Method for synthesizing two-dimensional bismuth tungstate nanosheets by one-step chemical vapor deposition

Abstract

The application discloses a method for synthesizing two-dimensional bismuth tungstate nanosheets by one-step chemical vapor deposition. The method uses Bi2O3 and Na2WO4.2H2O powders as precursors, puts the Bi2O3 powder into a high-temperature-resistant quartz boat and places the quartz boat in a first temperature zone of a tube furnace, places a quartz boat with an inverted clean single-polished sapphire substrate and loaded Na2WO4.2H2O powder in a second temperature zone, uses mixed high-purity Ar / O2 as a transport gas, and obtains two-dimensional Bi2WO6 nanosheets with different nucleation densities, sizes and thicknesses by adjusting temperature, holding time, pressure, transport distance, carrier gas flow and proportion. The method is convenient, efficient and environment-friendly, the obtained two-dimensional Bi2WO6 nanosheets have high nucleation density, adjustable size and thickness, and have good physical and chemical stability, and can be used for further development and integration of two-dimensional high-performance electronic and optoelectronic devices.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology and relates to a method for synthesizing two-dimensional bismuth tungstate (Bi2WO6) nanosheets by one-step chemical vapor deposition. Background Technology

[0002] Since the successful exfoliation of graphene to a two-dimensional scale, numerous two-dimensional materials have emerged, such as hexagonal boron nitride (h-BN), transition metal chalcogenides (TMDCs), black phosphorus (BP), indium selenide (InSe), and bismuth oxyselenide (Bi₂O₂Se). Two-dimensional materials possess a series of unique physicochemical properties, including atomic thinness, tunable bandgap, absence of dangling bonds, high carrier mobility, and excellent electrostatic tunability. They are considered among the most promising channel materials for continuing silicon-based semiconductor materials in sub-5nm semiconductor processes in the post-Moore's Law era. Two-dimensional metal-oxide-semiconductor (MODS) materials, combining high carrier mobility and ultra-high air stability, have become a recent hot research area. MODS materials, represented by Bi₂O₂Se, possess excellent physicochemical properties, electrical performance, and high air stability, and are expected to be used in the integration of high-performance transistor devices. However, there are relatively few members in the two-dimensional metal oxide semiconductor material family. Apart from some of the layered two-dimensional metal oxide semiconductor materials that have been reported, how to synthesize more non-layered metal oxide semiconductor materials on a two-dimensional scale is of great significance for the development of next-generation high-performance electronic devices based on two-dimensional metal oxide semiconductors.

[0003] Existing methods for synthesizing low-dimensional Bi2WO6 nanomaterials are mostly hydrothermal methods. However, the synthesized Bi2WO6 crystals are mostly zero-dimensional nanoparticles, one-dimensional nanowires, one-dimensional nanorods, or three-dimensional irregular shapes. The crystal quality is not high and the size and thickness cannot be controlled. They are mainly used in photocatalysis and other fields (Anurak W, Chuthamat D, et al. Controlling the Photocatalytic Activity and Benzylamine Photooxidation Selectivity of Bi2WO6 via Ion Substitution: Effects of Electronegativity[J]. Inorganic Chemistry 2023, 62(8):3506-3517). Furthermore, while epitaxial growth of Bi2WO6 crystals can achieve two-dimensional growth using step-like methods, it remains difficult to obtain high-quality single-crystal two-dimensional Bi2WO6 crystals. These crystals are primarily used for studying ferroelectric properties (S. Zhou, L. Liao, et al. Ferroelectricity in Epitaxial Perovskite Oxide Bi2WO6 Films with One-Unit-Cell Thickness[J]. Nano Letter 2023, 23, 4557-4563). In summary, existing research on low-dimensional Bi2WO6 crystals is insufficient for expanding the application of Bi2WO6 semiconductor materials in two-dimensional electronics and optoelectronics, and is not suitable for further development of low-dimensional electronic and optoelectronic devices. Summary of the Invention

[0004] The purpose of this invention is to provide a one-step chemical vapor deposition method for synthesizing two-dimensional Bi2WO6 nanosheets.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] A method for synthesizing two-dimensional Bi2WO6 nanosheets by one-step chemical vapor deposition includes the following steps:

