WO2016056661A1

WO2016056661A1 - Black phosphorus atom film, thermoelectric material, thermoelectric conversion element, and semiconductor element

Info

Publication number: WO2016056661A1
Application number: PCT/JP2015/078841
Authority: WO
Inventors: 貴博山本; 哲小鍋
Original assignee: 学校法人東京理科大学
Priority date: 2014-10-10
Filing date: 2015-10-09
Publication date: 2016-04-14
Also published as: JP2017214226A

Abstract

An embodiment of the present invention is a crystalline black phosphorus atom film stretched 2%–10% in the zigzag axial direction and/or the armchair axial direction, with a unit cell of an unstretched black phosphorus atom film as a reference.

Description

Black phosphorus atomic film, thermoelectric material, thermoelectric conversion element, and semiconductor element

The present invention relates to a black phosphorus atomic film, a thermoelectric material, a thermoelectric conversion element, and a semiconductor element.

Today, more than 60% of the consumed energy is released into the environment as waste heat, and it has been studied to use this waste heat energy effectively. In recent years, for example, thermoelectric conversion technology that converts thermal energy into electrical energy has been developed using a phenomenon called the Seebeck effect, which is a phenomenon in which a temperature difference of an object is directly converted into a voltage. ing.

As materials used for such thermoelectric conversion technology, for example, inorganic materials such as bismuth-tellurium-based materials have been known. However, inorganic materials have a very low mechanical strength and may have the disadvantage of being a fragile material, so their applications are limited. In addition, an inorganic material containing a rare element has a high cost and may be difficult to secure resources, and may be difficult to continuously manufacture. Therefore, a thermoelectric material that does not contain a rare element has been demanded.
On the other hand, as thermoelectric materials that do not contain rare elements, for example, carbon atom materials such as carbon nanotubes, and organic materials such as organic conductive polymer thin films are known. However, thermoelectric materials using these materials are not satisfactory because their thermoelectric conversion performance is not sufficient.

Recently, a monoatomic film of black phosphorus, which is a single light element, has attracted attention as a thermoelectric material that can replace these materials. A black phosphorus monoatomic film is composed of a phosphorus element. Phosphorus is a common element, which is advantageous in terms of securing resources. A study of using a black phosphorus monoatomic film as a thermoelectric material has just started (for example, Documents 1 and 2), and development of a higher performance black phosphorus monoatomic film is expected as a thermoelectric material.
Reference 1 Large thermoelectric power factors in black phosphorus and phosphorene, Hongyan Lv, Wenjian Lu, Dingfu Shao, and Yuping Sun, arXiv: 1404.5171
Reference 2 Enhanced Thermoelectric Efficiency via Orthogonal Electrical and Thermal Conductances in Phosphorene, Ruixiang Fei, Alireza Faghaninia, Ryan Soklaski, Jia-An Yan, Cynthia Lo, and Li Yang, arXiv: 1405.2836

The present invention has been made in view of the above circumstances, is useful for thermoelectric conversion materials, has excellent thermoelectric conversion performance, and has a stretched crystal structure that can modulate thermoelectric conversion performance according to the degree of stretching. The purpose is to provide.
It is another object of the present invention to provide a thermoelectric conversion material and a thermoelectric conversion element that have a high thermoelectric conversion output and can modulate thermoelectric conversion performance. Furthermore, it aims at providing a semiconductor element.

As a result of intensive studies, the present inventors have found that by extending the black phosphorus atomic film in a predetermined direction, the thermoelectric conversion performance can be improved, and the thermoelectric conversion performance can be modulated according to the degree of extension. The present embodiment has been completed.
That is, the means for solving the above-mentioned problems include, for example, the following aspects.

<1> A black phosphorus atomic film having a crystal structure that is stretched by 2% to 10% in at least one of the zigzag axis direction and the armchair axis direction with reference to the unit cell in the unstretched black phosphorus atomic film.

<2> The black phosphorus atomic film according to <1>, wherein the black phosphorus atomic film has holes.

<3> The black phosphorus atomic film according to <1> or <2>, wherein the black phosphorus atomic film is a monoatomic film.

<4> The black phosphorus atomic film according to <1> or <2>, wherein the black phosphorus atomic film is a multilayer atomic film.

<5> A thermoelectric material including the black phosphorus atom film according to any one of <1> to <4>.

<6> The thermoelectric material according to <5>, further including an unstretched black phosphorus atomic film.

<7> The doping amount in the black phosphorus monoatomic film having a crystal structure stretched in the zigzag axis direction is 0.0100 to 0.0700 (e / atom) as the number of carriers per phosphorus atom < The thermoelectric material according to 5> or <6>.

<8> The doping amount in the black phosphorus monoatomic film having a crystal structure extended in the armchair axial direction is 0.00280 to 0.00350 (e / atom) as the number of carriers per phosphorus atom. <5> The thermoelectric material according to <6>.

<9> The black phosphorus atomic film according to any one of <1> to <4>,
Electrodes,
An electrolyte material or a dielectric material disposed between the black phosphorus atomic film and the electrode;
A thermoelectric conversion element.

<10> The black phosphorus atomic film according to any one of <1> to <4>,
Electrodes,
A semiconductor device comprising:

According to an embodiment of the present invention, there is provided a black phosphorus atomic film that is useful for a thermoelectric conversion material, has excellent thermoelectric conversion performance, and has a stretched crystal structure that can modulate the thermoelectric conversion performance according to the degree of stretching. .
Moreover, according to embodiment of this invention, the thermoelectric conversion output is high, and the thermoelectric conversion material which can modulate thermoelectric conversion performance, and the thermoelectric conversion element are provided. Furthermore, a semiconductor device is provided.

FIG. 1A is a schematic diagram showing a crystal structure of a black phosphorus monoatomic film, and is a cross-sectional view of the crystal structure cut along the armchair axis direction. FIG. 1B is a schematic diagram showing a crystal structure of a black phosphorus monoatomic film, a cross-sectional view of the crystal structure cut along the zigzag axis direction; FIG. 1C is a schematic diagram showing the crystal structure of a black phosphorus monoatomic film, and is a plan view of the crystal structure of the black phosphorus monoatomic film. FIG. 2 is a schematic view showing an example of a thermoelectric conversion element using the black phosphorus monoatomic film of the present invention having a stretched crystal structure. FIG. 3 is a graph showing the power factor increase rate of the black phosphorus monoatomic film of the present invention having an extended crystal structure relative to an unstretched black phosphorus monoatomic film.

