WO2019155979A1

WO2019155979A1 - Boron atom layer sheet and layered sheet, methods for producing same, and liquid crystal

Info

Publication number: WO2019155979A1
Application number: PCT/JP2019/003380
Authority: WO
Inventors: 徹也神戸; 笙太郎今岡; 藍子渡邊; 山元　公寿
Original assignee: 国立大学法人東京工業大学
Priority date: 2018-02-07
Filing date: 2019-01-31
Publication date: 2019-08-15

Abstract

Provided are the following: an atomic layer sheet which has boron and oxygen as framework elements, in which a network is formed by non-equilibrium binding having a boron-boron bonds, and in which the molar ratio of oxygen and boron (oxygen/boron) is less than 1.5; a layered sheet that includes a plurality of the atomic layer sheets and metal ions between the sheets; and a thermotropic liquid crystal and lyotropic liquid crystal containing these. Also provided is a method for producing an atomic layer sheet and/or layered sheet containing boron and oxygen, the method including a step for preparing a solution by adding MBH₄ (M denotes an alkali metal ion) to an organic solvent-containing solvent in an inert gas atmosphere and a step for exposing the solution to an oxygen-containing atmosphere.

Description

Boron atomic layer sheet, laminated sheet, method for producing the same, and liquid crystal

The present invention relates to a boron atom layer sheet, a laminate sheet, a method for producing the same, and a liquid crystal.

Nanostructures with precisely controlled structures such as one-dimensional nanotubes and nanowires, two-dimensional layered materials and nanosheets, three-dimensional porous materials, and dendrimers exhibit various functions and physical properties by utilizing space and shape. To do.

Of these, graphene, an atomic layer material of carbon, was found in 2004 that it has excellent physical properties such as mechanical strength, thermal conductivity, and electrical conductivity, and can be obtained by attaching graphite to Scotch tape and peeling it off. Therefore, applied research has progressed. For example, graphene analogs have been studied from the viewpoint of modification of graphene and change of constituent elements.

From the viewpoint of changing the constituent elements, boron nitride (BN), silicene (Si), germanene (Ge), borophene (B) and the like are known. Borophene are boron monolayer nanosheets, Wang et al., Performs the synthesis of B ₃₆ clusters of 36 atoms by gas-phase vacuum system, by identifying the structure from a comparison of simulation by photoelectron spectra and theoretical calculations, borophene similar The synthesis of clusters was reported (Non-patent Document 1). After that, borophene as a sheet that spreads in two dimensions instead of a unit structure has been described by Guisinger et al. (Non-Patent Document 2) and Wu et al. (Non-Patent Document 3). Synthesis by vacuum deposition of boron on top has been reported. This borophene is a substance that cannot exist in the atmosphere. Borophane, on the other hand, is a boron single-layer nanosheet protected with hydrogen at the end, and the speed and mechanical strength of Dirac particles are expected to exceed that of graphene, and theoretical calculations have predicted that they can exist in the atmosphere. Its synthesis was reported (Non-Patent Document 4).

The liquid crystal materials used in all displays are very important functional materials that support modern society. A liquid crystal is a state of a substance that exhibits intermediate properties between crystals and liquids. It is characterized by having liquid-like fluidity while having a long-period orientation of molecules such as crystals, and a phase that appears at a temperature intermediate between the crystalline state at low temperature and the liquid crystal state at high temperature. is there. Since the discovery of the first liquid crystal state in organic molecules in 1888, the physical and chemical properties have been elucidated and the functions have been explored.

In order for such a liquid crystal state to be manifested, it is necessary to have an anisotropic site for aligning the directions and a site for producing fluidity in the molecule. General liquid crystal molecules have a rigid site containing a benzene ring and a terminal alkyl chain in the structure. Thereby, while the rigid part by a benzene ring orientates each other, since an alkyl chain shows fluidity | liquidity, long-period orientation of molecules like a crystal | crystallization and fluidity | liquidity like a liquid express simultaneously.

The liquid crystal that appears between the crystal and the liquid due to the temperature change is called a thermotropic liquid crystal. The thermotropic liquid crystal is characterized by having various liquid crystal phases depending on temperature. Even in the same liquid crystal molecule, a state called a smectic phase having a higher degree of orientation and regularity is obtained at a low temperature near the crystallization temperature, and a nematic phase having a lower degree of orientation is often obtained at a high temperature side near the transition temperature to the liquid. The liquid crystal phase formed by such liquid crystal molecules varies greatly depending on the structure and shape of the molecules. In addition, in the liquid crystal molecules having a chirality in the structure and the banana-type liquid crystal molecules having no asymmetric carbon, a chiral phase in which the molecules are aligned while spiraling appears.

All of the liquid crystal phases described above are for rod-like molecules having a one-dimensional anisotropy in the rigid part, but the liquid crystal phase is also formed by stacking disk-like molecules by planar molecules such as phthalocyanine and triphenylene introduced with an alkyl chain. To express. Thus, in the thermotropic liquid crystal, various liquid crystal phases can be expressed by utilizing the one-dimensional or two-dimensional anisotropy of the molecule.

On the other hand, not only changes in liquid crystal due to temperature, but also a liquid crystal phase called lyotropic liquid crystal that appears in solution. The lyotropic liquid crystal is a liquid crystal phase mainly found in a surfactant having a hydrophobic site due to an alkyl chain and an ionic hydrophilic site in the structure. Surfactant molecules in an aqueous solution form various micelle structures by self-assembly due to a hydrophobic effect or the like, and form a long-period structure particularly at a high concentration. This is a state in which molecules are periodically arranged like a crystal while being dissolved in a solution, and it is considered to be a liquid crystal and has been widely studied. Unlike the thermotropic liquid crystal, in which the phase change depends only on temperature, the lyotropic liquid crystal is characterized in that the phase change strongly depends on the concentration of liquid crystal molecules because it is in solution.

Most of the existing thermotropic liquid crystals are completely organic molecules, but there are cases where they are combined with inorganic compounds. This is a liquid crystal molecule in which an inorganic unit is introduced at a rigid site in the molecule. A liquid crystal molecule having a metal complex as a small one and a cluster or metal nanoparticle as an inorganic domain as a large one has been synthesized (Non-patent Documents 5 to 5). 7).

However, all liquid crystals having an inorganic domain always contain an alkyl chain in the structure. This is because the soft alkyl chain is almost melted in the liquid crystal state and serves as a solvent for dissolving the rigid portion in the liquid crystal. Therefore, even if the rigid part can be constructed with inorganic units, the alkyl chain that generates fluidity cannot be substituted, and there has been no report on a thermotropic liquid crystal composed entirely of inorganic compounds.

In thermotropic liquid crystals, there are no reports of completely inorganic liquid crystals, but in lyotropic liquid crystals, in 2001, Gabriel et al. Reported completely inorganic liquid crystals based on layered phosphates (Non-patent Document 8). The authors pay attention to the strong two-dimensional anisotropy of nanosheets in inorganic layered materials, and by dispersing phosphoric acid nanosheets peeled off from layered phosphates in water, the lyotropic liquid crystallinity is expressed in the dispersion. I found. The liquid crystallinity of the phosphoric acid nanosheet was confirmed by observing an interference color due to birefringence based on a long-period structure even when in a dispersion state when the dispersion liquid was observed under a polarizing microscope. Further, it has been confirmed that the change in the liquid crystal phase depends on the concentration of the nanosheet in the dispersion, as in the case of the lyotropic liquid crystal by the surfactant molecule.

Triggered by this discovery, attention was drawn to the possibility of liquid crystal expression of inorganic nanosheets, and a field called inorganic nanosheet liquid crystals developed (Non-patent Document 9). Such inorganic nanosheet liquid crystals have been reported for ionic layered materials such as metal oxides and clay minerals, which have already been established for exfoliation in dispersions. There are reports on nanosheets such as graphene (Non-Patent Document 10) and graphene oxide (Non-Patent Document 11) that are difficult to peel in solution.

In the above background, the following invention is provided based on the knowledge that a novel boron atom layer sheet and laminated sheet that have never been obtained.
[1A] An atomic layer sheet having a molar ratio of oxygen to boron (oxygen / boron) of less than 1.5, networked by non-equilibrium bonds having boron and oxygen as skeleton elements and having a boron-boron bond.
[2A] The atomic layer sheet of [1A], further containing alkali metal ions, wherein the molar ratio of alkali metal ions to boron (alkali metal ions / boron) is less than 1.
[3A] An atomic layer sheet of [1A] or [2A] that is an oxidation product of MBH ₄ (M represents an alkali metal ion).
[4A] The atomic layer sheet according to any one of [1A] to [3A], wherein the skeleton composition is B ₅ O ₃ .
[5A] The atomic layer sheet of [4A], wherein the skeleton has a three-fold symmetry having a boron-boron bond.
[6A] The atomic layer sheet according to [4A] or [5A], including the component X that is the skeleton part and the other component Y.
[7A] The atomic layer sheet of [6A], wherein the component Y is a terminal site and / or a defective site.
[8A] The atomic layer sheet of [6A] or [7A], wherein the constituent element Y is a boron oxide moiety containing B—OH.
[9A] In X-ray photoelectron spectroscopy, any one of [6A] to [8A] having peaks derived from B-1s levels at 190.5 to 193.0 eV and 192.5 to 194.0 eV, respectively Atomic layer sheet.
[10A] The atomic layer sheet of [9A], wherein a peak of 190.5 to 193.0 eV corresponds to the component X in the X-ray photoelectron spectroscopy measurement.
[11A] in IR measurement, having two peaks derived from BO stretch around 1300 ~ 1500 cm ^-1, and a peak derived from BO-H stretching in the vicinity of 3100cm ^-1 [6A] ~ [ 10A].
[12A] The atomic layer sheet according to [11A], wherein, in the IR measurement, a peak on the low wavenumber side of two types of peaks derived from BO stretching corresponds to the component X.
[13A] A laminated sheet comprising a plurality of atomic layer sheets of any one of [1A] to [12A] and metal ions between the atomic layer sheets.
[14A] The laminated sheet of [13A], wherein the metal ion is an alkali metal ion.
[15A] The laminated sheet of [14A], wherein the molar ratio of alkali metal ions to boron (alkali metal ions / boron) is less than 1.
[16A] A crystal comprising the laminated sheet of any one of [13A] to [15A].
[17A] A step of preparing a solution by adding MBH ₄ (M represents an alkali metal ion) in an inert gas atmosphere in a solvent containing an organic solvent, and a step of exposing the solution to an atmosphere containing oxygen A method for producing an atomic layer sheet and / or a laminated sheet containing boron and oxygen.
[18A] The atomic layer sheet has boron and oxygen as skeleton elements and is networked by a nonequilibrium bond having a boron-boron bond, and the molar ratio of oxygen to boron (oxygen / boron) is less than 1.5. The method according to [17A], wherein the laminated sheet includes a plurality of the atomic layer sheets and metal ions between the atomic layer sheets.
[19A] The method according to [18A], wherein the metal ions are alkali metal ions, and the molar ratio of alkali metal ions to boron (alkali metal ions / boron) is less than 1.
[20A] including a step of adding any one of the laminated sheets of [13A] to [15A] and at least one selected from crown ether and cryptand to a solvent containing an organic solvent, and peeling the laminated sheet. The manufacturing method of the peeling material of a lamination sheet.
[21A] A method for producing a peeled product of a laminated sheet, comprising a step of adding the laminated sheet of any one of [13A] to [15A] to an aprotic highly polar solvent and peeling the laminated sheet.
[22A] The method according to [20A] or [21A], wherein the exfoliated material includes a single-layer atomic layer sheet.