[0007] Sodium tungstate dihydrate (Na₂WO₄·2H₂O) powder was uniformly placed in a quartz boat as a tungsten precursor source. A clean sapphire substrate was then placed upside down on the quartz boat and placed in the second temperature zone of a tube furnace. Bismuth oxide (Bi₂O₃) powder was uniformly placed in another quartz boat as a bismuth precursor source and placed in the first temperature zone of the tube furnace. The center-to-center distance between the Bi₂O₃ powder and the Na₂WO₄·2H₂O powder was 30–35 cm. After purging with high-purity argon gas to remove residual air, the first temperature zone was heated to 865°C and held at that temperature. For 10–30 min, the second temperature zone is heated to 550–565 °C and held for 10–30 min. Argon gas is continuously introduced as the transport gas. When the second temperature zone reaches the reaction temperature, O2 is introduced. The Ar:O2 flow rate ratio is adjusted to 120–130 sccm: 20–30 sccm. The gas pressure inside the tubular furnace is adjusted to 150 Pa. The Bi2O3 powder that has volatilized and diffused in the first temperature zone is transported to the second temperature zone, where a chemical reaction occurs and the powder nucleates and grows on the sapphire substrate to obtain two-dimensional Bi2WO6 nanosheets.

[0008] Preferably, the mass ratio of Bi2O3 powder to Bi2WO6 powder is 150mg:100mg.

[0009] Preferably, the heat preservation time is 15 minutes.

[0010] Preferably, the heating rate is 15℃ / min.

[0011] Preferably, the Ar:O2 flow rate ratio is 120 sccm:30 sccm.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] This invention marks the first time that a one-step chemical vapor deposition method has been used to synthesize high-quality single-crystal Bi₂WO₆ nanosheets on a two-dimensional scale, with a maximum size reaching 50 μm. The preparation method of this invention is convenient, efficient, and environmentally friendly. The prepared two-dimensional Bi₂WO₆ nanosheets possess advantages such as high nucleation density, high air stability, controllable thickness and size, and good crystallinity. This not only enriches the family of two-dimensional metal-oxide-semiconductor materials but also provides material support for their application research in two-dimensional transistor devices, showing broad application prospects in the fields of integrated electronics and optoelectronic devices. Attached Figure Description

[0014] Figure 1 A schematic diagram of a one-step chemical vapor deposition method for synthesizing two-dimensional Bi2WO6 nanosheets;

[0015] Figure 2 OM image of the two-dimensional Bi2WO6 nanosheets grown on a sapphire substrate prepared in Example 1, scale bar 20 μm;

[0016] Figure 3 XPS plot of Bi element in two-dimensional Bi2WO6 nanosheets prepared in Example 1;

[0017] Figure 4 XPS image of W element in two-dimensional Bi2WO6 nanosheets prepared in Example 1;

[0018] Figure 5 XPS image of O element in two-dimensional Bi2WO6 nanosheets prepared in Example 1;

[0019] Figure 6 Raman spectra of Bi2WO6 nanosheets of different thicknesses prepared in Examples 1 and 4;

[0020] Figure 7 High-resolution transmission electron microscopy (HRTEM) image of a single rectangular two-dimensional Bi2WO6 nanosheet prepared in Example 1;

[0021] Figure 8 TEM diffraction pattern of the two-dimensional Bi2WO6 nanosheets prepared in Example 1;

[0022] Figure 9 OM image of a single crystal of two-dimensional Bi2WO6 nanosheets prepared in Example 1, scale bar 5 μm;

[0023] Figure 10 The in-situ atomic force microscopy (AFM) image corresponding to a single two-dimensional Bi2WO6 nanosheet prepared in Example 1;

[0024] Figure 11 EDS elemental distribution map of the two-dimensional Bi2WO6 nanosheets prepared in Example 1;

[0025] Figure 12 The UV-Vis-NIR spectrum of the two-dimensional Bi2WO6 nanosheets prepared in Example 1;

[0026] Figure 13 OM diagram of the nucleation density of two-dimensional Bi2WO6 nanosheets prepared in Example 1, scale bar 20 μm;

[0027] Figure 14 OM image of the two-dimensional Bi2WO6 nanosheets prepared in Example 2, scale bar 50 μm;

[0028] Figure 15 OM image of the two-dimensional Bi2WO6 nanosheets prepared in Comparative Example 1, scale bar 20 μm;

[0029] Figure 16 OM image of the two-dimensional Bi2WO6 nanosheets prepared in Example 3, scale bar 10 μm;

[0030] Figure 17 OM image of the two-dimensional Bi2WO6 nanosheets prepared in Example 4, scale bar 50 μm;

[0031] Figure 18 OM image of the two-dimensional Bi2WO6 nanosheets prepared in Example 5, scale bar 20 μm;

[0032] Figure 19 OM image of the two-dimensional Bi2WO6 nanosheets prepared in Comparative Example 2, scale bar 50 μm. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

[0034] Example 1

[0035] (1) Take Bi2O3 powder with a purity of 99.99% and Na2WO4·2H2O powder with a purity of 99.98% in sequence, weigh 150mg and 100mg respectively with an electronic balance, and place the high-temperature resistant quartz boat loaded with Bi2O3 powder in the heating center of the first temperature zone of the CVD tube furnace.

