Two-dimensional CrS nanosheets, their preparation method and applications

Abstract

This application discloses a two-dimensional CrS nanosheet, its preparation method, and its applications. The preparation method of the two-dimensional CrS nanosheet includes the following steps: sulfur powder and a chromium source precursor are placed upstream and centrally in a chemical vapor deposition system, respectively, in the direction of carrier gas flow. A substrate is positioned directly above the chromium source precursor. A reaction is carried out by programmed temperature rise to obtain two-dimensional cadmium sulfide nanosheets. The programmed temperature rise conditions are: increasing from 20-30°C to 650-680°C within 8-10 minutes, and then holding at that temperature. The preparation method of the CrS two-dimensional nanosheets provided in this application is simple, highly controllable, and has low production costs. The two-dimensional CrS nanosheets prepared using this method pave the way for magnetic materials and magnetic-related spintronics applications.

Description

Technical Field

[0001] This application relates to a two-dimensional CrS nanosheet, a preparation method thereof, and an application thereof, belonging to the technical field of magnetic two-dimensional non-layered materials. Background Art

[0002] The discovery of ferromagnetic two-dimensional van der Waals materials provides opportunities for exploring interesting physics and developing innovative spintronic devices. However, the controllable synthesis of these two-dimensional ferromagnets and enhancing their stability under ambient conditions remain challenging. Most of these magnetic two-dimensional materials are unstable in air, which hinders the study of their intrinsic magnetism and practical applications. Therefore, developing new magnetic materials is a major challenge. Non-layered two-dimensional materials have become excellent candidates due to their rich material systems and structures, and the ability to control the spin direction with excellent performance makes two-dimensional magnets excellent candidates for developing spintronic logic and storage devices. These magnetic materials provide extraordinary opportunities for studying intrinsic magnetism and physical phenomena at the nanoscale, opening the door to basic physics research and device applications.

[0003] Cr n CrX (X = S, Se, and Te; 0 < n < 1) is a new type of non-layered chromium-based chalcogenide that has been explored and has received great attention due to its magnetism. For example, Cr2S3 is a ferrimagnetic semiconductor with a Néel temperature of about 120 K. Cr2Te3 is a ferromagnet with a Curie temperature of about 200 K. Other compounds, such as CrTe and CrSe, also exhibit obvious ferromagnetism. However, there are few research reports on CrS, and there are even fewer reports on its synthesis methods and electrical and magnetic properties. The difficulty lies in the fact that chromium sulfide has many and complex crystal phases, which greatly affects the growth of chromium sulfide and the preparation of its devices. Therefore, there is an urgent need to develop efficient and controllable methods to synthesize two-dimensional CrS, which paves the way for further research on these magnetic materials and spintronics applications related to magnetism. Summary of the Invention

[0004] In this application, by controlling the growth temperature, ultrathin CrS nanosheets are successfully synthesized on a mica substrate by chemical vapor deposition. The synthesized CrS nanosheets can be as thin as 2.64 nm, and the Curie temperature is higher than room temperature, enriching the types of two-dimensional room-temperature ferromagnets. The controllable synthesis and research on the electrical and magnetic properties of CrS nanosheets will be of guiding significance for the future two-dimensional electronics field.

[0005] According to one aspect of this application, a preparation method of a two-dimensional CrS nanosheet is provided, including the following steps:

[0006] In the direction of carrier gas flow, sulfur powder and chromium source precursor are placed upstream and in the center of the chemical vapor deposition system, respectively. A substrate is placed directly above the chromium source precursor. The reaction is carried out by programmed temperature rise to obtain two-dimensional CrS nanosheets.

[0007] The conditions for the programmed temperature rise are: the temperature rises from 20-30°C to 650-680°C within a temperature rise time of 8-10 minutes, and then is held at that temperature.

[0008] Optionally, the chromium source precursor includes CrCl3 powder and KCl powder.

[0009] Optionally, the mass ratio of KCl powder to CrCl3 powder in the chromium source precursor is 1:5 to 20.

[0010] Optionally, the mass ratio of sulfur powder to CrCl3 powder is 0.5 to 5:1.

[0011] Optionally, the carrier gas is an inert gas.