The boron atomic layer sheet and laminated sheet of the present invention can be expected to be applied to various industries due to the structural features disclosed below. The bottom-up synthesis of boron atomic layer materials, liquid-phase synthesis at atmospheric pressure, and stability in the atmosphere are characteristic findings compared to conventional technologies. And can be monolayered by chemical dissolution methods. By applying a physical force to the crystal, a sheet material having a thickness corresponding to a single layer can be obtained on the substrate. The layered single crystal is not soluble in a general aprotic organic solvent, but is dissolved by the addition of cryptand or crown ether that traps metal ions between layers. In a state where metal ions are dissolved, it is presumed that the boron sheet is also dispersed in the solution as a single layer.

Moreover, the following invention is provided based on the knowledge that novel boron atom layer sheets and laminated sheets that have never been obtained can be obtained, and further exhibit liquid crystallinity.
[1B] An atomic layer sheet having boron and oxygen as skeleton elements and networked by a nonequilibrium bond having a boron-boron bond and having a molar ratio of oxygen to boron (oxygen / boron) of less than 1.5 Including thermotropic liquid crystal.
[2B] The thermotropic liquid crystal according to [1B], including a laminated sheet containing metal ions between the plurality of atomic layer sheets.
[3B] The thermotropic liquid crystal according to [2B], wherein the metal ions are alkali metal ions, and the laminated sheet has a molar ratio of alkali metal ions to boron (alkali metal ions / boron) of less than 1.
[4B] The thermotropic liquid crystal according to any one of [1B] to [3B], which maintains a liquid crystal state in a temperature range of at least −196 to 350 ° C.
[5B] The thermotropic liquid crystal according to any one of [1B] to [4B], which can control a reversible phase transition with respect to temperature between the liquid crystal phase I on the high temperature side and the liquid crystal phase II on the low temperature side.
[6B] The thermotropic liquid crystal according to any one of [1B] to [5B], wherein the atomic layer sheet is an oxidation product of MBH ₄ (M represents an alkali metal ion).
[7B] The thermotropic liquid crystal according to any one of [1B] to [6B], wherein the atomic layer sheet has a skeleton composition of B ₅ O ₃ .
[8B] The thermotropic liquid crystal according to [7B], wherein the skeleton of the atomic layer sheet has a three-fold symmetry having a boron-boron bond.
[9B] The thermotropic liquid crystal according to [7B] or [8B], wherein the atomic layer sheet includes the component X as the skeleton portion and the component Y other than the component X.
[10B] The thermotropic liquid crystal according to [9B], wherein the component Y is a terminal site and / or a defect site.
[11B] The thermotropic liquid crystal according to [9B] or [10B], wherein the constituent element Y is a boron oxide portion containing B ₂ O ₃ units.
[12B] A method for producing a thermotropic liquid crystal according to any one of [1B] to [11B], wherein the oxygen has a skeleton element containing boron and oxygen and is networked by a nonequilibrium bond having a boron-boron bond Of a thermotropic liquid crystal comprising a step of heating a crystal including a laminated sheet containing metal ions between a plurality of atomic layer sheets having a molar ratio of oxygen and boron (oxygen / boron) of less than 1.5 to 100 ° C. or higher Method.
[13B] The method for producing a thermotropic liquid crystal according to [12B], wherein the distance between the atomic layer sheets is increased by the heating.
[14B] The method for producing a thermotropic liquid crystal according to [12B] or [13B], in which a dehydration condensation reaction between B—OH at a terminal site and / or a defect site of the atomic layer sheet proceeds by the heating.
[15B] An atomic layer sheet having boron and oxygen as skeleton elements and networked by a nonequilibrium bond having a boron-boron bond and having a molar ratio of oxygen to boron (oxygen / boron) of less than 1.5 Including lyotropic liquid crystal.
[16B] The lyotropic liquid crystal according to [15B], including a laminated sheet containing metal ions between the plurality of atomic layer sheets.
[17B] The lyotropic liquid crystal according to [15B] or [16B], wherein the metal ions are alkali metal ions, and the laminated sheet has a molar ratio of alkali metal ions to boron (alkali metal ions / boron) of less than 1.
[18B] The lyotropic liquid crystal according to any one of [15B] to [17B], wherein the atomic layer sheet has a skeleton composition of B ₅ O ₃ .
[19B] The lyotropic liquid crystal according to [18B], wherein the skeleton of the atomic layer sheet has a three-fold symmetry having a boron-boron bond.
[20B] The lyotropic liquid crystal according to [18B] or [19B], wherein the atomic layer sheet includes the component X that is the skeleton portion and the other component Y.
[21B] The lyotropic liquid crystal according to [20B], wherein the component Y is a terminal site and / or a defect site.
[22B] The lyotropic liquid crystal according to [20B] or [21B], wherein the component Y is a boron oxide portion containing B—OH.
[23B] A composition comprising a solvent and the lyotropic liquid crystal according to any one of [15B] to [22B] in the solvent.
[24B] The composition of [23B], wherein the solvent is N, N-dimethylformamide.

The bottom-up synthesis and liquid phase synthesis of boron atomic layer materials, such as the above boron atomic layer sheet and laminated sheet, and being stable in the atmosphere are characteristic findings in comparison with the prior art, The boron layered crystal changes to a liquid crystal by heating. Such changes to liquid crystals by heat alone have never been seen with inorganic compounds, and the first inorganic-free liquid crystals have been achieved with complete inorganic compounds. The change from boron layered crystal to boron liquid crystal is an irreversible change accompanied by chemical change, but since the reversible phase transition with respect to the temperature between liquid crystal phases was shown, boron liquid crystal is the first completely solvent-free liquid crystal. Not only was the first thermotropic liquid crystal proved. The temperature range in which the boron liquid crystal can maintain the liquid crystal phase is from at least −50 ° C. on the low temperature side to at least 350 ° C. on the high temperature side. Looking at the liquid crystal temperature range of a general organic liquid crystal, for example, the most famous 5CB used for a display is 23 to 37 ° C., and the others are generally about 10 to 30 ° C. On the other hand, there exists a thing exceeding 100 degreeC in a fairly wide thing. On the other hand, the liquid crystal temperature range of boron liquid crystal is about 400 ° C., and the liquid crystal phase can be maintained in a very wide temperature range that cannot be realized by existing organic liquid crystals. Such extremely high stability of the boron liquid crystal is considered to be manifested by the two-dimensional strong anisotropy of the boron sheet, and is considered to be derived from the structure unique to the inorganic compound having a nanosheet. . Due to these characteristics, industrial applications are expected in various technical fields such as display optical elements, electronic devices, and external field response elements.

Boron atom layer sheets and laminated sheets are dispersed in a solvent at an appropriate concentration due to their extremely strong anisotropy, whereby the sheets are aligned and lyotropic liquid crystallinity is exhibited. Because of these characteristics, liquid crystallinity and properties unique to inorganic compounds are utilized in various technical fields, such as external field response, compounding with polymer materials, synthesis of microfibers, and use in high-efficiency photocatalysts. Industrial use is expected.

It is a photograph of the acicular crystal synthesize | combined in the Example. It is the figure which showed the structure of the boron layered crystal by X-ray structure analysis, (a) is a layered cross section, (b) and (c) show a planar crystal structure. It is the figure which showed the structure of the boron layered crystal by X-ray structural analysis, (a) is the estimation structure of the unit cell of a boron atom layer, (b) is the estimation structure of the unit cell of a terminal and a defect | deletion part, (c) is The distance between the BB bond and the BO bond is shown. It is an IR spectrum of boron layered crystal (upper) and B (OH) ₃ (lower). It is an XPS spectrum of (a) boron layered crystal and (b) B ₂ O ₃ and KBH ₄ . (A) is a plane index analysis in the X-ray single crystal structure analysis, and (b) is an XRD pattern of the boron layered crystal in the capillary. (A) UV-visible absorption spectrum and (b) near-infrared absorption spectrum of boron layered crystals, B (OH) ₃ and B ₂ O ₃ . (A) is the SEM image of a boron layered crystal, (b) is the SEM image of the nanosheet peeled from the boron layered crystal by mechanical pressure. It is an AFM image of the nanosheet peeled from the boron layered crystal. It is an AFM image and height profile of the nanosheet peeled from the boron layered crystal. It is an AFM image of the nanosheet which melt | dissolved the boron layered crystal with crown ether, and was cast to the HOPG board | substrate. It is the (a) STEM image and (b) high-resolution TEM image of the nanosheet peeled from the boron layered crystal. It is a high-resolution TEM image of the lattice pattern of the nanosheet peeled from the boron layered crystal. (A) is a phase transition process from a crystal of a boron layered crystal to a liquid crystal during heating from 50 ° C. to 120 ° C., and (b) is a polarization microscope of a shape change of the boron layered crystal during cooling from 120 ° C. to 35 ° C. It is a statue. (A) Boron layer crystal and (b) TG curve of B (OH) ₃ and (c) IR spectrum of boron layer crystal and boron liquid crystal. (A) shows an XPS spectrum of a boron layered crystal and boron liquid crystal, and (b) shows a mechanism considered as a change from the crystal to the liquid crystal. (A) is a TG curve and a DTG curve of a boron layered crystal, and (b) is a DSC curve of the boron crystal under argon and a vacuum atmosphere (in a capillary). (A) is a change of IR spectrum of boron liquid crystal in 2 hours, and (b) is a TG-DTA curve of boron liquid crystal during the cooling process in the atmosphere. It is a SEM image of the boron liquid crystal after solidification. It is the TEM image (upper) of the nanosheet of boron liquid crystal, and the lattice pattern (lower) of the nanosheet. 2 is a DSC curve of boron crystals under vacuum in a glass capillary. It is a polarization microscope image of boron liquid crystal during a phase transition from liquid crystal phase I to liquid crystal phase II (left) and during a reversible phase transition between liquid crystal phase I and liquid crystal phase II (right). (A) Polarization microscope image of boron liquid crystal at room temperature and (b) an enlarged image thereof. It is a XRD pattern of boron layered crystal (simulation) and boron liquid crystal of liquid crystal phase II. It is the TG curve (left) of the boron liquid crystal at high temperature, and the photograph (left) of the sample before and after processing. (A) is a polarization microscope image of the boron liquid crystal during the cooling process from 20 ° C. to −38.5 ° C., and (b) is a DSC curve of the boron liquid crystal under argon conditions. (A) Polarized microscopic images before (left) and after (right) immersion of boron liquid crystal in liquid nitrogen for 1 minute and 12 hours, (b) Polarized microscopic images of rapidly cooled boron liquid crystal and its phase change. It is. It is the optical microscope image (left) of the dissolved boron layered crystal, and the measurement result (right) of the solubility of the boron layered crystal in various solvents. (A) is formation of a lyotropic liquid crystal in DMF, (b) is an optical microscope image showing the DMF volatilization process and crystal formation of the lyotropic liquid crystal. It is a SEM image of the crystal | crystallization deposited after DMF volatilization. It is an AFM image of the boron nanosheet peeled off by dissolution in DMF.

