Sensor element

Abstract

To provide a high-sensitivity sensor element.SOLUTION: A sensor element comprises: a liquid; a substrate which is immobilized within the liquid and has a planar first surface; and a plate-like member with is suspended in the liquid and has a planar second surface facing the first surface. Graphene is disposed on at least one of the first surface and the second surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a sensor element. [Background technology]

[0002] There is a demand for highly sensitive chemical sensors to capture chemical reactions and biological phenomena at a microscopic level. Non-Patent Document 1 discloses a technique in which graphene is processed into a Hall bar shape, electrodes are attached, and the change in the resistance value of the graphene due to the surface adsorption of the target gas substance to be measured is measured. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] F. Schedin et al., “Detection of individual gas molecules adsorbed on graphene.” Nature materials 6, 652-655 (2007). Summary of the Invention [Problem to be solved by the invention]

[0004] In Non-Patent Document 1, changes in the physical properties of graphene caused by surface adsorption of chemical substances are detected by electrical signals. However, the change in resistance caused by a gas amount with a concentration of 1 ppm was only about a few percent, and the detection sensitivity was insufficient. [Means for solving the problem]

[0005] One embodiment of a sensor element disclosed in the present specification includes a liquid, a substrate fixedly disposed in the liquid and having a planar first surface, and a plate-like member disposed in a floating state in the liquid and having a planar second surface facing the first surface, with graphene disposed on at least one of the first surface and the second surface.

[0006] The plate-like member may have various configurations. For example, the plate-like member itself may be graphene. The positional relationship between the substrate and the plate-like member is not particularly limited. For example, the plate-like member may be located above the substrate in the direction of gravity, or may be located below the substrate.

[0007] According to the above structure, the Casimir force and gravity acting in opposite directions can be applied to the plate-like member. For example, gravity acts in a direction that brings the plate-like member closer to the substrate, and a repulsive Casimir force acts between the plate-like member and the substrate. Alternatively, gravity acts in a direction that moves the plate-like member away from the substrate, and an attractive Casimir force acts between the plate-like member and the substrate. Here, the Casimir force is a force acting in a near field on the order of nanometers, and increases rapidly and simply as the distance between the plate-like member and the substrate decreases. Therefore, the plate-like member can be converged to an equilibrium position where the magnitudes of the Casimir force and gravity are equal. The Casimir force has the characteristic of changing very sensitively to the reflection coefficient of the substance. Then, for example, when a substance to be measured is adsorbed to graphene, the chemical potential of the graphene changes, and the photoconductivity of the graphene changes. When the photoconductivity changes, the graphene reflection coefficient changes, and the magnitude of the Casimir force determined by the reflection coefficient changes. As a result, the equilibrium position (i.e., the distance between the plate-like member and the substrate) where the sum of the Casimir force, gravity, and buoyancy becomes zero changes. This change in distance makes it possible to capture in detail the adsorption state of the target substance to be measured on the graphene. This makes it possible to realize a sensor element with high detection sensitivity.

[0008] The graphene may be disposed on either the first surface or the second surface. The sensor element may further include a first layer disposed on one of the first surface and the second surface on which the graphene is not disposed. The first dielectric constant, which is the dielectric constant of the first layer in the infrared and visible light range, may be smaller than a liquid dielectric constant, which is the dielectric constant of the liquid in the infrared and visible light range. Note that in this specification, the magnitude relationship of the dielectric constant as a function of the imaginary frequency is discussed.

[0009] The first layer may further include a second layer laminated directly or via an intermediate layer on a surface opposite to the surface facing the graphene of the first layer. The second layer may have a second dielectric constant in the infrared and visible light range that is greater than the liquid dielectric constant.

[0010] The first layer and the second layer may be disposed on a plate-like member. The graphene may be disposed on a first surface of the substrate. The graphene may be configured to allow application of any voltage.

[0011] The graphene may be disposed on a plate-like member. The first layer may be disposed on a first surface of a substrate. The sensor element may be disposed on an inner side of the substrate relative to the first layer and further include an electrode layer made of graphene.

[0012] The graphene may be disposed on a second surface of the plate-like member. The sensor element may further include a first layer disposed on the first surface of the substrate, and a second layer laminated directly or via an intermediate layer on a surface of the graphene opposite to the surface facing the first layer. Each of the first and second dielectric constants, which are dielectric constants of the first and second layers in the infrared and visible light ranges, may be smaller than a liquid dielectric constant, which is a dielectric constant of a liquid in the infrared and visible light ranges.

