WO2017135136A1

WO2017135136A1 - Structure in which single atoms are dispersed on support, method for manufacturing structure in which single atoms are dispersed on support, and sputtering device

Info

Publication number: WO2017135136A1
Application number: PCT/JP2017/002670
Authority: WO
Inventors: 一壽郷原; 洋祐前原; 憲慈山崎
Original assignee: 国立大学法人北海道大学
Priority date: 2016-02-01
Filing date: 2017-01-26
Publication date: 2017-08-10
Also published as: JPWO2017135136A1; JP6957022B2

Abstract

The present invention relates to a structure in which single atoms are dispersed on a support. The structure comprises: a support on which an anchor site capable of adsorbing atoms which can be used in sputtering is formed; and the atoms which can be used in sputtering and which are adsorbed by the anchor site and dispersed as single atoms on the support. The structure enables atoms of more varied types to be dispersed as single atoms.

Description

Structure with monoatomic dispersion on support, method for producing structure with monoatomic dispersion on support, and sputtering apparatus

The present invention relates to a structure in which single atoms are dispersed on a support, a method for producing a structure in which single atoms are dispersed on a support, and a sputtering apparatus.

微小 Small size particles may have different properties from bulk materials. For example, transition metals such as platinum (Pt) and gold (Au) are known to exhibit various catalytic capabilities when made into nanoparticles. Non-Patent Document 1 describes that the smaller the particle size of the nanoparticle, the greater the number of coordination unsaturated sites of the metal atom, resulting in an increase in the catalytic ability of the particle.

From this point of view, it is expected that the catalytic ability will be further enhanced if the particle size of the particles is reduced. In fact, studies have been conducted to produce a monoatomic dispersion, which is a particle having an ultimately small particle size, and to measure its catalytic ability. Non-Patent Document 1, Non-Patent Document 2 and Non-Patent Document 3 report that Pt atoms and palladium (Pd) atoms dispersed by single atoms selectively and efficiently catalyze various reactions.

If a dispersion of particles with a smaller average particle size, particularly a monoatomic dispersion, can be produced, not only can it be applied to highly functional catalysts, It is expected to be applied in various fields, such as enabling research at the molecular level of physical or physical reactions.

However, as described in Non-Patent Document 1 and Non-Patent Document 2, when the particle size is reduced, the surface free energy of the molecule is higher and the particles are more likely to aggregate. Therefore, it is not easy to produce a dispersion of particles having a small average particle diameter (particularly, a monoatomic dispersion), and a special method is required. For example, in Non-Patent Document 1 and Non-Patent Document 2, a method of chemically bonding a precursor compound having Pt or Pd in a molecule and a substrate made of graphene partially depleted of carbon atoms by surface treatment (atomic layer) Monoatomic Pt or Pd is dispersed on the surface of the substrate by a deposition method or the like. In Non-Patent Document 3, monoatomic Pt is dispersed on the surface of a substrate made of copper (Cu) by an electron beam evaporation method in which the film formation rate is controlled to 0.02 layers per minute.

Note that the electron beam vapor deposition method employed in Non-Patent Document 3 is a kind of physical vapor deposition method. As the physical vapor deposition method, in addition to the vapor deposition method performed in an ultrahigh vacuum, sputtering is performed. Sputtering performed in the presence of gas is known. However, as described in Non-Patent Document 4 and Non-Patent Document 5, in sputtering, atoms repelled from the target collide with the sputtering gas and become charged, or conversely, trajectories are formed by the molecules of the sputtering gas. It was thought that it was easily changed and agglomerated between atoms.

However, in the methods described in Non-Patent Document 1 and Non-Patent Document 2, the types of precursor compounds that can be used are limited, and only limited types of molecules can be used. In addition, since it takes time to react the precursor compound in the system, it is difficult to increase the production efficiency of the dispersion.

On the other hand, since the vapor deposition method as described in Non-Patent Document 3 is performed in a high-temperature environment, the kinetic energy of the evaporated molecules increases, and tends to aggregate before adhering to the substrate. Therefore, a monoatomic dispersion cannot be produced particularly stably.

The present invention has been made in view of the above problems, and a structure in which atoms of various types are dispersed on a support capable of dispersing various types of atoms with a single atom, and such a structure are manufactured. It is an object of the present invention to provide a method and a sputtering apparatus capable of manufacturing such a structure.