[0012] Optionally, the inert gas is selected from at least one of helium, neon, and argon.

[0013] Optionally, the flow rate of the carrier gas is 30 to 50 sccm.

[0014] Optionally, the heat preservation time is 1 to 5 minutes.

[0015] Optionally, the chemical vapor deposition system may be evacuated and purged with argon gas before the temperature programmable.

[0016] The argon flow rate for the argon purging is 800–1500 sccm.

[0017] Optionally, the argon purging is performed 3 to 5 times.

[0018] Optionally, the sulfur powder is placed 5-10 cm upstream of the chromium source precursor.

[0019] Optionally, the substrate is mica.

[0020] A specific method for preparing two-dimensional CrS nanosheets includes the following steps:

[0021] The synthesis of two-dimensional CrS nanosheets was carried out in a chemical vapor deposition (CVD) system consisting of a single-temperature zone tube furnace and a 1-inch quartz tube. First, 10–20 mg of CrCl3 powder and 1–2 mg of KCl powder were weighed into a ceramic boat using an electronic balance and placed in the center of the tube furnace. Then, 10–50 mg of high-purity sulfur powder was weighed into the ceramic boat and placed approximately 10 cm above the CrCl3 powder in the tube furnace. Freshly peeled mica was used as a substrate and placed directly above the CrCl3 powder. A vacuum was created inside the tube using a vacuum pump, followed by purging with 800–1500 sccm of argon gas to remove oxygen and water vapor. Growth was carried out at atmospheric pressure using 30–50 sccm of Ar as the carrier gas. A temperature program was then set, increasing the temperature from room temperature to the growth temperature of 650–680 °C within 8–10 minutes and holding for 1–5 minutes. After growth, the tube furnace lid was opened, and the CVD system was rapidly cooled to room temperature using a fan.

[0022] According to another aspect of this application, a two-dimensional CrS nanosheet obtained according to the above preparation method is provided, wherein the CrS nanosheet has room temperature ferromagnetism.

[0023] Optionally, the CrS nanosheets are a single-crystal phase.

[0024] Optionally, the thickness of the CrS nanosheets is 2.64 nm to 36.5 nm.

[0025] According to another aspect of this application, a two-dimensional CrS nanosheet is provided for use in spintronics and in CrS field-effect transistors.

[0026] The beneficial effects that this application can produce include:

[0027] 1) The preparation method provided in this application uses a one-step CVD method to prepare stable two-dimensional CrS crystals, which are not easily contaminated and have strong controllability; the preparation process is simple, easy to operate, has low production cost, and short growth time.

[0028] 2) The two-dimensional CrS nanosheets provided in this application have room temperature ferromagnetism, which enriches the types of room temperature ferromagnetic materials and promotes the application of this material in the field of spintronics.

[0029] 3) The two-dimensional CrS nanosheets provided in this application are high-quality single crystals with metallic properties, and the CrS field-effect transistors (FETs) fabricated from them have good conductivity, which promotes the application of this material in the field of electricity. Attached Figure Description

[0030] Figure 1 An optical photograph of a two-dimensional CrS crystal controllably prepared on a mica substrate according to Example 1 of this application;

[0031] Figure 2 The Raman spectrum of the two-dimensional CrS crystal prepared in Example 1 of this application;

[0032] Figure 3 X-ray photoelectron spectroscopy of the two-dimensional CrS crystal prepared in Example 1 of this application;

[0033] Figure 4 An atomic force microscope image of the two-dimensional CrS crystal prepared in Example 1 of this application;

[0034] Figure 5 A transmission electron microscope image of the two-dimensional CrS crystal prepared in Example 1 of this application;

[0035] Figure 6 The CrS field-effect transistor prepared in Example 1 of this application and its transfer characteristic curve and output characteristic curve;

[0036] Figure 7 Room temperature magnetic domain images of the two-dimensional CrS crystal prepared in Example 1 of this application;

[0037] Figure 8 The field cooling and zero-field cooling curves of the CrS crystal and the hysteresis loop curves obtained at different temperatures were prepared for Example 1 of this application. Detailed Implementation

[0038] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0039] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0040] The analysis method in the embodiments of this application is as follows:

[0041] Morphological analysis was performed using an optical microscope (ECLLPSE LV150N, Nikon).