[0036] (2) Select a clean, cut 1×1cm piece 2 A single polished sapphire substrate is inverted and mounted on a high-temperature resistant quartz boat containing Na2WO4·2H2O powder, and placed in the second temperature zone of a CVD tube furnace, 35cm away from the heating center of the first temperature zone.

[0037] (3) Clean the CVD tubular furnace with high-purity Ar gas. Turn on the mechanical pump to evacuate the tubular furnace to a low vacuum (<10Pa), and then introduce Ar gas for cleaning. Repeat the cleaning three times to remove the air in the CVD tubular furnace. After the last cleaning, evacuate the tubular furnace to a low pressure.

[0038] (4) Set the CVD heating program. The first temperature zone is set to heat from room temperature (25℃) to 865℃ in 56 minutes and hold for 15 minutes; the second temperature zone is set to heat from room temperature (25℃) to 550℃ in 35 minutes and hold for 15 minutes.

[0039] (5) Set the carrier gas flow rate and pressure. Set the Ar carrier gas flow rate to 120 sccm and the O2 carrier gas flow rate to 30 sccm. Adjust the pressure value inside the tubular furnace to 150 Pa using a pressure gauge and gas valve knob. After the pressure value and flow rate stabilize, control the Ar carrier gas with the valve and shut off the O2 carrier gas. Run the program and wait for the temperature to reach the highest temperature before introducing O2.

[0040] (6) After the reaction process is completed, turn off the mechanical pump and the air inlet valve, and allow it to cool naturally to room temperature to obtain two-dimensional Bi2WO6 nanosheets. Take out the sample for further characterization and testing.

[0041] The optical microscope (OM) image of the two-dimensional Bi2WO6 nanosheets prepared in Example 1 is shown below. Figure 2 As shown. The X-ray photoelectron spectroscopy (XPS) analysis pattern of the two-dimensional rectangular Bi₂WO₆ nanosheets prepared in Example 1 is shown below. Figures 3-5 The figures shown are the main photoelectron peaks of Bi 4f orbital, W 4f orbital, and O 1s orbital, respectively. These demonstrate that Bi has a +3 valence state, W has a +6 valence state, and Bi-O and WO bonds are formed, proving that the prepared sample is two-dimensional Bi₂WO₆. Raman spectroscopy analysis of the two-dimensional rectangular Bi₂WO₆ nanosheets prepared in Example 1 is shown below. Figure 6 As shown, 257–307 cm -1 It is a stretching vibration mode of octahedral WO6 and a bending vibration mode of Bi-O bonds, 796–825 cm⁻¹ -1 A belonging to OWO antisymmetric and symmetric g Pattern. HRTEM image of a single two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 1 is shown below. Figure 7 As shown. The TEM diffraction pattern of the two-dimensional rectangular Bi2WO6 nanosheets prepared in Example 1 is as follows. Figure 8 As shown. The morphology and size (OM) images of a single crystal of the two-dimensional rectangular Bi₂WO₆ nanosheets prepared in Example 1 are shown below. Figure 9 As shown. AFM image of the two-dimensional rectangular Bi₂WO₆ nanosheets prepared in Example 1, as shown. Figure 10 As shown. The EDS elemental distribution map of the two-dimensional rectangular Bi₂WO₆ nanosheets prepared in Example 1 is shown below. Figure 11 As shown, Bi, W, and O elements are uniformly distributed on the nanosheets. The UV-Vis-NIR spectrum of the two-dimensional rectangular Bi₂WO₆ nanosheets prepared in Example 1 is shown below. Figure 12 As shown, its semiconductor bandgap is 2.46 eV. The nucleation density (OM) diagram of the two-dimensional rectangular Bi₂WO₆ nanosheets prepared in Example 1 is shown below. Figure 13 As shown.

[0042] Example 2

[0043] Similar to Example 1, the difference is that the highest temperature of the second temperature zone in the control step (4) is 565°C, and the heating time is consistent with that of the first temperature zone.

[0044] OM image of the two-dimensional rectangular Bi2WO6 nanosheets prepared in Example 2, as shown. Figure 14As shown in the figure, the color of the two-dimensional rectangular Bi2WO6 nanosheets changes. This is due to the change in the thickness of the deposited Bi2WO6 nanosheets caused by the increase in substrate temperature. A comparative analysis of the Raman spectra of two-dimensional rectangular Bi2WO6 nanosheets of different thicknesses prepared in Comparative Example 1 is shown below. Figure 6 As shown.