Hereinafter, an embodiment that is an example of the present invention will be described in detail. In the following description, embodiments of the present invention are collectively referred to as “the present invention”.

<Black phosphorus atomic film with stretched crystal structure>
The black phosphorus atomic film of the present invention having an extended crystal structure is 2% to 10% with respect to at least one of the zigzag axis direction and the armchair axis direction based on the unit cell in the unextended black phosphorus atomic film. An extended black phosphorus atomic film having an extended crystal structure (hereinafter, also referred to as “black phosphorus atomic film having an extended crystal structure”).

[Black phosphorus atomic film]
The black phosphorus atomic film is obtained from natural black phosphorus or synthesized black phosphorus. For example, silica sand and coke are added to ore containing apatite and the like, heated in an electric furnace at 1,300 ° C. to 1,400 ° C., distilled as steam, and then cooled to obtain yellow phosphorus. Then, the obtained yellow phosphorus is pressurized at, for example, about 12,000 atmospheres and heated at about 200 ° C. to obtain bulk black phosphorus.

The crystal structure of bulk black phosphorus is an orthorhombic layered structure. The method for obtaining the atomic film of black phosphorus is not particularly limited. For example, an atomic film of black phosphorus can be obtained by attaching a release member having an adhesive layer such as an adhesive tape and a base material layer to the surface of bulk black phosphorus and peeling the release member from black phosphorus. it can. This method is well known as a simple method. According to this method, a monoatomic film of black phosphorus can be obtained from bulk black phosphorus. In addition, a multilayer atomic film of black phosphorus having two or more layers can be obtained by this method. A monoatomic film or a multilayer atomic film of two or more layers of black phosphorus can be obtained, for example, by adjusting the peeling force when peeling the peeling member from bulk black phosphorus.

In this specification, “monoatomic film” refers to a single-layer atomic film. “Multilayer atomic film” refers to an atomic film having a structure of two or more layers. The multilayer atomic film is a concept that includes both a black phosphorus multilayer atomic film having two or more layers and a laminate in which monoatomic films are stacked. However, two or more layers of black phosphorus multilayer atomic films are distinguished from laminates of stacked black phosphorus monoatomic films in the following points. In the case of the former multilayer atomic film, the electronic states of the layers are mixed by van der Waals interaction between layers. On the other hand, in the case of the latter laminate, there is no hybridization of electronic states between layers due to van der Waals interaction, or hybridization of electronic states between layers is extremely small. That is, the interlayer strength generated by van der Waals force is different between the former multilayer atomic film and the latter laminate.

Even when the black phosphorus atomic film having the stretched crystal structure is a two or more black phosphorus multilayer atomic film, as in the case of the black phosphorus monoatomic film, with respect to at least one of the zigzag axis direction and the armchair axis direction, It is possible to stretch 2% to 10%.
In the case where the black phosphorus atomic film is a multilayer atomic film, a stress is required for stretching to the same stretching rate. Therefore, the number of layers of the multilayer atomic film is preferably 2 or more and 6 or less, and preferably 2 or more and 4 or less from the viewpoint of easy extension.

Moreover, the black phosphorus atomic film of the present invention (both monoatomic film and multilayer atomic film) may have an electron and may have a hole, but has a hole. It is preferable. For example, when a black phosphorus atomic film having holes is used as a material constituting a thermoelectric conversion element or a semiconductor element described later, stable performance can be exhibited. In addition, a black phosphorus atom film having holes is advantageous in that a state having holes is easily generated.

Hereinafter, as a black phosphorus atomic film having a stretched crystal structure, a black phosphorus monoatomic film having a stretched crystal structure will be described as an example.

[Black phosphorus monoatomic film with stretched crystal structure]
The black phosphorus monoatomic film peeled off from the bulk black phosphorus has a crystal structure as shown in FIGS. 1A to 1C. FIG. 1C is a plan view of the crystal structure of the black phosphorus monoatomic film. 1A is a cross-sectional view of the crystal structure cut along the armchair axis direction of FIG. 1C, and FIG. 1B is a cross-sectional view of the crystal structure cut along the zigzag axis direction of FIG. 1C.
1A to 1C, (z) represents an axial direction perpendicular to the armchair axial direction and the zigzag axial direction.
Here, in FIG. 1C, a region surrounded by the sides a and b is referred to as a unit cell in the crystal structure (hereinafter sometimes referred to as “unit cell”). The black phosphorus monoatomic film has two crystal axes. In the present invention, the crystal axis direction parallel to the direction along the a side is parallel to the zigzag direction and the direction along the b side. Such a crystal axis direction is referred to as an armchair direction.

Conventionally, bulk black phosphorus has poor flexibility and has been difficult to stretch. On the other hand, since the monoatomic film is a monolayer composed of monoatoms, flexibility is dramatically improved. Therefore, it is considered that a monoatomic film can be extended. It is known that a monolayer of black phosphorus has been obtained, but it is not known that thermoelectric properties are modulated when this monolayer is stretched. For example, graphite monolayer (graphene) Then, the modulation of thermoelectric conversion performance cannot be obtained. If the monoatomic film can be stretched, the crystal structure is considered to change. As a result, the thermoelectric properties of the black phosphorus monoatomic film may be modulated.
Therefore, as a result of diligent study, the present inventor has extended the black phosphorus monoatomic film in at least one of the zigzag axial direction and the armchair axial direction, and compared with the unstretched black phosphorus monoatomic film, the thermoelectric conversion performance. It has been found that the thermoelectric conversion performance can be modulated according to the degree of expansion. It was found that thermoelectric conversion performance improved dramatically when stretched in the zigzag axis direction compared to unstretched black phosphorus monoatomic film, and could be modulated according to the degree of stretching. Moreover, the thermoelectric conversion output of the armchair axial direction was very high, and the knowledge that the thermoelectric conversion performance could be further improved by extending in the armchair axial direction was obtained.
That is, according to the present invention, there is provided a black phosphorus monoatomic film having an extended crystal structure that has excellent thermoelectric conversion performance and can modulate the thermoelectric conversion performance in accordance with the degree of extension. Moreover, according to this invention, the thermoelectric conversion output is high, and the thermoelectric conversion material which can modulate thermoelectric conversion performance, and a thermoelectric conversion element are provided. Furthermore, since the black phosphorus monoatomic film of the present invention having an expanded crystal structure is a monoatomic film, it is excellent in flexibility.

