KR20220056261A - Layered compounds and nanosheets containing gallium and arsenic, and electrical devices using the same - Google Patents

Abstract

An object of the present invention is to provide a layered compound including gallium and arsenic, a nano-sheet manufactured by the layered compound, and an electric device including the above materials. In order to achieve the above object, the present invention may provide a layered structure compound or nano-sheet represented by M_(1-x)Ga_yAs_z (M is one or more of Group 2 elements, and 0 < x < 1.0, 0.6 <= y <= 2.25, and 1.25 <= z <= 2.25). Further, in the present invention, an electric device including the above-described layered structure compound or nano-sheet may be provided, and the electric device may be a memristor.

Description

Layered compounds and nanosheets containing gallium and arsenic, and electrical devices using the same

The present invention relates to a layered compound and nanosheet containing gallium and arsenic, and an electric device using the same, and more particularly, to a layered compound and nanosheet containing an alkaline earth metal and gallium and arsenic having various electrical properties And it relates to an electric device using the same.

Layered compounds connected to interlayers through van der Waals bonds can exhibit various properties, and by separating them by physical or chemical methods, two-dimensional (2D) nanosheets with a thickness of several nanometers to hundreds of nanometers are manufactured Research on this is active.

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

However, the layered structure compound having a two-dimensional crystal structure has been limited to materials such as graphite or transition metal chalcogen compounds so far, and there is a problem in that it cannot be developed into materials of various compositions.

Meanwhile, gallium arsenide is a compound semiconductor material and is widely used in high-power, high-frequency electrical devices, but there is no known known about gallium arsenide having a layered structure to date.

The gallium arsenide compound having a layered structure can be applied more diversified than the existing gallium arsenide compound having a different crystal structure, and application to new areas that have not been applied before can be expected.

An object of the present invention is to provide a layered compound containing gallium and arsenic, a nanosheet that can be made therethrough, and an electrical device including the materials.

In order to achieve the above object, in the present invention, M _1-x Ga _y As _z (M is at least one type of group 2 element, 0<x<1.0, 0.6≤y≤2.25, 1.25≤z≤2.25) It can provide a layered structure represented by the compound.

In addition, in the present invention, including a composition represented by M _1-x Ga _y As _z (M is at least one type of group 2 element, 0<x<1.0, 0.6≤y≤2.25, 1.25≤z≤2.25), , it is possible to provide a nanosheet made by a physical or chemical exfoliation method.

In addition, in the present invention, it is possible to provide an electric device including the layered structure compound or nanosheet as described above.

In addition, the electric device may be a memristor.

The layered structure compounds and nanosheets that can be provided through the present invention may have various electrical properties, thereby enabling the development of new electrical devices.

1 is a conceptual diagram showing a layered structure compound according to the present invention and a nanosheet made through the same.
2 is an XRD analysis graph of a sample according to an embodiment of the present invention.
3 shows a STEM (Sanning Transmission Electron Microscope) image and a Selected Area Electron Diffraction (SAED) pattern of a sample according to an embodiment of the present invention.
4 shows a STEM image and a SAED pattern of a sample according to an embodiment of the present invention.
5 shows STEM images and SAED patterns of samples according to an embodiment of the present invention.
6 shows a Selected Area Electron Diffraction (SAED) pattern of a sample according to an embodiment of the present invention.
7 shows a scanning electron microscope (SEM) image and a transmission electron microscope (TEM) image of a sample according to an embodiment of the present invention.
8 is an XRD analysis graph of a sample according to an embodiment of the present invention.
9 shows an atomic force microscope (AFM) image of a nanosheet according to an embodiment of the present invention and a line profile according thereto.
10 shows a hysteresis loop for a nanosheet according to an embodiment of the invention.
11 is a voltage-current characteristic graph for a nanosheet according to an embodiment of the present invention.

Hereinafter, the configuration and operation of the embodiment of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of a related well-known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, when a part 'includes' a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated.

