CN112928452B - Wideband spontaneous radiation enhanced tetramer metal nano antenna structure and manufacturing method and application thereof - Google Patents
Wideband spontaneous radiation enhanced tetramer metal nano antenna structure and manufacturing method and application thereof Download PDFInfo
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- H—ELECTRICITY
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Abstract
The invention discloses a tetramer metal nano antenna structure with enhanced broadband spontaneous radiation and a manufacturing method and application thereof, wherein the tetramer metal nano antenna structure comprises a metal substrate, a medium interlayer, a radiation point source and a metal nanowire, wherein: the medium interlayer is tightly attached and fixed to the top of the metal substrate, four metal nanowires are arranged, each metal nanowire is tightly attached and fixed to the upper surface of the medium interlayer, the periphery of each metal nanowire is surrounded by air, and the four metal nanowires are arranged in parallel in pairs, are symmetrical left and right and are symmetrical front and back; the medium interlayer enables a nanometer gap to be formed between the metal substrate and the metal nanowire, and the radiation point source is located in the medium interlayer and does not contact the metal substrate and the metal nanowire. The invention can realize the enhancement of the spontaneous radiation of the broadband.
Description
Technical Field
The invention relates to the field of metal micro-nano structure surface plasmon spontaneous radiation enhancement effects, in particular to a tetramer metal nano antenna structure with enhanced broadband spontaneous radiation and a manufacturing method and application thereof.
Background
The metal micro-nano structure surface plasmon spontaneous radiation enhancement effect means that surface plasmons are formed near the surface of the metal micro-nano structure by incident electromagnetic waves, and when the metal micro-nano structure and a radiation point source arranged near the metal micro-nano structure meet resonance conditions, the point source energy level transition rate is increased, so that the spontaneous radiation rate of the point source is enhanced.
In the prior art, most of metal structures interacting with an optical field (electromagnetic field) are metal nanostructures, and more researches are focused on the situation of various combined structures. Wherein, the simple structure comprises the combination structure of metal ball and medium interface; the complex structure comprises a multilayer hybrid structure of a nano metal antenna or grating, a metal layer, a dielectric layer and the like. The structure of the invention belongs to a complex structure.
In recent years, researches show that the spontaneous radiation effect can be enhanced by using surface plasmons generated by a metal micro-nano structure. However, the traditional metal micro-nano structure has weak surface plasmon spontaneous radiation enhancement effect, few adjustable parameters and the like, so that the structure is limited in application. It has also been found that the fluorescence emission range of molecules or quantum dots is typically in the wavelength range of tens to hundreds of nanometers, and therefore structures are required to be designed to provide broadband spontaneous emission enhancement. However, it is difficult to achieve broadband spontaneous emission enhancement for typical metal optical nano-antennas, such as single nano-antennas, dipole antennas, bow-tie antennas, open loop antennas, and the like. Meanwhile, most of the excitation light and radiation light wavelengths are not equal, and the broadband spontaneous radiation enhancement can realize the simultaneous enhancement of the excitation light and the radiation light wavelengths, so that the application performance and the efficiency of the device can be greatly improved.
Based on the defects of the conventional metal micro-nano structure and the requirement of broadband spontaneous radiation enhancement in the current research, the invention aims to provide a tetramer metal nano antenna structure with the broadband spontaneous radiation enhancement.
Disclosure of Invention
The invention aims to provide a tetramer metal nano antenna structure for enhancing broadband spontaneous radiation, aiming at the problems that the enhancement effect of surface plasmon spontaneous radiation generated by a metal micro-nano structure is weak and adjustable parameters are few in the prior art.
Another object of the present invention is to provide a method for manufacturing the tetrameric metal nano-antenna structure.
Another object of the present invention is to provide an application of the tetrameric metal nano-antenna structure.
