KR102484718B1 - 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 containing gallium and arsenic, a nanosheet that can be made therethrough, and an electric device including the materials. In order to achieve the above object, in the present invention, M _1-x Ga _y As _z (M is one or more of Group 2 elements, 0<x<1.0, 0.6≤y≤2.25, 1.25≤z≤2.25) A layered compound or nanosheet represented by may be provided. In addition, the present invention may provide an electrical device including the above layered compound or nanosheet, and the electrical 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 containing gallium and arsenic, a nanosheet, and an electrical device using the same, and more particularly, to a layered compound containing gallium and arsenic and a nanosheet containing alkaline earth metals and 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 physically or chemically separating them, two-dimensional (2D) nanosheets with a thickness of several nanometers to hundreds of nanometers are prepared. It can be done, and 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 next-generation future materials to replace existing materials.

However, layered compounds having a two-dimensional crystal structure have been limited to materials such as graphite or transition metal chalcogen compounds so far, and there has been a problem in that they are not developed into materials of various compositions.

On the other hand, gallium arsenide (Gallium Arsenide) is a compound semiconductor material, which is widely used in high-power, high-frequency electric devices, but until now, nothing has been known about gallium arsenide having a layered structure.

A gallium arsenide compound having a layered structure can have more diverse applications than conventional gallium arsenide compounds having a different crystal structure, and can also be expected to be applied to new areas that have not been previously applied.

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 electric device including the materials.

In order to achieve the above object, in the present invention, M _1-x Ga _y As _z (M is one or more of Group 2 elements, 0<x<1.0, 0.6≤y≤2.25, 1.25≤z≤2.25) A layered compound represented by can be provided.

In addition, the present invention includes a composition represented by M _1-x Ga _y As _z (M is at least one of Group 2 elements, 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, the present invention can provide an electric device including the layered compound or nanosheet as described above.

Also, the electric element may be a memristor.

Layered compounds and nanosheets that can be provided through the present invention can have various electrical properties, and through this, it is possible to develop new electrical devices.

1 is a conceptual diagram showing a layered compound according to the present invention and a nanosheet made therethrough.
2 is an XRD analysis graph of a sample according to an embodiment of the present invention.
3 shows a Sanning Transmission Electron Microscope (STEM) 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 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 corresponding line profile.
10 shows a hysteresis loop for a nanosheet according to an embodiment of the invention.
11 is a voltage-current characteristic graph of a nanosheet according to an embodiment of the present invention.

Hereinafter, the configuration and operation of embodiments 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 known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, when a certain part 'includes' a certain component, this means that it may further include other components without excluding other components unless otherwise stated.

The layered compound according to the present invention may be represented by a layered compound represented by Formula 1 below.

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

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

In general, GaAs is a three-dimensional Wurtzite or Zinc Blende crystal structure, and thus, it is impossible to exfoliate it to form a nanosheet.

In order to overcome this, the inventors placed the additive element between the Ga _y As _z layers by adding a Group 2 element (hereinafter referred to as “additional element”) to Ga _y As _z , resulting in a layered compound in which the Ga _y As _z layer was followed. have been able to make The additive elements located between these Ga _y As _z layers weakly bind the Ga _y As _z layers through van der Waals bonds, so that the plane on which these additive elements are located forms a cleavage plane that easily cracks along this plane. .

Accordingly, the layered compound according to the present invention can be easily exfoliated into a Ga _y As _z layer along such a cleavage plane through either physical or chemical methods, or both. It is done. Therefore, Ga _y As _z nanosheets can be easily prepared from these layered compounds through physical or chemical exfoliation, and some additive elements may remain in the Ga _y As _z nanosheets.

When the additive element is continuously removed, the distance between Ga _y As _z layers in the compound is gradually widened, and eventually cracks may appear between the layers as the bonding between the layers is lost. Therefore, the layered structure of the layered compound described in the present invention is not only the case where the repeated two-dimensional Ga _y As _z layers are bonded between layers by van der Waals bonding by an additive element, but also the bonding force between the Ga _y As _z layers is eliminated This includes the case where the distance between layers widens to show cracks.