The reason why the above-described effect can be obtained by the present invention is that, for example, when stretched in the zigzag axis direction, the lattice constant a on the a side in the unit cell of the black phosphorus monoatomic film is elongated and the lattice constant on the b side It is presumed that b shrinks that carriers such as electrons and holes easily move and the Seebeck coefficient increases.

As described above, the black phosphorus monoatomic film of the present invention having an extended crystal structure is based on a unit cell in an unstretched black phosphorus monoatomic film with respect to at least one of the zigzag axis direction and the armchair axis direction. Thus, it is a black phosphorus monoatomic film stretched by 2% to 10% and has a stretched crystal structure. Among these, a black phosphorus monoatomic film stretched by 4% to 10% is preferable. Within this range, the thermoelectric conversion performance is further improved. However, if the stretching exceeds 10%, the black phosphorus monoatomic film may be broken or cracked.
When the black phosphorus monoatomic film of the present invention having an expanded crystal structure is stretched by 2% to 10% with respect to the zigzag axis direction, the lattice constant a is 3.363Å-3. The range of 628 cm is shown, and the lattice constant b is in the range of 4.560 cm to 4.128 cm. Further, when the armchair is extended by 2% to 10% with respect to the axial direction of the armchair, the lattice constant a is in the range of 3.296 mm to 3.268 mm and the lattice constant b is 4.720 mm The range of 5.090cm is shown.

The black phosphorus monoatomic film of the present invention having an extended crystal structure is not particularly limited as a method for having a crystal structure extended in at least one of the zigzag axis direction and the armchair axis direction. For example, with the black phosphorus monoatomic film placed on an extensible material, at least both ends of the extensible material and the black phosphorus monoatomic film are fixed, and the extensible material and the black phosphorus monoatomic film are A stretch of the black phosphorus monoatomic film between the stretchable material and the black phosphorus monoatomic film with the black phosphorous monoatomic film sandwiched between two stretchable materials. A method in which at least both ends are fixed and the stretchable material and the black phosphorus monoatomic film are stretched together by moving both ends or one of the ends; and the like.

The mode of fixing at least both ends of the stretchable material and the black phosphorus monoatomic film is not particularly limited, and the entire surface of the stretchable material and the black phosphorus monoatomic film may be fixed, and only the end portion is fixed. It may be fixed. Moreover, any means may be used as the means for fixing. For example, it may be fixed by an adhesive, an adhesive, or the like, may be fixed by a fixing member such as a screw, or may be fixed by other means.
For example, a black phosphorus monoatomic film is attached to an adhesive layer of a peeling member (for example, an adhesive tape) having an adhesive layer and a base layer used for peeling a black phosphorus monoatomic film from bulk black phosphorus. In this state, both ends are gripped and stretched in at least one of the zigzag axial direction and the armchair axial direction to provide a crystal structure stretched in the black phosphorus monoatomic film.
When an elastic material (for example, a rubber material) is used as the stretchable material, the elastic material is used so as to include a stretched state.

Further, as another method, a black phosphorus monoatomic film is placed on a bendable material or a bendable material so that the bendable material or the bendable material and the black phosphorus monoatomic film are By fixing or bending the black phosphorus monoatomic film so that the bendable material or the bendable material is inside, the zigzag axis direction and the armchair axis It is also possible to provide a crystal structure stretched in at least one of the directions.
That is, in the black phosphorus monoatomic film of the present invention having an extended crystal structure, having an extended crystal structure means that at least a part of the black phosphorus monoatomic film is in at least one of the zigzag axis direction and the armchair axis direction. What is necessary is just to have a stretched crystal structure by being stretched. In other words, the entire black phosphorus monoatomic film does not have to have a crystal structure that is extended in at least one of the zigzag axis direction and the armchair axis direction.
Note that in the case where a crystal structure stretched in the black phosphorus monoatomic film by being bent or bent is provided, it is used so as to include a bent or bent state. Since the black phosphorus monoatomic film of the present invention can modulate the thermoelectric conversion action according to the degree of extension, it can be used for applications such as sensors as a thermoelectric material by utilizing such characteristics.
Specifically, for example, when a specimen is provided with a monoatomic film, the modulation function works when the specimen expands or deforms due to heat, stress, etc., and how much expansion or deformation occurs. Can be measured like a sensor according to the degree of extension (ie, the degree of modulation) of the monoatomic film.

Note that the black phosphorus monoatomic film has an effect of changing the electric resistance when the monoatomic film is deformed by simply applying a stress without depending on heat. Using this action, for example, a black phosphorus monoatomic film can be used as a material for a semiconductor element.

<Thermoelectric material>
Next, the thermoelectric material will be described.
In general, the figure of merit Z is used as an index for evaluating the performance of thermoelectric materials. The higher the figure of merit Z is, the higher the thermoelectric conversion performance. Here, Z is represented by the following formula A. Further, P in the formula A is a thermoelectric output factor (hereinafter sometimes referred to as “power factor”), and is represented by the following formula B. In Formula B, S represents the Seebeck coefficient, σ represents electrical conductivity, and in Formula A, λ represents thermal conductivity.

In the case where a black phosphorus monoatomic film is used as a thermoelectric material, it is considered that the thermal conductivity can be ignored. Therefore, if the thermoelectric output factor P is increased from the above equation, the thermoelectric conversion performance can be further improved. I understand. That is, it is considered that the performance as a thermoelectric material can be dramatically improved by improving the thermoelectric output factor P of the black phosphorus monoatomic film.

Therefore, by extending the black phosphorus monoatomic film in at least one of the zigzag axis direction and the armchair axis direction, the power factor of the expanded black phosphorus monoatomic film is larger than that of the unstretched black phosphorus monoatomic film. Can be achieved, the improvement of thermoelectric conversion performance as a thermoelectric material can be achieved.

The present inventor has described that the thermoelectric conversion performance as the thermoelectric material of the black phosphorus monoatomic film is improved by extending the crystal structure in at least one of the zigzag axis direction and the armchair axis direction. It was verified by stabilizing the crystal structure stretched in the axial direction and simulating the electronic state. Hereinafter, the simulation used for the verification of the present invention will be described in detail.