The technical scheme adopted for realizing the purpose of the invention is as follows:
a tetrameric metal nanoantenna structure with enhanced broadband spontaneous radiation, comprising a metal substrate, a dielectric spacer layer, a radiation point source and a metal nanowire, wherein:
the medium interlayer is tightly attached and fixed on the top of the metal substrate, four metal nanowires are arranged, and each metal nanowire is tightly attached and fixed on the mediumOn the upper surface of the interlayer, the periphery of each metal nanowire is filled with air (n)air1), four metal nanowires are arranged in parallel in pairs, and are symmetrical left and right and symmetrical front and back;
the medium interlayer enables a nanogap to be formed between the metal substrate and the metal nanowire, and the radiation point source is positioned in the medium interlayer and does not contact the metal substrate and the metal nanowire, otherwise, fluorescence quenching is caused, and fluorescence spontaneous radiation enhancement is not facilitated.
In the above technical solution, the metal nanowires are made of noble metals such as gold, silver or copper; its refractive index nmThe metal nano-wire can change the radiation direction of the radiation point source, so that the electromagnetic field in the nano-gap in the medium interlayer generates resonance and energy focusing effects, and the radiation rate of the radiation point source is enhanced.
The medium interlayer is made of SiO2Or PMMA. Refractive index neWhen the radiation point source exists in the nanometer gap, an electromagnetic field formed by the radiation point source is localized in the metal nanometer gap with the size far smaller than the diffraction limit in a gap surface plasmon mode, and finally a larger spontaneous radiation rate is obtained.
The material of the metal substrate is gold, silver or copper and other noble metals, and the refractive index n of the metal substratemIn relation to the wavelength of radiation of the radiation point source for: 1) supporting gap surface plasmon propagation to improve the spontaneous radiation rate; 2) compared with other non-metallic substrates, e.g. SiO2Or PMMA, etc., the metal substrate can eliminate the electromagnetic wave generated by the point source from radiating into the substrate, so that more energy is focused in the nanometer gap.
The radiation point source represents a fluorescence emitter, is a fluorescence molecule (such as Nile blue fluorescence molecule) or a quantum dot and the like, is positioned in the nanogap and generates a broadband spontaneous radiation enhancement effect.
In the technical scheme, each metal nanowire is in a cuboid shape, and the sizes of the four metal nanowires are the same. Furthermore, the arm length ranges of the four metal nanowires are as follows: l is 5-650 nm; the width ranges of the four metal nanowires are as follows: w is 5-100 nm; the height ranges are: h is 5-100 nm.
In the technical scheme, each metal nanowire is fixedly bonded on the plane of the medium interlayer, the bottom surface of each metal nanowire is completely overlapped with the top surface of the medium interlayer, the upper surface of the medium interlayer and the lower surface of each metal nanowire are both of a planar structure, and the situation that part of the antenna sinks into the medium interlayer is avoided. Further, the width of the gap between two metal nanowires along the x direction ranges from: gapx is 5-100 nm, and the range of the gap width between the two metal nano antennas along the y direction is as follows: 5-350 nm. The thickness of the medium interlayer along the z direction is as follows: the gapz is 5-100 nm, the size of the dielectric spacer layer along the x and y directions is required to be large enough and is far larger than the size of four metal nanowire structures.
In the technical scheme, the radiation point source is positioned right below any one metal nanowire and is positioned at the central position of a nanogap formed by the metal nanowire and the metal substrate along the z direction. The purpose of this setup is to have the point source of radiation located in the metal nanogap formed by the metal nanowire and the metal substrate, and the resulting electromagnetic field is localized in the form of gap surface plasmons within the metal nanogap of a size much smaller than the diffraction limit. The mode volume V of the gap surface plasmon is small, so that the spontaneous emission rate (proportional to Q/V, Q being the quality factor of the gap surface plasmon) takes a large value. In addition, the radiation point source can also be positioned at other positions in the medium interlayer just below the non-metal nanowire, but the enhancement effect is slightly poor because the formed electromagnetic field can not form gap surface plasmons. When the radiation point source is positioned in the metal nanometer gap of the medium interlayer, if the radiation point source deviates from the central position in the nanometer gap along the z direction, the broadband spontaneous radiation enhancement effect can be achieved, but the enhancement effect is slightly poor, and the fluorescence quenching phenomenon can occur.
In the technical scheme, the radiation wavelength of the radiation point source is 400-1800 nm.