A nanosheet made by exfoliation from such a layered compound may be a Ga _y As _z single layer, or may be several hundred nm thick because it may be made by overlapping a plurality of layers. In general, nanosheets can show anisotropy according to a two-dimensional shape when the thickness is less than a certain level compared 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 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 physically or chemically exfoliated from a layered compound, and includes a case in which the Ga _y As _z layer is a single layer as well as a case in which a plurality of layers are formed.

A conceptual diagram of an example of such a _{layered compound} and a _{nanosheet is shown} in _FIG . It shows that the bonding between the Ga _y As _z layers 10 is weakened as the additive element 11 is removed and becomes M _1-x Ga _y As _z , and when it is physically or chemically separated, it is finally It shows that it is made of Ga _y As _z nanosheets (20). The nanosheet thus formed may still contain some of the additive elements 11.

The layered compound according to the present invention can be synthesized using various group 2 elements in addition to the conventionally known layered compound, and the layered compound containing the known group 2 elements and gallium and arsenic through ICSD (Inorganic Crystal Structure Database). of Ca(GaAs) ₂ with a space group of R-3m, Sr ₃ (GaAs ₂ ) ₂ with a space group of C2/c, Sr(GaAs) ₂ with a space group of P2/m, and P2 ₁ /c There is 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 from ₁₉₁₅ to the present. It can be said that it is included in the scope of the invention.

Layered compounds and nanosheets can be made from these layered compounds even when some of the additive elements remain without completely removing them. Due to these remaining additives, the layered compounds and nanosheets exhibit various electrical properties. 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 can change to a wurtzite structure. Even in this case, the surface on which some additive elements remain still becomes a cleavage plane where physical exfoliation easily occurs or the bonding force between the Ga _y As _z layers is removed. As the distance between layers widens, cracks appear, and accordingly, the Ga _y As _z layer maintains a two-dimensional layer, so that the compound has a layered structure.

The remaining additive element may be in the range of 0.1≤x<0.90, based on the above-described [Formula 1].

As the additive element M is partially removed from the MGa _y As _z compound, the bonding force between the Ga _y As _z layers is weakened, and the Ga _y As _z layer can be easily peeled off. Therefore, x may be 0.1≤x<0.9 so that peeling is easy 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 some of the additive elements are removed and a certain amount remains, the additive elements remaining between the layers can move between the layers, thereby exhibiting various electrical properties. Therefore, in the M _1-x Ga _y As _z compound, it may be preferable that a certain fraction or more of the additive element be removed and some of the additive element remain. The range of x for this 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 where M is Ca. Therefore, the layered compound in the present invention may be a layered compound in which Ca is partially removed from CaGa ₂ As ₂ having a space group of R-3m.

For the removal of the additive element, a strong acid such as nitric acid or hydrochloric acid can be used. As the additive element is removed through the strong acid, the hydrogen ion contained in the strong acid is bound to the compound to provide a layered compound containing hydrogen and a nanosheet through it. be able to

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

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

(M is at least one of Group 2 elements, 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.

As a result of analysis, the above-described layered compound or nanosheet exhibits various properties, and these properties are described below. The layered compound or nanosheet described herein includes both cases with and without additive elements.

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

As described above, the layered compound or nanosheet can exhibit various electrical properties due to the inherent layered structure and the remaining additive elements.

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

Ferroelectric properties are generally found in oxides of an asymmetric structure, such as BaTiO ₃ of a perovskite structure, and ferroelectric properties appear according to changes in the position of Ba located in 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. It is thought that the reason why the ferroelectric-like characteristics are exhibited even though the structure is not asymmetric is that the position of the remaining additive element is moved according to the external electric field.

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

In addition, the layered compound or nanosheet according to the present invention exhibits resistance switching characteristics.

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, so the increase in current is insignificant and then 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, and recently, memory devices such as memristors capable of storing information such as flash memories have been actively developed using this characteristic, and the layered 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) Synthesis of layered CaGa ₂ As ₂

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

2) Removal of Ca

A CaGa ₂ As ₂ sample was reacted at a low temperature of about 5° C. in a 10% HNO ₃ solution 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) Nanosheeting process

For the samples prepared as shown in Table 2, ultrasonic waves were irradiated in ethanol, and nanosheets were prepared by using a tape.

