Terahertz plasma array fingerprint spectrum sensing device

Abstract

The present invention discloses a terahertz plasma array fingerprint spectrum sensing device. The fingerprint spectrum sensing device is constructed based on a substrate, with a plasma unit array drawn on the substrate, and cross-grooved unit cells densely arranged in each unit of the plasma unit array; in the plasma unit, the densely arranged cross-grooved unit cells constitute a complementary array of cross-grooved unit cells; the unit length of the cross-grooved unit cells of the plasma units in the plasma unit array is set according to the form of diagonal unidirectional gradient; in the plasma unit array, the unit length of the cross-grooved unit cells in each plasma unit is uniformly and discretely set within the range of 47μm to 104μm. The fingerprint spectrum sensing device of the present invention is provided with a complementary cross-shaped structure. Because this structure can excite the plasma local field mode, the resonance peak of the dielectric metasurface is relatively wide, and the spectral lines of both wide fingerprint spectrum and narrow fingerprint spectrum substances can be enhanced and amplified at the same time.

Description

Technical Field

[0001] The present invention relates to a terahertz wave trace detection technology, and in particular to a terahertz plasma array fingerprint spectrum sensing device. Background Art

[0002] Terahertz (THz) spectroscopy has attracted considerable attention in recent decades because its energy is close to the energy of intermolecular interactions such as hydrogen bonds, lattice vibrations, van der Waals forces, and the translational and rotational energies of molecules. Therefore, THz has become an effective means of measuring the low-frequency mode spectra of molecules or aggregates (such as crystals, polymers, and proteins), and has been widely used in biology and chemistry.

[0003] A widely used technique for spectroscopic measurements of samples in the terahertz frequency range involves mixing a powdered sample with a binding medium (such as polyethylene powder), pressing this mixture into a pellet, and placing it in the optical path. This technique is simple and well-established, but it is not suitable for sensing trace amounts of samples or thin films. Detecting molecular vibrations in thin films remains challenging due to the low interaction between terahertz waves and molecular and intermolecular vibrational modes.

[0004] To overcome this difficulty, many recent studies have proposed various metamaterial structures, such as metal hole arrays, ring resonators, and surface plasmon antennas utilizing metal stripes. These structures couple to terahertz waves and exhibit near-field enhancement. A common sensing approach using metamaterials is to detect the frequency shift response of the resonant peak caused by changes in the dielectric constant of the material coated on the metasurface. This method provides a sensitive method for molecular detection by revealing the non-dispersive component of the material's dielectric constant. However, it cannot reveal the spectral information of the molecule's vibrational fingerprint, which limits its application.

[0005] The vibrational spectrum of thin film molecules is of universal importance in the detection and identification of chemical and biological samples. Currently, there are two mechanisms that can realize thin film terahertz molecular fingerprint sensing. One is based on the absorption induced transparency (AIT) effect, which is due to the resonance of the broadband mode of the metasurface with the narrowband mode of the analyte, resulting in coherent coupling. The most interesting feature of AIT is that in the combined system of the artificial device and the material to be measured, the transmission peak appears at the spectral position of the resonant absorption of the material to be measured. This effect has been demonstrated by arranging metal gratings and split ring resonators. However, due to the non-dispersive component of the actual dielectric constant of the analyte and manufacturing errors, the additional shift of the metasurface resonance will make it difficult for the metasurface resonance to match the resonant frequency of the analyte-covered system. The other method is based on multiplexing technology, which utilizes the strong light-matter interaction between a series of narrowband resonance peaks of the dielectric metasurface and the broadband mode resonance of the analyte for detection.