[0042] Component analysis was performed using Raman spectroscopy (LabRAM HR).

[0043] XPS analysis was performed using an X-ray photoelectron spectroscopy system (Thermo Fisher ESCALAB 250Xi).

[0044] Thickness analysis was performed using atomic force microscopy (Dimension ICON, Bruker).

[0045] Atomic structure analysis was performed using a transmission electron microscope (TF20 Jeol 2100F).

[0046] Electrical analysis was performed using a vacuum probe station (CINDBEST CGO-4) and a semiconductor parameter analyzer (Agilent 14155B).

[0047] Magnetic domain analysis was performed using an atomic force microscope (Dimension ICON, Bruker).

[0048] Magnetic analysis was performed using the MPMS(SQUID)XL-5 fine magnetic measurement system.

[0049] Example 1

[0050] Step 1: Weigh 10 mg of CrCl3 powder and 1 mg of KCl powder using an electronic balance, mix thoroughly, and place in a ceramic boat. Place the boat in the center of a 1-inch single-zone tube furnace. Then weigh 50 mg of high-purity sulfur powder into the ceramic boat and place it approximately 10 cm above the CrCl3 powder in the tube furnace. Use freshly peeled mica as a substrate, placing it directly above the CrCl3 powder. Evacuate the tube using a vacuum pump, then flush with 1000 sccm of argon gas to remove oxygen and water vapor, ensuring a stable growth environment unaffected by external conditions. Growth is carried out at atmospheric pressure using 30 sccm of argon gas as the carrier gas. Then, set a programmed temperature increase, raising the temperature from room temperature to 650°C within 10 minutes. Push the sulfur powder into the heating zone and hold for 5 minutes. After growth, rapidly cool the CVD system to room temperature, resulting in two-dimensional CrS nanosheets grown on the mica substrate.

[0051] Step 2: The prepared two-dimensional CrS nanosheets were transferred onto a SiO2 / Si substrate using PMMA photoresist for device fabrication. Mica containing the sample was spin-coated with PMMA photoresist transfer solution (3800 rpm over 60 seconds) and then baked at 180°C for 1 hour. The treated mica was then immersed in a 1% hydrofluoric acid solution for 15 minutes. Afterward, it was removed and immersed in deionized water for 5 minutes. The floating PMMA film containing the two-dimensional CrS nanosheets was then retrieved using a gold-labeled SiO2 / Si substrate and dried on a heated stage. The dried target substrate containing the sample was then immersed in acetone solution for 30 minutes to remove the PMMA photoresist.

[0052] Step 3: Field-effect transistors (FETs) were fabricated on the SiO2 / Si substrate containing two-dimensional CrS nanosheets prepared above using standard electron beam lithography and electron beam evaporation techniques. First, PMMA photoresist was spin-coated onto the SiO2 / Si substrate at a spin speed of 2800 rpm for 40 seconds, followed by hardening on a 180°C heating stage for 5 minutes. Next, electrode patterns were etched onto the photoresist using an electron beam exposure device, followed by development and fixing with a developer and fixer. Then, electrodes were deposited using an electron beam deposition device, employing a 10nm Cr / 50nm gold metal material. Finally, the sample silicon wafer with deposited electrodes was immersed in boiling acetone at 80°C for metal stripping to remove the photoresist and excess metal electrodes. It was then rinsed with clean acetone to remove other impurities, dried, and heated to 150°C in a vacuum probe stage for 1 hour to obtain the CrS FET.

[0053] Step 4: Take the mica containing two-dimensional CrS nanosheets obtained in Step 1, divide the densely crystalline part into square pieces of 0.5cm-0.5cm in size, stack them together and perform magnetic tests.

[0054] The two-dimensional CrS nanosheets obtained on mica in Example 1 were analyzed using an optical microscope, such as... Figure 1 As shown, it can be clearly seen that the two-dimensional CrS synthesized at 650℃ exhibits a flat surface and a regular semi-hexagonal shape, with a size ranging from a few micrometers to 20 micrometers.

