Nitrided graphane

Abstract

To provide nitrided graphane, which is a graphane compound that can be used as a highly functional catalyst material or semiconductor material.SOLUTION: It has a structure in which some of the carbon atoms in graphane, which is graphene with added hydrogen, are replaced by nitrogen atoms.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to nitrogenated graphane. [Background technology]

[0002] Carbon-based materials are attracting attention as a sustainable element because they are lightweight, have excellent electrical conductivity, and are abundant on Earth. In particular, two-dimensional carbon materials have been actively researched because they have unique properties and are advantageous for making them smaller, lighter, and wearable. One such two-dimensional carbon material is graphene. Graphene is a planar sp 2 It is composed of a hexagonal lattice with covalent bonds.

[0003] It is known that adding N (nitrogen) to such graphene gives it n-type semiconductor properties. Nitrogen-added graphene exhibits a metallic band structure due to an increase in the Fermi level, and becomes thermodynamically unstable as the nitrogen concentration increases. On the other hand, it is known that when the dopant satisfies certain alignment conditions, anomalous stabilization resulting from band gap formation occurs (e.g., Non-Patent Document 1).

[0004] On the other hand, graphene (hydrogenated graphene) is also known, which is obtained by adding hydrogen atoms to graphene and completely hydrogenating the surface (for example, Patent Document 1). Graphene is characterized by its mechanical properties, thermal properties, and electrical properties as a semiconductor, and is expected to be used as a highly functional catalyst material or semiconductor material. For example, it is thought that such graphene can be used as a semiconductor material with high electron mobility by changing the electronic state and other physical properties by replacing some of the hydrogen atoms with different elements (for example, Non-Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2016-534010 [Non-patent literature]

[0006] [Non-Patent Document 1] T.Umeki and J.Nakamura et al., J.Phys. Chem. C 119, 6288(2015). [Non-Patent Document 2] Electronic transport properties of hydrogenated and fluorinated graphene: a computational study To cite this article: Mohammad Mahdi Khatami et al 2020 J. Phys.: Condens. Matter 32 495502. Summary of the Invention [Problem to be solved by the invention]

[0007] Graphane has the potential to be a novel high-performance material, and further improvements in its functionality are desirable. However, little is known about graphane compounds obtained by substituting carbon atoms of graphane with different elements.

[0008] The present invention has been made in consideration of the above technical background, and aims to provide nitrogenated graphane, which is a graphane compound that can be used as a high-performance catalyst material or semiconductor material. [Means for solving the problem]

[0009] In order to solve the above problems, the nitrogenated graphane of one embodiment of the present invention proposes the following configuration.

[0010] (1) The nitrogenated graphane of the first aspect of the present invention is characterized in that it has a structure in which hydrogen is added to graphene and some of the carbon atoms of the graphane are replaced with nitrogen atoms.

[0011] (2) A second aspect of the present invention is characterized in that, in the nitrogenated graphane of the first aspect, the concentration of the nitrogen atoms is in the range of 35 atomic % or more and 50 atomic % or less.

[0012] (3) A third aspect of the present invention relates to the nitrided graphane of the first or second aspect, wherein the nitrided graphane has an electron mobility of 9000 cm when the concentration of the nitrogen atoms is 50 atomic %. 2 / Vs or more.

[0013] (4) A fourth aspect of the present invention is the nitrided graphane of any one of the first to third aspects, characterized in that the nitrided graphane has a relative dielectric constant of 3.5 or more when the concentration of the nitrogen atoms is 50 atomic %.

[0014] (5) A fifth aspect of the present invention is characterized in that, in the nitrogenized graphane of any one of the first to fourth aspects, the nitrogenized graphane has an elastic modulus of 300 N / m or more when the concentration of the nitrogen atoms is 50 atomic %. Effect of the Invention

[0015] According to the present invention, it is possible to provide nitrogenated graphane, which is a graphane compound that can be used as a highly functional catalyst material or semiconductor material. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic structural diagram showing nitrogenated graphane according to one embodiment of the present invention. [Diagram 2] (a) A schematic diagram showing the triangular type in which nitrogen is replaced by graphane carbon in a triangular shape, and (b) a schematic diagram showing the honeycomb type in which nitrogen is replaced by graphane carbon in a hexagonal shape. [Diagram 3] 1 is a graph showing the relationship between the nitrogen concentration and the formation energy of nitrogenated graphene in which carbon atoms of graphene having sp2 covalent bonds are replaced with nitrogen atoms. [Figure 4]This is a graph showing the relationship between the nitrogen concentration and formation energy of nitrogenated graphane, in which the carbon atoms of graphane having sp3 covalent bonds are replaced with nitrogen atoms. [Diagram 5] 1 is a graph showing the relationship between the nitrogen concentration and electron mobility of nitrogenated graphane in which the carbon atoms of graphane having sp3 covalent bonds are replaced with nitrogen atoms. [Figure 6] 1 is a graph showing the phonon density of states (DOS) of nitrogenated graphane in the long wavelength region. [Figure 7] 1 is a graph showing the relationship between the nitrogen concentration and elastic modulus of nitrogenated graphane in which carbon atoms of graphane having sp3 covalent bonds are replaced with nitrogen atoms. [Figure 8] 1 is a graph showing the relationship between the nitrogen concentration and the relative dielectric constant of nitrogenated graphane in which carbon atoms of graphane having sp3 covalent bonds are substituted with nitrogen atoms. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. In addition, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited to them, and may be appropriately modified and implemented within a range that does not change the effects of the present invention.