In the technical scheme, the sizes of the metal substrate along the x direction and the y direction are the same as the size of the medium interlayer, and the thickness of the metal substrate is more than 100 nm. The flat surface of the metal substrate is beneficial to spin coating and bonding with the medium interlayer above the metal substrate.
In the above technical solution, each metal nanowire and the metal substrate are made of gold, the width and height of each of the four gold nanowires is W ═ H ═ 40nm, the gap width between the metal nanowires is gapx ═ 10nm, gapy ═ 10nm, the thickness of the dielectric interlayer is gapz ═ 10nm, the radiation point source is located right below the end face of one of the metal nanowires, the distance between the radiation point source and the lower surface of the metal nanowire and the upper surface of the metal substrate is 5nm, and the arm length of each gold nano antenna is 180 nm; when the radiation wavelength of a radiation point source is 1570nm, the spontaneous radiation rate enhancement factor is as high as 5117, the spontaneous radiation enhancement is realized in the ranges of 490-650 nm and 1320-1650 nm, and the wavelength range of a wide waveband reaches 330 nm. The spontaneous radiation rate enhancement factor is defined herein as the spontaneous radiation rate of a point source in the antenna divided by the spontaneous radiation rate of the point source in a uniform free space completely filled with dielectric spacer material, also referred to as normalized spontaneous radiation rate, or spontaneous radiation rate enhancement Purcell factor.
In the above technical solution, the tetrameric metal nano antenna structure is characterized by being manufactured by the following method:
In another aspect of the present invention, the application of the tetrameric metal nano antenna structure in enhancing spontaneous emission enhancement of a radiation point source includes, but is not limited to, enhancing raman scattering or fluorescence emission of molecules in a micro-nano structure, enhancing sensitivity of raman spectroscopy or fluorescence spectroscopy molecule sensing, and realizing high modulation rate and high brightness light source.
In the technical scheme, the wavelength of point source radiation is in the range of 900 nm-1250 nm, the phenomenon of broadband spontaneous radiation enhancement is achieved, and 1-4 broadband peaks with different numbers can be obtained by changing the width of gaps among the metal nanowires.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention has strong spontaneous radiation enhancement effect, simple structure, easy analog calculation, multiple adjustable parameters, wide parameter adjustable size range and can realize the spontaneous radiation enhancement of a wide waveband, and the central wavelength position of the wide waveband can realize the flexible adjustment from visible light to near infrared light waveband.
2. The size of the z-direction nanometer gap is easy to control, and the nano-scale industrial manufacturing can be easily achieved through a coating process. Therefore, the invention has good application prospect in the aspects of enhancing Raman scattering or fluorescence emission of molecules in the micro-nano structure, improving the molecular sensing sensitivity of Raman spectrum or fluorescence spectrum, and the like, and realizing high modulation rate and high brightness light source.
Drawings
FIG. 1 is a three-dimensional view of a tetrameric metal nanoantenna structure;
FIG. 2 is a front view of a tetrameric metal nanoantenna structure;
FIG. 3 is a top view of a tetrameric metal nanoantenna structure;
fig. 4 is a diagram of a tetramer metal nano antenna structure, where four metal nanowires and a metal substrate are made of gold, the four metal nanowires have a line width and a height of W ═ H ═ 40nm, a nanowire gap width is gapx ═ 10nm, gapy ═ 10nm, a dielectric spacer thickness is gapz ═ 10nm, a radiation point source is located right below an end face of one of the metal nanowires, and a distance between a lower surface of the metal nanowire and an upper surface of the metal substrate is 5nm, that is, at a position shown in fig. 1, under different antenna arm lengths L, a normalized spontaneous radiation rate is a curve varying with a radiation wavelength of the point source;
fig. 5 is a tetramer metal nano antenna structure, when the four metal nanowires and the metal substrate are made of gold, the length of each arm of the four gold nanowires is L120 nm, the width and the height of each arm of the four metal nanowires are W40 nm, the thickness of the medium interlayer is gapz 10nm, the radiation point source is located right below the end face of one of the metal nanowires, and the distance between the radiation point source and the lower surface of the metal nanowire is 5nm, that is, as shown in fig. 1, under the condition of different nanowire gap widths gapx and gapy, the normalized spontaneous radiation rate is along with the change curve of the radiation wavelength of the point source;