The present invention is described in detail below.
1. Boron atomic layer sheet and laminated sheet In the present invention, the “atomic layer sheet” is a sheet of a monoatomic layer containing boron and oxygen as main constituent atoms. Also included are single-layer sheets that exist as constituent elements, metal-ion-containing single-layer sheets in which metal ions that maintain charge balance are bound to independent single-layer sheets, and the like. In the present specification, it is also expressed as a boron atomic layer sheet, a nanosheet or the like. The “laminated sheet” is a layered material including the atomic layer sheet and metal ions between the atomic layer sheets, and is also referred to as a boron layered crystal in this specification.

Borofene is a sheet-like substance made of boron alone, but its structure and stability are discussed by the ratio of the triangular lattice made by boron and the hexagonal holes made of sp ² boron. The reason why the triangular lattice exists is that boron simple substances and clusters generally form a stable structure with the triangular lattice formed by multi-center coupling as a unit unit. In the present invention, “networked by a nonequilibrium bond having a boron-boron bond” represents a two-dimensional bonding mode in accordance with the conventional bonding mode discussion in boron-containing atomic layer sheets such as borophene. Is.
(Atomic layer sheet)
The atomic layer sheet of the present invention has boron and oxygen as skeleton elements and is networked by a nonequilibrium bond having a boron-boron bond, and the molar ratio of oxygen to boron (oxygen / boron) is less than 1.5. . In a certain aspect, it further contains an alkali metal ion, and the molar ratio of the alkali metal ion to boron (alkali metal ion / boron) is less than 1. These specifications are based on the case where the atomic layer sheet is an oxidation product of MBH ₄ (M represents an alkali metal ion), and conventional boric acid has only a boron-oxygen bond and is polymerized (polymerized). ) Is considered to be three-dimensional and not an atomic layer sheet. The molar ratio of oxygen to boron (oxygen / boron) may be 1.2 or less, 1.0 or less, or 0.8 or less. Moreover, it may be 0.1 or more and 0.3 or more. The molar ratio of alkali metal ions to boron (alkali metal ions / boron) may be 0.8 or less, 0.6 or less, or 0.4 or less. Moreover, it may be 0.01 or more, 0.05 or more, 0.1 or more.

As an example of the atomic layer sheet of the present invention as described above, an atomic layer sheet having a skeleton composition of B ₅ O ₃ will be described.
<Atomic layer sheet composition is _B 5 _{O 3>}
In the above, the “skeleton” of the atomic layer sheet has a regular structure as shown in FIGS. 2 (b) and 2 (c) and FIGS. 3 (a) and 3 (c) whose composition is B ₅ O ₃ . It is a part and mainly occupies a sheet part other than the terminal part and the defect part.

This atomic layer sheet has a skeletal composition of B ₅ O ₃ . 2 (b) and 2 (c) and FIGS. 3 (a) and 3 (c), it is an atomic layer composed of boron and oxygen, and bonded to form a hexagon in which boron bonded to oxygen is distorted. However, it forms a two-dimensional flat surface.

Boron atoms are classified into those that occupy hexagonal vertices and those that occupy each side of the hexagon in the crystal unit structure. Those that occupy each side of the hexagon are alternately positioned inside and outside the side. Therefore, the skeleton has a three-fold symmetry of a boron-boron bond.

Oxygen atoms occupy one of two sides of two boron atoms adjacent to three boron atoms on each side of the hexagon formed by boron atoms (FIGS. 2B and 2C). 3 (a) and (c), oxygen atoms are shown in two places for convenience, but the occupation ratio is 0.5 as shown in FIG. 2 (c).

The boron-boron bond distance is between 1.6 mm and 1.9 mm, and the value by X-ray structural analysis is 1.784 mm. This bond distance is close to the average value of the distance between the two types of boron-boron bonds present in borophene, and is an intermediate value between the value reported as a single bond and the value reported as an oxygen bridge.

The boron-oxygen bond distance is 1.339 mm for boron located at the hexagonal side and 1.420 mm for boron located at the apex of the hexagon, as determined by X-ray structural analysis.

This atomic layer sheet includes a component X that is a skeleton part and a component Y other than that. In typical embodiments, component Y is a terminal site and / or a defect site.

In a typical embodiment, component Y is a boron oxide moiety that includes B—OH. The component Y is a site whose structure is similar to trivalent B ₂ O ₃ or B (OH) ₃ (FIG. 3B), and the bonding state of B—O is different from the skeleton site. According to the identification by the measurement of the boron layered crystal including the atomic layer sheet, it is as follows.

In the IR measurement (infrared absorption spectrum), it has has two peaks derived from BO stretch around 1300 ~ 1500 cm ^-1, and a peak derived from BO-H stretching in the vicinity of 3100 cm ^-1. Of the two types of peaks derived from BO stretching, the peak on the low wavenumber side corresponds to the component X. Specifically, among the peaks in the BO region, the peak on the low wavenumber side (near 1350 cm ⁻¹ ) corresponds to the boron sheet of component X, and the BO stretching peak seen in B (OH) ₃ The peak on the high wavenumber side (1420 cm ⁻¹ vicinity) whose position is similar corresponds to the component Y. The peak derived from BO—H stretching in the vicinity of 3100 cm ⁻¹ also corresponds to the component Y.

In X-ray photoelectron spectroscopic measurement, peaks derived from the B-1s level are observed at 190.5 to 193.0 eV and 192.5 to 194.0 eV, respectively. The peak of 190.5 to 193.0 eV corresponds to component X. Specifically, the peak corresponding to the component X is slightly lower energy than B ₂ O ₃ (193.3 eV) in which boron is in a trivalent state. Is not progressing. The peak corresponding to the component X can be separated into two components, and each of the two types of boron in the boron sheet of the component X, that is, one that occupies the vertex of a hexagon in the crystal unit structure, and each side of the hexagon It corresponds to what occupies. The peak at 192.5 to 194.0 eV on the most oxidized side coincides with B ₂ O ₃ having trivalent boron and corresponds to the component Y.

Absorption in the ultraviolet region of 250 nm or less in the ultraviolet-visible absorption spectrum, and absorption including a band derived from the vibration structure of BO or BO—H in the near infrared region of 1000 to 2500 nm in the near infrared absorption spectrum. have.

As described above, in this atomic layer sheet, the constituent element X which is a skeleton part has a composition of B ₅ O ₃ , and the constituent element Y which is a boron oxide part containing B—OH has a trivalent B Similar to ₂ O ₃ and B (OH) ₃ . In this atomic layer sheet, the molar ratio of oxygen and boron (oxygen / boron) in the entire sheet including these components X and Y is less than 1.5, 1.2 or less, 1.0 or less. Good. Moreover, it is 0.6 or more and may be 0.7 or more.
(Laminated sheet)
The laminated sheet of the present invention includes a plurality of atomic layer sheets as described above and metal ions between the atomic layer sheets. The atomic layer sheet is as described above, and has a skeleton element containing boron and oxygen, networked by a nonequilibrium bond having a boron-boron bond, and a molar ratio of oxygen to boron (oxygen / boron). Is less than 1.5. The crystal of the present invention includes this laminated sheet.

In the laminated sheet of the present invention, examples of the metal ions between the atomic layer sheets include alkali metal ions and alkaline earth metal ions. Examples of alkali metal ions include lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, and the like. Examples of the alkaline earth metal ions include beryllium ions, magnesium ions, calcium ions, strontium ions, barium ions, and the like. Among these, alkali metal ions, particularly potassium ions are a preferred embodiment. The molar ratio of alkali metal ions to boron (alkali metal ions / boron) is less than 1.

In the case of an atomic layer sheet having a skeleton composition of B ₅ O ₃ , FIG. 2A is referred to as an example of a laminated sheet. This laminated sheet has a layered structure in which atomic layer sheets containing boron and oxygen as main atoms and metal ions are alternately laminated. In a typical embodiment, the metal ions are located inside the hexagonal shape of boron atoms in the unit structure of the atomic layer sheet in the lamination plane. The crystal is obtained as a rod-shaped single crystal in the manufacturing method described later. In a typical embodiment including this needle-like single crystal, the crystal elongation direction coincides with the c-axis direction that is the lamination direction, and the atomic layer sheets are laminated along the elongation direction. The laminated sheet (and crystal) has a weak interlayer bond, and can be easily cleaved in a direction perpendicular to the c-axis direction (extension direction) by applying mechanical pressure. For example, the crystal can be cleaved by pressing the HOPG substrate against the crystal from above, and it can be observed that the nanosheets of crystal pieces attached to the surface are stacked.
(Manufacturing method of peeled sheet of laminated sheet)
The laminated sheet (and crystal) of the present invention can be peeled off by adding this laminated sheet and at least one selected from crown ether and cryptand into a solvent containing an organic solvent. Since the laminated sheet of the present invention is laminated by an ionic interaction between an anionic boron sheet and a cationic metal ion, unlike graphite laminated by van der Waals force, at least selected from crown ether and cryptand By capturing the metal ions between the layers with one kind, the metal ions are eluted in the organic solvent, and the laminated sheet can be peeled while maintaining the sheet structure.

