Method for synthesizing two-dimensional bismuth tungstate nanosheet through one-step chemical vapor deposition

Abstract

The invention discloses a method for synthesizing a two-dimensional bismuth tungstate nanosheet through one-step chemical vapor deposition. The method comprises the following steps: taking Bi2O3 and Na2WO4. 2H2O powder as a precursor, putting the Bi2O3 powder into a high-temperature-resistant quartz boat, putting the high-temperature-resistant quartz boat into a first temperature zone of a tubular furnace, putting an inverted clean single-polished sapphire substrate and the quartz boat loaded with the Na2WO4. 2H2O powder into a second temperature zone, and carrying out high-purity Ar / O2 transportation by taking mixed high-purity Ar / O2 as transportation gas; the two-dimensional Bi2WO6 nanosheets with different nucleation densities, sizes and thicknesses are obtained by regulating and controlling the temperature, the heat preservation time, the pressure intensity, the transportation distance, the carrier gas flow and the proportion. The method disclosed by the invention is convenient, efficient and environment-friendly, and the prepared two-dimensional Bi2WO6 nanosheet is high in nucleation density and adjustable in size and thickness, has good physical and chemical stability and can be used for further developing and integrating two-dimensional high-performance electronic and optoelectronic devices.

Description

Technical Field

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

[0002] Since graphene was first successfully exfoliated to a two-dimensional scale, many two-dimensional materials have emerged, such as hexagonal boron nitride (h-BN), transition metal chalcogenides (TMDCs), black phosphorus (BP), indium selenide (InSe), bismuth selenide (Bi2O2Se), etc. Two-dimensional materials have a series of unique physical and chemical properties, including atomically thin thickness, adjustable band gap, no dangling bonds on the surface, high carrier mobility and excellent electrostatic tunability. They are considered to be one of the most promising channel materials for the sub-5nm semiconductor process of silicon-based semiconductor materials in the post-Moore era. Two-dimensional metal oxide semiconductor materials have both high carrier mobility and ultra-high air stability, and have become one of the recent hot research directions. Metal oxide semiconductor materials represented by Bi2O2Se have excellent physical and chemical properties, electrical properties, and high air stability, and are expected to be used in integrated high-performance transistor devices. However, there are relatively few members of two-dimensional metal oxide semiconductor materials. In addition to some reported layered two-dimensional metal oxide semiconductor materials, how to synthesize more non-layered metal oxide semiconductor materials on a two-dimensional scale is of great significance for the development of the next generation of two-dimensional metal oxide semiconductor-based high-performance electronic devices.

[0003] The existing methods for synthesizing low-dimensional Bi2WO6 nanomaterials are mostly hydrothermal methods, but 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). In addition, there are literature reports that although Bi2WO6 crystals grown by epitaxial methods can grow Bi2WO6 crystals on a two-dimensional scale based on steps, it is still difficult to obtain single-crystalline two-dimensional Bi2WO6 crystals with high crystallization quality, and they are mainly used to study their ferroelectric properties (S.Zhou,L.Liao,et al.Ferroelectricity in EpitaxialPerovskiteOxideBi2WO6 Films with One-Unit-Cell Thickness[J].Nano Letter2023,23,4557-4563). In summary, the existing research on low-dimensional Bi2WO6 crystals is difficult to expand the application of Bi2WO6 semiconductor materials in the fields of two-dimensional electronics and optoelectronics, and is not suitable for the further development of low-dimensional electronic and optoelectronic devices. Summary of the invention

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

[0005] The technical solution for achieving the purpose of the present invention is as follows:

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

[0007] Sodium tungstate dihydrate (Na2WO4·2H2O) powder is evenly placed in a quartz boat as a tungsten precursor source, and then a clean sapphire substrate is inverted on the above quartz boat and placed in the second temperature zone of the tube furnace. Bismuth oxide (Bi2O3) powder is evenly placed in another quartz boat as a bismuth precursor source and placed in the first temperature zone of the tube furnace. The center distance between Bi2O3 powder and Na2WO4·2H2O powder is 30-35cm. After high-purity argon gas is introduced to clean and exhaust residual air, the first temperature zone is heated to 865℃ and kept warm. The temperature in the second temperature zone is raised to 550-565°C for 10-30 minutes, and the temperature is kept at 550-565°C for 10-30 minutes. Argon is continuously introduced as a transport gas. When the second temperature zone reaches the reaction temperature, O2 is introduced, and the flow ratio of Ar:O2 is adjusted to 120-130sccm:20-30sccm. The gas pressure in the tubular furnace chamber is adjusted to 150Pa. The Bi2O3 powder volatilized and diffused in the first temperature zone is transferred to the second temperature zone in the gas phase, 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 insulation time is 15 minutes.

