Conductive structure for generating spin-polarized current, electrode using same, and method

Abstract

To provide a technique for enhancing a spin polarization rate of current.SOLUTION: An electroconductive structure 10 that generates a spin polarization current, comprises a plurality of structural units 16 being repeatedly present in a specified direction. Each of the structural units 16 includes an electroconductive body such as an electroconductive particle 12, and a chiral molecule 14 adsorbed to the electroconductive body. When current is allowed to flow in the specified direction, the current flows through the plurality of structural units 16, whereby the spin polarization rate of the current is amplified. The electroconductive structure 10 can be used as an electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a conductive structure for generating spin-polarized current, an electrode using the same, and a method thereof. [Background technology]

[0002] Existing electrochemical reactions are chemical reactions that utilize the degree of freedom of electrons, their "charge." Meanwhile, electrons possess another degree of freedom, their "spin angular momentum." The flow of electrons with actively controlled spin angular momentum is understood as a "spin-polarized current." In the fields of condensed matter physics and electronics, electronics technology based on the control of spin angular momentum, or "spintronics," has been actively researched. Research results in spintronics continue to produce various breakthroughs, ranging from industrial applications such as giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) to academic advances such as the recent discovery of topological insulators.

[0003] Spintronic devices typically require ferromagnetic materials, an external magnetic field, or both to control the spin direction. While attempts have been made to fabricate spintronic devices using organic molecules, it has generally been thought to be difficult to control the spin direction using organic molecules, which do not have strong magnetic properties.

[0004] A phenomenon that overturns this conventional understanding, that is, tunneling electrons passing through chiral molecules are spin-polarized at room temperature, has recently been reported (Non-Patent Document 1). This phenomenon is called chirality-induced spin selectivity (CISS). Chirality-induced spin selectivity suggests the possibility of generating spin-polarized current at room temperature without using ferromagnetic materials or external magnetic fields.

[0005] In fact, Non-Patent Document 2 describes the formation of a self-assembled two-dimensional film made of chiral molecules on the surface of an Au electrode to obtain a spin-polarized current.

[0006] Non-Patent Document 3 describes the generation of spin-polarized current by depositing Fe3O4 nanoparticles of less than 20 nm onto which chiral molecules are chemisorbed on the surface of an electrode. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] B. Gohler et al., "Spin Selectivity in Electron Transmission Through Self-Assembled Monolayers of Double-Stranded DNA", Science 331, 894 (2011). [Non-patent document 2] Massimo Innocenti et al., "Spin dependent electrochemistry: Focus on chiral vs achiral charge transmission through 2D SAMs adsorbed on gold", Journal of Electroanalytical Chemistry, Volume 856, 1 January 2020, 113705 [Non-patent document 3] Wenyan Zhang et al., "Enhanced Electrochemical Water Splitting with Chiral Molecule-Coated Fe3O4 Nanoparticles", ACS Energy Letters 2018, 3, 2308-2313 Summary of the Invention [Problem to be solved by the invention]

[0008] To apply spin-polarized current to various applications such as devices and electrochemical reactions, it is important to improve the spin polarization. However, previous reports on the CISS effect have been limited to tunneling currents in monolayers of chiral molecules. As a result, the spin polarization has not necessarily reached sufficient values. It is also not expected that the spin polarization can be dramatically improved by molecular design of chiral molecules alone.

[0009] An object of the present invention is to provide a technique for improving the spin polarization rate of a current. [Means for solving the problem]

[0010] The present invention provides 1. A conductive structure for generating a spin-polarized current, comprising: The structure includes a plurality of structural units that are repeatedly present in a predetermined direction, each of the plurality of structural units includes a conductor and a chiral molecule adsorbed to the conductor; When a current is passed in the predetermined direction, the current passes through the plurality of structural units, and the spin polarization of the current is amplified. A conductive structure is provided.

[0011] In another aspect, the present invention provides an electrode comprising the conductive structure of the present invention.

[0012] In yet another aspect, the present invention provides a method comprising carrying out an electrochemical reaction using the electrode of the present invention.

[0013] In yet another aspect, the present invention provides a method for producing an organic compound, which comprises causing an enantioselective reaction using the electrode of the present invention. [Effects of the Invention]

