CN109254337B - Method for enhancing single-layer graphene broadband absorption based on strong coupling effect - Google Patents
Method for enhancing single-layer graphene broadband absorption based on strong coupling effect Download PDFInfo
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- CN109254337B CN109254337B CN201811450280.0A CN201811450280A CN109254337B CN 109254337 B CN109254337 B CN 109254337B CN 201811450280 A CN201811450280 A CN 201811450280A CN 109254337 B CN109254337 B CN 109254337B
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Abstract
The invention discloses a method for enhancing single-layer graphene broadband absorption based on a strong coupling effect, which comprises the steps of selecting a graphene nano strip array as an absorption layer, using a metal groove array as a substrate, arranging corresponding filling media in the metal groove, exciting graphene surface plasmon resonance through the graphene nano strip array, supporting excitation of a magnetic resonance mode through the metal groove, enabling a hybrid field generated by strong coupling between the two modes to be intensively distributed at graphene, and finally achieving the effect of enhancing the graphene broadband absorption; the graphene nanoribbon array is only contacted with one edge of the metal trapezoidal groove array, and the resonance condition of a graphene plasmon mode with a high quality factor required by excitation of a strong coupling effect is met. The enhanced absorption bandwidth of the invention covers the mid-infrared band, has the characteristics of high band-pass, low fluctuation, high speed and the like, and can be applied to an integrated all-optical network.
Description
Technical Field
The invention relates to the technical field of nanophotonics, in particular to a method for enhancing single-layer graphene broadband absorption based on a strong coupling effect.
Background
Light absorption is an intrinsic property of materials, the size of which plays a crucial role for various advanced photonic device designs, such as: modulators, detectors, solar cells, and the like. However, the development of miniaturization of conventional thin film materials is severely hampered in the mid-infrared band due to the relatively low absorption and narrow parameter space of the materials themselves.
Meanwhile, graphene, as a thin film material of a single atomic layer, has been widely applied to the design of various functionalized optoelectronic devices due to its ultrahigh carrier mobility, excellent tuning capability and nonlinear effect. More importantly, the interaction of the mid-infrared photons with the graphene electrons can generate graphene surface plasmons. Compared with the traditional metal surface plasmon, the excited graphene surface plasmon has ultrahigh local field definition, lower energy loss and excellent tuning capability; these are all very important to develop future miniaturized photonic devices in the mid-infrared band.
Although graphene has the advantages described above, the significantly low mid-infrared absorption makes the device performance of graphene in this band extremely limited; although various physical principles include: interference, impedance matching, critical coupling, plasmon resonance enhancement and the like have been proposed to improve the absorption efficiency of graphene, but these theories are only designed for narrow-band absorption, and are far from meeting the requirements for actually required broadband absorption applications.
At present, a broadband absorber based on graphene is proposed, but most of the designs only aim at improving the absorption performance of the whole device, and whether the absorption performance of single-layer graphene is improved or not is unknown; the use of a multi-resonator structure is an alternative that can enhance the absorption of broadband single-layer graphene, but the excited graphene plasmon resonance in the mid-infrared band is relatively weak, and the coupling between adjacent resonators can cause inevitable absorption fluctuation, which are not favorable for the practical application of the device.
Disclosure of Invention
Aiming at the problems of low-intensity absorption and narrow bandwidth of the graphene material in the mid-infrared band, the method for enhancing the graphene broadband absorption based on the strong coupling effect is provided by utilizing the characteristic of redistribution of the hybrid mode field generated when the magnetic resonance mode and the graphene plasmon resonance mode are strongly coupled.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a method for enhancing single-layer graphene broadband absorption based on a strong coupling effect is characterized in that a graphene nano strip array is used as an absorption layer, a metal groove is used as a substrate, a filling medium is arranged in the metal groove, graphene surface plasmon resonance is excited through the graphene nano strip array, excitation of a magnetic resonance mode is supported through the metal groove, a hybrid field generated by strong coupling between the two modes is distributed at the graphene in a concentrated mode, and finally the absorption effect of the graphene broadband is enhanced.
The invention provides a method for enhancing graphene broadband absorption based on a strong coupling effect, wherein a plurality of trapezoidal metal grooves are uniformly distributed on a metal groove substrate, the top groove spacing of the metal grooves is smaller than the bottom groove spacing, filling media are arranged in the metal grooves, and a graphene nano-strip array is arranged on the upper surface of the metal grooves; the graphene nanoribbon array is in unilateral contact with the metal groove array; the unilateral contact can cause excited graphene surface plasmon resonance to have smaller intrinsic loss, so that the excitation of the strong coupling effect of the system is ensured.
The invention relates to a trapezoidal metal groove array; the material for constructing the metal groove can be one of gold, silver, copper and aluminum; meanwhile, the trapezoid metal groove structure can be replaced by a similar structure with the same physical effect, such as an open metal spherical shell. The trapezoidal structure is selected because the extremely narrow top groove space enables the two arms of the groove to have extremely strong coupling effect, so that a vector field limited in the groove is mainly along the transverse direction, and the graphene placed in the groove is ensured to have strong absorption capacity; the coupling and decoupling of two resonance modes excited by the system can be regulated and controlled by regulating the geometric structure of the metal trapezoidal groove. In addition, because the top of the trapezoidal groove has extremely strong field local area, the hybrid field of the splitting mode caused by coupling can be promoted to have stronger field constraint at the graphene, and further broadband graphene absorption is realized
Based on the strong coupling method, the enhanced graphene absorption bandwidth covers the mid-infrared band, and the realized bandwidth is 2.5 microns; the band generated by the bandwidth can be regulated by the medium in the filling groove.
The filling medium in the metal groove can be one of silicon dioxide, silicon, gallium arsenide, silicon carbide, boron nitride, aluminum oxide and silicon nitride; the trapezoidal metal groove realizes the regulation and control of the coupling strength by changing the method of filling the medium, and the coupling regulation and control can be carried out at the initial coupling point by controlling the strength of the metal groove exciting the magnetic resonance mode, thereby realizing the broadband flat-top absorption and eliminating the influence of absorption fluctuation caused by coupling
The invention discloses a preparation method of a structure selected by a method for enhancing graphene broadband absorption based on a strong coupling effect, which comprises the following specific steps:
step 1: plating a layer of filling medium film on the metal substrate, and etching the filling medium film after the plating is finished;
step 2: carrying out ultraviolet light etching on the filling medium film, and constructing a trapezoidal medium array structure through etching;
and 3, step 3: carrying out magnetron sputtering on the etched sample to form metal;
and 4, step 4: after the alignment or polishing, removing redundant metal materials on the surface of the sample after the magnetron sputtering;
and 5, step 5: transferring graphene to an upper surface of the post-treated sample;
and 6, step 6: and (3) constructing the graphene nano strip array by the sample subjected to transfer treatment through a maskless electron beam lithography technology.
The coating method adopted in the step 1 of the invention is one of a Plasma Enhanced Chemical Vapor Deposition (PECVD) method, a Chemical Vapor Deposition (CVD) method, a magnetron sputtering method and a thermal evaporation method.
The etching method adopted in the step 2 of the invention is one of inductively coupled plasma etching (ICP), reactive ion etching (IRE) and dry etching.
The magnetron sputtering method adopted in the step 3 of the invention is one of an electron beam evaporation method EBE, a magnetron sputtering method and a thermal evaporation method.
The method for enhancing single-layer graphene broadband absorption based on the strong coupling effect can be applied to infrared optical modulators, detectors and photovoltaic cells.
The invention has the advantages that: the invention uses two-dimensional nano material graphene, ensures high modulation bandwidth and ultra-fast modulation, can be applied to an integrated all-optical network, has the characteristics of high band-pass, low fluctuation, high speed and the like, and can be applied to intermediate infrared optical modulators and detectors.
Drawings
FIG. 1 is an orthogonal cross-sectional schematic view of a broadband flat-topped graphene absorber enhanced based on a strong coupling effect according to the present invention;
FIG. 2 is a graph of the result of the broadband absorption resulting from the strong coupling effect of the present invention;
FIG. 3 is a graph showing dispersion relation between a graphene surface plasmon resonance mode and a magnetic resonance mode according to the present invention;
FIG. 4 is a process flow diagram for constructing the device according to an embodiment of the present invention;
FIG. 5 is a graph showing the results of the absorption spectra of the metal trenches filled with media of different refractive indices;
fig. 6 is a diagram of broadband flat-top graphene absorption caused by adding a corresponding dielectric material according to the present invention.
Detailed Description
The invention is described in further detail below with reference to the following description of the drawings and the detailed description.
Example 1: as shown in fig. 1, a design structure for enhancing single-layer graphene broadband absorption based on a strong coupling effect includes a graphene nanoribbon array of an absorption layer and a metal trapezoid-groove substrate structure.
The graphene strip array period is 2 mu m, the strip width is 67 nm, the top width of the substrate trapezoid metal groove structure is 300 nm, the bottom width of the substrate trapezoid metal groove structure is 700 nm, and the groove height is 1.4 mu m. The metal material of the substrate layer is silver, which is a metal with low intrinsic loss.
In this example, the graphene nanoribbon of the absorption layer is only in contact with a single side of the metal trapezoidal groove, so that the excited graphene surface plasmon resonance can be ensured to have smaller intrinsic loss, and the excitation of the strong coupling effect of the system can be promoted.
Example 2: as shown in fig. 2 and 3, fig. 2 is a broadband graphene absorption spectrum generated by the design, and when a Transverse Magnetic (TM) wave is perpendicularly incident to the surface of a sample, the structure can simultaneously excite graphene surface plasmon resonance and magnetic resonance. Due to the extremely narrow top slot width limitation, the hybrid mode field caused by strong coupling between the two modes will be mainly bound at the graphene, thereby generating a broadband graphene absorption effect.
From fig. 2, it can be seen that a huge broadband graphene absorption effect with a bandwidth of 2.7 μm can be generated by using the structure, and the absorption rate is 60% and far exceeds the absorption efficiency of single-layer graphene, which is only 2.3%.
Fig. 3 shows a dispersion curve of a magnetic resonance mode and a graphene plasmon mode, and it can be clearly demonstrated that the broadband absorption effect caused by the device is caused by a strong coupling effect.
Example 3: as shown in fig. 4, a specific preparation flow chart of the graphene broadband absorption structure based on the strong coupling effect enhancement is selected;
1) film coating: plating a layer of filling medium film with the thickness of 1.4 microns on a metal substrate, wherein the metal substrate is made of silver, and the plated medium material is made of silicon dioxide;
2) etching: carrying out ultraviolet light etching on the filling medium film, and constructing a trapezoidal medium array structure through etching;
3) sputtering metal: sputtering metal on the etched sample, wherein the material is silver which is the same as the metal of the substrate;
4) and (3) post-treatment: after the alignment or polishing, removing redundant metal materials on the surface of the sample after the magnetron sputtering;
5) transferring: transferring graphene to an upper surface of the post-treated sample;
6) molding: and (3) constructing the graphene nano strip array by the sample subjected to transfer treatment through a maskless electron beam lithography technology.
The coating method adopted in the step 1) is Plasma Enhanced Chemical Vapor Deposition (PECVD); the etching method adopted in the step 2) is inductively coupled plasma etching (ICP); the sputtering method adopted in the step 3) is an electron beam evaporation method EBE.
In addition, the preparation method of the invention can relate to a plurality of methods, only one of which is adopted in the embodiment 3, and the implementation effect of the product prepared by other preparation processes is very close to that of the embodiment 3.
Example 4: as shown in fig. 5 and 6, fig. 5 and 6 show absorption spectra of media filled with different refractive indexes, and it can be seen from fig. 5 that the absorption fluctuation gradually decreases with the change of the filling refractive index, and completely disappears when the refractive index is 3. This is because the filled medium affects the intensity of the excited magnetic resonance in the slot, and when the intensity of the excited magnetic resonance mode happens to be strongly coupled with the graphene plasmon resonance, and the strong coupling is located at the initial coupling point, the generated absorption will not fluctuate.
As can be seen from FIG. 6, this structure can produce an ultra-wide absorption bandwidth with a bandwidth of 2.5 μm, and the absorption ripple is substantially 0.
It should be noted that the above-mentioned embodiments are merely preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and any combination or equivalent changes made on the basis of the above-mentioned embodiments are also within the scope of the present invention.
Claims (7)
1. A method for enhancing single-layer graphene broadband absorption based on a strong coupling effect is characterized in that a graphene nano-strip array is selected as an absorption layer, a metal groove array is used as a substrate, and a filling medium is arranged in the metal groove; exciting graphene surface plasmon resonance through the graphene nanoribbon array, supporting excitation of a magnetic resonance mode through a metal groove, and enabling hybrid fields generated by strong coupling between the two modes to be distributed on the graphene in a concentrated manner, so that the graphene broadband absorption effect is enhanced finally; the graphene nanoribbon array is arranged on the upper surface of the metal groove; and it contacts only one side of the metal slot array.
2. The method for enhancing single-layer graphene broadband absorption according to claim 1, wherein the metal trench top trench spacing is smaller than the bottom trench spacing.
3. The method for enhancing single-layer graphene broadband absorption based on the strong coupling effect according to claim 1, wherein the enhanced graphene absorption bandwidth covers a mid-infrared band, and the bandwidth range is as follows: 19.8 to 22.3 microns.
4. The method for enhancing single-layer graphene broadband absorption according to claim 1 or 2, wherein the metal grooves are formed by a trapezoidal metal groove array; the construction material of the metal groove can be one of gold, silver, aluminum and copper.
5. The method for enhancing single-layer graphene broadband absorption according to claim 1 or 2, wherein the filling medium is selected from one of silicon dioxide, silicon, gallium arsenide, silicon carbide, boron nitride, aluminum oxide, and silicon nitride.
6. The method for enhancing single-layer graphene broadband absorption according to claim 5, wherein the broadband flat-top absorption of graphene is achieved by changing a filling medium in a metal groove to regulate absorption fluctuation generated by the graphene.
7. A method of making a structure selected for use in the method of claim 1, said method comprising:
1) plating a layer of filling medium film on the metal substrate, and etching the filling medium film after the plating is finished;
2) carrying out ultraviolet light etching on the filling medium film, and constructing a trapezoidal medium array structure through etching;
3) carrying out magnetron sputtering on the etched sample to form metal;
4) after the alignment or polishing, removing redundant metal materials on the surface of the sample after the magnetron sputtering;
5) transferring graphene to an upper surface of the post-treated sample;
6) and (3) constructing the graphene nano strip array by the sample subjected to transfer treatment through a maskless electron beam lithography technology.
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