The peeled material includes a single atomic layer sheet. For example, by bringing the solution obtained by the above method into contact with a HOPG substrate and removing the solvent, the crystal pieces attached to the HOPG surface can be observed as a single layer sheet or a nanosheet close thereto.

In the above method, the organic solvent is not particularly limited. For example, aprotic medium polar solvents (nitriles such as acetonitrile and propionitrile, halogenated compounds such as dichloromethane, dichloroethane, chloroform (trichloromethane), and carbon tetrachloride. Hydrocarbons, diethyl ether, tetrahydrofuran, 1,4-dioxane, ethers such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ketones such as acetone, 2-butanone, methyl ethyl ketone, isobutyl methyl ketone, diisobutyl ketone, and cyclohexanone , Ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, methyl decanoate, methyl laurate, dii adipate Preferably contains esters) butyl, and the like.

In addition to these aprotic medium polar solvents, aprotic highly polar solvents (N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, sulfolane, dihexamethyl phosphate triamide that are compatible with them) 1,3-dimethyl-2-imidazolidinone, N, N′-dimethylpropyleneurea, 1-methyl-2-pyrrolidinone, etc.), aprotic low polarity solvents (aromatic hydrocarbons such as benzene, toluene, xylene, etc.) , Aliphatic hydrocarbons such as pentane, hexane, cyclohexane, and octane), protic solvents (methanol, ethanol, 2-propanol, 1-butanol, 1,1-dimethyl-1-ethanol, hexanol, decanol, etc.) Alcohols, carboxylic acids such as formic acid and acetic acid, nitromethane, etc.) Or a solvent. Further, the solvent containing an organic solvent may contain water.

In the above method, the crown ether is a macrocyclic ether represented by (—CH ₂ —CH ₂ —O—) _n , for example, 12-crown-4, 15-crown-5, 18-crown-6 , Dibenzo-18-crown-6, diaza-18-crown-6 and the like. The cryptand is a cage-like multidentate ligand composed of two or more rings, and examples thereof include [2.2.2] cryptand.

The addition amount of at least one selected from crown ether and cryptand is not particularly limited, but an excess amount with respect to the laminated sheet is preferable.

The laminated sheet (and crystals) of the present invention can also be peeled off by dissolving in an aprotic highly polar solvent. By bringing the obtained solution into contact with the HOPG substrate and removing the solvent, the crystal pieces attached to the HOPG surface can be observed as a single layer sheet or a nanosheet close thereto. Examples of the aprotic highly polar solvent include N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, sulfolane, dihexamethylphosphoric triamide, 1,3-dimethyl-2-imidazolidinone, N , N′-dimethylpropyleneurea, 1-methyl-2-pyrrolidinone and the like.
(Atomic layer sheet, laminated sheet manufacturing method)
The atomic layer sheet and / or laminated sheet containing boron and oxygen, such as the atomic layer sheet and laminated sheet of the present invention, is prepared by, for example, MBH ₄ (M is an alkali) in an inert gas atmosphere in a solvent containing an organic solvent. A metal ion.) Can be added to prepare a solution, and this solution can be produced by exposure to an atmosphere containing oxygen. In the step of exposing to an atmosphere containing oxygen, crystals of an atomic layer sheet or a laminated sheet can be grown.

Examples of the alkali metal ions M of MBH ₄ include alkali metal ions and alkaline earth metal ions. Among these, potassium ion is a preferred embodiment.

The concentration of MBH ₄ is not particularly limited, but is preferably 0.5 to 10 mM, more preferably 1 to 2 mM.

The inert gas is not particularly limited as long as it does not have reactivity with MBH _4, and examples thereof include rare gases such as argon, nitrogen and the like. For example, in an environment that can block atmospheric oxygen such as a glove box, the solution is replaced with an inert gas that is not reactive with MBH ₄ and MBH ₄ is added to a solvent containing an organic solvent. Prepare.

The organic solvent is not particularly limited. For example, aprotic medium polar solvents (nitriles such as acetonitrile and propionitrile, halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform (trichloromethane), carbon tetrachloride, Ethers such as diethyl ether, tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ketones such as acetone, 2-butanone, methyl ethyl ketone, isobutyl methyl ketone, diisobutyl ketone, cyclohexanone, ethyl acetate , Butyl acetate, propylene glycol monomethyl ether acetate, methyl decanoate, methyl laurate, diisobutyl adipate, etc. Preferably includes a class, etc.). In addition to these aprotic medium polar solvents, aprotic highly polar solvents (N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, sulfolane, dihexamethyl phosphate triamide that are compatible with them) 1,3-dimethyl-2-imidazolidinone, N, N′-dimethylpropyleneurea, 1-methyl-2-pyrrolidinone, etc.), aprotic low polarity solvents (aromatic hydrocarbons such as benzene, toluene, xylene, etc.) , Aliphatic hydrocarbons such as pentane, hexane, cyclohexane, and octane), protic solvents (methanol, ethanol, 2-propanol, 1-butanol, 1,1-dimethyl-1-ethanol, hexanol, decanol, etc.) Alcohol, carboxylic acids such as formic acid and acetic acid, nitromethane, etc.) It may be a solvent. Further, the solvent containing an organic solvent may contain water.

Although the atmosphere containing oxygen is not particularly limited, it is a preferable aspect to release it to the atmosphere.

¡After exposure to an atmosphere containing oxygen, heating may be performed once. The heating temperature is not particularly limited, but 30 to 40 ° C. is preferable. The heating time is preferably 30 minutes to 2 hours.

After exposure to an atmosphere containing oxygen, it is preferable to stand still in the atmosphere. The temperature and time of exposure to the oxygen-containing atmosphere are not particularly limited. However, from the viewpoint of sufficiently growing the crystal, the temperature is preferably room temperature (15 to 25 ° C.) after the heating, and the time is 3 days to One month is preferred.

The atomic layer sheet and the laminated sheet of the present invention can be expected to be used for a thermotropic liquid crystal that is a heating product and various other industries.
2. Thermotropic liquid crystal The thermotropic liquid crystal of the present invention includes the atomic layer sheet described above. A typical embodiment includes a laminated sheet containing metal ions between a plurality of atomic layer sheets. Details regarding the atomic layer sheet, the laminated sheet, the metal ions, and the like in the thermotropic liquid crystal of the present invention are as described above, and a description thereof is omitted.

According to the thermotropic liquid crystal of the present invention, the solidified product formed by opening to the atmosphere and standing is observed by SEM, the plate-like domains are aligned to form spirals, and the boron sheet is aligned concentrically in the liquid crystal. It is thought that. From TEM observation, it is considered that the sheet is a very thin sheet such as a single layer, two layers, or four to five layers.

The thermotropic liquid crystal of the present invention can control a reversible phase transition with respect to temperature between the liquid crystal phase I on the high temperature side and the liquid crystal phase II on the low temperature side. The transition of the liquid crystal phases I and II is reversible with temperature and accompanied by endothermic heat generation. The temperature of the phase transition is not limited, but the transition from the liquid crystal phase II to the liquid crystal phase I is observed, for example, in the vicinity of 145 to 155 ° C. during the temperature rising process, and the transition from the liquid crystal phase I to the liquid crystal phase II is In the case of passing through the supercooled state, the temperature can be lower, but for example, it is observed at around 50 to 60 ° C. in the cooling process. Compared with the liquid crystal phase I in which the interference color is visible only at the peripheral edge of the liquid crystal, the liquid crystal phase II that exhibits the interference color on the entire liquid crystal is considered to be in a higher degree of orientation. In the thermotropic liquid crystal of the present invention, both the liquid crystal phase I and the liquid crystal phase II have fluidity like a liquid but exhibit an interference color like a crystal under a polarizing microscope.

The thermotropic liquid crystal of the present invention can be obtained by heating a crystal containing a laminated sheet containing metal ions between a plurality of atomic layer sheets to 100 ° C. or higher. The heating temperature may be 105 ° C. or higher, 110 ° C. or higher, or 120 ° C. or higher, and the upper limit is not particularly limited as long as it does not exceed the temperature at which the liquid crystal is thermally decomposed.

The obtained liquid crystal becomes irreversible with respect to the heating temperature. That is, once the temperature of the crystal is raised to change to a liquid crystal, even if it is cooled, it does not transition to the crystal again, and the liquid crystal state is maintained. This orientation of the liquid crystal is generated from the two-dimensional strong anisotropy of the boron sheet, and the fluidity is considered to be manifested by the weak interlayer bonding.

The thermotropic liquid crystal of the present invention maintains a liquid crystal state in a temperature range of at least −196 to 350 ° C. When heated from room temperature, it showed a stable interference color of liquid crystal phase I up to 350 ° C. When the cooling process of liquid crystal phase II to -50 ° C was measured by DSC under argon, other than the phase transition between liquid crystal phases I and II No peak is observed on the low temperature side. From this, it is considered that the transition point from the liquid crystal to the crystal exists on the lower temperature side than −50 ° C. Further, even when the boron liquid crystal is immersed in liquid nitrogen (−196 ° C.), no change is observed in the liquid crystal structure.

When the thermotropic liquid crystal of the present invention is produced by heating the crystal to 100 ° C. or higher, the heating increases the distance between the atomic layer sheets. The boron sheet structure of the liquid crystal phase II includes (001), (101), and (111) peaks containing a component in the c-axis direction, which is the stacking direction, as shown in FIG. According to the measurement results to be described later, the (001) plane spacing indicating the layer spacing is 3.47 mm in the crystalline state, whereas it is 3.54 mm in the liquid crystal phase II, which is about 0. It has expanded by 1cm. That is, the liquid crystal phase II is in a state where only the stacking direction is expanded while maintaining the alignment order in the in-plane direction of the boron sheet, and it is considered that the fluidity of the liquid crystal is caused by the expansion in the interlayer direction.

In the thermotropic liquid crystal of the present invention, when the skeleton composition of the atomic layer sheet is B ₅ O ₃ , the atomic layer sheet includes the component X that is the skeleton portion and the other component Y. The component X is as described above, and a detailed description thereof is omitted.