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

[Formula 1] M _1-x Ga _y As _z

(M is at least one type of group 2 element, 0<x<1.0, 0.6≤y≤2.25, 1.25≤z≤2.25)

In general, GaAs has a 3D crystal structure of Wurtzite or Zinc Blende, and a layered structure cannot appear, so it is impossible to make a nanosheet by exfoliating it.

In order to overcome this, the inventors place an additive element between Ga _y As _z layers by adding a Group 2 element (hereinafter referred to as "additive element") to Ga _y As _z , resulting in a layered structure compound followed by a Ga _y As _z layer. was able to make The additive elements positioned between these Ga _y As _z layers weakly bond the Ga _y As _z layers through van der Waals bonds, so the plane on which these additional elements are positioned forms a cleavage plane that is easily split along this plane. .

Accordingly, the layered compound according to the present invention can be easily exfoliated through either or both physical or chemical methods as a Ga _y As _z layer along this cleavage plane, and this exfoliation becomes easier as the additive element is removed. is done Therefore, Ga _y As _z nanosheets can be easily made from such a layered compound by a physical or chemical exfoliation method, where some additional elements may remain in the Ga _y As _z nanosheets.

If the additive element is continuously removed, the Ga _y As _z interlayer distance in the compound gradually widens, and eventually the bond between the layers is lost and cracks may appear between the layers. Therefore, in the layered structure of the layered structure compound described in the present invention, the bonding force between the Ga _y As _z layers is removed as well as when the repeated two-dimensional Ga _y As _z layer is bonded to each other by van der Waals bonding by an additive element. This includes the case where the distance between the layers increases and cracks appear.

The nanosheet made by exfoliating from such a layered compound may be a Ga _y As _z single layer, but may be several hundred nm thick because it may be made by overlapping a plurality of layers. In general, nanosheets can exhibit anisotropy according to a two-dimensional shape only when the thickness is less than a certain level in relation to the width in the transverse direction. is preferably 0.1 or less. Since the width of the nanosheet made through the present invention can be 5 μm or more, the thickness of the nanosheet is preferably 500 nm or less. Here, some of the additive elements may remain in the Ga _y As _z nanosheet.

As such, the nanosheet according to the present invention refers to a sheet that is peeled off by a physical or chemical method from a layered structure compound, and includes not only a case in which the Ga _y As _z layer is a single layer but also a case in which it is composed of a plurality of layers.

A conceptual diagram of an example of such a layered compound and nanosheet is shown in FIG. 1 , in which the additive element 11 is positioned between the Ga _y As _z layer 10 of MGa _y As _z and the Ga _y As _z layer 10 . It shows that the bond is maintained between the layers, where as the additive element 11 is removed, it becomes M _1-x Ga _y As _z , and the bond between the Ga _y As _z layers 10 is weakened, and when it is physically or chemically peeled, finally It is shown that Ga _y As _z nanosheets 20 are made. The nanosheets made in this way may still contain some of the additive elements 11 .

The layered structure compound according to the present invention can be synthesized using various Group 2 elements in addition to the conventionally known layered structure compounds. is Ca(GaAs) ₂ having a space group of R-3m, Sr ₃ (GaAs ₂ ) ₂ having a space group of C2/c, Sr(GaAs) ₂ having a space group of P2/m, P2 ₁ /c and Ba(GaAs) ₂ having a space group, and through this, various M _1-x Ga _y As _z compounds can also be synthesized. _Here , _ICSD is _a database that contains information on all _inorganic crystal structures reported since ₁₉₁₅ until now. It can be said that it is included in the scope of the invention.