[0014] According to the present invention, the spin polarization of the current can be improved. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view of a conductive structure according to the first embodiment. [Figure 2] FIG. 2 is a flowchart showing a method for manufacturing the conductive structure shown in FIG. [Figure 3] FIG. 3 is a schematic diagram of a conductive structure according to the second embodiment. [Figure 4] FIG. 4 is a diagram illustrating a method for manufacturing the conductive structure shown in FIG. [Figure 5] Figure 5 shows a TEM image of Au nanoparticles. [Figure 6A] FIG. 6A is a graph showing the measurement results of the electrical resistance of devices according to the example and comparative example. [Figure 6B] FIG. 6B is a graph showing the measurement results of the magnetoresistance of the devices of the example and the comparative example. [Figure 7A] FIG. 7A is a graph showing the measurement results of the electrical resistance of the device of Comparative Example 5. [Figure 7B] FIG. 7B is a graph showing the measurement results of the magnetoresistance of the device of Comparative Example 5. [Figure 8] FIG. 8 is a graph showing the results of cyclic voltammetry measurements using the electrodes of the example and comparative example. [Figure 9] FIG. 9 is a graph showing the results of ultraviolet-visible spectroscopic measurement and circular dichroism spectroscopic measurement of the eluent of high performance liquid chromatography. [Figure 10] FIG. 10 is a graph showing the relationship between the enantiomeric excess (ee) and the number of chiral molecular layers. [Figure 11] FIG. 11 is a graph showing the results of chronocoulometry measurements. [Figure 12] FIG. 12 is a graph showing the visible absorption spectrum of the reaction solution in the water splitting reaction. DETAILED DESCRIPTION OF THE INVENTION

[0016] (Findings that form the basis of the present invention) The inventors suspected that the spin polarization could be amplified by applying multiple CISS effects to an electric current, i.e., by applying the "multiple CISS effect." Specifically, they conceived the idea of constructing a conductor network using chiral molecules and using this network to apply the multiple CISS effect to an electric current, which led to the completion of the present invention.

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, but is not limited to the following embodiments.

[0018] (Embodiment 1) FIG. 1 is a schematic cross-sectional view of a conductive structure 10 for generating a spin-polarized current according to a first embodiment. The conductive structure 10 includes multiple structural units 16 that are repeated along a predetermined direction D. Each of the multiple structural units 16 includes a conductive particle 12 and a chiral molecule 14. The chiral molecules 14 act as ligands, forming a network of the conductive particles 12. When a current is applied in the predetermined direction D, the current passes through the multiple structural units 16, amplifying the spin polarization of the current. The conductive structure 10 can impart multiple CISS effects to the current, i.e., a multiple CISS effect. The conductive structure 10 can generate a spin-polarized current with an improved spin polarization. The "predetermined direction D" can be parallel to the direction in which the structural units 16 are repeated.

[0019] In the conductive structure 10, a plurality of conductive particles 12 may be contained in the structural unit 16. In the conductive structure 10, a plurality of chiral molecules 14 may be contained in the structural unit 16. A plurality of chiral molecules 14 may be adsorbed to a single conductive particle 12. A conductive particle 12 may be surrounded by a plurality of chiral molecules 14. In this case, aggregation of the conductive particles 12 is effectively prevented, and the conductive particles 12 can exist discretely in both the in-plane direction and the stacking direction. This suppresses relaxation of the spin-polarized current and enhances the multiple CISS effect.

[0020] In this embodiment, the structural units 16 are layered. A plurality of structural units 16 are stacked to form the conductive structure 10. With this structure, the spin polarization can be increased in accordance with the number of stacked structural units 16.

[0021] In the schematic diagram of FIG. 1 , adjacent conductive particles 12 in a direction parallel to a predetermined direction D are crosslinked by chiral molecules 14. However, adjacent conductive particles 12 in a direction parallel to the plane of the layered structural unit 16 may be bonded by chiral molecules 14, or adjacent conductive particles 12 in an oblique direction may be bonded by chiral molecules 14. As long as the conductive particles 12 in adjacent layers are isolated from each other by chiral molecules 14, the conductive structure 10 as a whole may form a three-dimensional network structure. Note that the "oblique direction" refers to a direction inclined with respect to both the direction parallel to the predetermined direction D and the direction parallel to the plane of the layered structural unit 16.

[0022] The conductive particles 12 are an example of a conductor. As will be described later, it is also possible to use a conductor in a shape other than particles.

[0023] In this embodiment, the spin-polarized current obtained through the conductive structure 10 can be confirmed by measuring the change in magnetoresistance (MR) with the sweep of the magnetic field.

[0024] In this embodiment, the conductive structure 10 includes a conductive substrate 18. The substrate 18 supports the conductive structure 10. A plurality of structural units 16 are arranged on the surface of the substrate 18. A predetermined direction D, which is the direction in which a current flows, is perpendicular to the surface of the substrate 18. The substrate 18 can ensure the rigidity of the conductive structure 10. Because the substrate 18 is conductive, it is easy to supply a current to the network of conductive particles 12 formed by the chiral molecules 14. By fixing the network of conductive particles 12 formed by the chiral molecules 14 to the substrate 18, the conductive structure 10 can be used for a variety of applications.

[0025] The material of the substrate 18 is not particularly limited. Examples of the material of the substrate 18 include metal materials, conductive ceramics, carbon materials, and conductive resins. The shape of the substrate 18 is also not particularly limited. The substrate 18 may be plate-shaped or rod-shaped.

