KR20220035598A - Layered compounds and nanosheets containing aluminum and antimony, and electrical devices using the same - Google Patents

Abstract

The purpose of the present invention is to provide an aluminum antimonide layered structure compound containing an alkali metal, a nanosheet which can be made therethrough, and an electrical element including materials. In the present invention to achieve the above purpose, provided is the layered structure compound which can be represented by [Formula 1] M_(1-x)Al_ySb_z (M is at least one of group 1 elements, 0 < x <= 1.0, 0.75 <= y <= 1.25, 1.25 <= z <= 1.75).

Description

Layered compounds and nanosheets containing aluminum and antimony, and electrical devices using the same}

The present invention relates to a layered structure compound and nanosheet containing aluminum and antimony and an electrical device using the same. More specifically, the present invention relates to a layered structure compound and nanosheet containing aluminum and antimony that contain an alkali metal and have various electrical properties. and electric devices using the same.

Layered structure compounds connected through van der Waals bonds between interlayers can exhibit various characteristics, and by separating them by physical or chemical methods, two-dimensional (2D) nanosheets with a thickness of several nanometers to hundreds of nanometers can be manufactured. It can be done, so research on this is active.

In particular, low-dimensional materials such as nanosheets are expected to have groundbreaking new functions that existing bulk materials do not have, and have great potential as next-generation future materials to replace existing materials.

However, layered compounds with a two-dimensional crystal structure have so far been limited to materials such as graphite and transition metal chalcogenides, and have had the problem of not being developed into materials of various compositions.

Meanwhile, aluminum antimonide is a compound semiconductor material that can be used in various electrical devices, but to date, nothing is known about aluminum antimonide having a layered structure.

Antimonized aluminum compounds with a layered structure not only have more diverse applications than existing antimonized aluminum compounds with different crystal structures, but can also be expected to be applied to new areas that have not been previously applied.

The purpose of the present invention is to provide an antimonized aluminum layered structure compound containing an alkali metal, a nanosheet that can be made therefrom, and an electrical device containing the materials.

In order to achieve the above object, in the present invention, [Formula 1] M _1-x Al _y Sb _z (M is one or more group 1 elements, 0<x≤1.0, 0.75≤y≤1.25, 1.25≤z ≤1.75) can be provided.

In addition, in the present invention, the composition expressed by [Formula 1] M _1-x Al _y Sb _z (M is one or more group 1 elements, 0<x≤1.0, 0.75≤y≤1.25, 1.25≤z≤1.75) It is possible to provide a nanosheet made by a physical or chemical peeling method.

Additionally, the present invention can provide an electric device containing the layered structure compound or nanosheet as described above.

Additionally, the electrical device may be a memristor.

The layered structure compounds and nanosheets that can be provided through the present invention can have various electrical properties, which makes it possible to develop new electrical devices.

Figure 1 is a conceptual diagram of a layered structure compound and nanosheet made according to the present invention.
Figure 2 is a graph showing the XRD diffraction pattern for the layered structure compound according to the present invention.
Figure 3 shows SEM (Scanning Electron Microscope) images and EDS (Energy Dispersive Spectroscopy) analysis results for the layered structure compound according to the present invention.
Figure 4 shows a schematic diagram showing the structure of the layered compound according to the present invention and the results of Scanning Transmission Electron Microscope (STEM) analysis.
Figure 5 is a graph showing the XRD diffraction pattern for the layered structure compound according to the present invention.
Figure 6 is an SEM and TEM (Transmission Electron Microscope) image of the layered structure compound and nanosheet according to the present invention.
Figure 7 shows SEM images and EDS analysis results for the layered structure compound according to the present invention.
Figure 8 shows a schematic diagram showing the structure of the layered compound according to the present invention and the results of STEM analysis.
Figure 9 shows an atomic force microscopy (AFM) image and the resulting line profile for the nanosheet according to the present invention.
Figure 10 shows the results of evaluating ferroelectric properties through PFM (Piezoresponse Force Microscopy) for the nanosheet according to the present invention.
Figure 11 shows a TEM image and diffraction pattern for the nanosheet according to the present invention.

Hereinafter, the configuration and operation of an embodiment of the present invention will be described with reference to the attached drawings. In describing the present invention below, if a detailed description of a related known function or configuration is judged to unnecessarily obscure the gist of the present invention, the detailed description will be omitted. In addition, when a part is said to 'include' a certain component, this does not mean excluding other components, but may include other components, unless specifically stated to the contrary.

The layered structure compound or nanosheet according to the present invention may be represented by the following formula (1).

