105 can be an organic material or an inorganic material; the organic material is any one of an organic polymer; the inorganic material is silicon, germanium, titanium dioxide, gallium phosphide, gallium arsenide, cadmium sulfide , zinc oxide, gallium nitride, cadmium selenide, or a material with a high refractive index that can be processed using micro-manufacturing technology or nano-manufacturing technology.

The shape of the dielectric particles 105 can be any shape, for example, sphere, cylinder, pyramid, polyhedron, which is not limited in the present invention. In this specific implementation manner, the material of the dielectric particle 105 is silicon, selected as a sphere, and its radius r is selected to be 65 nm.

Further, the electric field enhancement structure is excited by electromagnetic waves of a certain wavelength, and the ratio of the size of the dielectric particles 105 to the wavelength of the electromagnetic waves is in the range of 0.05-1. The size of the dielectric particle 105 refers to the maximum length of the dielectric particle 105 in all directions.

The base layer 101 functions as a supporting substrate, and the material of the base layer 101 is not limited in the present invention.

The material of the dielectric layer 102 may be graphene or metal, and the metal may be any one or an alloy of gold, silver, aluminum, copper, titanium, nickel, and chromium. Adopt silver material in this embodiment, complex dielectric function dispersion relation is: _Ep = 9.5eV, γ = 0.04eV. Among them, ε _Ag is the complex dielectric function of silver, ε _b is the dielectric constant part of silver, E _p is the plasma oscillation energy of the free electron gas of silver, γ is the oscillation relaxation time of the free electron gas of silver, E is the electromagnetic wave oscillation energy.

The isolation layer 103 is made of low refractive index dielectric materials such as MgF ₄ , Al ₂ O ₃ , Si ₃ N ₄ . The refractive index of the dielectric particle layer 104 is greater than the refractive index of the isolation layer 103, preferably, the ratio of the refractive index of the dielectric particle layer 104 to the refractive index of the isolation layer 103 is greater than 1.4, the isolation Layer 103 has a refractive index greater than one. The isolation layer 103 adjusts the electromagnetic distribution between the dielectric layer 102 and the dielectric particle layer 104, so that more electromagnetic energy is localized in the sub-wavelength region below the dielectric particle layer 104 and above the dielectric layer 102, further away from the metal surface , thereby reducing the heat consumption of the metal and enhancing the local strength of the electromagnetic field. When the electric field enhanced structure of the present invention is applied to a Raman experiment, the isolation layer 103 can prevent the direct contact between the fluorescent detection molecules and the metal, and avoid the quenching effect of the enhanced performance of these chemically active molecules.

The electric field enhanced structure of the present invention can excite the coupled resonant mode of the dielectric particle and the metal substrate by properly selecting the excitation electromagnetic field characteristics (such as the electric field excitation direction and frequency) from the light source. The excitation light source can include any A suitable source for emitting electromagnetic waves at a wavelength, and capable of tunable wavelength radiation. For example, commercially available semiconductor lasers, helium-neon lasers, carbon dioxide lasers, light-emitting diodes, incandescent lamps, and many other known radiation-emitting sources. For a given refraction The frequency and geometry of the dielectric particles, the coupled resonance mode occurs at a specific frequency. In addition, changing the size, shape and refractive index of the dielectric particles can obviously change the electric field enhancement spectrum of the coupled resonance mode.

Dielectric particles in free space can generate resonance modes of a certain wavelength under the irradiation of an electromagnetic field. This type of resonance mode is also called Mie scattering oscillation of dielectric particles. As this resonant mode approaches the metal interface, the individual resonant modes excited in each dielectric particle are subject to metal reflection and metal plasmon interaction, which can enhance localized excitation between the dielectric particle and the metal. The electric field of the electromagnetic field, the electric field enhancement is mainly localized in the area above the metal below the dielectric particles. The individual evanescent electric fields associated with each resonant mode of the dielectric particles and the metal mirror-generated dielectric particles couple with each other and the action of the metal plasmons to locally enhance the electric field of the excitation source in the intermediate enhancement region. The enhancement of the electric field between the dielectric particles and the metal may be between about 10 times and about 400 times the excitation electric field.

The electric field enhanced structure of this embodiment is simulated by using the finite difference time domain method. Figure 2 shows that the electric field enhanced structure of the present invention is under the excitation wavelength of 485nm electromagnetic waves and the thickness d of the isolation layer 103 is 1 nanometer. The electric field intensity distribution diagram of the center of the electric particle 105 along the XY plane. It can be seen from FIG. 2 that most of the electric field energy resides on the silicon dioxide isolation layer 103 under the silicon dielectric particle layer 104, especially tens of nanometers on both sides of the contact point between the silicon dielectric particle layer 104 and the silicon dioxide isolation layer 103. area, the electric field strength has been greatly enhanced.

Figure 3 shows that when the electromagnetic excitation wavelength is 440-700nm, the electric field enhancement between the silicon dielectric particle layer 104 and the metal silver dielectric layer 102 in the specific embodiment of the present invention and the electric field enhancement near the silicon dielectric particle 105 in the air are different. Plotted as a function of electromagnetic excitation wavelength. It can be seen from Fig. 3 that the silicon dielectric particles 105 have a certain electromagnetic resonance mode under the excitation of electromagnetic waves, and the electric field enhancement curve shows two electric field enhancement peaks, that is, there are two coupling resonance modes with different wavelengths, and the low wavelength mode is the electric field enhancement peak. Dipole mode, the high wavelength mode is a magnetic dipole mode. In the electric field enhancement structure in this specific embodiment, the electromagnetic resonant mode of the silicon dielectric particles 105 couples with the underlying metal plasmons, which greatly enhances the electric field strength of the silicon dielectric particles 105 .

FIG. 4 shows the variation curve of the electric field enhancement degree with different thickness d of the isolation layer 103 in the specific embodiment provided by the present invention. It can be seen from Fig. 4 that the electric field enhancement strength increases with the decrease of the thickness d of the isolation layer 103, which is mainly because the smaller the thickness of the isolation layer 103, the greater the coupling strength between the resonant mode of the dielectric particle 105 and the metal plasmon, resulting in an increased degree of electromagnetic localization.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be considered Be the protection scope of the present invention.

Claims (7)

1. An electric field enhancement structure, comprising a base layer and a dielectric layer arranged on the surface of the base layer, characterized in that, it also includes an isolation layer arranged on the surface of the dielectric layer and a dielectric layer arranged on the surface of the isolation layer A particle layer, the dielectric particle layer is formed by a plurality of dielectric particles, the refractive index of the dielectric particles is greater than the refractive index of the isolation layer, and the dielectric layer is made of a material capable of exciting metal plasmon modes to make. 2 . The electric field enhancement structure according to claim 1 , wherein the ratio of the refractive index of the dielectric particles to the refractive index of the isolation layer is greater than 1.4. 3 . The electric field enhancing structure according to claim 1 , wherein the refractive index of the isolation layer is greater than 1. 4 . 4. The electric field enhancement structure according to claim 1, wherein the dielectric particles are scattered on the surface of the isolation layer to form a layer of dielectric particles. 5. The electric field enhancement structure according to claim 1, characterized in that, the electric field enhancement structure is excited by electromagnetic waves of a certain wavelength, and the ratio range of the size of the dielectric particles to the wavelength of the electromagnetic waves is 0.05- 1. 6 . The electric field enhancement structure according to claim 1 , wherein the material of the dielectric particles is one of inorganic materials or organic materials. 7. The electric field enhancement structure according to claim 1, characterized in that, the material of the dielectric layer is graphene or metal.