[0026] The conductive particles 12 may be nanoparticles, i.e., particles having nanometer-order dimensions. When the conductive particles 12 have nanometer-order dimensions, the decay of the spin polarization of the current passing through the conductive particles 12 during the relaxation process can be suppressed.

[0027] The conductive particles 12 may have a diameter equal to or less than the spin diffusion length. Spin polarization is largely preserved within particles with diameters smaller than the spin diffusion length. For example, assume that the conductive particles 12 are Au nanoparticles. The spin diffusion length of Au is approximately 50 nm. Therefore, the decay of the spin polarization of the current during the relaxation process through an Au nanoparticle with a diameter of several nanometers is small. If the current flows into the next structural unit 16 while maintaining a high spin polarization and transitions to the polarization process by the chiral molecules 14, further improvement in spin polarization can be expected. By repeating the relaxation and polarization processes, it is possible to ultimately achieve a spin polarization close to 100%. The "spin diffusion length" refers to the approximate length over which the spin current disappears.

[0028] The conductive particles 12 have an average particle size in the range of, for example, 1 nm or more and 50 nm or less. The average particle size of the conductive particles 12 can be determined by the following method. The conductive particles 12 are observed using a transmission electron microscope (TEM). The equivalent area circle diameter of 100 conductive particles 12 randomly selected from the obtained TEM image is calculated by image processing. The average of the obtained equivalent area circle diameters can be considered as the average particle size of the conductive particles 12.

[0029] The conductive particles 12 are made of a conductive material. The material of the conductive particles 12 is not particularly limited as long as it is conductive. The conductive particles 12 may contain metal nanoparticles or non-metal nanoparticles. Examples of metal nanoparticles include Au nanoparticles, Ag nanoparticles, Cu nanoparticles, and Pt nanoparticles. The metal nanoparticles may be noble metal nanoparticles. Examples of non-metal nanoparticles include carbon nanoparticles and semiconductor nanoparticles. Using metal nanoparticles as the conductive particles 12 makes it easier to control the arrangement of the conductive particles 12 and the chiral molecules 14, facilitating the manufacture of the conductive structure 10. Non-metal nanoparticles such as carbon nanoparticles and semiconductor nanoparticles are expected to improve spin polarization due to their long spin diffusion length. Examples of semiconductor nanoparticles include nanoparticles of semiconductor materials such as CdSe, CdS, PbSe, and PbS.

[0030] The conductive particles 12 typically include Au nanoparticles. Because the spin diffusion length of Au is relatively long, Au is suitable as a material for the conductive particles 12. Furthermore, Au nanoparticles of uniform size can be easily produced by known methods such as reduction.

[0031] In the conductive structure 10, a conductive layer may be constructed by a plurality of conductive particles 12. In this case, it is possible to adjust the spin polarization rate by changing the number of conductive layers.

[0032] The chiral molecules 14 are molecules having chirality. The chiral molecules 14 are, for example, chemically or physically adsorbed to the conductive particles 12. The chiral molecules 14 are in the L- or D-form. The conductive structure 10 may contain only the L- or D-chiral molecules 14. The greater the enantiomeric excess of the chiral molecules 14 in the conductive structure 10, the greater the spin polarization rate. If the L- or D-form is 100%, the spin polarization effect is maximized. The enantiomeric excess of the chiral molecules 14 in the conductive structure 10 is not zero, and may be, for example, 50% to 100%, or 90% to 100%.

[0033] The type of chiral molecule 14 can be appropriately selected depending on the conductor, such as the conductive particle 12. In one example, the chiral molecule 14 is a compound having a thiol group. The compound having a thiol group specifically binds to Au through a gold-sulfur bond. That is, the compound having a thiol group has excellent compatibility with Au nanoparticles as the conductive particle 12. The chiral molecule 14 may be a dithiol compound. The dithiol compound is a compound having two thiol groups in the molecule. The thiol groups can be located at both ends of the molecule. Specifically, the thiol groups can be located at both ends of an alkyl chain.

[0034] The substrate 18 may have a surface formed by a thin Au film. In this case, the chiral molecules 14 having a thiol group are immobilized on the surface of the substrate 18 by gold-sulfur bonds. As a result, the chiral molecules 14 can form a self-assembled monolayer with high orientation.

[0035] The molecular length of the chiral molecules 14 is, for example, 1 nm or less. In this case, the interparticle distance of the conductive particles 12 can be reduced to 1 nm or less. When the interparticle distance of the conductive particles 12 is reduced, the electron conduction process between the conductive particles 12 becomes an almost complete tunneling process, and the conductive structure 10 exhibits electrical conductivity close to that of a metal. In other words, to achieve long-distance metallic conduction, it is desirable to select chiral molecules 14 with a short molecular length. The chiral molecules 14 may be compounds having a linear carbon chain. In this case, the number of carbon atoms in the carbon chain, in terms of the main chain of the molecule, can be, for example, 2 or more and 10 or less.