[0045] Comparative Example 1

[0046] Similar to Example 1, the difference is that the highest temperature of the second temperature zone in the control step (4) is 535°C, and the heating time is consistent with that of the first temperature zone.

[0047] Too low a temperature will result in too low a nucleation energy, making it difficult to obtain ideal rectangular nanosheet single crystals. The growth result is shown in the OM diagram. Figure 15 As shown.

[0048] Example 3

[0049] Similar to Example 1, the difference is that in the control step (5), the Ar carrier gas flow rate is 130 sccm, the O2 carrier gas flow rate is 20 sccm, and the pressure value inside the tubular furnace is adjusted to 150 Pa by using a pressure gauge and a gas valve knob.

[0050] OM image of the two-dimensional rectangular Bi2WO6 nanosheets prepared in Example 3, as shown. Figure 16 As shown in the figure, the nucleation density of the two-dimensional rectangular Bi2WO6 nanosheets increases. This is because O2 in the carrier gas can inhibit the volatilization of Bi2O3, thereby reducing the nucleation density. Therefore, reducing the concentration of O2 in the carrier gas will lead to an increase in the nucleation density of Bi2WO6 nanosheets.

[0051] Example 4

[0052] Similar to Example 1, the difference is that in the control step (5), the Ar carrier gas flow rate is 120 sccm, the O2 carrier gas flow rate is 20 sccm, and the pressure value inside the tubular furnace is adjusted to 150 Pa by using a pressure gauge and a gas valve knob.

[0053] Increasing the proportion of O2 in the carrier gas can result in a lower nucleation density, as shown in the post-deposition OM diagram. Figure 17 As shown.

[0054] Example 5

[0055] Similar to Example 1, the difference is that the transport distance from Bi precursor source to W precursor source in step (2) is adjusted to 30cm.

[0056] OM image of a single two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 5, as shown. Figure 18As shown in the figure, closer transport distances lead to a further increase in the nucleation density and average size of two-dimensional rectangular Bi2WO6 nanosheets, resulting in the continuous growth of multiple rectangular Bi2WO6 nanosheets into irregular shapes.

[0057] Comparative Example 2

[0058] Similar to Example 1, the difference is that the transport distance from Bi precursor source to W precursor source in step (2) of Example 1 is adjusted to 40cm.

[0059] Excessive transport distances can lead to unsatisfactory deposition results, specifically low nucleation density and small size of the resulting rectangular single crystals, as shown in the OM diagram. Figure 19 As shown.

[0060] In summary, this invention is simple to operate. By adjusting the growth parameters, two-dimensional rectangular Bi2WO6 nanosheets with different thicknesses, sizes, and good crystallinity can be obtained. Temperature, carrier gas ratio, and transport distance are the key factors affecting the preparation of two-dimensional rectangular Bi2WO6 nanosheets. The two-dimensional rectangular Bi2WO6 nanosheets prepared by this invention have high nucleation density, regular shape, high crystal quality, adjustable size and thickness, and good air stability.

Claims

1. A method for synthesizing two-dimensional Bi2WO6 nanosheets by one-step chemical vapor deposition, characterized in that, The method comprises the following steps: Na2WO4·2H2O powder is uniformly placed in a quartz boat as a tungsten precursor source, then a clean sapphire substrate is inverted on the quartz boat and placed in a second temperature zone of a tube furnace, Bi2O3 powder is uniformly placed in another quartz boat as a bismuth precursor source and placed in a first temperature zone of the tube furnace, the center distance between the Bi2O3 powder and the Na2WO4·2H2O powder is 30-35 cm, after high-purity argon is introduced to clean the residual air, the first temperature zone is heated to 865 ℃, and the temperature is kept for 10-30 min, the second temperature zone is heated to 550-565 ℃, and the temperature is kept for 10-30 min, argon is continuously introduced as a transport gas, O2 is introduced when the second temperature zone is raised to the reaction temperature, the flow ratio of Ar:O2 is adjusted to 120-130 sccm:20-30 sccm, the gas pressure in the tube furnace cavity is adjusted to 150 Pa, the Bi2O3 powder volatilized and diffused in the first temperature zone is transported to the second temperature zone in a gas phase, a chemical reaction occurs, and nucleation and growth are carried out on the sapphire substrate to obtain two-dimensional Bi2WO6 nanosheets.

2. The method of claim 1, wherein, The mass ratio of the Bi2O3 powder to the Bi2WO6 powder is 150 mg:100 mg.

3. The method of claim 1, wherein, The temperature keeping time is 15 min.

4. The method of claim 1, wherein, The heating rate is 15 ℃ / min.

5. The method of claim 1, wherein, The flow ratio of Ar:O2 is 120 sccm:30 sccm.

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