fig. 6 is a tetramer metal nano-antenna structure, when the four metal nano-wires and the metal substrate are made of gold, the length of each arm of the four metal nano-wires is 120nm, the width and the height of each arm of the four metal nano-wires are 40nm, the thickness of the dielectric spacer layer is gapz 10nm, the distance between the radiation point source and the lower surface of the metal nano-wire and the upper surface of the metal substrate is 5nm, fig. 6(a) shows that the radiation point source is located under the antenna end surface, i.e., at the position shown in fig. 1, the normalized spontaneous radiation rate is along with the change curve of the radiation wavelength of the point source under the condition of different nanowire gap widths gapx and gapy, and fig. 6(b) shows that the radiation point source is located under the antenna, 10nm away from the antenna end surface, i.e., as the radiation point source position shown in fig. 2, the normalized spontaneous radiation rate is along with the change curve of the radiation wavelength under the condition of different nanowire gap widths gapx and gapy;
Detailed Description
The present invention will be described in further detail with reference to specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
A tetrameric metal nanoantenna structure with enhanced broadband spontaneous radiation, comprising a metal substrate (1), a dielectric spacer layer (2), a radiation point source (3) and a metal nanowire (4), wherein:
the medium interlayer (2) is tightly attached and fixed to the top of the metal substrate (1), four metal nanowires (4) are arranged, each metal nanowire (4) is tightly attached and fixed to the upper surface of the medium interlayer (2), the periphery of each metal nanowire (4) is surrounded by air, and the four metal nanowires (4) are arranged in parallel in pairs, are symmetrical left and right and are symmetrical front and back;
the medium interlayer (2) enables a nanogap to be formed between the metal substrate (1) and the metal nanowire (4), and the radiation point source (3) is positioned in the medium interlayer (2) and does not contact the metal substrate (1) and the metal nanowire (4), so that fluorescence quenching is caused and fluorescence spontaneous radiation enhancement is not facilitated.
The tetrameric metal nano-antenna structure is prepared by the following steps:
and 2, coating a medium interlayer by a secondary spin coating method, coating the radiation point source (3) (fluorescent molecules are adopted here) on the first medium interlayer, and coating a medium interlayer finally, so that the radiation point source (3) can be arranged in the medium interlayer (2), and the sum of the thickness of the first medium interlayer and the thickness of the second medium interlayer is the total medium interlayer thickness gapz. See in particular the literature "Journal of Materials Chemistry C,2019,7(43): 13526-;
In this embodiment, the point source of radiation is located directly below one of the metal nanowires. The four metal nanowires are bonded on the plane of the medium interlayer, the bottom surfaces of the four metal nanowires are completely overlapped with the top surface of the medium interlayer, and the situation that part of the antenna sinks into the medium interlayer is avoided.
The structure uses metal as a substrate, and the metal substrate has the following functions: 1) forming a nano gap with the metal nanowire, and supporting the propagation of a gap surface plasmon so as to improve the spontaneous radiation rate; 2) the metal substrate can eliminate the electromagnetic wave generated by the point source from radiating into the substrate, so that more energy is focused in the nanometer gap. A medium interlayer material (SiO) is arranged between the metal substrate and the four metal nanowires2Or PMMA) that when excited by a point source of radiation, generates surface plasmons that travel back and forth in the gap. Due to the good resonance and energy focusing characteristics of the metal nano optical antenna, strong electromagnetic field enhancement can be generated in a nano gap between the metal nanowire and the metal substrate, and further point source spontaneous radiation enhancement is realized.
Example 2
On the basis of the embodiment 1, the flexible adjustment of the center wavelength position of the spontaneous radiation enhancement waveband from the visible light to the near infrared light waveband can be realized by changing the arm length of the metal nanowire, and the adjustment of the peak value of the spontaneous radiation rate enhancement factor and the wavelength range of the spontaneous radiation enhancement broadband can be realized.