[0036] The chiral molecules 14 that satisfy the above requirements are not particularly limited as long as they can crosslink the conductive particles 12, and examples thereof include dithiols, diamines, etc. Examples of dithiols include L-dithiothreitol and D-dithiothreitol.

[0037] The conductive structure 10 can be used for various purposes. For example, the conductive structure 10 can be used as an electrode (e.g., a working electrode) in an electrochemical reaction. In this case, it becomes possible to cause an electrochemical reaction using a spin-polarized current having a high spin polarization rate.

[0038] An electrode including the conductive structure 10 of this embodiment can produce optically active organic compounds. That is, optically active organic compounds can be produced by electrochemical reactions using an electrode including the conductive structure 10. For example, a racemic compound can be enantioselectively reacted to produce an optically active compound. An example of this will be described later in the Examples. Naturally occurring optically active compounds (such as sugars and amino acids) can also be diastereoselectively reacted to produce an optically active compound. By using an electrode including the conductive structure 10, asymmetric synthesis can be performed without using special catalysts or the like.

[0039] In relation to the above, one example of an electrochemical reaction is an enantioselective reaction. An enantioselective reaction is a reaction in which a specific reaction, such as an oxidation reaction, reduction reaction, addition reaction, or substitution reaction, is carried out on a compound that does not have an asymmetric component, thereby preferentially producing one enantiomer. Enantioselective reactions using spin-polarized current have the potential to achieve high enantiomeric excess (ee). While ordinary current is an achiral phenomenon, spin-polarized current is chiral. In other words, as the opposite effect of the CISS effect, spin-polarized current can act as a "source of asymmetry" in electrochemical reactions.

[0040] Another example of an electrochemical reaction is the water splitting reaction. Unlike ordinary electric currents with random spin angular momentum, spin-polarized currents have spin angular momentum in the same direction, which can preferentially generate spin triplet states during the electrochemical reaction. In the electrolysis of water (H2O), the production of oxygen (O2), whose ground state is a spin triplet, competes with the production of hydrogen peroxide (H2O2), whose ground state is a spin singlet. When a spin-polarized current with a high spin polarization is used for the water splitting reaction, the production of H2O2, which competes with the reaction that produces O2, can be suppressed. This is because the production of O2 in the spin triplet state is selectively suppressed, while the production of O2 in the singlet state is suppressed. As a result, the water electrolysis reaction can proceed efficiently.

[0041] Next, a method for manufacturing the conductive structure 10 will be described.

[0042] Fig. 2 is a flowchart showing a method for manufacturing the conductive structure 10 shown in Fig. 1. In step S1, the substrate 18 is coated with chiral molecules 14. For example, a solution containing the chiral molecules 14 may be applied, or the substrate 18 may be immersed in the solution containing the chiral molecules 14. A self-assembled monolayer of the chiral molecules 14 may be formed on the surface of the substrate 18.

[0043] Next, the conductive particles 12 are deposited. The conductive particles 12 can be synthesized in advance by a known method such as a reduction method. For example, the conductive particles 12 can be deposited on the surface of the substrate 18 by contacting the substrate 18 with a dispersion of the conductive particles 12. This forms a structural unit 16 containing the conductive particles 12 and the chiral molecules 14.

[0044] In step S3, the current layer number n of the structural unit 16 is changed to the desired layer number n t Determine whether the desired number of layers n has been reached. t Steps S1 and S2 are repeatedly performed until the structural unit 16 is formed, thereby obtaining the conductive structure 10 shown in Fig. 1. The order of steps S1 and S2 may be reversed.

[0045] (Embodiment 2) FIG. 3 is a schematic diagram of a conductive structure 20 that generates a spin-polarized current according to the second embodiment. The conductive structure 20 has a plurality of structural units 26 including layers 22 and chiral molecules 14. In this embodiment, the layers 22 are any layers of a layered compound. The layers 22 are an example of a conductor. The chiral molecules 14 are intercalated between the layers of the layered compound. When a current is passed in a direction perpendicular to each layer of the layered compound, i.e., in a direction parallel to the stacking direction of the layers, the spin polarization of the current is amplified.

[0046] The layered compound may be a transition metal dichalcogenide. The transition metal dichalcogenide may suitably constitute a part of the conductive structure 20 of this embodiment. The transition metal dichalcogenide is a substance group represented by MX2. M is a transition metal atom, and X is a chalcogen atom other than oxygen. The transition metal is typically a Group VI transition metal such as Mo or W. The transition metal dichalcogenide often has a layered crystal structure. The thickness of one layer of the layered transition metal dichalcogenide is, for example, several angstroms, and is suitable as the skeleton of the conductive structure 20 of this embodiment.

[0047] Another example of a layered compound is MXene. MXene is a general term for compounds containing transition metals such as titanium and vanadium and light elements such as carbon and nitrogen, and has a sheet-like structure similar to graphene. A specific example of MXene is Ti3C2MXene.

[0048] Another example of a layered compound is a layered perovskite compound.

