CN109543220B - Metal nanoparticle micro-nano structure and method for enhancing spontaneous radiation in gap thereof - Google Patents
Metal nanoparticle micro-nano structure and method for enhancing spontaneous radiation in gap thereof Download PDFInfo
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- 230000005855 radiation Effects 0.000 title claims abstract description 91
- 239000002082 metal nanoparticle Substances 0.000 title claims abstract description 23
- 238000000034 method Methods 0.000 title claims abstract description 20
- 239000002086 nanomaterial Substances 0.000 title claims abstract description 20
- 230000002269 spontaneous effect Effects 0.000 title claims abstract description 18
- 230000002708 enhancing effect Effects 0.000 title abstract description 8
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims abstract description 71
- 239000010931 gold Substances 0.000 claims abstract description 70
- 229910052737 gold Inorganic materials 0.000 claims abstract description 70
- 239000002105 nanoparticle Substances 0.000 claims abstract description 61
- 229920003229 poly(methyl methacrylate) Polymers 0.000 claims abstract description 23
- 239000004926 polymethyl methacrylate Substances 0.000 claims abstract description 23
- 239000000758 substrate Substances 0.000 claims abstract description 20
- 239000002096 quantum dot Substances 0.000 claims abstract description 19
- 239000002184 metal Substances 0.000 claims abstract description 15
- 229910052751 metal Inorganic materials 0.000 claims abstract description 15
- 230000001965 increasing effect Effects 0.000 claims abstract description 4
- 239000002077 nanosphere Substances 0.000 claims description 8
- 230000010287 polarization Effects 0.000 claims description 4
- 230000005684 electric field Effects 0.000 claims description 3
- 230000001276 controlling effect Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000011258 core-shell material Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000005424 photoluminescence Methods 0.000 description 1
- 238000006862 quantum yield reaction Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 125000006850 spacer group Chemical group 0.000 description 1
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- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
- G06F30/23—Design optimisation, verification or simulation using finite element methods [FEM] or finite difference methods [FDM]
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Abstract
The invention discloses a metal nanoparticle micro-nano structure and a method for enhancing spontaneous radiation in a gap of the metal nanoparticle micro-nano structure, which comprises gold nanoparticles (1), a PMMA layer (2) and a metal substrate (3), wherein the gold nanoparticles (1) are arranged on the PMMA layer (2) at equal intervals, and a molecular or quantum dot radiation source (4) is positioned under the central gold nanoparticles; step 1, calculating the total radiation rate and the far-field radiation rate of single gold nanoparticles on a gold substrate by using a finite element method, and selecting a proper gold nanoparticle radius; and 2, selecting the radius of the gold nanoparticles in the step 1, calculating the change of the total radiation rate and the far-field radiation rate when the distance between every two gold nanoparticles is gradually increased by using a finite element method, and calculating the change of the radiation pattern along with the distance between each gold nanoparticle in the MATLAB-COMSOL based on the Lorentz reciprocity theorem. Compared with the prior art, the invention can enhance the spontaneous radiation rate of the molecular or quantum dot radiation source and change the radiation direction.
Description
Technical Field
The invention relates to the technical field of enhancing spontaneous emission, in particular to a novel micro-nano design structure of metal nano particles on a metal substrate and a method for enhancing spontaneous emission in a metal nano gap structure based on the metal nano particles.
Background
Spontaneous radiation refers to the process in which excited atoms spontaneously migrate from a high energy level to a low energy level without any external effect while radiating one photon. Currently, metal nanogap structures based on metal nanoparticles are receiving a great deal of attention. The spacer layer is coated between the nano particles and the metal substrate, and the structure can enhance radiation efficiency, shorten fluorescence lifetime, enhance photoluminescence, control far-field radiation direction and the like. The radiation pattern shows the radiation direction of the nanostructure and also reflects the magnitude of the radiation intensity. Common structures for adjusting the radiation direction of the nanostructure include a Yagi-Uda antenna, a periodic metal groove, a gold nanorod, triangular gold nanoparticles, a core-shell nanostructure, a V-shaped antenna and the like. The radiation rate of the nano-structure enhanced point source has important practical value, and can improve the quantum yield of fluorescent signals in the field of molecular fluorescent sensing. The directional emission, even the central emission, of the single photon source can be realized by the design of some micro-nano structures, all light can be collected without an objective lens with a large numerical aperture, and the conversion from spherical wave to plane wave can be realized.