The invention adopts a DIF CODE program package of a non-periodic Fourier mode algorithm, specifically referring to The calculation of The performance with an in-house software, Haitao Liu, DIF CODE for Modeling Light Diffraction in nanostrucrures (Nankai University,2010), and carries out simulation calculation by means of LAB MATLAB software. Using point electric dipole to represent radiation point source in calculationThe mathematical expression of the point electric dipole (i.e., the point current source) is J ═ δ (x-x)0,y-y0,z-z0) n, delta are dirac functions, (x)0,y0,z0) Representing the rectangular coordinates of the point electric dipole, and n is a unit vector along the polarization direction of the point electric dipole. In order to obtain a strong spontaneous emission rate, a point dipole polarized in the z direction is used, where J is δ (x-x)0,y-y0,z-z0) z, the spontaneous emission rate of the point source may be expressed as Γ ═ Re [ E ═ Ez(x0,y0,z0)]/2 wherein Ez(x0,y0,z0) For the z-component of the electric field strength vector at a point electric dipole location, see in particular "Jia H, Liu H, Zhong Y. role of surface plasma polarities and other waves in the radiation of resistive optical antipodes [ J]Scientific Reports,2015,5:8456. If the normalized spontaneous radiation rate is greater than 1, the method can enhance the spontaneous radiation rate of the radiation point source.
As shown in fig. 4, when the four metal nanowires and the metal substrate are made of gold, the thickness of the metal substrate is 400nm, the thickness of the dielectric interlayer is 10nm, the width and height of each of the four gold nanowires is W ═ H ═ 40nm, the gap width between the nanowires is gapx ═ 10nm, gapy ═ 10nm, the thickness of the dielectric interlayer is gapz ═ 10nm, the radiation point source is located right below the end face of one of the metal nanowires, and the distance between the lower surface of the metal nanowire and the upper surface of the metal substrate is 5nm, that is, as shown in fig. 1, when the radiation point source position is shown, the normalized spontaneous radiation rate varies with the radiation wavelength under different antenna arm lengths L, that is, L ═ 30nm, L ═ 80nm, L ═ 105nm, L ═ 130nm, and L ═ 180 nm.
As can be seen from fig. 4, 1) as the arm length of the antenna increases, the center wavelength of the spontaneous emission enhanced broadband increases continuously, and the wavelength shifts from the visible light to the near-infrared band; 2) in a near infrared band, the peak value of a spontaneous radiation rate enhancement factor is increased along with the increase of the arm length of an antenna, from the situation that no near infrared broadband enhancement phenomenon exists when L is 30nm, the peak value of a broadband is 1646 when L is 80nm, the peak value of the broadband is 2233 when L is 105nm, the peak value of the broadband is 3304 when L is 130nm, and finally the peak value of the broadband spontaneous radiation rate enhancement factor is as high as 5117 when L is 180 nm; 3) in a near infrared band, the wavelength range of a spontaneous radiation enhanced broadband is widened along with the increase of the arm length of the antenna, and finally when L is 180nm, the spontaneous radiation enhancement is realized in the ranges of 490nm to 650nm and 1320nm to 1650nm, and the wavelength range of the spontaneous radiation enhanced broadband reaches 330 nm.
Example 3
On the basis of the embodiment 1, the number of the broadband peaks can be adjusted by changing the gaps among the metal nanowires (4).
In this embodiment, it is calculated that when the four metal nanowires and the metal substrate are made of gold, the length of each arm of the four gold nanowires is L120 nm, the width and the height of each arm of the four metal nanowires are W40 nm, the thickness of the medium interlayer is gapz 10nm, the radiation point source is located right below the end face of one metal nanowire, and the distance between the lower surface of the metal nanowire and the upper surface of the metal substrate is 5nm, that is, when the positions are shown in fig. 1, the normalized spontaneous radiation rate changes with the radiation wavelength of the point source under the condition of different nanowire gap widths gapx and gapy. As can be seen from fig. 5, when the fixed gapx is 10nm, the gapy increases from 20nm to 50nm, and the number of broad-band peaks increases from 3 to 4 in the band range of 900nm to 1250 nm; when the fixed gapy is 10nm, the gapx is increased from 20nm to 30nm, and the number of peaks in the wide waveband is increased from 1 to 2 in the waveband range of 900nm to 1250 nm.