The component Y is as follows. The change from the boron layered crystal to the boron liquid crystal due to the heating at 100 ° C. or higher is not a thermal phase transition observed in a general organic liquid crystal but a change accompanied by a chemical change. Specifically, B (OH) ₃ undergoes dehydration condensation between B—OH at the end of the boron sheet and at the defect site where B (OH) ₃ undergoes dehydration condensation and changes to B ₂ O ₃ . According to the IR measurement, the peak derived from the terminal site BO—H, which was observed in the vicinity of 3100 cm ^{−1 in the} boron layered crystal, disappears after changing to the liquid crystal. According to XPS measurement, the peak corresponding to boron in a highly oxidized state derived from the terminal / defect site, which was observed in the crystal, is relatively decreased as compared with the peak on the low energy side. B (OH) ₃ is a molecule having a perfect planar structure, but takes a three-dimensional tetrahedral structure by dehydrating condensation and changing to B ₂ O ₃ . Therefore, it is considered that B (OH) _x on the plane of the boron sheet end / deletion site also causes a three-dimensional structural change by dehydration condensation with the adjacent end in the sheet. It is considered that fluidity is generated between the sheets and liquid crystallinity is developed by the change of the end and the defect that breaks the lamination of the sheets. The reason why the transition from the liquid crystal to the crystal is not observed even after cooling the boron layered crystal once it is liquid crystallized is that the dehydration condensation between B—OH that produces a liquid crystal state is irreversible.
3. Lyotropic liquid crystal The lyotropic liquid crystal of the present invention includes the atomic layer sheet described above. A typical embodiment includes a laminated sheet containing metal ions between a plurality of atomic layer sheets. Details regarding the atomic layer sheet, the laminated sheet, the metal ions, and the like in the lyotropic liquid crystal of the present invention are as described above, and the description thereof is omitted.

The lyotropic liquid crystal of the present invention can be obtained by dissolving a crystal containing a laminated sheet in a solvent. For example, when the solvent is volatilized after being dissolved in the solvent, the solution has fluidity but exhibits an interference color like crystals and a hemispherical liquid crystal phase appears. This liquid crystal phase has an interference color along the periphery of the droplet, and when observed with a polarizing microscope, a dark color portion appears in the vertical cross direction along the direction of the two polarizing plates. It is thought to be derived from the orientation of the boron sheet.

The lyotropic liquid crystal of the present invention can be prepared as a composition comprising a solvent and a lyotropic liquid crystal in the solvent. Although it does not specifically limit as a solvent, The solvent containing an organic solvent and the solvent containing an aprotic highly polar solvent are preferable among these. Examples of the aprotic highly polar solvent include N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, sulfolane, dihexamethylphosphoric triamide, 1,3-dimethyl-2-imidazolidinone, N , N′-dimethylpropyleneurea, 1-methyl-2-pyrrolidinone and the like. Among these, N, N-dimethylformamide is a preferred solvent.

Other solvents include, but are not limited to, aprotic medium polar solvents (nitriles such as acetonitrile and propionitrile, halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform (trichloromethane), and carbon tetrachloride. , Diethyl ether, tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and other ethers, acetone, 2-butanone, methyl ethyl ketone, isobutyl methyl ketone, diisobutyl ketone, cyclohexanone and other ketones, acetic acid Ethyl, butyl acetate, propylene glycol monomethyl ether acetate, methyl decanoate, methyl laurate, diisobutyl adipate, etc. Tellurium), aprotic low polarity solvents (aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as pentane, hexane, cyclohexane and octane), protic solvents (methanol, ethanol, Examples thereof include alcohols such as 2-propanol, 1-butanol, 1,1-dimethyl-1-ethanol, hexanol and decanol, carboxylic acids such as formic acid and acetic acid, nitromethane and the like, and water. These solvents are preferably used in a form compatible with them together with an aprotic highly polar solvent.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
1. 1. Boron layer single crystal 1-1. Crystal Synthesis In a glove box under an argon gas atmosphere, a MeOH solution (5.0 mg / mL) of KBH ₄ was added in a solvent of CHCl ₃ : MeCN = 1: 1. The concentration of KBH ₄ was 1.4 mM.

After the obtained solution was released to the atmosphere, it was heated at 40 ° C. for 1 hour. Then, it left still at room temperature for 2 weeks.

After standing, formation of needle-like crystals having a maximum length of about 2 cm was confirmed (FIG. 1).
1-2. Single crystal X-ray structural analysis The single crystal X-ray structural analysis of the obtained acicular crystal was performed.

As a result of performing single crystal XRD measurement and analyzing the structure, a layered structure in which atomic layers composed of boron and oxygen and potassium ions are alternately stacked was obtained (FIG. 2A). In the layer of boron and oxygen, it was found that an atomic layer sheet that spreads in a two-dimensional form is formed while the boron bonded to oxygen is bonded to form a distorted hexagon (FIG. 2B). (C)). It was also found that this boron atomic layer is a perfect plane with no distortion.

Occupancy rate is 1 for K, B at the hexagonal apex is 1, B on the side of the hexagon is 0.635, and O is 0.5. O is considered to occupy one of the two positions on each side of the hexagon formed by B (FIG. 2 (c)). The composition was determined in consideration of the presence of the terminal portion in the boron sheet (FIGS. 3A and 3B described later).

The boron-boron bond distance of 1.784 km was close to the average value of the two types of boron-boron bond distances (1.876 mm, 1.614 mm) present in borophene. In addition, BB in the crystal is intermediate between a single bond of 1.61Z (Z. Anorg. Allg. Chem. 2017,3643, 517) and oxygen bridge of 1.824Å (Inorg. Chem. 2015, 54, 2910). (Fig. 3 (c)).

Since the bonding state of B—O is expected to be different between the boron sheet and its terminal / defect site, an attempt was made to evaluate the bonding state in the boron layered crystal by IR measurement (FIG. 4). As a result, two types of peaks were obtained in the vicinity of 1300 to 1500 cm ⁻¹ where B—O stretching was observed (FIG. 4). Among the peaks in the BO region, the broad peak on the high wavenumber side (1420 cm ⁻¹ ) is similar in position to the BO stretching peak seen in B (OH) ₃ , so the BO region Of these two types of peaks, it is considered that the peak on the high energy side is derived from the terminal / defect site, and the sharp peak on the low wave number side (1350 cm ⁻¹ ) is derived from the boron sheet. Further, since a peak derived from BO—H stretching was observed in the vicinity of 3100 cm ⁻¹ , it was found that a B—OH bond was present at the terminal site. From the above, it was suggested that a boron atom layer sheet and the existence of B (OH) ₃ -like sites as the ends and defects in the boron layered crystal were suggested.
1-3. Evaluation of oxidation state by XPS measurement and quantification of terminal site XPS measurement was performed to evaluate the oxidation state of boron (FIG. 5). As a result of the measurement, the peak of B 1s appears at 185.6 eV in the raw material KBH ₄ , whereas the peak top shifts to about 6 eV on the high energy side in the boron layered crystal, and boron accompanying the formation of the crystal Oxidation was suggested (FIGS. 5 (a) and (b)). On the other hand, when compared with B ₂ O ₃ (193.3 eV) in which B is in a trivalent state, it was found that complete oxidation up to trivalent did not proceed since it was on the slightly lower energy side (see FIG. 5 (a), (b)).

Furthermore, it was found that the broad peak of the obtained boron layered crystal can be separated into three components (FIG. 5 (a)). As a result of peak separation, it was found that peak 3 on the most oxidized side coincided with B ₂ O ₃ having trivalent boron, and peaks 1 and 2 were located on the reducing side more than that. Therefore, it is considered that peak 3 corresponds to a B (OH) ₃ similar end site, and peaks 1 and 2 correspond to two types of boron in the boron sheet, respectively. As a result of calculating the abundance ratio between the boron sheet and the terminal site from the area ratio of these peaks, it was found that the unit cell ratio was 3.1: 1.0.

From the single crystal X-ray structural analysis, as a result of performing the surface indexing of the boron layered crystal, it can be seen that the elongation direction of the crystal is coincident with the c-axis direction which is the stacking direction. It turned out that it has laminated | stacked (FIG. 6 (a)).

The elongation direction of the crystal can also be confirmed from powder XRD measurement. The powder XRD measurement of the boron layered crystal in the capillary was performed, and the obtained diffraction pattern was compared with the simulation of the diffraction pattern calculated from the crystal structure (FIG. 6B). Since the boron layered crystal has a rod-like shape, it is oriented in the capillary so that the extending direction of the crystal is parallel to the tube. Since the X-rays are incident on the rotating capillary from the vertical direction, it is expected that almost no diffraction lines in the crystal elongation direction are observed. As a result of the measurement, the diffraction peak of the surface including only the a and b axis components such as (100), (110), and (200) was observed at the diffraction angle that coincided with the simulation, while the peak including the c axis component was Almost no appearance was observed, and only a very weak diffraction peak of (001) which was a layer interval was observed. From this, it was confirmed that the stacking direction coincided with the elongation direction of the crystal, and it was found that the rod-shaped crystal was formed by stacking the boron atom layers.
1-4. Absorption spectrum of boron layered crystal The absorption spectrum of the boron layered crystal was measured (FIG. 7). Using a solid diffuse reflection cell, a diffuse reflection spectrum was measured in a crystalline state, and an absorption spectrum was obtained by performing Kubelka-Munk conversion. As a result of the measurement, absorption was observed in the ultraviolet region of 250 nm or less (FIG. 7A). As a result of calculating the band gap from this absorption edge, it was found that the boron layered crystal is a semiconductor having a band gap of about 5.4 eV.

As a result of spectrum measurement in the long wavelength region, it was found that the boron layered crystal has absorption in the near infrared region of 1000 to 2500 nm (4000 to 10,000 cm ⁻¹ ) (FIG. 7B). In the near-infrared region, B ₂ O ₃ and B (OH) ₃ are also absorbed at a wavelength different from that of the boron layered crystal, so these are absorptions derived from the vibrational structure of BO and OH. it is conceivable that.
1-5. Shape observation by SEM and mechanical properties of boron layered crystal As a result of FE-SEM observation to investigate the shape of the boron layered single crystal in more detail, it was confirmed that the crystal was a hexagonal rod shape (FIG. 8). (A)). When the side surface portion of the rod is enlarged, it can be observed that the layered structure develops along the crystal extension direction, and it is found that the single crystal stripe pattern is derived from the layered structure.