Disclosure of Invention
Aiming at the defects in the prior art and the defects in the prior art, the invention provides a metal nanoparticle micro-nano structure and a method for enhancing spontaneous radiation in gaps of the metal nanoparticle micro-nano structure, which not only designs five metal nanoparticle micro-nano structures, but also realizes the enhancement of spontaneous radiation of a molecular or quantum dot radiation source and the control of radiation direction by changing the nano gaps of metal nanoparticles on a metal substrate.
The metal nanoparticle micro-nano structure comprises gold nanoparticles 1, a PMMA layer 2 and a metal substrate 3, wherein the metal nanoparticles 1 are placed on the PMMA layer 2, PMMA is coated on the metal substrate 3, molecular or quantum dot radiation sources 4 are arranged in the middle of the PMMA layer 2, the gold nanoparticles 1 are arranged on the PMMA layer 2 at equal intervals, and the molecular or quantum dot radiation sources 4 are positioned right below the central gold nanoparticles.
Different numbers of gold nanoparticles 1 are designed to act on the structures of molecular or quantum dot radiation sources, including single, two, three, five and nine gold nanoparticles.
By controlling the spacing of two, three, five or nine gold nanoparticles, a change in radiation direction and an enhancement in total and far field radiation rates is achieved.
The metal substrate 3 is a gold substrate.
The gold nanoparticle 1 is a nanosphere, the radius of the nanosphere is determined by calculating the spontaneous radiation rate according to a finite element method, and the first resonance radius, namely 45nm, is selected.
The PMMA layer 2 was chosen to have a thickness of 10nm.
The invention relates to a method for enhancing spontaneous radiation in a metal nanoparticle gap in a metal nanoparticle micro-nano structure, which comprises the following steps:
step 1, calculating the total radiation rate and far-field radiation rate of single gold nanoparticles on a gold substrate by using a finite element method, and selecting a proper gold nanoparticle radius, wherein the total radiation rate calculation formula is as follows:
wherein ,the real part of the electric field component along the polarization direction of the point current source;
the far field radiation rate is expressed as:
wherein A is a closed curved surface containing a point current source, S is a time average energy flow density vector, n is an external normal vector of the curved surface A, and a is a closed curved surface element;
the radiation rate in free space is expressed as:
wherein ,ηvac Is wave impedance in vacuum, k 0 =2pi/λ, λ is wavelength, k 0 Is the wave number, n a Is the refractive index in air;
step 2, selecting the radius of the gold nanoparticles in the step 1, and calculating the normalized total radiation rate gamma when the distance between every two gold nanoparticles is gradually increased by using a finite element method total /Γ air Far field radiation rate Γ rad /Γ air The radiation pattern was calculated as a function of the individual gold nanosphere spacing in MATLAB-COMSOL based on the Lorentz reciprocity theorem.
Compared with the prior art, the invention can not only enhance the spontaneous radiation rate of the molecular or quantum dot radiation source, but also change the radiation direction of the molecular or quantum dot radiation source.
Drawings
Fig. 1 is a block diagram of an embodiment of the present invention. (a) (c), (e), (g), (i) are side views of single, two, three, five, nine gold nanoparticle structures, respectively; (b) (d), (f), (h), (j) are respectively single, two, three, five and nine gold nanoparticle structure top views; the molecular or quantum dot radiation sources are all positioned right below the central gold nano particles;
FIG. 2 is a plot of total and far field radiation rates as a function of the individual gold nanoparticle radius R for an embodiment of the invention;
reference numerals: 1. gold nanoparticles, 2, PMMA layer, 3, gold substrate, 4, molecular or quantum dot radiation source.
Detailed Description
The technical scheme of the present invention will be described in further detail with reference to examples.