Example 4
On the basis of the embodiment 1, the adjustment of the spontaneous radiation enhancement intensity can be realized by changing the position of the radiation point source.
As shown in fig. 6, the spontaneous radiation rates of the radiation point source at two different positions along the x-direction were calculated. Fig. 6(a) shows the radiation point source located right below the end face of the antenna, i.e. the radiation point source position as shown in fig. 1; fig. 6(b) shows that the radiation point source is located right below the antenna and 10nm away from the end face of the antenna, i.e., the radiation point source position shown in fig. 2. The radiation point sources at the two positions are calculated respectively, and the curve of the normalized spontaneous radiation rate along with the change of the radiation wavelength of the point source is calculated under the conditions of different nanowire gap widths gapx and gapy. As can be seen from FIG. 6, the obtained spontaneous radiation rate curves of the radiation point sources at different positions have the same trend, and all have the phenomenon of broadband spontaneous radiation enhancement, but the obtained spontaneous radiation enhancement of the radiation point sources is stronger than that of the radiation point sources at the former position. Such as: a structure of gapx 10nm and gapy 50nm, which corresponds to a wavelength 990nm corresponding to a peak point in fig. 6(a), and a normalized spontaneous emission rate of 4142, and corresponds to a wavelength 990nm corresponding to a peak point in fig. 6(b), but the normalized spontaneous emission rate reaches 5087; the wavelength corresponding to the peak point in fig. 6(a) is 980nm and the normalized spontaneous emission rate is 3544, while the wavelength corresponding to the peak point in fig. 6(b) is 980nm, but the normalized spontaneous emission rate reaches 4328. Similarly, the gap size structures of other different metal nanowires (4) have the phenomenon.
The phenomenon of broadband spontaneous emission enhancement of the invention is explained as follows: one radiation point source in the structure is equivalent to a superposition of four radiation point sources with amplitude 1/4 and satisfying the following four symmetric relationships, namely: four excitation point sources having symmetry about each of the x-0 plane and the y-0 plane; four excitation point sources having antisymmetry with respect to the x-0 plane and symmetry with respect to the y-0 plane; four excitation point sources having antisymmetry with respect to both the x-0 plane and the y-0 plane; four excitation point sources (symmetry is shown as sym, and antisymmetry is shown as asym) with symmetry about an x-0 plane and antisymmetry about a y-0 plane, respectively establishing a surface plasmon resonance model according to the four symmetry relations, and respectively establishing a structure scattering coefficient (a nanowire end surface reflection coefficient r, a nanowire gap reflection coefficient rho and a transmission coefficient tau) and an equivalent refractive index n by using the scattering coefficient (a nanowire end surface reflection coefficient r, a nanowire gap reflection coefficient rho and a nanowire transmission coefficient tau) and the equivalent refractive index neffLength L of antenna arm when resonating with surface plasmon propagating in structureresTo obtain four phase matching conditions:
2k0Re(neff,sym)Lres,sym+arg(rsym)+arg(ρsym+τsym)＝2mπ(m＝0,±1,±2...) (1)
2k0Re(neff,asym)Lres,asym+arg(rasym)+arg(ρasym+τasym)＝2mπ(m＝0,±1,±2...) (2)
2k0Re(neff,sym)Lres,sym+arg(rsym)+arg(ρsym-τsym)＝2mπ(m＝0,±1,±2...) (3)
2k0Re(neff,asym)Lres,asym+arg(rasym)+arg(ρasym-τasym)＝2mπ(m＝0,±1,±2...) (4)
the four phase matching conditional expressions can explain the broadband spontaneous radiation enhancement phenomenon, and the four radiation point sources in each symmetrical relation correspond to peaks at different positions in the range of the broadband spontaneous radiation enhancement. As shown in FIGS. 5 and 6, when the wavelength of the point source radiation is in the range of 900nm to 1250nm, the broadband spontaneous radiation enhancement phenomenon can be seen more clearly, and the gap width between the metal nanowires (4) is changed, so that 1 to 4 spontaneous radiation rate peaks with different numbers can be obtained.