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

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

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

[0013] The present invention uses a one-step chemical vapor deposition method for the first time to synthesize high-quality single-crystal Bi2WO6 nanosheets on a two-dimensional scale, and the maximum size can reach 50μm. The preparation method of the present invention is convenient, efficient, and environmentally friendly. The prepared two-dimensional Bi2WO6 nanosheets have the advantages of high nucleation density, high air stability, controllable thickness and size, and good crystallinity. It not only enriches the family of two-dimensional metal oxide semiconductor materials, but also provides material support for its application research in two-dimensional transistor devices, and has broad application prospects in the fields of integrated electronics and optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the method for synthesizing two-dimensional Bi2WO6 nanosheets by one-step chemical vapor deposition;

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

[0016] Figure 3 This is the XPS graph of Bi element of the two-dimensional Bi2WO6 nanosheet prepared in Example 1;

[0017] Figure 4 This is the XPS graph of the W element of the two-dimensional Bi2WO6 nanosheet prepared in Example 1;

[0018] Figure 5 This is the XPS graph of the O element of the two-dimensional Bi2WO6 nanosheet prepared in Example 1;

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

[0020] Figure 7 A 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 nanosheet prepared in Example 1;

[0022] Fig. 9 OM image of a single crystal of a two-dimensional Bi2WO6 nanosheet prepared in Example 1, scale 5 μm;

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

[0024] Fig.11 This is the EDS element distribution diagram of the two-dimensional Bi2WO6 nanosheet prepared in Example 1;

[0025] Fig.12 UV-Vis-NIR image of the two-dimensional Bi2WO6 nanosheet prepared in Example 1;

[0026] Fig.13 OM image of the nucleation density of the two-dimensional Bi2WO6 nanosheets prepared in Example 1, scale 20 μm;

[0027] Fig.14 OM image of the two-dimensional Bi2WO6 nanosheet prepared in Example 2, scale 50 μm;

[0028] Fig.15 OM image of the two-dimensional Bi2WO6 nanosheet prepared in Comparative Example 1, scale 20 μm;

[0029] Fig.16 OM image of the two-dimensional Bi2WO6 nanosheet prepared in Example 3, scale 10 μm;

[0030] Fig.17 OM image of the two-dimensional Bi2WO6 nanosheet prepared in Example 4, scale 50 μm;

[0031] Fig.18 OM image of the two-dimensional Bi2WO6 nanosheet prepared in Example 5, scale 20 μm;

[0032] Fig.19 OM image of the two-dimensional Bi2WO6 nanosheets prepared in Comparative Example 2, scale 50 μm. DETAILED DESCRIPTION

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

[0034] Example 1

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

[0036] (2) Select a clean 1×1 cm 2 A single polished sapphire substrate was loaded upside down on a high temperature resistant quartz boat filled with Na2WO4·2H2O powder and placed in the second temperature zone of the CVD tube furnace, 35 cm away from the heating center of the first temperature zone;

[0037] (3) Clean the CVD tube furnace with high-purity Ar gas, turn on the mechanical pump to pump the tube furnace to a low vacuum (<10Pa), then introduce Ar gas for cleaning, repeat the cleaning three times to remove the air in the CVD tube furnace, and after the last cleaning, pump the tube furnace to a low pressure;

[0038] (4) Set up the CVD heating program. The first temperature zone is set to heat up from room temperature (25°C) to 865°C in 56 minutes, and keep warm for 15 minutes; the second temperature zone is set to heat up from room temperature (25°C) to 550°C in 35 minutes, and keep warm 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. Use the pressure gauge and the gas valve knob to adjust the pressure value in the tube furnace to 150 Pa. After the pressure value and its flow rate are stable, control the Ar carrier gas with the valve, turn off the O2 carrier gas, run the program, and introduce O2 after heating to the highest temperature.

[0040] (6) After the reaction process is completed, the mechanical pump and the air inlet valve are turned off, and the mixture is naturally cooled to room temperature to obtain two-dimensional Bi2WO6 nanosheets. The samples are then taken out for further characterization and testing.

[0041] The optical microscope (OM) image of the two-dimensional Bi2WO6 nanosheet prepared in Example 1 is as follows: Figure 2 The X-ray photoelectron spectroscopy (XPS) analysis diagram of the two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 1 is as shown in FIG. Figures 3 to 5 As shown in the figure, they are the main peaks of Bi 4f orbital photoelectrons, W 4f orbital photoelectrons, and O 1s orbital photoelectrons, respectively, which illustrate that the chemical valence of Bi is +3, the chemical valence of W is +6, and the formation of Bi-O and WO bonds, proving that the prepared sample is a two-dimensional Bi2WO6. Raman spectrum analysis of the two-dimensional rectangular Bi2WO6 nanosheets prepared in Example 1, as shown in Figure 6 As shown, 257~307cm -1 It is the stretching vibration mode of octahedral WO6 and the bending vibration mode of Bi-O bond, 796~825cm -1 A belonging to the antisymmetric and symmetric OWO g The HRTEM image of a single two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 1 is shown in FIG. Figure 7 The TEM diffraction pattern of the two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 1 is as shown in FIG. Figure 8 The morphology and size of a single crystal of a two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 1 are shown in the OM diagram. Fig. 9 The AFM image of the two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 1 is shown in FIG. Fig.10 The EDS element distribution diagram of the two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 1 is shown in FIG. Fig.11 As shown, it can be seen that Bi, W, and O elements are evenly distributed on the nanosheets. The UV-Vis-NIR spectrum of the two-dimensional rectangular Bi2WO6 nanosheets prepared in Example 1 is as follows: Fig.12 As shown in FIG. 1 , the semiconductor bandgap width is 2.46 eV. The nucleation density OM diagram of the two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 1 is shown in FIG. Fig.13 shown.

[0042] Example 2

[0043] Similar to Example 1, the difference is that the maximum 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] The OM image of the two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 2 is as follows: Fig.14As shown in the figure, it can be seen that the color of the two-dimensional rectangular Bi2WO6 nanosheet changes. This is caused by the change in thickness of the deposited Bi2WO6 nanosheet due to the increase in substrate temperature. The Raman spectra of the two-dimensional rectangular Bi2WO6 nanosheets of different thicknesses prepared in Example 1 are compared and analyzed, as shown in Figure 6 shown.

[0045] Comparative Example 1

[0046] Similar to Example 1, the difference is that the maximum 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 an ideal rectangular nanosheet single crystal. The OM diagram of the growth result is shown in Fig.15 shown.

[0048] Example 3

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

[0050] The OM image of the two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 3 is as follows: Fig.16 As shown in the figure, it can be seen that 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 the Bi2WO6 nanosheets.

[0051] Example 4

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

[0053] Increasing the proportion of O2 in the carrier gas can result in a smaller nucleation density. The OM diagram after deposition is as follows: Fig.17 shown.

[0054] Example 5

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

[0056] OM image of a single two-dimensional rectangular Bi2WO6 nanosheet prepared in Example 5, as shown Fig.18As shown in the figure, it can be seen that a closer transport distance will lead to a further increase in the nucleation density of the two-dimensional rectangular Bi2WO6 nanosheets and an increase in the average size, resulting in the continuous growth of multiple rectangular Bi2WO6 nanosheets and the appearance of irregular shapes.

[0057] Comparative Example 2

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

[0059] Too long a transport distance will lead to unsatisfactory deposition results, which are manifested in low nucleation density and small size of the obtained rectangular single crystal. Its OM diagram is as follows: Fig.19 shown.

[0060] In summary, the present invention is simple to operate. By adjusting the growth parameters, two-dimensional rectangular Bi2WO6 nanosheets with different thicknesses, different sizes and good crystallinity can be obtained. Temperature, carrier gas ratio and transport distance are key factors affecting the preparation of two-dimensional rectangular Bi2WO6 nanosheets. The two-dimensional rectangular Bi2WO6 nanosheets prepared by the present invention have high nucleation density, regular shape, high crystallization 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 following steps are involved: Na2WO4·2H2O powder was evenly placed in a quartz boat as a tungsten precursor source, and then a clean sapphire substrate was inverted on the above quartz boat and placed in the second temperature zone of the tube furnace. Bi2O3 powder was evenly placed in another quartz boat as a bismuth precursor source and placed in the first temperature zone of the tube furnace. The center distance between Bi2O3 powder and Na2WO4·2H2O powder was 30~35cm. After high-purity argon gas was introduced to clean and exhaust the residual air, the first temperature zone was heated to 865 ℃ and kept warm for 10~30 min. The second temperature zone was heated to 550~565 ℃ and kept warm for 10~30 min. Argon was continuously introduced as a transport gas. When the second temperature zone was raised to the reaction temperature, O2 was introduced, and the flow ratio of Ar:O2 was adjusted to 120~130 sccm: 20~30 sccm. The gas pressure in the tube furnace chamber was adjusted to 150 Pa, the Bi2O3 powder volatilized and diffused in the first temperature zone is transferred to the second temperature zone in the gas phase, a chemical reaction occurs and the powder nucleates and grows on the sapphire substrate to obtain a two-dimensional Bi2WO6 nanosheet.

2. The method according to claim 1, characterized in that The mass ratio of Bi2O3 powder to Bi2WO6 powder is 150 mg:100 mg.

3. The method according to claim 1, characterized in that The insulation time was 15 min.

4. The method according to claim 1, characterized in that The heating rate is 15 °C / min.

5. The method according to claim 1, characterized in that The flow ratio of Ar:O2 is 120 sccm:30 sccm.

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