[Formula 1] M _1-x Al _y Sb _z

(M is one or more types of group 1 elements, 0<x≤1.0, 0.75≤y≤1.25, 1.25≤z≤1.75)

In general, AlSb has a zinc blende crystal structure and cannot exhibit a layered structure, so it was impossible to create nanosheets by exfoliating it.

To overcome this, the inventors placed the added element between the Al _y Sb _z layers by adding a group 1 element (hereinafter referred to as “additional element”) to Al _y Sb _z , resulting in a layered structure compound with Al _y Sb _z layers connected. It was possible to make it. The added elements located between these Al _y Sb _z layers weakly bond the Al _y Sb _z layers through van der Waals bonds, so that the side where these added elements are located forms a cleavage plane that is easily split along this side.

Accordingly, the layered structure compound according to the present invention can be easily peeled off into the Al _y Sb _z layer along the cleavage plane through either or both physical or chemical methods. This peeling becomes easier as the additive element is removed. It comes true. Therefore, Al _y Sb _z nanosheets can be easily made from these layered structure compounds through physical or chemical peeling methods, where some additive elements may remain in the Al _y Sb _z nanosheets.

If additional elements are continuously removed, the distance between Al _y Sb _z layers in the compound gradually widens, weakening the bonding between layers, and eventually cracks may appear between layers as bonding between layers disappears. Therefore, the layered structure of the layered compound described in the present invention not only occurs when repeated two-dimensional Al _y Sb _z layers are bonded between layers through van der Waals bonds by added elements, but also when the bonding force between Al _y Sb _z layers is removed. This includes cases where cracks appear as the distance between layers widens.

The nanosheet created by peeling from such a layered structure compound may be a single layer of Al _y Sb _z , but since it may be made by overlapping multiple layers, it may be hundreds of nm thick. In general, a nanosheet can exhibit anisotropy according to its two-dimensional shape only when its thickness relative to the lateral width is below a certain level. For this, the ratio of the thickness (d) to the width (L) of the nanosheet (d/L) is It is preferable that it is 0.1 or less. Since the width of the nanosheet produced through the present invention can be 5 ㎛ or more, the thickness of the nanosheet is preferably 500 nm or less. Here, some added elements may remain in the Al _y Sb _z nanosheet.

As such, the nanosheet according to the present invention refers to a sheet that is peeled off from a layered structure compound by physical or chemical methods, and includes not only cases where the Al _y Sb _z layer is a single layer, but also cases where the Al y Sb z layer is composed of a plurality of layers.

A conceptual diagram of an example of such a layered structure compound and nanosheet is shown in Figure 1, where M(11), an additive element, is located between the Al _y Sb _z layers (10) of MA _y Sb _z , forming the Al _y Sb _z layer ( 10), where M(11) is removed to become M _1-x Al _y Sb _z , the bond between the Al _y Sb _z layers 10 is weakened, and when this is physically or chemically peeled off, the final It shows that it is made of Al _y Sb _z nanosheets (20). Nanosheets created in this way can still contain some M(11).

The layered structure compound before the added elements are removed may be Na ₂ Al ₂ Sb ₃ or K ₂ Al ₂ Sb ₃ having a space group of P2 ₁ /c, which is known in the art, and M _1-x that can be made through this. It can be said that a layered structure compound of the formula Al _y Sb _z is included within the scope of the present invention.

In addition, as a result of predictions made through calculations, it can be seen that a layered structure compound according to the chemical formula MAl _y Sb _z is possible using various group 1 elements such as Li, Na, and K, which can be created through M _1-x Layered structure compounds or nanosheets of the formula Al _y Sb _z can also be said to fall within the scope of the present invention.

Layered structure compounds and nanosheets can be made even without completely removing the added elements from these layered structure compounds and with some remaining. Due to these remaining added elements, the layered structure compounds and nanosheets exhibit various electrical properties. It becomes possible.

On the other hand, if the added element is excessively removed when x exceeds 0.95, the crystal structure of MAl _y Sb _z may change and appear in an amorphous phase. Even in this case, the surface from which some additive elements remain or has been removed still becomes a cleavage surface where physical separation easily occurs, or the bonding force between the Al _y Sb _z layers is removed, causing cracks to appear as the distance between the layers widens, resulting in a two-dimensional Al _y Sb _z layer. By maintaining the layer, the compound has a layered structure, from which exfoliated nanosheets can be manufactured.

Therefore, the layered structure compound or nanosheet according to the present invention is easy to peel, maintains the crystal structure before removal of the added element, and at the same time maintains various electrical properties due to the added element. In the above-mentioned [Chemical Formula 1], x is 0.10≤x≤0.95. It may be, and more preferably, it may be in the range of 0.3≤x≤0.8.

