Graphene stress optical sensor based on plasmon resonance

Abstract

The present invention relates to the field of optical sensor technology, and in particular to a graphene stress optical sensor based on plasmon resonance, comprising a periodic graphene nanoribbon array and a substrate, wherein the periodic graphene nanoribbon array is placed on the substrate. Graphene plasmons have very strong spatial localization and field enhancement effect, can achieve high quality factors, and are very conducive to the realization of nanophotonic devices based on graphene plasmons in integrated photonics.

Description

Technical Field

[0001] The present invention relates to the technical field of optical sensors, and in particular to a graphene stress optical sensor based on plasmon resonance. Background Art

[0002] In addition to its excellent light transmittance and good electrical conductivity, graphene also has excellent mechanical properties. For example, the tensile strength of graphene is 125GPa and the Young's modulus is 1TPa, making it the strongest material known so far. At present, graphene-based stress sensors have received widespread attention from researchers. Compared with silicon stress sensors, graphene stress sensors have higher sensitivity, lower energy consumption, easy integration, easy to realize intelligence, and nanoscale size. This means that graphene pressure sensors can be used in more occasions. For example, in the biomedical field, they can be used to detect blood pressure or tissue pressure inside the human body, wearable electronic products, robot "skin", etc. In recent years, graphene stress sensors with different mechanisms have been deeply studied, including piezoresistive graphene stress sensors, capacitive strain sensors, optical fiber graphene stress sensors, or optical sensors based on Raman spectroscopy enhancement. Graphene-based piezoresistive sensors have been widely studied due to their relatively simple electrical systems. However, resistive graphene strain sensors are susceptible to electromagnetic interference from nearby instruments and charged objects. On the other hand, obtaining high sensitivity often requires applying large stress, which is difficult to obtain in practice. In addition, excessive pressure can also lead to irreversible deformation of graphene, greatly limiting the application of graphene strain sensors. Therefore, it is necessary to explore new ways to achieve high-sensitivity strain sensing without destroying the graphene lattice structure. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the above-mentioned technology and provide a graphene stress optical sensor based on plasmon resonance.

[0004] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a graphene stress optical sensor based on plasmon resonance, characterized in that it includes a periodic graphene nanoribbon array and a substrate, wherein the periodic graphene nanoribbon array is placed on the substrate.

[0005] Preferably, the periodic graphene nanoribbon array is a single-layer graphene grown by CVD or mechanically exfoliated.

[0006] Preferably, the substrate is a flexible substrate PDMS or PET to achieve dynamic stretching of graphene.

[0007] Preferably, when tension is applied to the graphene nanoribbon array, the graphene plasmon resonance peak will move significantly, and the movement of the peak can be detected by Fourier transform infrared spectrometer to achieve the detection of graphene stress.

[0008] The beneficial effects of the present invention are as follows: 1. As a new type of material, graphene is environmentally friendly and has abundant sources, and it is possible to achieve cheap large-scale production, thereby effectively reducing costs. 2. Graphene plasmons have very strong spatial localization and field enhancement effect, and can achieve high quality factors, which is very beneficial to the realization of nanophotonic devices based on graphene plasmons in integrated photonics. 3. The present invention has a simple configuration, is easy to process and stretch, and thus provides an ideal subwavelength stress sensor device for the design and integration of nano-photonic electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic diagram of the structure of a graphene nanoribbon array according to an embodiment of the present invention;

[0010] Figure 2 is the graphene plasmon resonance position under the tensile force at different angles in the embodiment of the present invention;

[0011] Figure 3a-3d is a graph showing the relative movement of the plasmon resonance position as a function of the Fermi level and the nanoribbon width under different strain moduli k and directions according to an embodiment of the present invention;

[0012] Figure 4 is the relative movement of the resonance frequency with different strain moduli k and different pulling directions in the embodiment of the present invention;

[0013] Figure 5a and Figure 5b is the sensitivity and quality factor of the embodiment of the present invention;