The layered structure compound and nanosheets can be made with the layered structure compound and nanosheets using it even in a partially remaining state without completely removing the additive elements from the layered structure compound. be able to

As the additive element is removed, the crystal structure of the layered compound may change. As the additive element is removed, the M _1-x Ga _y As _z compound may change to a wurtzite structure. In particular, when x exceeds 0.9, the Ga _y As _z layer may change to a wurzite structure. Even in this case, the surface on which some additional elements remain remains a cleaved surface on which physical exfoliation easily occurs, or the bonding force between the Ga _y As _z layers is removed. As the distance between the layers increases, cracks appear. Accordingly, the Ga _y As _z layer maintains a two-dimensional layer, and the compound has a layered structure.

The remaining additional elements may be in the range where x is 0.1≤x<0.90 based on the above-mentioned [Formula 1].

As M, an additive element, is partially removed from the MGa _y As _z compound, the bonding force between the Ga _y As _z layers is weakened, so that the Ga _y As _z layer can be easily peeled off. Accordingly, x may be 0.1≤x<0.9 to facilitate peeling while maintaining the crystal structure. The crystal structure maintained here may have a space group of R-3m.

Also, the range of x may be in the range of 0.20≤x≤0.80. In the layered structure compound in which the additive element is partially removed and a certain amount remains, the additive element remaining between the layers can move between the layers, thereby exhibiting various electrical properties. Therefore, it may be preferable that more than a certain fraction of the additional elements are removed from the M _1-x Ga _y As _z compound and some remain. For this purpose, the range of x may be in the range of 0.20≤x≤0.80.

The M _1-x Ga _y As _z layered compound or nanosheet may in particular be Ca _1-x Ga _y As _z wherein M is Ca. Therefore, in the present invention, the layered compound may be a layered compound in which Ca is partially removed from CaGa ₂ As ₂ having a space group of R-3m.

A strong acid such as nitric acid or hydrochloric acid can be used to remove the additive element. As the additive element is removed through such a strong acid, the hydrogen ions contained in the strong acid are bound to the compound to provide a layered structure compound containing hydrogen and a nanosheet through it. be able to

The layered structure compound and the nanosheet containing hydrogen ions can be expressed by the following [Formula 2].

[Formula 2] M _1-x H _a Ga _y As _z

(M is at least one type of group 2 element, 0<x<1.0, 0.6≤y≤2.25, 1.25≤z≤2.25)

Here, hydrogen ions are added below the amount of the additive element removed by replacing the additive element.

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

As the additive element is removed from the layered structure compound, there may be a slight change in the peak of the XRD measurement. According to this change, in the XRD measurement using CuKα rays, The value of I ₍₀₀₆₎ /I ₍₀₀₃₎ , which is the peak intensity, may be in the range of 2 to 10. This is a phenomenon that occurs as the interlayer distance gradually widens and the peak intensity changes as the additive element is removed from the layered compound. When the layered structure compound is CaGa ₂ As ₂ , which is the space group of R-3m, the value of I ₍₀₀₆₎ /I ₍₀₀₃₎ is 1.32 before the removal of the additive element Ca, and when Ca is completely removed, I ₍₀₀₆₎ /I It can be seen through calculation that the value of ₍₀₀₃₎ is 11.48, therefore, in the layered compound from which Ca is partially removed, the value of I ₍₀₀₆₎ /I ₍₀₀₃₎ is in the range of 2 to 10, more preferably 3 to It could be 8. The same is true for nanosheets.

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

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

The ferroelectric characteristic is generally a characteristic of an oxide having an asymmetric structure such as a perovskite structure BaTiO ₃ , and the ferroelectric characteristic appears according to a change in the position of Ba located at the center.

However, the layered compound or nanosheet according to the present invention does not have such an asymmetric structure, but nevertheless exhibits ferroelectric-like properties. The reason why it exhibits ferroelectric-like properties even though it is not an asymmetric structure is thought to be that the positions of the remaining additive elements move according to the external electric field.

Through the ferroelectric-like properties of the layered structure compound or nanosheet according to the present invention, it is possible to apply it to various electrical devices.

In addition, the layered 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 an initial voltage is applied, the material maintains a high resistance state and the increase in current is insignificant and reaches a certain critical point. As it changes to a low-resistance state, the current rapidly increases.