Here, the crystal structure of the layered compound or nanosheet can maintain the space group of P2 ₁ /c, which is the crystal structure before removing the added element.

To remove the added element, a strong acid such as nitric acid or hydrochloric acid can be used. As the added element is removed through this strong acid, the hydrogen ion contained in the strong acid is replaced by the site where the added element was removed, forming a layered structure compound containing hydrogen. Through this, it is possible to provide nanosheets.

The above-described layered structure compound or nanosheet exhibits various characteristics as a result of analysis, and these characteristics are described below. The layered structure compound or nanosheet described herein includes both cases with and without additional elements.

In XRD measurement using CuKα rays, the layered structure compound or nanosheet described above may have a space group of P2 ₁ /c.

Additionally, depending on the remaining amount of added elements, the layered structure compound may include an amorphous phase.

On the other hand, the above-described layered structure compound or nanosheet has 2θ = 25.1° ± 0.50°, 29.1° ± 0.50°, 41.6° ± 0.50°, 49.2° ± 0.50° and 51.6° ± 0.50° in XRD measurement using CuKα line. It may be a layered structure compound or nanosheet with no peak at that location. The peak may mean a peak with an intensity of 5% or more compared to the peak with the greatest intensity.

In general, naturally occurring AlSb compounds have a three-dimensional zinc blend structure and exhibit diffraction patterns at 25.1°, 29.1°, 41.6°, 49.2°, and 51.6°, but the layered structure compound or nanosheet according to the present invention has a zinc blend structure. Because it is not, the diffraction pattern does not appear at this angle.

The layered structure compound or nanosheet as described above can exhibit various electrical properties due to its inherent layered structure and remaining additive elements.

First, the layered structure compound or nanosheet according to the present invention exhibits ferroelectric-like properties.

Ferroelectric properties are generally found in oxides with an asymmetric structure, such as BaTiO ₃ in the perovskite structure, and the ferroelectric properties appear according to changes in the position of Ba located at the center.

However, the layered structure compound or nanosheet according to the present invention does not have such an asymmetric structure, but nevertheless exhibits ferroelectric-like properties. The reason it exhibits ferroelectric-like characteristics despite not having an asymmetric structure is thought to be because the position of the remaining additive element moves according to the external electric field.

The ferroelectric-like properties of the layered structure compound or nanosheet according to the present invention enable its application to various electrical devices.

Additionally, the layered structure compound or nanosheet according to the present invention exhibits resistance switching properties.

If a material has resistance switching characteristics, the current does not increase linearly according to the voltage applied to the material, but when the initial voltage is applied, the material maintains a high resistance state and the increase in current is minimal, but when a certain critical point is reached, the material maintains a high resistance state. As it changes to a low-resistance state, the current rapidly increases.

This resistance switching characteristic is generally a characteristic of oxides, and recently, the development of memory devices such as memristors capable of storing information such as flash memory has been actively developed using this characteristic, and the layered structure compound of the present invention and Nanosheets can be actively used in the development of memory devices such as memristors by utilizing their resistance switching characteristics.

[Example]

1) Layered Na ₂ Al ₂ Sb ₃ synthesis

Na, Al, and Sb metal pieces were weighed and mixed according to the molar ratio and then placed into an alumina crucible. Afterwards, it was placed in a quartz tube and double sealed to block external air. This process was carried out in a glove box with an argon atmosphere. Afterwards, the temperature was raised to 750°C in a box furnace for 3 hours and maintained for 40 hours. Afterwards, the Na ₂ Al ₂ Sb ₃ sample was obtained by slowly cooling to room temperature for 200 hours for recrystallization and crystal growth.

2) Removal of Na

AlCl ₃ was dissolved in acetonitrile to a concentration of 0.05 M, and a solution was prepared by adding 2 ml of ethanol-based HCl. Then, the solution was reacted over time to remove Na from layered Na ₂ Al ₂ Sb ₃ . The results are shown in the table below. In Table 1, residual Na represents the results obtained through EDS analysis.

sample name reaction time Residual Na (at%) Sample A - 28.5 Sample B 0.5 hours 13.9 Sample C 2 hours 8.8 Sample D 4 hours 4.1 Sample E 12 hours 0.25

3) Nanosheeting process

The samples prepared as shown in Table 2 above were irradiated with ultrasonic waves in ethanol and then peeled off using tape to produce nanosheets.