[0018] FIG. 1 is a schematic structural diagram showing nitrogenated graphane according to one embodiment of the present invention. The nitrogenated graphane of one embodiment of the present invention has a two-dimensional structure in which some of the carbon atoms of graphene, in which hydrogen is added to the carbon atoms constituting graphene, are replaced with nitrogen atoms. Note that FIG. 1 shows a case in which the concentration of nitrogen atoms is 25 atomic %.

[0019] The nitrogenated graphane of this embodiment may be one in which the carbon atoms of graphane are substituted with nitrogen atoms at a concentration of at least 1 atomic % or more, but from the viewpoint of the effect of improving electron mobility when used as a semiconductor material, the concentration of nitrogen atoms is preferably in the range of 35 atomic % or more and 50 atomic % or less. If the concentration of nitrogen atoms is less than 35 atomic %, there is a concern that a sufficient effect of improving electron mobility cannot be obtained. Furthermore, due to the structure of nitrogenated graphane, the concentration of nitrogen atoms is limited to 50 atomic %. When the concentration of nitrogen atoms is 50 atomic %, the carbon atoms and nitrogen atoms are present in a ratio of 1:1.

[0020] The thermodynamic stability (formation energy) of the nitrogenated graphane of this embodiment was evaluated using first-principles calculations. The evaluation was performed on a triangular type in which nitrogen is substituted for carbon of graphane in a triangular shape as shown in Figure 2(a), and a honeycomb type in which nitrogen is substituted for carbon of graphane in a hexagonal shape as shown in Figure 2(b). The nitrogen concentration was in the range of 0.78 to 50 atomic %.

[0021] Figure 3 shows sp 2 The relationship between the nitrogen concentration and the formation energy of nitrogenated graphene, in which the carbon atoms of graphene with covalent bonds are replaced with nitrogen atoms, is shown in the graph. 3 The graph shows the relationship between the nitrogen concentration and the formation energy of nitrogenated graphane, in which the carbon atoms of graphane having covalent bonds are replaced with nitrogen atoms.

[0022] sp 2 In the case of graphene with covalent bonds, the formation energy increases with increasing nitrogen concentration, and the thermodynamic stability tends to decrease. 3 In the case of graphane with covalent bonds, it was found that the formation energy is almost constant regardless of the nitrogen concentration.

[0023] Considering the effect of doping with a different element on the thermodynamic stability from the viewpoint of electronic state, sp 2The Fermi level of graphene, which has covalent bonds, is located on the Dirac point. When doped with nitrogen, the Fermi level shifts toward the conduction:CB (valence:VB) band, and a band exists across the Fermi level, resulting in a metallic electronic state.

[0024] On the other hand, sp 3 When covalently bonded graphane is doped with nitrogen, a state with small dispersion is added to the VBM, which is quite different from nitrogen-doped graphene. 2 In the case of graphene with covalent bonds, the electrons from nitrogen act as π * It is fed into the orbit and delocalized. Therefore, π * Due to the long-range orbital interactions, the doping tends to become thermodynamically unstable as the nitrogen doping concentration increases.

[0025] On the other hand, nitrogen-doped sp 3 In graphane with covalent bonds, localized lone pairs are formed on the nitrogen atoms. Hence, sp 3 Since interactions between nitrogen atoms via the skeleton are unlikely to occur, it is believed that the formation energy is almost constant regardless of the nitrogen doping concentration.

[0026] The electron mobility, which is related to the semiconductor properties, was evaluated when the nitrided graphane of this embodiment was used as a semiconductor element. 3 The graph shows the relationship between the nitrogen concentration and electron mobility of nitrogenized graphane, in which the carbon atoms of graphane having covalent bonds are replaced with nitrogen atoms.

[0027] As shown in Figure 5, compared to graphane (pure) that is not doped with nitrogen, the electron mobility tends to increase as the nitrogen concentration increases. In particular, when the nitrogen concentration exceeds 30 atomic %, the electron mobility begins to increase rapidly, and at a nitrogen concentration of 50 atomic %, the electron mobility is 9000 cm 2 / Vs or more.