[0013] The sensor element may further include an electrode layer that is disposed on the inner side of the substrate relative to the first layer and is made of graphene.

[0014] The graphene may be disposed on a first surface of the substrate. The sensor element may further include a first layer disposed on the inner side of the substrate relative to the graphene, the first layer being laminated directly or via an intermediate layer on a surface of the graphene opposite to the surface facing the plate-like member, and a second layer disposed on a second surface of the plate-like member. Each of the first and second dielectric constants, which are dielectric constants of the first and second layers in the infrared and visible light ranges, may be smaller than a liquid dielectric constant, which is a dielectric constant of a liquid in the infrared and visible light ranges.

[0015] The graphene may be configured so that any voltage can be applied to it.

[0016] The graphene may be disposed on either the first surface or the second surface, and the device may further include a device capable of measuring the distance between the surface of the graphene and one of the first surface and the second surface on which the graphene is not disposed. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view of a sensor element 1. FIG. [Diagram 2] FIG. 2 is an explanatory diagram of the direction of the Casimir force in a liquid. [Diagram 3] 1 is a calculation example simulating the operating state of the sensor element 1. [Figure 4] FIG. 2 is a schematic cross-sectional view of a sensor element 1a. [Diagram 5] FIG. 2 is a schematic cross-sectional view of a sensor element 1b. [Figure 6] FIG. 2 is a schematic cross-sectional view of a sensor element 1c. [Figure 7] FIG. 2 is a schematic cross-sectional view of a sensor element 1d. [Figure 8] 13 is a calculation example simulating the operating state of a sensor element 1d. [Figure 9] FIG. 1 is a schematic cross-sectional view of a sensor element 1e. [Figure 10] FIG. 2 is a schematic cross-sectional view of a sensor element 1f. [Figure 11] FIG. 2 is a schematic cross-sectional view of a sensor element 1g. [Figure 12] FIG. 2 is a schematic cross-sectional view of a sensor element 1h. [Figure 13] FIG. 2 is a schematic cross-sectional view of a sensor element 1i. [Figure 14] 13 is a calculation example simulating the operating state of the sensor element 1i. [Figure 15] FIG. 2 is a schematic cross-sectional view of a sensor element 1j. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0018] (Structure of sensor element 1) FIG. 1 shows a schematic cross-sectional view of the sensor element 1 of Example 1. In FIG. 1, the z-axis is the vertical direction, and the x- and y-axes are the horizontal directions. The sensor element 1 mainly includes a container 2, a liquid 10, a substrate 11, a nanoplate 12, and graphene 13. The container 2 is configured so as to be capable of storing the liquid 10, the substrate 11, the nanoplate 12, etc. therein. The shape and material of the container 2 are not particularly limited and may be various. Various materials can be used for the liquid 10. In this example, the liquid 10 is ethanol.

[0019] The substrate 11 is fixed to the bottom surface of the container 2. The substrate 11 is placed in the liquid 10. The substrate 11 has a planar surface 11s. Various materials can be used for the substrate 11. In this embodiment, the substrate 11 is made of Teflon (registered trademark).

[0020] The nanoplate 12 has a planar surface 12s on its underside. A two-dimensional material, graphene 13, is disposed on the surface 12s. The planar shapes (shapes when viewed from the z direction) of the nanoplate 12 and the graphene 13 may be various, for example, circular, polygonal, square, etc. The nanoplate 12 is disposed in a floating state in the liquid 10. As described later, the distance d between the surface 11s of the substrate 11 and the surface of the graphene 13 is maintained constant by gravity and the Casimir force.

[0021] An interferometer 51 and a gas supply device 52 are arranged around the sensor element 1. The interferometer 51 is a device capable of measuring the distance d. In this embodiment, the interferometer 51 is a Fabry-Perot interferometer. Note that the measurement principle and measurement contents of the Fabry-Perot interferometer are known, so a description thereof will be omitted.

[0022] The gas supply device 52 is a device that blows gas G1 containing a target gas substance to be measured into the liquid 10. This allows the target gas substance to be dissolved in the liquid 10. The target gas substance may be various, and examples of the target gas substance include NH3, CO, H2O, and NO2.