In the verification by the simulation of the black phosphorus monoatomic film of the present invention having the stretched crystal structure, a two-step process was performed to calculate the power factor of the stretched black phosphorus monoatomic film. The first stage is the calculation of the electronic state of the black phosphorus monoatomic film having the stretched crystal structure, and the second stage is the calculation of the power factor. Note that the first-principles calculation software “Quantum ESPRESSO” was used for the first stage electronic state calculation, and the transport coefficient calculation software “BoltzTrap” was used for the second-stage power factor calculation. In the following, formulas of basic equations used in the first stage and the second stage and parameter values used in the simulation are shown. These software are standard software used all over the world. Moreover, the verification result by the simulation of the black phosphorus monoatomic film of the present invention having the stretched crystal structure will be described later.

[Electronic state calculation]
In the simulation of the black phosphorus monoatomic film of the present invention having the stretched crystal structure, first-principles calculation based on density functional theory is used to calculate the electronic state of the black phosphorus monoatomic film having the stretched crystal structure. Went. In the density functional theory, a cone-sham equation represented by the following formula 1 was used. By solving this equation, the cone-sham orbit and the orbital energy are obtained. Further, the cone-sham potential is expressed by the following formula 2.

In the simulation of the black phosphorus monoatomic film of the present invention having an extended crystal structure, an ultrasoft pseudopotential was used as the external potential, and GGA-PW91 was used as the exchange correlation interaction functional. The Monkhorst-Pack method was used for the k-point sampling method, and the k-point mesh was 12 × 10 × 1. Further, the cutoff energy of the wave function was 30 Ry, and the cutoff energy of the electron density was 300 Ry.

[Calculation of thermoelectric power factor]
In the simulation of the black phosphorus monoatomic film of the present invention having the stretched crystal structure, the Boltzmann based on the relaxation time approximation is used to calculate the thermoelectric power factor of the black phosphorus monoatomic film having the stretched crystal structure. Semiclassical transport theory was adopted.
The power factor P _{α in} either the zigzag axis direction or the armchair axis direction of the black phosphorus monoatomic film having the stretched crystal structure is given by the following equation 3 using the electrical conductivity σ _α and the Seebeck coefficient S _α. . In the following formulas 3 to 5, α indicates the axial direction and indicates either the zigzag axial direction or the armchair axial direction.

Here, the electrical conductivity σ _α and the Seebeck coefficient S _α are given by the following formula 4.
L _α (ε) is given by the following equation (5). In the following formula 5, the orbital energy and the group velocity are both calculated by the first principle calculation.

In the simulation of the black phosphorus monoatomic film of the present invention having the stretched crystal structure, the power factor was calculated when the stretch ratio for stretching in the zigzag axis direction and the armchair axis direction was changed. In the simulation of extending in the zigzag axis direction according to the present invention, the k-point mesh used in the calculation of L _α (ε) is 120 × 100 × 1. Further, τ _α is a current relaxation time in the direction along the α axis (zigzag axis direction or armchair axis direction). In the simulation of the present invention, 1.34 × 10 ⁻¹³ sec, which is an experimental value of bulk black phosphorus, was adopted as the current relaxation time in the direction along the zigzag axis.
In the simulation of extending in the armchair axial direction in the present invention, the k-point mesh used for calculating L _α (ε) is 120 × 100 × 1. In the simulation according to the present invention, the experimental value of 6.20 × 10 ⁻¹⁴ sec of bulk black phosphorus was adopted as the current relaxation time in the direction along the armchair axis.

[Aspect of thermoelectric material]
When used as a thermoelectric material, any form can be used as long as the black phosphorous monoatomic film of the present invention having an extended crystal structure is included in the thermoelectric material, and the mode is not particularly limited. For example, the black phosphorus monoatomic film of the present invention having an extended crystal structure can be used as a single monolayer. In addition, two or more layers of black phosphorus monoatomic films adjusted to the same stretching ratio may be stacked to form two or more layers, or two or three or more black phosphorus monoatoms adjusted to different stretching ratios. Two or more layers may be formed by stacking the films. A black phosphorus monoatomic film having a crystal structure extended in the zigzag axis direction and a black phosphorus monoatomic film having a crystal structure extended in the armchair axis direction may be stacked to form a multilayer. Further, the black phosphorus monoatomic film of the present invention having an expanded crystal structure and an unstretched black phosphorus monoatomic film may be stacked to form a multilayer.
Note that, as described above, a laminated body having a multilayer structure in which black phosphorus monoatomic films are stacked is distinguished from a multilayer atomic film having two or more layers.

[Dope]
In order to further improve the thermoelectric conversion performance, it is conceivable to perform chemical doping or electrical doping on the black phosphorus monoatomic film of the present invention having an extended crystal structure. In chemical doping, carriers such as electrons and holes that carry electricity are supplied to a material by replacing or attaching a black phosphorus monoatomic film with an impurity element having a different valence. In the electrical doping, electrical carrier doping using electric field effect is performed, and carriers such as electrons and holes that conduct electricity are supplied to the material without element substitution.
In addition, when performing chemical doping, labor is required in order to set the optimal dope amount for exhibiting the performance as a thermoelectric material to the maximum. However, since electrical doping can change the amount of carriers without changing the chemical composition, it is useful in that the optimum doping amount can be easily set.

For example, as an example of chemical doping, holes can be supplied by doping oxygen black by adsorbing the black phosphorus monoatomic film of the present invention having an extended crystal structure. A thermoelectric material in which oxygen is adsorbed on a black phosphorus monoatomic film having an expanded crystal structure can be used as a thermoelectric conversion element as it is, for example. As for electrical doping, when a positive voltage is applied to the black phosphorus monoatomic film, holes are supplied, and when a negative voltage is applied, electrons are supplied.