The present invention relates to a structure in which single atoms are dispersed on the following support, a method for producing a structure in which single atoms are dispersed on a support, and a sputtering apparatus.
[1] A support on which an anchor site capable of adsorbing atoms capable of sputtering is formed, and an atom capable of being sputtered and adsorbed on the anchor site and dispersed as single atoms on the support. A structure in which single atoms are dispersed on a support.
[2] The support is a laminate in which one or more layers made of nanographene are stacked in an island shape on graphene, and the anchor site is on the surface of the layer made of graphene or nanographene. The structure according to [1], which is a region in contact with an end of the formed nanographene layer.
[3] The structure according to [1] or [2], wherein the support is activated carbon.
[4] The structure according to any one of [1] to [3], which is a dispersion in which 90% or more of the atoms are dispersed as single atoms.
[5] The structure according to any one of [1] to [4], wherein the atoms that can be sputtered are transition metal atoms.
[6] The structure according to any one of [1] to [5], wherein the atoms that can be sputtered are platinum (Pt), gold (Au), iridium (Ir), and ruthenium (Ru).
[7] A target including a sputtering-capable atom and a support on which an anchor site capable of adsorbing a sputterable atom is disposed and obtained in advance in a chamber into which a sputtering gas is introduced. And applying a voltage between the target and the support under sputtering conditions that allow at least a part of the atoms that can be sputtered to be dispersed on the support as single atoms. A method for producing a structure in which single atoms are dispersed on a support, including a step of sputtering.
[8] The support is a support in which one or more layers made of nanographene are stacked in an island shape on graphene, and the anchor site is on the surface of the layer made of graphene or nanographene. The method according to [7], which is a region in contact with an end of the formed layer of nanographene.
[9] The method according to [7] or [8], wherein the support is activated carbon.
[10] The method according to any one of [7] to [9], wherein the voltage is 150 V or less.
[11] The method according to any one of [7] to [10], wherein the voltage is applied for 1.5 seconds or less.
[12] The method according to any one of [7] to [11], wherein the sputtering gas is a gas containing 70% by volume or more of nitrogen (N ₂ ).
[13] The method according to any one of [7] to [12], wherein the target includes a transition metal.
[14] The method according to any one of [7] to [13], wherein the target is platinum (Pt), gold (Au), iridium (Ir), or ruthenium (Ru).
[15] Further, before the step of sputtering the target, a step of sequentially feeding the copper foil wound around the feed roller, and a graphene film is formed on the copper foil by chemical vapor deposition (CVD), The method according to any one of [7] to [14], comprising a step of forming a support.
[16] A chamber that can be sealed, a target placement portion in which a target containing atoms that can be sputtered is placed, and an atom that can be sputtered in the chamber can be adsorbed A voltage is applied between the target and the support, and a support arrangement part where a support on which a simple anchor site is formed is arranged; a sputtering gas introduction part for introducing a sputtering gas into the chamber; A sputtering condition in which at least a part of the atoms that can be sputtered is dispersed in a single atom on the support by controlling the application unit, the sputtering gas introduction unit, and the voltage application unit in advance. And a controller that applies a voltage between the target and the support.

According to the present invention, it is possible to disperse more various kinds of atoms with a single atom, a structure in which single atoms are dispersed on a support, a method for producing such a structure, and such a structure. A sputtering apparatus capable of producing a body is provided.

FIG. 1A is a high-angle scattering dark field / scanning transmission electron microscope showing a structure in which Pt single atoms are dispersed on a support that is a laminate in which one or more layers of nanographene are stacked in an island shape on graphene. It is the image imaged by (HAADF-STEM). FIG. 1B is a diagram in which the region surrounded by the dotted line in FIG. 1A is enlarged and color-coded for each region where the pixel intensities are substantially the same. FIG. 2A is an image of a structure in which gold (Au) is dispersed on a support that is a stacked body in which one or a plurality of layers made of nanographene are stacked in an island shape on graphene, using HAADF-STEM. FIG. 2B is an image of a structure in which iridium (Ir) is dispersed in a support that is a stacked body in which one or a plurality of layers made of nanographene is stacked in an island shape on graphene, which is captured by HAADF-STEM. FIG. 2C is an image of a structure in which ruthenium (Ru) is dispersed in a support, which is a stacked body in which one or a plurality of layers made of nanographene are stacked in an island shape on graphene, captured by HAADF-STEM. FIG. 3 is a schematic view showing a state in which sputtered atoms reach the support in a single atom state, diffuse on the support, and are adsorbed on the anchor site. FIG. 4 shows that when the support is a laminate in which a layer made of nanographene is stacked in an island shape on a graphene substrate, the sputtered atoms arrive in a single atom state and diffuse on the support It is a schematic diagram which shows a mode that it adsorb | sucks to an anchor site. FIG. 5A is a schematic view showing a method for producing a structure in which single atoms are dispersed on a support, which is graphene formed on a copper foil, by a roll-to-roll (RTR) method. FIG. 5B is a schematic diagram showing a method of manufacturing the structure on graphene transferred to another sheet after being formed on a copper foil. FIG. 6 is a schematic view showing a sputtering apparatus according to an embodiment of the present invention. FIG. 7A is an image obtained by capturing the support manufactured in Example 1 with HAADF-STEM. FIG. 7B is a graph in which the distance from the start point is plotted on the horizontal axis and the intensity for each pixel is plotted on the vertical axis for the region set in the image shown in FIG. 7A. FIG. 7C is a diagram in which FIG. 7A is color-coded for each region where the pixel intensities are substantially the same. FIG. 8A is an image obtained by imaging a region set on the substrate surface with HAADF-STEM after sputtering with a sputtering time of 1 second in Example 1. FIG. 8B is an image obtained by imaging a region set on the substrate surface with HAADF-STEM after sputtering with a sputtering time of 2 seconds in Example 1. FIG. FIG. 8C is an image obtained by imaging a region set on the substrate surface with HAADF-STEM after sputtering with a sputtering time of 5 seconds in Example 1. FIG. 8D is an image obtained by imaging a region set on the substrate surface with HAADF-STEM after sputtering with a sputtering time of 10 seconds in Example 1. FIG. 8E is an image obtained by imaging a region set on the substrate surface with HAADF-STEM after sputtering with a sputtering time of 30 seconds in Example 1. FIG. FIG. 9A is an image obtained by imaging a region set on the substrate surface with HAADF-STEM when the sputtering time is 10 seconds. FIG. 9B is an image obtained by capturing the same region as FIG. 9A with characteristic X-rays having a wavelength corresponding to Pt by energy dispersive X-ray analysis (EDX). FIG. 10 is a graph in which the sputtering time (unit: seconds) is plotted on the horizontal axis, and the relative value of the number of Pt atoms present on the substrate surface at each sputtering time is plotted on the vertical axis. FIG. 11A is an image obtained by imaging a region set on the substrate surface with HAADF-STEM when the sputtering time is 1 second. FIG. 11B is an image obtained by performing noise processing on FIG. 11A using a low-pass filter and threshold processing. FIG. 12 shows the number of points where the distance between the closest points is rounded to the nearest decimal point for each point in FIG. 11B, and the result is represented as a histogram. It is. FIG. 13 shows, for each number of points constituting each dispersion in FIG. 11B, the number of dispersions having the value of the number of points, and the result is represented as a histogram. FIG. 14A is an image obtained by imaging a region set on the substrate surface with HAADF-STEM after sputtering using He atmosphere as the atmosphere gas in Example 5. FIG. 14B is an image obtained by changing the magnification of FIG. 14A. FIG. 14C is an image obtained by imaging a region set on the substrate surface with HAADF-STEM after sputtering using atmospheric gas as the atmosphere in Example 5. FIG. 14D is an image obtained by changing the magnification of FIG. 14C.

