A terahertz sensing metasurface device based on quasi-continuum bound states

Abstract

Disclosed is a terahertz sensing superstructure device based on quasi-continuous domain bound state, which comprises, from bottom to top, a substrate layer, a metal layer and an analyte layer, the metal layer comprises an array formed by metal split ring structures arranged in a square lattice, the metal split ring structure is a central symmetric structure, the development process of evolving quasi-continuous domain bound state to continuous domain bound state is realized by changing the left and right opening size of the metal split ring structure, the pixelated superstructure is constructed by adjusting the distance between the metal split ring structure and the upper and lower boundaries of the square lattice to realize terahertz fingerprint identification, and fingerprint signal detection and refractive index sensing detection can be performed on small molecule substances such as sucralose and ascorbic acid, thereby realizing high-sensitivity qualitative and quantitative detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz molecular fingerprint and refractive index sensing and super-structured surface, in particular to a terahertz sensing super-structured surface device based on quasi-continuous domain bound state. BACKGROUND

[0002] Terahertz waves have attracted great attention in chemical and biomedical detection due to their non-invasive and non-ionizing properties, and the intramolecular and intermolecular vibrational spectra of substances are located in the terahertz band, which provides an opportunity to construct a substance-specific "fingerprint spectrum". However, the size mismatch between the substance molecules and terahertz waves results in a weak fingerprint signal, which is difficult to meet the current demand for high sensitivity and high specificity in trace detection. In recent years, super-structured surfaces have been widely studied for adjusting various electromagnetic modes to enhance the interaction between substances and terahertz waves by using strong electric field localization enhancement, such as Fano resonance, guided mode resonance, ring dipole resonance and quasi-continuous domain bound state. However, these studies mostly focus on the dependence between frequency shift and substance concentration, which is embodied in refractive index sensing, and can only achieve quantitative detection, while qualitative detection of substance fingerprint characteristics is less explored. There is no report on the application of super-structured surfaces to realize trace terahertz molecular fingerprint and refractive index dual sensing. SUMMARY

[0003] In view of the technical problems of low sensitivity and specificity, and inability to achieve qualitative detection in the prior art, the present application provides a terahertz sensing super-structured surface device based on quasi-continuous domain bound state, which can be used to evolve the development process from quasi-continuous domain bound state to continuous domain bound state by adjusting the structural parameters in the metal layer, and can realize terahertz fingerprint identification and refractive index sensing by constructing a pixelated super-structured surface, thereby revealing the refractive index and extinction coefficient of the substance and achieving high-sensitivity qualitative and quantitative detection.

[0004] According to an aspect of the present application, a terahertz sensing super-structured surface device based on quasi-continuous domain bound state is provided, which includes a substrate layer, a metal layer and an analyte layer integrated from bottom to top, the metal layer includes an array formed by metal split ring structures arranged in a square lattice, the metal split ring structure is a center-symmetric structure, the development process from quasi-continuous domain bound state to continuous domain bound state is evolved by changing the left and right opening sizes of the metal split ring structure, and terahertz fingerprint identification is realized by constructing a pixelated super-structured surface by adjusting the distance between the metal split ring structure and the upper and lower boundaries of the square lattice.

[0005] Further, the line width of the metal split ring structure is w, the left and right opening sizes are both d1, the middle opening size is d2, the x-axis distance intervals between the three openings are equal, and the x-axis side length L x , the y-axis side length Ly , the distance g of the metal split ring structure from the left and right boundaries of the square lattice x , the distance g of the metal split ring structure from the upper and lower boundaries of the square lattice y , the period p of the x axis of the square lattice x , the period p of the y axis y (p y = L y + g y μm).

[0006] Further, the material of the metal layer includes gold, silver or copper, and the material of the substrate layer includes silicon dioxide, high resistance silicon or polyimide.

[0007] Further, the refractive index of the silicon dioxide ranges from 1.9 to 2.

[0008] Further, the thickness t1 of the metal layer ranges from 100 nm to 300 nm, and the thickness t2 of the substrate layer ranges from 100 μm to 2 mm.