In the thermoelectric material using the black phosphorus monoatomic film of the present invention having an extended crystal structure, the doping amount when the extended black phosphorus monoatomic film is doped depends on chemical doping and electrical doping. In the black phosphorus monoatomic film stretched in the zigzag axis direction, the number of carriers per phosphorus atom is preferably in the range of 0.0100 to 0.0700 (e / atom). The number of carriers may be in this range regardless of whether the carriers are holes or electrons. From the viewpoint of further improving the thermoelectric conversion performance, a range of 0.0100 to 0.0300 (e / atom) is more preferable. When the doping amount is within this range, an elongated black phosphorus monoatomic film having better thermoelectric conversion performance can be obtained.
The doping amount when the black phosphorus monoatomic film extended in the armchair axial direction is doped is 0.00280 as the number of carriers per phosphorus atom regardless of chemical doping or electrical doping. The range is preferably -0.00350 (e / atom), more preferably in the range of 0.0300-0.0345 (e / atom). Similarly to the above, the number of carriers may be in the range of any carrier of holes or electrons.

<Thermoelectric conversion element>
The black phosphorus monoatomic film of the present invention having an expanded crystal structure has high thermoelectric conversion performance as described above. The black phosphorus monoatomic film of the present invention having an expanded crystal structure can be suitably used as a thermoelectric material for a thermoelectric conversion element.

The thermoelectric conversion element of the present invention comprises the black phosphorus monoatomic film of the present invention having an extended crystal structure and an electrode, and is provided between the black phosphorus monoatomic film of the present invention having an extended crystal structure and the electrode. In addition, a structure in which an electrolyte material or a dielectric material is disposed is provided. Moreover, the thermoelectric conversion element of this invention may be further provided with members, such as a board | substrate and another electrode.
When the thermoelectric conversion element of the present invention is a thermoelectric conversion element having a structure in which an electrolyte material is disposed between the black phosphorus monoatomic film of the present invention having an elongated crystal structure and an electrode, the following: The structure can be formed as follows.
For example, a substrate showing flexibility of a resin material or the like on the side where the electrolyte material of the black phosphorus monoatomic film of the present invention having an extended crystal structure provided opposite to the electrode with the electrolyte material interposed is not disposed Can be provided.
Further, for example, when the electrode provided opposite to the black phosphorus monoatomic film of the present invention having a crystal structure stretched across the electrolyte material is used as the first electrode, the following structure is formed. It may be. That is, a second electrode different from the first electrode can be provided on the side where the electrolyte material of the black phosphorus monoatomic film of the present invention having an expanded crystal structure is not disposed. Further, the first electrode in the direction of the plane including the black phosphorus monoatomic film having the stretched crystal structure is disposed on the side where the electrolyte material of the black phosphorus monoatomic film of the present invention having the stretched crystal structure is disposed. It is also possible to provide a second electrode and a third electrode different from the above, and to provide the second electrode and the third electrode so as to face each other with an electrolyte material interposed therebetween. Further, on the plane including the first electrode provided facing the black phosphorus monoatomic film of the present invention having an expanded crystal structure with the electrolyte material interposed therebetween, the first material is in contact with the electrolyte material. A second electrode can be provided apart from the other electrode. A functional layer can be provided between the electrode and the electrolyte material, or between the electrolyte material and the black phosphorus monoatomic film of the present invention having a stretched crystal structure, or both.
In the case of a thermoelectric conversion element having a structure in which a dielectric material is disposed between a black phosphorus monoatomic film of the present invention having an expanded crystal structure and an electrode, the structure exemplified above is used. In the provided thermoelectric conversion element, a structure using a dielectric material may be formed instead of the electrolyte material.

FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the thermoelectric conversion element of the present invention. In FIG. 2, 1 is a black phosphorus monoatomic film of the present invention having an expanded crystal structure, 2 is an electrolyte material, and 3 is an electrode.

In the thermoelectric conversion element shown in FIG. 2, for example, the electrolyte material 2 is provided on the electrode 3, and the black phosphorus monoatomic film 1 of the present invention having a crystal structure stretched on the electrolyte material 2 is provided. However, it is not limited to this. In FIG. 2, a circuit is formed to connect the electrode 3 and the black phosphorus monoatomic film 1 of the present invention having an expanded crystal structure so that a voltage can be applied. In FIG. 2, a circuit for connecting the electrode 3 and the black phosphorus monoatomic film 1 of the present invention having the stretched crystal structure is formed. However, in the thermoelectric conversion element of the present invention, the electrode 3 is stretched. The circuit for connecting the black phosphorus monoatomic film 1 of the present invention having the above crystal structure may not be formed.
Hereinafter, although the thermoelectric conversion element shown in FIG. 2 will be described as an example, the thermoelectric conversion element of the present invention is not limited to the thermoelectric conversion element shown in FIG.

For example, in the thermoelectric conversion element of the present invention shown in FIG. 2, when a voltage is applied between the electrode 3 and the black phosphorus monoatomic film 1 having a stretched crystal structure, black phosphorus having a stretched crystal structure is generated by the electric field effect. Thermoelectric conversion performance is improved by injecting holes or electrons into the monoatomic film 1. When applying a voltage, injection of holes or electrons can be selected by selecting a positive voltage or a negative voltage. In FIG. 2, when a voltage is applied between the electrode 3 and the black phosphorus monoatomic film 1 having an expanded crystal structure, for example, when a temperature difference is generated between the A side and the B side, the expanded crystal The black phosphorus monoatomic film 1 having a structure exhibits an excellent thermoelectric conversion action and can efficiently generate power. Note that one of the temperature differences between the A side and the B side may be heated and the other may be cooled. Any means may be sufficient as a heating means and a cooling means, and the means which can produce a temperature difference should just be employ | adopted.

As described above, in the thermoelectric conversion element of the present invention shown in FIG. 2, in the state where a voltage is applied between the electrode 3 and the black phosphorus monoatomic film 1 having the stretched crystal structure, If a temperature difference is generated at, power is generated efficiently.

As an example of the thermoelectric conversion element of the present invention, the black phosphorus monoatomic film 1 of the present invention having a stretched crystal structure can be used as an anode or a cathode. A thermoelectric conversion element using the black phosphorus monoatomic film 1 of the present invention having an expanded crystal structure as an anode, and a thermoelectric conversion element using the black phosphorus monoatomic film 1 having an expanded crystal structure as a cathode, Can be used in series.

In the thermoelectric conversion element of the present invention, when an ionic gel that is a gel-like electrolyte material is used as the electrolyte material 2, the black phosphorus monoatomic film 1 of the present invention having an expanded crystal structure is used as an anode, It can also be used as a cathode.

Hereinafter, each member constituting the thermoelectric conversion element of the present invention will be described in detail. In the following description, the reference numerals are omitted.