One embodiment of the present invention relates to a structure in which single atoms are dispersed on a support. An anchor site capable of adsorbing atoms that can be sputtered is formed on the support, and at least a part of the atoms that can be sputtered is adsorbed to the anchor sites as single atoms.

Further, another embodiment of the present invention relates to a method for producing a structure in which single atoms are dispersed on the support. In the structure in which single atoms are dispersed on the support, a target including an atom that can be sputtered and a support on which an anchor site capable of adsorbing an atom that can be sputtered is disposed, and sputtering is performed. A voltage is applied between the target and the support under sputtering conditions in which at least a part of the atoms that can be sputtered can be dispersed on the support as single atoms in a gas-introduced chamber. It can be manufactured by applying and sputtering the target.

In addition, being dispersed by single atoms means that the distance between adjacent single atoms is larger than the distance between atoms (bonding distance) when the atoms are bonded to each other. For example, a Pt atom is dispersed as a single atom means that the distance between the Pt atom and another Pt atom that is the shortest distance from the Pt atom is the interatomic distance between Pt and Pt. It means that it is larger than a certain 2.7cm. When a plurality of types of atoms are dispersed as single atoms, the interatomic distance can be the smallest among the interatomic distances required for all combinations of atoms constituting the dispersion.

The sputtering conditions can be determined in advance for each combination with atoms to be dispersed as a condition for producing a structure in which single atoms are dispersed. If sputtering is performed from the next time under the conditions thus obtained, the structure can be easily manufactured.

Sputtering is a technique for forming a thin film, and formation of a monoatomic dispersion by sputtering has not been conceived until now. Further, in view of the common technical knowledge described in Non-Patent Document 4 and Non-Patent Document 5, even if an attempt is made to form a monoatomic dispersion by sputtering, a stable dispersion (in particular, a monoatomic dispersion). The formation of is usually considered difficult. On the other hand, the present inventors have found that, even in sputtering, the sputtered atoms can reach the support in a single atom state by appropriately controlling the conditions. In addition, the present inventors have made it possible to disperse atoms that have reached the support in the state of the single atom as a single atom by allowing the sputtered atoms to reach the support on which the anchor site is formed. I found it. The inventors of the present invention have completed the present invention through further studies based on these findings.

The sputtering conditions for allowing the sputtered atoms to reach the support in a single atom state are the type of atoms, the distance between anchor sites, the amount of single atoms that reach the support per unit time, and the support. It is thought that it depends on the rate at which the single atom diffuses on the support. Therefore, it is considered that there are many appropriate sputtering conditions depending on these combinations. However, once an appropriate condition is searched and found, the same process can be performed without changing the condition from the next process, and the present invention can be implemented without excessive burden. According to the knowledge of the present inventors, the sputtering conditions are not greatly different from the normal sputtering conditions for forming a thin film except that the time for applying a voltage is shorter. . Therefore, it is considered that the sputtering conditions suitable for each atom can be found relatively easily.

The conditions for causing the sputtered atoms to reach the support in the state of a single atom can be obtained by the following method, for example. Sputtering is performed while changing the conditions to attach atoms constituting the target to the support surface, and for each condition, the atoms attached to the support surface are imaged by energy dispersive X-ray analysis (EDX) or the like. Temporarily selecting an image in which particles having a particle size of several sparsely sparsely disperse on the surface of the support among images taken for each condition. For the particles observed in the selected image, the size (particle size) of the particles is the same as the atomic radius of the sputtered atoms (usually about several microns), and the distance between adjacent particles is the above If the distance is greater than the interatomic distance (bonding distance: usually several tens of kilometers), it can be determined that the particle is a single atom. When a certain region (for example, a region of 50 nm × 50 nm) was observed, and a predetermined ratio of all atoms present in the region was a single atom, sputtering was performed under the condition that the image was obtained. It can be determined that the predetermined proportion of atoms can reach the support in a single atom state.

The predetermined ratio can be determined according to the use of the structure to be manufactured, and is, for example, 20% or more, 30% or more, 50% or more, 70% or more, 90% or more, 95% or more and 99%. % May be arbitrarily selected.

Further, if the treatment is performed without changing the sputtering conditions, the number of atoms reaching the support increases substantially in proportion to the time for applying the voltage. Therefore, it is considered that the number of atoms reaching the support can be controlled almost accurately by changing only the voltage application time. At this time, if the time for applying the voltage is made longer, a dispersion of clusters in which a plurality of atoms are aggregated is formed, so that the ratio of dispersion with single atoms is reduced. The proportion of the above-mentioned single atom dispersed as a single atom is 99% or more, 95% or more, 90% or more, 70% or more, 50% or more. It can be controlled to 30% or more and 20% or more.

Note that the electron beam evaporation method must be performed under ultra-high vacuum. If even a slight amount of residual gas exists, atoms or molecules evaporated in a high-temperature environment react with oxygen or hydrogen, and the dispersion becomes There is a risk that the composition of the constituent molecules will change. On the other hand, in the present invention, when an inert gas is used as the sputtering gas, a dispersion having a higher purity composition can be obtained without reacting before the sputtered atoms reach the support. .

Furthermore, in the electron beam evaporation method, the target evaporates only from the point-like region irradiated with the electron beam, so it is difficult to fly a large number of atoms at the same time, and it is difficult to form a large number of dispersions. Then, a larger number of dispersions can be formed simultaneously.