[0055] Raman spectroscopy and X-ray photoelectron spectroscopy were performed on the two-dimensional CrS nanosheets prepared in Example 1 to characterize the composition and structure of the synthesized two-dimensional CrS nanosheets. Figure 2 As shown, CrS at 252 cm⁻¹ -1 and 283cm -1 There are two distinct Raman peaks at this point, representing the A of CrS. 1g and E g The vibrational modes. The photoelectron spectroscopy analysis results are as follows: Figure 3 As shown, the S2p spectrum of CrS shows two strong peaks at 161.8 eV and 160.6 eV, respectively, while the 2p spectrum of Cr shows two strong peaks at 584 eV and 574.2 eV, respectively.

[0056] The thickness and surface morphology of the CrS nanosheets obtained in Example 1 were characterized using atomic force microscopy. The results are as follows: Figure 4 As shown, the synthesized two-dimensional CrS nanosheets have a smooth surface, with the thinnest layer being approximately 2.64 nm thick. The crystal structure of the synthesized CrS was characterized using high-resolution transmission electron microscopy (HRTEM), as shown in the figure. Figure 5As shown, the two-dimensional CrS nanosheets exhibit perfect lattice fringes and a high-quality single-crystal phase.

[0057] The electrical performance of transistor devices fabricated from the two-dimensional CrS nanosheets obtained in Example 1 was studied. Figure 6 The field-effect transistor of Example 1 and its transfer and output characteristic curves are shown. The transfer characteristic curve of the two-dimensional CrS field-effect transistor indicates that it exhibits metallic conductivity and good electrical conductivity.

[0058] The magnetic domain structure of the two-dimensional CrS nanosheets obtained in Example 1 was characterized using an atomic force microscope equipped with a magnetic probe. The results are as follows: Figure 7 The synthesized two-dimensional CrS nanosheets shown in the MFM phase diagram have a smooth surface and obvious striped magnetic domains at room temperature.

[0059] The magnetic response of the two-dimensional CrS nanosheets obtained in Example 1 was characterized using a superconducting quantum interference device. The results are as follows: Figure 8 As shown in figure a. For temperature-dependent magnetic susceptibility (MT) measurements, hysteresis still exists at room temperature. For example... Figure 8 As shown in b, both zero-field cooling (ZFC) and field cooling (FC) modes were performed under an external field of 0.1T, which indicates that our CVD-grown CrS sample exhibits significant ferromagnetism.

[0060] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing two-dimensional CrS nanosheets, characterized by, The method comprises the following steps: Sulfur powder and a chromium source precursor are respectively arranged upstream and in the center of a chemical vapor deposition system in the flow direction of a carrier gas, the sulfur powder is arranged 5-10 cm upstream of the chromium source precursor, a substrate is arranged above the chromium source precursor, and a reaction is performed through programmed temperature rising to obtain two-dimensional CrS nanosheets; The programmed temperature rising is performed at a temperature rising from 20-30 DEG C to 650-680 DEG C in 8-10 min and a holding for 1-5 min; The chromium source precursor comprises CrCl3 powder and KCl powder.

2. The production method according to claim 1, characterized by, The mass ratio of the KCl powder to the CrCl3 powder is 1:5-20.

3. The production method according to claim 1, characterized by, The mass ratio of the sulfur powder to the CrCl3 powder is 0.5-5:

1.

4. The method of claim 1, wherein, The carrier gas is an inert gas; The inert gas is at least one of helium, neon and argon; The flow rate of the carrier gas is 30-50 sccm.

5. The preparation method according to claim 1, wherein, Before the programmed temperature rising, the chemical vapor deposition system is vacuumized and flushed with argon; The argon flow rate of the argon flushing is 800-1500 sccm; The number of times of the argon flushing is 3-5.

6. The method of claim 1, wherein, The substrate is mica.

7. The two-dimensional CrS nanosheets obtained by the preparation method according to any one of claims 1 to 6, characterized in that, The CrS nanosheets have room-temperature ferromagnetism.

8. The two-dimensional CrS nanosheets according to claim 1, wherein, The CrS nanosheets are single-crystal phase; The thickness of the CrS nanosheets is 2.64-36.5 nm.

9. Application of the two-dimensional CrS nanosheets according to claim 7 or 8 in the field of spintronics and CrS field effect transistors.

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