It was found that the boron layered crystal can be easily cleaved in the direction perpendicular to the extension direction by applying mechanical pressure with a spatula or the like. As a result of observing the cleaved crystal with SEM, it was confirmed that the nanosheet was partially generated due to the collapse of the layer structure (FIG. 8B). In some cases, a very smooth nanosheet surface of micron order was observed. Such ease of mechanical peeling suggested that the interlayer bonding of the boron layered crystal was very weak.
1-6. Nanosheet observation by AFM Since it was found that nanosheets were easily generated by mechanical peeling of boron layered crystals, the surface of the nanosheet was observed by AFM (FIGS. 9 and 10). The crystal was cleaved by pressing the HOPG substrate against the boron layered crystal from above, and the crystal piece adhering to the surface was directly observed by AFM (FIG. 9A). Although there were many parts where the nanosheets were distorted and not completely horizontal, we observed that some of the nanosheets were stacked almost horizontally (FIG. 9B). Since the phase was clearly different between the sheet portion and the underlying HOPG portion, it was determined to be a boron sheet. As a result of actually measuring the height of the sheet with the smallest thickness of the shape image, it was found that the thickness was about 2.0 nm on average although the sheet was not completely flat and varied. (FIG. 10). From the above, it is considered that these sheets are very thin sheets of about a single layer to several layers. As a result of the AFM observation, a plurality of laminated sheets were confirmed, and a single layer sheet having a height of about 0.9 nm was successfully observed at the thinnest portion. It is correlated with the fact that the height of the single-layer graphene by AFM measurement is 0.8 nm (Science, 2004, 306, 666.). .

Next, dissolution and monolayering of boron layered crystals with crown ether and cryptand were attempted. The crystals were dispersed in a solvent of CHCl ₃ : MeCN = 1: 1, and 18-crown-6 or cryptand was added to dissolve the boron layered single crystal. This solution was cast on a HOPG substrate and washed with chloroform to remove excess 18-crown-6 or cryptand. Attempts were made to observe single-layer sheets. In AFM, crystal fragments attached to the surface are observed with AFM, and a nanosheet with a height of about 0.9 nm, which seems to be a single-layer sheet, is observed on the HOPG substrate (Fig. 11 18-Crown-6 is used). The sheet was successfully observed about 0.7 nm in height. These results suggest the achievement of monolayer formation of boron layered crystals by crown ether or the like.
1-7. Nanosheet observation by TEM The shape and surface of the nanosheet were also observed by TEM observation. It is the same as the preparation method of the AFM sample. The crystal is cleaved by pressing a TEM grid with a micromesh from the top of the boron layered crystal, and the sheet adhering to the grid surface is observed with TEM (FIG. 12 (a): STEM). Image, FIG. 12 (b) and FIG. 13: high resolution TEM image). As a result, the laminated structure of the sheet and the nanosheet were directly observed in the STEM (FIG. 12A), and a very thin sheet having a lower contrast than the grid mesh was successfully observed in the high resolution TEM (FIG. 12B). . It was confirmed that the thinnest sheet in the observation location was about 15 layers.

Furthermore, the lattice was successfully observed by observing these sheets at a high magnification (FIG. 13). Hexagonal diffraction points were obtained from the surface of some sheets, and the same hexagonal symmetry as the boron sheet was observed. In some cases, a lattice with an interval of 0.343 nm was also observed. This coincides with the 0.347 nm spacing between the boron layered crystals, which indicates that the atomic layer stack was actually measured. From these facts, it was proved that peeling to a very thin nanosheet was possible by mechanical peeling, and it was shown that the interlayer interaction of boron layered crystals was weak.
2. 2. Liquidation of boron layered crystals by heat and its characteristics 2-1. Liquidation of boron layered crystals by heat The change to liquid crystals can be confirmed by observation with a polarizing microscope. A liquid crystal is a state that exhibits interference color like a crystal under a polarizing microscope while having fluidity like a liquid. In order to cut off the influence of oxygen and water, the crystal was vacuum sealed in a capillary, and changes in morphology and interference color during the heating process were observed using a polarizing microscope with a heating stage.

As a result of slowly heating from 50 ° C. to 120 ° C. at a heating rate of 5 ° C./min or less, it was observed that the rod-like boron layered crystal began to melt from around 105 ° C. and the shape started to change into a liquid state (FIG. 14). (A)). Although the shape is liquid, an interference color is seen at the peripheral edge thereof, which indicates that the boron crystal is changed to liquid crystal instead of liquid.

Furthermore, as a result of observing the process of heating to 120 ° C. and then cooling to 35 ° C. at 5 ° C./min, it was observed that the shape of the liquid crystal gradually changed to a circular shape (FIG. 14B). Although the interference color is always present at the peripheral edge, the shape is fluidly changed, so that it is understood that the liquid crystal is in the cooling process. From this, it was found that after the temperature of the crystal was once raised and changed to a liquid crystal, it was not transferred again to the crystal even when cooled to 35 ° C., and the liquid crystal state was maintained. The orientation of this liquid crystal is produced from the strong two-dimensional anisotropy of the boron sheet, and the fluidity is considered to be manifested by the weak interlayer bonding. The reason why the dark portion of the cross is visible at the peripheral edge is that the optical axis of the liquid crystal domain is aligned along the direction of the orthogonal polarizing plate, and the polarized light is transmitted without interference. Therefore, it is considered that the boron sheets are aligned concentrically in the liquid crystal.

We tried to observe the change from boron layered crystal to boron liquid crystal by thermal analysis. As a result of the TG measurement of the boron layered crystal under argon, a weight loss of about 19% was observed at about 100 to 120 ° C. in which the change to the liquid crystal was confirmed by the polarization microscope observation (FIG. 15 (a)). . From this, it was found that the change from the boron layered crystal to the boron liquid crystal is not a thermal phase transition observed in a general organic liquid crystal but a change accompanied by a chemical change. Further, this weight reduction temperature is similar to the temperature at which B (OH) ₃ is dehydrated and condensed to change to B ₂ O ₃ (FIG. 15 (b)). It was suggested that this was accompanied by dehydration condensation between B-OH at the sheet end and the defect site.

In order to confirm whether dehydration condensation between B—OH at the terminal and defect sites of the boron sheet has progressed with the transition from the crystal to the liquid crystal, an attempt was made to observe BO—H stretching by IR measurement. As a result of measuring after changing to liquid crystal by heating at about 120 ° C. under vacuum, the peak derived from the terminal site BO—H, which was seen in the vicinity of 3100 cm ^{−1 in the} boron layered crystal, disappears after the change to liquid crystal. It was found (FIG. 15 (c)). From this, it was shown that dehydration condensation proceeds between B-OH at the terminal and defect sites with the change from boron layered crystal to boron liquid crystal.

Furthermore, by XPS measurement, the oxidation state of boron before and after liquid crystal formation was compared. Boron crystals were converted into liquid crystals on a HOPG substrate and measured. As a result, it was found that the peak corresponding to the highly oxidized boron derived from the terminal / defect site, which was observed in the crystal, was relatively decreased compared to the peak on the low energy side (FIG. 16 ( a)). From this, it was confirmed that the liquid crystallizing process is accompanied by a structural change of the B (OH) ₃ site at the terminal / defect site.

The mechanism of liquid crystal formation was considered from the fact that it changed to liquid crystal with dehydration condensation between B-OH at the boron sheet end and defect site. B (OH) ₃ is a molecule having a perfect planar structure, but takes a three-dimensional tetrahedral structure by dehydrating condensation and changing to B ₂ O ₃ . Therefore, it is considered that B (OH) _x on the plane of the boron sheet end / deletion site also causes a three-dimensional structural change by dehydration condensation with the adjacent end in the sheet. It is considered that fluidity is generated between the sheets due to changes in the ends and defects so as to break the lamination of the sheets, and liquid crystallinity is expressed (FIG. 16B). Even if the boron layered crystal is once liquid crystallized and then cooled to 35 ° C, the transition from liquid crystal to crystal is not observed because of the irreversible dehydration condensation between B and OH that produces a liquid crystal state. It is done.

The weight loss of about 19% in the vicinity of the liquid crystallizing temperature observed in the TG measurement is a value more than 5 times when it is assumed that all the boron sheet ends and defect sites are dehydrated and condensed. It can also be seen that the decrease starts from the low temperature side even compared with the dehydration temperature of B (OH) ₃ . In order to elucidate this weight loss, a differential curve was created for the weight loss of TG near 100 ° C. As a result, it can be separated into two stages of weight loss: a broad decrease from around 75 ° C and a sharp decrease around 125 ° C. Okay (Figure 17 (a)). Since the decrease on the high temperature side corresponds to the dehydration condensation temperature of B (OH) ₃ , the decrease of about 3% on the high temperature side corresponds to the dehydration condensation between B—OH at the end of the boron sheet. It is thought that the decrease of about 16% is due to the desorption of the adsorption solvent such as H ₂ O.

Measured heat flow around the liquid crystalization temperature by DSC measurement. The crystal was placed directly on an Al pan and measured under argon. As a result, two endothermic peaks overlapped at about 110 ° C and about 125 ° C in the vicinity of the liquid crystallizing temperature in the first round of heating. (FIG. 17B). On the other hand, as a result of measuring by placing the crystal in an Al pan with the vacuum sealed tube, two endothermic peaks were obtained, but no change in position was observed at the 125 ° C. peak on the high temperature side. On the other hand, the peak on the low temperature side decreased in intensity and shifted to a low temperature around 75 ° C. From this, the peak on the high temperature side where the temperature does not change even under vacuum corresponds to the dehydration condensation between the sheet end B-OH, and the peak on the low temperature side where the intensity decreased and shifted to low temperature under vacuum originated from desorption of adsorbed water It was suggested to do.

The results of DTG and DSC measurements suggested that the boron crystals and liquid crystals were hygroscopic, so water adsorption was monitored from IR and TG-DTA. Boron layered crystals were heated to about 150 ° C. under vacuum to form liquid crystals, and the time course of IR after opening to the atmosphere was measured. As a result, the intensity of the peak derived from the O—H stretching of H ₂ O of about 3400 cm ⁻¹ increases with the passage of 5 minutes, 1 hour, and 2 hours from the first measurement after liquid crystallization. A state was observed (FIG. 18A). From this, it was shown that boron liquid crystal has hygroscopicity.

Further, in order to quantify the amount of water adsorbed on the liquid crystal, the change in mass after liquidification and release to the atmosphere was measured by TG-DTA. As a result, a mass increase of about 21% was observed from about 40 ° C. or less (FIG. 18B). When combined with the IR measurement results, it can be seen that this corresponds to the adsorption of H ₂ O. It can also be seen that this amount of adsorption is almost consistent with the weight loss in the crystals. From the above, it is suggested that the boron liquid crystal has hygroscopicity, and that the first stage of weight reduction in the TG measurement seen above corresponds to the desorption of adsorbed water, and the second stage is between B-OH. It was found to correspond to the dehydration condensation.
2-2. SEM and TEM observation When a boron liquid crystal is observed with a polarizing microscope, it looks like a droplet having a particularly intense interference color at the periphery. By observing this liquid crystal with an SEM, an attempt was made to observe the liquid crystal structure and domain. However, as a result of SEM observation, the hemispherical liquid crystal was successfully observed, but the inside of the liquid crystal moved vigorously due to its fluidity, and the domain and structure could not be directly observed. Further, the liquid crystal did not solidify even when irradiated with an electron beam for a long time.