[0009] According to another aspect of the present application, an application of a terahertz sensing superstructure device based on quasi-continuous domain bound states is proposed, in which a terahertz spectrum system is used to obtain terahertz time domain spectrum information of an analyte layer as air and a to-be-detected substance, and a fast Fourier transform is used to obtain frequency domain transmission spectrum information, so as to perform fingerprint identification and refractive index sensing on the to-be-detected substance.

[0010] Further, the fast Fourier transform operation includes: obtaining terahertz frequency domain amplitude information of pure air, the analyte layer as air and the to-be-detected substance, respectively named as E ref (ω), E sam0 (ω) and E sam1 (ω), and defining the air-loaded transmission spectrum as T0(ω) = E sam0 (ω) / E ref (ω) and the loaded transmission spectrum as T1(ω) = E sam1 (ω) / E ref (ω).

[0011] Further, the fingerprint identification includes a pixelated super surface module, the pixelated super surface module includes changing the distance g y of the metal split ring structure from the upper and lower boundaries of the square lattice to construct a pixelated super surface module, obtaining a wide spectrum resonance band with a resonance frequency covering 0.9 THz-1.2 THz, defining the air-loaded transmission spectrum resonance peak amplitude envelope as A0(ω) and the loaded transmission spectrum resonance peak amplitude envelope as A1(ω), and obtaining the corresponding fingerprint signal A = A1(ω)-A0(ω).

[0012] Further, the refractive index sensor includes any selected sub-module of the pixelated metasurface module for processing, and the processing flow of the refractive index sensor includes defining the resonant frequency of the resonant peak of the empty transmission spectrum as f0 and the resonant frequency of the resonant peak of the loaded transmission spectrum with different contents of the analyte as f1, defining Δf = f1-f0, and obtaining the relationship between the corresponding content of the analyte and the resonant peak resonant frequency offset.

[0013] Further, when the analyte layer is sucralose and ascorbic acid, the detection limit of the fingerprint signal is 0.18 mg and 0.54 mg, respectively.

[0014] The beneficial effects of the present application are:

[0015] (1) The present application provides a terahertz sensing metasurface device based on quasi-continuous domain bound state, which has high electric field enhancement benefit, up to 336 times, and can realize strong interaction between terahertz waves and matter;

[0016] (2) Fingerprint identification and refractive index sensing are realized simultaneously in the terahertz wave band, qualitative and quantitative detection of matter can be realized, the detection limit of the refractive index sensing is 100 ng, and the detection limit of the fingerprint signal of sucralose and ascorbic acid is 0.18 mg and 0.54 mg, respectively, compared with the existing conventional tabletting scheme, the detection limit is decreased by 139 times;

[0017] (3) The present application can be applied to the recognition and detection of small molecules such as sugars and amino acids, and has wide application market. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments and, together with the description, serve to explain the principles of the present application. Other embodiments and many of the intended advantages of the embodiments will be readily appreciated as the same becomes better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.

[0019] Figure 1 The structure schematic diagram of the terahertz sensing metasurface device based on quasi-continuous domain bound state of the present application is shown;

[0020] Figure 2 The development process of the present application from quasi-continuous domain bound state to continuous domain bound state is shown, and the obtained simulation and experimental transmission spectrum are shown;

[0021] Figure 3 The transmission spectrum resonant peak amplitude envelope curve of the empty sensor device without coating analyte according to one specific embodiment of the present application is shown;

[0022] Figure 4 The transmission spectral resonance peak amplitude envelope curve of the loaded sensor device coated with 1.5 μm thick sucralose is shown according to one specific embodiment of the present application;

[0023] Figure 5 The electromagnetic field intensity distribution map of the sensor device designed by the present application at the resonance frequency is shown;

[0024] Figure 6 The transmission spectral resonance peak amplitude envelope curve of the loaded sensor device coated with 4.5 μm thick ascorbic acid is shown according to one specific embodiment of the present application;

[0025] Figure 7 The corresponding fingerprint signals of sucralose and ascorbic acid obtained by the present application are shown;

[0026] Figure 8 The transmission spectrum obtained according to one specific embodiment of the present application with the analyte layer thickness set to 4 μm and the refractive index varying from 1.0 to 2.0 at intervals of 0.2 is shown;

[0027] Figure 9 The sensitivity S distribution map according to one specific embodiment of the present application is shown;