(Sputtering conditions)
The target may be a sputtering target that contains atoms constituting the dispersion to be manufactured in the vicinity of the surface. Note that the vicinity of the surface means a three-dimensional region defined in the thickness direction from the surface of the target, which can be sputtered by a sputtering gas by applying a voltage.

The atomic composition of the target in the vicinity of the surface only needs to include atoms constituting the dispersion to be manufactured. For example, when a dispersion composed of a single kind of atom is to be obtained, the ratio of the atoms in the vicinity of the surface is preferably 99% or more, and more preferably 99.9% or more. On the other hand, when it is intended to obtain a dispersion containing a plurality of types of atoms at a certain ratio, it is preferable to include each atom at the same ratio as the ratio at which the atoms are to be dispersed.

The shape and size of the target are not particularly limited, and can be arbitrarily determined according to the configuration of a sputtering apparatus.

The atoms constituting the dispersion may be atoms that can exist as a solid near the surface of the target and can be sputtered by a sputtering gas, and may be aluminum (Al), gallium (Ga), titanium (Ti ), Zinc (Zn), copper (Cu), or other metal element atoms, or silicon (Si) or other non-metal element atoms. The atoms constituting the dispersion may exist as oxides or nitrides in the target. For example, when producing a dispersion used as a catalyst, the atom is preferably a metal atom of a transition metal, more preferably a metal atom of a noble metal, platinum (Pt), palladium (Pd), gold (Au), iridium (Ir), ruthenium (Ru) or silver (Ag) is more preferable.

The sputtering gas may be any gas that can repel single atoms from the target and has no reactivity with the atoms constituting the dispersion, and may be air, helium (He), argon (Ar). ), A known sputtering gas such as nitrogen (N ₂ ) gas can be used. From the viewpoint of making the reaction between the atoms and the sputtering gas difficult to occur, the sputtering gas is preferably an inert gas containing a rare gas such as helium (He) and argon (Ar) and nitrogen (N ₂ ) gas. Further, from the viewpoint of facilitating the repelling of single atoms from the target, the sputtering gas preferably contains atoms having a small molecular weight, while from the viewpoint of facilitating the repelling of a sufficient amount of single atoms at a time, The sputtering gas preferably contains a gas having a molecular weight that is somewhat large. From such a viewpoint, the sputtering gas is more preferably a gas containing 70% by volume or more of N ₂ . Examples of the sputtering gas containing 70% by volume or more of N ₂ include air and nitrogen gas.

The pressure of the sputtering gas can be arbitrarily set as long as the atoms can reach the support with the predetermined proportion of atoms constituting the target being a single atom.

The chamber may be a chamber provided in a normal apparatus capable of performing sputtering. For example, the distance between the target and the support can be arbitrarily set as long as the atoms can reach the support with the predetermined proportion of atoms constituting the target being a single atom. Also, the temperature in the chamber can be arbitrarily set as well, but from the viewpoint of suppressing the kinetic energy of the sputtered molecules and suppressing the aggregation of atoms in flight, the temperature in the chamber is It is preferable that it is 40 degrees C or less, and it is more preferable that it is normal temperature.

The magnitude of the voltage may be any intensity that can repel single atoms from the target. From the viewpoint of reducing the amount of energy applied to the target by the collision of the sputtering gas and facilitating the repelling of more single molecules from the target, the voltage is preferably 500 V or less, more preferably 300 V or less. Preferably, it is 150 V or less, more preferably 50 V or less.

The above voltage may be continuously applied or may be repeatedly applied for a predetermined time. As described above, the number of atoms that reach the support increases substantially in proportion to the time during which the voltage is applied. Further, when the number of atoms reaching the support increases, the atoms may aggregate to form a cluster. Therefore, it is preferable to obtain a relationship between the time for applying the voltage and the number of atoms reaching the support in advance, and to apply the voltage only for the time during which a desired proportion of atoms are dispersed as single atoms.

According to the knowledge of the present inventors, when producing a monoatomic dispersion, the total time for applying a voltage, both in the case of continuing to apply continuously and in the case of repeatedly applying for a predetermined time Is preferably 1.5 seconds or less.

In addition, when voltage application for a predetermined time is repeatedly performed, it is easier to produce a monoatomic dispersion by reducing the number of atoms reaching the support by one voltage application. From the above viewpoint, the time for applying the voltage per time is preferably 1.5 seconds or less. On the other hand, from the viewpoint of producing the dispersion in a short time, the time for applying the voltage per time is preferably 0.5 seconds or more.

(Support)
An anchor site capable of adsorbing the sputtered atoms is formed on the support. An anchor site is a site that can adsorb a single atom without using a covalent bond. Anchor sites can adsorb atoms by electrostatic interactions such as van der Waals forces.

For example, the support may be a laminate in which one or more layers made of nanographene are stacked in an island shape on graphene. FIG. 1A shows an image obtained by imaging a structure in which Pt single atoms are dispersed on such a support by high-angle scattering dark field / scanning transmission electron microscopy (HAADF-STEM). As shown in FIG. 1A, in this structure, Pt shown in white in the figure is dispersed as a single atom. FIG. 1B is a diagram in which the region surrounded by the dotted line in FIG. 1A is enlarged and color-coded for each region (layer made of nanographene) in which the pixel intensity is substantially the same. In FIG. 1B, the nano graphene laminated on the graphene in an island shape is shown at different concentrations for each layer. As is clear from FIG. 1B, Pt exists in a region (anchor site) in contact with an end of the layer made of nanographene formed on the surface of the layer made of graphene or nanographene.

Note that graphene has a six-membered ring structure consisting of carbon that is continuous in the plane direction. Among graphene, atoms are easily adsorbed at the ends of voids in which carbon atoms are partially lost or at the ends of sheet-like graphene (these ends are also referred to as “edges”). I know that.