Example 5
This example illustrates the use of the tetrameric metal nanoantenna structures to enhance the enhancement of spontaneous emission from a radiation point source.
The main points are as follows:
1. the antenna structure has good application prospect in the aspects of enhancing Raman scattering or fluorescence emission of molecules in the micro-nano structure, improving the molecular sensing sensitivity of Raman spectrum or fluorescence spectrum and the like. Based on the spontaneous radiation enhancement characteristic of the tetramer metal nano antenna structure, when the molecules are subjected to Raman or fluorescence spectrum detection, stronger Raman or fluorescence signals can be detected.
2. The antenna structure has good application prospect in the aspect of realizing high modulation rate and high-brightness light source. Based on the spontaneous radiation enhancement characteristic of the tetrameric metal nano antenna structure, when the spontaneous radiation rate enhancement factor is larger, the following two effects can be achieved: firstly, the shorter the fluorescence lifetime of a radiation point source is, the shorter the response time of the fluorescence emission of the structure to the loaded modulation signal is, so that the structure can realize optical communication with high modulation rate; second, fluorescence intensity enhancement factor fFEqual to the excitation rate enhancement factor fexcAnd quantum yield enhancement factor fηProduct of (i), i.e. fF＝fexc×fη. When the spontaneous emission rate enhancement factor increases, fexcAnd fηAll increase, and further lead to the fluorescence intensity enhancement factor fFThe size is increased, so that the structure can form a high-brightness light source.
3. The invention includes but is not limited to enhancing Raman scattering or fluorescence emission of molecules in a micro-nano structure, improving the molecular sensing sensitivity of Raman spectrum or fluorescence spectrum, and the application in realizing high modulation rate and high brightness light source. Any other applications that can be realized by the structure of the present invention and the spontaneous emission enhancement characteristics of the structure of the present invention are within the scope of the present invention.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (14)
1. A tetrameric metal nano-antenna structure with enhanced broadband spontaneous radiation is characterized by comprising a metal substrate, a medium interlayer, a radiation point source and a metal nanowire, wherein:
the medium interlayer is tightly attached and fixed to the top of the metal substrate, four metal nanowires are arranged, each metal nanowire is tightly attached and fixed to the upper surface of the medium interlayer, the periphery of each metal nanowire is surrounded by air, each metal nanowire is in a cuboid shape, and the four metal nanowires are arranged in parallel in pairs, are symmetrical left and right and are symmetrical front and back;
the medium interlayer enables a nanometer gap to be formed between the metal substrate and the metal nanowires, the radiation point source is located in the medium interlayer and does not contact the metal substrate and the metal nanowires, and the radiation point source is located right below any one metal nanowire.
2. The tetrameric metal nanoantenna structure with enhanced broadband spontaneous radiation according to claim 1, wherein the metal nanowires are made of noble metals;
the medium interlayer is made of SiO2Or PMMA;
the metal substrate is made of noble metal;
the radiation point source is a fluorescent emitter.
3. The tetrameric metal nanoantenna structure with enhanced broadband spontaneous radiation according to claim 2, wherein the metal nanowires are made of gold, silver or copper, the metal substrate is made of gold, silver or copper, and the radiation point source is a fluorescent molecule or a quantum dot.
4. The wideband spontaneous emission enhanced tetrameric metal nanoantenna structure of claim 1, wherein the four metal nanowires are all the same size.
5. The structure of claim 4, wherein each metal nanowire has an arm length L = 5-650 nm; the width range W of each metal nanowire is = 5-100 nm, and the height range H = 5-100 nm.
6. The tetrameric metal nanoantenna structure with enhanced broadband spontaneous radiation according to claim 1, wherein each metal nanowire is bonded and fixed on the plane of the dielectric spacer layer, the bottom surface of each metal nanowire is completely overlapped with the top surface of the dielectric spacer layer, and the upper surface of the dielectric spacer layer and the lower surface of each metal nanowire are planar structures.