[0028] Figure 10 The transmission spectrum obtained according to one specific embodiment of the present application with the analyte layer being 0.1 μg, 1 μg, 5 μg and 15 μg of sucralose is shown;

[0029] Figure 11 The transmission spectrum obtained according to one specific embodiment of the present application with the analyte layer being 0.1 μg, 1 μg, 5 μg and 15 μg of ascorbic acid is shown;

[0030] Figure 12 The corresponding relationship between different contents of sucralose and the resonance frequency shift of the resonance peak according to one specific embodiment of the present application is shown;

[0031] Figure 13 The corresponding relationship between different contents of ascorbic acid and the resonance frequency shift of the resonance peak according to one specific embodiment of the present application is shown.

[0032] The meanings of the numbers in the figure are as follows: 100, substrate layer; 101, metal layer; 102, analyte layer; 103, square lattice; 104, metal split ring structure. DETAILED DESCRIPTION

[0033] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] Example 1

[0036] Figure 1 A schematic diagram of the terahertz sensing metasurface device based on quasi-continuous domain bound states of the present invention is shown, as follows: Figure 1 As shown, the sensing metasurface device includes a substrate layer 100, a metal layer 101, and an analyte layer 102, which are integrally composited sequentially from bottom to top. The period p of the square lattice 103 in the substrate layer 100 along the x-axis is... x The y-axis period is 120 μm. y The thickness t1 is 200 μm, the material is SiO2, and the thickness t2 is 120 μm. The metal layer 101 consists of an array of metal split ring structures 104 arranged in a square lattice 103. The metal split ring structures 104 are made of Au, with a thickness t1 of 200 nm. The linewidth w of each unit metal split ring structure 104 in the metal layer 101 is 3 μm, the left and right opening sizes d1 are 6 μm, the middle opening size d2 is 16 μm, and the x-axis side length L of the metal split ring structure 104 is... x The y-axis side length L of the metal split ring structure 104 is 108 μm. y The distance g between the metal split ring structure 104 and the left and right boundaries of the square lattice 103 is 72 μm. x The distance g between the metal split ring structure 104 and the upper and lower boundaries of the square lattice 103 is 6 μm. y The thickness is 24 μm, and the analyte layer 102 is air of semi-infinite thickness.

[0037] By changing the size d1 of the left and right openings of the metal split ring structure 104 arranged in the square lattice 103 in the metal layer 101, the evolution process from the quasi-continuous domain bound state to the continuous domain bound state was observed. The d1 values ​​were selected as 6 μm, 14 μm, 22.35 μm, 34 μm, and 38 μm, and the resulting simulated and experimental transmission spectra are shown below. Figure 2As shown, it can be seen that as d1 increases from 6μm to 38μm, the resonance peak undergoes a process of gradual disappearance and reappearance. The quality factor of the resonance peak first increases and then decreases. This process is consistent with the typical characteristics of the bound state in the random continuous domain, that is, the destructive interference of electromagnetic modes in the radiation channel is achieved by adjusting the structural parameters.

[0038] Example 2

[0039] The structural parameters of the sensor for trace terahertz fingerprint recognition are: the period p of the square lattice 103 in the substrate layer 100 along the x-axis. x The y-axis period is 120 μm. y The metal layer 101 has a thickness of 120 μm, is made of SiO2, and has a thickness t2 of 200 μm. It consists of an array of metal split ring structures 104 arranged in a square lattice 103. The metal split ring structures 104 are made of Au, have a thickness t1 of 200 nm, a linewidth w of 3 μm for each unit metal split ring structure 104 in the metal layer 101, left and right opening sizes d1 of 6 μm, and a center opening size d2 of 16 μm. The x-axis side length L of the metal split ring structure 104 is... x The y-axis side length L of the metal split ring structure 104 is 108 μm. y =p y -g y The distance g between the metal split ring structure 104 and the left and right boundaries of the square lattice 103 x The distance g between the metal split ring structure 104 and the upper and lower boundaries of the square lattice 103 is 6 μm. y The thickness of the analyte layer 102 changes from 16 μm to 33 μm. It is a composite layer formed by uniformly coating 1.5 μm thick sucralose and 4.5 μm thick ascorbic acid on the surface of the substrate layer and the metal layer 101.

[0040] The transmission spectrum resonance peak amplitude envelope A0(ω) of the uncoated sensor device without analyte coating and the transmission spectrum resonance peak amplitude envelope A1(ω) of the loaded sensor device coated with 1.5 μm thick sucralose are obtained to obtain the corresponding fingerprint signal A = A1(ω) - A0(ω), as shown below. Figure 3 As shown in Figures 4 and 7, the designed sensor device exhibits a strong electric field enhancement effect, up to 336 times, such as... Figure 5 As shown, this leads to a strong interaction between terahertz waves and matter, which in turn reflects the fingerprint information of sucralose through changes in the amplitude of the resonance peak, such as... Figure 7 As shown, the absorption coefficient of 25mg sucralose obtained using a conventional tableting method is compared with the obtained fingerprint signal, demonstrating that the present invention can effectively reflect the fingerprint information of a substance.

[0041] To verify the universality of this invention, ascorbic acid was selected and subjected to the same study, such as... Figure 6 As shown, the transmission spectrum resonance peak amplitude envelope of the onboard sensor device coated with 4.5 μm thick ascorbic acid is displayed, and... Figure 7 The comparison between the absorption coefficient of 73 mg ascorbic acid obtained using a conventional tableting method and the obtained fingerprint signal demonstrates that the proposed method has good universality.

[0042] Experimental results showed that the detection limits of fingerprint signals for sucralose and ascorbic acid were 0.18 mg and 0.54 mg, respectively. Compared with the same fingerprint signals obtained by conventional tableting methods, the content of detectable substances decreased by 139 times and 135 times, respectively.

[0043] Example 3

[0044] The structural parameters of the sensor used to achieve trace terahertz refractive index sensing can be selected from the distances g between the metal split ring structure 104 of different sizes and the upper and lower boundaries of the square lattice 103 in Example 2. y In this embodiment, g is selected. y =24μm is used for explanation.

[0045] Sensitivity was used as the evaluation criterion for the terahertz metasurface sensing performance. Sensitivity S was defined as: S = Δf / Δn, where Δf is the shift in the resonant frequency of the resonant peak. The resonant frequency of the unloaded transmission spectrum was defined as f0, and the resonant frequency of the loaded transmission spectrum covered with different amounts of analytes was defined as f1. Δf = f1 - f0, and Δn is the change in the refractive index of the analyte. The thickness of the analyte layer 102 was set to 4 μm, and the refractive index was varied from 1.0 to 2.0 in increments of 0.2 to simulate the change in refractive index. The resulting transmission spectrum is shown below. Figure 8 As shown, the resonant frequency of the resonance peak shifts to lower frequencies as the refractive index increases. By summing the resonant frequency shift and the change in refractive index, the corresponding sensitivity S is obtained, as shown below. Figure 9 As shown, its sensitivity is as high as 127.7 GHz / RIU.

[0046] In the experiment, the analyte layer 102 was changed to contain 0.1 μg, 1 μg, 5 μg, and 15 μg of sucralose and ascorbic acid, respectively, to evaluate the relationship between the analyte content and the resonant frequency shift of the resonance peak. The resulting transmission spectra are shown below. Figure 10 , 11 As shown, it can be seen that with the increase of analyte content, the resonant frequency of the resonance peak shifts to lower frequencies, and the total shift of sucralose is less than that of ascorbic acid. This is because the refractive index of sucralose is lower than that of ascorbic acid. The relationships between the content of sucralose and ascorbic acid and the resonant frequency shift of the resonance peak are summarized in [the table below]. Figure 12 ,13 As shown, the detection limit of the trichlorosucrose and ascorbic acid sensing is 0.1 μg, which shows excellent sensing performance.

[0047] According to the above method, the application provides a sensor device of a pixelated super-structured surface module based on quasi-continuous domain bound state with strong electric field enhancement benefit, which can be used for enhancing the interaction between terahertz waves and substances, and can be used for revealing the two most critical optical parameters of substances, i.e., refractive index and extinction coefficient, so as to realize high-sensitivity qualitative and quantitative detection, and improve the accuracy and specificity of detection.

[0048] The specific embodiments of the application are described above, but the protection scope of the application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the application, which should be covered in the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

[0049] In the description of the application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. The word 'comprising' does not exclude the existence or presence of elements or steps not listed in the claims. The word 'a' or 'an' in front of an element does not exclude the existence of multiple such elements. The simple fact that certain measures are recorded in mutually different dependent claims does not mean that the combination of these measures cannot be used to improve. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. An application of a terahertz sensing metasurface device based on quasi-continuous domain bound states, characterized in that, The terahertz spectrum system is used to obtain terahertz time-domain spectrum information of an analyte layer being air and a to-be-detected substance, and fast Fourier transformation is used to obtain frequency-domain transmission spectrum information, so as to perform fingerprint identification and refractive index sensing on the to-be-detected substance; The sensing metasurface device comprises a substrate layer, a metal layer and an analyte layer integrated from bottom to top, the metal layer comprises an array formed by metal split ring structures arranged in a square lattice, the metal split ring structure is a central symmetric structure, the development process from quasi-continuous domain bound state to continuous domain bound state is evolved by changing the left and right opening sizes of the metal split ring structure, and the pixelated metasurface is constructed by adjusting the distance between the metal split ring structure and the upper and lower boundaries of the square lattice to realize terahertz fingerprint identification. The fingerprint recognition includes a pixelated metasurface module, which includes a metal split ring structure with a distance g from the upper and lower boundaries of the square lattice y The pixelated metasurface module is constructed, a wide-spectrum resonance band with a resonance frequency of 0.9 THz-1.2 THz is obtained, an amplitude envelope of a resonance peak of an unloaded transmission spectrum is defined as A0(ω), an amplitude envelope of a resonance peak of a loaded transmission spectrum is defined as A1(ω), and a corresponding fingerprint signal A=A1(ω)-A0(ω) is obtained. The refractive index sensing comprises processing of any selected sub-module of the pixelated metasurface module, and the processing flow of the refractive index sensing comprises defining the resonant frequency of the unloaded transmission spectrum resonant peak as f0 and the resonant frequency of the loaded transmission spectrum resonant peak as f1, defining Δf = f1-f0, and obtaining the relationship between the content of the corresponding analyte and the resonant frequency shift.

2. Use of a quasi-continuous domain bound state based terahertz sensing metasurface device according to claim 1, characterized in that, The line width of the metal split ring structure is w, the left and right opening sizes are d1, the middle opening size is d2, the x-axis distance intervals between the three openings are equal, the x-axis side length L x , the y-axis side length L y , the distance of the metal split ring structure from the left and right boundaries of the square lattice is g x , the distance of the metal split ring structure from the upper and lower boundaries of the square lattice is g y , the x-axis period of the square lattice is p x , the y-axis period of the square lattice is p y , and p y = L y + g y μm.

3. Use of a quasi-continuous domain bound state based terahertz sensing metasurface device according to claim 1, characterized in that, The material of the metal layer comprises gold, silver or copper, and the material of the substrate layer comprises silicon dioxide, high-resistance silicon or polyimide.

4. Use of a quasi-continuous domain bound state based terahertz sensing metasurface device according to claim 3, characterized in that, The refractive index of the silicon dioxide ranges from 1.9 to 2.

5. Use of a quasi-continuous domain bound state based terahertz sensing metasurface device according to claim 3, wherein, The thickness t1 of the metal layer ranges from 100 nm to 300 nm, and the thickness t2 of the substrate layer ranges from 100 μm to 2 mm.

6. Use of a quasi-continuous domain bound state based terahertz sensing metasurface device according to claim 1, wherein, The fast Fourier transform operation includes: obtaining pure air, the terahertz frequency domain amplitude information of the analyte layer as air and the to-be-detected substance, respectively named as E ref (ω), E sam0 (ω) and E sam1 (ω), and defining the no-load transmission spectrum as T0(ω) = E sam0 (ω) / E ref (ω) and the load transmission spectrum as T1(ω) = E sam1 (ω) / E ref (ω).

7. Use of a quasi-continuous domain bound state based terahertz sensing metasurface device according to claim 1, wherein, When the analyte layer is sucralose and ascorbic acid, the detection limit of the fingerprint signal is 0.18 mg and 0.54 mg, respectively.

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