[0014] Figure 6a and Figure 6b It is the change of the plasmon resonance position of the embodiment of the present invention on PDMS. DETAILED DESCRIPTION

[0015] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between one device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" may include both "above" and "below". The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0016] like Figure 1 As shown in the figure, due to the single atomic layer thickness of graphene, the optical response of graphene can be effectively regulated by external stress. During the stretching process of graphene, the two carbon sublattices of graphene are deformed, and its band structure is regulated as the lattice changes, thereby inducing the anisotropy of graphene optical conductivity. For doped graphene micro-nanostructures, localized surface plasmon modes can be supported, and plasmon resonance is very sensitive to changes in conductivity.

[0017] Based on this, a graphene stress optical sensor based on plasmon resonance is designed for the first time. This strain sensor is a typical optical sensor. A periodic graphene nanoribbon array 1 is placed on a flexible substrate 2. When tension is applied to this configuration, the graphene plasmon resonance peak will move significantly. The peak movement can be detected by Fourier infrared spectrometer to detect graphene stress. Compared with other types of graphene stress sensors reported in previous literature, the stress sensor based on graphene plasmon is an optical sensor based on graphene micro-nano structure. On the one hand, it is conducive to the design of integrated photonic devices. On the other hand, for slight deformation without destroying the lattice structure, a higher quality factor can be obtained, which is conducive to efficient detection of strain.

[0018] The graphene can be a single-layer graphene grown by CVD or mechanically exfoliated. The substrate is a commonly used flexible substrate PDMS or PET to achieve dynamic stretching of graphene.

[0019] The present invention is based on the following two principles: 1. When incident light is irradiated onto doped graphene with a micro-nano structure, graphene surface plasmons can be excited at a specific resonant wavelength. The properties of the excited graphene surface plasmons are related to the in-plane conductivity of the graphene. By regulating the graphene through field effects or applying stress, the resonance of the graphene plasmons can be effectively changed. 2. When tension is applied to graphene, the conductivity of the graphene surface will change anisotropically, and the magnitude of the in-plane conductivity depends not only on the magnitude of the tension, but also on the direction of the tension, and the change in conductivity will effectively change the resonant position of the graphene micro-nano structure plasmons. Conversely, the magnitude and direction of the tension of the graphene plasmons can be effectively detected by changing the resonant position of the graphene micro-nano structure plasmons.

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0021] In this embodiment, the width W of the graphene nanoribbon array is in the nanometer range. The core goal of the present invention is stress sensing, and the coupling between nanoribbons does not need to be considered, so the period L can be set to 10 W. The substrate is a flexible substrate PDMS or PET that can be used for stretching.

[0022] Graphene conductivity under stress:

[0023]

[0024]

[0025] Where θ represents the angle between the pulling direction and the zigzag, and ρ = 0.165 is the Poisson's ratio of graphene

[0026] Where σ(ω) is the graphene conductivity formula using the random phase approximation

[0027]

[0028] in,

[0029]

[0030] The temperature T is set to 300K, and the thickness of graphene is taken as d=0.5nm.

[0031] The finite element method is used for simulation.

[0032] Figure 2 : Graphene nanoribbon width W = 50nm, Fermi level EF = 0.4eV, carrier mobility μ = 10000cm 2 / Vs, assuming that there is no tension, graphene is isotropic, and the transmission spectrum of the graphene nanoribbon array is shown as the solid line in the figure, and its resonance position is at 52.9THz. Under the action of tension (assuming the deformation size k is 0.2), the transmission spectrum line moves. When θ=0°, the resonance position is at 33.2THz (dashed line), and the resonance spectrum line is red-shifted. When θ=90°, the resonance position is at 59.6THz (dotted line), and the resonance spectrum line is blue-shifted.

[0033] Figure 3a-3d Graphene plasmon resonance depends on the Fermi level of graphene and the width W of the graphene nanoribbon. Therefore, we studied the relative movement of the plasmon resonance position with the change of the Fermi level and the width of the nanoribbon under different pulling forces and directions. The relative movement of the resonance frequency can be expressed as Δf = (ff 0 ) / f 0 × 100%, where f 0 is the resonance position of the graphene nanoribbon array without tension. Figure 3a and Figure 3b It shows the influence of different graphene Fermi levels and external tension on the relative movement of the resonant frequency when the width of the graphene nanoribbon is 50nm. When the graphene Fermi level ranges from 0.1eV to 0.8eV, under the same tension magnitude and direction, the resonant frequency of the graphene nanoribbon array hardly moves. However, for different external tensions, the resonance position will move. Figure 3a When θ = 0°, the resonance position is red-shifted, and when the maximum deformation is 0.2, the relative frequency shift Δf = -38%. Figure 3b When θ=90°, the resonance position blue-shifts, and when the maximum deformation is 0.2, the relative frequency shift Δf=14%.

[0034] Similarly, we studied the effect of different nanoribbon widths on the resonance position of graphene nanoribbon arrays. Figure 3c and Figure 3d It can be seen that the change in the width of the nanoribbon has no effect on the change in the resonant position of the graphene nanoribbon array. Therefore, we can conclude that the stress sensor based on the graphene plasmon resonance effect proposed in the embodiment of the present invention does not depend on factors such as the graphene Fermi level and the size of the graphene structure.

[0035] Figure 4 :The relative movement of the resonance position of the graphene nanoribbon array changes with different strain modulus k and different pulling directions. It can be seen from the figure that when the pulling direction changes from 0° to 90°, as the strain modulus k increases, the relative movement of the resonance frequency changes from -38% to 13%. By using the change of the relative position of the frequency, the magnitude and direction of the stress can be detected, thereby realizing stress sensing.

[0036] Figure 5a and Figure 5b It is the sensitivity and quality factor of the stress sensor based on the graphene plasmon effect. The sensitivity calculation formula is: S = (ff 0 ) / Δk, Figure 5a Indicates sensitivity. (a) When θ = 0°, the sensitivity S / / =3260.6cm -1 , when θ=90°, the sensitivity S ⊥ =1109.1cm -1 ,In order to be consistent with the technical parameters of the mid-infrared Fourier spectrometer, wave number is used here as the unit. The quality factor is an important parameter for measuring sensors based on the localized surface plasmon resonance effect. Its calculation formula is: FOM = S / FWHM, S is the sensitivity, and FWHM is the half-height width. The half-height width of the localized plasmon is determined by the loss. For graphene, it depends largely on the zero rate of carrier mobility. Figure 5b The figure shows the change of the quality factor FOM with the graphene carrier mobility. When the graphene carrier mobility changes from 2000 to 10000 cm 2 / Vs, for θ = 0°, the quality factor increases from 50 to 320, and for θ = 90°, the quality factor increases from 10 to 110. This shows that even if the mobility of graphene is not high in specific experiments and applications, we can still get a higher quality factor, which will be very beneficial for stress sensing.

[0037] Figure 6a and Figure 6b For simplicity, the above studies all consider the graphene suspension state. When considering the flexible substrate, take PDMS as an example ( Figure 6a is the dielectric constant of PDMS), it can be seen that the stress sensing properties of graphene considering the substrate are still maintained.

[0038] The present invention discloses a graphene stress sensor based on localized plasmon resonance effect. As a new type of optical sensor, the present invention has the advantages of simple structure configuration and easy detection, and will have great application potential in nano-photoelectric integrated circuits.

[0039] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A graphene stress optical sensor based on plasmon resonance, characterized in that: It comprises a periodic graphene nanoribbon array and a substrate, wherein the periodic graphene nanoribbon array is disposed on the substrate; The periodic graphene nanoribbon array is a single-layer graphene grown by CVD or mechanically exfoliated; The substrate is a flexible substrate PDMS or PET to achieve dynamic stretching of graphene; When tension is applied to the graphene nanoribbon array, the graphene plasmon resonance peak will move significantly. The movement of the peak is detected using a Fourier transform infrared spectrometer to detect graphene stress.

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