Fig. 1 is a schematic view of a micro-nano structure of a metal nanoparticle according to the present invention. The embodiment of the invention has five structural designs, each of the five designed micro-nano structures comprises gold nanoparticles, a PMMA layer and a gold substrate from top to bottom, and the different structures are characterized in that the number of the gold nanoparticles is different. A molecular or quantum dot radiation source 4 is placed in the middle of PMMA and gold nanoparticles 1 are placed on the PMMA layer 2 in an equidistant array. Different numbers of gold nanoparticles are designed to act on structures of molecular or quantum dot radiation sources, wherein the structures comprise single gold nanoparticles, two gold nanoparticles, three gold nanoparticles, five gold nanoparticles and nine gold nanoparticles, and the molecular or quantum dot radiation sources are all positioned right below the central gold nanoparticles. The structural design can enhance the spontaneous radiation rate of a molecular or quantum dot radiation source and change the radiation direction. The incident wavelength is 632.8nm, the refractive index of air is 1.5, the refractive index of PMMA is 1.5, and the thickness of the PMMA layer is 10nm (thinner PMMA gel can ensure that gold nanoparticles and quantum dots are fully coupled, thereby playing a role of a fixed structure). The radius of the gold nano-particles is R, and the interval is d.
The gold nanoparticles are nanospheres, and the radius R of the nanospheres is calculated by a finite element method (COMSOL Multiphysics software) to obtain the total radiation rate and the far-field radiation rate. When the radius of the gold nanoparticles meets the plasmon resonance condition, the peak value of the total radiation rate and the far-field radiation rate can appear, and the corresponding radius of the gold nanoparticles is the resonance radius, and the invention selects 45nm of the gold nanoparticles as research.
Let the current density direction be the z direction, the expression of the point radiation source be j=δ (x, y, z) z, where δ is a dirac function, and z is a unit length vector of the point current source in the polarization direction.
The total radiation rate of the radiation point current source is expressed as:
wherein ,is the real part of the electric field component of the point current source along the polarization direction.
The far field radiation rate is expressed as:
wherein A is a closed curved surface containing a point current source, S is a time average energy flow density vector, n is an external normal vector of the curved surface A, and a is a closed curved surface element.
The radiation rate in free space is expressed as:
wherein ,ηvac Is wave impedance in vacuum, k 0 =2pi/λ, λ is wavelength, k 0 Is the wave number, n a Is the refractive index in air.
Defining a normalized total radiation rate is expressed as:
Γ total /Γ air
the normalized far field radiation rate is expressed as:
Γ rad /Γ air
the spontaneous emission rate, Γ, of the single point radiation source in (a), (b) of FIG. 1 was first calculated using the finite element method (COMSOLMultiphics software) total /Γ air and Γrad /Γ air The curves as a function of the radius of the gold nanoparticles are shown in FIGS. 2 (a) and (b), respectivelyShown. When the radius of the gold nanoparticles meets the plasmon resonance condition, the peak value of the total radiation rate and the far-field radiation rate can appear, and the corresponding radius of the gold nanoparticles is the resonance radius, as can be seen from fig. 2, four resonance radii, namely R=45 nm, 120nm, 180nm, 260nm, exist, and Γ total /Γ air And F-shaped structure rad /Γ air Decreasing with increasing resonance radius of the gold nanoparticles.
The total and far-field radiation rates for the different gold nanoparticle structures of fig. 1 can then be calculated, as can the case where the radiation pattern varies with the gold nanoparticle spacing d.
The invention discloses a method for enhancing spontaneous radiation in a metal nanoparticle nano gap on a metal substrate, which comprises the steps of arranging a PMMA layer between gold nanoparticles and the gold substrate, placing a point source in the PMMA layer, researching the influence of the quantity, layout and size of the gold nanoparticles on the point source radiation rate and radiation direction, and reproducing a far-field radiation pattern by a method of pushing out a far field from a near field based on the Lorentz reciprocity theorem. This structure can enhance the spontaneous radiation efficiency and change the radiation direction. Compared with the existing structure, the method for regulating and controlling the spontaneous radiation in the metal nanoparticle nano gap on the metal substrate can change the radiation direction of a molecular or quantum dot radiation source, has a simple structure, and is convenient for experimental test.