Figure 2 is a graph showing the XRD diffraction peaks, including the diffraction peak of non-layered AlSb of a general zinc blend structure (3D AlSb), the reference diffraction peak of Na ₂ Al ₂ Sb ₃ single crystal (Na ₂ Al ₂ Sb ₃ Ref), and the above-described method. Shows the diffraction peak for Na ₂ Al ₂ Sb ₃ (sample A) made of.

Comparing the AlSb diffraction peaks (3D AlSb) of sample A and the zinc blend structure, it was seen that sample A did not have diffraction peaks at 25.1°, 29.1°, 41.6°, 49.2°, and 51.6° that appeared in the zinc blend structure. .

Meanwhile, when comparing the reference diffraction peak of Na ₂ Al ₂ Sb ₃ single crystal (Na ₂ Al ₂ Sb ₃ Ref) with the diffraction peak of sample A, it can be seen that the intensity of the main peak is slightly different, but the angle at which the main peak appears is the same. I was able to. Therefore, it was found that Sample A synthesized through the above-described synthesis process was Na ₂ Al ₂ Sb ₃ with a layered structure.

In addition, it was confirmed through XRD analysis that the synthesized sample A had a monoclinic crystal structure of the space group P2 ₁ /c.

Figure 3 shows the SEM (Scanning Electron microscope) image and EDS (Energy Dispersive Spectroscopy) results for the synthesized sample A. Sample A's layered structure was confirmed in the SEM image, and as a result of EDS analysis, the molar ratio of Na:Al:Sb was obtained close to the theoretical composition ratio of 2:2:3.

Figure 4 shows a schematic diagram showing the structure of Na ₂ Al ₂ Sb ₃ , the results of a Scanning Transmission Electron Microscope (STEM) analysis in the [110] direction for sample A, and a Selected Area Diffraction (SAED) pattern. As a result of analyzing the SAED pattern, the measured interplanar distance of the (002) plane pattern was 7.76Å, and the measured (11-3) plane pattern was 7.76Å. The interplanar distance of the pattern was 4.01Å.

Theoretically, the interplanar distance between the (200) plane and the (002) plane was 7.776 Å and 4.05 Å, respectively, so the measured value was close to the theoretical value. However, these measured values are values that cannot be obtained from AlSb with a non-layered zinc blend structure. The measured pattern is a pattern that appears only in the P2 ₁ /c space group. In the SAED pattern, the zone-axis can be obtained through the cross product from the surface measured by the pattern, and the vector obtained through the cross product of the (002) and (11-3) planes is [1-10]. Therefore, it was confirmed that the zone-axis is [1-10], and when comparing the lattice structure in the actually measured STEM image visible from the [1-10] zone and the shape of the atomic structure model obtained in theory, It matched exactly. Through this, it was confirmed that the synthesized sample was Na ₂ Al ₂ Sb ₃ with a P2 ₁ /c space group.

In this way, through XRD, SEM, EDS, and STEM results, it was confirmed that sample A was Na ₂ Al ₂ Sb ₃ with a layered P2 ₁ /c space group.

Figure 5 shows the diffraction peak of non-layered AlSb (3D AlSb) of a typical zinc blend structure, the diffraction peak of sample A (sample A), and the diffraction peak of sample C from which Na has been partially removed. The XRD diffraction pattern of sample C showed major peaks in the same angle range compared to sample A due to Na removal, and it was determined that the monoclinic crystal structure of sample A, P2 ₁ /c, was still maintained.

Figure 6 shows a nanosheet made by removing Na from Sample A to become Sample C and peeling it off using a tape. In sample A, cleavage surfaces between layers were observed, but in sample C, as Na was removed, not only the cleavage surfaces but also the gap between layers widened, forming cracks.

Figure 7 shows SEM (Scanning Electron microscope) images and EDS (Energy Dispersive Spectroscopy) results of Sample C and Sample D. Samples C and D both had a layered structure with cleavage planes or cracks in SEM images, and EDS analysis showed that the Na content was 8.84 at% and 4.1 at%, respectively.

Figure 8 is a schematic diagram of the layered Na _2-x Al ₂ Sb ₃ atomic structure after selective removal of Na, a STEM image in the [010] direction, and a SAED pattern image for sample B. As a result of SAED analysis, the interplanar distance of the diffraction pattern of the (002) plane was 7.79Å, and the interplanar distance of the diffraction pattern of the (020) plane was 3.63Å. Compared to the theoretical interplanar distances of the (002) plane and (020) plane of 7.776 Å and 3.61 Å, respectively, the measured value was considered to be the same as the theoretical value. These measured values cannot be obtained from AlSb, which has a non-layered zinc blend structure. In addition, the Na ratio of the parent phase structure Na ₂ Al ₂ Sb ₃ is 28.5%, but the measured Na ratio of Na _2-x Al ₂ Sb ₃ is 13.9%, so it can be confirmed that some Na has been removed. Additionally, the measured pattern is a pattern that appears only in the P2 ₁ /c space group. In the SAED pattern, the zone-axis can be obtained through the cross product from the surface measured by the pattern, and the vector obtained through the cross product of the (002) and (020) planes is [100]. Therefore, it was confirmed that the zone-axis was [100], and when comparing the lattice structure in the actually measured STEM image seen from the [100] zone and the shape of the atomic structure model obtained in theory, they matched exactly. Through this, it was confirmed that the material from which Na was removed also maintained the P2 ₁ /c space group of the parent material Na ₂ Al ₂ Sb ₃ .