[electrode]
The material used for the electrode is not particularly limited as long as it is formed of a substance exhibiting conductivity. Specifically, for example, metals, metal oxides, conductive polymers and the like are used.
Specific examples of the metal include magnesium, aluminum, gold, silver, copper, chromium, titanium, nickel, molybdenum, tantalum, indium, palladium, lithium, calcium, and alloys thereof.
Specific examples of the metal oxide include metal oxide films such as lithium oxide, magnesium oxide, aluminum oxide, indium tin oxide (ITO), tin oxide (NESA), indium oxide, zinc oxide, and indium zinc oxide. can give.
Specific examples of the conductive polymer include polyaniline, polythiophene, polythiophene derivatives, polypyrrole, polypyridine, a complex of polyethylenedioxythiophene and polystyrene sulfonic acid, and the like.

[Electrolyte material]
The shape used for the electrolyte material may be solid, gel, or liquid, and is not particularly limited. An ionic liquid that is in the form of a liquid in that it exists stably in air, the types of cations and anions, and their combinations can be created without limit, and the vapor pressure is substantially zero. It can be preferably used. Moreover, it is more preferable to use an ionic gel from the point of handleability. Furthermore, if an ionic gel is used as an electrolyte material, a thermoelectric conversion element superior in flexibility can be obtained. In the following, “(meth) acryl” is an expression including both “acryl” and “methacryl”.

Specific examples of solid electrolyte materials include CuI, CuBr, CuSCN, polyaniline, polypyrrole, polythiophene, arylamine-based polymers, polymers having (meth) acrylic groups, polyvinylcarbazole, triphenyldiamine polymers, and polyoligomers. Examples thereof include fluorine ion exchange resins having proton conductivity such as ethylene glycol methacrylate and perfluorosulfonate, perfluorocarbon copolymers, and perfluorocarbon sulfonic acids.

As described above, the liquid electrolyte material can produce an unlimited number of types of cations and anions and combinations thereof. For example, as an example of an ionic liquid that is a liquid electrolyte material, an imidazolium ion, a pyrrolidinium ion, a pyridinium ion, a piperidinium ion, or the like may be used as a cationic substance. A halide ion (Cl ⁻ , Br ⁻ ), tetrafluoroborate ion (BF ₄ ⁻ ), hexafluorophosphate ion (PF ₆ ⁻ ), bis (trifluoromethanesulfonyl) imide ion ((CF ₃ SO ₂ ) ₂ N ⁻ ) and the like are used as anions Is mentioned. These cationic substances and anionic substances may be used alone or in combination of two or more.

Examples of the gel electrolyte material include an ionic gel obtained by gelling an ionic liquid. The substance that gels the ionic liquid is not particularly limited as long as it is a substance that can gel the ionic liquid. The ionic gel is obtained, for example, as follows. It can be obtained by adding poly (meth) acrylic acid or a salt thereof to the ionic liquid. Or (meth) acrylic acid monomers and acrylic acid alkyl esters, alkyl branched acrylic acids and their esters, vinyl halides, vinyl acetate, vinyl alcohol, divinyl ether, maleic anhydride, acrylonitrile, styrene, and the like It is obtained by adding a copolymer obtained by copolymerizing at least one monomer selected from the group consisting of:
The gel electrolyte material may be a polymer ionic gel obtained by reacting an imidazolium compound or a salt thereof with an acid monomer such as acrylic acid, methacrylic acid, or vinyl sulfonic acid.

[Dielectric material]
Specific examples of the dielectric material include silicon oxide (SiO ₂ ), silicon oxynitride (SiO _x N _y ), silicon nitride (SiN _y ), hafnium oxide (HfO ₂ ), and lanthanum oxide (La ₂ O). ₃ ), zirconium oxide (ZrO ₂ ), aluminum oxide (Al ₂ O ₃ ), barium titanate (BaTiO ₃ ), strontium titanate (SrTiO ₃ ) and the like, and are not particularly limited. These dielectric materials can be used in the form of a film, for example. A known method may be adopted as a method for forming the film-like dielectric material.

[Black phosphorus monoatomic film with stretched crystal structure]
The black phosphorus monoatomic film having the stretched crystal structure is as described above. The thermoelectric conversion element of the present invention has a stretched crystal structure so that at least one of the zigzag axis direction and the armchair axis direction, which is the extension direction of the black phosphorus monoatomic film, is parallel to the direction in which the temperature difference occurs. It is preferable to dispose a black phosphorus monoatomic film. In addition, the black phosphorus monoatomic film of the present invention having an expanded crystal structure can modulate thermoelectric conversion performance according to the degree of expansion by stretching in at least one of the zigzag axis direction and the armchair axis direction. Depending on the desired thermoelectric conversion performance, the black phosphorus monoatomic film with the degree of expansion being changed may be arranged so that at least one of the zigzag axis direction and the armchair axis direction is parallel to the direction in which the temperature difference occurs. . Note that the term “parallel” means that at least one of the zigzag axis direction and the armchair axis direction and the direction in which the temperature difference occurs are in a parallel relationship, and even if it is not in a completely parallel state, it can be regarded as having a parallel relationship at a glance. The parallel case is also included.

When the thermoelectric conversion element is configured using the black phosphorus monoatomic film of the present invention having the stretched crystal structure, for example, the electrolyte material is stretched in advance in at least one of the zigzag axial direction and the armchair axial direction. You may provide on. Further, an unstretched black phosphorus monoatomic film is provided on the electrolyte material, and the black phosphorus monoatomic film is stretched along with the electrolyte material in at least one of the zigzag axial direction and the armchair axial direction, and then the electrolyte is placed on the electrode Materials may be provided. Further, after obtaining a thermoelectric conversion element by providing an unstretched black phosphorus monoatomic film on the electrolyte material, a black phosphorus monoatom is obtained by bending or bending the electrode side inside. The membrane may be stretched in at least one of the zigzag axial direction and the armchair axial direction. In this case, what is necessary is just to be used for the use used in the state bent or bent with the electrode side of the thermoelectric conversion element inside.