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

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

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

4 shows a STEM image and SAED pattern of sample B from which Ca was partially removed. It was found that even though Ca was partially removed, the same crystal structure of the space group of R-3m as that of Sample A before being removed was maintained.

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

In FIG. 6, (a) shows the SAED pattern of GaAs having a wurzite structure, and (b) shows the SAED pattern of sample D. These patterns coincided with each other, and through this, it was found that sample D had a wurtzite structure.

7 shows that sample A is treated in nitric acid to form sample B, and nanosheets are formed therefrom.

8 shows reference data of XRD peak data (sample B), GaAs simulation data (3R-GaAs), and CaGa ₂ As ₂ (CaGa ₂ As ₂ _ref) for sample B. GaAs simulation data (3R-GaAs) means simulated data using the 'VESTA' program for the case where Ca is completely removed while maintaining the layered R-3m structure.

As Ca is removed, the interplanar distance increases and the peak gradually shifts to a low angle by 0.1~0.3°, 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 values through calculation.

9 shows an atomic force microscopy (AFM) image of a nanosheet exfoliated from sample B and a line profile thereof. It was confirmed that the nanosheets were exfoliated into nanosheets having a thickness of about 10 nm.

FIG. 10 shows a PFM (Piezoresponse Force Microscopy) measurement result of the nanosheet exfoliated from Sample B. A hysteresis loop was observed in the nanosheet, confirming that the nanosheet had ferroelectric-like characteristics.

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

At the initial voltage, the high-resistance state (1) is maintained to show low current flow, but when the voltage exceeds a certain level, the low-resistance state (2) is displayed, indicating that the current rapidly increases, and the same characteristics appear in the opposite electrode direction It can be seen that it exhibits resistance switching characteristics.

It was found that using these resistance switching characteristics, it can be applied to a memristor device, which has recently been actively developed as a neuromorphic memory device.

Claims (26)

A layered compound represented by the following Chemical Formula 1 and having ferroelectric-like properties, wherein the ferroelectric-like properties exhibit ferroelectric properties while having a symmetrical crystal structure.
[Formula 1] M _1-x Ga _y As _z (M is at least one of Group 2 elements , 0.3≤x≤0.8, 0.75≤y≤2.25, 1.25≤z≤2.25) delete delete According to claim 1,
Wherein M is Ca, a layered compound. According to claim 1,
The layered compound further comprises H, the layered compound. delete According to claim 1,
The layered compound, wherein the crystal structure of the layered compound represents the space group of R-3m. delete According to claim 1,
The layered compound has a 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 rays, in the range of 2 to 10. . delete According to claim 1,
The layered compound exhibits resistance switching characteristics, the layered compound. A nanosheet comprising a composition represented by Formula 1 below, produced by a physical or chemical exfoliation method, and having ferroelectric-like properties, wherein the ferroelectric-like properties exhibit ferroelectric properties while having a symmetrical crystal structure.
[Formula 1] M _1-x Ga _y As _z
(M is at least one of Group 2 elements, 0.3≤x≤0.8, 0.75≤y≤2.25, 1.25≤z≤2.25) According to claim 12,
Wherein M is Ca, the nanosheet. delete delete According to claim 12,
The nanosheet, wherein the composition further comprises H. delete According to claim 12,
The nanosheet, wherein the crystal structure of the composition represents the space group of R-3m. delete According to claim 12,
In the composition, the peak intensity of the (006) plane compared to the peak intensity of the (003) plane in XRD measurement using CuKα rays, the value of I ₍₀₀₆₎ / I ₍₀₀₃₎ is in the range of 2 to 10, nanosheet. delete According to claim 12,
The nanosheet, wherein the composition exhibits resistance switching properties. According to claim 12,
The thickness of the nanosheet is 500 nm or less, nanosheet. An electric element comprising the layered structure compound according to claim 1. An electrical device comprising the nanosheet according to claim 12 . 26. The electrical component according to claim 24 or 25, wherein the electrical component is a memristor.

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