[0006] The current problem is:

[0007] 1) The frequency coverage of a series of narrow-band resonance peaks of dielectric metasurfaces is currently less than 0.3 THz, which limits the frequency range of material fingerprint spectrum amplification;

[0008] 2) The currently used dielectric metasurface array technology has an uneven surface, which causes uneven sample coating and thus leads to measurement errors;

[0009] 3) The resonance peak of the dielectric metasurface is narrow, and the frequency resolution of commercial time-domain terahertz spectroscopy systems cannot meet actual measurement requirements;

[0010] 4) The resonance peak of the dielectric metasurface is narrow, which makes it difficult to stimulate the AIT effect of the material fingerprint spectrum. Summary of the Invention

[0011] The object of the present invention is to provide a terahertz plasma array fingerprint spectrum sensing device, which can simultaneously enhance and amplify the spectral lines of materials with wide fingerprint spectra and narrow fingerprint spectra.

[0012] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0013] A terahertz plasma array fingerprint spectrum sensing device is provided. The fingerprint spectrum sensing device is based on a substrate, a plasma unit array is arranged on the substrate, and cross-groove unit cells are densely arranged in each unit of the plasma unit array.

[0014] Furthermore, in the plasma unit, the densely arranged cross-grooved unit cells constitute a complementary array of cross-grooved unit cells.

[0015] Furthermore, the unit length of the cross-grooved unit cell of the plasma unit in the plasma unit array is set in a diagonal unidirectional gradient form.

[0016] Furthermore, the diagonal unidirectional gradient is diagonally decreasing or diagonally increasing.

[0017] Furthermore, in the plasma unit array, the unit length of the cross-grooved unit cell in each plasma unit is uniformly and discretely arranged in the range of 47 μm to 104 μm.

[0018] Furthermore, the plasma unit array is a 6×6 array.

[0019] Furthermore, in the plasma unit array, each plasma unit is square with a side length of 5 mm. Each plasma unit is divided into an effective area and a surrounding area. The 3 mm × 3 mm square area in the middle of the plasma unit is the effective area, and the peripheral area surrounding the effective area is the surrounding area. The width of the surrounding area is 2 mm; the cross-groove unit cells arranged in the plasma unit are all arranged in the effective area.

[0020] Furthermore, the structure of the cross-groove unit cell is realized as follows: in a tiny area in the plasma unit, a cross-groove is opened in the middle of the area by photolithography, and a metal film is evaporated outside the cross-groove and solidified to form the cross-groove unit cell.

[0021] Furthermore, the metal film evaporated outside the cross groove is gold, silver, copper or aluminum.

[0022] Furthermore, the substrate is quartz, or a polyimide substrate with a thickness of 20 μm to 100 μm, or a silicon substrate with a thickness of 200 μm to 2 mm, or a silicon dioxide substrate with a thickness of 200 μm to 2 mm.

[0023] The fingerprint spectrum sensing device of the present invention adopts a complementary cross-shaped plasma structure, which is conducive to improving the plasma enhancement effect of the terahertz transmission spectrum at a single frequency point.

[0024] The fingerprint spectrum sensing device of the present invention adopts a plasma unit array structure, which is conducive to achieving the enhancement and amplification function of the fingerprint spectrum envelope of the wide spectrum.

[0025] The fingerprint spectrum sensing device of the present invention is provided with a 6×6 plasma unit array. Since the unit array evenly distributes the plasma enhancement peak frequency points in the range from 0.9THz to 2THz, the frequency range of the material fingerprint spectrum amplification is relaxed.

[0026] In the fingerprint spectrum sensing device of the present invention, a metal film is evaporated on the surface of the plasma unit. Since the thickness of the metal film is at the level of hundreds of nanometers, the surface is very flat, thereby improving the uniformity of sample coating and avoiding measurement errors.

[0027] The fingerprint spectrum sensing device of the present invention is provided with a complementary cross-shaped structure. Since this structure can excite the plasma local field mode, the resonance peak of the dielectric metasurface is wider.

[0028] Compared with the prior art, the fingerprint spectrum sensing device of the present invention can simultaneously enhance and amplify the spectral lines of substances with broad fingerprint spectra and narrow fingerprint spectra, and has good robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of a plasma unit array in a fingerprint spectrum sensing device of the present invention;

[0030] Figure 2 Schematic diagram of a cross-grooved unit cell provided in a plasma unit;

[0031] Figure 3 Schematic diagram of FAFS transmission spectra with different unit length L values when a=5μm,DL=8μm;

[0032] Figures 4a to 4b Schematic diagram of the absorption spectrum of α-lactose (red) and AIT observed in the FAFS / α-lactose system in Example 1, wherein: Figure 4a Set the unit length L = 65μm, Figure 4b The unit length L is set to 67 μm;

[0033] Figures 5a to 5d Schematic diagram of the result of multiplexing by FAFS in Example 2, wherein:

[0034] Figure 5a is a schematic diagram of the normalized absorption spectrum of D-carnitine,

[0035] Figure 5b is a schematic diagram of the normalized absorption spectrum of L-carnitine,

[0036] Figure 5c Schematic diagram of the absorption spectrum of D-carnitine.

[0037] Figure 5d Schematic diagram of the absorption spectrum of L-carnitine. DETAILED DESCRIPTION

[0038] The present invention will be further described below with specific embodiments:

[0039] This embodiment provides a terahertz plasma array fingerprint spectrum sensing device, which is a frequency agile fingerprint sensor (FAFS) for short, and is used to enhance terahertz fingerprint spectrum trace sensing.

[0040] See also Figure 1 The fingerprint spectrum sensing device of this embodiment is constructed based on a substrate, on which a 6×6 plasma unit array is arranged. In other words, the substrate is divided into 36 small areas arranged in a rectangular array ( Figure 1 In the figure, 01 to 36), each small area is called a plasma unit, and the 36 plasma units arranged in a rectangular array are the 6×6 plasma unit array.

[0041] It should be noted that in the plasma unit array, each plasma unit is square with a side length of 5 mm. Each plasma unit is also divided into an effective area and a surrounding area. The 3mm×3mm square area in the middle of the plasma unit is the effective area, and the peripheral area surrounding the effective area is the surrounding area. The width of the surrounding area is 2 mm. In this way, two adjacent plasma units can be easily cut and reorganized.

[0042] Cross-groove unit cells are densely arranged in the effective area of each plasma unit, and the densely arranged cross-groove unit cells in the plasma unit constitute a complementary array of cross-groove unit cells.

[0043] More specifically,

[0044] See also Figure 2 The cross-groove unit cell is a very small regional structure, and its specific structure is implemented as follows:

[0045] In a very small area (usually a square area with a side length of about 100 μm), a cross groove (in the shape of a regular cross) is opened in the middle of the area by photolithography.

[0046] The width of the cross groove is called the slit width of the cross groove unit cell, which is represented by "a". The slit width a can be between 2 μm and 11 μm.

[0047] The length of the cross groove is called the unit length of the cross groove unit cell, which is represented by "L";

[0048] The side length of the micro area where the cross groove is located is called the periodicity of the cross groove unit cell, which is represented by "D".

[0049] The difference between the periodicity and the unit length (DL) may be between 5 μm and 11 μm.

[0050] It should be noted that the cross-shaped grooves are formed on the substrate by photolithography. A metal (gold, silver, copper, aluminum) film is evaporated outside the cross-shaped grooves and solidified to form the cross-shaped groove unit cell. The thickness of the evaporated metal film is on the order of hundreds of nanometers, ranging from 100nm to 200nm.

[0051] In the plasma unit, a cross-groove cell complementary array composed of a plurality of cross-groove cell combinations can achieve the efficiency of a high-Q plasma field-enhanced resonance peak.

[0052] The plasma unit array formed by combining all the plasma units can achieve a wide frequency coverage of the resonance peak-to-peak frequency. In this embodiment, the frequency range covered is 0.9 THz to 2.0 THz.

[0053] It should be noted that the cross-grooved unit cells arranged in different plasma units are all different. The differences mentioned here mainly refer to the different dimensional parameters of the cross-grooved unit cells, that is, the unit length L of the cross-grooved unit cells is different. The slit width a is the same, set to 5 microns. The "difference between the periodicity and the unit length (DL)" of the cross-grooved unit cells is the same, set to 8 microns.

[0054] See also Figure 3 , Figure 3 The FAFS transmission spectra are shown for different unit length L values while maintaining a=5 μm and DL=8 μm.

[0055] Specifically,

[0056] The unit length L of the cross-grooved unit cell of the plasma unit in the plasma unit array is set according to the rule of diagonal decreasing.

[0057] The "diagonal decreasing" rule mentioned here refers to the rule that the unit length L of the cross slot unit cell of all plasma units in the plasma unit array "gradually decreases from one array angle of the plasma unit array to its diagonal array angle".

[0058] See also Figure 1 In this embodiment, the unit length L of the cross-grooved unit cell of the plasma unit (numbered 01) at the upper left corner of the plasma unit array is set to 104 microns (corresponding to the resonant peak frequency of 1.978 THz), and the unit length L of the cross-grooved unit cell of the plasma unit (numbered 36) at the lower right corner of the plasma unit array (the diagonal corner of the upper left corner) is set to 47 microns (corresponding to the resonant peak frequency of 0.932 THz).

[0059] The unit length L (micrometer) of the cross slot unit cell of all 36 plasma units is set as follows (reference Figure 1 Watch together):

[0060] 104 101 98 95 92 89 86 83 80 78 76 74 72 70 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47

[0061] From this we can understand that Figure 1In the figure, the unit length L of the cross-grooved unit cell of the plasma unit decreases from 01 to 06 horizontally, from 06 to 36 vertically, from 01 to 31 vertically, from 31 to 36 horizontally, and from 01 to 36 diagonally. In general, the unit length L of the cross-grooved unit cell of the plasma unit decreases along any path starting from 01 and ending at 36. This is the so-called "diagonal decreasing" law.

[0062] It should be noted that the above 01, 06, 31, and 36 are Figure 1 The number of the plasma unit in .

[0063] The unit length of the cross-groove unit cell of each unit in the plasma unit array is set according to the rule of diagonal decreasing. Such a setting makes all frequency points in the frequency band of the wide spectrum fingerprint spectrum uniformly enhanced.

[0064] The above-mentioned law of diagonal decrease, if understood in reverse, can also be understood as the law of diagonal increase, or the two can be collectively referred to as the law of diagonal unidirectional change.

[0065] In this embodiment, the unit length of the cross-groove unit cell in each plasma unit is uniformly and discretely set in the range of 47 μm to 104 μm, and the corresponding resonant peak frequency is 0.932 THz to 1.978 THz, thereby achieving a broadband setting of the resonant peak frequency of the entire plasma unit array.

[0066] It should be noted that the setting of the unit length L of the cross slot unit cell is essentially to set the resonant peak frequency of the cross slot unit cell.

[0067] For example, if the resonant peak frequency of the cross-grooved unit cell in the plasma unit numbered 01 needs to be set to 0.932 THz, then the unit length L of the cross-grooved unit cell can be set to 104 μm (104 μm corresponds to 0.932 THz).

[0068] For example, if the resonant peak frequency of the cross-grooved unit cell in the plasma unit numbered 10 needs to be set to 1.226 THz, the unit length L of the cross-grooved unit cell can be set to 78 μm (78 μm corresponds to 1.226 THz).

[0069] In the fingerprint spectrum sensing device of this embodiment, the resonance peak frequency interval between two adjacent units in the plasma unit array is less than 7 GHz, and the 36 frequency points in the frequency band of the wide spectrum fingerprint spectrum are uniformly enhanced.

[0070] The fingerprint spectrum sensing device of this embodiment is provided with a plurality of cross-groove unit cells. This cross-groove structure is conducive to the plasma field enhancement effect of a single frequency point, thereby achieving a good technical effect of enhancing and amplifying the transmission intensity of a single frequency point.

[0071] In addition, the fingerprint spectrum sensing device of this embodiment arranges cross-groove unit cells of different sizes in an array form. Such a structural setting is conducive to achieving the plasma field enhancement effect of multiple frequency points within a wide frequency range, thereby achieving the good technical effect of enhancing and amplifying the wide-spectrum fingerprint spectrum envelope.

[0072] It should be noted that the substrate may be quartz (dielectric constant of 3.84, loss tanδ=0.001), or a polyimide substrate with a thickness of 20 μm to 100 μm, or a silicon or silicon dioxide substrate with a thickness of 200 μm to 2 mm.

[0073] The fingerprint spectrum sensing device of this embodiment is equipped with 36 plasma unit arrays. Since the plasma enhancement peak frequency points are evenly distributed in the range of 0.9THz to 2THz in the 36 unit arrays, this solves the technical problem mentioned in the background technology that "the frequency coverage range of a series of narrow-band resonance peaks of dielectric metasurfaces is currently less than 0.3THz, which limits the frequency range of material fingerprint spectrum amplification."

[0074] In the fingerprint spectrum sensing device of this embodiment, a metal film is evaporated on the surface of the plasma unit. Since the thickness of the metal film is at the level of hundreds of nanometers, the surface roughness is two orders of magnitude lower than that of the dielectric metasurface. This solves the technical problem mentioned in the background technology that "the currently used dielectric metasurface array technology has an uneven surface, which causes uneven sample coating and thus measurement errors."

[0075] The fingerprint spectrum sensing device of this embodiment is provided with a complementary cross-shaped structure (a complementary array of cross-groove unit cells). Since this structure can excite the local field mode of the plasma, it solves the technical problem mentioned in the background technology that "the resonance peak of the dielectric metasurface is narrow and the frequency resolution of the commercial time-domain terahertz spectroscopy system cannot meet the actual measurement requirements."

[0076] In addition, the complementary cross-shaped structure excites the plasma local field mode, which is easy to produce strong interactions with the vibration mode of the molecular structure. This solves the technical problem mentioned in the background technology that "the resonance peak of the dielectric metasurface is narrow and it is not easy to excite the AIT effect of the material fingerprint spectrum."

[0077] The following two examples are provided to specifically illustrate the detection and identification of substances using the fingerprint spectrum sensing device of this embodiment:

[0078] Example 1,

[0079] A 1 μm thick α-lactose layer is coated on the fingerprint spectrum sensing device. The absorption spectrum of 1 μm thick α-lactose is measured, as shown in the figure. Figure 4a and Figure 4b To obtain a thin lactose film, α-lactose powder was diluted in a saturated aqueous solution and deposited on the surface of the plasma cell array. The amplitude transmission spectra of FAFS with (dashed line) and without (solid line) 1 μm thick α-lactose were measured at L = 65 μm (P18) and 67 μm (P16), respectively. Figure 4a and Figure 4b As shown in the figure. The results show that under the excitation of AIT, the resonance shape has changed significantly. There is a vibration signal peak at 1.38THz, which is close to the results of previous studies in the literature (1.37THz). The AIT transmission curve obtained by experimental measurement is shown in the figure. Figure 4a and Figure 4b As shown, the enhancement factor is defined as the ratio of the smaller AIT tilt difference to the conventional absorption amplitude (e.g. Figure 4a and Figure 4b At P18 (L = 65 μm), the maximum enhancement factor reaches 7x, and the AIT effect is observed across a wide pixel range from P13 to P23. FAFS can capture the narrow absorption lines of the analyte without being affected by the uncertainty of the analyte thickness, and covering a wider pixel range improves the robustness of AIT.