However, according to the knowledge of the present inventors, in the laminate, the end portion of the layer made of nanographene formed on the surface of the layer made of graphene or nanographene rather than the void or edge A single atom is more likely to be adsorbed in a region in contact with (hereinafter also simply referred to as “step edge”). This is because a void or edge does not generate enough force interaction to adsorb a single atom, but a step edge interacts with a single atom from two directions: the lower surface and the end of the layer formed above. It is thought that this is because a stronger adsorption force is generated because it can act. In addition, in a stacked body in which one or more layers made of nanographene are stacked in an island shape, a large number of step edges are formed, and single atoms that have reached the support are adsorbed by the step edges and dispersed on the support. It is thought that.

Also, as shown in FIGS. 2A to 2C, when the single atoms of gold (Au) (FIG. 2A), iridium (Ir) (FIG. 2B) and ruthenium (Ru) (FIG. 2C) are allowed to reach the laminate. , Both were adsorbed on the step edge and dispersed on the support. As these results show, the laminate can adsorb various atoms to the step edge with a single atom and disperse them on the support.

The distance in the stacking direction between successive layers of the layer made of nanographene is usually 0.33 nm or more and 0.35 nm or less. The number of layers is not particularly limited, and can be, for example, 2 or more and 15 or less, and preferably 2 or more and 7 or less.

In addition, the average of the distance between islands of the nanographene stacked in the above-mentioned island shape may be longer than the distance between atoms to be dispersed. However, as the average distance between the islands is shorter, the number of step edges in the unit area increases, and a larger number of single atoms can be adsorbed and dispersed in the unit area. Therefore, the average distance between islands may be adjusted according to the number of atoms desired to be dispersed in the unit area. Even if the average distance between the islands is long, the single atom that has reached the support as shown below diffuses at high speed on the support and is instantly adsorbed to the anchor site. Aggregation of single atoms is considered to hardly occur.

When the sputtered atoms arrive in a single atom state on the support on which the anchor site is formed, as shown in FIG. 3, the reached single atom is on the support 100 (the substrate 110 in FIG. 3). To diffuse. It is considered that the diffused monoatom reaches the anchor site 120 and is adsorbed on the anchor site 120 to be dispersed in a monoatomic state on the support.

According to the knowledge of the present inventors, the adsorption energy at which the anchor site adsorbs the atoms is much stronger than the adsorption energy at which the surface of the layer made of graphene or nanographene adsorbs the atoms. Therefore, in FIG. 3, the single atom that has reached the support 100 is adsorbed to the anchor site instantaneously, and the diffusion ends instantaneously. Therefore, even if single atoms successively reach the support 100, it is considered that the single atoms being diffused on the support 100 do not aggregate with each other and are adsorbed on the anchor site 120 as they are.

For example, as shown in FIG. 4, in the case where the support 200 is a stacked body in which the layer 230 made of nanographene is stacked in an island shape on the substrate 210 made of graphene, atoms that have reached a single atom move on the substrate 210. It diffuses and is adsorbed to the end of the layer 230 made of nanographene, which is the anchor site 220.

Conventionally, graphene has been produced so that a flat film composed of a single atomic layer spreads in a planar shape. On the other hand, by forming a layer made of nanographene on the graphene, many step edges as anchor sites are formed, and more single atoms can be dispersed per unit area. The amount of the layer made of nanographene can be adjusted by adjusting the pressure and temperature at the time of graphene film formation, or by irradiating the formed graphene with an electron beam.

Further, a material having the above laminated body such as activated carbon may be used as the support. Activated carbon has many fine pores with a diameter of about 1 nm to 20 nm, and the ratio of the surface area to the volume is very high. Therefore, if activated carbon is used as a support, it is considered that the content of single atoms per unit volume can be dramatically increased.

In addition, graphene may be manufactured by a roll-to-roll (RTR) method. With the RTR method, as shown in FIG. 5A, the copper foil wound around the delivery roller 510 is sequentially delivered, and the graphene film is formed on the copper foil by CVD by the chemical vapor deposition (CVD) unit 520. In this method, the copper foil on which the graphene film is formed is taken up by the take-up roller 530. According to the RTR method, graphene having a large area can be produced continuously and in large quantities. Note that the CVD unit 520 is preferably a plasma generating apparatus capable of forming graphene using surface wave excited microwave plasma because CVD at low temperature is possible and industrial applicability is high.

At this time, the graphene production apparatus 500 using the RTR method can include a single atom sputtering unit 540 downstream of the CVD unit 520 and upstream of the winding unit 530.

The single-atom sputtering unit 540 performs sputtering under the above-described conditions, causes the atoms that can be sputtered to reach the graphene formed by the CVD unit 320, and allows the atoms to be formed on the formed graphene. At least a part is dispersed with a single atom.

As shown in FIG. 5B, the graphene production apparatus 500 ′ transfers the formed graphene to another sheet (polypropylene sheet or the like) downstream of the CVD unit 520 and upstream of the single atom sputtering unit 540. The transfer section 550 may be provided.

With such a configuration, a structure in which single atoms are dispersed on a support made of graphene can be manufactured continuously and in large quantities.

(Sputtering equipment)
The structure in which single atoms are dispersed on the above-described support can be manufactured by the sputtering apparatus 600 illustrated in FIG.

The sputtering apparatus 600 includes a chamber 610, a target placement unit 620, a support placement unit 630, a sputtering gas introduction unit 640, a voltage application unit 650, and a control unit 660.

The chamber 610 may be a chamber whose inside can be sealed. The target placement unit 620 is provided in the chamber 610 and holds the target T described above. The support body arrangement | positioning part 630 is provided in the chamber 610, and hold | maintains the support body S mentioned above. At this time, the target placement unit 620 and the support placement unit 630 are provided in the chamber 610 so that the surface on which the target T is sputtered and the surface on which the anchor site of the support S is formed face each other. It is done. The sputtering gas introduction unit 640 introduces the above-described sputtering gas into the chamber 610. The sputtering gas introduction unit 640 may adjust the pressure inside the chamber 610 to a predetermined pressure. The voltage application unit 650 applies a voltage between the target T and the support S.