On the other hand, it was found that boron liquid crystal can stably maintain a liquid crystal phase under vacuum, but solidifies when released to the atmosphere. This is thought to be due to structural changes due to oxidation or water. Since direct observation in the liquid crystal state was not possible, the shape after solidification was observed.

Boron crystals were converted into liquid crystal on HOPG, and then exposed to the atmosphere overnight to solidify, and then observed with SEM. As a result, it was observed that the plate-like domains were oriented to form a spiral (FIG. 19). A plate-like domain stands on the inner side and sleeps on the outer side. When locally expanded, it was also possible to observe that the plate-like flakes were oriented in one direction. From this, it is thought that it solidified, maintaining the orientation in a liquid crystal state. Moreover, this plate-like flake is considered to be formed of a boron sheet.

Furthermore, in order to observe a finer shape, TEM measurement was performed. The crystals were crystallized by heating on a grid under vacuum, and observed after being allowed to solidify in the atmosphere for several days. As a result, a very thin sheet similar to that obtained when the boron crystals were peeled was observed (FIG. 20). Furthermore, the observation of the grating on the surface of this sheet was successful, and hexagonal diffraction spots with a grating interval of 0.20 nm were observed. This coincides with the symmetry in the in-plane direction of the boron sheet, and also coincides with the interval (0.20 nm) of the (200) plane, so it is considered that the boron sheet is directly observed. From this, it was shown that the sheet structure was maintained even after the liquid crystal formation. Further, depending on the sheet to be observed, it was found that there were one set of hexagonal diffraction points, two sets, and four to five sets. This is a phenomenon observed in graphene, and it is considered that the number of sheets to be laminated becomes the number of hexagonal groups and appears at the diffraction point because the stacking of sheets shifts from layer to layer. From this, it was found that the sheets in which the lattice was observed were very thin sheets of single layer, two layers, and 4 to 5 layers, respectively.
2-3. Thermotropic characteristics of boron inorganic liquid crystal The phase transition behavior of two liquid crystal phases of boron liquid crystal could be confirmed by DSC. As a result of DSC measurement of boron liquid crystal sealed in a capillary with a cooling / heating rate of 5 ° C./min, it was derived from the transition from liquid crystal phase I to liquid crystal phase II during the first round of cooling. A sharp exothermic peak was obtained (FIG. 21). Furthermore, a broad endothermic peak derived from the transition from the liquid crystal phase II to the liquid crystal phase I was obtained at about 150 ° C. during the second temperature increase process. The reason why the exothermic peak in the cooling process is sharper on the lower temperature side than the endothermic peak in the temperature raising process is considered to be due to the transition from the liquid crystal phase I to II via the supercooled state. From the above, thermal phase transition behavior was observed between liquid crystal phases I and II in boron liquid crystals.

The transition between liquid crystal phases observed by DSC measurement can be confirmed with a polarizing microscope using a temperature variable stage. When the crystal was vacuum sealed in a capillary and heated to 200 ° C. while observing with a polarizing microscope, a phenomenon of changing to liquid crystal phase I was observed (FIG. 22 left). This is a liquid crystal phase exhibiting an interference color only at the peripheral edge as seen above. As a result of observing the process of cooling this liquid crystal phase II at a rate of 10 ° C./min, an interference color appears on the whole at about 57 ° C., and a rainbow-colored interference color that is gradual as seen in organic liquid crystals appears on the entire liquid crystal. The transition to liquid crystal phase II shown was observed. This phase transition behavior is considered to correspond to the exothermic peak observed by DSC. Compared with the liquid crystal phase I in which the interference color is visible only at the peripheral edge of the liquid crystal, the liquid crystal phase II that exhibits the interference color on the entire liquid crystal is considered to be in a higher degree of orientation.

Furthermore, the reversibility of the transition between the liquid crystal phases was verified. As a result of cooling to room temperature after transitioning to liquid crystal phase II and raising the temperature again, it was found that the interference color of liquid crystal phase II began to disappear at around 140 ° C. and transitioned to liquid crystal phase I again (right side of FIG. 22). . This is considered to be a behavior corresponding to an endothermic peak in the DSC temperature rising process. As a result of recooling the liquid crystal phase I from 150 ° C., it was found that the liquid crystal phase I changed again to the liquid crystal phase II at about 54 ° C. From these, it was shown that the transition of liquid crystal phases I and II is reversible with respect to temperature.

In the cooling process of DSC, it was suggested that the change from liquid crystal phase I to II goes through a supercooled state. Therefore, the cooling rate was changed from 10 ° C./min to 20 ° C./min, and the change in the transition behavior from the liquid crystal phase I to II was observed with a polarizing microscope. As a result, the transition from liquid crystal phase I to II was observed at about 55 ° C. at 10 ° C./min, but the interference color of liquid crystal phase II began to appear only after cooling to room temperature at 20 ° C./min (FIG. 23 (a)). As a result of high-magnification observation, a liquid crystal domain of about several tens of micrometers, which is considerably smaller than that at 20 ° C./min, was observed. Further, it was found that this liquid crystal domain has a liquid crystal structure called a schlieren structure, which is characterized by a dark color portion extending in a cross shape from the center along the polarization direction of the two polarizing plates (FIG. 23B). The change in the transition temperature and the liquid crystal domain size of the liquid crystal phase II due to the cooling rate indicated that the phase transition from the liquid crystal phase I to II passed through the supercooled state.

In order to elucidate the structure of liquid crystal phase II, powder XRD measurement was performed at room temperature on boron liquid crystal sealed in a capillary in a vacuum. As a result, diffraction patterns (100), (110), and (200) corresponding to the boron layered crystals were obtained, and it was found that the liquid crystal phase II retained the boron sheet structure (FIG. 24). On the other hand, it was found that the peaks of (001), (101), and (111) including the component in the c-axis direction that is the stacking direction are shifted to the low angle side. It was found that the (001) plane spacing, which indicates the layer spacing, was 3.47 mm in the crystalline state, but 3.54 mm in the liquid crystal phase II, which was expanded by about 0.1 mm. From this, it was found that the liquid crystal phase II was in a state in which only the stacking direction was expanded while maintaining the alignment order in the in-plane direction of the boron sheet. It is considered that the fluidity of the liquid crystal is caused by the expansion in the interlayer direction.

The stability of liquid crystal phase I in the high temperature region was evaluated using a polarizing microscope. Boron liquid crystal sealed in a capillary tube was heated to verify how many times the liquid crystal interference color was retained. As a result of heating from room temperature, it was found that the interference color of liquid crystal phase I was stably exhibited up to 350 ° C. On the other hand, after exceeding 350 ° C., it was found that the interference color at the peripheral portion showed an unstable behavior in which blinking repeated, and the interference color disappeared completely from around 365 ° C. Once the interference color disappears, the interference sheet did not appear again even after cooling, so the boron sheet is probably decomposed.
From this, it was found that the maximum temperature at which the boron liquid crystal maintains the liquid crystal phase is 350 ° C. The reason why it does not become an isotropic liquid and keeps the liquid crystal phase until it decomposes is that the aligned state is very stable due to the strong two-dimensional anisotropy of the boron sheet that is the liquid crystal domain. Conceivable.

The decomposition behavior at 350 ° C. or higher can also be confirmed from TG. As a result of TG measurement under argon, a weight loss of about 12% was observed from around 350 ° C. (FIG. 25). The boron layered crystal, which is a white crystal before the measurement, has turned black after the measurement and has a shape that once melted and solidified again, suggesting that the weight loss at 350 ° C is due to thermal decomposition. It was done.

The stability of the boron liquid crystal in the low temperature region was evaluated by cooling the liquid crystal phase II under a polarizing microscope. In order to eliminate the possibility of supercooling, it was gradually cooled at a rate of 5 ° C./min or less using a cooling device, and an attempt was made to verify the temperature at which the liquid crystal phase II transitions to crystals. As a result of cooling from 20 ° C., the liquid crystal structure did not change even when cooled to the device limit temperature of −38.5 ° C. (FIG. 26A). From this, it was found that the liquid crystal phase can be stably maintained at least up to about −40 ° C.

Further, as a result of verifying the cooling process to −50 ° C. by DSC measurement under argon, no peak was observed on the low temperature side other than the phase transition between liquid crystal phases I and II (FIG. 26B). . From this, it is considered that the transition point from the liquid crystal to the crystal exists on the lower temperature side than −50 ° C.

From the above, it was found that since the boron liquid crystal is stable in a low temperature region, the transition point to the crystal cannot be observed by the polarization microscope observation using a cooling device. Therefore, crystallization was attempted by immersing boron liquid crystal in liquid nitrogen. Although the capillary was immersed in liquid nitrogen for 1 minute and overnight, no change was observed in the liquid crystal structure (FIG. 27 (a)). While the boron liquid crystal may be very stable in the low temperature range, it may be possible to transition to a glass state by quenching, but at least a transition to a crystal by cooling with liquid nitrogen was not observed.

Since the liquid crystal phase II may be very stable at low temperatures, the liquid crystal phase I was crystallized directly without going through the liquid crystal phase II by quenching from the liquid crystal phase I state. As a result of quenching from the state of the liquid crystal phase I at 200 ° C. to room temperature, it was found that a crystal phase in which numerous structures such as very sharp lines developed immediately after the quenching appeared (FIG. 27B). However, when standing at room temperature, the sharp lines of the crystal phase began to disappear gradually, and a change in the structure was observed. And 40 minutes after quenching, it turned out that it changed into the liquid crystal phase II completely. From the fact that the transition to the crystalline phase was visible, it was found that the boron liquid crystal can also be a crystal. And since it changed to the liquid crystal phase II gradually after changing to a crystal phase once, it turns out that the liquid crystal phase II is not a supercooled state at room temperature. Therefore, the high stability of liquid crystal phase II at room temperature was demonstrated.
3. 3. Atomic layering by dissolution and lyotropic liquid crystallinity 3-1. Solubility verification boron layered crystal of the boron layer crystal Unlike such as graphite to be stacked in the van der Waals forces, since the laminated by ionic interaction of an anionic boron sheets and potassium cations, the K ⁺ by highly polar solvent By elution, dissolution of the boron sheet can be expected while maintaining the sheet structure.