[0023] (Summary of Casimir Power) The sensor element 1 is a sensor that operates using the Casimir force. Here is an overview of the Casimir force. It is known that when two metal plates are placed close to each other with a gap of a few micrometers or less, the field between the plates is quantized, causing the Casimir force to act on the plates. The Casimir force is small enough to be ignored when the two objects are placed far enough apart. However, when the two objects are brought close together to a gap of a few micrometers or less, it begins to show a measurable value, and the magnitude of the Casimir force increases as the gap becomes smaller.

[0024] When two plates placed in a vacuum are perfect conductors, the Casimir force F C It is known that ideally, the following equation (1) is satisfied.

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[0025] In the case of two objects placed in a vacuum, the Casimir force is attractive. However, in the case of two objects placed in a liquid, cases have been reported in which the Casimir force is repulsive. Specifically, the direction of the Casimir force in a liquid (attractive or repulsive) is determined by the magnitude relationship of the dielectric constants of the two objects and the medium. This will be explained using Figure 2. Figure 2 shows a structure in which a liquid 10 is interposed between a substrate 11 and graphene 13. Here, the magnitude relationship of each dielectric constant is considered. The dielectric constant ε_gra of graphene 13 is very high, so it can be considered to have the highest dielectric constant. Therefore, the direction of the Casimir force is determined by the magnitude relationship between the dielectric constant ε_liq of the liquid 10 in the infrared and visible light range and the dielectric constant ε_sub of the substrate 11 in the infrared and visible light range.

[0026] 2A, when the dielectric constant ε_sub is smaller than the dielectric constant ε_liq, the order of magnitude of the dielectric constants is as follows: the dielectric constant ε_gra is the largest, the dielectric constant ε_liq is the second largest, and the dielectric constant ε_sub is the third largest. In this way, when a magnitude relationship is established in which the order of the dielectric constants matches the order of the materials, a Casimir repulsive force RF is generated between the graphene 13 and the substrate 11.

[0027] 2B, when the dielectric constant ε_sub is larger than the dielectric constant ε_liq, the order of magnitude of the dielectric constants is as follows: the dielectric constant ε_gra is the largest, the dielectric constant ε_sub is the second largest, and the dielectric constant ε_liq is the third largest. In this way, when a relationship of magnitude of the dielectric constants is established in which the order of the dielectric constants does not match the arrangement order of the materials, a Casimir attractive force AF is generated between the graphene 13 and the substrate 11.

[0028] (Casimir Force Theory) The theory of Casimir force used in this specification will be described. The Casimir force P per unit area acting on a nanoplate placed in close proximity to a substrate in a liquid is C is given by the following equations (2) and (3).

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[0029] For materials other than graphene, the dielectric constant as a function of frequency can be given according to the Drude model and the Lorentz model, and the Fresnel coefficients can be calculated using them. On the other hand, when calculating the Fresnel coefficients taking into account the effect of graphene, the following formulas (4) and (5) are used, considering the situation where a wave is incident from medium 1 in an arrangement where there is a single layer of graphene at the interface between medium 1 and medium 2.

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[0030] The optical conductivity of graphene is the sum of the intraband and interband terms, σ(ω,μ,T)=σ intra (ω,μ,T)+σ inter (ω,μ,T), which are expressed by the following equations (7) and (8), respectively.

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[0031] From the above, we can see that the chemical potential of graphene affects its optical conductivity, reflection coefficient, and Casimir force.

[0032] In addition to the Casimir force, gravity and buoyancy are thought to act on the nanoplate. Therefore, the force acting on the nanoplate per unit area (i.e., the total pressure P total ) is given by the following equation (10).

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[0033] (Operation principle of sensor element 1) Consider the case where the relationship of the dielectric constants as shown in FIG. 2(A) is established, and a Casimir repulsive force RF is generated between the substrate 11 and the graphene 13. In this case, as shown in FIG. 1, the nanoplate 12 is subjected to the Casimir repulsive force RF acting upward in the figure and the gravity GF acting downward in the figure. Note that the buoyant force acts in the opposite direction to gravity and is smaller in magnitude than gravity, so in this specification, the gravity minus the magnitude of the buoyant force is represented as GF. As described above, the Casimir repulsive force RF increases rapidly as the distance d becomes smaller. Therefore, there is an equilibrium point where the force acting on the nanoplate 12 becomes zero because the Casimir repulsive force RF and the gravity GF are balanced. In addition, the closer the nanoplate 12 is to the substrate 11 from the equilibrium point, the larger the Casimir repulsive force RF becomes, so that a force pulling it back to the equilibrium point is generated. This allows the nanoplate 12 to be stably levitated in the liquid 10 while maintaining the distance d at the equilibrium point.

[0034] In addition, as explained in the above-mentioned theory of the Casimir force, the Casimir force has the property of changing very sensitively to the reflection coefficient of graphene. Then, for example, when a substance to be measured is adsorbed to graphene, the chemical potential of graphene changes, and the photoconductivity of graphene changes. When the photoconductivity changes, the graphene reflection coefficient changes, and the magnitude of the Casimir repulsive force RF determined by the reflection coefficient changes. As a result, the distance d at which the Casimir force and gravity are in equilibrium changes. By detecting the change in this distance d, the adsorption state of the substance to be measured to the graphene can be captured in detail. This makes it possible to realize a sensor element with high detection sensitivity.

[0035] As described above, the sensor element 1 of Example 1 has a configuration in which the nanoplate 12 stably levitated in the liquid 10 by the Casimir repulsive force RF is combined with the graphene 13, whose physical properties change upon adsorption of chemical substances. This makes it possible to realize a chemical sensor with a novel mechanism that converts the amount of adsorbed chemical substances into a positional change of the levitated object for sensing.

[0036] (First Modification of the First Example) The sensor element 1 (FIG. 1) of Example 1 may not include the nanoplate 12. In this case, the single layer of graphene 13 is maintained in a floating state at the position of the equilibrium point described above.

[0037] (Numerical calculation example) FIG. 3 shows a calculation example simulating the operating state of the sensor element 1 of the first modified example. The simulation was performed using the above formulas (2) to (10). The horizontal axis of FIG. 3 is the chemical potential of the graphene 13, and the change in the chemical potential corresponds to the amount of adsorption of the substance to be measured. The vertical axis is the distance d. The sign of the force acting on the nanoplate 12 defines the direction so that the attractive force between the substrate and the nanoplate 12 is positive and the repulsive force is negative. The equilibrium point EP where the force acting on the nanoplate 12 becomes zero is shown by a black circle. Also, the equilibrium line DL connecting the multiple equilibrium points EP is shown by a dashed line. The region above the equilibrium line DL is an attractive region where the attractive force (gravity GF) mainly acts. The region below the black dashed line is a repulsive region where the Casimir repulsive force RF mainly acts. The larger the attractive force or repulsive force is in the region, the darker the fill color is. Also, at the equilibrium point EP, the fill color is white.

[0038] It can be seen that the further upwards one moves from each equilibrium point EP (i.e., the greater the distance), the darker the color of the fill, and the stronger the attractive force. It can also be seen that the further downwards one moves from each equilibrium point EP (i.e., the closer the distance), the darker the color of the fill, and the stronger the repulsive force. In other words, it can be seen that the force pulling back to the equilibrium point EP increases the further away one moves from the equilibrium point EP. This allows the nanoplate 12 to be stably levitated to the position that becomes the equilibrium point EP. It can also be seen that the greater the chemical potential of the graphene 13, the greater the distance d at which the equilibrium point EP becomes. It can also be seen that the distance d changes significantly from 430 [nm] to 570 [nm] as the chemical potential changes from 0.2 [eV] to 1.0 [eV].

[0039] From the above, it is clear that it is possible to realize a sensor element 1 equipped with a novel mechanism that senses the amount of adsorbed chemical substance by converting it into a change in the position of the levitating nanoplate. Therefore, it is possible to realize a sensor element with higher detection sensitivity than conventional sensors that "detect the change in the physical properties of graphene due to the surface adsorption of chemical substances with an electrical signal."

[0040] (Second Modification of the First Embodiment) 4 shows a schematic cross-sectional view of a sensor element 1a according to a second modified example of the first embodiment. In the following drawings, the same reference numerals are used to designate common parts, and the description thereof will be omitted. Graphene 13 is disposed on a surface 11s of a substrate 11. A surface 12s of a nanoplate 12 is exposed.

[0041] In FIG. 4, the direction of the Casimir force is determined by the magnitude relationship between the dielectric constant ε_liq of the liquid 10 in the infrared-visible light region and the dielectric constant ε_pla of the nanoplate 12 in the infrared-visible light region. When the dielectric constant ε_pla is smaller than the dielectric constant ε_liq, the order of the magnitude of the dielectric constant is as follows: the dielectric constant ε_gra is the largest, the dielectric constant ε_liq is the second largest, and the dielectric constant ε_pla is the third largest. In this way, when a magnitude relationship is established in which the order of the magnitude of the dielectric constant matches the order of the materials, a Casimir repulsive force RF is generated between the graphene 13 and the nanoplate 12. As a result, an equilibrium point can be generated by the balance between the Casimir repulsive force RF and gravity GF in the same manner as in the sensor element 1 of the first embodiment (FIG. 1). In the sensor element 1a of the second modified example, the dielectric constant of the material constituting the substrate 11 is not particularly limited. EXAMPLES

[0042] FIG. 5 shows a schematic cross-sectional view of the sensor element 1b of Example 2. A first layer 11_1 is disposed on a surface 11s of a substrate 11. The dielectric constant ε_sub1 of the first layer 11_1 in the infrared and visible light range is smaller than the dielectric constant ε_liq of the liquid 10 in the infrared and visible light range. In this example, the substrate 11 is made of SiO2. The first layer 11_1 is made of Teflon having a thickness of 50 nm.

[0043] In the sensor element 1b of the second embodiment, the order of the magnitude of the dielectric constant is as follows: dielectric constant ε_gra is the largest, dielectric constant ε_liq is the second largest, and dielectric constant ε_sub1 is the third largest. Since a magnitude relationship is established in which the order of the magnitude of the dielectric constant matches the order of the materials, it is possible to generate the Casimir repulsive force RF. Therefore, it is possible to generate the above-mentioned equilibrium point. In addition, since the dielectric constant of the material constituting the substrate 11 is not limited, it is possible to form the substrate 11 from various materials.

[0044] It should be noted that the sensor element 1b does not necessarily have to include the nanoplates 12. In this case, the single layer of graphene 13 is maintained in a floating state at the position of the above-mentioned equilibrium point.

[0045] (First modified example of the second embodiment) 6 shows a schematic cross-sectional view of a sensor element 1c according to a first modified example of Example 2. Graphene 13 is disposed on a surface 11s of a substrate 11. A first layer 12_1 is disposed on a surface 12s of a nanoplate 12. The dielectric constant ε_pla1 of the first layer 12_1 in the infrared and visible light range is smaller than the dielectric constant ε_liq of the liquid 10 in the infrared and visible light range.

[0046] In the sensor element 1c, the order of the magnitude of the dielectric constant is the largest for the dielectric constant ε_gra, the second largest for the dielectric constant ε_liq, and the third largest for the dielectric constant ε_pla1. Since a magnitude relationship is established in which the order of the dielectric constants matches the order of the materials, a Casimir repulsive force RF can be generated. In addition, since the dielectric constant of the material that constitutes the nanoplate 12 is not limited, it is possible to form the nanoplate 12 from various materials. EXAMPLES

[0047] FIG. 7 shows a schematic cross-sectional view of the sensor element 1d of Example 3. The sensor element 1d of Example 3 has a configuration in which the sensor element 1b of Example 2 (FIG. 5) further includes a second layer 11_2. A specific description will be given. The first layer 11_1 has a back surface 11_1r on the opposite side to the surface facing the graphene 13. The second layer 11_2 is laminated on the back surface 11_1r via an intermediate layer 11m. The second layer 11_2 may be directly laminated on the back surface 11_1r without the intermediate layer 11m. The dielectric constant ε_sub2 of the second layer 11_2 in the infrared and visible light range is larger than the dielectric constant ε_liq of the liquid 10 in the infrared and visible light range. In this example, the second layer 11_2 is SiO2.

[0048] Focus on the Casimir force acting between the graphene 13 and the second layer 11_2. The order of the magnitude of the dielectric constant is the largest for the dielectric constant ε_gra, the second largest for the dielectric constant ε_sub2, and the third largest for the dielectric constant ε_liq. Since a relationship of magnitude of the dielectric constants is established in which the order of the magnitude of the dielectric constants does not match the order of the materials, a Casimir attractive force AF can be generated between the graphene 13 and the second layer 11_2. As described above in the second embodiment, a Casimir repulsive force RF acts between the graphene 13 and the first layer 11_1. This allows an equilibrium point where the attractive force and the repulsive force are balanced to be created by only the Casimir force.

[0049] The lower limit of the thickness of the first layer 11_1 located on the outermost surface of the substrate 11 may be set to a value that ensures a sufficient magnitude of the Casimir repulsive force RF acting between the graphene 13 and the first layer 11_1. The upper limit of the thickness of the first layer 11_1 may be set to a value that ensures a sufficient magnitude of the Casimir attractive force AF acting between the graphene 13 and the second layer 11_2.

[0050] A calculation example simulating the operating state of the sensor element 1d in Fig. 7 is shown in Fig. 8. The content of Fig. 8 is the same as that of Fig. 3. As shown in Fig. 8, it can be seen that the larger the chemical potential of the graphene 13, the smaller the distance d at which the equilibrium point EP is.

[0051] (First modified example of the third embodiment) 9 shows a schematic cross-sectional view of a sensor element 1e according to a first modified example of the third embodiment. The modified sensor element 1e has a structure in which the order of the elements in the z direction (vertical direction) of the sensor element 1d (FIG. 7) of the third embodiment is reversed. That is, in the sensor element 1e, gravity GF acts in a direction that moves the nanoplates 12 away from the substrate 11. The substrate 11 is fixed to the container 2.

[0052] As described in the third embodiment, the sensor element 1e can generate attractive and repulsive forces only by the Casimir force, and therefore can maintain the equilibrium point due to the Casimir force even when the sensor element 1e is turned upside down in the vertical direction.

[0053] In this case, the gravity GF only has the effect of slightly shifting the equilibrium point. In the simulation results, the shift of the equilibrium point due to upside-down rotation was less than 1 nm.

[0054] (Second modified example of the third embodiment) FIG. 10 shows a schematic cross-sectional view of a sensor element 1f according to a second modified example of Example 3. Graphene 13 is disposed on a surface 11s of a substrate 11. The first layer 12_1 has a back surface 12_1r on the opposite side to the surface facing the graphene 13. A second layer 12_2 is laminated on the back surface 12_1r via an intermediate layer 12m. The second layer 12_2 may be laminated directly on the back surface 12_1r without the intermediate layer 12m. The dielectric constant ε_pla2 of the second layer 12_2 in the infrared and visible light range is larger than the dielectric constant ε_liq of the liquid 10 in the infrared and visible light range.

[0055] A Casimir attractive force AF acts between the graphene 13 and the second layer 12_2. This is because the order of magnitude of the dielectric constants is as follows: the dielectric constant ε_gra is the largest, the dielectric constant ε_pla2 is the second largest, and the dielectric constant ε_liq is the third largest. As described above with reference to FIG. 6, a Casimir repulsive force RF acts between the graphene 13 and the first layer 11_1. This makes it possible to create an equilibrium point where the attractive and repulsive forces are balanced by only the Casimir force.

[0056] (Third modified example of the second embodiment) FIG. 11 shows a schematic cross-sectional view of a sensor element 1g according to a third modified example of the third embodiment. A first layer 11_1 is disposed on a surface 11s of a substrate 11. The graphene 13 has a back surface 13r on the opposite side to the surface facing the first layer 11_1. A second layer 12_2 is laminated on the back surface 13r via an intermediate layer 12m. The second layer 12_2 may be laminated directly on the back surface 13r without the intermediate layer 12m. The dielectric constant ε_sub1 of the first layer 11_1 in the infrared and visible light range and the dielectric constant ε_pla2 of the second layer 12_2 in the infrared and visible light range are smaller than the dielectric constant ε_liq of the liquid 10 in the infrared and visible light range.

[0057] A Casimir repulsive force RF acts between the graphene 13 and the first layer 11_1. This is because the order of magnitude of the dielectric constants is that of the dielectric constant ε_gra, which is the largest, followed by the dielectric constant ε_liq, which is the second largest, and the dielectric constant ε_sub1, which is the third largest. On the other hand, a Casimir attractive force AF acts between the first layer 11_1 and the second layer 12_2. This is because the order of magnitude of the dielectric constants does not match the order of the materials arranged in the order of the materials, since the dielectric constant ε_liq is larger than the dielectric constants ε_sub1 and ε_pla2. This makes it possible to create an equilibrium point where the attractive and repulsive forces are balanced by only the Casimir force.

[0058] (Fourth Modification of the Second Embodiment) FIG. 12 shows a schematic cross-sectional view of a sensor element 1h according to a third modified example of the third embodiment. The graphene 13 has a back surface 13r on the opposite side to the surface facing the nanoplate 12. The first layer 11_1 is laminated on the back surface 13r via the intermediate layer 11m. In other words, the first layer 11_1 is disposed on the inner side of the substrate than the graphene 13. The first layer 11_1 may be laminated directly on the back surface 13r without the intermediate layer 11m. The second layer 12_2 is disposed on the surface 12s of the nanoplate 12. The dielectric constant ε_sub1 of the first layer 11_1 in the infrared and visible light range and the dielectric constant ε_pla2 of the second layer 12_2 in the infrared and visible light range are smaller than the dielectric constant ε_liq of the liquid 10 in the infrared and visible light range.

[0059] A Casimir repulsive force RF acts between the graphene 13 and the second layer 12_2. This is because the order of magnitude of the dielectric constants is that the dielectric constant ε_gra is the largest, the dielectric constant ε_liq is the second largest, and the dielectric constant ε_pla2 is the third largest. On the other hand, a Casimir attractive force AF acts between the first layer 11_1 and the second layer 12_2. This is because the dielectric constant ε_liq is larger than the dielectric constants ε_sub1 and ε_pla2. As a result, an equilibrium point where the attractive and repulsive forces are balanced can be created by the Casimir force alone. EXAMPLES

[0060] FIG. 13 shows a schematic cross-sectional view of the sensor element 1i of Example 4. The sensor element 1i of Example 4 further includes an electrode layer 14 made of graphene in addition to the sensor element 1d of Example 3 (FIG. 7). A more specific description will be given. Between the first layer 11_1 and the second layer 11_2, the electrode layer 14 is laminated with an intermediate layer 11m therebetween. In other words, the electrode layer 14 is disposed closer to the inside of the substrate than the first layer 11_1. The electrode layer 14 may be directly laminated without the intermediate layer 11m.

[0061] A voltage control unit 53 is disposed around the sensor element 1i. The electrode layer 14 is connected to the voltage control unit 53 via wiring 54. The voltage control unit 53 can apply any voltage to the electrode layer 14.

[0062] The operation of the sensor element 1i will be described. FIG. 14 shows a calculation example simulating the operating state of the sensor element 1i. The horizontal axis of FIG. 14 is the chemical potential of the electrode layer 14 made of graphene. The chemical potential of the electrode layer 14 corresponds to the voltage value applied by the voltage control unit 53. In the calculation of FIG. 14, the chemical potential of the graphene 13 is fixed to 0 [eV]. The vertical axis of FIG. 14 is the distance d.

[0063] A Casimir attractive force acts between the electrode layer 14 and the graphene 13 in the substrate. The magnitude of this Casimir attractive force can be changed by modulating the chemical potential of the electrode layer 14 by applying a voltage. That is, the Casimir attractive force between the electrode layer 14 and the graphene 13 can be increased by increasing the chemical potential of the electrode layer 14. Therefore, as shown in FIG. 14, the equilibrium point EP can be shifted so that the distance d becomes smaller by increasing the chemical potential of the electrode layer 14. The smaller the equilibrium distance d, the larger the attractive and repulsive components of the Casimir force that the nanoplate 12 receives at the equilibrium point EP, and therefore the larger the restoring force and the improved response speed. On the other hand, the smaller the equilibrium distance d, the smaller the amount of equilibrium point shift due to chemical adsorption to the graphene 13, and therefore the lower the sensor sensitivity. In this way, by providing the electrode layer 14 made of graphene, it is possible to impart a function of modulating the sensor sensitivity and response speed according to the purpose of the device.

[0064] (First modified example of the fourth embodiment) Fig. 15 shows a schematic cross-sectional view of a sensor element 1j according to a first modified example of Example 4. The sensor element 1j according to the first modified example further includes an electrode layer 14 made of graphene in comparison with the sensor element 1g according to the third modified example of Example 3 (Fig. 11). The electrode layer 14 is disposed on the inner side of the substrate relative to the first layer 11_1. The operation and effects of the sensor element 1j are similar to those of the sensor element 1i (Fig. 13) described above, and therefore will not be described.

[0065] (Second modified example of the fourth embodiment) In the sensor element 1f according to the second modified example of the third embodiment (FIG. 10) and the sensor element 1h according to the third modified example of the third embodiment (FIG. 12), a voltage control unit 53 may be connected to the graphene 13 disposed on the surface 11s of the substrate 11. This makes it possible to apply an arbitrary voltage to the graphene 13. Therefore, the graphene 13 can function as an adsorption layer for chemical substances and as a control layer for the sensor sensitivity and response speed.

[0066] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful.

[0067] (Modification) The graphene 13 may be disposed on at least one of the surface 12s of the nanoplate 12 and the second surface 11s of the substrate 11. Thus, graphene may be disposed on both the surface 12s and the second surface 11s of the substrate 11.

[0068] The method of supplying the chemical substance to be measured is not limited to the embodiment using the gas supply device 52. For example, the liquid 10 containing the chemical substance to be measured may be supplied to the container 2.

[0069] The chemical substances to be measured are not limited to those contained in gas, but various substances such as liquids and solids can be measured. [Explanation of symbols]

[0070] 1: sensor element 2: container 10: liquid 11: substrate 11s: surface 12: nanoplate 12s: surface 13: graphene 51: interferometer 52: gas supply device

Claims

1. A liquid; a substrate disposed immobile in the liquid and having a planar first surface; a plate-like member disposed in a floating state in the liquid and having a planar second surface facing the first surface; Equipped with Graphene is disposed on at least one of the first surface and the second surface. Sensor element.

2. the graphene is disposed on either the first surface or the second surface; The sensor element further includes a first layer disposed on one of the first surface and the second surface on which the graphene is not disposed, The sensor element according to claim 1 , wherein a first dielectric constant which is a dielectric constant that the first layer has in the infrared and visible light regions is smaller than a liquid dielectric constant which is a dielectric constant that the liquid has in the infrared and visible light regions.

3. Further comprising a second layer laminated directly or via an intermediate layer on a surface of the first layer opposite to the surface facing the graphene; The sensor element according to claim 2 , wherein a second dielectric constant which is a dielectric constant of the second layer in the infrared and visible light regions is greater than the liquid dielectric constant.

4. the first layer and the second layer are disposed on the plate-like member, the graphene is disposed on the first surface of the substrate; The sensor element according to claim 3 , wherein the graphene is configured so that any voltage can be applied to the graphene.

5. the graphene is disposed on the plate-like member, the first layer is disposed on the first surface of the substrate; The sensor element according to claim 3 , further comprising an electrode layer arranged on an inner side of the substrate relative to the first layer and made of graphene.

6. the graphene is disposed on the second surface of the plate-shaped member, The sensor element includes: a first layer disposed on the first surface of the substrate; A second layer is laminated directly or via an intermediate layer on a surface of the graphene opposite to the surface facing the first layer; It also has 2. The sensor element according to claim 1, wherein each of a first dielectric constant and a second dielectric constant which are dielectric constants of the first layer and the second layer in the infrared and visible light ranges is smaller than a liquid dielectric constant which is a dielectric constant of the liquid in the infrared and visible light ranges.

7. The sensor element according to claim 6 , further comprising an electrode layer arranged on an inner side of the substrate relative to the first layer and made of graphene.

8. the graphene is disposed on the first surface of the substrate; The sensor element includes: a first layer that is disposed on an inner side of the substrate relative to the graphene, the first layer being laminated directly or via an intermediate layer on a surface of the graphene opposite to a surface facing the plate-like member; a second layer disposed on the second surface of the plate-like member; It also has 2. The sensor element according to claim 1, wherein each of a first dielectric constant and a second dielectric constant which are dielectric constants of the first layer and the second layer in the infrared and visible light ranges is smaller than a liquid dielectric constant which is a dielectric constant of the liquid in the infrared and visible light ranges.

9. The sensor element according to claim 8 , wherein the graphene is configured so that any voltage can be applied thereto.

10. the graphene is disposed on either the first surface or the second surface; The sensor element according to any one of claims 1 to 9, further comprising a device capable of measuring a distance between a surface of the graphene and one of the first surface and the second surface on which the graphene is not arranged.

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