The thermoelectric conversion element of the present invention can be used as, for example, a power system integrated with a solar power generation element and a storage element.
Moreover, since the thermoelectric conversion element of this invention uses the black phosphorus monoatomic film | membrane, it is excellent in a softness | flexibility. Therefore, it can be used as a thermoelectric conversion element that is portable (portability, portability) or wearable (wearability, worn). Since the black phosphorus monoatomic film of the present invention can modulate the thermoelectric conversion action according to the degree of expansion, it can be used for applications such as sensors as described above using such characteristics. In addition, when used as a wearable thermoelectric conversion element, the thermoelectric conversion action can be modulated by the stretching action caused by the operation at the time of wearing, so that it can be used for applications such as sensors.
Further, it can be used for a field effect transistor or a thin film transistor.

<Semiconductor element>
The black phosphorus monoatomic film having the stretched crystal structure of the present invention can be used as a material for a semiconductor element. The semiconductor element includes an electrode and a black phosphorus monoatomic film having an extended crystal structure. Specifically, for example, a semiconductor element in which a black phosphorus monoatomic film is disposed between one electrode and the other electrode, and a circuit for connecting the one electrode to the other electrode is disposed. At this time, both electrodes may be arranged at both ends in the zigzag axis direction of the black phosphorus monoatomic film, or may be arranged at both ends in the armchair axis direction. What is necessary is just to arrange | position an electrode according to the intended purpose.
Hereinafter, a semiconductor element having a structure in which a black phosphorus monoatomic film having a stretched crystal structure is disposed between one electrode and the other electrode will be described as an example.

When a voltage is applied between one electrode and the other electrode, for example, holes can be injected into the black phosphorus monoatomic film having an expanded crystal structure disposed between both electrodes due to the field effect. it can. The black phosphorus monoatomic film into which holes are injected becomes a black phosphorus monoatomic film having holes. A black phosphorus monoatomic film having holes functions as a so-called P-type semiconductor. When the black phosphorus monoatomic film is a black phosphorus monoatomic film having holes, this semiconductor element has a black phosphorus monoatomic film having holes between one electrode and the other electrode. It becomes a structure.
Although the material of an electrode is not specifically limited, For example, the material similar to the material illustrated with the above-mentioned electroconversion element can be used.

In the semiconductor device having the above structure, a black phosphorus monoatomic film having a hole and having an extended crystal structure is disposed between one electrode and the other electrode, and a constant voltage is applied between both electrodes. Applied. For example, when stress is applied to the semiconductor element to deform the semiconductor element, the resistance value of the black phosphorus monoatomic film changes according to the degree of expansion of the black phosphorus monoatomic film. Therefore, the value of current flowing through the semiconductor element varies depending on the degree of deformation of the semiconductor element, that is, the degree of expansion of the black phosphorus monoatomic film. By utilizing this principle, the semiconductor element is expected to be used as a stress sensor (for example, a strain sensor) by being attached to a subject, for example.

In the above description, the case where the black phosphorus monoatomic film having the stretched crystal structure is used for the thermoelectric material, the thermoelectric conversion element, and the semiconductor element has been described. However, the black phosphorus monoatomic film having the stretched crystal structure is described. Instead, it is also possible to use a black phosphorus multilayer atomic film having a stretched crystal structure. For example, a black phosphorus multilayer atomic film stretched by 2% to 10% can improve the power factor as compared with a non-stretched black phosphorus monoatomic film stretched by 2% to 10%. However, the multilayer atomic film requires a stress for stretching. Therefore, when a multilayer atomic film is used, the degree of extension is preferably in the range of 2% to less than 8%, and preferably in the range of 2% to 6%.

Assuming the thermoelectric conversion element shown in FIG. 2, the power when the black phosphorus monoatomic film of the present invention having the stretched crystal structure is stretched in the zigzag axis direction or the armchair axis direction by the method described above. The change of the factor was verified by simulation. The results are shown in Tables 1 and 2. The hole doping amount assumes that hole carriers are supplied by electrical doping. Further, the hole doping amount represents the number of carriers per phosphorus atom.

As a result of verification by simulation, it was found that the power factor of the black phosphorus monoatomic film of the present invention having an expanded crystal structure is improved as compared with the unstretched black phosphorus monoatomic film. Thereby, the black phosphorus monoatomic film of the present invention having an extended crystal structure having an extended crystal structure exhibits excellent performance as a thermoelectric material. In addition, since the power factor was changed depending on the extension ratio, an excellent black phosphorus monoatomic film capable of modulating the thermoelectric conversion performance according to the extension degree was obtained.

From the result of the verification by the above simulation, the increase rate of the power factor of the black phosphorus monoatomic film of the present invention having the stretched crystal structure with respect to the power factor of the unstretched black phosphorus monoatomic film was obtained. The results are shown in FIG. For example, the black phosphorus monoatomic film stretched by 10% in the zigzag axis direction on the basis of the unit cell in the unstretched black phosphorus monoatomic film is increased to over 160%. It was found that the thermoelectric conversion performance is dramatically improved by extending in the zigzag axis direction. Further, the power factor of the black phosphorus monoatomic film stretched by 10% in the armchair axial direction is increased by about 20% with respect to the power factor of the unstretched black phosphorus monoatomic film, and the thermoelectric conversion performance is improved. I understood it.

In Tables 1 and 2, the hole doping amount indicates an optimum doping amount for maximizing the effect as a thermoelectric material. As a result of simulation verification, when stretched in the zigzag axis direction, the stretch rate of the black phosphorus monoatomic film is larger than that of the unstretched black phosphorus monoatomic film, and the amount of hole doping is increased. It can be seen that the optimum amount is reduced. That is, it can be seen that the black phosphorus monoatomic film shows an excellent thermoelectric material having a higher thermoelectric conversion performance with a small amount of doping by stretching in the zigzag axis direction.
On the other hand, when the armchair is stretched in the axial direction, the optimum amount of hole doping tends to slightly increase compared to the case of an unstretched black phosphorus monoatomic film. It turns out that it is very few. That is, it can be seen that in the black phosphorus monoatomic film stretched in the armchair axial direction, the optimum amount of hole doping does not depend on the stretch rate and varies within a very narrow range. Then, it can be seen that the effect as a thermoelectric material can be maximized with a very small amount of hole doping as compared with the case of extending in the zigzag axis direction.

In Tables 1 and 2, the lattice constant a indicates the lattice constant in the zigzag axis direction in the unit cell shown in FIG. 1C, and the lattice constant b indicates the lattice constant in the armchair axis direction in the unit cell shown in FIG. 1C. As can be seen from the results shown in Table 1, in the black phosphorus monoatomic film, the lattice constant a increases and the lattice constant b decreases according to the degree of extension. That is, it is considered that the power factor of the stretched black phosphorus monoatomic film is improved when the lattice constant a and the lattice constant b have the above crystal structure.