The control unit 660 controls the sputtering gas introduction unit 640 and the voltage application unit 650 to disperse the above-described at least a part of the atoms that can be sputtered on the support S as single atoms. A voltage is applied between the target T and the support S under the possible sputtering conditions. For example, the control unit 660 sets a voltage and a time determined according to the type of atoms, the type of anchor site, the sputtering gas, and the like included in the target T, and the target T, the support S, A voltage is applied during When a voltage is applied, the molecules Mg of the sputtering gas collide with the target T, the molecules Mt contained in the target T are repelled, and reach the support S. The molecules Mt that reach the support S diffuse on the support S and are adsorbed on the anchor sites to form a monoatomic dispersion.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[Example 1]
(Support)
A 1 cm square copper foil was immersed in acetic acid for one night or longer to remove the natural oxide film on the surface of the copper foil, and the copper foil from which the natural oxide film was removed was rinsed with pure water several times and then introduced into the CVD apparatus. Graphene was grown at 60 kPa and 1000 ° C., and methane gas diluted with argon was used as a carbon source. The pressure in the apparatus was controlled by an electronic controller with an error of 0.1% or less from the set value. After graphene growth, the copper foil was moved away from the heater coil, and the sample was rapidly cooled.

The grown graphene was transferred onto the upper surface of a transmission electron microscope TEM grid having a cylindrical shape with a diameter of 3 mm to obtain a support. At this time, in order to prevent multilayering due to transfer of graphene grown on the back surface, the back surface of the copper foil was immersed in a mixed solution of sulfuric acid and hydrogen peroxide solution. Thereafter, only the back surface of the copper foil was immersed in a 100 mM ammonium persulfate aqueous solution to dissolve the copper foil. After the copper foil is dissolved, the ammonium persulfate aqueous solution is replaced with pure water, and the graphene floating on the water surface is scooped up with a cylindrical TEM grid having a diameter of 3 mm, and the graphene is placed on the upper surface of the TEM grid. Transcribed.

The transferred graphene was observed by high-angle scattering dark field / scanning transmission electron microscopy (HAADF-STEM) at an acceleration voltage of 80 kV using an aberration correction electron microscope (manufactured by FEI, Titan3 G2, 60-300). The image obtained at this time is shown in FIG. 7A.

As shown in FIG. 7A, black and white contrast regions existed in the image. FIG. 7B shows a graph in which the distance from the starting point is plotted on the horizontal axis and the intensity for each pixel is plotted on the vertical axis for the region set in the image shown in FIG. 7A (indicated by a dotted line in FIG. 7A). The strength is divided into three different regions, labeled 0, 1, 2 and analyzed to be a hole without graphene, a region where nanographene is stacked in one layer, and a region where nanographene is stacked in two layers, respectively. It was done.

FIG. 7C is a diagram in which FIG. 7A is color-coded for each region where the pixel intensities are substantially the same. As shown in FIG. 7C, it was found that the obtained graphene was entirely composed of island-shaped nano-sized regions. Detailed analysis reveals that there is a single-layer graphene at the bottom and a structure in which nano-sized graphene is stacked on top of it, and up to seven layers are stacked in the largest region.

(Sputtering)
As a sputtering target, a cylindrical Pt target having a diameter of 57 mm and a thickness of 0.2 mm was prepared. The purity of this Pt target was 99.99%.

The Pt target and the support are placed in a chamber of a sputtering apparatus (JFC-1600, manufactured by JEOL Ltd.) so that the Pt target and the transferred graphene face each other, and the Pt target and the support A voltage was applied between the body and the body under the following conditions to pass a direct current.

(Condition inside chamber)
Atmospheric gas: Atmospheric pressure: 4.5Pa
Temperature: Room temperature (Current condition)
Voltage: 100V
Current: 10mA

The above voltage was applied for 1 second and sputtering was performed for 1 second. When performing sputtering for 2 seconds or more, the sputtering for 1 second was repeated with an interval of 10 seconds. At this time, the number of times of repeating the sputtering for 1 second was adjusted so that a value obtained by integrating the sputtering time became a target time.

Sputtering was performed under the above conditions with a sputtering time of 1 second, 2 seconds, 3 seconds, 4 seconds, 5 seconds, 7 seconds, 10 seconds, or 30 seconds. After each time of sputtering, using an aberration-corrected transmission electron microscope (JEM-ARM200F, manufactured by JEOL Ltd.), four regions arbitrarily set on the support surface (each about 50 nm × about 50 nm) ) Was imaged by high angle scattering dark field / scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray analysis (EDX). In the following images, when the device name is not indicated, it means an image captured using JEM-ARM200F manufactured by JEOL Ltd.

8A to 8E are each one of images taken by HAADF-STEM of the region set on the support surface after sputtering. 8A is an image when the sputtering time is 1 second, FIG. 8B is a sputtering time of 2 seconds, FIG. 8C is a sputtering time of 5 seconds, FIG. 8D is a sputtering time of 10 seconds, and FIG. 8E is an image when the sputtering time is 30 seconds. is there. From FIG. 8A to FIG. 8E, it was found that when the sputtering time is short (for example, 1 second or 2 seconds), an isolated point dispersion is formed on the support surface. Further, it was found that when the sputtering time was made longer, a cluster-like dispersion in which dots were aggregated was formed.

FIG. 9A shows one of images obtained by HAADF-STEM imaging the above-described region set on the support surface (however, a region different from FIG. 8D) when the sputtering time is 10 seconds. FIG. 9B is an image obtained by imaging the same region as FIG. 9A with characteristic X-rays having a wavelength corresponding to Pt by energy dispersive X-ray analysis (EDX). Since the dispersion state in FIG. 9A coincides with the dispersion state in FIG. 9B, it was found that the point existing in the image captured by the HAADF-STEM is Pt atoms.