[0049] The chiral molecule 14 may be a chiral amine. Examples of chiral amines include methylbenzylamine (MBA). Methylbenzylamine may be in either the R or S configuration. As shown in FIG. 3, multiple molecules (e.g., two molecules) of methylbenzylamine may be intercalated between layers of a layered compound. Between the layers, aromatic rings of the methylbenzylamine may overlap to form a π bond.

[0050] The conductive structure 20 may include the substrate 18 described in embodiment 1. In this case, a plurality of structural units 26 may be arranged on the substrate 18 so that the layer 22 is parallel to the surface of the substrate 18. This allows current to flow in the stacking direction of the plurality of structural units 26.

[0051] The conductive structure 20 shown in FIG. 3 can be manufactured by the following method. FIG. 4 is a diagram illustrating a method for manufacturing the conductive structure 20 shown in FIG. 3. The conductive structure 20 can be manufactured by intercalating a chiral molecule 14 into a transition metal dichalcogenide 32 having a layered structure. For example, the LUMO of a Group VI transition metal dichalcogenide is in the range of −6.0 eV to −5.5 eV. Therefore, intercalation is possible through an acid-base reaction between the LUMO of the transition metal dichalcogenide and the HOMO (e.g., −6.2 eV) of amines, which are weak Lewis bases. [Example]

[0052] [Electrode preparation] Electrodes of the examples and comparative examples were prepared by the following method.

[0053] Example 1 (Synthesis of Au nanoparticles) AuPPh3Cl was heated in benzene in the presence of 1-dodecanethiol at 55°C for 1 hour using tert-butylamine borane complex as a reducing agent. This resulted in Au nanoparticles. Ethanol was added to the reaction solution to precipitate the Au nanoparticles, which were then collected by centrifugation. This process was repeated three times to purify the Au nanoparticles.

[0054] The Au nanoparticles were observed using a transmission electron microscope (TEM). Figure 5 shows a TEM image of the Au nanoparticles. The average particle size of the Au nanoparticles was calculated from the TEM image. The average particle size of the Au nanoparticles was approximately 5 nm.

[0055] After redispersing the Au nanoparticles in hexane, they were mixed with a dimethyl sulfoxide (DMSO) solution of K2S (5 mg / mL) and the mixture was stirred. 2- The DMSO phase was separated from the mixture to obtain a DMSO dispersion of Au nanoparticles.

[0056] (Integration of Au nanoparticles on a substrate) A thin gold film (50 nm thick) was deposited on a glassy carbon substrate by sputtering. The thin gold film was annealed at 200°C (ambient temperature) for 12 hours to obtain a substrate with a (111)-oriented gold film. The substrate was then cleaned by oxygen plasma treatment and immersed in an ethanol solution of L-dithiothreitol (~1 mg / mL). This thiolated the surface of the gold film.

[0057] Next, the substrate was immersed in a DMSO dispersion of Au nanoparticles, and the Au nanoparticles were adsorbed onto the surface of the substrate.

[0058] The thiolation process and the Au nanoparticle adsorption process were alternately repeated five times to aggregate the Au nanoparticles, forming a multilayer film of Au nanoparticles crosslinked by chiral molecules on the surface of the substrate. In this way, the conductive structure (electrode) of Example 1 was fabricated.

[0059] Example 2 An electrically conductive structure (electrode) of Example 2 was produced in the same manner as in Example 1, except that D-dithiothreitol was used instead of L-dithiothreitol.

[0060] Example 3 The conductive structure (electrode) of Example 3 was produced in the same manner as in Example 1, except that the thiolation step and the Au nanoparticle adsorption step were alternately repeated seven times.

[0061] Example 4 The conductive structure (electrode) of Example 4 was produced in the same manner as in Example 2, except that the thiolation step and the Au nanoparticle adsorption step were alternately repeated seven times.

[0062] (Comparative Example 1) An electrically conductive structure (electrode) of Comparative Example 1 was produced in the same manner as in Example 1, except that dithioerythritol, an achiral molecule (meso form), was used instead of L-dithiothreitol.

[0063] (Comparative Example 2) A conductive structure (electrode) of Comparative Example 2 was produced in the same manner as in Example 2, except that the thiolation step and the Au nanoparticle adsorption step were each carried out only once.

[0064] (Comparative Example 3) A thin Au film was formed on a glassy carbon substrate by sputtering, and the resulting structure was used as an electrode in Comparative Example 3.

[0065] Comparative Example 4 The conductive structure (electrode) of Comparative Example 4 was prepared in the same manner as in Example 1, except that racemic D,L-dithiothreitol was used instead of L-dithiothreitol, and the thiolation step and the Au nanoparticle adsorption step were alternately repeated seven times.

[0066] (Comparative Example 5) (Synthesis of Ag nanoparticles) AgNO3 was heated at 180°C for 10 minutes in the presence of 1-octadecylamine. This resulted in Ag nanoparticles with an average particle size of approximately 5 nm. Ethanol was added to the reaction solution to precipitate the Ag nanoparticles, which were then collected by centrifugation. This process was repeated three times to purify the Ag nanoparticles.

[0067] After redispersing the Ag nanoparticles in toluene, a large excess of L-alanine was added and the mixture was stirred overnight. This resulted in a ligand exchange reaction from 1-octadecylamine to L-alanine. Further ethanol was added to the reaction solution to precipitate the Ag nanoparticles, which were then collected by centrifugation. This process was repeated three times to remove unreacted 1-octadecylamine and L-alanine. This yielded a powder of Ag nanoparticles modified with L-alanine. The Ag nanoparticle powder was compressed using a piston cylinder for tablet molding to produce solid pellets of Ag nanoparticles.

[0068] The electrode configurations of the examples and comparative examples are shown in Table 1. The "repetition number" indicates the number of times the thiolation step and the Au nanoparticle adsorption step were repeated. The "repetition number" corresponds to the number of stacks of structural units containing linker molecules and conductors.

[0069] [Table 1]

[0070] The structures of L-dithiothreitol, dithioerythritol (meso form), and D-dithiothreitol are shown below.

[0071] [ka]

[0072] [Measurement of spin-polarized current and evaluation of spin polarization] An alumina insulating film (thickness 2 to 3 nm) was formed on the surface of the electrode of Example 1 by sputtering. Furthermore, a Ni thin film, which is a magnetic thin film for detecting spin-polarized current, was formed on the alumina insulating film by sputtering. In this way, the magnetoresistive detection device of Example 1 was fabricated. The magnetoresistive detection devices of Example 2 and Comparative Example 1 were also fabricated by the same method. The alumina insulating film serves to prevent Ni from penetrating the conductive structure and establishing electrical continuity between the Ni thin film and the underlying substrate.

[0073] First, the temperature dependence of the electrical resistance of the devices of Example 1 and Comparative Example 1 was measured without applying an external magnetic field. The results are shown in Figure 6A. The horizontal axis of the graph in Figure 6A represents temperature (K), and the vertical axis represents electrical resistance R at 300K. 300K 6A shows the ratio of the electrical resistance R at each temperature to the temperature at which the device is heated. As shown in FIG. 6A, both the device of Example 1 and the device of Comparative Example 1 exhibited metallic temperature dependence in which the electrical resistance monotonically decreased from room temperature to extremely low temperatures.

[0074] Next, an external magnetic field was applied perpendicular to the surface of the glassy carbon substrate, i.e., parallel to the direction of the current flow, and the change in magnetoresistance (MR) was measured as the magnetic field was swept. The results are shown in Figure 6B. MR (%) was calculated using the following formula (1):

[0075] MR(%)=100×[R(H)-R(H=0)] / R(H=0)...(1) R(H): Resistance under magnetic field R(H=0): Resistance in zero magnetic field

[0076] The horizontal axis of the graph in Figure 6B represents the magnetic field strength, and the vertical axis represents the magnetoresistance (MR). As shown in Figure 6B, the device of Example 1, which was fabricated using the L-body, produced an MR curve with a positive slope relative to the applied magnetic field. The device of Example 2, which was fabricated using the D-body, produced an MR curve with a negative slope. No clear MR signal was obtained from the device of Comparative Example 1, which was fabricated using the meso-body.

[0077] The above results indicate that down-spin selectivity was obtained from the L-isomer and up-spin selectivity was obtained from the D-isomer. Assuming that the spin polarization in the Ni electrode is approximately 30%, the spin polarization in the current flowing through the devices of Examples 1 and 2 corresponds to 80%. In other words, the devices of Examples 1 and 2 achieved extremely high spin polarization. Note that a spin whose spin angular momentum is parallel to the direction of electron motion is defined as up-spin. A spin whose spin angular momentum is antiparallel to the direction of electron motion is defined as down-spin.

[0078] Furthermore, the above facts demonstrate that the electrodes of Examples 1 and 2 achieved both metallic electrical conductivity and spin polarization due to the CISS effect. The electrical conductivity of a metal is important for electrodes to be used in various applications such as electrochemical reactions.

[0079] The spin polarization in the current flowing through the devices of Examples 1 and 2 was calculated using the following formula (2). The spin polarization in the Ni electrode (=30%) was based on the value in the literature "EY Tsymbal et al., J. Phys.: Cond. Matter 2003, 15, R109."

[0080] (spin polarization) = (MR value) / (spin polarization in Ni electrode) × 100(%) (2)

[0081] Next, the pellet of Comparative Example 5 was fixed on an Au electrode with Ag paste. After that, an alumina insulating film (thickness 2 to 3 nm) was formed on the surface of the pellet by sputtering. Furthermore, a Ni thin film was formed on the alumina insulating film by sputtering. In this way, the magnetoresistance detection device of Comparative Example 5 was produced.