In addition, the power factor of the carbon nanotube thin film in the thermoelectric conversion element using the conventionally known carbon nanotube thin film was 0.11 mW / m · K ² . On the other hand, the black phosphorus monoatomic film of the present invention having an extended crystal structure, when extended in the zigzag axis direction as shown in Table 1, has a capacity of up to about 10 mW / m · K ² . The power factor can be modulated in the range, and when it is extended in the armchair axial direction, a huge power factor exceeding 10 mW / m · K ² is obtained, and approximately 14 W / m · K ² to 17 W / m · since K ² about power factor in the range of possible modulation, it is found to exhibit excellent thermoelectric conversion performance as compared with the conventional thermoelectric material.
Further, when the power factor is modulated in the zigzag axial direction and the lower limit value is 1 mW / m · K ² , a thermoelectric conversion material exhibiting excellent thermoelectric conversion performance can be obtained.

Since the black phosphorus monoatomic film of the present invention having an extended crystal structure has excellent thermoelectric conversion performance, it has an extended crystal structure even if a black phosphorous monoatomic film is laminated. By including the black phosphorus monoatomic film of the present invention, it is considered that a thermoelectric material exhibiting thermoelectric conversion performance superior to that of mere bulk black phosphorus can be obtained.

As shown in the above results, when stretched in the zigzag axis direction, when the black phosphorus monoatomic film of the present invention having the stretched crystal structure is electrically doped, the thermoelectric conversion performance is maximized. Therefore, the amount of doping for the purpose is reduced. In addition, in the case where the armchair is stretched in the axial direction, when the black phosphorus monoatomic film of the present invention having the stretched crystal structure is electrically doped, the doping for maximizing the thermoelectric conversion performance is performed. The amount is extremely small.
Therefore, for example, when the black phosphorus monoatomic film of the present invention having a stretched crystal structure is used for a thermoelectric conversion element, and this thermoelectric conversion element is used for a field effect transistor, the voltage applied to the gate electrode should be lowered. As a result, it is expected that leakage current can be suppressed and energy saving can be achieved.

Next, assuming the thermoelectric conversion element shown in FIG. 2, the black phosphorus multilayer atomic film having the stretched crystal structure of the present invention was stretched in the zigzag axial direction or the armchair axial direction by the method described above. The change in power factor was verified by simulation. The results are shown in Tables 3 and 4. The hole doping amount assumes that hole carriers are supplied by electrical doping. Further, the hole doping amount represents the number of carriers per phosphorus atom. The black phosphorus multilayer atomic film was assumed to be a two-layer multilayer atomic film.

As a result of the verification by simulation, it was found that the power factor was improved also in the case of the two-layer black phosphorus multilayer atomic film having the stretched crystal structure as compared with the case where it was not stretched. Thereby, even if the black phosphorus atomic film having the stretched crystal structure is a multilayer atomic film having two or more layers, excellent performance as a thermoelectric material can be obtained. In addition, as in the case of the monolayer film, the two-layer black phosphorus multi-layer atomic film has a change in power factor depending on the expansion rate. Therefore, the black phosphorus atomic film that can modulate the thermoelectric conversion performance according to the degree of expansion. Is obtained.
Therefore, the black phosphorus multilayer atomic film is expected to be used in the same manner as the black phosphorus monoatomic film.

However, when a two-layer black phosphorus multilayer atomic film is stretched in a zigzag direction, the power factor tends to reach its peak when stretched by 8% or more. This is because the electronic state of the stretched monoatomic film is different from the electronic state of the stretched multilayer atomic film of two or more layers. Therefore, when extending in the zigzag direction, the black phosphorus multilayer atomic film is preferably extended by 2% to 6%.

In addition, as shown in the above simulation results, when the two-layer black phosphorus multilayer atomic film is stretched in the zigzag direction, the black phosphorus single-layer film is stretched to the same extent in the range of 2% to 8%. The power factor is superior compared to the case where From this, it can be seen that by using the black phosphorus multilayer atomic film, a higher effect can be obtained with a smaller elongation rate than in the case of using the black phosphorus single layer film.

In the black phosphorus multilayer atomic film extended in the zigzag axis direction, the number of carriers per phosphorus atom is, for example, in the range of 0.0300 to 0.1200 (e / atom) in the case of hole carriers. It is preferable. If the doping amount is within this range, an elongated black phosphorus multilayer atomic film having better thermoelectric conversion performance can be obtained.

The entire disclosure of Japanese Patent Application No. 2014-209402 filed on October 10, 2014 is incorporated herein by reference.
All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually described to be incorporated by reference, Incorporated herein by reference.

Claims

A black phosphorus atomic film having a crystal structure that is stretched 2% to 10% in at least one of the zigzag axis direction and the armchair axis direction based on the unit cell in the unstretched black phosphorus atomic film.
The black phosphorus atomic film according to claim 1, wherein the black phosphorus atomic film has holes.
The black phosphorus atomic film according to claim 1 or 2, wherein the black phosphorus atomic film is a monoatomic film.
The black phosphorus atomic film according to claim 1 or 2, wherein the black phosphorus atomic film is a multilayer atomic film.
A thermoelectric material comprising the black phosphorus atomic film according to any one of claims 1 to 4.
The thermoelectric material according to claim 5, further comprising an unstretched black phosphorus atomic film.
The doping amount in the black phosphorus monoatomic film having a crystal structure stretched in the zigzag axis direction is 0.0100 to 0.0700 (e / atom) as the number of carriers per phosphorus atom. The thermoelectric material according to claim 6.
6. The doping amount in the black phosphorus monoatomic film having a crystal structure extended in the armchair axis direction is 0.00280 to 0.00350 (e / atom) as the number of carriers per phosphorus atom. Or the thermoelectric material of Claim 6.
The black phosphorus atomic film according to any one of claims 1 to 4,
Electrodes,
An electrolyte material or a dielectric material disposed between the black phosphorus atomic film and the electrode;
A thermoelectric conversion element.
The black phosphorus atomic film according to any one of claims 1 to 4,
Electrodes,
A semiconductor device comprising: