CN104568809A - Intermediate infrared molecular vibration spectrum sensing method based on graphene array structure - Google Patents

Abstract

The invention belongs to the technical field of detection, and specifically relates to a mid-infrared molecular vibration spectrum sensing method based on a graphene array structure, comprising the following steps: A. providing a graphene array structure for the interaction between a mid-infrared frequency band field and a substance, composed of graphene The periodic array is attached to the base medium layer and is vertically irradiated by the mid-infrared parallel beam; B1. For the detection of liquid chemical substances, a layer of sample to be tested is covered on the graphene array structure; B2. For the detection of gaseous chemical substances, the The graphene array structure is placed in a closed cavity, and the gas to be measured is passed through; C. The mid-infrared light source with adjustable wavelength is transformed into a parallel beam through the lens, and the graphene array structure is excited by vertical irradiation, and the detection array is used to detect and obtain the characterization The transmission spectrum of the molecular vibration characteristics of the sample to be measured is used to obtain the molecular vibration spectrum. The invention is conducive to the development of simple and real-time molecular vibration spectrum measuring instruments.

Description

A mid-infrared molecular vibrational spectrum sensing method based on graphene array structure

technical field

The invention belongs to the technical field of detection, and in particular relates to a mid-infrared molecular vibration spectrum sensing method based on a graphene array structure.

Background technique

Mid-infrared molecular vibrational spectroscopy is widely used in the determination of the molecular structure of compounds, the identification of unknowns, and the analysis of mixed components. It is an important parameter for sensing and identifying the properties and characteristics of substances, also known as molecular vibrational fingerprints. At present, the molecular vibration spectrum can be obtained by using an infrared spectrometer, but the infrared spectrometer is complex and expensive.

Contents of the invention

Aiming at the problems of complex and expensive infrared spectrometers, the present invention provides a low-cost and easy-to-implement method for sensing mid-infrared molecular vibrational spectra based on a graphene array structure.

The technical scheme of the present invention is achieved in that a kind of mid-infrared molecular vibration spectrum sensing method based on graphene array structure comprises the following steps:

A. The graphene array structure that provides the interaction between the mid-infrared frequency field and the substance is composed of a graphene periodic array attached to the base dielectric layer, and is vertically irradiated by the mid-infrared parallel beam;

B1. For the detection of liquid chemical substances, a layer of the sample to be tested is covered on the graphene array structure;

B2. For the detection of gaseous chemical substances, the graphene array structure is placed in a closed cavity, and the gas to be tested is introduced;

C. The mid-infrared light source with adjustable wavelength is transformed into a parallel beam through the lens, and the graphene array structure is excited by vertical irradiation, and the detection array is used for detection to obtain the transmission spectrum that characterizes the molecular vibration characteristics of the sample to be tested, so as to obtain the molecular vibration spectrum.

Further, in step A, by adjusting the chemical potential, the transmission coefficient of the graphene array structure has a broadband transmission spectrum, covering the molecular vibration spectrum of the specific sample to be measured in the mid-infrared frequency range, and forming a molecular vibration spectrum with the mid-infrared frequency band. Coupling resonance enhancement. The reason for using graphene is that in the infrared and terahertz frequency bands, the dielectric constant of graphene is negative, which can form a surface plasmon resonance mode, and the resonance frequency can be smoothly changed by adjusting the chemical potential, thereby selectively enhancing the field and The interaction of matter; the purpose of arranging the graphene ribbons in an array structure is to enhance the transmission.

Further, in step B2, the closed cavity does not absorb electromagnetic waves, and is made of wave-transmissive materials such as quartz, which functions as a closed gas, but does not affect the transmission of electromagnetic waves.

The invention uses the interaction between the sample to be measured attached to the graphene array structure and the local field, causing the broadband transmission spectrum of the graphene array structure and the molecular vibration spectrum of the sample to be measured to form a coupling resonance enhancement, thereby realizing the detection of molecular vibration spectrum, which is conducive to development Simple and real-time molecular vibrational spectroscopy measurement instrument.