Claims (4)
1. A metal nanoparticle micro-nanostructure comprising gold nanoparticles (1), a PMMA layer (2) and a metal substrate (3), the metal nanoparticles (1) being placed on the PMMA layer (2), the PMMA being coated on the metal substrate (3), a molecular or quantum dot radiation source (4) being placed in the middle of the PMMA layer (2), characterized in that the gold nanoparticles (1) are arranged on the PMMA layer (2) at equal intervals, and the molecular or quantum dot radiation source (4) being located directly below the central gold nanoparticles; the structure of different numbers of gold nanoparticles (1) acting on a molecular or quantum dot radiation source is designed, wherein the structure comprises single, two, three, five and nine gold nanoparticles, and the change of radiation direction and the enhancement of total radiation rate and far-field radiation rate are realized by controlling the distance between the two, three, five or nine gold nanoparticles:
step 1, calculating the total radiation rate and the far-field radiation rate of single gold nanoparticles on a gold substrate by using a finite element method, and selecting the radius of the gold nanoparticles, wherein:
the total radiation rate calculation formula is:
wherein ,the real part of the electric field component along the polarization direction of the point current source;
the far field radiation rate is expressed as:
wherein A is a closed curved surface containing a point current source, S is a time average energy flow density vector, n is an external normal vector of the curved surface A, and a is a closed curved surface element; the radiation rate in free space is expressed as:
wherein ,ηvac Is wave impedance in vacuum, k 0 =2pi/λ, λ is wavelength, k 0 Is the wave number, n a Is the refractive index in air;
step 2, selecting the radius of the gold nanoparticles in the step 1, and calculating the normalized total radiation rate gamma when the distance between every two gold nanoparticles is gradually increased by using a finite element method total /Γ air Far field radiation rate Γ rad /Γ air The radiation pattern was calculated as a function of the individual gold nanosphere spacing in MATLAB-COMSOL based on the Lorentz reciprocity theorem.
2. A metal nanoparticle micro-nano structure according to claim 1, wherein the metal substrate (3) is a gold substrate.
3. A metal nanoparticle micro-nano structure according to claim 1, wherein the gold nanoparticles (1) are nanospheres, and the nanosphere radius selection is determined by calculating the spontaneous emission rate according to the finite element method, and the first resonance radius, 45nm, is selected.
4. The metal nanoparticle micro-nano structure according to claim 1, wherein the PMMA layer (2) is 10nm thick.
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| CN112928452B (en) * | 2021-01-27 | 2022-04-22 | 南开大学 | Wideband spontaneous radiation enhanced tetramer metal nano antenna structure and manufacturing method and application thereof |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20040093531A (en) * | 2003-04-30 | 2004-11-06 | 한국과학기술연구원 | Polymer electroluminescent device using emitting layer of nanocomposites |
| CN102680453A (en) * | 2011-11-21 | 2012-09-19 | 南开大学 | Raman spectrum high electromagnetic enhancement substrate coated with gain medium and preparation |
| CN204029875U (en) * | 2014-06-27 | 2014-12-17 | 京东方科技集团股份有限公司 | Organic electroluminescence device, array base palte and display unit |
| CN106847797A (en) * | 2017-01-17 | 2017-06-13 | 电子科技大学 | A kind of noble metal nano particles quantum dot array luminescent device preparation method |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20040093531A (en) * | 2003-04-30 | 2004-11-06 | 한국과학기술연구원 | Polymer electroluminescent device using emitting layer of nanocomposites |
| CN102680453A (en) * | 2011-11-21 | 2012-09-19 | 南开大学 | Raman spectrum high electromagnetic enhancement substrate coated with gain medium and preparation |
| CN204029875U (en) * | 2014-06-27 | 2014-12-17 | 京东方科技集团股份有限公司 | Organic electroluminescence device, array base palte and display unit |
| CN106847797A (en) * | 2017-01-17 | 2017-06-13 | 电子科技大学 | A kind of noble metal nano particles quantum dot array luminescent device preparation method |
Non-Patent Citations (1)
| Title |
|---|
| Probing the mechanisms of large Purcell enhancement in plasmonic nanoantennas;Gleb M. Akselrod等;《Nature Photonics》;20141012;第8卷;正文第835-839页 * |
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