After performing sputtering for each time, the relative value of the number of Pt atoms present on the support surface was measured. Of the characteristic X-rays corresponding to Pt obtained from the above region, the integrated intensity of M rays is considered to be proportional to the number of Pt atoms present in the region. Therefore, the above four areas are imaged by EDX, and the integrated intensities of the M-rays are obtained, and the obtained integrated intensity is set as a relative value of the number of Pt atoms existing in the area. FIG. 10 is a graph in which the sputtering time (unit: seconds) is plotted on the horizontal axis, and the relative value of the number of Pt atoms existing on the surface of the support at each sputtering time is plotted on the vertical axis. It can be seen that the relative value of the number of Pt atoms increases linearly as the sputtering time increases. From this, it was found that the number of Pt atoms attached to the support surface can be controlled by changing the sputtering time. From this, if the relationship between the number of Pt atoms and the integrated intensity of M rays when imaged with characteristic X-rays is examined in advance, the total number of Pt atoms existing in the region imaged with characteristic X-rays is obtained. You can also see that you can. In addition, when the sputtering time is increased, the atoms aggregate to form a large cluster, so that the proportion dispersed as a single atom with respect to the total number of sputtered atoms decreases. Using this result, it is possible to control the proportion of atoms dispersed as single atoms.

FIG. 11A is one of the images obtained by HAADF-STEM imaging the above-described region set on the support surface (however, a region different from FIG. 8A) when the sputtering time is 1 second. In the upper right of FIG. 11A, an enlarged image of two points showing particularly strong intensity is shown. As is clear from the enlarged view shown in the upper right of FIG. 11A, the diameter of each dispersion was 2 mm or less, which was almost the same as the atomic radius of Pt (about 1.4 mm). This suggested that the point dispersion was a single atom. Further, since there are many isolated points in FIGS. 8A and 8B, it was found that sputtered Pt atoms adhered to the support as single atoms under the above conditions.

FIG. 11B is an image obtained by performing noise processing on FIG. 11A using a low-pass filter and threshold processing. Each point shown in FIG. 11B is assumed to be a single atom of Pt. The number of points (number of Pt atoms) in this region (2690 nm ² ) was 710.

Further, in FIG. 11B, the distance from each point to the closest point (distance between nearest contacts: unit is Å) was obtained. In addition, since the interatomic distance (bonding distance) of Pt atoms is 2.7 mm or less, a plurality of points where the distance between the closest contacts is 2.7 mm or less are bonded together and aggregated, and the distance between the closest contacts is A point of 2.7 mm or more is considered to exist in isolation. In the following description, in order to facilitate the aggregation, it is assumed that the value obtained by rounding the first decimal place of the distance between the closest points is 3 or more is isolated and the points 2 or less are aggregated.

FIG. 12 shows the number of points where the distance between the closest points is the value for each value obtained by rounding off the first decimal place of the distance between the closest points, and the result is represented as a histogram. As is apparent from FIG. 12, among the 710 points, 704 have a distance between the nearest contacts of 3 mm or more (exist in isolation). Recently, there were only 6 points (3 pairs of 2 points) where the distance between contact points was 2 mm or less (coagulated).

FIG. 13 shows that a point where the distance between closest points is 3 mm or more (is present in isolation) forms a dispersion with one point, and a set of points where the distance between closest points is 2 mm or less is aggregated. Assuming that a dispersion is formed, the number of points constituting each dispersion is obtained, and for each number of points constituting each dispersion, the number of dispersions having the value of the number of points is obtained. The result is represented as a histogram. As is clear from FIG. 13, 704 out of 710 points (about 99.2%) formed a dispersion at one point.

FIG. 1 shows the above-mentioned region set on the support surface when the sputtering time is 1 second (however, a region different from FIG. 8A) at an acceleration voltage of 80 kV and HAADF- It is the image imaged by STEM. Note that FIG. 1 corrects the image so that the intensity difference between the pixels becomes clearer. FIG. 1B is an enlarged view of a region surrounded by a dotted line in FIG. 1A and is color-coded for each region (layer) where the pixel intensities are substantially the same. As shown in FIG. 1A, Pt does not exist in voids (voids: black portions in the figure) in which carbon is partially lost, but on graphene or the surface of a layer made of nanographene (gray portions in the figure). Existed. As is clear from FIG. 1B, Pt atoms (white circles) existed in a region (step edge) in contact with the end of the layer made of nanographene.

[Example 2]
A cylindrical Au target having a diameter of 57 mm and a thickness of 0.2 mm was prepared as a sputtering target. The purity of this Au target was 99.99%.

Using the above target, sputtering was performed in the same manner as in Example 1 except that the sputtering conditions were changed as follows.

(Condition inside chamber)
Atmospheric gas: Atmospheric pressure: 5.0Pa
Temperature: Room temperature (Current condition)
Voltage: 200V
Current: 10mA

FIG. 2A shows an image obtained by imaging a region arbitrarily set on the support surface with HAADF-STEM after the sputtering for 5 seconds under the above conditions is completed. The same region as in FIG. 2A is imaged by characteristic X-rays with a wavelength corresponding to Au by energy dispersive X-ray analysis (EDX), and is present in FIG. 2A because it matches the dispersion state of FIG. 2A. The point to do was found to be Au atoms.

[Example 3]
As a sputtering target, a cylindrical Ir target having a diameter of 57 mm and a thickness of 0.2 mm was prepared. The purity of this Ir target was 99.99%.