[0080] Example 2,

[0081] The FAFS was used to identify trace chiral substances by scanning and enhancing the absorption spectrum. The terahertz absorption spectrum of carnitine (D-carnitine and L-carnitine) showed two broadband absorption lines. The frequencies corresponding to the absorption peaks were 1.39 THz and 1.72 THz, respectively. Figure 5a and Figure 5b In the results shown, the 10μm carnitine layer covering the FAFS results in modulation of the transmission spectrum intensity of a single cell due to the coupling between molecular vibrations and the enhanced electric field around the cross-slot resonator. This transmission modulation is related to the molecular vibrations of D-carnitine and L-carnitine. The pixel absorption spectrum envelopes of 1μm and 10μm chiral carnitine are shown in Figure 2. Figure 5c and Figure 5d shown. Figure 5c and Figure 5dThis is a conventional terahertz absorption spectrum of D-carnitine and L-carnitine. The absorption peaks of D-carnitine and L-carnitine are essentially identical, with two peak frequencies at 1.39 THz and 1.72 THz. However, the absorption of D-carnitine at 1.39 THz is lower than that of L-carnitine, while the absorption of D-carnitine at 1.72 THz is higher than that of L-carnitine. When the thickness is less than 10 μm, the error in qualitative analysis increases, and conventional sensing cannot locate the absorption peak. FAFS reproduces the broadband carnitine absorption signature, increasing the absorption amplitudes at 1.39 THz and 1.72 THz by approximately 8 times for 10 μm thickness analysis and by approximately 10 times for 1 μm thickness analysis. The linewidths provided by the plasmon resonances in the plasmon cell near 1.39 THz and 1.72 THz are narrower than the spectral characteristic sizes of the D-carnitine and L-carnitine absorption bands. This advantage enables the readout of the absorption signatures of chiral substances at a broadband discrete frequency.

[0082] The above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A terahertz plasma array fingerprint spectrum sensing device, characterized by: The fingerprint spectrum sensing device is based on a substrate, a plasma unit array is arranged on the substrate, and cross-grooved unit cells are densely arranged in each unit of the plasma unit array; In the plasma unit, densely arranged cross-groove unit cells form a complementary array of cross-groove unit cells; The unit length of the cross-grooved unit cell of the plasma unit in the plasma unit array is set in a diagonal unidirectional gradient form.

2. The terahertz plasma array fingerprint spectrum sensing device according to claim 1, characterized in that: The diagonal unidirectional gradient is diagonally decreasing or diagonally increasing.

3. The terahertz plasma array fingerprint spectrum sensing device according to claim 1, characterized in that: In the plasma cell array, the unit length of the cross-grooved unit cell in each plasma cell is uniformly and discretely arranged in the range of 47 μm to 104 μm.

4. The terahertz plasma array fingerprint spectrum sensing device according to claim 1, characterized in that: The plasma unit array is a 6×6 array.

5. The terahertz plasma array fingerprint spectrum sensing device according to claim 1, characterized in that: In the plasma cell array, each plasma cell is square with a side length of 5 mm. Each plasma cell is divided into an active area and a surrounding area. The 3 mm × 3 mm square area in the middle of the plasma cell is the active area, and the peripheral area surrounding the active area is the surrounding area. The width of the surrounding area is 2 mm. The cross-grooved unit cells arranged in the plasma unit are all arranged in the effective area.

6. The terahertz plasma array fingerprint spectrum sensing device according to claim 1, characterized in that: The structure of the cross groove unit cell is realized as follows: in a tiny area of the plasma unit, a cross groove is opened in the middle of the area by photolithography, and a metal film is evaporated outside the cross groove and solidified to form the cross groove unit cell.

7. The terahertz plasma array fingerprint spectrum sensing device according to claim 6, characterized in that: The metal film evaporated outside the cross groove is gold, silver, copper or aluminum.

8. The terahertz plasma array fingerprint spectrum sensing device according to claim 1, characterized in that: The substrate is quartz, Alternatively, a polyimide substrate having a thickness of 20 μm to 100 μm, Alternatively, a silicon substrate with a thickness of 200 μm to 2 mm, Alternatively, a silicon dioxide substrate with a thickness of 200 μm to 2 mm.

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