Thus, the solubility of boron layered crystals in various solvents was verified. 10 μL of each solvent was cast on boron crystals placed on a petri dish, and the dissolution process was observed with an optical microscope. As a result, it was confirmed that when a solvent having solubility was cast, the rod-like crystals gradually became smaller and finally completely dissolved and disappeared (FIG. 28). As a result of verifying the solubility in nine types of solvents, it was found that the compound was soluble in protic solvents such as H ₂ O, methanol, and ethanol and aprotic highly polar solvents such as DMF and DMSO.

In order to confirm the retention of the sheet structure after dissolution in the solvent, the absorption spectrum of the solution in which the boron crystals were dissolved was measured. As a result of measuring the absorption spectrum in the near-infrared region of the DMF solution, absorption corresponding to the spectrum obtained by solid diffuse reflection of the boron layered crystal was obtained. This suggested that the DMF solution retains the boron sheet structure even after dissolution.
3-2. Verification of lyotropic liquid crystallinity Boron layered crystals were completely dissolved in DMF on a HOPG substrate, and the process of volatilization of the solvent was observed with a polarizing microscope to verify the lyotropic liquid crystallinity of the boron layered crystals. The expression of liquid crystallinity can be confirmed by observation with a polarizing microscope. If the solution has fluidity but exhibits an interference color like a crystal, it can be said to be in a liquid crystal state. As a result, a transparent solution was obtained immediately after dissolution of the crystals, but the appearance of a hemispherical liquid crystal phase was observed in the process of volatilization of the solvent (FIG. 29 (a)). From this, it was shown that the boron layered crystal develops lyotropic liquid crystallinity like the existing inorganic layered crystal when dissolved in DMF.

This liquid crystal phase has an interference color along the peripheral edge of the droplet, and a dark color portion appears in the vertical cross direction along the direction of the two polarizing plates (FIG. 29B). This is thought to be a liquid crystal phase derived from the orientation of the boron sheet.If this liquid crystal phase is further allowed to stand and DMF volatilization proceeds, the interference color at the periphery of the liquid crystal gradually becomes weaker and finally becomes polycrystalline. Was found to produce.

The shape of the residual crystal after DMF volatilization was observed by SEM measurement. Successful direct observation of polycrystals observed with a polarizing microscope. As a result, a large amount of plate-like flakes of about 20 nm were observed, and it was found that the plate-like flakes were laminated to form a polycrystal (FIG. 30). When the flakes were partially enlarged, a layered structure in which sheets were laminated was observed. Thus, even after the boron layered crystals were dissolved in DMF, the sheets were not decomposed, indicating that the sheet structure was maintained.
3-3. Atomic layer separation by DMF dissolution Since DMF dissolution of boron layered crystals was shown, atomic layer separation was performed using this. Boron crystals were dissolved in DMF and cast on a HOPG substrate to try to apply a boron sheet to the substrate.

Boron layered crystal DMF solution was cast on a HOPG substrate and AFM observation was performed. Since DMF has a high boiling point, it was measured after drying for one week under vacuum after casting. As a result of AFM observation, a uniform atomic layer having a height of about 2 nm was successfully observed (FIG. 31). Although it is thicker than the thickness of the boron sheet predicted from the crystal structure (interlayer 0.35 nm), this is thought to be due to the offset of AFM and the adsorption of potassium ions and DMF on the layer surface.

Claims

An atomic layer sheet having a molar ratio of oxygen to boron (oxygen / boron) of less than 1.5, networked by non-equilibrium bonds having boron and oxygen as skeleton elements and having a boron-boron bond.
The atomic layer sheet according to claim 1, further comprising alkali metal ions, wherein the molar ratio of alkali metal ions to boron (alkali metal ions / boron) is less than 1.
The atomic layer sheet according to claim 1 or 2, which is an oxidation product of MBH 4 (M represents an alkali metal ion).
The atomic layer sheet according to any one of claims 1 to 3, wherein the skeleton composition is B 5 O 3 .
The atomic layer sheet according to claim 4, wherein the skeleton has a 3-fold symmetry having a boron-boron bond.
The atomic layer sheet according to claim 4 or 5, comprising the constituent element X which is the skeleton part and the other constituent element Y.
The atomic layer sheet according to claim 6, wherein the constituent element Y is a terminal site and / or a defective site.
The atomic layer sheet according to claim 6 or 7, wherein the constituent element Y is a boron oxide portion containing B-OH.
The atom according to any one of claims 6 to 8, which has peaks derived from B-1s levels at 190.5 to 193.0 eV and 192.5 to 194.0 eV, respectively, in X-ray photoelectron spectroscopy measurement. Layer sheet.
The atomic layer sheet according to claim 9, wherein a peak of 190.5 to 193.0 eV corresponds to the component X in the X-ray photoelectron spectroscopy measurement.
In the IR measurement, any one of claims 6 to 10 having has two peaks derived from BO stretch around 1300 ~ 1500 cm -1, and a peak derived from BO-H stretching in the vicinity of 3100 cm -1 The atomic layer sheet according to one item.
The atomic layer sheet according to claim 11, wherein, in the IR measurement, a peak on the low wavenumber side of the two types of peaks derived from BO stretching corresponds to the component X.
A laminated sheet comprising a plurality of atomic layer sheets according to any one of claims 1 to 12 and metal ions between the atomic layer sheets.
The laminated sheet according to claim 13, wherein the metal ions are alkali metal ions.
The laminated sheet according to claim 14, wherein the molar ratio of alkali metal ions to boron (alkali metal ions / boron) is less than 1.
A crystal comprising the laminated sheet according to any one of claims 13 to 15.
A step of preparing a solution by adding MBH 4 (M represents an alkali metal ion) in an inert gas atmosphere in a solvent containing an organic solvent;
A method for producing an atomic layer sheet and / or a laminated sheet containing boron and oxygen, comprising the step of exposing the solution to an atmosphere containing oxygen.
An atom having a molar ratio of oxygen to boron (oxygen / boron) of less than 1.5, wherein the atomic layer sheet is networked by non-equilibrium bonds having boron and oxygen as skeleton elements and having a boron-boron bond The method according to claim 17, wherein the laminated sheet includes a plurality of the atomic layer sheets and metal ions between the atomic layer sheets.
The method according to claim 18, wherein the metal ions are alkali metal ions, and the molar ratio of alkali metal ions to boron (alkali metal ions / boron) is less than 1.
Adding the laminate sheet according to any one of claims 13 to 15 and at least one selected from crown ether and cryptand to a solvent containing an organic solvent, and peeling the laminate sheet; A method for producing a peeled sheet of a laminated sheet.
A method for producing a peeled product of a laminated sheet, comprising the step of adding the laminated sheet according to any one of claims 13 to 15 to an aprotic highly polar solvent and peeling the laminated sheet.
The method according to claim 20 or 21, wherein the exfoliated material includes a single-layer atomic layer sheet.
A thermotropic liquid crystal comprising the atomic layer sheet according to claim 1.
The thermotropic liquid crystal according to claim 23, comprising a laminated sheet containing metal ions between the plurality of atomic layer sheets.
The thermotropic liquid crystal according to claim 24, wherein the metal ions are alkali metal ions, and the laminated sheet has a molar ratio of alkali metal ions to boron (alkali metal ions / boron) of less than 1.
The thermotropic liquid crystal according to any one of claims 23 to 25, which maintains a liquid crystal state in a temperature range of at least -196 to 350 ° C.
The thermotropic liquid crystal according to any one of claims 23 to 26, wherein a reversible phase transition with respect to temperature can be controlled between the liquid crystal phase I on the high temperature side and the liquid crystal phase II on the low temperature side.
The thermotropic liquid crystal according to any one of claims 23 to 27, wherein the atomic layer sheet is an oxidation product of MBH 4 (M represents an alkali metal ion).
The thermotropic liquid crystal according to any one of claims 23 to 28, wherein the atomic layer sheet has a skeleton composition of B 5 O 3 .
30. The thermotropic liquid crystal according to claim 29, wherein the skeleton of the atomic layer sheet has a three-fold symmetry having a boron-boron bond.
The thermotropic liquid crystal according to claim 29 or 30, wherein the atomic layer sheet includes a component X that is the skeleton portion and a component Y other than the component X.
32. The thermotropic liquid crystal according to claim 31, wherein the component Y is a terminal site and / or a defect site.
The thermotropic liquid crystal according to claim 31 or 32, wherein the constituent element Y is a boron oxide portion containing B 2 O 3 units.
A method for producing the thermotropic liquid crystal according to any one of claims 23 to 33,
Between atomic sheets with a molar ratio of oxygen to boron (oxygen / boron) of less than 1.5, networked by non-equilibrium bonds having boron and oxygen as skeletal elements and having a boron-boron bond The manufacturing method of thermotropic liquid crystal including the process of heating the crystal | crystallization containing the lamination sheet which includes a metal ion to 100 degreeC or more.
The method for producing a thermotropic liquid crystal according to claim 34, wherein the distance between the atomic layer sheets is increased by the heating.
36. The method for producing a thermotropic liquid crystal according to claim 34 or 35, wherein a dehydration condensation reaction between B—OH at a terminal site and / or a defect site of the atomic layer sheet proceeds by the heating.
A lyotropic liquid crystal comprising the atomic layer sheet according to claim 1.
The lyotropic liquid crystal according to claim 37, comprising a laminated sheet containing metal ions between the plurality of atomic layer sheets.
The lyotropic liquid crystal according to claim 37 or 38, wherein the metal ions are alkali metal ions, and the laminated sheet has a molar ratio of alkali metal ions to boron (alkali metal ions / boron) of less than 1.
The lyotropic liquid crystal according to any one of claims 37 to 39, wherein the atomic layer sheet has a skeleton composition of B 5 O 3 .
The lyotropic liquid crystal according to claim 40, wherein the skeleton of the atomic layer sheet has a three-fold symmetry having a boron-boron bond.
42. The lyotropic liquid crystal according to claim 40, wherein the atomic layer sheet includes a component X that is the skeleton part and a component Y other than the component X.
43. The lyotropic liquid crystal according to claim 42, wherein the component Y is a terminal site and / or a defective site.
44. The lyotropic liquid crystal according to claim 42, wherein the constituent element Y is a boron oxide portion containing B—OH.
A composition comprising a solvent and the lyotropic liquid crystal according to any one of claims 37 to 44 in the solvent.
46. The composition according to claim 45, wherein the solvent is N, N-dimethylformamide.