[0082] The temperature dependence of the electrical resistance of the device of Comparative Example 5 was measured using the method described above. The results are shown in Figure 7A. As shown in Figure 7A, the device of Comparative Example 5 also exhibited metallic temperature dependence, in which the electrical resistance monotonically decreased from room temperature to extremely low temperatures.

[0083] Next, the magnetoresistance of the device of Comparative Example 5 was measured. Specifically, the change in magnetoresistance (MR) with the sweep of the magnetic field was measured. The measurement was performed at two temperatures, 300 K and 2 K, according to the method described above. The results are shown in Figure 7B. As shown in Figure 7B, no clear MR signal was obtained from the device of Comparative Example 5. This result is thought to be due to the fact that, during the process of forming the pellet of Comparative Example 5, contact (conduction) occurred between Ag nanoparticles without the L-alanine ligands, causing non-spin-polarized current not mediated by chiral molecules to become dominant.

[0084] [Enantioselective Reduction] Using the electrode of Example 4, Comparative Example 2, or Comparative Example 3 as the working electrode, Ag / AgCl as the reference electrode, and Pt as the counter electrode, the reduction reaction of 10-camphorsulfonic acid to 10-sulfonic acid borneol was carried out. Specifically, a KCl solution of (1R)-(-)-10-camphorsulfonic acid, a KCl solution of (1S)-(+)-10-camphorsulfonic acid, and a KCl solution of the racemic mixture containing equal amounts of these were prepared, each at a concentration of 0.1 mol / L. Each electrode was immersed in these solutions and subjected to cyclic voltammetry measurements. The results are shown in Figure 8.

[0085] FIG. 8(a) is a graph showing the results of cyclic voltammetry measurements using the electrode of Comparative Example 3. FIG. 8(b) is a graph showing the results of cyclic voltammetry measurements using the electrode of Comparative Example 2. FIG. 8(c) is a graph showing the results of cyclic voltammetry measurements using the electrode of Example 4. The horizontal axis of each graph indicates the applied potential, and the vertical axis indicates the detected current value. "rac-CSA" indicates the results for the racemic form. "R-CSA" indicates the results for the R-form. "S-CSA" indicates the results for the S-form.

[0086] As shown in FIG. 8(a), when the achiral electrode having no chiral molecular layer, that is, the achiral electrode of Comparative Example 3, was used, no difference was observed in the reduction current density for the R-isomer, S-isomer, and racemic mixture.

[0087] As shown in Figure 8(b), when the electrode of Comparative Example 2, which has one layer of chiral molecules and one layer of conductor, was used, a slightly higher current density was observed for the R-isomer. In other words, the R-isomer was selectively reduced. The electrode of Comparative Example 2 exhibited enantioselectivity. Because the R-isomer is also present in the racemic mixture, a difference in current density was also observed between the racemic mixture and the S-isomer.

[0088] As shown in Figure 8(c), when the electrode of Example 4, in which the number of stacked layers of the chiral molecule and conductor structural units was 7, was used, the enantioselectivity was significantly improved. The reaction in which racemic 10-camphorsulfonic acid is enantioselectively reacted to produce 10-sulfonic acid borneol (R-SAB) is as follows:

[0089] [ka]

[0090] [Quantitative determination of enantiomeric excess] The reduction reaction of the racemic 10-camphorsulfonic acid was carried out using the electrode of Example 2, Example 4, Comparative Example 2, or Comparative Example 3 as the working electrode, Ag / AgCl as the reference electrode, and Pt as the counter electrode. Specifically, each electrode was immersed in a racemic KCl aqueous solution (0.1 mol / L) containing equal amounts of (1R)-(-)-10-camphorsulfonic acid and (1S)-(+)-10-camphorsulfonic acid, and the reduction reaction was carried out at -0.9 V for 6 hours. The reaction mixture was then subjected to high-performance liquid chromatography using a chiral column (CHIRALPAK-IB, manufactured by Daicel Corporation) for optical resolution. The presence of enantiomers in the HPLC eluent was detected over time using an ultraviolet-visible spectrophotometer (UV) and a circular dichroism spectrophotometer (CD). A mixture of n-hexane and ethanol in a volume ratio of 3:1 at 20°C was used as the eluent. The flow rate of the eluent was 8 mL / min. While the eluent was flowing, 1 mL of a sample with a concentration of 2.0 g / L was injected into the column to separate the samples. The measurement wavelength for UV-visible spectroscopy was 200 nm. The results are shown in Figure 9.

[0091] 9 is a graph showing the results of ultraviolet-visible spectroscopy and circular dichroism spectroscopy of the eluent of high-performance liquid chromatography. Specifically, FIGS. 9(a), (b), (c), and (d) show the results of Comparative Example 3, Comparative Example 2, Example 2, and Example 4, respectively. The horizontal axis of each graph in FIG. 9 indicates the elapsed time of separation by high-performance liquid chromatography. The vertical axis indicates signal intensity. The number of layers shown in each graph indicates the number of chiral molecular layers and corresponds to the number of repetitions shown in Table 1.

[0092] As shown in Figure 9(a), when a reduction reaction was performed using the achiral electrode of Comparative Example 3, equal amounts of R and S isomers were produced. In other words, no enantioselectivity was observed. In contrast, as can be seen from Figures 9(b), (c), and (d), the enantiomeric excess (ee) of the R isomer increased as the number of chiral molecular layers increased.

[0093] Figure 10 is a graph showing the relationship between the enantiomeric excess (ee) and the number of chiral molecular layers. The enantiomeric excess was estimated from the peak areas of the UV and CD detection results (Figure 9). As the number of chiral molecular layers increased, the enantiomeric excess of the R-isomer increased, ultimately achieving an enantiomeric excess of approximately 25%. This value significantly exceeds the enantiomeric excess of 11.5% reported for ferromagnetic Ni electrodes.

[0094] [Water decomposition reaction] Using the electrodes of Example 3, Example 4, or Comparative Example 4 as the working electrode, Ag / AgCl as the reference electrode, and Pt as the counter electrode, electrochemical water splitting of a 0.1 mol / L NaSO solution was performed. Each electrode was immersed in the solution, and chronocoulometry measurements were performed at 1.4 V for 40 minutes. The results are shown in Figure 11.

[0095] FIG. 11 is a graph showing the results of chronocoulometry measurements. The horizontal axis represents elapsed time. The vertical axis represents total charge. The graph in FIG. 11 shows the change in total charge over time. When the chiral electrodes of Example 3 (L-isomer) and Example 4 (D-isomer) were used, a higher current density was obtained than when the achiral electrode of Comparative Example 4 (racemic form) was used. In other words, when the electrodes of Example 3 and Example 4 were used, the water splitting reaction proceeded efficiently.

[0096] After 40 minutes of reaction, the amount of hydrogen peroxide in the reaction solution was quantified by ultraviolet-visible absorption spectroscopy using o-tolidine as a redox indicator. The results are shown in Figure 12.

[0097] 12 is a graph showing the visible absorption spectrum of the reaction solution in a water splitting reaction. The reaction solution using the achiral electrode of Comparative Example 4 had a strong absorption band at λ=440 nm, which was due to the oxidation of o-tolidine by hydrogen peroxide. The reaction solutions using the chiral electrodes of Example 3 (L-isomer) and Example 4 (D-isomer) showed an overall lower absorbance than the absorbance of the reaction solution using the achiral electrode. The visible absorption spectrum revealed that the chiral electrode suppressed the production of hydrogen peroxide to about 1 / 6 of that of the achiral electrode. [Industrial Applicability]

[0098] The present invention is useful for applications in a variety of fields, including electrochemistry and electronics. [Explanation of symbols]

[0099] 10,20 Conductive structures 12 Conductive particles 14 Chiral Molecules 16,26 structural units 18 PCB 22 layers 32 Transition metal dichalcogenides

Claims

1. 1. A conductive structure for generating a spin-polarized current, comprising: The structure includes a plurality of structural units that are repeatedly present in a predetermined direction, each of the plurality of structural units includes a conductor and a chiral molecule adsorbed to the conductor; When a current is passed in the predetermined direction, the current passes through the plurality of structural units, amplifying the spin polarization of the current; the conductor is an arbitrary layer of a layered compound, The layered compound is a transition metal dichalcogenide or maxine; conductive structure.

2. An electrically conductive structure for generating a spin-polarized current, comprising: The structure includes a plurality of structural units that are repeatedly present in a predetermined direction, each of the plurality of structural units includes a conductor and a chiral molecule adsorbed to the conductor; When a current is passed in the predetermined direction, the current passes through the plurality of structural units, amplifying the spin polarization of the current; the conductor comprises metal nanoparticles; conductive structure.

3. The structural unit is layered The plurality of structural units are stacked. The conductive structure of claim 2 .

4. the metal nanoparticles include Au nanoparticles; The conductive structure according to claim 2 or 3.

5. The chiral molecule is a compound having a thiol group. The conductive structure according to any one of claims 1 to 4.

6. The molecular length of the chiral molecule is 1 nm or less. The conductive structure according to any one of claims 1 to 5.

7. Further comprising a conductive substrate, the plurality of structural units are disposed on a surface of the substrate; the predetermined direction is a direction perpendicular to the surface of the substrate; The conductive structure according to any one of claims 1 to 6.

8. A conductive structure comprising the conductive structure according to any one of claims 1 to 7. electrode.

9. 9. A method for producing an electrochemical reaction using the electrode of claim 8. method.

10. The electrochemical reaction is an enantioselective reaction or a water splitting reaction.

10. The method of claim 9.

11. 9. The method of claim 8, wherein the electrode is used to carry out an enantioselective reaction. Methods for producing organic compounds.

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