Figure 9 shows an atomic force microscopy (AFM) image of the nanosheet exfoliated from sample C and the resulting line profile. It was confirmed that it was exfoliated into nanosheets with a thickness of 20 nm or less.

In addition, after making a nanosheet for Sample C from which Na was removed, the ferroelectric properties were measured through PFM (Piezoresponse Force Microscopy), and the results are shown in FIG. 10. Through this, it was observed that ferroelectric-like characteristics were appearing.

It was found that by using these ferroelectric-like characteristics, it can be applied to various electrical devices and to memristor devices, which have recently been actively developed as neuromorphic memory devices.

Meanwhile, TEM analysis was performed on Sample E from which Na was excessively removed, and the results are shown in FIG. 11. TEM analysis results showed that the nanosheets from sample D were in an amorphous phase.

Claims (26)

A layered structure compound represented by the following formula (1).
[Formula 1] M _1-x Al _y Sb _z
(M is one or more group 1 elements, 0<x≤1.0, 0.75≤y≤1.25, 1.25≤z≤1.75) According to claim 1,
Wherein x is 0.10≤x≤0.95, a layered structure compound. According to claim 1,
Wherein x is 0.3≤x≤0.8, a layered structure compound. According to claim 1,
Wherein M is Na, a layered structure compound. According to claim 1,
The layered structure compound further contains H. According to claim 1,
Wherein x is 0.95<x, a layered structure compound. The method according to any one of claims 1 to 5,
The crystal structure of the layered structure compound represents a space group of P2 ₁ /c. According to claim 6,
The layered structure compound includes an amorphous phase. The method according to any one of claims 1 to 6,
The layered structure compound does not show peaks at the positions of 2θ = 25.1°±0.50°, 29.1°±0.50°, 41.6°±0.50°, 49.2°±0.50°, and 51.6°±0.50° in XRD measurement using CuKα rays. A layered structure compound, wherein the peak refers to a peak having an intensity of 3% or more compared to the peak with the highest intensity. The method according to any one of claims 1 to 6,
The layered structure compound exhibits ferroelectric-like characteristics. The method according to any one of claims 1 to 6,
The layered structure compound exhibits resistance switching characteristics. A nanosheet comprising a composition represented by the following formula (1) and made by a physical or chemical exfoliation method.
[Formula 1] M _1-x Al _y Sb _z
(M is one or more group 1 elements, 0<x≤1.0, 0.75≤y≤1.25, 1.25≤z≤1.75) According to claim 12,
The nanosheet where x is 0.10≤x≤0.95. According to claim 12,
The nanosheet where x is 0.3≤x≤0.8. According to claim 12,
Wherein M is Na, a nanosheet. According to claim 12,
The composition further comprises H. According to claim 12,
The x is 0.95<x, nanosheet. The method according to any one of claims 12 to 16,
The crystal structure of the layered compound is a nanosheet showing a space group of P2 ₁ /c. According to claim 17,
The composition is a nanosheet comprising an amorphous phase. The method according to any one of claims 12 to 17,
The layered structure compound does not show peaks at the positions of 2θ = 25.1°±0.50°, 29.1°±0.50°, 41.6°±0.50°, 49.2°±0.50°, and 51.6°±0.50° in XRD measurement using CuKα rays. and the peak refers to a peak having an intensity of 3% or more compared to the peak with the greatest intensity. The method according to any one of claims 12 to 17,
The composition is a nanosheet that exhibits ferroelectric-like properties. The method according to any one of claims 12 to 17,
The composition is a nanosheet that exhibits resistance switching properties. The method according to any one of claims 12 to 17,
The thickness of the nanosheet is 500 nm or less, Nanosheet. An electrical device comprising the layered compound according to any one of claims 1 to 6. An electrical device comprising the nanosheet according to any one of claims 12 to 17. 26. An electrical device according to claim 24 or 25, wherein the electrical device is a memristor.

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