7. The structure of claim 6, wherein the width of the gap between two metal nanowires along the x-direction is in the range of: gapx = 5-100 nm, and the width of the gap between two metal nano-antennas along the y direction is in the range: the thickness of the dielectric interlayer along the z direction is as follows: gapz = 5-100 nm.
8. The structure of claim 1, wherein the radiation wavelength of the radiation point source is 400-1800 nm.
9. The structure of claim 1, wherein the radiation point source is located at the center of the nanogap formed by the metal nanowire and the metal substrate along the z direction.
10. The structure of claim 1, wherein the dimensions of the metal substrate in the x and y directions are the same as the dimensions of the dielectric spacer, and the thickness of the metal substrate is greater than 100 nm.
11. The structure of claim 1, wherein the metal nanowires and the metal substrate are each made of gold, the four gold nanowires have a line width and a height of W = H = 40nm, the metal nanowires have a gap width of gapx =10nm, gapy =10nm, the dielectric spacer has a thickness of gapz =10nm, the distance between the radiation source and the lower surface of the metal nanowires and the upper surface of the metal substrate is 5nm, and the arm length of each gold nanowire is 180 nm; when the radiation wavelength of a radiation point source is 1570nm, the spontaneous radiation rate enhancement factor is as high as 5117, the spontaneous radiation enhancement is realized in the ranges of 490-650 nm and 1320-1650 nm, and the wavelength range of a wide waveband reaches 330 nm.
12. A broad-band spontaneous emission enhanced tetrameric metal nanoantenna structure according to any one of claims 1 to 11, manufactured by a method comprising:
step 1, preparing a metal film on a flat substrate by adopting a magnetron sputtering method or an evaporation method;
step 2, coating a medium interlayer on the metal substrate by a secondary spin coating method, coating the radiation point source on the first medium interlayer, and finally coating a medium interlayer, so that the radiation point source is arranged in the medium interlayer;
step 3, coating photoresist on the upper surface of the medium interlayer in a spinning mode, when reverse photoresist is used, exposing and developing the regions except the four metal nanowires, reserving the photoresist in the exposed regions, and enabling the photoresist in the regions where the four metal nanowires are not exposed to disappear; then plating a metal film, wherein the film is attached to the photoresist and a part of the exposed medium interlayer, and the thickness of the film is controlled by the film plating time; and finally, stripping the photoresist, namely the remaining four metal nanowires attached to the medium interlayer, when the positive photoresist is used, exposing and developing the regions where the four metal nanowires are located, wherein the regions where the four metal nanowires are located are exposed regions, the photoresist in the exposed regions disappears, the photoresist in the unexposed regions is remained, and the later steps are the same as the steps when the reverse photoresist is used.
13. The use of the tetrameric metal nanoantenna structure of any one of claims 1 to 11 for enhancing spontaneous emission of a radiation point source, enhancing raman scattering or fluorescence emission of molecules in a micro-nano structure, improving molecular sensing sensitivity of raman spectroscopy or fluorescence spectroscopy, and realizing a high modulation rate and high brightness light source.
14. The use according to claim 13, wherein the enhancement of spontaneous radiation from the radiation point source has a broadband phenomenon;
by changing the arm length of the metal nanowire, the adjustment of the wavelength range from visible light to near-infrared light in the center of the wavelength band can be realized, the adjustment of the peak value of a spontaneous radiation rate enhancement factor between 1646 and 5117 can be realized, the wavelength range of a spontaneous radiation enhanced wide wavelength band is widened along with the increase of the arm length of the antenna in the near-infrared wavelength band, when L =180nm, the spontaneous radiation enhancement is realized in the ranges of 490-650 nm and 1320-1650 nm, and the wavelength range of the spontaneous radiation enhanced wide wavelength band reaches 330 nm;
by changing the gap width among the metal nanowires, the radiation wavelength is in the range of 900 nm-1250 nm, and 1-4 broadband peaks with different numbers can be obtained;
by varying the position of the radiation point source, modulation of the spontaneous emission rate enhancement factor can be achieved.
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