This resistance switching characteristic is a characteristic generally found in oxides. Recently, the development of memory devices such as memristors that can store information such as flash memories using these characteristics is active, and the layered structure compound of the present invention or Nanosheets can be actively used in the development of memory devices such as memristors by utilizing resistance switching characteristics.

[Example]

1) Layered CaGa ₂ As ₂ Synthesis

Ca, Ga, and As were weighed according to the molar ratio, mixed, and then put into an alumina crucible. After that, it was put in a quartz tube and double-sealed to block outside air. This process was carried out in a glove box in an argon atmosphere. After that, the temperature was raised to 1000° C. so that all of the materials put in the liquid phase in the box furnace, maintained for 20 hours, and then cooled slowly for 300 hours to obtain a CaGa ₂ As ₂ sample. The obtained sample was treated in an ethanol solution in which isopropyl amine and hydrochloric acid were mixed to remove by-products.

2) Removal of Ca

In a 10% HNO ₃ solution, CaGa ₂ As ₂ samples were reacted at a low temperature of about 5° C. to partially remove Ca. The results are shown in the table below. In Table 2, residual Ca shows the results obtained through EDS analysis.

sample name reaction time Residual Ca (at%) sample A - 21 sample B 2 hours 11 sample C 3 hours 2 sample D 4.5 hours 0.3

3) Nanosheet formation process

After irradiating ultrasonic waves in ethanol with respect to the samples prepared as shown in Table 2, peeled nanosheets were prepared using a tape.

FIG. 2 shows XRD reference data of general CaGa ₂ As ₂ (CaGa ₂ As ₂ _ref) and XRD data of sample A before (CaGa ₂ As ₂ _syn) and after (CaGa ₂ As ₂ _syn.ipa_HCl) cleaning. . After removal of by-products through washing, peaks consistent with the XRD reference data (CaGa ₂ As ₂ _ref) were shown.

3 shows a STEM (Sanning Transmission Microscopy) image and a Selected Area Electron Diffraction (SAED) pattern for Sample A. FIG.

Through the analysis of FIGS. 2 and 3, it was found that the layered CaGa ₂ As ₂ having a space group of R-3m was synthesized in Sample A.

4 shows a STEM image and SAED pattern for sample B from which Ca is partially removed. It was found that even if Ca was partially removed, the crystal structure of the space group of R-3m identical to that of Sample A before the removal was maintained.

5 shows STEM images and SAED patterns as Ca is removed. Here, samples A and B show the same structure, but it was observed that a new pattern appeared in sample C containing 2 at% Ca and sample D with only 0.3 at% remaining.

In FIG. 6, (a) is the SAED pattern of GaAs having a wurtzite structure, and (b) is the SAED pattern of Sample D. These patterns coincided with each other, indicating that sample D had a wurzite structure.

7 shows that sample A is treated in nitric acid to prepare sample B and nanosheets are made therefrom.

FIG. 8 shows reference data of XRD peak data (Sample B) and GaAs simulation data (3R-GaAs) and CaGa ₂ As ₂ (CaGa ₂ As ₂ _ref) for sample B. FIG. GaAs simulation data (3R-GaAs) refers to data simulated using the 'VESTA' program for a case in which Ca is completely removed while maintaining the layered R-3m structure.

As Ca is removed, the interplanar distance increases, and the peak gradually shifts 0.1~0.3° to a lower angle, and there is also a change in intensity. In 3R-GaAs and _{CaGa 2} As ₂ _ref _, the The results were 1.3188 and 11.4773, respectively. The result of I ₍₀₀₆₎ /I ₍₀₀₃₎ in the actual sample B was 4.24, indicating the middle of the result value through calculation.

9 shows an atomic force microscopy (AFM) image of a nanosheet peeled from sample B and a line profile accordingly. It was confirmed that the nanosheet was peeled off with a thickness of about 10 nm.