Description of drawings

Figure 1 is a schematic diagram of the detection model;

Figure 2 is a cross-section of the detection model;

Fig. 3 is the relation of graphene dielectric constant and wavelength;

Fig. 4 is the molecular vibration spectrum of acetic anhydride liquid in the mid-infrared frequency band;

Figure 5 is the measurement results obtained by simulating the detection array with/without sample coverage;

Figure 6 shows the effect of the sample coverage thickness on the test results.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

A kind of mid-infrared molecular vibration spectrum sensing method based on graphene array structure, comprising the following steps:

A. The graphene array structure that provides the interaction between the mid-infrared frequency field and the substance, as shown in Figure 1 and Figure 2, is composed of a graphene periodic array 1 attached to the substrate dielectric layer 2, and is vertically irradiated by the mid-infrared parallel beam; the substrate The material is silicon dioxide, the refractive index n=1.45; the thickness of the graphene ribbon is t=1nm, the width w=0.25μm, and the period p=0.5μm; the dielectric constant of the graphene ribbon is ε=1+iσ/ε ₀ ωt, where σ = σ _intra + σ _inter is the conductivity, and σ _intra and σ _inter are the contributions of the inter-band and intra-band respectively; according to the Kubo formula:

where T is temperature, Γ carrier mobility, μ is chemical potential, is Planck’s constant; take temperature as room temperature, set T=300×k _B , k _B is Boltzmann’s constant, Γ=0.1meV, μ=0.3eV, and the relationship between graphene dielectric constant and frequency is shown in the figure 3. It can be seen that in the mid-infrared 3-50 μm, the real part of the dielectric constant is negative, while the imaginary part (loss) is small.

B1. For the detection of liquid chemical substances, the sample 3 to be tested is acetic anhydride liquid, which is covered on the graphene array structure, and the thickness is used to represent the covering amount. The thickness h=1 μm, the absorption coefficient of acetic anhydride molecules in the mid-infrared band and the frequency The relationship shown in Figure 4 is derived from molecular vibrations, also known as molecular vibrational spectra;

B2. For the detection of gaseous chemical substances, the graphene array structure is placed in a closed cavity 4, and the gas to be measured is introduced, and the closed cavity 4 does not absorb electromagnetic waves;

C. As shown in Figure 2, use a mid-infrared light source with an adjustable wavelength to convert it into a parallel beam through the lens 5, and vertically irradiate the excitation graphene array structure. The wavelength range of the excitation source is 8-11 μm, and it is detected by the detection array 6 to obtain the characterization The transmission spectrum of the molecular vibration characteristics of the sample to be measured is used to obtain the molecular vibration spectrum.

This embodiment uses the finite difference time domain method software Lumerical FDTD to carry out modeling and simulation, under the situation that does not cover acetic anhydride liquid sample, the transmission coefficient measured by the detection array is shown in the solid line in Figure 5, as can be seen, The transmission coefficient is a near-smooth straight line covering the vibrational spectrum range of acetic anhydride molecules in the mid-infrared band, and its value approaches 1, indicating that the structure is transparent to the incident beam. In the case of covering the liquid sample of acetic anhydride, the transmission coefficient measured by the detection array is shown as the dotted line in Figure 5. Compared with Figure 4, it can be seen that the change trend of the transmission coefficient is consistent with the molecular vibration spectrum, and the purpose of detecting the molecular vibration spectrum is achieved. . When the thickness of the acetic anhydride sample to be tested is different, the transmission coefficient obtained by detection is shown in Figure 6. It can be seen that the greater the thickness, the greater the transmission attenuation, which is more convenient for detection, and because increasing the thickness does not affect the shape of the envelope of the transmission coefficient, the present invention has good robustness and is less susceptible to external random factors, such as sample The effect of filling thickness and non-uniformity.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (3)

1. A mid-infrared molecular vibrational spectrum sensing method based on a graphene array structure, characterized in that it may further comprise the steps: A. The graphene array structure that provides the interaction between the mid-infrared frequency field and the substance is composed of a graphene periodic array (1) attached to the base dielectric layer (2), and is vertically irradiated by the mid-infrared parallel beam; B1. For the detection of liquid chemical substances, a layer of sample to be tested is covered on the graphene array structure (3); B2. For the detection of gaseous chemical substances, the graphene array structure is placed in a closed cavity (4), and the gas to be measured is introduced; C. The mid-infrared light source with adjustable wavelength is converted into a parallel beam through the lens (5), and the graphene array structure is excited by vertical irradiation, and detected by the detection array (6), and the transmission spectrum characterizing the molecular vibration characteristics of the sample to be tested is obtained, thereby obtaining Molecular Vibrational Spectrum. 2. the mid-infrared molecular vibration spectrum sensing method based on graphene array as claimed in claim 1, is characterized in that: in described step A, make described graphene array structure transfer coefficient have broadband by adjusting chemical potential The transmission spectrum covers the molecular vibration spectrum of a specific sample to be tested in the mid-infrared frequency range, and forms a coupling resonance enhancement with the molecular vibration in the mid-infrared frequency range. 3. The graphene array-based molecular vibrational spectrum sensing method according to claim 1, characterized in that: in the step B2, the closed cavity (4) does not absorb electromagnetic waves.