(Condition inside chamber)
Atmospheric gas: He
Pressure: 5.0Pa
Temperature: Room temperature (Current condition)
Voltage: 200V
Current: 10mA

FIG. 2B shows an image of a region arbitrarily set on the surface of the support by HAADF-STEM after completion of sputtering for 5 seconds under the above conditions. The same region as FIG. 2B is imaged by characteristic X-rays with a wavelength corresponding to Ir by energy dispersive X-ray analysis (EDX), and is present in FIG. 2B because it matches the dispersion state of FIG. 2B. It was found that the point to do was an Ir atom.

[Example 4]
As a sputtering target, a columnar Ru target having a diameter of 57 mm and a thickness of 0.2 mm was prepared. The purity of this Ru target was 99.99%.

FIG. 2C shows an image obtained by imaging a region arbitrarily set on the support surface with HAADF-STEM after the sputtering for 5 seconds under the above conditions is completed. The same region as FIG. 2C is imaged by characteristic X-rays with a wavelength corresponding to Ru by energy dispersive X-ray analysis (EDX), and is present in FIG. 2C because it matches the dispersion state of FIG. 2C. It was found that the point to do was a Ru atom.

[Example 5]
Sputtering was performed in the same manner as in Example 1 except that the atmospheric gas inside the chamber during sputtering was changed to He. Sputtering was performed again in the same manner as in Example 1 except that the atmosphere gas inside the chamber was changed to air.

FIGS. 14A to 14D show images obtained by HAADF-STEM of regions arbitrarily set on the support surface after the sputtering for 1 second under the above conditions is completed. FIG. 14A and FIG. 14B in which the magnification is changed are images when the atmospheric gas is He, and FIG. 14C and FIG. 14D in which the magnification is changed are images when the atmospheric gas is the atmosphere.

From FIG. 14, it was found that a structure in which single atoms are dispersed on a support by sputtering can be manufactured without depending on the atmospheric gas. Sputtering with an atmospheric gas having a high molecular weight (N ₂ : 28) causes a larger amount of single atoms to be ejected at a time than when sputtering with an atmospheric gas having a low molecular weight (He: 2). It has been found that higher structures can be produced.

From the above results, it is possible to produce a monoatomic dispersion by appropriately setting the sputtering conditions, and to adjust the sputtering time, so that the number of atoms attached to the support can be substantially accurately determined. It was found that it can be controlled.
This application claims priority based on the Japanese application No. 2016-016872 filed on February 1, 2016 and the Japanese application No. 2016-176829 filed on September 9, 2016. The contents described in the specification, claims and drawings are incorporated into the present application.

A structure in which single atoms are dispersed on a support according to the present invention and a method for producing a structure in which single atoms are dispersed on a support according to the present invention are used to form a thinner film and to produce a more efficient catalyst. Expected to be able to.

500, 500 ′ Graphene production apparatus 510 Delivery roller 520 Chemical vapor deposition (CVD) section 530 Winding section 540 Single atom sputtering section 550 Transfer section 600 Sputtering apparatus 610 Chamber 620 Target arrangement section 630 Support arrangement section 640 Sputter gas introduction section 650 Voltage application unit 660 control unit

Claims

A support on which an anchor site capable of adsorbing atoms capable of sputtering is formed;
The sputterable atoms adsorbed to the anchor sites and dispersed as single atoms on the support,
A structure in which single atoms are dispersed on a support.
The support is a laminate in which one or more layers made of nanographene are stacked in an island shape on graphene,
The anchor site is a region in contact with an end portion of the layer made of nanographene formed on the graphene or the surface of the layer made of nanographene,
The structure according to claim 1.
The structure according to claim 1 or 2, wherein the support is activated carbon.
The structure according to any one of claims 1 to 3, which is a dispersion in which 90% or more of the atoms are dispersed as single atoms.
The structure according to any one of claims 1 to 4, wherein the atoms that can be sputtered are atoms of a transition metal.
6. The structure according to claim 1, wherein the atoms that can be sputtered are platinum (Pt), gold (Au), iridium (Ir), or ruthenium (Ru).
In a chamber in which a target including an atom capable of sputtering and a support on which an anchor site capable of adsorbing an atom capable of sputtering is formed and a sputtering gas is introduced,
Applying a voltage between the target and the support under a sputtering condition that is obtained in advance and allows at least a part of the atoms that can be sputtered to be dispersed on the support as single atoms. A method for producing a structure in which single atoms are dispersed on a support, including a step of sputtering a target.
The support is a support in which one or more layers made of nanographene are stacked in an island shape on graphene,
The anchor site is a region in contact with an end portion of the layer made of nanographene formed on the graphene or the surface of the layer made of nanographene,
The method of claim 7.
The method according to claim 7 or 8, wherein the support is activated carbon.
The method according to any one of claims 7 to 9, wherein the voltage is 150 V or less.
The method according to any one of claims 7 to 10, wherein the voltage is applied for 1.5 seconds or less.
The method according to any one of claims 7 to 11, wherein the sputtering gas is a gas containing 70% by volume or more of nitrogen (N 2 ).
The method according to any one of claims 7 to 12, wherein the target includes a transition metal.
The method according to any one of claims 7 to 13, wherein the target is platinum (Pt), gold (Au), iridium (Ir), or ruthenium (Ru).
Furthermore, before the step of sputtering the target,
A step of sequentially feeding the copper foil wound around the feed roller;
Including forming a graphene film on the copper foil by chemical vapor deposition (CVD) to form the support.
The method according to any one of claims 7 to 14.
A sealable chamber;
A target placement part in which a target including atoms capable of sputtering provided in the chamber is placed;
A support body placement portion in which a support body provided with an anchor site capable of adsorbing atoms that can be sputtered is provided in the chamber;
A sputtering gas introduction section for introducing a sputtering gas into the chamber;
A voltage application unit that applies a voltage between the target and the support;
By controlling the sputtering gas introduction part and the voltage application part, the target is obtained under sputtering conditions that can be obtained in advance and can disperse at least a part of the atoms that can be sputtered as single atoms on the support. A controller for applying a voltage between the support and the support;
A sputtering apparatus comprising: