Liquid phase infrared sensor structure based on mirror image hybrid graphene plasmon

Abstract

The invention discloses a liquid phase infrared sensor structure based on mirror image hybrid graphene plasmons, and belongs to the technical field of infrared optical sensing. Comprising a graphene layer; the metal grating structure is arranged adjacent to the graphene layer, and a nano gap is formed between the metal grating structure and the graphene layer; wherein the graphene layer can induce to generate mirror image charges on the surface of the metal grating structure, and hybrid coupling of graphene plasmons of the graphene layer and the mirror image charges is realized in a plane, so that hot spots are locally exposed in a liquid phase environment while being locally located in nanometer gaps; the method is used for enhancing a local electromagnetic field and improving infrared sensing sensitivity. According to the invention, highly localized plasmon hot spots can be provided in a liquid phase, and dynamic performance regulation and control can be realized, so that the requirements of liquid-phase molecule infrared sensing are met.

Description

Technical Field

[0001] The present invention relates to the field of infrared optical sensing technology, and more particularly to a liquid-phase infrared sensor structure based on image hybrid graphene plasmonics. Background Art

[0002] Infrared spectroscopy can rapidly and non-destructively detect the fingerprint information of molecular chemical bonds and group vibrations, as shown in Fig. 2(a). However, the O-H bending vibration mode of water has strong and broad infrared absorption near 1300 - 2000 cm -1 -1, overlapping with the fingerprint region related to the analysis of molecular structure, as shown in Fig. 2(b). Therefore, the analysis of the chemical structure of nano-scale molecules in a liquid phase environment has always been a major challenge for infrared spectroscopy.

[0003] Image hybrid graphene plasmon (image hybrid graphene plasmon) is a collective oscillation phenomenon caused by the interaction between free electrons in graphene and mirror charges in metal under the excitation of incident electromagnetic waves. It is an antisymmetric electromagnetic mode highly compressed in the nano-gap between graphene and metal. It has a wide-band response (covering the infrared fingerprint region), high wavelength compression ability, and excellent electromagnetic field enhancement ability (Fig. 3(a)) (about an order of magnitude higher than traditional graphene plasmonics (Fig. 3(b)). Most of the currently widely studied i image hybrid graphene plasmon modes are through the construction of out-of-plane structures - graphene / insulator / metal. The i image hybrid graphene plasmon mode supported by this structure is similar to the short-wavelength graphene plasmon mode with antisymmetric properties supported in bilayer graphene, obtaining a nearly linear dispersion relationship. Because it is similar to acoustic waves, it is also called acoustic graphene plasmon (AGP).

[0004] Previous research work has designed various device structures for exciting image hybrid graphene plasmonics. Experiments have confirmed or theoretically predicted many of its excellent properties, including: extremely high wavelength compression, excellent electromagnetic field enhancement, and high-sensitivity detection ability, indicating its important application prospects in protein detection in an aqueous solution environment in the future. However, the design of the image hybrid graphene plasmon structure of these structures is difficult to dynamically regulate, and its hot spots are mainly localized inside the insulator spacer layer, and it is difficult to be applied to SEIRA testing after the device is fabricated.

[0005] Therefore, how to provide a new liquid-phase infrared sensor structure based on image hybrid graphene plasmonics is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a liquid-phase infrared sensor structure based on mirror hybrid graphene plasmons. In a liquid-phase environment, the O–H bending vibration of water generates a strong and broad infrared absorption at about 1300-2000 cm -1 where, which overlaps with the infrared fingerprint region, seriously interfering with the extraction of molecular infrared absorption characteristic signals. The infrared sensor based on mirror hybrid graphene plasmons realizes a detection sensitivity of sub-ten nanometers in a liquid-phase environment by localizing infrared light at the nanoscale.

[0007] In the reported mirror hybrid graphene plasmon structures, the hot spots are mainly confined inside the insulator spacer layer and cannot be directly exposed to the liquid-phase environment, which limits the detection of molecules in the liquid phase. The novel liquid-phase infrared sensor structure based on mirror hybrid graphene plasmons provided by the present invention can not only provide highly localized plasmon hot spots in the liquid phase but also realize dynamic performance regulation, thus meeting the requirements of liquid-phase molecular infrared sensing.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A liquid-phase infrared sensor structure based on mirror hybrid graphene plasmons, comprising:

[0010] A graphene layer;

[0011] A metal grating structure disposed adjacent to the graphene layer, a nano-gap being formed between the metal grating structure and the graphene layer;

[0012] Wherein, the graphene layer can induce mirror charges on the surface of the metal grating structure, and the graphene plasmons of the graphene layer are hybridized and coupled with the mirror charges in the plane, thereby localizing the hot spots in the nano-gap while being exposed to the liquid-phase environment for enhancing the local electromagnetic field and improving the infrared sensing sensitivity.

[0013] Further, the graphene layer is a periodic nanostructure, including a graphene structure and an etched graphene region.

[0014] Further, the shape of the graphene structure is any planar geometric shape.

[0015] Further, the shape of the metal grating structure is any planar geometric shape.

[0016] Further, the size of the array unit of the graphene layer and the metal grating structure is independently 5-1000 nm in any one direction.

[0017] Further, the metal grating is prepared by evaporation coating with one or more of the following metals: gold, silver, aluminum, iron, titanium, palladium, platinum, copper, magnesium, zinc.

[0018] Furthermore, the nano-gap formed between the metal grating structure and the graphene layer is 0 - 100 nm.

[0019] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a liquid-phase infrared sensor structure based on mirror hybrid graphene plasmon. By introducing the nano-gap between graphene and the gold grating, mirror hybrid graphene plasmon is excited, so that the nano-gap has a region with enhanced local electromagnetic field (up to 200 times). Combining with the electrical background subtraction method, the interference of the water background signal can be excluded, and the infrared absorption of molecules in the plasmon region can be enhanced. The chemical composition and structure of molecules are identified by the infrared characteristic absorption peaks in the obtained enhanced infrared spectrum. The plasmon wavelength is in the mid-infrared band (resonance frequency is 400 - 3000 wavenumbers). The novel sensor provided by the present invention can be dynamically modulated, reused, and integrated. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the provided drawings.

[0021] Figure 1 Fig. 1 is a front and side view of an example of the liquid-phase infrared sensor structure based on mirror hybrid graphene plasmon;

[0022] Fig. 2(a) is a schematic diagram showing the molecular chemical structure information provided by infrared spectroscopy;

[0023] Fig. 2(b) is a schematic diagram showing the infrared absorption of water covering the protein secondary structure information;

[0024] Fig. 3(a) is a distribution diagram of the electromagnetic field of the mirror hybrid graphene plasmon structure;

[0025] Fig. 3(b) is a distribution diagram of the electromagnetic field of the ordinary graphene plasmon structure;

[0026] Fig. 4(a) is an example of the detection of silk nanofibril (SNF) protein molecules by the present sensor structure in a liquid-phase environment (water and heavy water);

[0027] Fig. 4(b) is an example of the detection of the assembly process of silk nanofibril (SNF) protein molecules by the present sensor structure in a liquid-phase environment (water);

[0028] Figure 5 Fig. 5 is an example of the top view of the liquid-phase infrared sensor structure capable of exciting mirror hybrid graphene plasmon. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] The object of the present invention is to provide a liquid-phase infrared sensor structure based on mirror hybridized graphene plasmons, including: a graphene layer; a metal grating structure disposed below the graphene layer, and a nano-gap is formed between the metal grating structure and the graphene layer; wherein, the graphene layer can induce mirror charges on the surface of the metal grating, and the graphene plasmons of the graphene layer and the mirror charges are hybridized and coupled in-plane, so as to localize the hot spots in the nano-gap while exposing them to the liquid-phase environment, for enhancing the local electromagnetic field and improving the infrared sensing sensitivity. In the reported mirror hybridized graphene plasmon structure, the hot spots are mainly confined inside the insulator spacer layer and cannot be directly exposed to the liquid-phase environment, which limits the detection of molecules in the liquid phase. The novel infrared sensing structure provided by the present invention enables the in-plane hybridization and coupling of graphene plasmons and the mirror charges induced on the surface of the metal grating by designing the in-plane structure of graphene / nano-gap / metal grating, so as to localize the hot spots in the nano-gap while exposing them to the liquid-phase environment. Combining the liquid top-gate method can provide highly localized plasmon hot spots in the liquid phase and achieve enhanced frequency dynamic regulation of the sensor, thus meeting the requirements of liquid-phase molecular infrared sensing.

[0031] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0032] See Figure 1 The embodiments of the present invention disclose a liquid-phase infrared sensor structure based on mirror hybridized graphene plasmons, including:

[0033] A graphene layer;

[0034] A metal grating structure disposed adjacent to the graphene layer (such as a metal grating structure disposed at any position above, below, or in the middle of the graphene layer), and a nano-gap is formed between the metal grating structure and the graphene layer;

[0035] Among them, the graphene layer can induce mirror charges on the surface of the metal grating, and the graphene plasmons of the graphene layer and the mirror charges are hybrid-coupled in the plane, so as to localize the hot spots in the nano-gap while being exposed to the liquid phase environment, for enhancing the local electromagnetic field and improving the infrared sensing sensitivity.

[0036] Specifically, by designing the in-plane structure of graphene / nano-gap / metal grating, the graphene plasmons and the mirror charges induced by them on the surface of the metal grating are hybrid-coupled in the plane, so as to localize the hot spots in the nano-gap while being exposed to the liquid phase environment.

[0037] Specifically, the graphene layer is monolayer or few-layer, with periodic / aperiodic nanostructures, including graphene structures and etched graphene regions, where the shape of the graphene structures is any planar geometric shape, such as: rectangle, square, circle, ellipse, triangle, etc.

[0038] In a specific embodiment, as shown in Figure 5 The shape of the metal grating structure is any planar geometric shape, such as: rectangle, square, circle, ellipse, triangle, etc.

[0039] Specifically, the size of the graphene and metal microstructure array units in any one direction is independently 5 - 1000 nm.

[0040] Specifically, the evaporated metal grating materials include gold (Au), silver (Ag), aluminum (Al), iron (Fe), titanium (Ti), palladium (Pd), platinum (Pt), copper (Cu), magnesium (Mg), zinc (Zn), or other metal materials with similar properties.

[0041] Specifically, the nano-gap between the graphene and the adjacent metal grating is opened, 0 - 100 nm.

[0042] Specifically, referring to FIGS. 3(a)-(b), the present invention realizes the excitation of mirror hybrid graphene plasmons in the liquid phase environment for the first time, which can not only provide highly localized plasmon hot spots in the liquid phase, but also realize the dynamic regulation of the enhanced frequency of the sensor; further, the present invention realizes the application of the mirror hybrid graphene plasmon infrared sensing structure in the detection of sub-ten-nanometer molecular liquid phase infrared spectra; the present invention improves the signal-to-noise ratio of the graphene plasmon enhanced infrared spectrum, and the electromagnetic field enhancement factor (E / E0) of this sensing structure is about 260 (FIG. 3(a)), while the electromagnetic field enhancement factor (E / E0) of the ordinary graphene plasmon infrared sensing structure is only 13 (FIG. 3(b)).

[0043] The beneficial effects of the present invention are as follows:

[0044] By introducing the nano-gap between graphene and gold grating, the present invention excites mirror hybrid graphene plasmons, enabling the nano-gap to have a region with enhanced local electromagnetic field (up to 200 times). Combining with the electrical background subtraction method, it can eliminate the interference of water background signals and enhance the infrared absorption of molecules in the plasmon region. The chemical composition and structure of molecules are identified through the infrared characteristic absorption peaks in the obtained enhanced infrared spectrum. The plasmon wavelength is in the mid-infrared band (resonance frequency is 400 - 3000 wavenumbers), and the sensor can be dynamically modulated, reused, and integrated.

[0045] In a specific embodiment, a mirror hybrid graphene plasmon infrared sensor structure is used to characterize the secondary structure changes during the assembly process of silk nanofibers (SNF) in aqueous solution.

[0046] The in-plane gap between graphene and the gold antenna enables the excitation of mirror hybrid graphene plasmon response in aqueous solution, thus realizing enhanced infrared sensing and recognition of proteins. A solution of silk fibroin protein (SF) with a concentration of 30 μg / mL and a temperature of 298 K is injected into the sensor. As shown in Fig. 4(a), increasing the liquid top gate ΔVG (i.e., |VG - VCNP|) causes the resonance peak of mirror hybrid graphene plasmons to blue-shift. The alignment of the protein amide bands with the resonance of mirror hybrid graphene plasmons enhances the coupling strength between them, resulting in the appearance of two absorption peaks. The dips indicated by the grey and red shaded regions represent the amide II band (v AmideII ) and amide I band (v AmideI ) of the protein molecules, respectively. To distinguish the contributions of ν_(AmideI) of SNF and ν_OH of H -1 O in the range of 1600–1700 cm 2 , in this embodiment, 99.9% D 2 O is injected to completely replace H 2 O in the sensor (shown by the dashed curve in Fig. 4(a)). It can be found that the amide bands of SNF are still detected. These results indicate that due to the extremely low content of H 2 O in the mirror hybrid graphene plasmon hot spots, the infrared absorption characteristics of proteins are successfully detected.

[0047] The excellent properties of mirror hybrid graphene plasmons make it a super-sensitive platform for in-situ and real-time detection of trace assembly intermediates during the SNF assembly process. Next, an SF solution with a concentration of 10 μg / mL and a temperature of 248 K was injected into an unused sensor, and the spectra of mirror hybrid graphene plasmons during the assembly process (0–236 minutes) were continuously collected. As shown in Fig. 4(b), an example of detecting the protein molecule assembly process of silk nanofibrils (SNF) in a liquid phase environment (water). The concave peaks indicated by the red and blue shaded regions represent the combined contribution of the amide I band (v AmideI ) of the protein molecule and the bending vibration mode v OH of water. As the time of the assembly process increases, the frequency of the v AmideI concave peak blue-shifts from 1605 cm -1 to 1628 cm -1 (indicated by the black arrow). This frequency shift indicates that the SF molecules adsorbed on the graphene have undergone a conformational change, forming an assembly intermediate with a β-sheet structure.

[0048] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same and similar parts among the various embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section.

[0049] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A liquid phase infrared sensor structure based on mirror hybridized graphene plasmon, characterized in that: include: Graphene layer; a metal grating structure disposed adjacent to the graphene layer, wherein a nanogap is formed between the metal grating structure and the graphene layer; The graphene layer can induce image charges on the surface of the metal grating structure, and the graphene plasmons of the graphene layer are hybridized with the image charges in the plane, thereby localizing the hot spots in the nanogap while exposing them to the liquid environment, which is used to enhance the local electromagnetic field and improve the infrared sensing sensitivity.

2. The liquid phase infrared sensor structure based on mirror hybridized graphene plasmon according to claim 1, characterized in that: The graphene layer is a periodic / non-periodic nanostructure, including a graphene structure and an etched graphene region.

3. The liquid phase infrared sensor structure based on mirror hybridized graphene plasmon according to claim 2, characterized in that: The shape of the graphene structure is any planar geometric shape.

4. The liquid phase infrared sensor structure based on mirror hybridized graphene plasmon according to claim 1, characterized in that: The shape of the metal grating structure is any planar geometric shape.

5. The liquid phase infrared sensor structure based on mirror hybridized graphene plasmon according to claim 1, characterized in that: The size of the array units of the graphene layer and the metal grating structure in any direction is independently 5 to 1000 nm.

6. The liquid phase infrared sensor structure based on mirror hybridized graphene plasmon according to claim 1, characterized in that: The metal grating is made of one or more of the following metals: gold, silver, aluminum, iron, titanium, palladium, platinum, copper, magnesium, and zinc.

7. The liquid phase infrared sensor structure based on mirror hybridized graphene plasmon according to claim 1, characterized in that: The nanogap formed between the metal grating structure and the graphene layer is 0-100 nm.

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