10 is a PFM (Piezoresponse Force Microscopy) measurement result of the nanosheet peeled from the sample B. As a result, a hysteresis loop was observed in the nanosheet, confirming that the nanosheet had ferroelectric-like properties.

In addition, a change in current according to voltage was measured for the nanosheet peeled from Sample B, and the results are shown in FIG. 11 .

At the initial voltage, the high resistance state (1) is maintained to indicate a low current flow, but when the voltage exceeds a certain level, it becomes a low resistance state (2) and the current rapidly increases, and the same characteristics are exhibited in the opposite electrode direction. As it can be seen, it can be seen that the resistance switching characteristic is exhibited.

It was found that by using such resistance switching characteristics, it can be applied to a memristor device, which is being actively developed as a neuromorphic memory device in recent years.

Claims (26)

A layered structure compound represented by the following formula (1).
[Formula 1] M _1-x Ga _y As _z
(M is at least one type of group 2 element, 0<x<1.0, 0.6≤y≤2.25, 1.25≤z≤2.25) The method of claim 1,
Wherein x is 0.1≤x<0.90, the layered structure compound. The method of claim 1,
Wherein x is 0.20≤x≤0.80, the layered structure compound The method of claim 1,
The M is Ca, the layered structure compound. The method of claim 1,
The layered structure compound further comprises H, the layered structure compound. The method of claim 1,
Wherein x is 0.90≤x, the layered structure compound. 6. The method according to any one of claims 1 to 5,
The crystal structure of the layered structure compound represents a space group of R-3m, a layered structure compound. 7. The method of claim 6,
of the layered structure compound The crystal structure is a Wurzite (Wurzite) structure, a layered structure compound 7. The method according to any one of claims 1 to 6,
The layered structure compound, in XRD measurement using CuKα ray, the value of I ₍₀₀₆₎ /I ₍₀₀₃₎ , which is the peak intensity of the (006) plane compared to the peak intensity of the (003) plane, is in the range of 2 to 10, the layered structure compound . 7. The method according to any one of claims 1 to 6,
The layered structure compound exhibits a ferroelectric-like property, a layered structure compound. 7. The method according to any one of claims 1 to 6,
The layered structure compound exhibits resistance switching characteristics, a layered structure compound. A nanosheet comprising a composition represented by the following formula (1) and made by a physical or chemical peeling method.
[Formula 1] M _1-x Ga _y As _z
(M is at least one type of group 2 element, 0<x<1.0, 0.6≤y≤2.25, 1.25≤z≤2.25) 13. The method of claim 12,
The M is Ca, nanosheets. 13. The method of claim 12,
Wherein x is 0.1≤x<0.9, the nanosheet. 13. The method of claim 12,
Wherein x is 0.20≤x≤0.80, the nanosheet. 13. The method of claim 12,
The composition further comprises H, nanosheets. 13. The method of claim 12,
Wherein x is 0.9≤x, nanosheets. 17. The method according to any one of claims 12 to 16,
The crystal structure of the composition represents a space group of R-3m, nanosheets. 18. The method of claim 17,
of the composition the crystal structure Nanosheets showing the Wurzite structure. 18. The method according to any one of claims 12 to 17,
In the composition, the value of I ₍₀₀₆₎ /I ₍₀₀₃₎ , which is the peak intensity of the (006) plane compared to the peak intensity of the (003) plane in XRD measurement using CuKα ray, is in the range of 2 to 10, nanosheet. 18. The method according to any one of claims 12 to 17,
wherein the composition exhibits ferroelectric-like properties. 18. The method according to any one of claims 12 to 17,
The composition exhibits resistance switching properties, nanosheets. 18. The method according to any one of claims 12 to 17,
The thickness of the nanosheet is less than 500nm, nanosheet. An electric device comprising the layered compound according to any one of claims 1 to 6. 18. An electrical device comprising the nanosheet according to any one of claims 12 to 17. 26. An electrical component according to any one of claims 24 to 25, wherein the electrical component is a memristor.

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