[0028] This electron mobility is comparable to the electron mobility of single crystal silicon, 1500 cm2 / Vs, which is significantly higher than the electron mobility of 8500 cm in gallium arsenide crystals. 2 Therefore, for example, if nitrided graphane with a nitrogen concentration of 50 atomic % is used as a semiconductor material, it is possible to manufacture a semiconductor element with better semiconductor characteristics than a conventional semiconductor element using a silicon single crystal.

[0029] Since it is believed that the carrier-phonon interaction has a large effect on the nitrogen concentration dependence of the electron mobility, we performed phonon calculations to obtain the phonon density of states (DOS) in the long wavelength region. The results are shown in the graph in Figure 6.

[0030] Figure 6 confirms that there is no change in low-frequency acoustic phonons due to the nitrogen concentration. However, analysis of the phonon dispersion diagram reveals that hardening of acoustic phonons (LA mode) occurs in the long-wavelength region. Therefore, it is believed that the higher the nitrogen concentration, the more the scattering of carriers by acoustic phonons in the long-wavelength region is suppressed, and therefore the higher the electron mobility can be.

[0031] Next, the elastic modulus of the nitrogenized graphane of this embodiment was examined. In this embodiment, the elastic modulus was calculated by the finite difference method. In Figure 7, sp 3 The graph shows the relationship between the nitrogen concentration of nitrogenized graphane, in which the carbon atoms of graphane with covalent bonds are replaced with nitrogen atoms, and the elastic modulus. The elastic modulus was calculated for the triangular type (see Figure 2(a)) and the honeycomb type (see Figure 2(b)). For reference, sp 2 The elastic modulus of nitrogenated graphene, in which the carbon atoms of graphene having covalent bonds are replaced with nitrogen atoms, is also shown.

[0032] According to Figure 7, the elastic modulus increases linearly with increasing nitrogen concentration, and it can be seen that nitrogen substitution of carbon atoms tends to make the material harder. This is due to the effect that the C-C bonds between carbon atoms are replaced by C-N bonds by doping with nitrogen, and ionic bonds are added in addition to covalent bonds.

[0033] Also, sp 2 Covalent bonds and sp 3 It can be seen that at the same nitrogen concentration, there is a continuous difference in elastic modulus of about 100 N / m between the covalent bond and the sp 2 Covalent bonds and sp 3 This is thought to be due to differences in covalent bonds. From the above results, it is possible to control the elastic modulus from 200N / m to about 300N / m by changing the nitrogen concentration of nitrogenated graphane.

[0034] Next, the relative dielectric constant of the nitrogenated graphane of this embodiment was examined. Since it is inappropriate to directly show the calculation result of the dielectric constant using the perturbation theory in the calculation of a two-dimensional system model, the influence of the vacuum layer was removed and the dielectric constant of the material itself was calculated. Figure 8 shows the relationship between the nitrogen concentration and the relative dielectric constant of the nitrogenated graphane in a graph. According to FIG. 8, the higher the nitrogen concentration of nitrogenized graphane, the higher the relative dielectric constant becomes, and when the nitrogen concentration is 50 atomic %, the relative dielectric constant is 3.5 or more.

[0035] As described above, according to the present embodiment, by substituting a portion of the carbon atoms of graphane in which hydrogen is added to graphene with nitrogen atoms, it is possible to provide nitrogenated graphane, which is a graphane compound that can be used as a semiconductor material with excellent electron mobility or a highly functional catalyst material.

[0036] Note that examples of the method for producing the nitrogenated graphane of this embodiment include a method of hydrogenating triazine (C3H3N3) and a method of polymerizing graphene in the presence of nitrogen gas and hydrogen gas.

[0037] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Industrial Applicability]

[0038] The nitrided graphane of the present invention can realize the production of semiconductor materials with excellent electron mobility and highly functional catalyst materials, and therefore has industrial applicability.

Claims

1. Nitrogenated graphane is characterized in that it has a structure in which some of the carbon atoms in graphane, in which hydrogen is added to graphene, are replaced with nitrogen atoms.

2. 2. The nitrided graphene according to claim 1, wherein the concentration of the nitrogen atoms is in the range of 35 atomic % to 50 atomic %.

3. The nitrogenated graphene has an electron mobility of 9000 cm when the concentration of the nitrogen atoms is 50 atomic %. ２ 3. The nitrogenated graphane according to claim 1, wherein the N-type nitride semiconductor layer has a capacitance Cs / Vs or more.

4. 3. The nitrided graphene according to claim 1, wherein the nitrided graphene has a relative dielectric constant of 3.5 or more when the concentration of the nitrogen atoms is 50 atomic %.

5. 3. The nitrogenized graphene according to claim 1, wherein the nitrogenized graphene has an elastic modulus of 300 N / m or more when the concentration of the nitrogen atoms is 50 atomic %.

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